Article pubs.acs.org/est
One for Two: Conversion of Waste Chicken Feathers to Carbon Microspheres and (NH4)HCO3 Lei Gao,†,‡ Haibo Hu,† Xuelin Sui,‡ Changle Chen,*,‡ and Qianwang Chen*,† †
Hefei National Laboratory for Physical Sciences at Microscale, CAS Key Laboratory of Soft Matter Chemistry, University of Science and Technology of China, Jinzhai Rd 96, Hefei 86-551-63601495, China ‡ CAS Key Laboratory of Soft Matter Chemistry and Department of Polymer Science and Engineering, University of Science and Technology of China, Jinzhai Rd 96, Hefei 86-551-63601495, China S Supporting Information *
ABSTRACT: Pyrolysis of 1 g of waste chicken feathers (quills and barbs) in supercritical carbon dioxide (sc-CO2) system at 600 °C for 3 h leads to the formation of 0.25 g well-shaped carbon microspheres with diameters of 1−5 μm and 0.26 g ammonium bicarbonate ((NH4)HCO3). The products were characterized by powder X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Raman spectroscopic, FT-IR spectrum, X-ray electron spectroscopy (XPS), and N2 adsorption/desorption measurements. The obtained carbon microspheres displayed great superhydrophobicity as fabric coatings materials, with the water contact angle of up to 165.2 ± 2.5°. The strategy is simple, efficient, does not require any toxic chemicals or catalysts, and generates two valuable materials at the same time. Moreover, other nitrogen-containing materials (such as nylon and amino acids) can also be converted to carbon microspheres and (NH4)HCO3 in the sc-CO2 system. This provides a simple strategy to extract the nitrogen content from natural and man-made waste materials and generate (NH4)HCO3 as fertilizer.
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INTRODUCTION Chicken meat consumption had exceeded 65 million tons in 2007 according to the report from Food and Agriculture Organization of the United Nations.1 Feather accounts for 5− 7% of the body weight of poultry, leaving the annual generation of chicken feather waste to be ca. 5 million tons.1,2 Feather is composed of 90−92% protein (keratin) and 1−8% lipids.3,4 Keratin is very stable, mechanically permanent and chemically unreactive, most likely due to the tight packaging of the polypeptide chain to α-helix and β-sheet conformations, which makes the biodegradation of chicken feather very slow.5−7 Poultry feathers are mostly disposed in landfills due to the lack of an efficient and cost-effective treatment strategy. This not only leads to the discarding of a potentially valuable biopolymer but also arouses environmental concerns.8−10 Recently, some effort has been made to turn feathers into valuable materials.11−17 Barone et al.8 prepared a cohesive film by modifying poultry feathers with glycerol, which acted as a plasticizer. The film displayed good mechanical properties with an elastic modulus of 40−500 MPa, stress at break of 6−15 MPa, and strain at break of 8−50%. Jin et al.16 altered the poor thermoplasticity of chicken feather through graft polymerization with methyl acrylate. The compression-molded films developed from the grafted feathers had substantially higher tensile properties than soy protein isolate and starch acetate films. Senoz et al.18 obtained pyrolyzed chicken feather fibers from a two-step process (215 °C/15 h + 400−450 °C/1 h), which demonstrated a strong H2 adsorption at low pressures © XXXX American Chemical Society
and 77 K due to their microporous nature. As biological materials, poultry feathers can also be used to prepare biogas. Brandelli et al.19 produced keratinases from diverse microorganisms including Eucarya, Bacteria, and Archea domains, which displayed good capability to degrade keratin and may possess potential applications in agroindustrial, pharmaceutical, and biomedical fields. Supercritical carbon dioxide (sc-CO2) (Tc = 31.8 °C, Pc = 7.4 MPa) possesses many unique properties, including low viscosity, high diffusivity, and zero surface tension like a gas and the capability of dissolving substances like a liquid. Because of the low cost and superior features, it is widely applied as a nonpolar solvent in synthetic chemistry.20−23 Recently, we developed a strategy to convert waste polyethylene terephthalate (PET) and other waste polymers (PE, PP, and PVC) to well-shaped micrometer carbon spheres in supercritical carbon dioxide systems.24−26 The application of these carbon microspheres as negative electrode material for lithium ion batteries was evaluated. As one of our continuous efforts, the degradation of chicken feathers was investigated in sc-CO2 system. Herein, we report the conversion of chicken feathers (whole feathers with quills and barbs) to (NH4)HCO3 and carbon microspheres at the same time in sc-CO2 systems Received: February 10, 2014 Revised: April 4, 2014 Accepted: April 25, 2014
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Figure 1. Schematic diagram of the total experiment process. (a) chicken feathers, (b) (NH4)HCO3 product, (c) carbon product, (d) SEM image of the CMS sample, (e) superdrophobicity of the CMS sample, (f) SEM image of the ACMS sample, (g) superdrophobicity of the ACMS sample.
air atmosphere. Subsequently, 1.0 g chicken feather and 12 g of solid CO2 was put into a 25 mL stainless steel autoclave. The autoclave was closed tightly and placed inside a furnace and heated at a rate of 10 °C/min. It was then kept at 600 °C for 3 h. The reaction took place under the autogenic pressure of the reaction. When the autoclave was gradually cooled down to room temperature, white powder formed at the top of the autoclave (Figure 1b), while some black powder was formed at the bottom of the autoclave (Figure 1c). Then two kinds of powder were washed with absolute alcohol, filtered. The white powder was dried at a low temperature for 12 h, because it was volatile at high temperatures. The black powder was dried at 80 °C for 12h. Finally, about 0.26 g white powder ((NH4)HCO3 powder) and 0.25 g black powder (carbon microspheres powder) were obtained. The treatment was also carried out at lower temperatures, such as 400 and 500 °C, it is found that only 0.026 and 0.042 g black powder were obtained respectively, and there was no (NH4)HCO3 powder produced, meaning that the reaction was incomplete. The obtained carbon microsphere products were further vacuum-annealed to change their structures. 0.40 g carbon microspheres (CMS) were put into a sealed tube furnace equipped with a vacuum pump. Before heating, the furnace was vacuumed to evacuate air for 10 min. The CMS sample was heated in vacuum at a heating rate of 10 °C/min up to 1500 °C and kept for 1 h. After cooling down to room temperature, about 0.20 g annealed carbon microsphere (hereafter named ACMS) sample was obtained (loss of 50%). The superhydrophobic fabric materials were produced as follows:27 First, 0.2 g ACMS sample was dispersed in 15 mL tetrahydrofuran (THF) with the aid of ultrasonication. Subsequently, 0.10 g polydimethylsiloxane (PDMS) precursor Part-A (Sylgard186 elastomer base) was added to the solution. The solution was ultrasonicated for 1 h to form Solution A. Then 0.01 g PDMS precursor Part-B (Sylgard186 curing agent) was dissolved in 15 mL THF to form Solution B. Prior to coating treatment, the Solution A and B were mixed together at room temperature to form a coating solution. Fabric samples (2.5·4.0 cm2) were dip-coated with the as-prepared coating solution for 2 min and then cured at 60 °C for 12 h.
without any catalyst. Moreover, other nitrogen-containing materials including amino acids and nylon-6 can also be converted to (NH4)HCO3 and carbon microspheres using this strategy. Nylon-6 is widely used in various fields due to its excellent properties, most of which is disposed in landfills or by incineration, neither of which is environmentally friendly. The carbon microspheres product has many potential applications. Besides our previously demonstrated applications as negative electrode material for lithium ion batteries,24−26 the application of the carbon microspheres as superhydrophobic fabric coatings materials was studied. Ammonium bicarbonate is an important market product with wide applications in the food, plastics, and rubber industry. In particular, it has been used as a nitrogen fertilizer for a long time. More importantly, it is the intermediate for urea production, the most widely used nitrogen fertilizer worldwide (more than 108 metric tons per year). Currently, Harber process, which converts N2 and H2 to NH3 at very high temperature and pressure, produces 500 million tons of nitrogen fertilizer per year, and consumes 1−2% of the world’s annual energy supply. Our strategy can operate at much milder conditions and extract the nitrogen in the form of (NH4)HCO3, which will save a lot of energy. Most of the previously reported chicken feather treating methods involve complicated processes, the usage of toxic chemicals and catalysts, the generation of waste materials or the requirement of bioequipment or enzymes. Moreover, most of these methods require the separation of the quills and barbs, and only quills can be efficiently converted. In contrast, our one-step strategy only requires the usage of CO2, can efficiently treat the whole chicken feather and generates two highly valuable materials in one process. More importantly, this strategy may find more applications in extracting/converting the C atom from the waste materials to useful carbon-based materials and N atom to (NH4)HCO3.
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EXPERIMENTAL SECTION Materials and synthesis: Chicken feathers (whole feathers with quills and barbs, shown in Figure 1a) used in the experiments were collected from poultry market. First, chicken feathers were washed with distilled water and dried at 60 °C for 24 h under B
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ascribed to the characteristic peaks of (002), (101), and (004) for carbon (Figure 2b, JCPDS card No. 75-1621). The broadening of the three peaks suggests a low degree of graphitization. SEM analysis of the black powder indicates the formation of CMS (Figure 1d). After annealing at 1500 °C and for 1 h, ACMS was generated (Figure 1f). Both CMS and ACMS are able to generate fabric materials with good superdrophobicity (Figure 1e,g). FT-IR spectra of the obtained (NH4)HCO3 and the authentic (NH4)HCO3 sample are shown in Figure S6 in the Supporting Information. By comparison, it can be seen that the FT-IR spectra of the two samples are identical, and each peak can be matched. Combined with the XRD analysis, it is concluded that the white powder is really (NH4)HCO3 with high purity. Moreover, the elemental analysis of the obtained (NH4)HCO3 and the authentic (NH4)HCO3 sample is shown in Table S2 in the Supporting Information, which further confirms the purity of the obtained (NH4)HCO3 sample. The pyrolysis of chicken feathers at 400 °C (Figure 3a) afforded irregular small pieces without carbon microspheres. The reaction at 500 °C (Figure 3b) led to little amount of carbon product (0.042 g), with nonuniform sizes and rough surface. In both cases, no (NH4)HCO3 were generated at all. At 600 °C, 0.25 g smooth carbon microspheres with diameters of 1−5 μm are formed (Figure 3c), accompanied by 0.26 g (NH4)HCO3. As the temperature is further increased to 650 °C, carbon spheres with a perfect spherical morphology are produced. It can be seen that the sample comprises carbon microspheres with diameter of 1−3 μm (Figure 3d). However, the amount of (NH4)HCO3 production and carbon microspheres remains almost the same (also 0.26 and 0.25 g, respectively). About 30.6 wt % of the N element from the chicken feather was transferred into the (NH4)HCO3 product, and ca. 21.1 wt % is transferred into the nitrogen-containing CMS product (Table 1). Clearly, the reaction temperature is critical for the decomposition of chicken feathers. Higher temperature favors a more spherical particle shape with a narrow size distribution. The feather quills and barbs are separately pyrolyzed under the same condition, leading to very similar CMS products based on SEM and FTIR analysis (Supporting Information Figure S1−S3). The amount of (NH4)HCO3 is also similar for both cases. This suggests no distinction between the feather quills and barbs when they are pyrolyzed in the sc-CO2 systems. At the end of the reaction,
Sample characterization: The powder X-ray diffraction (XRD) was performed on a Japan Rigaku D/MAX-cA X-ray diffractometer equipped with Cu−Kα radiation (λ = 1.542 Å) over the 2θ range of 5−60°. Field emission scanning electron microscopy (FE-SEM) was performed on a JEOL JSM-6700 M scanning electron microscope. The Raman spectroscopic analysis was carried out on a LABRAM-HR confocal laser micro-Raman spectrometer using the 514.5 nm line of an Ar ion laser as the excitation source at room temperature. The FTIR spectrum was obtained using a Magna-IR 750 spectrometer in the range of 500−4000 cm−1 with a resolution of 4 cm−1. Xray electron spectroscopy (XPS) was performed on an ESCALAB 250 X-ray photoelectron spectrometer with Al Kα radiation. Specific surface areas were calculated from the results of N2 physisorption at 77 K (Micromeritics ASAP 2020) by using the BET (Brunauer−Emmet−Teller) and BJH (Barrett− Joyner−Halenda) methods. Elemental analysis of the Chicken feathers and the samples: The elemental composition of the chicken feather, feather quills, and barbs, and the products was performed on Elementar Vario EL cube and the results are shown in Table 1. Table 1. Elemental Composition of the Samples sample
C, wt %
N, wt %
H, wt %
others, wt %
chicken feathers feathers quills feathers barbs CMS sample ACMS sample
47.40 47.51 46.19 77.93 89.94
15.12 15.20 14.18 12.78 1.01
7.16 7.11 6.88 2.09 0.41
30.32 30.18 32.7 7.2 8.64
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RESULTS AND DISCUSSIONS Figure 1 shows a schematic diagram of the total experimental process. 1g of the chicken feathers (Figure 1a, whole feathers with quills and barbs) led to 0.26g of white powder (Figure 1b) and 0.25g of black powder (Figure 1c) after pyrolysis at 600 °C for 3 h in sc-CO2 systems. The white powder was confirmed to be (NH4)HCO3 from XRD analysis (Figure 2a), an important chemical fertilizer in agriculture. The major peaks in the XRD pattern are in agreement with standard JCPDS card (no. 090415). The strong and sharp reflection peaks and the smooth baseline indicated good crystallinity. In the XRD pattern of the black powder, the three peaks at 26.2°, 44.0°, and 53.1° are
Figure 2. XRD patterns of (a) the white powder, (b) the black powder (CMS sample), all prepared at 600 °C in sc-CO2 system for 3 h. C
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feather. We are currently optimizing reaction conditions to increase the yield of the (NH4)HCO3 and recycle these CO2 gas. It should be noted that CO2 plays a crucial role in this process. Under our conditions, the pyrolysis of 1.0 g chicken feathers in stainless steel autoclave without dry ice generated 0.12 g (NH4)HCO3 and 0.16 g carbon material. Only 14.1 wt % of the N element from the chicken feather was transferred into the (NH4)HCO3 product. Also, the generated (NH4)HCO3 and carbon materials were mixed together, not like the samples prepared in sc-CO2 system, which were separated at the top and bottom of the autoclave, respectively. This means a lot more extra work for separation. Also the carbon product contained almost no carbon microspheres (Supporting Information Figure S4). After the CMS sample was heated at 1500 °C under vacuum for 1 h, the surface of the resulting ACMS is no longer smooth, and nanoscale cracks appear on the surface of these carbon microspheres (Figure 3e,f). Raman spectroscopy is used to analyze different carbon atoms bonding in the product (Figure 4a). The E2g mode of perfectly ordered graphite is situated at 1600 cm−1 (labeled Gband).28,29 It originates from the stretching vibration of sp2 CC sites (whether in linear chains or in aromatic rings) in the two-dimensional hexagonal lattice of a graphite layer. With the increasing of disorder, this band broadens and shifts to a higher frequency, and a new band appears at 1340 cm−1 (labeled D-band).30,31 It corresponds to an A1g mode, and the intensity of this band is commonly used for practical applications to evaluate the amount of disorders in carbon materials. Such a mode is forbidden in a perfect graphite and becomes active only in the presence of disorder, and it is quite common in the sample obtained via mild temperature routes.32 It was found that the relative peak intensity ratio of G-band to
Figure 3. FESEM images of samples prepared by dissociating 1.0 g of chicken feather in 12 g of CO2 at different conditions: (a) 400 °C, 3 h, (b) 500 °C, 3 h, (c) 600 °C, 3 h (the CMS sample), (d) 650 °C, 3 h, (e, f) annealed at 1500 °C for 1 h (the ACMS sample).
when the autoclave was open, the CO2 gas rushed out of the autoclave and the smell of ammonia can be detected, which might be part of the destinations for the N content in chicken
Figure 4. (a) Raman, (b) FT-IR, and XPS (c) C 1s, (d) N 1s spectra of the CMS and ACMS sample. D
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surface must has a water contact angle larger than 150°. Surface etching technologies can also be used to improve the hydrophobicity of PDMS coating, such as laser cutting method.36,37 By directly changing the surface morphology with PDMS, hydrophobicity can be improved. However, most of these methods employed expensive materials and/or harsh conditions. For example, silicon wafer or glass substrates are usually required, which also limits their practical applications. This work is aiming not only to explore an effective method to convert waste chicken feathers to potentially useful carbon materials, but also to search for new possible applications of various carbon materials based on their unique structures. It is a simple, low-cost, environmentally friendly and resource-saving process and other organic waste can also be treated with this method. When 0.2 g CMS sample (0.55 mmol/L) is used in the coating solution, the WCA is increased to 153.2 ± 1.7° (Figure 5c). For ACMS case, the WCA is further increased to 165.2° ± 2.5°, indicating an excellent superdrophobicity. When 0.1 (0.28 mmol/L) and 0.3 g (0.83 mmol/L) ACMS sample is used, the WCA is 151.3 ± 1.5° and 156.0 ± 3.3°. Therefore, 0.2 g ACMS sample is the optimal amount to achieve a good superhyrophobicity. Only when the surface of the fabrics is coated by one layer of PDMS/annealed carbon microspheres uniformly, the surface roughness can reach the maximum and have the best hydrophobicity. If the amount of ACMS is not enough, some parts of the fabrics are not coated by ACMS and these parts are relatively smooth, the hydrophobicity is decreased. However, too much ACMS will leave some part of the fabrics coated by more than one layer of ACMS. Possibly, the following ACMS will fill the void on the surface of the fabrics. As such, the surface roughness will be decreased, leading to lower hydrophobicity. The surface of the fabrics was analyzed by SEM (Figure 6). Figure 6a is the SEM images of the uncoated fabric, and Figure 6b is the PDMS coated fabrics. The morphology is similar for both cases. Figure 6c−f showed that the coating of the CMS and ACMS samples to the fabric surface was highly efficient. The low WCA of the CMS sample might due to the high nitrogen content and the surface smoothness. The dramatic increase in WCA for the ACMS sample is believed to be due to the increased surface roughness from cracking and nanoscale flaws.38 The N2 absorption−desorption isotherms at 77 K of the ACMS sample is shown in Figure 7, and the inserted picture shows the size distribution of pores. The isotherms are characteristic of a type IV with a type H3 hysteresis loop, indicating a mesoporous structure. The BET surface area of the ACMS sample is calculated to be 16.99 m2g−1. Furthermore, the pore size distribution has a narrow peak at 20 and 23 nm and a wide peak at 65 nm, which also reveals the distinct pore sizes in the sample, corresponding well with the previous SEM characterizations. Moreover, the increase in the defects of the ACMS sample (Raman analysis) further reduces the surface free energy. All of these features favor the superhydrophobic properties of the fabric coatings. The energy bonds of CO, O−H, amide, C−C, and N−C on the side chains are 192.1, 111.8, 84−85, 80−81, and 70−73 kcal/mol.39 In the protein backbone, the weakest bond is HNCα bond. The cleavage of the HN-Cα bond is more probable, affording ammonium, which will react with H2O and CO2 and lead to the formation of (NH4)HCO3. H2O might come from the decomposition of chicken feather, or from the contamination from dry ice. Wool et al. studied the chemical and
D-band (IG/ID peak height ratio, after a level baseline at 800 cm−1 is taken out) for the CMS and ACMS sample is 1.11 and 0.89 respectively. The increase in the intensity of D band related to sp3 defects may due to the decrease of N content (from 12.78 wt % for CMS to 1.01 wt % for ACMS, Table 1) after annealing. This decrease will generate defects in the structure and sp3 hybrid carbon atoms are also present on the edge of these carbon microspheres (Figure 3f), causing the increase in disorder. Interestingly, the nitrogen doping causes symmetry-breaking of the carbon network, leaving the CMS sample to become IR-active.33 G-band and D-band of the CMS sample are clearly present in the FTIR analysis, which cannot be observed at all in ACMS sample (Figure 4b). After annealing C 1s peak of ACMS in XPS spectra becomes narrower and shifts to a higher binding energy (from 284.4 to 284.8 eV, Figure 4c). The two peaks in the N 1s core-level spectra of the CMS sample at 398 and 400 eV are attributed to NC and NC (Figure 4d).34,35 In contrast, these two peaks completely disappear in the ACMS sample. This confirms the significant decrease of the nitrogen content in the samples after annealing. The mole ratio of C, N and O in the CMS sample is 86.97%, 7.92%, and 5.11%, respectively. The mole ratio of C and O in the ACMS sample is 96.45% and 3.55%, respectively. The N element in the ACMS sample was detected by XPS. In the hydrophobicity study, a plain weave polyester fabric was used as a model substrate, and water was colored by rhodamine B. Statistical analysis is used to obtain the contact angles of all the samples. The contact angles of all the samples are shown in Supporting Information Table S1. In each treatment, five different pieces of fabrics were used to measure the contact angles. The contact angles of two water drops on each piece of fabric were obtained. Figure 5 shows the photos
Figure 5. Photos of water droplets on (a) uncoated fabric, and (b) PDMS coated fabric, (c) CMS/PDMS coated fabric, (d) ACMS/ PDMS coated fabric. The inserts were side views of a 3 μL water droplet.
of water droplets on the uncoated and coated fabrics. Water droplets spread into the pristine fabric (Figure 5a), and no water contact angle (WCA) could be observed. In contrast, nearly sphere-like water droplets were formed on the coated fabric (Figure 5b−d). These spherical droplets are stable and can stay on the supported fabric for a long time. WCA is 146.0 ± 1.7° for the fabric with only PDMS coating, which is not categorized as superhydrophobic because superhydrophobic E
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Figure 6. FESEM images of (a) uncoated fabrics, (b) PDMS coated fabrics, (c,d) 0.2 g CMS sample and PDMS coated fabrics, and (e,f) 0.2 g ACMS sample and PDMS coated babrics.
hydrocarbon molecules, such as hydrocarbon molecules were dissolved in the supercritical CO2, concentrated, grew to clusters made of aromatic rings and aliphatic chains, formed graphene layers, finally yielding carbon spheres at the bottom of the autoclave. Considering (NH4)HCO3 decomposes above 60 °C, the formation of (NH4)HCO3 probably happens during the cooling process. When the autoclave was opened at the end of the reaction, unreacted ammonium rushed out, which explained the ammonia smell. Currently, we are working on detailed mechanistic studies and optimizing reaction conditions to increase the yield of (NH4)HCO3. Based on the above studies, we became interested in investigating the applicability of this strategy to other nitrogen containing materials. Five nitrogen containing materials were tested under the same conditions (Table 2). All of these materials can be converted to (NH4)HCO3 and carbon products. The morphology of these carbon products are in the form of carbon microspheres (Supporting Information Figure S5), except Polyacrylamide which is not pyrolyzed adequately and the yield of (NH4)HCO3 is also the lowest (ca. 3.6 wt %). From the pyrolysis of two kinds of amino acid, it can be seen that as the content of nitrogen increases, the quality of the (NH4)HCO3 product also increases. However, the yield of (NH4)HCO3 was only increased moderately from 26.1 to 29.5 wt %, respectively. The reactant containing benzene ring (such as P-aminobenzoic acid) can also be pyrolyzed in sc-CO2 system to afford (NH4)HCO3 and carbon microspheres. Interestingly, nylon-6 gave the highest (NH4)HCO3 yield at
Figure 7. N2 adsorption/desorption isotherm (77 K) curves of the ACMS sample and porous volume distribution of the pore size (inset).
physical changes of chicken feathers during pyrolysis under air in great details, and only detected abundant aromatic carbons and cyclic amines.40,41 It was found that cyclic amines were formed around 400 °C during pyrolysis. Our results showed that only little amount of (NH4)HCO3 was formed when the reaction was carried out below 600 °C, suggesting that the generation of ammonium is not efficient under 600 °C. It is believed that chicken feathers initially dissociated to aromatic F
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Science Foundation of China (NSFC, 21071137 and 21374108), Anhui Provincial Natural Science Foundation (1408085QB28), the Fundamental Research Funds for the Central Universities (WK2060200012), and the Recruitment Program of Global Experts.
Table 2. Pyrolysis Results of Five Nitrogen Containing Materials
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(1) Poole, A. J.; Church, J. S.; Huson, M. G. Biomacromolecules 2009, 10 (1), 1−9. (2) Gessesse, A.; Hatti-Kaul, R.; Gashe, B. A.; Mattiasson, B. Novel alkaline proteases from alkaliphilic bacteria grown on chicken feather. Enzyme Microb. Technol. 2003, 32 (5), 519−524. (3) Onifade, A.; Al-Sane, N.; Al-Musallam, A.; Al-Zarban, S. A review: Potentials for biotechnological applications of keratin-degrading microorganisms and their enzymes for nutritional improvement of feathers and other keratins as livestock feed resources. Bioresour. Technol. 1998, 66 (1), 1−11. (4) Salminen, E.; Rintala, J. Anaerobic digestion of organic solid poultry slaughterhouse waste−a review. Bioresour. Technol. 2002, 83 (1), 13−26. (5) Forgács, G.; Alinezhad, S.; Mirabdollah, A.; Feuk-Lagerstedt, E.; Horváth, I. S. Biological treatment of chicken feather waste for improved biogas production. J. Environ. Sci. 2011, 23 (10), 1747− 1753. (6) Coward-Kelly, G.; Chang, V. S.; Agbogbo, F. K.; Holtzapple, M. T. Lime treatment of keratinous materials for the generation of highly digestible animal feed: 1. Chicken feathers. Bioresour. Technol. 2006, 97 (11), 1337−1343. (7) Sangali, S.; Brandelli, A. Feather keratin hydrolysis by a Vibrio sp. strain kr2. J. Appl. Microbiol. 2000, 89 (5), 735−743. (8) Barone, J. R.; Schmidt, W. F.; Liebner, C. F. Thermally processed keratin films. J. Appl. Polym. Sci. 2005, 97 (4), 1644−1651. (9) Reddy, N.; Hu, C.; Yan, K.; Yang, Y. Thermoplastic films from cyanoethylated chicken feathers. Mater. Sci. Eng., C 2011, 31 (8), 1706−1710. (10) Reddy, N.; Yang, Y. Light-weight polypropylene composites reinforced with whole chicken feathers. J. Appl. Polym. Sci. 2010, 116 (6), 3668−3675. (11) Zhan, M.; Wool, R. P.; Xiao, J. Q. Electrical properties of chicken feather fiber reinforced epoxy composites. Composites, Part A 2011, 42 (3), 229−233. (12) Fakhfakh-Zouari, N.; Hmidet, N.; Haddar, A.; Kanoun, S.; Nasri, M. A novel serine metallokeratinase from a newly isolated Bacillus pumilus A1 grown on chicken feather meal: Biochemical and molecular characterization. Appl. Biochem. Biotechnol. 2010, 162 (2), 329−344. (13) Agrahari, S.; Wadhwa, N. Degradation of chicken feather a poultry waste product by keratinolytic bacteria isolated from dumping site at Ghazipur poultry processing plant. Int. J. Poult. Sci. 2010, 9 (5), 482−489. (14) Cheng, S.; Lau, K.-t.; Liu, T.; Zhao, Y.; Lam, P.-M.; Yin, Y. Mechanical and thermal properties of chicken feather fiber/PLA green composites. Composites, Part B 2009, 40 (7), 650−654. (15) Schrooyen, P. M.; Dijkstra, P. J.; Oberthür, R. C.; Bantjes, A.; Feijen, J. Partially carboxymethylated feather keratins. 2. Thermal and mechanical properties of films. J. Agric. Food Chem. 2001, 49 (1), 221− 230. (16) Jin, E.; Reddy, N.; Zhu, Z.; Yang, Y. Graft polymerization of native chicken feathers for thermoplastic applications. J. Agric. Food Chem. 2011, 59 (5), 1729−1738. (17) Hu, C.; Reddy, N.; Yan, K.; Yang, Y. Acetylation of Chicken Feathers for Thermoplastic Applications. J. Agric. Food Chem. 2011, 59 (19), 10517−10523. (18) Senoz, E.; Wool, R. P. Hydrogen storage on pyrolyzed chicken feather fibers. Int. J. Hydrogen Energy 2011, 36 (12), 7122−7127. (19) Brandelli, A.; Daroit, D. J.; Riffel, A. Biochemical features of microbial keratinases and their production and applications. Appl. Microbiol. Biotechnol. 2010, 85 (6), 1735−1750.
37.1%, and very high carbon microspheres yield with good morphology (Supporting Information Figure S5e,f). This makes this strategy highly useful considering the huge annual consumption of nylon based materials.
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CONCLUSIONS In summary, pyrolysis of chicken feathers in sc-CO2 system led to the formation of carbon microspheres and (NH4)HCO3. Reaction temperature plays a critical role in the product formation. Below 600 °C, no (NH4)HCO3 and little carbon product could be generated. The CMS product has very high nitrogen content (12.8 wt %). Using this strategy, ca. 30.6 wt % of the nitrogen content in the chicken feathers is transferred to (NH4)HCO3 and ca. 21.1 wt % is transferred into nitrogencontaining CMS product. Furthermore, we developed a simple coating strategy to prepare superhydrophobic fabric materials using CMS and ACMS products, the WCA which can reach 153.2 ± 1.7° and 165.2 ± 2.5°. The biggest advantage of this strategy is that the whole chicken feather (quills and barbs) can be converted to two valuable materials at the same time. Furthermore, other nitrogen-containing materials (such as nylon-6) can also be converted to carbon microspheres and (NH4)HCO3 highly efficiently, suggesting the generality of this process. This strategy possesses great potentials for practical applications being able to convert one waste material chicken feathers into two valuable materials (NH4)HCO3 and carbon microsphere materials.
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ASSOCIATED CONTENT
S Supporting Information *
Additional information as noted in the text. This material is available free of charge via the Internet at http://pubs.acs.org.
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REFERENCES
AUTHOR INFORMATION
Corresponding Authors
*Phone: +86-551-63607251; fax: +86-551-63603005; e-mail: [email protected] or . *E-mail: [email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by a project of the National 863 HiTech Plan (Grant 2008AA06Z337) and the National Natural G
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(20) Yazdizadeh, M.; Eslamimanesh, A.; Esmaeilzadeh, F. Thermodynamic modeling of solubilities of various solid compounds in supercritical carbon dioxide: Effects of equations of state and mixing rules. J. Supercrit. Fluids 2011, 55 (3), 861−875. (21) Cao, F.; Chen, C.; Wang, Q.; Chen, Q. Synthesis of carbon− Fe3O4 oaxial nanofibres by pyrolysis of ferrocene in supercritical carbon dioxide. Carbon 2007, 45 (4), 727−731. (22) Cooper, A. I. Recent developments in materials synthesis and processing using supercritical CO 2. Adv.Mater. 2001, 13 (14), 1111− 1114. (23) Lou, Z.; Chen, Q.; Zhang, Y.; Wang, W.; Qian, Y. Diamond formation by reduction of carbon dioxide at low temperatures. J. Am. Chem. Soc. 2003, 125 (31), 9302−9303. (24) Gao, L.; Zhong, H.; Chen, Q. Synthesis of 3C-SiC nanowires by reaction of poly (ethyleneterephthalate) waste with SiO2 Microspheres. J. Alloys Compd. 2013, 566, 212−216. (25) Wei, L.; Yan, N.; Chen, Q. Converting poly (ethylene terephthalate) waste into carbon microspheres in a supercritical CO2 system. Environ. Sci. Technol. 2010, 45 (2), 534−539. (26) Yu, B.; Kong, X.; Wei, L.; Chen, Q. Treatment of discarded oil in supercritical carbon dioxide for preparation of carbon microspheres. J. Mater. Cycles Waste Manage. 2011, 13 (4), 298−304. (27) Zhou, H.; Wang, H.; Niu, H.; Gestos, A.; Wang, X.; Lin, T. Fluoroalkyl silane modified silicone rubber/nanoparticle composite: A super durable, robust superhydrophobic fabric coating. Adv. Mater. 2012, 24 (18), 2409−2412. (28) Dresselhaus, M.; Dresselhaus, G.; Hofmann, M. Raman spectroscopy as a probe of graphene and carbon nanotubes. Philos. Trans. R. Soc., A 2008, 366 (1863), 231−236. (29) Tuinstra, F.; Koenig, J. L. Raman spectrum of graphite. J. Chem. Phys. 1970, 53, 1126−1130. (30) Colomban, P. Raman analyses and “smart” imaging of nanophases and nanosized materials. Spectrosc. Eur. 2003, 15 (6), 8−16. (31) Robertson, J. Diamond-like amorphous carbon. Mater. Sci. Eng., R 2002, 37 (4), 129−281. (32) Calderon Moreno, J. M.; Swamy, S. S.; Fujino, T.; Yoshimura, M. Carbon nanocells and nanotubes grown in hydrothermal fluids. Chem. Phys. Lett. 2000, 329 (3), 317−322. (33) Kaufman, J.; Metin, S.; Saperstein, D. Symmetry breaking in nitrogen-doped amorphous carbon: Infrared observation of the Raman-active G and D bands. Phys. Rev. B 1989, 39 (18), 13053. (34) Kobayashi, S.; Nozaki, S.; Morisaki, H.; Fukui, S.; Masaki, S. Carbon nitride thin films deposited by the reactive ion beam sputtering technique. Thin Solid Films 1996, 281, 289−293. (35) Galan, L.; Montero, I.; Rueda, F. An X-ray photoelectron spectroscopy study of carbon nitride films grown by low energy ion implantation. Surf. Coat. Technol. 1996, 83 (1), 103−108. (36) Cortese, B.; D’Amone, S.; Manca, M.; Viola, I.; Cingolani, R.; Gigli, G. Superhydrophobicity due to the hierarchical scale roughness of PDMS surfaces. Langmuir 2008, 24 (6), 2712−2718. (37) Jin, M.; Kang, M.; Jing, Lei Preparation of Super-hydrophobic PDMS Films and Study on Surface Adhesion. Chem. J. Chin. Univ. 2007, 28 (5), 996−998. (38) Verho, T.; Bower, C.; Andrew, P.; Franssila, S.; Ikkala, O.; Ras, R. H. Mechanically durable superhydrophobic surfaces. Adv. Mater. 2011, 23 (5), 673−678. (39) Sanderson, R. Chemical Bonds and Bonds Energy; Academic Press: New York, 1971; Vol. P 142. (40) Senoz, E.; Wool, R. P.; McChalicher, C. W.; Hong, C. K. Physical and chemical changes in feather keratin during pyrolysis. Polym. Degrad. Stab. 2012, 97 (3), 297−307. (41) Senoz, E.; Wool, R. P. Microporous carbon−nitrogen fibers from keratin fibers by pyrolysis. J. Appl. Polym. Sci. 2010, 118 (3), 1752−1765.
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One for Two: Conversion of Waste Chicken Feathers to Carbon Microspheres and (NH4)HCO3 Lei Gao,†,‡ Haibo Hu,† Xuelin Sui,‡ Changle Chen,*,‡ and Qianwang Chen*,† †
Hefei National Laboratory for Physical Sciences at Microscale, CAS Key Laboratory of Soft Matter Chemistry, University of Science and Technology of China, Jinzhai Rd 96, Hefei 86-551-63601495, China ‡ CAS Key Laboratory of Soft Matter Chemistry and Department of Polymer Science and Engineering, University of Science and Technology of China, Jinzhai Rd 96, Hefei 86-551-63601495, China S Supporting Information *
ABSTRACT: Pyrolysis of 1 g of waste chicken feathers (quills and barbs) in supercritical carbon dioxide (sc-CO2) system at 600 °C for 3 h leads to the formation of 0.25 g well-shaped carbon microspheres with diameters of 1−5 μm and 0.26 g ammonium bicarbonate ((NH4)HCO3). The products were characterized by powder X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Raman spectroscopic, FT-IR spectrum, X-ray electron spectroscopy (XPS), and N2 adsorption/desorption measurements. The obtained carbon microspheres displayed great superhydrophobicity as fabric coatings materials, with the water contact angle of up to 165.2 ± 2.5°. The strategy is simple, efficient, does not require any toxic chemicals or catalysts, and generates two valuable materials at the same time. Moreover, other nitrogen-containing materials (such as nylon and amino acids) can also be converted to carbon microspheres and (NH4)HCO3 in the sc-CO2 system. This provides a simple strategy to extract the nitrogen content from natural and man-made waste materials and generate (NH4)HCO3 as fertilizer.
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INTRODUCTION Chicken meat consumption had exceeded 65 million tons in 2007 according to the report from Food and Agriculture Organization of the United Nations.1 Feather accounts for 5− 7% of the body weight of poultry, leaving the annual generation of chicken feather waste to be ca. 5 million tons.1,2 Feather is composed of 90−92% protein (keratin) and 1−8% lipids.3,4 Keratin is very stable, mechanically permanent and chemically unreactive, most likely due to the tight packaging of the polypeptide chain to α-helix and β-sheet conformations, which makes the biodegradation of chicken feather very slow.5−7 Poultry feathers are mostly disposed in landfills due to the lack of an efficient and cost-effective treatment strategy. This not only leads to the discarding of a potentially valuable biopolymer but also arouses environmental concerns.8−10 Recently, some effort has been made to turn feathers into valuable materials.11−17 Barone et al.8 prepared a cohesive film by modifying poultry feathers with glycerol, which acted as a plasticizer. The film displayed good mechanical properties with an elastic modulus of 40−500 MPa, stress at break of 6−15 MPa, and strain at break of 8−50%. Jin et al.16 altered the poor thermoplasticity of chicken feather through graft polymerization with methyl acrylate. The compression-molded films developed from the grafted feathers had substantially higher tensile properties than soy protein isolate and starch acetate films. Senoz et al.18 obtained pyrolyzed chicken feather fibers from a two-step process (215 °C/15 h + 400−450 °C/1 h), which demonstrated a strong H2 adsorption at low pressures © XXXX American Chemical Society
and 77 K due to their microporous nature. As biological materials, poultry feathers can also be used to prepare biogas. Brandelli et al.19 produced keratinases from diverse microorganisms including Eucarya, Bacteria, and Archea domains, which displayed good capability to degrade keratin and may possess potential applications in agroindustrial, pharmaceutical, and biomedical fields. Supercritical carbon dioxide (sc-CO2) (Tc = 31.8 °C, Pc = 7.4 MPa) possesses many unique properties, including low viscosity, high diffusivity, and zero surface tension like a gas and the capability of dissolving substances like a liquid. Because of the low cost and superior features, it is widely applied as a nonpolar solvent in synthetic chemistry.20−23 Recently, we developed a strategy to convert waste polyethylene terephthalate (PET) and other waste polymers (PE, PP, and PVC) to well-shaped micrometer carbon spheres in supercritical carbon dioxide systems.24−26 The application of these carbon microspheres as negative electrode material for lithium ion batteries was evaluated. As one of our continuous efforts, the degradation of chicken feathers was investigated in sc-CO2 system. Herein, we report the conversion of chicken feathers (whole feathers with quills and barbs) to (NH4)HCO3 and carbon microspheres at the same time in sc-CO2 systems Received: February 10, 2014 Revised: April 4, 2014 Accepted: April 25, 2014
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Figure 1. Schematic diagram of the total experiment process. (a) chicken feathers, (b) (NH4)HCO3 product, (c) carbon product, (d) SEM image of the CMS sample, (e) superdrophobicity of the CMS sample, (f) SEM image of the ACMS sample, (g) superdrophobicity of the ACMS sample.
air atmosphere. Subsequently, 1.0 g chicken feather and 12 g of solid CO2 was put into a 25 mL stainless steel autoclave. The autoclave was closed tightly and placed inside a furnace and heated at a rate of 10 °C/min. It was then kept at 600 °C for 3 h. The reaction took place under the autogenic pressure of the reaction. When the autoclave was gradually cooled down to room temperature, white powder formed at the top of the autoclave (Figure 1b), while some black powder was formed at the bottom of the autoclave (Figure 1c). Then two kinds of powder were washed with absolute alcohol, filtered. The white powder was dried at a low temperature for 12 h, because it was volatile at high temperatures. The black powder was dried at 80 °C for 12h. Finally, about 0.26 g white powder ((NH4)HCO3 powder) and 0.25 g black powder (carbon microspheres powder) were obtained. The treatment was also carried out at lower temperatures, such as 400 and 500 °C, it is found that only 0.026 and 0.042 g black powder were obtained respectively, and there was no (NH4)HCO3 powder produced, meaning that the reaction was incomplete. The obtained carbon microsphere products were further vacuum-annealed to change their structures. 0.40 g carbon microspheres (CMS) were put into a sealed tube furnace equipped with a vacuum pump. Before heating, the furnace was vacuumed to evacuate air for 10 min. The CMS sample was heated in vacuum at a heating rate of 10 °C/min up to 1500 °C and kept for 1 h. After cooling down to room temperature, about 0.20 g annealed carbon microsphere (hereafter named ACMS) sample was obtained (loss of 50%). The superhydrophobic fabric materials were produced as follows:27 First, 0.2 g ACMS sample was dispersed in 15 mL tetrahydrofuran (THF) with the aid of ultrasonication. Subsequently, 0.10 g polydimethylsiloxane (PDMS) precursor Part-A (Sylgard186 elastomer base) was added to the solution. The solution was ultrasonicated for 1 h to form Solution A. Then 0.01 g PDMS precursor Part-B (Sylgard186 curing agent) was dissolved in 15 mL THF to form Solution B. Prior to coating treatment, the Solution A and B were mixed together at room temperature to form a coating solution. Fabric samples (2.5·4.0 cm2) were dip-coated with the as-prepared coating solution for 2 min and then cured at 60 °C for 12 h.
without any catalyst. Moreover, other nitrogen-containing materials including amino acids and nylon-6 can also be converted to (NH4)HCO3 and carbon microspheres using this strategy. Nylon-6 is widely used in various fields due to its excellent properties, most of which is disposed in landfills or by incineration, neither of which is environmentally friendly. The carbon microspheres product has many potential applications. Besides our previously demonstrated applications as negative electrode material for lithium ion batteries,24−26 the application of the carbon microspheres as superhydrophobic fabric coatings materials was studied. Ammonium bicarbonate is an important market product with wide applications in the food, plastics, and rubber industry. In particular, it has been used as a nitrogen fertilizer for a long time. More importantly, it is the intermediate for urea production, the most widely used nitrogen fertilizer worldwide (more than 108 metric tons per year). Currently, Harber process, which converts N2 and H2 to NH3 at very high temperature and pressure, produces 500 million tons of nitrogen fertilizer per year, and consumes 1−2% of the world’s annual energy supply. Our strategy can operate at much milder conditions and extract the nitrogen in the form of (NH4)HCO3, which will save a lot of energy. Most of the previously reported chicken feather treating methods involve complicated processes, the usage of toxic chemicals and catalysts, the generation of waste materials or the requirement of bioequipment or enzymes. Moreover, most of these methods require the separation of the quills and barbs, and only quills can be efficiently converted. In contrast, our one-step strategy only requires the usage of CO2, can efficiently treat the whole chicken feather and generates two highly valuable materials in one process. More importantly, this strategy may find more applications in extracting/converting the C atom from the waste materials to useful carbon-based materials and N atom to (NH4)HCO3.
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EXPERIMENTAL SECTION Materials and synthesis: Chicken feathers (whole feathers with quills and barbs, shown in Figure 1a) used in the experiments were collected from poultry market. First, chicken feathers were washed with distilled water and dried at 60 °C for 24 h under B
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ascribed to the characteristic peaks of (002), (101), and (004) for carbon (Figure 2b, JCPDS card No. 75-1621). The broadening of the three peaks suggests a low degree of graphitization. SEM analysis of the black powder indicates the formation of CMS (Figure 1d). After annealing at 1500 °C and for 1 h, ACMS was generated (Figure 1f). Both CMS and ACMS are able to generate fabric materials with good superdrophobicity (Figure 1e,g). FT-IR spectra of the obtained (NH4)HCO3 and the authentic (NH4)HCO3 sample are shown in Figure S6 in the Supporting Information. By comparison, it can be seen that the FT-IR spectra of the two samples are identical, and each peak can be matched. Combined with the XRD analysis, it is concluded that the white powder is really (NH4)HCO3 with high purity. Moreover, the elemental analysis of the obtained (NH4)HCO3 and the authentic (NH4)HCO3 sample is shown in Table S2 in the Supporting Information, which further confirms the purity of the obtained (NH4)HCO3 sample. The pyrolysis of chicken feathers at 400 °C (Figure 3a) afforded irregular small pieces without carbon microspheres. The reaction at 500 °C (Figure 3b) led to little amount of carbon product (0.042 g), with nonuniform sizes and rough surface. In both cases, no (NH4)HCO3 were generated at all. At 600 °C, 0.25 g smooth carbon microspheres with diameters of 1−5 μm are formed (Figure 3c), accompanied by 0.26 g (NH4)HCO3. As the temperature is further increased to 650 °C, carbon spheres with a perfect spherical morphology are produced. It can be seen that the sample comprises carbon microspheres with diameter of 1−3 μm (Figure 3d). However, the amount of (NH4)HCO3 production and carbon microspheres remains almost the same (also 0.26 and 0.25 g, respectively). About 30.6 wt % of the N element from the chicken feather was transferred into the (NH4)HCO3 product, and ca. 21.1 wt % is transferred into the nitrogen-containing CMS product (Table 1). Clearly, the reaction temperature is critical for the decomposition of chicken feathers. Higher temperature favors a more spherical particle shape with a narrow size distribution. The feather quills and barbs are separately pyrolyzed under the same condition, leading to very similar CMS products based on SEM and FTIR analysis (Supporting Information Figure S1−S3). The amount of (NH4)HCO3 is also similar for both cases. This suggests no distinction between the feather quills and barbs when they are pyrolyzed in the sc-CO2 systems. At the end of the reaction,
Sample characterization: The powder X-ray diffraction (XRD) was performed on a Japan Rigaku D/MAX-cA X-ray diffractometer equipped with Cu−Kα radiation (λ = 1.542 Å) over the 2θ range of 5−60°. Field emission scanning electron microscopy (FE-SEM) was performed on a JEOL JSM-6700 M scanning electron microscope. The Raman spectroscopic analysis was carried out on a LABRAM-HR confocal laser micro-Raman spectrometer using the 514.5 nm line of an Ar ion laser as the excitation source at room temperature. The FTIR spectrum was obtained using a Magna-IR 750 spectrometer in the range of 500−4000 cm−1 with a resolution of 4 cm−1. Xray electron spectroscopy (XPS) was performed on an ESCALAB 250 X-ray photoelectron spectrometer with Al Kα radiation. Specific surface areas were calculated from the results of N2 physisorption at 77 K (Micromeritics ASAP 2020) by using the BET (Brunauer−Emmet−Teller) and BJH (Barrett− Joyner−Halenda) methods. Elemental analysis of the Chicken feathers and the samples: The elemental composition of the chicken feather, feather quills, and barbs, and the products was performed on Elementar Vario EL cube and the results are shown in Table 1. Table 1. Elemental Composition of the Samples sample
C, wt %
N, wt %
H, wt %
others, wt %
chicken feathers feathers quills feathers barbs CMS sample ACMS sample
47.40 47.51 46.19 77.93 89.94
15.12 15.20 14.18 12.78 1.01
7.16 7.11 6.88 2.09 0.41
30.32 30.18 32.7 7.2 8.64
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RESULTS AND DISCUSSIONS Figure 1 shows a schematic diagram of the total experimental process. 1g of the chicken feathers (Figure 1a, whole feathers with quills and barbs) led to 0.26g of white powder (Figure 1b) and 0.25g of black powder (Figure 1c) after pyrolysis at 600 °C for 3 h in sc-CO2 systems. The white powder was confirmed to be (NH4)HCO3 from XRD analysis (Figure 2a), an important chemical fertilizer in agriculture. The major peaks in the XRD pattern are in agreement with standard JCPDS card (no. 090415). The strong and sharp reflection peaks and the smooth baseline indicated good crystallinity. In the XRD pattern of the black powder, the three peaks at 26.2°, 44.0°, and 53.1° are
Figure 2. XRD patterns of (a) the white powder, (b) the black powder (CMS sample), all prepared at 600 °C in sc-CO2 system for 3 h. C
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feather. We are currently optimizing reaction conditions to increase the yield of the (NH4)HCO3 and recycle these CO2 gas. It should be noted that CO2 plays a crucial role in this process. Under our conditions, the pyrolysis of 1.0 g chicken feathers in stainless steel autoclave without dry ice generated 0.12 g (NH4)HCO3 and 0.16 g carbon material. Only 14.1 wt % of the N element from the chicken feather was transferred into the (NH4)HCO3 product. Also, the generated (NH4)HCO3 and carbon materials were mixed together, not like the samples prepared in sc-CO2 system, which were separated at the top and bottom of the autoclave, respectively. This means a lot more extra work for separation. Also the carbon product contained almost no carbon microspheres (Supporting Information Figure S4). After the CMS sample was heated at 1500 °C under vacuum for 1 h, the surface of the resulting ACMS is no longer smooth, and nanoscale cracks appear on the surface of these carbon microspheres (Figure 3e,f). Raman spectroscopy is used to analyze different carbon atoms bonding in the product (Figure 4a). The E2g mode of perfectly ordered graphite is situated at 1600 cm−1 (labeled Gband).28,29 It originates from the stretching vibration of sp2 CC sites (whether in linear chains or in aromatic rings) in the two-dimensional hexagonal lattice of a graphite layer. With the increasing of disorder, this band broadens and shifts to a higher frequency, and a new band appears at 1340 cm−1 (labeled D-band).30,31 It corresponds to an A1g mode, and the intensity of this band is commonly used for practical applications to evaluate the amount of disorders in carbon materials. Such a mode is forbidden in a perfect graphite and becomes active only in the presence of disorder, and it is quite common in the sample obtained via mild temperature routes.32 It was found that the relative peak intensity ratio of G-band to
Figure 3. FESEM images of samples prepared by dissociating 1.0 g of chicken feather in 12 g of CO2 at different conditions: (a) 400 °C, 3 h, (b) 500 °C, 3 h, (c) 600 °C, 3 h (the CMS sample), (d) 650 °C, 3 h, (e, f) annealed at 1500 °C for 1 h (the ACMS sample).
when the autoclave was open, the CO2 gas rushed out of the autoclave and the smell of ammonia can be detected, which might be part of the destinations for the N content in chicken
Figure 4. (a) Raman, (b) FT-IR, and XPS (c) C 1s, (d) N 1s spectra of the CMS and ACMS sample. D
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surface must has a water contact angle larger than 150°. Surface etching technologies can also be used to improve the hydrophobicity of PDMS coating, such as laser cutting method.36,37 By directly changing the surface morphology with PDMS, hydrophobicity can be improved. However, most of these methods employed expensive materials and/or harsh conditions. For example, silicon wafer or glass substrates are usually required, which also limits their practical applications. This work is aiming not only to explore an effective method to convert waste chicken feathers to potentially useful carbon materials, but also to search for new possible applications of various carbon materials based on their unique structures. It is a simple, low-cost, environmentally friendly and resource-saving process and other organic waste can also be treated with this method. When 0.2 g CMS sample (0.55 mmol/L) is used in the coating solution, the WCA is increased to 153.2 ± 1.7° (Figure 5c). For ACMS case, the WCA is further increased to 165.2° ± 2.5°, indicating an excellent superdrophobicity. When 0.1 (0.28 mmol/L) and 0.3 g (0.83 mmol/L) ACMS sample is used, the WCA is 151.3 ± 1.5° and 156.0 ± 3.3°. Therefore, 0.2 g ACMS sample is the optimal amount to achieve a good superhyrophobicity. Only when the surface of the fabrics is coated by one layer of PDMS/annealed carbon microspheres uniformly, the surface roughness can reach the maximum and have the best hydrophobicity. If the amount of ACMS is not enough, some parts of the fabrics are not coated by ACMS and these parts are relatively smooth, the hydrophobicity is decreased. However, too much ACMS will leave some part of the fabrics coated by more than one layer of ACMS. Possibly, the following ACMS will fill the void on the surface of the fabrics. As such, the surface roughness will be decreased, leading to lower hydrophobicity. The surface of the fabrics was analyzed by SEM (Figure 6). Figure 6a is the SEM images of the uncoated fabric, and Figure 6b is the PDMS coated fabrics. The morphology is similar for both cases. Figure 6c−f showed that the coating of the CMS and ACMS samples to the fabric surface was highly efficient. The low WCA of the CMS sample might due to the high nitrogen content and the surface smoothness. The dramatic increase in WCA for the ACMS sample is believed to be due to the increased surface roughness from cracking and nanoscale flaws.38 The N2 absorption−desorption isotherms at 77 K of the ACMS sample is shown in Figure 7, and the inserted picture shows the size distribution of pores. The isotherms are characteristic of a type IV with a type H3 hysteresis loop, indicating a mesoporous structure. The BET surface area of the ACMS sample is calculated to be 16.99 m2g−1. Furthermore, the pore size distribution has a narrow peak at 20 and 23 nm and a wide peak at 65 nm, which also reveals the distinct pore sizes in the sample, corresponding well with the previous SEM characterizations. Moreover, the increase in the defects of the ACMS sample (Raman analysis) further reduces the surface free energy. All of these features favor the superhydrophobic properties of the fabric coatings. The energy bonds of CO, O−H, amide, C−C, and N−C on the side chains are 192.1, 111.8, 84−85, 80−81, and 70−73 kcal/mol.39 In the protein backbone, the weakest bond is HNCα bond. The cleavage of the HN-Cα bond is more probable, affording ammonium, which will react with H2O and CO2 and lead to the formation of (NH4)HCO3. H2O might come from the decomposition of chicken feather, or from the contamination from dry ice. Wool et al. studied the chemical and
D-band (IG/ID peak height ratio, after a level baseline at 800 cm−1 is taken out) for the CMS and ACMS sample is 1.11 and 0.89 respectively. The increase in the intensity of D band related to sp3 defects may due to the decrease of N content (from 12.78 wt % for CMS to 1.01 wt % for ACMS, Table 1) after annealing. This decrease will generate defects in the structure and sp3 hybrid carbon atoms are also present on the edge of these carbon microspheres (Figure 3f), causing the increase in disorder. Interestingly, the nitrogen doping causes symmetry-breaking of the carbon network, leaving the CMS sample to become IR-active.33 G-band and D-band of the CMS sample are clearly present in the FTIR analysis, which cannot be observed at all in ACMS sample (Figure 4b). After annealing C 1s peak of ACMS in XPS spectra becomes narrower and shifts to a higher binding energy (from 284.4 to 284.8 eV, Figure 4c). The two peaks in the N 1s core-level spectra of the CMS sample at 398 and 400 eV are attributed to NC and NC (Figure 4d).34,35 In contrast, these two peaks completely disappear in the ACMS sample. This confirms the significant decrease of the nitrogen content in the samples after annealing. The mole ratio of C, N and O in the CMS sample is 86.97%, 7.92%, and 5.11%, respectively. The mole ratio of C and O in the ACMS sample is 96.45% and 3.55%, respectively. The N element in the ACMS sample was detected by XPS. In the hydrophobicity study, a plain weave polyester fabric was used as a model substrate, and water was colored by rhodamine B. Statistical analysis is used to obtain the contact angles of all the samples. The contact angles of all the samples are shown in Supporting Information Table S1. In each treatment, five different pieces of fabrics were used to measure the contact angles. The contact angles of two water drops on each piece of fabric were obtained. Figure 5 shows the photos
Figure 5. Photos of water droplets on (a) uncoated fabric, and (b) PDMS coated fabric, (c) CMS/PDMS coated fabric, (d) ACMS/ PDMS coated fabric. The inserts were side views of a 3 μL water droplet.
of water droplets on the uncoated and coated fabrics. Water droplets spread into the pristine fabric (Figure 5a), and no water contact angle (WCA) could be observed. In contrast, nearly sphere-like water droplets were formed on the coated fabric (Figure 5b−d). These spherical droplets are stable and can stay on the supported fabric for a long time. WCA is 146.0 ± 1.7° for the fabric with only PDMS coating, which is not categorized as superhydrophobic because superhydrophobic E
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Figure 6. FESEM images of (a) uncoated fabrics, (b) PDMS coated fabrics, (c,d) 0.2 g CMS sample and PDMS coated fabrics, and (e,f) 0.2 g ACMS sample and PDMS coated babrics.
hydrocarbon molecules, such as hydrocarbon molecules were dissolved in the supercritical CO2, concentrated, grew to clusters made of aromatic rings and aliphatic chains, formed graphene layers, finally yielding carbon spheres at the bottom of the autoclave. Considering (NH4)HCO3 decomposes above 60 °C, the formation of (NH4)HCO3 probably happens during the cooling process. When the autoclave was opened at the end of the reaction, unreacted ammonium rushed out, which explained the ammonia smell. Currently, we are working on detailed mechanistic studies and optimizing reaction conditions to increase the yield of (NH4)HCO3. Based on the above studies, we became interested in investigating the applicability of this strategy to other nitrogen containing materials. Five nitrogen containing materials were tested under the same conditions (Table 2). All of these materials can be converted to (NH4)HCO3 and carbon products. The morphology of these carbon products are in the form of carbon microspheres (Supporting Information Figure S5), except Polyacrylamide which is not pyrolyzed adequately and the yield of (NH4)HCO3 is also the lowest (ca. 3.6 wt %). From the pyrolysis of two kinds of amino acid, it can be seen that as the content of nitrogen increases, the quality of the (NH4)HCO3 product also increases. However, the yield of (NH4)HCO3 was only increased moderately from 26.1 to 29.5 wt %, respectively. The reactant containing benzene ring (such as P-aminobenzoic acid) can also be pyrolyzed in sc-CO2 system to afford (NH4)HCO3 and carbon microspheres. Interestingly, nylon-6 gave the highest (NH4)HCO3 yield at
Figure 7. N2 adsorption/desorption isotherm (77 K) curves of the ACMS sample and porous volume distribution of the pore size (inset).
physical changes of chicken feathers during pyrolysis under air in great details, and only detected abundant aromatic carbons and cyclic amines.40,41 It was found that cyclic amines were formed around 400 °C during pyrolysis. Our results showed that only little amount of (NH4)HCO3 was formed when the reaction was carried out below 600 °C, suggesting that the generation of ammonium is not efficient under 600 °C. It is believed that chicken feathers initially dissociated to aromatic F
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Science Foundation of China (NSFC, 21071137 and 21374108), Anhui Provincial Natural Science Foundation (1408085QB28), the Fundamental Research Funds for the Central Universities (WK2060200012), and the Recruitment Program of Global Experts.
Table 2. Pyrolysis Results of Five Nitrogen Containing Materials
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37.1%, and very high carbon microspheres yield with good morphology (Supporting Information Figure S5e,f). This makes this strategy highly useful considering the huge annual consumption of nylon based materials.
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CONCLUSIONS In summary, pyrolysis of chicken feathers in sc-CO2 system led to the formation of carbon microspheres and (NH4)HCO3. Reaction temperature plays a critical role in the product formation. Below 600 °C, no (NH4)HCO3 and little carbon product could be generated. The CMS product has very high nitrogen content (12.8 wt %). Using this strategy, ca. 30.6 wt % of the nitrogen content in the chicken feathers is transferred to (NH4)HCO3 and ca. 21.1 wt % is transferred into nitrogencontaining CMS product. Furthermore, we developed a simple coating strategy to prepare superhydrophobic fabric materials using CMS and ACMS products, the WCA which can reach 153.2 ± 1.7° and 165.2 ± 2.5°. The biggest advantage of this strategy is that the whole chicken feather (quills and barbs) can be converted to two valuable materials at the same time. Furthermore, other nitrogen-containing materials (such as nylon-6) can also be converted to carbon microspheres and (NH4)HCO3 highly efficiently, suggesting the generality of this process. This strategy possesses great potentials for practical applications being able to convert one waste material chicken feathers into two valuable materials (NH4)HCO3 and carbon microsphere materials.
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ASSOCIATED CONTENT
S Supporting Information *
Additional information as noted in the text. This material is available free of charge via the Internet at http://pubs.acs.org.
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REFERENCES
AUTHOR INFORMATION
Corresponding Authors
*Phone: +86-551-63607251; fax: +86-551-63603005; e-mail: [email protected] or . *E-mail: [email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by a project of the National 863 HiTech Plan (Grant 2008AA06Z337) and the National Natural G
dx.doi.org/10.1021/es5006708 | Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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