Accepted Manuscript Title: Functionalized bacterial cellulose derivatives and nanocomposites Author: Weili Hu Shiyan Chen Jingxuan Yang Zhe Li Huaping Wang PII: DOI: Reference:

S0144-8617(13)01004-7 http://dx.doi.org/doi:10.1016/j.carbpol.2013.09.102 CARP 8191

To appear in: Received date: Revised date: Accepted date:

9-8-2013 23-9-2013 29-9-2013

Please cite this article as: Hu, W., Chen, S., Yang, J., Li, Z., & Wang, H., Functionalized bacterial cellulose derivatives and nanocomposites, Carbohydrate Polymers (2013), http://dx.doi.org/10.1016/j.carbpol.2013.09.102 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.



Functionalized bacterial cellulose derivatives and nanocomposites



Weili Hu, Shiyan Chen*, Jingxuan Yang, Zhe Li, Huaping Wang*



State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Key



Laboratory of High-performance Fibers and Products, Ministry of Education College



of Materials Science and Engineering, Donghua University, Shanghai, 201620, China;



Tel: +86-21-67792950; Fax: +86-21-67792726



E-mail: [email protected], [email protected].

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ABSTRACT

M

11 

Bacterial cellulose (BC) is a fascinating and renewable natural nanomaterial

13 

characterized by favorable properties such as remarkable mechanical properties,

14 

porosity, water absorbency, moldability, biodegradability and excellent biological

15 

affinity. Intensive research and exploration in the past few decades on BC

17  18  19 

te

Ac ce p

16 

d

12 

nanomaterials mainly focused on their biosynthetic process to achieve the low-cost preparation and application in medical, food, advanced acoustic diaphragms, and other fields. These investigations have led to the emergence of more diverse potential applications exploiting the functionality of BC nanomaterials. This review gives a

20 

summary of construction strategies including biosynthetic modification, chemical

21 

modification, and different in situ and ex-situ patterns of functionalization for the

22 

preparation of advanced BC-based functional nanomateirals. The major studies being

23 

directed toward elaborate designs of highly functionalized material systems for 1   

Page 1 of 83

many-faceted prospective applications. Simple biosynthetic or chemical modification

25 

on BC surface can improve its compatibility with different matrix and expand its

26 

utilization in nano-related applications. Moreover, based on the construction strategies

27 

of functional nanomaterial system, different guest substrates including small molecules,

28 

inorganic nanoparticles or nanowires, and polymers can be incorporated onto the

29 

surfaces of BC nanofibers to prepare various functional nanocomposites with

30 

outstanding properties, or significantly improved physicochemical, catalytic,

31 

optoelectronic, as well as magnetic properties. We focus on the preparation methods,

32 

formation mechanisms, and unique performances of the different BC derivatives or

33 

BC-based nanocomposites. The special applications of the advanced BC-based

34 

functional nanomaterials, such as sensors, photocatalytic nanomaterials, optoelectronic

35 

devices,

36 

comprehensively reviewed.

38  39  40  41 

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responsive

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magnetically

membranes

are

also

critically

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Key words: bacterial cellulose; modification; nanocomposites; functionalization

42  43  44  45  2   

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46 

Contents

47 

1.

Introduction.............................................................................................................4

48 

2.

Construction strategies of BC–based functional nanomaterials .............................7 2.1.

49 

Biosynthetic modification.............................................................................8

2.1.1.

Altered BC structure ..........................................................................8

51 

2.1.2.

Nanocomposites...............................................................................10

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2.2.

Chemical surface modification...................................................................12

53 

2.3.

In situ formation of nanostructures ............................................................15

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2.3.1.

In situ formation of nanostructures through reduction reaction.......16

55 

2.3.2.

In situ formation of nanostructures through precipitation reaction .17

56 

2.3.3.

In situ formation of nanostructures through sol-gel reaction...........19

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2.4.

Ex-situ introduction of components ...........................................................20

58 

2.5.

Other combined strategies ..........................................................................22

59 

3.

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Applications of BC-based functional nanomaterials ............................................23 3.1.

Sensors........................................................................................................24

61 

3.2.

Photocatalytic nanomaterials......................................................................26

62 

3.3.

Optoelectronics...........................................................................................28

66  67  68  69 

Electrically conductive films ...........................................................28

Ac ce p

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3.3.1.

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d

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3.3.2.

Optically transparent films...............................................................30

3.3.3.

Flexible displays ..............................................................................31

3.3.4.

Photoluminescent and photochromic films......................................32

3.4.

4.

Magnetically responsive films....................................................................34

Concluding remarks ..............................................................................................36

Acknowledgement ..................................................................................................38 References ..............................................................................................................38

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73 

1. Introduction

74 

It is well known that cellulose is a very important and fascinating biopolymer and an

76 

almost inexhaustible and sustainable natural polymeric raw material, which is of

77 

special importance both in industries and in daily lives. In the past decade, the design

78 

and development of renewable resources and innovative products for science,

79 

medicine and technology have led to a global revival of interdisciplinary research and

80 

utilization of this abundant natural polymer. Formed by repeated connection of glucose

81 

building blocks, cellulose possesses abundant surface hydroxyl groups forming

82 

plentiful inter- and intra-molecular hydrogen bonds, characterized by its hydrophilicity,

83 

chirality, biodegradability, and broad chemical-modifying capacity(Klemm, Heublein,

84 

Fink & Bohn, 2005). The properties of cellulose largely depend on the specific

85 

assembling and supramolecular order controlled by the origin and treatment of

87  88  89 

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cellulose(Eichhorn et al., 2010). Bacterial cellulose (BC) has the same molecular formula as plant cellulose, but with unique and sophisticated three-dimensional porous network structures. Intrinsically originated from the unique structure, BC demonstrates a serious of distinguished structural features and properties such as high purity, high

90 

degree of polymerization (up to 8000), high crystallinity (of 70 to 80%), high water

91 

content to 99%, and high mechanical stability, which is quite different from the natural

92 

cellulose(Barud, Regiani, Marques, Lustri, Messaddeq & Ribeiro, 2011). These

93 

specific parameters are determined by the biofabrication approach of BC (Fig. 1) and

4   

Page 4 of 83

the controllable shape and supramolecular structure through the alteration of

95 

cultivation conditions during fermentation. These amazing physicochemical properties

96 

have attracted significant interest from both research scientists and industrialists. So far,

97 

BC has wide application in various fields such as medical, food, advanced acoustic

98 

diaphragms, and so on(Klemm et al., 2011). These research and exploration have led to

99 

the emergence of more diverse potential applications exploiting the functionality of

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BC nanomaterials.

In view of expanding the scope of BC applications, it is important to take full

102 

advantage of the unique structure and properties of BC nanomaterials to develop novel

103 

BC-based nanomaterials with ground-breaking new features. Various modification

104 

methods have been explored to open up possibilities for endowing BC with new

105 

functionalities(Klemm et al., 2011). Simple biosynthetic or chemical modification on

106 

BC surface can improve its compatibility with different matrixes and expand its

107 

utilization in nano-related applications. Another notable feature of BC is its high aspect

109  110  111 

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101 

ratio and abundant active functional hydroxyl groups, which makes it suitable for combination with different nanostructures by providing powerful interaction of BC with surrounding species, such as inorganic and polymeric nanoparticles and nanowires(Huang & Gu, 2011). This novel concept breaks new ground to make

112 

optimum use of the specific chemical properties of the guest substrates, in association

113 

with the unique features of renewable BC resources. As a promising template in the

114 

synthesis of a great variety of nanostructures with designed properties and

115 

functionalities, BC can play the role of reducing agent, structure-directing agent and 5   

Page 5 of 83

stabilizer(Yang, Xie, Deng, Bian & Hong, 2012). The polymeric or inorganic

117 

ingredients can be incorporated and cooperatively interact with BC nanofibers to attain

118 

some functional products. Such new high-value materials are the subject of continuing

119 

research and are commercially interesting in terms of new products from the

120 

inexhaustible and sustainable natural polymeric raw material.

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In the last few years, growing worldwide activity can be observed regarding

122 

extensive scientific investigation and increasing efforts for the practical use of the BC

123 

materials. There is an increasing annual publication activity on BC (also known as

124 

microbial cellulose or bacterial nanocellulose) since 2000 as presented in Fig. 2. In

125 

recent years, the investigation and utilization of BC in functional materials have been

126 

the focus of research, and a growing number of works have been included in this field.

127 

Functional BC-based nanomaterials are especially an attractive topic because they

128 

enable the creation of materials with improved or new properties by mixing multiple

129 

constituents and exploiting synergistic effects, such as electronic, optical, magnetic,

131  132  133 

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catalytic properties or bioactivity, etc. With a special property or several remarkable functions, functional BC-based nanomaterials are a type of high value-added materials possessing potential applications in specific fields. In this review, recent developments on BC-based advanced functional nanomaterials including modified BC nanomaterials,

134 

functional BC-based nanocomposites and their applications will be discussed and

135 

reviewed. A variety of surface functionalisation through biosynthetic or chemical

136 

modification will be considered, which can improve the functionality of BC

137 

nanomaterials and expand its potential application fields. Various approaches to the 6   

Page 6 of 83

preparation of functional BC-based nanocomposites by incorporating different guest

139 

substrates including small molecules, inorganic nanoparticles or nanowires, and

140 

polymers on the surfaces of BC nanofibers are summarized, which mainly focus on the

141 

preparation methods, performances and some formation mechanisms of specific

142 

functional nanomaterials.

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2. Construction strategies of BC–based functional nanomaterials

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143 

145 

Although BC nanomaterial has unique physical and chemical characteristics, its

147 

high degree of crystallinity and sole functional group lead to its poor dissolubility and

148 

processability, thereby limiting the application fields. BC possesses an abundance of

149 

hydroxyl groups on the surface, where modification can be easily achieved. It can be

150 

modified to achieve alternative functional groups and patterns of functionalization

154 

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146 

155 

properties combined with a controlled pre-set functionalization pattern is in the center

156 

of interest.

151  152  153 

using in situ and ex-situ modification methods as shown in Fig. 3. The properties of BC derivatives are primarily determined by the type of the functional groups. In particular, modified BC with more than one functional group possessing different surface characteristics such as lipophilic-hydrophlic properties, magnetic and optical

157 

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158 

2.1. Biosynthetic modification

159 

The shape and supramolecular structure of BC can be controlled by the change of

161 

cultivation conditions such as the type of strain, carbon source, and additives (Hessler

162 

& Klemm, 2009; Klemm et al., 2006). Studies have demonstrated the potential for

163 

manipulating the biogenesis of BC in order to produce modified BC nanofibers with a

164 

controlled composition, morphology, and properties. The inclusion of additives in the

165 

nutrient media components during biosynthesis can influence the assembly and

166 

microstructure of BC including the crystallinity, crystalline polymorphism, crystallite

167 

size and ribbon width. The presence of additives in the media may interfere with the

168 

bacterial cells or bind directly to the cellulose during production, thereby affecting the

169 

yield, structure, morphology and physical properties of BC. The in situ generation of

170 

composites can also be effectively regulated during biosynthesis by the inclusion of

171 

additives and dispersed particles.

173 

174 

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2.1.1. Altered BC structure

175 

As a remarkable benefit of BC, the ultrastructure and morphology of BC can be

176 

altered by introducing additives not specifically required for bacterial cell growth in

177 

the media. The effects of the water-soluble agents in culture media on the aggregation

178 

and crystallization of BC microfibrils were intensively studied. Adding various 8   

Page 8 of 83

water-soluble chemical reagents can modify the microfibrillar features of the cellulosic

180 

ribbons. Adding nalidixic acid or chloramphenicol produced ribbons with an

181 

apparently larger width, probably because several ribbons from a cluster of cells whose

182 

dividing process was inhibited, combined or intertwined. While adding dithiothreitol

183 

produced ribbons with only 45% width of the control ribbons on average(Yamanaka &

184 

Sugiyama, 2000).

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The pore system and water content of BC can be controlled in situ by the

186 

incorporation of water soluble polymers such as carboxymethylcellulose (CMC),

187 

hydroxypropylmethyl cellulose (HPMC), methylcellulose (MC), poly(vinyl alcohol)

188 

(PVA) and polyethylene glycol (PEG) to the culture medium (Seifert, Hesse, Kabrelian

189 

& Klemm, 2004). In the presence of these additives, the pore system and elasticity of

190 

BC, as well as the water adsorption and water holding capacity can be controlled. It has

191 

been claimed the addition of HPMC, CMC and MC can cause decreased crystallinity

192 

and crystal size, as well as greater thermal stability and pore size (Chen, Chen, Huang

194  195  196 

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193 

an

185 

& Lin, 2011). Along with the formation of porelike network structure, the water retention ability and the ion absorption capacity increase. The functionalized BC produced with CMC also showed good adsorption performances for copper and lead ions (Chen et al., 2009). Nevertheless the presence of PVA in the culture medium

197 

results in a reduced water absorption ability and a slightly higher copper ion capacity

198 

in comparison with original BC. The addition of β-cyclodextrin or PEG 400 causes a

199 

remarkable pore size increase (Heßler & Klemm, 2009). Surprisingly, these

200 

co-substrates act as removable auxiliaries not incorporated in the BC samples. 9   

Page 9 of 83

Other polymers such as Tween 80, urea, fluorescent brightener and sodium alginate

202 

(NaAlg) have also been incorporated into the BC fermentation medium, with the

203 

observed differences in pore size, degree of polymerization, crystallinity, fibre widths

204 

and mechanical strength (Huang, Chen, Lin, Hsu & Chen, 2010; Ruka, Simon & Dean,

205 

2013; Zhou, Sun, Hu, Li & Yang, 2007). The results revealed that the addition of urea

206 

can increase the mechanical strength. The bundle widths of BC produced with

207 

fluorescent brightener increased and the cellulose network void grew. BC produced

208 

with NaAlg added has a lower crystallinity, a smaller crystalline size and an enhanced

209 

yield.

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2.1.2. Nanocomposites

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212 

In particular, the additives can be in situ incorporated into the growing BC fibrils to

215  216  217 

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210 

create a novel type of nanocomposites, which represents a very specific and important modification method of BC. This in situ technique can combine the properties of altered supramolecular structure of BC with those of the incorporated components. So far, researchers have put different efforts to obtain BC nanocomposites by applying

218 

various additives such as organic compounds, polymers and inorganic substances

219 

(Klemm et al., 2011).

220 

The biological fermentation of BC in presence of cationic starch leads to the

221 

formation of double-network BC composites by incorporation of the starch derivative

10   

Page 10 of 83

in the BC network (Heßler & Klemm, 2009). This double-stage structure consists of an

223 

opaque upper and a transparent under part. As shown in Fig. 4a, in case of the upper

224 

layer, the additive adsorbs at the cellulose fibers and causes an irregular distribution of

225 

the pore sizes. The under layer indicates the incorporation of the starch into the solvate

226 

shells of the BC prepolymer, forming an exciting skinny film structure (Fig. 4b). Other

227 

characteristic examples include the additives of poly(ethylene oxide)(Brown &

228 

Laborie, 2008), PVA (Gea, Bilotti, Reynolds, Soykeabkeaw & Peijs, 2010) and

229 

starch(Grande, Torres, Gomez, Troncoso, Canet-Ferrer & Martinez-Pastor, 2009) in

230 

the media for the formation of nanocomposites with the incorporation of these

231 

additives into the network of BC. Along with the increase of the additive content, the

232 

cellulose crystallized into smaller nanofibers, which further bonded together into

233 

bundles. The BC nanofibers were well dispersed in the composites and the

234 

nanocomposites typically show significantly improved mechanical properties.

236  237  238  239 

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The inorganic additives can drastically modify the performance of BC.

Ac ce p

235 

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222 

BC/multiwalled carbon nanotubes (MWCNTs) composites can be obtained in the presence of MWCNTs in an agitated culture (Park, Kim, Kwon, Hong & Jin, 2009; Yan, Chen, Wang, Wang & Jiang, 2008). Interestingly, a core-shell structure model was demonstrated, with the packed MWNTs attached nascent sub-elementary fibrils as the

240 

core of the cellulose assemblies as shown in Fig. 4c. While in the static culture method,

241 

band-like assemblies with sharp bends and rigidness were produced in the presence of

242 

MWCNTs. Similarly, the crystallinity index, crystallite size, and cellulose Iα content

243 

also changed, which may be attributed to the interaction between the hydroxyl groups 11   

Page 11 of 83

of treated MWCNTs and the sub-elementary BC fibrils, interfering with the

245 

aggregation and crystallization of BC microfibrils. By adding silica or titanium

246 

precursor into the static growth medium, the SiO2 and TiO2 nanoparticles about several

247 

tens of nanometers in size can be incorporated onto BC microfibrils (Geng, Yang, Zhu,

248 

Cao, Jiang & Sun, 2011; Yano, Maeda, Nakajima, Hagiwara & Sawaguchi, 2008) (Fig.

249 

4d). It is inferred that the basic proteins in the outer membrane of bacterium cell act as

250 

the catalyst for the hydrolysis and condensation of inorganic precursor, the surface of

251 

both outer membrane and BC nanofibers renders the nucleation and growth sites for

252 

inorganic nanoparticles. The space-temporal effect endows bacteria the delicate

253 

control ability over formation of the nanocomposites.

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2.2. Chemical surface modification

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254 

257  258  259  260 

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Although the biosynthetic modification of BC is a kind of green sustainable

technology, the strict microbial fermentation environment restricts the introduction of some additives. Other questions involving the interaction mechanism between the additives and microfibrils growth, as well as the structure control of BC nanofibers still

261 

need to be addressed. While chemically modified methods are not limited by the

262 

required types of additives. Compared to the biosynthesis method, its more clearly

263 

defined objectives and principles make it a feasible modified method for BC material.

264 

Since the chemical composition of BC is similar to plant fibers, it can also be

12   

Page 12 of 83

carboxymethylated, acetylated, phosphorylated, and modified by other graft

266 

copolymerization and crosslinking reaction to obtain a series of BC derivatives. The

267 

introduction of new functional groups to the BC structure can endow BC with various

268 

features such as hydrophobicity, ions adsorption capacity and optical properties while

269 

maintaining the unique three-dimensional nano network and excellent mechanical

270 

properties of BC.

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In most cases, the modification of BC focuses on the improvement of its

272 

applicability and performance in different application fields. Several methods have

273 

been employed to achieve BC derivatives with improved metal ions absorption

274 

capacity. The functionalized diethylenetriamine-BC (EABC), amidoximated BC

275 

(Am-BC) and phosphorylated BC have been prepared as new adsorbents for metal ions

276 

(Chen, Shen, Yu, Hu & Wang, 2010; Oshima, Kondo, Ohto, Inoue & Baba, 2008; Shen

277 

et al., 2009). The experimental data showed that the microporous network structure of

278 

BC was maintained after the modification and these novel adsorbent showed good

280  281  282 

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an

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adsorption performances for different metal ions. To anchor metallic ions on BC nanofibers, the carboxylate groups have been introduced onto the BC nanofiber surface

using

the

2,2,6,6-tetramethylpiperidine-1-oxyradical(TEMPO)-mediated

oxidation system (Ifuku, Tsuji, Morimoto, Saimoto & Yano, 2009). The oxidation can

283 

proceed under mild aqueous conditions maintaining the crystallinity and crystal size of

284 

BC nanofibers.

285 

In order to improve the dispersability and compatibility in different solvents or

286 

matrices that are suitable in the production of nanocomposites, the acetylation of BC 13   

Page 13 of 83

based on a non-swelling reaction mechanism was reported recently. BC could be

288 

partially acetylated by the fibrous acetylation method to modify its physical properties,

289 

while preserving the microfibrillar morphology(Kim, Nishiyama & Kuga, 2002). The

290 

hydrophobicity of the acetylated surface is advantageous for maintaining a large

291 

surface area on drying from water and would make the microfibrils compatible with

292 

other hydrophobic materials. While most of the chemically modified techniques

293 

require tedious solvent exchanges that strongly diminish the environmental benefit of

294 

the use of BC. A major thrust of recent BC modification research focused on the design

295 

of more economical and environmentally friendly method to obtain novel BC

296 

derivatives. Thus, a solvent-free derivatization system appears as an important goal to

297 

get BC derivative products with hydrophobic surfaces with a minimum environment

298 

impact. In line with the solvent-free BC derivatization concept, BC preserving the

299 

microfibrillar morphology has been partially acetylated using acetic anhydride in the

300 

presence of iodine as a catalyst (Hu, Chen, Xu & Wang, 2011). Another example is the

302  303  304 

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reported vapor-phase technique which has been applied recently for the surface esterification of BC microfibrils with the help of gaseous trifluoroacetic acid mixed with acetylating agents (Berlioz, Molina-Boisseau, Nishiyama & Heux, 2009). Experimental results have shown the acetylation proceeded from the surface to the

305 

interior crystalline core of BC nanfibers. Hence, for moderate degree of substitution,

306 

the surface was fully grafted whereas the cellulose core remained unmodified and the

307 

original fibrous morphology was maintained. The obtained acetylated BC membrane

308 

shows more hydrophobic surface and good mechanical properties as shown in Fig. 5, 14   

Page 14 of 83

309 

which is in favor of enhancing the hydrophobic non-polar polymeric matrix.

310 

2.3. In situ formation of nanostructures

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BC has unique micro-nano porous three-dimensional network, which can facilitate

314 

the penetration of various metal ions into the interior. It also possesses a great deal of

315 

hydroxyl and ether bonds, forming the effective reactive sites to anchor metallic ions

316 

on the surface of the nanofibers. Then a variety of inorganic nanoparticles or

317 

nanowires can be formed through precipitation, oxidation-reduction and sol-gel

318 

reaction as shown in Fig. 6. Different from the doped nanoparticles into BC matrix, the

319 

size and morphology of the nanoparticles can be regulated by adjusting the structure of

320 

BC template and the in situ preparation conditions. At the same time, the nanospace in

321 

the BC fibers can behave as an effective nanoreactor to prevent the unwanted

323  324  325 

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agglomeration phemnonmenon, ensuring the effective dispersion of the formed nanoparticles in the BC matrix. In the process of in situ preparation of BC-based nanocomposites, the second

components such as metal and polymer in the form of particles or fibers can be

326 

introduced into the BC matrix, while retaining the unique three-dimensional

327 

nanoporous network of BC. BC can be viewed as a soft template to control the

328 

synthesis of desired nano-materials or nano-structure with specific size and shape. This

329 

can obtain a variety of novel functional materials with unique features and outstanding

15   

Page 15 of 83

performances. Using BC as a template in the in situ synthesis of nano-materials has the

331 

following advantages: BC is a kind of environment-friendly and renewable material

332 

which can be produced from a wide range of raw materials. The shape, structure and

333 

properties can be easily adjusted during the biosynthesis, pretreatment and chemical

334 

modification process. Furthermore, the BC matrix can be removed by calcination to

335 

obtain the pure inorganic nanoparticles and nanowires structure.

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Therefore, BC with controllable structure and pore size can provide restrictive

337 

environment to ensure a variety of nanostructures effectively embedded in the matrix.

338 

The method does not require severe conditions, and is simple and easy to implement,

339 

which can obtain the nano-particles with narrow size distribution. So far, this method

340 

has been applied to synthesize different nanomaterials such as metal, semiconductor

341 

and electrically conducting polymers through different preparation methods.

342 

2.3.1. In situ formation of nanostructures through reduction reaction

344  345  346 

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There have been some reports regarding the application of BC as a soft template to

in situ form different metal nanoparticles by the reduction reaction as shown in Table 1. The size and morphology of the formed nanoparticles can be controlled by using different reducing agents such as sodium borohydride (NaBH4), triethanolamine,

347 

hydrazine (NH2NH2), hydroxylamine (NH2OH), ascorbic acid, polyethylenimine (PEI)

348 

and so on (Barud et al., 2008; Yang, Xie, Hong, Cao & Yang, 2012; Zhang et al., 2010).

349 

These reducing agents can serve as an assistant material for stabilizing nanoparticles,

350 

preventing their aggregation. In addition, BC itself can be used as a reductant to

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Page 16 of 83

produce metal nanoparticles (Yang, Xie, Deng, Bian & Hong, 2012), without

352 

introducing additional reducing agent or stabilizing agent, thus avoiding the secondary

353 

pollutants and guaranteeing the feasibility of its applications in medical and catalytic

354 

field.

355 

2.3.2. In situ formation of nanostructures through precipitation reaction

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Well-separated nanofibrils of BC create an extensive surface area forming active

357 

sites for metal ion adsorption, and the subsequent introduction of precipitating agent

358 

will react with the immobilized metal ions to generate the initial nuclei of metal or

359 

oxide. Then the nuclei continue to grow, thereby further forming functional inorganic

360 

nanoparticles as shown in Fig. 7. The growth of the nanoparticles was readily

361 

controlled by repeated alternating dipping of BC membranes in the metal ion and

362 

precipitating agent solution followed by a rinse step. So it is feasible for BC to serve as

363 

an excellent matrix in the synthesis of nanoparticles through the in situ precipitation

365  366  367 

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reaction.

CdS and CdSe nanoparticles have been synthesized and stabilized on BC nanofibers

using in situ precipitation method (Li et al., 2009a; Yang et al., 2012a). At first, hydroxyl and ether groups of BC anchored Cd2+ or thioglycolic acid capped Cd2+, then

368 

the anchored Cd2+ reacted with S2- or Se2- to generate CdS or CdSe nanoparticles on

369 

the BC nanofibers as shown in Fig. 8. The results indicated that nanoparticles with the

370 

diameter of 20-30 nm deposited on BC nanofibres are well-dispersed in the BC

371 

nanofibre-network. AgCl nanoparticles with a size of several tenths of nanometers

17   

Page 17 of 83

have been in situ synthesized in the three-dimensional non-woven network of BC

373 

nanofibrils (Hu et al., 2009). The growth of the nanoparticles was readily obtained by

374 

repeated alternating dipping of BC membranes in the solution of silver nitrate or

375 

sodium chloride followed by a rinse step. The nanopore is essential for introduction of

376 

silver ions and reaction with Cl− to form AgCl particles into BC fibers and removal of

377 

the excess chemicals from BC fibers.

us

cr

ip t

372 

BC can serve as an excellent matrix in the in situ synthesis of the Fe3O4

379 

nanoparticles through the coprecipitation reaction (Zhang et al., 2011). The ultrafine

380 

network architecture of BC gives a good tunnel for Fe2+/Fe3+ adsorption and ensures

381 

the effective anchoring of absorbed ions onto the BC nanofibers through ion–dipole

382 

interactions. After being rinsed with distilled water to remove the unanchored ions, the

383 

obtained ions/BC complexes were immersed into the excessive NaOH solution. The

384 

interaction between Fe2+/Fe3+ and OH− can induce the formation of Fe3O4

385 

nanoparticles with the diameter of 80-100 nm as shown in Fig. 9.

387  388  389 

M

d

te

Ac ce p

386 

an

378 

During the in situ formation process of different nanostructures, the size and size

distribution of the formed nanoparticles are controllable by adjusting synthetic parameters such as the concentration of metal ions. When the concentration of metal ions is too high, the BC nanofibers fails to fully immoblize and disperse the large

390 

number of metal ions due to the limited hydroxyl reactive sites shown in Fig. 10.

391 

Meanwhile, the presence of excess metal ions would result in the agglomeration of the

392 

nanoparticles due to the higher aggregation speed than the orientation speed in the

393 

particle growth process. Therefore the concentration of the reaction solution needs to 18   

Page 18 of 83

be reduced appropriately to ensure the metal ions and nanoparticles effectively

395 

dispersed and fixed onto the surface of the nanofibers. However, when the

396 

concentration is too low, the loading amount of the nanoparticles will be significantly

397 

reduced, which would degrade the performance of the final products. The exploration

398 

of optimal reaction conditions would be particularly important to achieve the effective

399 

dispersion of nanoparticles with sufficient loading amount, thereby obtaining the

400 

functional nanocomposite materials with excellent optical, electrical, magnetic and

401 

antibacterial properties.

402 

2.3.3. In situ formation of nanostructures through sol-gel reaction

M

an

us

cr

ip t

394 

Taking advantage of the ultrafine nanofibrous structure, as well as abundant porous

404 

channels inside the network, BC nanomaterials can be used as the templates to in situ

405 

prepare metal oxides through the sol-gel reaction. The schematic diagram of the in situ

406 

preparation process is described in Fig. 11. When immersing BC into the precursor

408  409  410 

te

Ac ce p

407 

d

403 

solution, the inorganic ions can be immobilized onto the BC nanofibers. Then it can be solidified to form the gel through hydrolysis and condensation, and subsequently heated to form the desired oxides. BC template can stabilize and disperse the formed oxides nanoparticles through van der Waals forces and hydrogen bonding interaction,

411 

prompting generated nanoparticles distributed along the surface of nanofibers. The BC

412 

template can also be removed by calcination to obtain hollow nanofibers with a

413 

three-dimensional network structure. TiO2/BC hybrid composites were prepared using BC as a hydrophilic substrate for

414 

19   

Page 19 of 83

synthesizing TiO2 nanoparticles via sol–gel (Gutierrez, Tercjak, Algar, Retegi &

416 

Mondragon, 2012) as shown in Fig. 12. The spherical TiO2 nanoparticles with an

417 

average size of 25 nm in diameter were located on the surface of the nanofibers due to

418 

hydrogen bonding interactions. The BC template could also be removed in order to

419 

change or optimize the properties of the in situ formed nanomaterial. The process also

420 

can make use of the synergy between the BC template and inorganic materials to

421 

synthesize a variety of nanoscale metal oxides with the hollow network. Mesoporous

422 

titania networks consisting of interconnected anatase nanowires typically 20–30 nm in

423 

diameter have been synthesized by using BC as natural biotemplates through the

424 

sol-gel titania coating (Zhang & Qi, 2005). The titania networks exhibit enhanced

425 

photocatalytic activity due to the larger accessible surface areas.

427 

2.4. Ex-situ introduction of components

429  430  431 

Ac ce p

428 

te

426 

d

M

an

us

cr

ip t

415 

The functional BC-based nanocomposites can also be formed through the ex-situ

introduction of different components by the solution impregnation method. BC nanocomposites loaded with nano-scale silica nanoparticles have been prepared by

432 

immersing BC hydrogel into different concentrations of silica sols, allowing nano scale

433 

silica to be trapped and fixed in the spaces between the ribbon-shaped fibrils in the BC

434 

hydro-gel matrix (Fig. 13) (Ashori, Sheykhnazari, Tabarsa, Shakeri & Golalipour,

435 

2012; Maeda, Nakajima, Hagiwara, Sawaguchi & Yano, 2006; Yano, Maeda,

20   

Page 20 of 83

436 

Nakajima, Hagiwara & Sawaguchi, 2008). This method improved the modulus and

437 

strength compared to the pure BC matrix, but it was difficult to load the BC with more

438 

than 10% silica in this way. This strategy also can utilize the nanoeffect of the ribbon-shaped fibrils of BC to

440 

prepare optically transparent materials. Transparent poly(L-lactic acid)(PLLA)/BC

441 

nanocomposites was prepared by incorporating microbial nanofibrils into PLLA matrix

442 

(Kim, Jung, Kim & Jin, 2009). The nanocomposite retained the transparency of the

443 

pure PLLA film due to the nanofibrillar structure of the BC, which is smaller than the

444 

wavelength of visible rays. An increase in the mechanical properties was observed by

445 

incorporating BC as reinforcement into the PLLA matrix. The highly translucent

446 

bionanocomposites have been prepared by simply incorporating BC into the pullulan

447 

or poly (3-hydroxybutyrate) (PHB) matrix (Trovatti, Fernandes, Rubatat, Freire,

448 

Silvestre & Neto, 2012; Zhijiang & Guang, 2011; Zhijiang, Guang & Kim, 2011) (Fig.

449 

14a and b), which have improved the mechanical performance and thermal stability of

451  452  453 

cr

us

an

M

d

te

Ac ce p

450 

ip t

439 

the nanocomposite films. Novel nanocomposite films based on chitosan and BC were prepared by a fully green procedure by casting a water based suspension of chitosan and BC nanofibrils (Fernandes et al., 2009). They were highly transparent, flexible and displayed better mechanical properties than the corresponding unfilled chitosan films

454 

(Fig. 14c). These new renewable nanocomposite materials also presented reasonable

455 

thermal stability and low O2 permeability.

21   

Page 21 of 83

456 

2.5. Other combined strategies In most cases, we can adopt the combined strategies mentioned above to obtain the

458 

nanocomposites with designed structures and required performance. The hydrophobic

459 

BC-based nanocomposite sheets can be produced by the in situ synthesis of BC/CNTs

460 

nanocomposite by biosynthetic modification and the subsequent heterogeneous

461 

acetylated surface modification (Adnan & Radiah Awang Biak, 2012). The epoxidized

462 

soybean oil (ESO)/BC nanofibers have been prepared through the acetylated

463 

modification and the following solution impregnation in the ESO resin (Retegi et al.,

464 

2012). An electromagnetic composite of BC has been synthesized by culturing

465 

gluconacetobacter xylinus in a medium containing magnetite nanoclusters (MNP) and

466 

the subsequently in situ formation of PANI on the magnetic BC fibers by chemical

467 

oxidative polymerization with ammonium persulfate (APS) as the oxidant (Fig. 15)

468 

(Park, Cheng, Choi, Kim & Hyun, 2013).

te

d

M

an

us

cr

ip t

457 

Ac ce p

For BC to be suitable as a more effective nanoreactor to control the formation of

473  474 

hydrolysis of zinc acetate in a polyol medium to form the ZnO/Am-BC

475 

nanocomposites as shown in Fig. 16. The TEMPO-mediated oxidized BC nanofibers

476 

has been applied as reaction templates to prepare fine silver nanoparticles with a

477 

controlled size distribution (Ifuku, Tsuji, Morimoto, Saimoto & Yano, 2009). The

469  470  471  472 

nanomaterials, the chemical functionalization should be employed to modify the BC fibers for imparting BC membranes with new functionalities and producing BC nanocomposites with tailored characteristics. The Am-BC as host matrix can stably anchor numerous zinc ions and then as nanoreactors to fabricate ZnO nanoparticles by

22   

Page 22 of 83

478 

amidoximation and oxidation of BC can provide more reactive sites to immobilize the

479 

formed nanoparticles with high density, which are important factors for electronic,

480 

catalytic, and biomedical applications. Thus, the functional nanostructures can be achieved by in situ formation of

482 

nanoparticles or ex-situ introduction of components into the biosynthetically or

483 

chemically modified BC matrix. At the same time, the fabrication steps can be adjusted

484 

or even reversed to construct the BC-based functional nanomaterials with controllable

485 

structures and designed functional performance.

an M

486 

3. Applications of BC-based functional nanomaterials

d

487 

us

cr

ip t

481 

te

488 

BC has been recently investigated as an attractive eco-friendly nanomaterial for the

490 

preparation of high value-added nanocomposites. The functionalization of BC with

494 

Ac ce p

489 

495 

nanomaterials like antibacterial, optical, electrical and magnetic properties, as well as

496 

catalytic and biomedical activity. Several recent reviews giving a summary and

497 

discussion regarding the applications of BC-based materials as medical devices or

498 

reinforcement materials for polymer nanocomposite have been published (Eichhorn et

491  492  493 

inorganic or polymeric materials opens up new pathways for the fabrication of novel multifunctional nanocomposites with promising performances. BC was used as a template for the preparation of novel functional nanocomposites that gather together excellent properties of BC with the ones displayed by typical inorganic or organic

23   

Page 23 of 83

al., 2010; Klemm et al., 2011; Petersen & Gatenholm, 2011). Here we reviewed the

500 

potential advantages and different applications of BC based functional nanomaterials,

501 

which mainly focus on the application such as sensors, photocatalytic nanomaterials,

502 

optoelectronic materials and devices, and magnetically responsive membranes.

ip t

499 

3.1. Sensors

us

504 

cr

503 

an

505 

BC as a kind of environmentally friendly and low-cost material has high surface

507 

area and a large number of surface hydroxyl groups which make it an attractive

508 

medium for applications such as sensors. BC can be considered as prime material or

509 

substrate material for the construction of high-performance moisture or gas sensor due

510 

to their large specific surface areas, a large number of surface hydroxyl groups, good

511 

water absorbance and water holding capacity. With the combination of quartz crystal

513  514  515 

d

te

Ac ce p

512 

M

506 

microbalance (QCM) system (Fig. 17), the BC nanofibrous membrane coating can be a good consideration for constructing highly sensitive humidity and gas sensors. The BC dispensed onto the surface of the QCM electrode was installed in the testing chamber. Through injecting water or gas into the chamber, the sensing properties of the sensors

516 

were examined by measuring the resonance frequency shifts of QCM due to the

517 

additional mass loading. A highly stable and sensitive humidity sensor based on BC

518 

coated QCM has been fabricated (Hu, Chen, Zhou, Liu, Ding & Wang, 2011). The

519 

results showed that the sensors possessed good sensing characteristics by increasing

24   

Page 24 of 83

520 

more than two orders of magnitude with increasing relative humidity (RH) from 5 to

521 

97%, and the Log(Δf) showed good linearity (20–97% RH). The resultant sensors

522 

exhibited a good reversible behavior and good long term stability. By introducing other detective components to the BC substrate, the modified

524 

nanoporous BC membranes with the high specific surface area and high porosity

525 

would be an ideal candidate for further improving the sensitivity of gas sensors. A

526 

formaldehyde sensor based on nanofibrous PEI/BC membranes coated QCM has been

527 

fabricated (Hu, Chen, Liu, Ding & Wang, 2011). PEI has been introduced as the

528 

detective material to strengthen the interaction between the sensing materials and

529 

formaldehyde molecules as shown in Fig. 18. The sensor showed high sensitivity with

530 

good linearity and exhibited a good selectivity and repeatability towards formaldehyde

531 

in the concentration range of 1-100 ppm at room temperature. It has a detection limit of

532 

1 ppm which is enhanced compared to other nanostructured coatings because of the

533 

large specific surface area of the sensing materials. This strategy also can be applied in

535  536  537 

cr

us

an

M

d

te

Ac ce p

534 

ip t

523 

other system to introduce various detective materials combined with BC nanofibers to detect other gases.

BC with the ultrafine nanofibrous network, high stability, excellent biocompatibility

and extensive surface area, would be a very promising support for the construction of

538 

biosensors. The gold nanoparticles–BC nanofibers (Au-BC) nanocomposite has been

539 

synthesized and used for enzyme immobilization and glucose biosensor fabrication

540 

(Wang et al., 2010; Wang et al., 2011; Zhang et al., 2010). The developed biosensor

541 

based on horseradish peroxidase (HRP)/Au-BC nanocomposite exhibited excellent 25   

Page 25 of 83

performance in terms of a wider linear range, lower limit of detection (lower than 1 μm)

543 

and fast response toward hydrogen peroxide (Zhang et al., 2010) (Fig. 19), suggesting

544 

the Au–BC nanocomposite a suitable matrix for enzyme immobilization. The

545 

biosensor for glucose exhibits a detection limit as low as 2.3 mM with a linear range

546 

from 10 mM to 400 mM, which could be used to monitor glucose in real blood samples

547 

(Wang et al., 2010).

us

cr

ip t

542 

548 

3.2. Photocatalytic nanomaterials

an

549 

M

550 

BC can be viewed as a template with the main controlling sites made up of hydroxyl

552 

and ether bonds to guide the synthesis of photocatalytic nanoparticles or

553 

nanocomposites. Well-dispersed and regular ZnO nanoparticles with a narrow size

554 

distribution of 20–50 nm and high photocatalytic activity have been successfully

556  557  558 

te

Ac ce p

555 

d

551 

synthesized through decomposing BC infiltrated with zinc acetate aqueous solution at high temperature (Hu, Chen, Zhou & Wang, 2010). In addition, the photocatalytic ZnO/BC and ZnO/Am-BC nanocomposite membranes can be synthesized through a facile polyol method using BC or Am-BC as a template (Chen, Zhou, Hu, Zhang, Yin

559 

& Wang, 2013). The resulting nanocomposites containing ZnO nanoparticles with a

560 

uniform distribution and an average diameter of 50 nm show good mechanical

561 

properties and high photocatalytic activity in the degradation of methyl orange.

562 

Compared to the ZnO/BC nanocomposite films, the ZnO/Am-BC nanocomposites

26   

Page 26 of 83

563 

with higher loading content of ZnO nanoparticles displayed a higher decolorization

564 

efficiency of 91% at 120 min, indicating an excellent candidate for photocatalyst. The photocatalytic mesoporous TiO2/BC hybrid nanofibers have been fabricated by

566 

surface hydrolysis with molecular precision (Sun, Yang & Wang, 2010). The uniform

567 

and well-defined nanofibers consist of large quantities of oriented TiO2 nanoparticle

568 

arrays implanted on the BC nanofibers with diameters in the 4.3–8.5 nm range. The

569 

TiO2/BC nanocomposites were used as photocatalyst for methyl orange degradation

570 

under UV irradiation, and they showed higher efficiency than that of the commercial

571 

photocatalyst due to the high surface area of 208.17 m2/g. Furthermore, the

572 

photocatalytic ability can be improved by dopping with nitrogen. The BC template

573 

also can be removed by calcinations to obtain the mesoporous TiO2 networks

574 

consisting of interconnected anatase nanowires (Zhang & Qi, 2005). The mesoporous

575 

titania networks exhibit a considerably enhanced photocatalytic activity compared

576 

with the macroporous titania networks obtained through a similar sol-gel nanocasting

578  579  580 

cr

us

an

M

d

te

Ac ce p

577 

ip t

565 

procedure.

The photocatalytic micrometer-long CdS/BC hybrid nanofibers have been prepared

via a simple hydrothermal reaction at relatively low temperature (Yang, Yu, Fan, Sun, Tang & Yang, 2011). Hexagonal phase CdS nanoparticles were homogeneously

581 

deposited onto the hydrated BC nanofibers and stabilized via coordination effect. The

582 

CdS/BC hybrid nanofibers demonstrated high-efficiency photocatalysis with 82%

583 

methyl orange degradation after 90 min irradiation and good recyclability. The results

584 

indicate that the CdS/BC hybrid nanofibers are promising candidate as robust visible 27   

Page 27 of 83

585 

light responsive photocatalysts.

586 

3.3. Optoelectronics

ip t

587 

cr

588 

BC-based electroconductive composites can be prepared by combining conducting

590 

electroactive materials with hydrophilic biocompatible BC. These conductive

591 

materials including metal ions and oxides, carbon nanotubes and conducting polymers

592 

in the form of nanoparticles or nanowires can be introduced into the BC matrix by in

593 

situ synthesis, doping, blending or coating.

594 

3.3.1. Electrically conductive films

d

M

an

us

589 

The MWCNTs-incorporated BC was prepared by dipping a BC pellicle in an

596 

aqueous MWCNT dispersion containing a cetyl trimethyl ammonium bromide (CTAB)

598  599  600  601 

Ac ce p

597 

te

595 

surfactant (Yoon, Jin, Kook & Pyun, 2006). This composite process produced electrically conducting BC pellicles containing well-dispersed and embedded MWCNTs as shown in Fig. 20a. The electrical conductivity of the BC/MWCNT composite was found to be approximately 1.4 ×10-1 S/cm. The transparency of the MWCNTs-incorporated BC can also be improved by incorporating an aqueous silk

602 

fibroin solution into BC membranes to obtain an electrically conductive transparent

603 

paper (Fig. 20b) (Jung, Kim, Kim, Kwon, Lee & In, 2008). Good optimal transparency

604 

and electrical properties were obtained with a transmittance of 70.3% at 550 nm and

605 

electrical conductivity of 2.1×10-3 S/cm. This strategy can also be applied in the 28   

Page 28 of 83

preparation of single-walled carbon nanotubes (SWCNTs) adsorbed BC membranes to

607 

obtain the transparent conducting film with a transmittance of 77.1% and surface

608 

resistance of 2.8 kΩ/sq (Kim, Kim, Bak, Yun, Cho & Jin, 2009). The resultant

609 

electrically conductive transparent films showed remarkable flexibility without any

610 

loss of their initial properties (Fig. 20c). Thus, the prepared electrically conductive

611 

paper can be applied as a transparent electrode in photoelectronics such as flexible

612 

displays and touch screens.

us

cr

ip t

606 

Recently, the polyaniline (PANI)/BC and polypyrrole (PPy)/BC composites have

614 

been intensively researched (Hu, Chen, Yang, Liu & Wang, 2011; Lee, Kim & Yang,

615 

2012; Marins, Soares, Dahmouche, Ribeiro, Barud & Bonemer, 2011; Muller, Rambo,

616 

Recouvreux, Porto & Barra, 2011; Wang, Bian, Zhou, Tang & Tang, 2013). Our group

617 

has fabricated conductive PANI/BC nanocomposite membranes by oxidative

618 

polymerization of aniline with ammonium persulfate as an oxidant and BC as a

619 

template (Hu, Chen, Yang, Liu & Wang, 2011). The schematic diagram of the

621  622  623 

M

d

te

Ac ce p

620 

an

613 

formation of PANI/BC nanocomposites is shown in Fig. 21. It was found that the PANI nanoparticles deposited on the surface of BC connected to form a continuous nanosheath by taking along the BC template, and the conductivity could be enhanced when PANI is doped by protonic acids. The resulting PANI-coated BC nanofibrils

624 

exhibit excellent electrical conductivity of 5.0×10-2 S/cm and good mechanical

625 

properties with Young’s modulus of 5.6 GPa and tensile strength of 95.7 MPa. The

626 

electrical conductivity of PANI/BC composites can be further improved to 3.8×10-1

627 

S/cm by adopting the interfacial polymerization (Lee, Chung, Kwon, Kim & Tze, 29   

Page 29 of 83

2012). Furthermore, by using FeCl3·6H2O as oxidant, the free-standing films of

629 

PANI/BC composites with high electrical conductivity values (0.9 S cm-1) and PPy/BC

630 

with outstanding electrical conductivities as high as 77 S cm-1 were prepared through

631 

the in situ oxidative chemical polymerization of aniline or pyrrole on the surface of BC

632 

nanofibers (Müller et al., 2012; Wang, Bian, Zhou, Tang & Tang, 2013). The

633 

nanocomposites synergistically combine the electronic characteristics of PANI or PPy

634 

with the outstanding mechanical characteristics of the BC matrix, which could be

635 

applied in flexible electrodes, flexible displays and other electronic devices.

636 

3.3.2. Optically transparent films

M

an

us

cr

ip t

628 

BC has been applied as the flexible substrate for the fabrication of organic light

638 

emitting diodes (OLEDs) by depositing indium tin oxide (ITO) thin films onto the

639 

BC membrane at room temperature using radio frequency magnetron sputtering

640 

(Legnani et al., 2008). However, the average transmittance of BC membrane substrates

642  643  644 

te

Ac ce p

641 

d

637 

at 550 nm is only 40%. Thus many researchers have made efforts to improve the clarity of BC. BC comprising weblike networks of ribbon-shaped nanofibers has high tensile strength and low coefficient of thermal expansion (CTE) of less than 0.1 pp/K in the axial direction, which is a perfect candidate to reinforce transparent plastics (Yano et

645 

al., 2005). The transparent BC/epoxy resin and BC/acrylic resin composites have been

646 

fabricated at a fiber content as high as 70%, which showed a incredibly low CTE of 3

647 

pp/K (similar to that of silicon crystal) and a high tensile strength (325 MPa), while

648 

maintaining the flexibility and ductility of the resin plastics as shown in Fig. 22 (Yano

30   

Page 30 of 83

et al., 2005). Furthermore, due to the nanofiber size effect, the high transparency was

650 

demonstrated for several different resins with a wide distribution of refractive indexes,

651 

from 1.492 to 1.636 at 20 °C (Shah & Brown, 2005). The optical transparency was also

652 

insensitive to temperature up to 80 °C. The hygroscopicity of BC nanocomposites also

653 

have been significantly reduced by using acetylated BC nanofibers to improve the

654 

dimensional stability against temperature while maintaining optical transparency and

655 

thermal stability (Ifuku, Nogi, Abe, Handa, Nakatsubo & Yano, 2007; Nogi, Abe,

656 

Handa, Nakatsubo, Ifuku & Yano, 2006). These nanofiber-network-reinforced

657 

optically transparent composites are expected to lead the way to a wider use of many

658 

different optically transparent polymers in optoelectronic devices such as substrates for

659 

flexible displays and components for precision optical devices, which demand high

660 

transparency and low thermal expansion.

661 

3.3.3. Flexible displays

663  664  665 

cr

us

an

M

d

te

Ac ce p

662 

ip t

649 

Flexible displays have been produced by using BC as the substrate or the basic

optical film to improve their electronic properties. For the fabrication of OLED, the hygroscopicity and surface roughness of BC needs to be adjusted. The Si–O thin film can be deposited on BC surface via plasma enhanced chemical vapor deposition as

666 

transparent barrier against water vapor (Ummartyotin, Juntaro, Sain & Manuspiya,

667 

2011). The deposited Si–O layer offered uniform and exceptionally smooth surface

668 

with the surface smoothness of 15 nm. The surface roughness of BC can be further

669 

reduced to 5 nm by using the ferrofluid solution as nano-abrasion media (Ummartyotin,

31   

Page 31 of 83

Juntaro, Sain & Manuspiya, 2012b). Nanocomposite film composed of BC (10–50

671 

wt.%) and polyurethane (PU) based resin was fabricated and utilized as a substrate for

672 

flexible OLED display (Ummartyotin, Juntaro, Sain & Manuspiya, 2012a). The visible

673 

light transmittance of the nanocomposite film was as high as 80%. Its thermal stability

674 

was stable up to 150 °C while its dimensional stability in terms of CTE was less than

675 

20 ppm/K. After OLED was fabricated on the substrate through thermal evaporation

676 

technique, the OLED performed highest current efficiency of 0.085 cd/A and power

677 

efficiency of 0.021 lm/W at 200 cd/m2 while retaining its flexible feature as shown in

678 

Fig. 23, suggesting that BC nanocomposite is a promising material for the

679 

development of substrate for flexible OLED display.

680 

3.3.4. Photoluminescent and photochromic films

d

M

an

us

cr

ip t

670 

For BC to be suitable for more diverse optoelectronic applications, some of its

682 

properties need to be modified such as endowing it the photoluminescent and

684  685  686 

Ac ce p

683 

te

681 

photochromic properties. Manipulating the different methods to obtain the functional BC can be a useful approach for finetuning BC properties to satisfy appropriate applications or producing BC composites with tailored characteristics. To design and synthesize BC-based new materials is also more significant in exploring new

687 

applications for the unique natural nanofibers. Flexible luminescent CdSe/BC and

688 

CdS/BC membranes have been fabricated by the in situ synthesis of the CdSe and CdS

689 

nanoparticles on the BC nanofibers (Li et al., 2009b; Yang et al., 2012b). The formed

690 

nanoparticles with a size of 20-30 nm were homogeneously dispersed in the BC matrix.

32   

Page 32 of 83

The nanocomposites exhibited good photoluminescence properties and excellent

692 

mechanical properties as shown in Fig. 24. This work provides an effective method for

693 

the construction of flexible BC membranes with photoluminescence properties, which

694 

are promising for applications in optics, electronics and biology. The

photochromic

BC

nanofibrous

membranes

containing

cr

695 

ip t

691 

10,30,30-trimethyl-6-nitrospiro(2H-1-benzopyran-2,20-indoline)

697 

successfully prepared by surface modification of BC nanofibers with spiropyran

698 

photochromes (Hu, Liu, Chen & Wang, 2011) or in situ incorporation of sol-gel

699 

synthesized photoswitchable

700 

(Gutierrez, Fernandes, Mondragon & Tercjak, 2012). The modified BC-NO2SP

701 

membranes exhibited a pink color and had an absorption peak at 568 nm in the

702 

UV–visible spectrum and the color change was reversible due to the reversible

703 

isomerization of the spiropyran moieties in BC-NO2SP as shown in Fig. 25.

704 

Alternating illumination with UV-and-visible light switches the fluorescence of the

706  707  708 

were

an

te

d

M

vanadium nanoparticles using BC as a template

Ac ce p

705 

(NO2SP)

us

696 

membranes on and off and makes the wetting properties of the membranes controllable, confirming that such modified BC membranes have potential application in sensitive displays and optical devices. The addition of vanadium nanoparticles led to the generation of photochromic nanopaper, which was able to reversibly switch the color

709 

from green to dark purple by irradiation under ambient conditions. Moreover, the

710 

flexible, conductive, and optically active photochromic hybrid nanopapers maintained

711 

the semiconductive properties of the well-dispersed vanadium oxide nanoparticles.

712  33   

Page 33 of 83

713 

3.4. Magnetically responsive films

714 

In recent years, the hybrid nanocomposites consisting of BC nanofibers and

716 

magnetic nanoparticles have attracted much attention due to their potential novel

717 

applications in biomedicine, security papermaking and packaging. The incorporation

718 

of the magnetic nanoparticles with controllable collective magnetic properties can

719 

endow BC with new functionalities. The magnetically responsive BC sheets

720 

containing Fe3O4 nanoparticles were prepared by using an ammonia gas-enhancing in

721 

situ co-precipitation method operated in a closed system without oxygen (Katepetch &

722 

Rujiravanit, 2011). The homogeneous dispersion of the magnetic nanoparticles

723 

throughout the BC matrix could enhance the percent incorporation of magnetic

724 

nanoparticles into BC samples, leading to high and uniform magnetic properties. The

725 

saturation magnetization of the magnetic nanoparticle-incorporated BC sheet ranged

726 

from 1.92 to 26.20 emu/g with very low remnant magnetization (0.15–2.67 emu/g) and

730 

Ac ce p

te

d

M

an

us

cr

ip t

715 

731 

contact angle (WCA) of 130° and oil contact angle (OCA) of 112°. Additionally, the

732 

membranes exhibited the superparamagnetic behavior and can be magnetically

733 

actuated. Magnetically responsive BC membrane with hydrophobic and lipophobic

734 

surface would have potential applications in electronic actuators, magnetographic

727  728  729 

coercive field (40–65 G) at the room temperature. The fluoroalkyl silane (FAS) modification on the magnetic Fe3O4/BC membrane can convert the surface wettability of BC membrane from amphiphilicity to amphiphobicity (Zhang et al., 2011) (Fig. 26). The fluorinated membrane with appropriate roughness showed the highest water

34   

Page 34 of 83

735 

printing, information storage, electromagnetic shielding coating and anti-counterfeit. The BC-based magnetic nanocomposite has been constructed that enables

737 

tunability from highly porous, flexible, magnetically actuating aerogel to solid and stiff

738 

magnetic nanopaper with high particle loading as shown in Fig. 27 (Olsson et al.,

739 

2010). Magnetic ferromagnetic cobalt ferrite nanoparticles (diameter, 40–120 nm)

740 

were precipitated on a BC hydrogel, and the porosity of the resulting dried

741 

nanocomposite was controlled from 98% (upon removal of water during freeze-drying)

742 

in the aerogel to 10% (upon compaction) in the nanopaper (Fig. 27a and b). The

743 

lightweight porous magnetic aerogel can be actuated by a small household magnet as

744 

shown in Fig. 27c. Moreover, it can absorb water and release it upon compression (Fig.

745 

27d). Owing to their flexibility, high porosity and surface area, these aerogels are

746 

expected to be useful in microfluidics devices and as electronic actuators.

te

d

M

an

us

cr

ip t

736 

In addition, the magnetically responsive BC can also been provided by precipitation

748 

of ferromagnetic Ni nanoparticles with the size of 10 to 60 nm by room temperature

749  750  751  752 

Ac ce p

747 

chemical reduction of Ni-chloride hexahydrate (Vitta, Drillon & Derory, 2010). The Ni loaded BC exhibits a complex magnetic behavior with characteristics of both superparamagnetism

and

ferromagnetism.

The

magnetization

data

shows

superparamagnetism with a blocking temperature of ~20 K. The hysteresis of

753 

magnetization on the other hand, even at room temperature, clearly indicates that a

754 

ferromagnetic phase always coexists together with the superparamagnetic phase. This

755 

work clearly shows that the Ni loaded BC can be used both for nonbiological

756 

applications such as magnetic printing and biological applications such as magnetic 35   

Page 35 of 83

757 

tissue scaffolds.

758 

4. Concluding remarks

ip t

759 

cr

760 

Looking over the studies summarized in this article, the different biosynthetic or

762 

chemical modification and incorporation of various guest substrates into BC matrix

763 

bring up new opportunities for the development of novel nanostructured materials with

764 

designed functionalities. By combining the unique physicochemical properties of BC

765 

and optical, electronic and magnetic features of guest substrates, the significant

766 

synergetic effects can be observed, aiming at the advance of a great variety of

767 

advanced BC-based nanomaterials. The development and challenges of BC in

768 

functional nanomaterial application in the future include several aspects as follows.

te

d

M

an

us

761 

Ac ce p

First, it is very meaningful to conduct a systematic study of electrochemical

773  774 

nanomaterials according to the application requirements, fulfilling the controllable

775 

preparation of different nanostructures on the molecular level. It should be noted that

776 

the analysis and investigation of these inherent properties can greatly support and

777 

promote their application in the field of functional nanomaterials. Meanwhile, the more

769  770  771  772 

and surface properties of BC, especially the investigation of the accurate accessible hydroxyl groups on the surface of BC nanofiber under different conditions. This is an interesting and significant topic deserving study, which can establish the reaction model system to design and simulate the in situ preparation of diversified functional

36   

Page 36 of 83

economical and environmentally friendly controllable methods should be developed to

779 

modify the surface of nanocellulose while preserving the nanostructural morphology

780 

and excellent mechanical properties. The thermal stability of BC can also be improved

781 

by choosing the appropriate modification methods, which can facilitate the

782 

processability and application of BC on a higher level and broader scope, such as

783 

high-temperature filter, catalytic carrier, and porous electrode materials.

us

cr

ip t

778 

In addition, all the applications of BC in the field of functional nanomaterials are

785 

based on their inherent physicochemical properties, such as remarkable mechanical

786 

properties, porosity, water absorbency, moldability, biodegradability, excellent

787 

biological affinity, and so on. Therefore, these unique properties should be utilized to

788 

the fullest with contributions from multidisciplinary areas like physics, chemistry,

789 

materials science and medicine to construct novel advanced functional BC-based

790 

nanomaterial system which can greatly expand the application field of BC

791 

nanomaterials. In particular, derived from the unique three-dimensional network and

793  794  795 

M

d

te

Ac ce p

792 

an

784 

the interactions between formed nanoparticle and cellulosic nanofibers, BC or modified BC can be potentially useful in the application of some special nanomaterials, such as stimulus-responsive and maintenance-free self-healing materials. However, it should be pointed out that the current research on BC in the field of functional

796 

nanomaterials is still largely confined to the laboratory. Increasing attention should be

797 

devoted to produce BC in larger quantities at low cost, and to explore various

798 

construction strategies that enhance the properties of BC, making it attractive for use in

799 

a wide range of industrial sectors. New and emerging industrial processes need to be 37   

Page 37 of 83

optimized to achieve more efficient operations and this will require active research

801 

participations from the academic and industrial sectors. The next decade should

802 

witness the industrial use of a wide spectrum of products derived from this effort.

ip t

800 

803 

Acknowledgement

cr

804 

This work was financially supported by the National Natural Science Foundation of

806 

China (51273043), Program of Introducing Talents of Discipline to Universities

807 

(B07024) and Shanghai Leading Academic Discipline Project (B603)

an

us

805 

M

808 

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810 

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811 

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876 

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877 

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D. (2011). Structure and properties of conducting bacterial cellulose-polyaniline

950 

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epoxidized soy-bean oil (ESO) matrix and high contents of bacterial cellulose (BC).

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980 

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987 

Adsorption of Cu(II) and Pb(II) onto diethylenetriamine-bacterial cellulose.

988 

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990  991  992 

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975 

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994 

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995 

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996 

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997 

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998 

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999 

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1002 

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1003 

Chemical Engineering Journal, 193-194, 16-20.

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1005 

Synthesis and magnetic studies. Journal of Applied Physics, 108(5).

1006 

Wang, H. H., Bian, L. Y., Zhou, P. P., Tang, J., & Tang, W. H. (2013). Core-sheath

1007 

structured bacterial cellulose/polypyrrole nanocomposites with excellent conductivity

1008 

as supercapacitors. Journal of Materials Chemistry A, 1(3), 578-584.

1009 

Wang, W., Li, H. Y., Zhang, D. W., Jiang, J., Cui, Y. R., Qiu, S., Zhou, Y. L., & Zhang,

1010 

X. X. (2010). Fabrication of Bienzymatic Glucose Biosensor Based on Novel Gold

1012  1013  1014 

cr

us

an

M

d

te

Ac ce p

1011 

ip t

1000 

Nanoparticles-Bacteria Cellulose Nanofibers Nanocomposite. Electroanalysis, 22(21), 2543-2550.

Wang, W., Zhang, T. J., Zhang, D. W., Li, H. Y., Ma, Y. R., Qi, L. M., Zhou, Y. L., & Zhang, X. X. (2011). Amperometric hydrogen peroxide biosensor based on the

1015 

immobilization of heme proteins on gold nanoparticles-bacteria cellulose nanofibers

1016 

nanocomposite. Talanta, 84(1), 71-77.

1017 

Yamanaka, S., & Sugiyama, J. (2000). Structural modification of bacterial cellulose.

1018 

Cellulose, 7(3), 213-225. 47   

Page 47 of 83

Yan, Z. Y., Chen, S. Y., Wang, H. P., Wang, B. A., & Jiang, J. M. (2008). Biosynthesis

1020 

of bacterial cellulose/multi-walled carbon nanotubes in agitated culture. Carbohydrate

1021 

Polymers, 74(3), 659-665.

1022 

Yang, G., Xie, J. J., Deng, Y. X., Bian, Y. G., & Hong, F. (2012). Hydrothermal

1023 

synthesis of bacterial cellulose/AgNPs composite: A "green" route for antibacterial

1024 

application. Carbohydrate Polymers, 87(4), 2482-2487.

1025 

Yang, G., Xie, J. J., Hong, F., Cao, Z. J., & Yang, X. X. (2012). Antimicrobial activity

1026 

of silver nanoparticle impregnated bacterial cellulose membrane: Effect of

1027 

fermentation carbon sources of bacterial cellulose. Carbohydrate Polymers, 87(1),

1028 

839-845.

1029 

Yang, J. Z., Yu, J. W., Fan, J., Sun, D. P., Tang, W. H., & Yang, X. J. (2011).

1030 

Biotemplated preparation of CdS nanoparticles/bacterial cellulose hybrid nanofibers

1031 

for photocatalysis application. Journal of Hazardous Materials, 189(1-2), 377-383.

1032 

Yang, Z., Chen, S., Hu, W., Yin, N., Zhang, W., Xiang, C., & Wang, H. (2012a).

1034  1035  1036 

cr

us

an

M

d

te

Ac ce p

1033 

ip t

1019 

Flexible

luminescent

CdSe/bacterial

cellulose

nanocomoposite

membranes.

Carbohydrate Polymers, 88(1), 173-178. Yang, Z. H., Chen, S. Y., Hu, W. L., Yin, N., Zhang, W., Xiang, C., & Wang, H. P. (2012b). Flexible luminescent CdSe/bacterial cellulose nanocomoposite membranes.

1037 

Carbohydrate Polymers, 88(1), 173-178.

1038 

Yano, H., Sugiyama, J., Nakagaito, A. N., Nogi, M., Matsuura, T., Hikita, M., & Handa,

1039 

K. (2005). Optically Transparent Composites Reinforced with Networks of Bacterial

1040 

Nanofibers. Advanced Materials, 17(2), 153-155. 48   

Page 48 of 83

Yano, S., Maeda, H., Nakajima, M., Hagiwara, T., & Sawaguchi, T. (2008).

1042 

Preparation and mechanical properties of bacterial cellulose nanocomposites loaded

1043 

with silica nanoparticles. Cellulose, 15(1), 111-120.

1044 

Yoon, S. H., Jin, H. J., Kook, M. C., & Pyun, Y. R. (2006). Electrically conductive

1045 

bacterial cellulose by incorporation of carbon nanotubes. Biomacromolecules, 7(4),

1046 

1280-1284.

1047 

Zhang, D. Y., & Qi, L. M. (2005). Synthesis of mesoporous titania networks consisting

1048 

of anatase nanowires by templating of bacterial cellulose membranes. Chemical

1049 

Communications(21), 2735-2737.

1050 

Zhang, T. J., Wang, W., Zhang, D. Y., Zhang, X. X., Ma, Y. R., Zhou, Y. L., & Qi, L. M.

1051 

(2010). Biotemplated Synthesis of Gold Nanoparticle-Bacteria Cellulose Nanofiber

1052 

Nanocomposites and Their Application in Biosensing. Advanced Functional Materials,

1053 

20(7), 1152-1160.

1054 

Zhang, W., Chen, S. Y., Hu, W. L., Zhou, B. H., Yang, Z. H., Yin, N., & Wang, H. P.

1056  1057  1058 

cr us

an

M

d

te

Ac ce p

1055 

ip t

1041 

(2011). Facile fabrication of flexible magnetic nanohybrid membrane with amphiphobic surface based on bacterial cellulose. Carbohydrate Polymers, 86(4), 1760-1767.

Zhijiang, C., & Guang, Y. (2011). Optical nanocomposites prepared by incorporating

1059 

bacterial cellulose nanofibrils into poly(3-hydroxybutyrate). Materials Letters, 65(2),

1060 

182-184.

1061 

Zhijiang, C., Guang, Y., & Kim, J. (2011). Biocompatible nanocomposites prepared by

1062 

impregnating bacterial cellulose nanofibrils into poly(3-hydroxybutyrate). Current 49   

Page 49 of 83

Applied Physics, 11(2), 247-249.

1064 

Zhou, L. L., Sun, D. P., Hu, L. Y., Li, Y. W., & Yang, J. Z. (2007). Effect of addition of

1065 

sodium alginate on bacterial cellulose production by Acetobacter xylinum. Journal of

1066 

Industrial Microbiology and Biotechnology, 34(7), 483-489.

ip t

1063 

cr

1067 

us

1068  1069 

an

1070  1071 

M

1072  1073 

te

d

1074 

1076  1077  1078  1079  1080 

Ac ce p

1075 

Figure captions

Fig.1. The illustration of biofabrication process of BC. Fig. 2. The illustration of the annual number of publications on BC since 2000 (SciFinder Scholar search system, search term “bacterial cellulose”).

1081 

Fig. 3. Schematic illustration of the generalized synthetic routes to modified BC

1082 

nanomaterials (Chen, Shen, Yu, Hu & Wang, 2010; Geng, Yang, Zhu, Cao, Jiang &

1083 

Sun, 2011; Hessler & Klemm, 2009; Hu, Chen, Xu & Wang, 2011; Ifuku, Tsuji,

1084 

Morimoto, Saimoto & Yano, 2009; Oshima, Kondo, Ohto, Inoue & Baba, 2008; Shen 50   

Page 50 of 83

et al., 2009; Yamanaka & Sugiyama, 2000).

1086 

Fig. 4. SEM images of freeze-dried upper part of BC/starch composite (a), under part

1087 

of BC/starch composite (b), middle layer of BC/MWCNTs composites (c), and

1088 

BC/SiO2 nanocomposites (d) (Geng, Yang, Zhu, Cao, Jiang & Sun, 2011; Heßler &

1089 

Klemm, 2009; Park, Kim, Kwon, Hong & Jin, 2009).

1090 

Fig. 5. (a) FE-SEM image of vacuum-dried acetylated BC, and the inset shows the

1091 

profile of water droplets on the membrane surface. (b) Tensile stress–strain behaviors

1092 

of air dried BC and acetylated BC (Hu, Chen, Xu & Wang, 2011).

1093 

Fig.6. Schematic diagram of the in situ preparation of nanoparticles/BC

1094 

nanocomposites.

1095 

Fig.7. Schematic diagram of the in situ preparation of nanoparticles onto the BC

1096 

nanofibers through the precipitation reaction (Hu et al., 2009; Li et al., 2009a; Zhang et

1097 

al., 2011).

1098 

Fig. 8. Schematic diagram of the formation of CdSe/BC nanocomposite (Yang et al.,

1100  1101  1102 

cr

us

an

M

d

te

Ac ce p

1099 

ip t

1085 

2012a).

Fig. 9. Schematic illustration for the flexible magnetic nanohybrid membrane (Zhang et al., 2011).

Fig. 10. Schematic diagram of the effect of different concentrations of metallic ions on

1103 

the size and size distribution of the in situ formed nanoparticles.

1104 

Fig. 11. Schematic diagram of the in situ preparation of inorganic hollow nanofibers

1105 

using BC as a template through the sol-gel reaction (Hu et al., 2009; Li et al., 2009a;

1106 

Zhang et al., 2011). 51   

Page 51 of 83

Fig. 12. (a) Illustration of the synthesis of TiO2/BC composites (Gutierrez, Tercjak,

1108 

Algar, Retegi & Mondragon, 2012). (b) SEM images of BC–titania hybrid membranes,

1109 

and (c) titania networks templated by BC membranes (Zhang & Qi, 2005). The arrow

1110 

indicates the twisted structure of ribbon-like nanofibers.

1111 

Fig. 13. Preparation process and AFM image of BC/silica composites by the solution

1112 

impregnation method (Ashori, Sheykhnazari, Tabarsa, Shakeri & Golalipour, 2012;

1113 

Yano, Maeda, Nakajima, Hagiwara & Sawaguchi, 2008).

1114 

Fig. 14. FESEM images of PHB/BC nanocomposite: (a) surface morphology, and (b)

1115 

cross-section morphology. (c) Image of chitosan and BC nanocomposite films placed

1116 

in front of a green plant (Trovatti, Fernandes, Rubatat, Freire, Silvestre & Neto, 2012;

1117 

Zhijiang & Guang, 2011; Zhijiang, Guang & Kim, 2011).

1118 

Fig. 15. Schematic diagram of the preparation of electromagnetic BC nanocomposites

1119 

(Park, Cheng, Choi, Kim & Hyun, 2013).

1120 

Fig. 16. Schematic diagram of the formation of ZnO nanoparcticles onto nanofibers of

1122  1123  1124  1125 

cr

us

an

M

d

te

Ac ce p

1121 

ip t

1107 

Am-BC membrane.

Fig. 17. Schematic of the experimental setup for humidity and gas detection (Hu, Chen, Zhou, Liu, Ding & Wang, 2011).  Fig. 18. Schematic diagram of the interaction of BC and PEI, and formaldehyde and PEI (Hu, Chen, Liu, Ding & Wang, 2011). 

1126 

Fig. 19. (a) The SEM image of Au–BC nanocomposite. (b) Amperometric response

1127 

curves of HRP/Au–BC/glassy carbon electrode for successive additions of different

1128 

concentrations of H2O2 in stirring phosphate buffer (pH 7.4) containing 0.5 mM

1129 

hydroquinone (HQ) at the applied potential of −150 mV. The inset shows the 52   

Page 52 of 83

amperometric response at time range from 200 s to 350 s (Zhang et al., 2010).

1131 

Fig. 20. (a) FESEM image of surface of the MWCNTs-incorporated BC pellicle (Yoon,

1132 

Jin, Kook & Pyun, 2006). Optical photographs of (b) electrically conductive

1133 

transparent paper, and (c) flexibility of the electrically conductive transparent paper

1134 

(Jung, Kim, Kim, Kwon, Lee & In, 2008).

1135 

Fig. 21. Schematic diagram of the formation of PANI/BC nanocomposites (Hu, Chen,

1136 

Yang, Liu & Wang, 2011).

1137 

Fig. 22. (a) Appearance of 65μm thick BC, BC/acrylic resin and BC/epoxy resin sheets.

1138 

(b) Flexibility of a 65μm thick BC/acrylic resin sheet (Yano et al., 2005).

1139 

Fig. 23. OLED on BC nanocomposite (Ummartyotin, Juntaro, Sain & Manuspiya,

1140 

2012a).

1141 

Fig. 24. (a) PL spectra of BC and CdS/BC nanocomposite with excitation wavelength

1142 

at 370 nm (Li et al., 2009b). (b) Micrograph of the CdSe/BC nanocomposite

1143 

membrane with excitation (Yang et al., 2012a). (c)Tensile stress–strain behaviors of

1145  1146  1147 

cr

us

an

M

d

te

Ac ce p

1144 

ip t

1130 

pure BC and CdSe/BC nanocomposite membrane, inset is the photograph of the CdSe/BC nanocomposite membrane (Yang et al., 2012a). Fig. 25. (a) The UV-visible spectra of BC-NO2SP membrane (0.06 wt% SP) under different irradiation time at 365 nm UV light conditions: (a) before UV irradiation, (b)

1148 

after UV 10 s, (c) after UV 30 s, (d) after UV 60 s, and (e) after UV 120 s. The inset

1149 

shows a sketch of the immobilized spiropyran that undergoes conversions to

1150 

merocyanine form and back under UV and visible irradiation, respectively. (b) BC

1151 

membrane and the BC-NO2SP membranes (0.06 wt% SP) after being treated by UV 53   

Page 53 of 83

irradiation for (b) 0 s, (c) 30 s and (d) 60 s ; e and f were the membrane recovered in

1153 

the dark for 10 and 30 minutes after irradiated by UV light for 60 s (Hu, Liu, Chen &

1154 

Wang, 2011).

1155 

Fig. 26. The flexible magnetically responded Fe3O4/BC nanohybrid membrane with

1156 

amphiphobic surface after FAS modification (Zhang et al., 2011).

1157 

Fig. 27. (a) Representative SEM image of a 98% porous magnetic aerogel containing

1158 

cobalt ferrite nanoparticles after freeze-drying. Insets: photograph and schematic of the

1159 

aerogel. Right inset: nanoparticles surrounding the nanofibrils. Left insets: photograph

1160 

and schematic of the aerogel. (b) SEM image of a stiff magnetic nanopaper obtained

1161 

after drying and compression. Inset: higher magnification image. (c) A piece of

1162 

magnetic aerogel is held using tweezers (left panel). Applying a small household

1163 

magnet bends the magnetic aerogel upwards (right panel). (d) The magnetic aerogel

1164 

bends downwards in response to the magnet and absorbs the water droplet below (left

1165 

panel). The aerogel recovers its original shape upon removal of the magnet (right panel)

1167  1168  1169  1170 

cr

us

an

M

d

te

Ac ce p

1166 

ip t

1152 

(Olsson et al., 2010) .

Tables

Table 1 The in situ preparation of metal nanoparticles using BC as the template through reduction reaction.

1171 

54   

Page 54 of 83

1171 

Table 1 The in situ preparation of metal nanoparticles using BC as the template

1172 

through reduction reaction.

1173 

NH2NH2 NH2 OH

5–14

0.86-1.60

70–10 0

50–70 20–50

>100

40–60 80–100

22.4

4.9 4.9

>100

30–50



7.8

25.0

19.6 6.0

NaBH4

(Cai, Kimura, Wada & Kuga, 2009)

NaBH4

(Cai, Kimura, Wada & Kuga, 2009) (Yang et al., 2009)

Pt

(Pinto, Neves, Neto & Trindade, 2012) (Zhou, Wang, Yang, Tang, Sun & Tang, 2012)

Cu

Au

8.0

10-20



~8.5

21

M

(Ifuku, Tsuji, Morimoto, Saimoto & Yano, 2009) (Barud et al., 2008)

~9

65.4

7.0±3.2

d



NaBH4 KBH4

1174  1175 

te

Ac ce p

HCHO

5.6±2.3

19.2

~3.9

14.4%

~36



Pd

Application

ip t

Content (w/w%) 1.78

70–100

Oxidized BC triethanol amine PEI

(Zhang et al., 2010)

Particle size (nm) 17.1±5.9

Artificial skin; wound dressings; food packaging; water treatment; anti-counterfeit ing; bio-sensing; catalysis; textiles

cr

Ascorbic acid

(Yang, Xie, Deng, Bian & Hong, 2012) (Yang, Xie, Hong, Cao & Yang, 2012) (Maria, +Gelatin Santos, +PVP Oliveira, +Gelatin Barud, +PVP Messaddeq & Ribeiro, +Gelatin 2009) +PVP

Metal NPs Ag

us

NaBH4

Ref.

an

Reducing agent BC

8.15 %

Biosensing; catalytic; electronic devices; drugs and protein release; smart clothing Catalytic

Antibacterial; catalytic Catalytic

‫׽‬20

 

55   

Page 55 of 83

Functionalized bacterial cellulose derivatives and nanocomposites 

1176 

 

1177 

Weili Hu, Shiyan Chen*, Jingxuan Yang, Zhe Li, Huaping Wang* 

ip t

1175 

1178 

cr

The construction strategies of BC-based functional nanomateirals were

1179 

summarized.

1181 

The  biosynthetic  and  chemical  modification  of  BC  can  expand  its  application 

1182 

fields. 

1183 

Different  components  can  be  incorporated  in‐situ  or  ex‐situ  for  functionalizing 

1184 

BC. 

1185 

We focus on the preparation method, mechanism and performance of functional 

1186 

BC.   

1187 

The  sensor,  photocatalytic,  magnetic  and  optoelectronic  applications  were 

1188 

reviewed. 

1190 

an

M

d te

Ac ce p

1189 

us

1180 

56   

Page 56 of 83

Fig.1.

Ac

ce pt

ed

M

an

us

cr

ip t

Fig.1. The illustration of biofabrication process of BC.

57

Page 57 of 83

Fig.2

Fig. 2. The illustration of the annual number of publications on BC since 2000 (SciFinder Scholar search system, search term “bacterial cellulose or microbial

Ac

ce pt

ed

M

an

us

cr

ip t

cellulose or bacterial nanocellulose”).

58

Page 58 of 83

Fig.3.

Fig. 3. Schematic illustration of the generalized synthetic routes to modified BC nanomaterials (Chen, Shen, Yu, Hu & Wang, 2010; Geng, Yang, Zhu, Cao, Jiang & Sun, 2011; Hessler & Klemm, 2009; Hu, Chen, Xu & Wang, 2011; Ifuku, Tsuji,

ip t

Morimoto, Saimoto & Yano, 2009; Oshima, Kondo, Ohto, Inoue & Baba, 2008; Shen

Ac

ce pt

ed

M

an

us

cr

et al., 2009; Yamanaka & Sugiyama, 2000).

59

Page 59 of 83

Fig.4.

Fig. 4.

SEM images of freeze-dried upper part of BC/starch composite (a), under

part of BC/starch composite (b), middle layer of BC/MWCNTs composites (c), and BC/SiO2 nanocomposites (d) (Geng, Yang, Zhu, Cao, Jiang & Sun, 2011; Heßler &

Ac

ce pt

ed

M

an

us

cr

ip t

Klemm, 2009; Park, Kim, Kwon, Hong & Jin, 2009).

60

Page 60 of 83

Fig.5.

Fig. 5. (a) FE-SEM image of vacuum-dried acetylated BC, and the inset shows the profile of water droplets on the membrane surface. (b) Tensile stress–strain behaviors

Ac

ce pt

ed

M

an

us

cr

ip t

of air dried BC and acetylated BC (Hu, Chen, Xu & Wang, 2011).

61

Page 61 of 83

Fig.6.

Fig.6. Schematic diagram of the in situ preparation of nanoparticles/BC

Ac

ce pt

ed

M

an

us

cr

ip t

nanocomposites.

62

Page 62 of 83

Fig.7.

Fig.7. Schematic diagram of the in situ preparation of nanoparticles onto the BC nanofibers through the precipitation reaction (Hu et al., 2009; Li et al., 2009a; Zhang

Ac

ce pt

ed

M

an

us

cr

ip t

et al., 2011).

63

Page 63 of 83

Fig.8.

Fig. 8. Schematic diagram of the formation of CdSe/BC nanocomposite (Yang et al.,

Ac

ce pt

ed

M

an

us

cr

ip t

2012a).

64

Page 64 of 83

Fig.9.

Fig. 9. Schematic illustration for the flexible magnetic nanohybrid membrane (Zhang

us

cr

ip t

et al., 2011).

Ac

ce pt

ed

M

an

.

65

Page 65 of 83

Fig.10.

Fig. 10. Schematic diagram of the effect of different concentrations of metallic ions

Ac

ce pt

ed

M

an

us

cr

ip t

on the size and size distribution of the in situ formed nanoparticles.

66

Page 66 of 83

Fig.11.

Fig. 11. Schematic diagram of the in situ preparation of inorganic hollow nanofibers using BC as a template through the sol-gel reaction (Hu et al., 2009; Li et al., 2009a;

Ac

ce pt

ed

M

an

us

cr

ip t

Zhang et al., 2011).

67

Page 67 of 83

Fig.12.

Fig. 12. (a) Illustration of the synthesis of TiO2/BC composites (Gutierrez, Tercjak, Algar, Retegi & Mondragon, 2012). (b) SEM images of BC–titania hybrid membranes, and (c) titania networks templated by BC membranes (Zhang & Qi, 2005). The arrow

Ac

ce pt

ed

M

an

us

cr

ip t

indicates the twisted structure of ribbon-like nanofibers.

68

Page 68 of 83

Fig.13.

Fig. 13. Preparation process and AFM image of BC/silica composites by the solution impregnation method (Ashori, Sheykhnazari, Tabarsa, Shakeri & Golalipour, 2012;

Ac

ce pt

ed

M

an

us

cr

ip t

Yano, Maeda, Nakajima, Hagiwara & Sawaguchi, 2008).

69

Page 69 of 83

Fig.14.

Fig. 14. FESEM images of PHB/BC nanocomposite: (a) surface morphology, and (b) cross-section morphology. (c) Image of chitosan and BC nanocomposite films placed in front of a green plant (Trovatti, Fernandes, Rubatat, Freire, Silvestre & Neto, 2012;

Ac

ce pt

ed

M

an

us

cr

ip t

Zhijiang & Guang, 2011; Zhijiang, Guang & Kim, 2011).

70

Page 70 of 83

Fig.15.

Fig. 15. Schematic diagram of the preparation of electromagnetic BC nanocomposites

Ac

ce pt

ed

M

an

us

cr

ip t

(Park, Cheng, Choi, Kim & Hyun, 2013).

71

Page 71 of 83

Fig.16.

Fig. 16. Schematic diagram of the formation of ZnO nanoparcticles onto nanofibers of

Ac

ce pt

ed

M

an

us

cr

ip t

Am-BC membrane.

72

Page 72 of 83

Fig.17.

Fig. 17. Schematic of the experimental setup for humidity and gas detection (Hu,

Ac

ce pt

ed

M

an

us

cr

ip t

Chen, Zhou, Liu, Ding & Wang, 2011).

73

Page 73 of 83

Fig.18.

Fig. 18. Schematic diagram of the interaction of BC and PEI, and formaldehyde and

Ac

ce pt

ed

M

an

us

cr

ip t

PEI (Hu, Chen, Liu, Ding & Wang, 2011).

74

Page 74 of 83

Fig.19.

Fig. 19. (a) The SEM image of Au–BC nanocomposite. (b) Amperometric response curves of HRP/Au–BC/glassy carbon electrode for successive additions of different concentrations of H2O2 in stirring phosphate buffer (pH 7.4) containing 0.5 mM

ip t

hydroquinone (HQ) at the applied potential of −150 mV. The inset shows the

Ac

ce pt

ed

M

an

us

cr

amperometric response at time range from 200 s to 350 s (Zhang et al., 2010).

75

Page 75 of 83

Fig.20.

Fig. 20. (a) FESEM image of surface of the MWCNTs-incorporated BC pellicle (Yoon, Jin, Kook & Pyun, 2006). Optical photographs of (b) electrically conductive transparent paper, and (c) flexibility of the electrically conductive transparent paper

Ac

ce pt

ed

M

an

us

cr

ip t

(Jung, Kim, Kim, Kwon, Lee & In, 2008).

76

Page 76 of 83

Fig.21.

Fig. 21. Schematic diagram of the formation of PANI/BC nanocomposites (Hu, Chen,

Ac

ce pt

ed

M

an

us

cr

ip t

Yang, Liu & Wang, 2011).

77

Page 77 of 83

Fig.22.

Fig. 22. (a) Appearance of 65μm thick BC, BC/acrylic resin and BC/epoxy resin

Ac

ce pt

ed

M

an

us

cr

ip t

sheets. (b) Flexibility of a 65μm thick BC/acrylic resin sheet (Yano et al., 2005).

78

Page 78 of 83

Fig.23.

Fig. 23. OLED on BC nanocomposite (Ummartyotin, Juntaro, Sain & Manuspiya,

Ac

ce pt

ed

M

an

us

cr

ip t

2012a).

79

Page 79 of 83

Fig.24.

Fig. 24. (a) PL spectra of BC and CdS/BC nanocomposite with excitation wavelength at 370 nm (Li et al., 2009b). (b) Micrograph of the CdSe/BC nanocomposite membrane with excitation (Yang et al., 2012a). (c)Tensile stress–strain behaviors of

Ac

ce pt

ed

M

an

us

cr

CdSe/BC nanocomposite membrane (Yang et al., 2012a).

ip t

pure BC and CdSe/BC nanocomposite membrane, inset is the photograph of the

80

Page 80 of 83

Fig.25.

Fig. 25. (a) The UV-visible spectra of BC-NO2SP membrane (0.06 wt% SP) under different irradiation time at 365 nm UV light conditions: (a) before UV irradiation, (b) after UV 10 s, (c) after UV 30 s, (d) after UV 60 s, and (e) after UV 120 s. The inset

ip t

shows a sketch of the immobilized spiropyran that undergoes conversions to merocyanine form and back under UV and visible irradiation, respectively. (b) BC

cr

membrane and the BC-NO2SP membranes (0.06 wt% SP) after being treated by UV

us

irradiation for (b) 0 s, (c) 30 s and (d) 60 s ; e and f were the membrane recovered in the dark for 10 and 30 minutes after irradiated by UV light for 60 s (Hu, Liu, Chen &

Ac

ce pt

ed

M

an

Wang, 2011).

81

Page 81 of 83

Fig.26.

Fig. 26. The flexible magnetically responded Fe3O4/BC nanohybrid membrane with

Ac

ce pt

ed

M

an

us

cr

ip t

amphiphobic surface after FAS modification (Zhang et al., 2011).

82

Page 82 of 83

Fig.27

Fig. 27. (a) Representative SEM image of a 98% porous magnetic aerogel containing cobalt ferrite nanoparticles after freeze-drying. Insets: photograph and schematic of the aerogel. Right inset: nanoparticles surrounding the nanofibrils. Left insets:

ip t

photograph and schematic of the aerogel. (b) SEM image of a stiff magnetic nanopaper obtained after drying and compression. Inset: higher magnification image.

cr

(c) A piece of magnetic aerogel is held using tweezers (left panel). Applying a small

us

household magnet bends the magnetic aerogel upwards (right panel). (d) The magnetic aerogel bends downwards in response to the magnet and absorbs the water

Ac

ce pt

ed

M

magnet (right panel) (Olsson et al., 2010) .

an

droplet below (left panel). The aerogel recovers its original shape upon removal of the

83

Page 83 of 83

Functionalized bacterial cellulose derivatives and nanocomposites.

Bacterial cellulose (BC) is a fascinating and renewable natural nanomaterial characterized by favorable properties such as remarkable mechanical prope...
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