- Email: [email protected]
hydroxyapatite nanocomposites
Materials Letters 159 (2015) 51–53
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Microwave-assisted rapid synthesis of lignocellulose/hydroxyapatite nanocomposites Lian-Hua Fu, Yi-Ming Xie, Jing Bian, Ming-Guo Ma n, Chun-Han Tian, Xiao-Juan Jin Engineering Research Center of Forestry Biomass Materials and Bioenergy, Beijing Key Laboratory of Lignocellulosic Chemistry, College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 20 May 2015 Received in revised form 15 June 2015 Accepted 22 June 2015 Available online 24 June 2015
Hydroxyapatite (HA) is the main inorganic constituent in vertebrate bones and teeth, and it is also an important biomaterial for the applications in tissue engineering and bone repair. Herein, we report the microwave-assisted method for the rapid synthesis of lignocellulose/HA nanocomposites using lignocellulose, CaCl2 and NaH2PO4 in the NaOH–urea aqueous solution. The effects of the microwave heating time and the concentration of the inorganic substances on the size and morphology of the products are investigated. The as-prepared products are characterized by X-ray powder diffraction (XRD), Fourier-transform infrared (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The microwave-assisted synthetic strategy reported here may open a new window to synthesize composites for potential biomedical applications. & 2015 Elsevier B.V. All rights reserved.
Keywords: Microstructure Composite materials Lignocellulose Hydroxyapatite Microwave
1. Introduction Hydroxyapatite (Ca10(PO4)6(OH)2, HA), as the main inorganic component of vertebrate bones and teeth [1,2], has been used in protein adsorption [3], drug delivery [4], tissue engineering [5] and bone repair [6] for the excellent osteoconductivity, biocompatibility, and bioactivity. But it is difficult to meet the biomedical demand due to its insufficient mechanical properties. Therefore, it is important to find the filler or substrate to improve the mechanical properties and biological properties of these material. Many natural substrates such as cellulose [7], chitosan [8], starch [9], and protein [10] were employed for the preparation of HA-based composites. However, as far as we know, the microwave-assisted rapid synthesis of HA particles in lignocellulose substrate has not been reported. Lignocelluloses are consisted of lignin, cellulose and hemicelluloses, which are promising substrates for organic/inorganic composites with the advantages of eliminating the separate of the lignocelluloses and utilizing all of the components [11]. There are reports on the synthesis of lignocelluloses-based organic/inorganic composites, such as lignocellulose/polypropylene composites [12], lignocellulose/organic montmorillonite composite [13], lignocellulose/pitch-Al2O3 composites [14]. The introduction of lignocellulose could not only reduce the production costs, but also improve the performances of the materials [15]. However, to the n
Corresponding author. Fax: þ 86 10 62336972. E-mail address: [email protected] (M.-G. Ma).
http://dx.doi.org/10.1016/j.matlet.2015.06.082 0167-577X/& 2015 Elsevier B.V. All rights reserved.
best of our knowledge, there is no report about the microwaveassisted rapid synthesis of HA particles in lignocellulose substrate. In this paper, we report a microwave-assisted rapid synthesis of lignocellulose/HA nanocomposites using lignocellulose, CaCl2, and NaH2PO4 in the NaOH–urea aqueous solution. Microwave-assisted method has been accepted as a promising method for the advantages of high reaction rate, shorter reaction time, reduced energy consumption, and environment friendliness [16,17]. The effects of the microwave heating time and the concentration of the inorganic substances on the size and morphology of the products are investigated. The as-prepared lignocellulose/HA nanocomposites are promising materials for potential applications in biomedical fields such as tissue engineering and bone repair.
2. Experimental All chemicals used here were of analytical grade and used as received without further purification. For the preparation of lignocellulose solution, 7.00g NaOH and 12.00g urea were added into 81 mL deionized water to form NaOH–urea aqueous solution. Then, 2.00g dewaxed lignocellulose was added into the above solution under vigorous stirring. After that, the above solution was cooled to 12 °C for 12 h. For the synthesis of lignocellulose/HA nanocomposites, 0.110 g CaCl2 and 0.093 g NaH2PO4 were added into 20 mL the obtained lignocellulose solution under vigorous stir. The obtained solution was heated to 90 °C for a certain time by microwave heating (XH100A, Xianhu, Beijing). The product was
L.-H. Fu et al. / Materials Letters 159 (2015) 51–53
(c)
(b) (a) 10
20
30
40
50
60
70
2 θ( degree )
Transmittance(%)
222 123
112
002
300
Intensity (a.u.)
21.8
121
52
(c) (b) (a) 3428
871 1668 1618 1454
609 567 1417 1045 4000 3500 3000 2500 2000 1500 1000 500
Wavenumbers(cm-1)
Fig. 1. XRD patterns (A) and IR spectra (B) of the products prepared using 0.111 g CaCl2 and 0.093 g NaH2PO4 by microwave heating at 90 °C for (a) 10 min, (b) 30 min, and (c) 60 min.
2 μm
2 μm
2 μm
500 nm
500 nm
500 nm
Fig. 2. SEM images of the products prepared using 0.111 g CaCl2 and 0.093 g NaH2PO4 by microwave heating at 90 °C for (a,b) 10 min, (c,d) 30 min, and (e,f) 60 min.
100
TGA
DTA 250
Weight (100%)
90 80
200
70
with a Hitachi S-3400N. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were carried out on Shimadzu DTG-60 with a heating rate of 10 °C min 1 in flowing air.
150
60 100
50 40
50
30
0
20 100
200
300
400
500
600
o
Temperature( C) Fig. 3. TGA and DTA curves of the products prepared using 0.111 g CaCl2 and 0.093 g NaH2PO4 by microwave heating at 90 °C for 30 min.
separated from the solution by centrifugation, washed by deionized water and ethanol several times and dried at 60 °C for further characterization. The control samples were also prepared using 0.055 g CaCl2 and 0.047 g NaH2PO4, while other reaction conditions were the same. X-ray powder diffraction (XRD) patterns of the as-prepared samples were recorded on Rigaku D/Max 2200-PC. Fourier-transform infrared (FT-IR) spectra were performed on Bruker Vertex 70V. Scanning electron microscopy (SEM) images were recorded
3. Results and discussion The crystal phases and functional groups of the as-prepared products were characterized by XRD and FTIR. It is well known that only cellulose has a crystallized phase in the lignocellulose. As shown in Fig. 1A, the diffraction peak at 2θ ¼ 21.8° was attributed to cellulose I, and all the other diffraction peaks can be indexed to HA with a hexagonal structure (JCPS 84-1998). The XRD patterns exhibited the single phase of HA could be obtained by microwaveassisted method at 90 °C for a short period of time (10 min). When the heating time was 60 min, the crystal faces of (222) and (123) of HA could be observed, suggesting the high crystallinity of HA. Fig. 1B showed the FT-IR spectra of the products. The absorptions at 3428 cm 1 and 1618 cm 1 are attributed to the characteristic of –OH and the bending mode of absorbed water in the composites. The peak at 1668 cm 1 is related to the conjugated carbonyl stretching in the lignin fractions. The obtained composites showed the typical bands at 1050 cm 1 (the C–O–C in cellulose and v3 1 /567 cm 1v4 PO3− PO3− 4 in HA), and 609 cm 4 together with those
L.-H. Fu et al. / Materials Letters 159 (2015) 51–53
53
2 μm
2 μm
2 μm
500 nm
500 nm
500 nm
Fig. 4. SEM images of the control samples prepared using 0.055 g CaCl2 and 0.047 g NaH2PO4 by microwave heating at 90 °C for (a,b) 10 min, (c,d) 30 min, and (e,f) 60 min. 1 1 at 1454 cm 1 (v3–3 CO2− (v3–4 CO2− (v2 3 )/1417 cm 3 ) and 871 cm
CO2− 3 ),
[PO3− 4 ]
[CO2− 3 ]
suggesting that the was partly replaced by from the urea. The morphology of the products was recorded with SEM, as shown in Fig. 2. When the heating time was 10 min, the lignocellulose substrate was covered by aggregated HA particles (Fig. 2a and b). When the heating time was 30 min, the HA particles with smaller crystal sizes and irregular morphologies could be observed (Fig. 2c and d). The crystal sizes of HA particles were further decreased and the composites turned into loose and porous structure with the heating time expanded to 60 min (Fig. 2e and f). These results indicated that the heating time affected the size and morphology of HA crystals, the smaller sizes and porous structure could be obtained through prolonging the heating time. There are plenty of hydroxyl groups in the lignocellulose and HA, which can form hydrogen bonds leading to the HA particles combined with the lignocellulose substrate. Fig. 3 showed the thermal stability of the samples. The small weight loss around 97 °C in TGA curve is originated from desorption of water, which is accompanied with an endothermic peak around 65 °C in DTA curve. The weight loss around 200–350 °C and 350–550 °C can be attributed to the thermal degradation and complete decomposition of lignocelluloses, respectively. The strong exothermic peaks around at 315 and 453 °C in the DTA curve are fit well with the temperature ranges of weight loss in the TGA curve. The weight of the composites achieved an equilibrium beyond 550 °C, and the total weight loss of the lignocellulose/HA composites was 73.3% from room temperature to 600 °C. In order to investigate the effect of inorganic substances concentration on the morphology of the nanocomposites, the control samples were prepared using 0.055 g CaCl2 and 0.047 g NaH2PO4 by microwave heating at 90 °C for different times. A few HA particles could be observed in the composites prepared for 10 min (Fig. 4a and b). When the heating time was increased to 30 min, the HA particles with irregular morphology were loosely dispersed on the substrate (Fig. 4c and d). Increased the heating time to 60 min, more HA particles were observed (Fig. 4e and f). These results indicated that the concentration of inorganic substances had a great influence on the morphology and dispersion of the HA particles, and lower inorganic substances concentration led to the HA particles with irregular morphology and poor dispersion on the lignincellulose substrate.
4. Conclusions In summary, we have developed a green microwave-assisted method for the rapid preparation of lignocellulose/HA nanocomposites. The morphologies and sizes of the as-prepared HA particles could be regulated by controlling the heating time. The concentration of the inorganic substances had an important influence on the morphology and dispersion of HA particles on the lignocellulose substrate. The experimental results indicated that the lignocellulose is a suitable substrate for the rapid synthesis of HA particles under microwave-assisted conditions. In addition, the lignocellulose is a promising substrate to be extended to synthesize other materials in the future.
Acknowledgments Financial support from the Fundamental Research Funds for the Central Universities (No. TD2011-11), Beijing Nova Program (Z121103002512030), and the Program for New Century Excellent Talents in University (NCET-11-0586) is gratefully acknowledged.
References [1] L.C. Palmer, C.J. Newcomb, S.R. Kaltz, E.D. Spoerke, S.I. Stupp, Chem. Rev. 108 (2008) 4754–4783. [2] S.V. Dorozhkin, Materials 2 (2009) 399–498. [3] T. Lan, Z.Q. Shao, J.Q. Wang, M.J. Gu, Chem. Eng. J. 260 (2015) 818–825. [4] F.J. Martinez-Vazquez, M.V. Cabanas, J.L. Paris, D. Lozano, M. Vallet-Regi, Acta Biomater. 15 (2015) 200–209. [5] X.Y. Xie, K.W. Hu, D.D. Fang, L.H. Shang, S.D. Tran, M. Cerruti, Nanoscale 7 (2015) 7992–8002. [6] A.B. Kutikov, J.D. Skelly, D.C. Ayers, J. Song, ACS Appl. Mater. Interface 7 (2015) 4890–4901. [7] A. Kumar, Y.S. Neqi, V. Choudhary, N.K. Bhardwaj, Cellulose 21 (2014) 3409–3426. [8] Z.Y. Zhong, J.L. Qin, J. Ma, Mater. Sci. Eng. C 49 (2015) 251–255. [9] M. Meskinfam, M.A.S. Sadjadi, H. Jazdarreh, K.J. Zare, Biomed. Nanotechnol. 7 (2011) 455–459. [10] M. Sadat-Shojai, M.T. Khorasani, A. Jamshidi, Mater. Sci. Eng. C 49 (2015) 835–843. [11] L.H. Fu, M.G. Ma, J. Bian, F. Deng, X. Du, Mater. Sci. Eng. C 44 (2014) 216–224. [12] S.J. Borysiak, Appl. Polym. Sci. 127 (2013) 1309–1322. [13] M.M. Wang, L. Wang, A.Q. Wang, Desalin. Water Treat. 51 (2013) 7120–7129. [14] P. Alvarez, R. Menendez, M.J. Granda, Anal. Appl. Pyrolysis 82 (2008) 151–157. [15] V. Blanchard, P. Blanchet, Bioresources 6 (2011) 1219–1229. [16] Y.J. Zhu, F. Chen, Chem. Rev. 114 (2014) 6462–6555. [17] C. Qi, Y.J. Zhu, F. Chen, ACS Appl. Mater. Interfaces 6 (2014) 4310–4320.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Microwave-assisted rapid synthesis of lignocellulose/hydroxyapatite nanocomposites Lian-Hua Fu, Yi-Ming Xie, Jing Bian, Ming-Guo Ma n, Chun-Han Tian, Xiao-Juan Jin Engineering Research Center of Forestry Biomass Materials and Bioenergy, Beijing Key Laboratory of Lignocellulosic Chemistry, College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 20 May 2015 Received in revised form 15 June 2015 Accepted 22 June 2015 Available online 24 June 2015
Hydroxyapatite (HA) is the main inorganic constituent in vertebrate bones and teeth, and it is also an important biomaterial for the applications in tissue engineering and bone repair. Herein, we report the microwave-assisted method for the rapid synthesis of lignocellulose/HA nanocomposites using lignocellulose, CaCl2 and NaH2PO4 in the NaOH–urea aqueous solution. The effects of the microwave heating time and the concentration of the inorganic substances on the size and morphology of the products are investigated. The as-prepared products are characterized by X-ray powder diffraction (XRD), Fourier-transform infrared (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The microwave-assisted synthetic strategy reported here may open a new window to synthesize composites for potential biomedical applications. & 2015 Elsevier B.V. All rights reserved.
Keywords: Microstructure Composite materials Lignocellulose Hydroxyapatite Microwave
1. Introduction Hydroxyapatite (Ca10(PO4)6(OH)2, HA), as the main inorganic component of vertebrate bones and teeth [1,2], has been used in protein adsorption [3], drug delivery [4], tissue engineering [5] and bone repair [6] for the excellent osteoconductivity, biocompatibility, and bioactivity. But it is difficult to meet the biomedical demand due to its insufficient mechanical properties. Therefore, it is important to find the filler or substrate to improve the mechanical properties and biological properties of these material. Many natural substrates such as cellulose [7], chitosan [8], starch [9], and protein [10] were employed for the preparation of HA-based composites. However, as far as we know, the microwave-assisted rapid synthesis of HA particles in lignocellulose substrate has not been reported. Lignocelluloses are consisted of lignin, cellulose and hemicelluloses, which are promising substrates for organic/inorganic composites with the advantages of eliminating the separate of the lignocelluloses and utilizing all of the components [11]. There are reports on the synthesis of lignocelluloses-based organic/inorganic composites, such as lignocellulose/polypropylene composites [12], lignocellulose/organic montmorillonite composite [13], lignocellulose/pitch-Al2O3 composites [14]. The introduction of lignocellulose could not only reduce the production costs, but also improve the performances of the materials [15]. However, to the n
Corresponding author. Fax: þ 86 10 62336972. E-mail address: [email protected] (M.-G. Ma).
http://dx.doi.org/10.1016/j.matlet.2015.06.082 0167-577X/& 2015 Elsevier B.V. All rights reserved.
best of our knowledge, there is no report about the microwaveassisted rapid synthesis of HA particles in lignocellulose substrate. In this paper, we report a microwave-assisted rapid synthesis of lignocellulose/HA nanocomposites using lignocellulose, CaCl2, and NaH2PO4 in the NaOH–urea aqueous solution. Microwave-assisted method has been accepted as a promising method for the advantages of high reaction rate, shorter reaction time, reduced energy consumption, and environment friendliness [16,17]. The effects of the microwave heating time and the concentration of the inorganic substances on the size and morphology of the products are investigated. The as-prepared lignocellulose/HA nanocomposites are promising materials for potential applications in biomedical fields such as tissue engineering and bone repair.
2. Experimental All chemicals used here were of analytical grade and used as received without further purification. For the preparation of lignocellulose solution, 7.00g NaOH and 12.00g urea were added into 81 mL deionized water to form NaOH–urea aqueous solution. Then, 2.00g dewaxed lignocellulose was added into the above solution under vigorous stirring. After that, the above solution was cooled to 12 °C for 12 h. For the synthesis of lignocellulose/HA nanocomposites, 0.110 g CaCl2 and 0.093 g NaH2PO4 were added into 20 mL the obtained lignocellulose solution under vigorous stir. The obtained solution was heated to 90 °C for a certain time by microwave heating (XH100A, Xianhu, Beijing). The product was
L.-H. Fu et al. / Materials Letters 159 (2015) 51–53
(c)
(b) (a) 10
20
30
40
50
60
70
2 θ( degree )
Transmittance(%)
222 123
112
002
300
Intensity (a.u.)
21.8
121
52
(c) (b) (a) 3428
871 1668 1618 1454
609 567 1417 1045 4000 3500 3000 2500 2000 1500 1000 500
Wavenumbers(cm-1)
Fig. 1. XRD patterns (A) and IR spectra (B) of the products prepared using 0.111 g CaCl2 and 0.093 g NaH2PO4 by microwave heating at 90 °C for (a) 10 min, (b) 30 min, and (c) 60 min.
2 μm
2 μm
2 μm
500 nm
500 nm
500 nm
Fig. 2. SEM images of the products prepared using 0.111 g CaCl2 and 0.093 g NaH2PO4 by microwave heating at 90 °C for (a,b) 10 min, (c,d) 30 min, and (e,f) 60 min.
100
TGA
DTA 250
Weight (100%)
90 80
200
70
with a Hitachi S-3400N. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were carried out on Shimadzu DTG-60 with a heating rate of 10 °C min 1 in flowing air.
150
60 100
50 40
50
30
0
20 100
200
300
400
500
600
o
Temperature( C) Fig. 3. TGA and DTA curves of the products prepared using 0.111 g CaCl2 and 0.093 g NaH2PO4 by microwave heating at 90 °C for 30 min.
separated from the solution by centrifugation, washed by deionized water and ethanol several times and dried at 60 °C for further characterization. The control samples were also prepared using 0.055 g CaCl2 and 0.047 g NaH2PO4, while other reaction conditions were the same. X-ray powder diffraction (XRD) patterns of the as-prepared samples were recorded on Rigaku D/Max 2200-PC. Fourier-transform infrared (FT-IR) spectra were performed on Bruker Vertex 70V. Scanning electron microscopy (SEM) images were recorded
3. Results and discussion The crystal phases and functional groups of the as-prepared products were characterized by XRD and FTIR. It is well known that only cellulose has a crystallized phase in the lignocellulose. As shown in Fig. 1A, the diffraction peak at 2θ ¼ 21.8° was attributed to cellulose I, and all the other diffraction peaks can be indexed to HA with a hexagonal structure (JCPS 84-1998). The XRD patterns exhibited the single phase of HA could be obtained by microwaveassisted method at 90 °C for a short period of time (10 min). When the heating time was 60 min, the crystal faces of (222) and (123) of HA could be observed, suggesting the high crystallinity of HA. Fig. 1B showed the FT-IR spectra of the products. The absorptions at 3428 cm 1 and 1618 cm 1 are attributed to the characteristic of –OH and the bending mode of absorbed water in the composites. The peak at 1668 cm 1 is related to the conjugated carbonyl stretching in the lignin fractions. The obtained composites showed the typical bands at 1050 cm 1 (the C–O–C in cellulose and v3 1 /567 cm 1v4 PO3− PO3− 4 in HA), and 609 cm 4 together with those
L.-H. Fu et al. / Materials Letters 159 (2015) 51–53
53
2 μm
2 μm
2 μm
500 nm
500 nm
500 nm
Fig. 4. SEM images of the control samples prepared using 0.055 g CaCl2 and 0.047 g NaH2PO4 by microwave heating at 90 °C for (a,b) 10 min, (c,d) 30 min, and (e,f) 60 min. 1 1 at 1454 cm 1 (v3–3 CO2− (v3–4 CO2− (v2 3 )/1417 cm 3 ) and 871 cm
CO2− 3 ),
[PO3− 4 ]
[CO2− 3 ]
suggesting that the was partly replaced by from the urea. The morphology of the products was recorded with SEM, as shown in Fig. 2. When the heating time was 10 min, the lignocellulose substrate was covered by aggregated HA particles (Fig. 2a and b). When the heating time was 30 min, the HA particles with smaller crystal sizes and irregular morphologies could be observed (Fig. 2c and d). The crystal sizes of HA particles were further decreased and the composites turned into loose and porous structure with the heating time expanded to 60 min (Fig. 2e and f). These results indicated that the heating time affected the size and morphology of HA crystals, the smaller sizes and porous structure could be obtained through prolonging the heating time. There are plenty of hydroxyl groups in the lignocellulose and HA, which can form hydrogen bonds leading to the HA particles combined with the lignocellulose substrate. Fig. 3 showed the thermal stability of the samples. The small weight loss around 97 °C in TGA curve is originated from desorption of water, which is accompanied with an endothermic peak around 65 °C in DTA curve. The weight loss around 200–350 °C and 350–550 °C can be attributed to the thermal degradation and complete decomposition of lignocelluloses, respectively. The strong exothermic peaks around at 315 and 453 °C in the DTA curve are fit well with the temperature ranges of weight loss in the TGA curve. The weight of the composites achieved an equilibrium beyond 550 °C, and the total weight loss of the lignocellulose/HA composites was 73.3% from room temperature to 600 °C. In order to investigate the effect of inorganic substances concentration on the morphology of the nanocomposites, the control samples were prepared using 0.055 g CaCl2 and 0.047 g NaH2PO4 by microwave heating at 90 °C for different times. A few HA particles could be observed in the composites prepared for 10 min (Fig. 4a and b). When the heating time was increased to 30 min, the HA particles with irregular morphology were loosely dispersed on the substrate (Fig. 4c and d). Increased the heating time to 60 min, more HA particles were observed (Fig. 4e and f). These results indicated that the concentration of inorganic substances had a great influence on the morphology and dispersion of the HA particles, and lower inorganic substances concentration led to the HA particles with irregular morphology and poor dispersion on the lignincellulose substrate.
4. Conclusions In summary, we have developed a green microwave-assisted method for the rapid preparation of lignocellulose/HA nanocomposites. The morphologies and sizes of the as-prepared HA particles could be regulated by controlling the heating time. The concentration of the inorganic substances had an important influence on the morphology and dispersion of HA particles on the lignocellulose substrate. The experimental results indicated that the lignocellulose is a suitable substrate for the rapid synthesis of HA particles under microwave-assisted conditions. In addition, the lignocellulose is a promising substrate to be extended to synthesize other materials in the future.
Acknowledgments Financial support from the Fundamental Research Funds for the Central Universities (No. TD2011-11), Beijing Nova Program (Z121103002512030), and the Program for New Century Excellent Talents in University (NCET-11-0586) is gratefully acknowledged.
References [1] L.C. Palmer, C.J. Newcomb, S.R. Kaltz, E.D. Spoerke, S.I. Stupp, Chem. Rev. 108 (2008) 4754–4783. [2] S.V. Dorozhkin, Materials 2 (2009) 399–498. [3] T. Lan, Z.Q. Shao, J.Q. Wang, M.J. Gu, Chem. Eng. J. 260 (2015) 818–825. [4] F.J. Martinez-Vazquez, M.V. Cabanas, J.L. Paris, D. Lozano, M. Vallet-Regi, Acta Biomater. 15 (2015) 200–209. [5] X.Y. Xie, K.W. Hu, D.D. Fang, L.H. Shang, S.D. Tran, M. Cerruti, Nanoscale 7 (2015) 7992–8002. [6] A.B. Kutikov, J.D. Skelly, D.C. Ayers, J. Song, ACS Appl. Mater. Interface 7 (2015) 4890–4901. [7] A. Kumar, Y.S. Neqi, V. Choudhary, N.K. Bhardwaj, Cellulose 21 (2014) 3409–3426. [8] Z.Y. Zhong, J.L. Qin, J. Ma, Mater. Sci. Eng. C 49 (2015) 251–255. [9] M. Meskinfam, M.A.S. Sadjadi, H. Jazdarreh, K.J. Zare, Biomed. Nanotechnol. 7 (2011) 455–459. [10] M. Sadat-Shojai, M.T. Khorasani, A. Jamshidi, Mater. Sci. Eng. C 49 (2015) 835–843. [11] L.H. Fu, M.G. Ma, J. Bian, F. Deng, X. Du, Mater. Sci. Eng. C 44 (2014) 216–224. [12] S.J. Borysiak, Appl. Polym. Sci. 127 (2013) 1309–1322. [13] M.M. Wang, L. Wang, A.Q. Wang, Desalin. Water Treat. 51 (2013) 7120–7129. [14] P. Alvarez, R. Menendez, M.J. Granda, Anal. Appl. Pyrolysis 82 (2008) 151–157. [15] V. Blanchard, P. Blanchet, Bioresources 6 (2011) 1219–1229. [16] Y.J. Zhu, F. Chen, Chem. Rev. 114 (2014) 6462–6555. [17] C. Qi, Y.J. Zhu, F. Chen, ACS Appl. Mater. Interfaces 6 (2014) 4310–4320.