Chemosphere 100 (2014) 146–151

Contents lists available at ScienceDirect

Chemosphere journal homepage: www.elsevier.com/locate/chemosphere

Cu-doped zinc oxide and its polythiophene composites: Preparation and antibacterial properties Ge Ma, Xiaoxi Liang, Liangchao Li ⇑, Ru Qiao, Donghua Jiang, Yan Ding, Haifeng Chen Zhejiang Key Laboratory for Reactive Chemistry on Solid Surface, Zhejiang Normal University, Jinhua 321004, China

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 Cu-doped zinc oxide and its

polythiophene nanocomposites were prepared successfully.  There exists some synergistic effect between components in the ternary composites.  The ternary composites present excellent antibacterial properties on three types species of bacteria.  The antibacterial mechanisms of the samples were discussed in detail.

a r t i c l e

i n f o

Article history: Received 24 May 2013 Received in revised form 23 November 2013 Accepted 23 November 2013 Available online 14 December 2013 Keywords: Sol–Gel method In-situ polymerization Polythiophene Cu-doped zinc oxide Antibacterial property

a b s t r a c t Cu-doped zinc oxide and its polythiophene nanocomposites were prepared by the Sol–Gel and in situ polymerization methods, respectively. The structures, morphologies and compositions of the samples were characterized. The antibacterial properties of the samples on three kinds of strains were determined by using powder inhibition zones, minimum inhibitory concentrations and minimal bactericidal concentrations. The study confirmed that the antibacterial activities of the composites were better than those of their each component. The antibacterial mechanisms of the samples were discussed further. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction The conductive polymers with a large p conjugation system, such as polythiophene (PTh), polypyrrole and polyaniline have made considerable progress for their easy polymerization, good thermal stability and low cost since they were discovered (Soares et al., 2012; Yslasa et al., 2012). As one of the most potential conducting polymers, PTh and its derivatives have attracted researchers’ great interests. However, the conductivity of pure PTh is very low because of the wide energy gap and no electrons in its antibonding orbitals. To expand the application scope of PTh, the ⇑ Corresponding author. Tel.: +86 579 82282384; fax: +86 579 82282489. E-mail address: [email protected] (L. Li). 0045-6535/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.11.053

doped PTh and its composites, especially PTh composites embedˇ íka ded with inorganic nanoparticles, are researched widely (C et al., 2006; Zhang et al., 2006; Wang et al., 2007; Lanzi and Paganin, 2010; Gao et al., 2012; Guo et al., 2012; Higashihara et al., 2013). The composites can not only improve the properties of PTh itself but also reveal some new performances that a single component does not possess due to the synergistic effect among components. Some efforts have been paid to study the composites for catalyst (Wang et al., 2008), solar cells (Lanzi and Paganin, 2010; Higashihara et al., 2013), low-temperature NO2 sensors (Guo et al., 2012), molecular recognition system (Zhang et al., 2006), etc. Zinc oxide (ZnO), a kind of vital multifunctional semiconductor material, possesses broad forbidden band. Its unique properties in

G. Ma et al. / Chemosphere 100 (2014) 146–151

optics, electrics, magnetism and antimicrobial activity can be improved obviously through doping ions, coating rare metals or metallic oxide on its surface (Ba-Abbada et al., 2013). It was reported that nano-ZnO was toxic to bacteria, copepods, microalgae, mammalian cells, etc. (Wiench et al., 2009; Wang et al., 2011, 2012; Saifa et al., 2013). And its antibacterial activity for many pathogens under the ultraviolet radiation is higher than that of nano-TiO2 (Kasemets et al., 2009; Wang et al., 2009). Besides nanosized ZnO, CuO nanoparticles are also an excellent antimicrobial material with broad foreground for application (Heinlaan et al., 2008; Karlsson et al., 2008; Perelshtein et al., 2009). As is well known, photoinduced carriers can be generated when PTh is exposed in the sunlight. But no report was available on the preparation and evaluation of antimicrobial activity of the PTh nanocomposites with Cu doped ZnO nanoparticles. Based on our previous work, the antibacterial activities of a series of Cu-doped zinc oxide (CuxZn1xO) nanocomposites were evaluated (Liang et al., 2011). Considering both the antibacterial property and doped content of Cu2+ in ZnO, Cu0.05Zn0.95O (CZ) is the optimal composition in the series samples. Herein, we report our recent efforts on the preparation and characterization of CZ/ PTh nanocomposites. The antibacterial performance of the samples were evaluated by the experiments of powder inhibition zone (IZ), minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) under the irradiation of sunlight against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Candida albicans (C. albicans). And the antibacterial mechanisms of the samples were discussed in detail. 2. Experimental 2.1. Materials Zinc nitrate (Zn(NO3)26H2O), copper nitrate (Cu(NO3)23H2O), citric acid, thiophene (Th), trichloromethane (CHCl3), ferric chloride anhydrous (FeCl3), aqueous ammonia (NH3H2O, 25–28%), poly vinyl alcohol (PVA) and methanol were all purchased from SCRC, China. All chemical reagents were of analytical grade and used without purification. 2.2. Preparation of CZ/PTh CZ was prepared by the Sol–Gel method, as reported in the literature (Liang et al., 2012). 2.82 g of zinc nitrate and 0.07 g of copper nitrate were dissolved in appropriate content distilled water to form a transparent solution. And then 2.16 g of citric acid was added to the above solution with stirring. The pH value of the mixed solution was adjusted to 8 with NH3H2O. It was maintained at 80 °C with constant stirring to form a sol and then dried further at 80 °C to form a solid precursor. Finally, the CZ powder was obtained after sintering the precursor for 2 h at 500 °C. CZ/PTh nanocomposites were prepared by in situ polymerization method. The procedure of CZ/PTh nanocomposite with 20 wt% of CZ was as follows: 50 mL of CHCl3 and 1 g of Th were mixed in three-necked flask with magnetic stirring. And 0.25 g of as-prepared CZ was added into the mixture above and dispersed with ultrasonication for 30 min at room temperature. 3 g of FeCl3 was dispersed in 150 mL of CHCl3 and added into the flask with mechanical raking. As Th began to be polymerized, the solution turned to dark from yellow gradually. The reaction was performed for 12 h in ice water bath. Finally, the filtered product was washed with methanol and CHCl3 several times respectively until the filtrate became colorless, and dried in vacuum for 24 h at 50 °C. The CZ/PTh nanocomposite with 20 wt% of CZ was obtained. A series of CZ/PTh nanocomposites with 40 wt%, 60 wt%, 80 wt% of CZ

147

and pure PTh were prepared according to the condition and procedure above-mentioned. 2.3. Characterizations The element content in CZ and CZ/PTh nanocomposites was confirmed by chemical analysis methods, i.e., the content of Cu2+ was determined by iodometry method; the content of Zn2+ was carried out by disodium ethylenediamine tetra-acetate titration method used xylenol orange as indicator. The X-ray diffraction (XRD) patterns of the samples were characterized using an X-ray diffractometer (Philips-PW3040/60) with Cu Ka radiation. The microstructures of the samples were observed by a scanning electron microscope (SEM, Hitachi S-4800) and a transmission electron microscope (TEM, JEOL-2010), respectively. The FT-IR spectra were recorded in KBr on a FT-IR spectrometer (Nicolet-Avatar 360). UV–Vis spectra were studied by a UV–visible spectrophotometer (Shimadzu-UV-2501PC). The thermogravimetric curves were recorded by a thermal analyzer (Mettler ToledoTGA/SDTA 851) under air atmosphere, the heating rate was 10 °C min1 and the flow rate was 40 mL min1. The electrical conductivities were carried out on a four-probe resistivity instrument (SDY-4) at room temperature (The tested samples mixed as-prepared samples with PVA (adhesive) in the mass rate of 3:1 were pressed to a column with the thickness of 3.30 mm under the pressure of 3 MPa). The growth of bacterial strains was monitored by UV–visible spectrophotometer. The concentrations Zn2+ and Cu2+ released from the CZ/PTh composite suspension were determined by an atomic absorption spectrometer (PE, AA800). 2.4. The evaluation of antibacterial performance E. coli (ATCC25922), S. aureus (ATCC25923) and C. albicans (ATCC10231) were used as test strains. All the strains were purchased from WKZ, China. The antibacterial properties of the samples were measured by IZ, MIC and MBC against the three strains above. 2.4.1. Preparation of media Beef peptone (bacterial culture): beef extract 0.13 g, peptone 1 g, NaCl 0.15 g, agar 115–210 g, deionized water 100 mL, pH 7.10–7.12; Sabouraud agar medium (fungal culture): peptone 1 g, glucose 4 g, agar 118 g, deionized water 100 mL, pH 5.60. 2.4.2. Preparation of bacterial suspension The test strains inoculated to the sterilized fluid medium in a incubator shaker with constant temperature of 37 °C, and oscillated for 24 h at the rate of 100 r min1. Concentration of the inoculums was controlled in the range of 1  105  9  105 cfu mL1 with the sterile saline. Bacterial suspension was prepared for using by shaking uniformly. 2.4.3. Antibacterial property test Antibacterial properties (IZ, MIC and MIC) of samples against E. coli, S. aureus and C. albicans were measured according to the literature (Liang et al., 2012). 3. Results and discussion 3.1. Chemical composition and XRD The chemical compositions of CZ and CZ/PTh nanocomposites confirmed by chemical analysis method are given in Table S1 in Supplementary materials. The measured values of metal ions are consistent well with theoretical value for the samples, which

148

G. Ma et al. / Chemosphere 100 (2014) 146–151

indicates that the compositions of as-obtained samples basically tally with those of anticipated stoichiometry. The XRD patterns of PTh (a), CZ/PTh nanocomposites with 20 wt%, 40 wt%, 60 wt%, 80 wt% (b–e) of CZ and CZ (f) are presented in Fig. 1. The broad peak located at 2h = 15–25° is ascribed to the amorphous structure of PTh (Fig. 1(a)). The peaks at 2h = 31.75°, 34.38°, 36.22°, 47.55°, 56.55°, 62.85°, 66.31°, 69.15°, 72.63° are indexed to ZnO with a hexagonal wurtzite structure (JCPDS-ICDD 89-510). No other peaks related to CuO are observed in the XRD patterns of CZ (Fig. 1(f)), which indicates that Cu2+ ions have entered into the ZnO lattice and have almost no effect on the intrinsic structure of ZnO. The average size of CZ grain calculated by the Scherrer equation (Klong and Alexander, 1954) is approximately 20 nm:

Dhkl ¼

kk bhkl  cos hhkl

ð1Þ

where Dhkl is the particle size perpendicular to the normal line of (h k l) plane, k is a constant (it is approximately equal to 0.89), bhkl is the full width at half-maximum (1 0 1) n peak, hhkl is the Bragg diffraction angle of (h k l) peak and k (0.15418 nm) is the wavelength of X-ray. It is observed from in Fig. 1(b)–(e) that the broad peak at 2h of 15–30° is attributed to PTh and other peaks are related to CZ, demonstrating that the CZ/PTh nanocomposites are prepared sucessfully. And the relative peak intensity of CZ in the composites increases as the content of CZ increases, while that of PTh is opposite. The results show clearly that it is CZ that impacts on the regular arrangement of the PTh chains. The reason may be that there is some interface effect between PTh coating and CZ particles in the in situ polymerization process due to the small size, high surface energy and surface defects of CZ, which limits the movement and growth of the PTh chains and finally leads to decreasing in crystallinity for PTh. It can be proved further from TGA curves of the PTh and CZ/PTh nanocomposite with 80 wt% of CZ (see Fig. S1, Supplementary materials). 3.2. Morphology

(112) (200)

(004)

Intensity (a.u.)

(201)

(103)

(002)

a

(110)

(101)

(100)

f

(102)

Fig. 2 shows the SEM and TEM images of CZ, PTh, and CZ/PTh composite with 80 wt% of CZ. As seen in Fig. 2(a) and (d), CZ particles with irregular hexagonal structure are about 20–30 nm in size (it is consistent with the obtained results from XRD analysis) and distribute homogeneously. PTh is of amorphous structure

and agglomerate obviously with broad size distribution of particles (Fig. 2(b) and (e)). The reason may be that PTh chains with different polymerization degrees are formed during the polymerization process. The particle size of the spherical CZ/PTh nanocomposites increases obviously compared with that of CZ and the particle surface is much rougher than pure PTh. As shown in Fig. 2(c), PTh coating on CZ particles forms a ‘‘core–shell’’ structure with CZ as black core and PTh as light shell. 3.3. FT-IR spectra Fig. 3 depicts the FT-IR spectra of CZ (a), CZ/PTh nanocomposite with 80 wt% of CZ (b), and PTh (c). It can be seen from Fig. 3(a) that the absorption peak at 461 cm1 is due to the lattice vibration of ZnAO bond (Peng et al., 2010). The broad band around 3300– 3700 cm1 is associated with the OAH stretching of hydroxyl group or physical water absorbed on the surface of CZ. In Fig. 3(c), the strong peaks at 3436 cm1 and 1632 cm1 are caused by water adsorbed on the PTh surface. Moreover, several weak peaks at 1195, 1106 and 1025 cm1 can be attributed to the CbAH out-of-plane bending vibrations of the PTh ring, and the peak at 698 cm1 is denoted the vibration of Th rings (Wang, 1994; Guo et al., 2012). For the CZ/PTh nanocomposite (Fig. 3(b)), the peak of carbonyl (C@O) located at 1655 cm1 indicates that PTh has been oxidized to some degree (Todd et al., 2008). Moreover, the characteristic peaks of PTh weaken compared to pure PTh in intensity owing to the quantum size effect of CZ particles in CZ/PTh nanocomposite. 3.4. UV–Vis spectra The UV–Vis spectra of CZ (a), CZ/PTh nanocomposite with 80 wt% of CZ (b), and PTh (c) are depicted in Fig. 4. In Fig. 4(a), the maximum peak at 387.5 nm belongs to the intrinsic absorption of CZ. PTh has a strong absorption in the whole ultraviolet and visible light region. The absorption peak located at about 635 nm is assigned to the p–p* electron transition of PTh, which is beneficial to broaden the spectrum response range of CZ. In Fig. 4(b), the strong absorption peak near 378 nm attributes to the intrinsic absorption of CZ, indicating that the spectrum response range of CZ nanoparticles is broadened greatly due to the photosensitization of PTh. Simultaneously, the intrinsic absorption band of CZ has an obvious blue-shift in the CZ/PTh nanocomposite compared with that in pure CZ, which results from the good dispersion of CZ in the PTh medium and the lower band gap of PTh. The electrons located at p–p* transition band in PTh are transferred to the conduction band in CZ semiconductor under the natural light, and the electrons in the valence band of CZ semiconductor move to PTh. It can promote the photoinduced electron–hole pairs in CZ semiconductor to separate and improve photocatalytic quantum efficiency, which is of important influence to enhance the photocatalytic performance of nanocomposites. 3.5. The electrical conductivity

10

20

30

40

50

60

70

2Theta (degree) Fig. 1. XRD patterns of PTh (a), CZ/PTh nanocomposites with 20 wt% (b), 40 wt% (c), 60 wt% (d), 80 wt% (e) of CZ and CZ (f).

The electrical conductivities of PTh and CZ/PTh nanocomposites are listed in Table 1. It can be learned that the conductivity of CZ is much higher than those of ZnO and CuO, and the conductivities of CZ/PTh nanocomposites are also higher than those of CZ and PTh. It is because that the band gap of CuO (1.70 eV) is much narrower than that of ZnO (3.37 eV) (Auret et al., 2007; Lupan et al., 2011; Amornpitoksuk et al., 2012). And electrons of conduction band (e CB ) in CuO can be transferred into the conduction band of ZnO by absorbing sunlight, which can improve the conductivity of CZ particles and the responsive ability to the visible light of ZnO.

149

G. Ma et al. / Chemosphere 100 (2014) 146–151

Fig. 2. SEM and TEM images of CZ (a and d), PTh (b and e), CZ/PTh nanocomposite with 80 wt% of CZ (c and f).

Table 1 The electrical conductivities of the samples.

Transmittance (a.u.)

c

b

a

3500

3000

2500 2000 1500 Wavelength (nm)

1000

500

Fig. 3. FT-IR spectra of CZ (a), CZ/PTh nanocomposite with 80 wt% of CZ (b) and PTh (c).

c Absorbance (a.u.)

Conductivities (S cm1)

ZnO CuO CZ CZ/PTh nanocomposites with x wt% of CZ

Cu-doped zinc oxide and its polythiophene composites: preparation and antibacterial properties.

Cu-doped zinc oxide and its polythiophene nanocomposites were prepared by the Sol-Gel and in situ polymerization methods, respectively. The structures...
806KB Sizes 0 Downloads 0 Views