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Facile one-step green synthesis of gold nanoparticles using Citrus maxima aqueous extracts and its catalytic activity
Materials Letters 166 (2016) 110–112
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Facile one-step green synthesis of gold nanoparticles using Citrus maxima aqueous extracts and its catalytic activity Jia Yu a, Di Xu b, Hua Nan Guan a,c, Chao Wang b, Li Kun Huang c, De Fu Chi a,n a
College of Forestry, Northeast Forestry University, Harbin 150040, People's Republic of China College of life and Science, Northeast Forestry University, Harbin 150040, People's Republic of China c College of Food Engineering, Harbin University of Commerce, Harbin 150076, People's Republic of China b
art ic l e i nf o
a b s t r a c t
Article history: Received 14 July 2015 Received in revised form 20 October 2015 Accepted 6 December 2015 Available online 8 December 2015
A low cost eco-friendly method for the synthesis of gold nanoparticles (AuNPs) using Citrus maxima (C. maxima) fruit extracts was reported. The nanoparticles obtained were characterized by UV–vis spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform-infrared spectroscopies (FTIR) analysis. The synthesized AuNPs using 50% concentration of C. maxima fruit extracts were characterized by a peak at 535 nm in the UV–vis spectrum. The mean particle size for AuNPs was observed to be 25.77 10 nm. FTIR spectrum indicated that C. maxima fruit had the ability to perform dual functions of reduction and stabilization of AuNPs. The synthesized AuNPs also showed the good catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol by excess NaBH4. & 2015 Elsevier B.V. All rights reserved.
Keywords: Gold nanoparticles Green synthesis Catalysis Citrus maxima
1. Introduction Gold nanoparticles (AuNPs) have attracted wide attention due to their potential applications in catalysis, electrical conductivity, optical properties, etc. [1]. These can be readily synthesized and display high chemical as well as thermal stability [2]. Although various physical and chemical routes have been approved for the synthesis of AuNPs, such methods are not considered environmentally friendly which limited their applications in food and medical fields [3–5]. In recent years, the development of efficient green chemistry methods for the synthesis of AuNPs has become a major focus of researchers. One of the methods is the production of AuNPs using biological system such as microbes, fungi and plant extracts [6–8]. Plant mediated synthesis of AuNPs are noteworthy due to its simplicity, rapid rate of synthesis, ecofriendliness and it can potentially render more biocompatibility with biomolecules [9]. Green synthesis of AuNPs by plants such as Olive leaf, Citrus sinensis, Pear fruit, Trigonella foenum-graecum, Edible coconut oil, black tea leaves and Cypress leaves, have been reported earlier [10–14]. In the present work, we report the green synthesis of AuNPs using the extracts of Citrus maxima (C. maxima) fruit as reducing and capping agents. This method is simple, efficient, economic and environmentally benign. Moreover, the catalytic activity in reduction of 4-nitrophenol to 4-aminophenol in n
Correspondence to: No. 26, He Xing Road, Harbin, People's Republic of China. E-mail address: [email protected] (D.F. Chi).
http://dx.doi.org/10.1016/j.matlet.2015.12.031 0167-577X/& 2015 Elsevier B.V. All rights reserved.
the presence of NaBH4 and its rate constant was also evaluated. To the best of our knowledge, this is the first report for the synthesis of AuNPs using C. maxima fruit extracts.
2. Experimental Chloroauric acid tetrahydrate (HAuCl4 4H2O) was purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China, http://sinoreagent.cn.alibaba.com/). Sodium borohydride (NaBH4) and 4-nitrophenol were obtained from Huanwei Fine Chemical Co., Ltd., (Tianjin, China). First, C. maxima were cleaned with deionized water, and then finely cut into small pieces. These pieces were squeezed to extracts the juice which was later strained through a fine pore nylon mesh. Obtained extraction was centrifuged at 12,000 rpm for 5 min to remove any undesired impurities. The extraction was considered as a stock solution and other concentrations of the extracts were prepared using this. The AuNPs colloids (C1) was prepared at room temperature (298 K) by adding 2 mL of stock solution to vigorously stirred 10 mL aqueous solution of HAuCl4 4H2O (1%,W/V) and stirring continued for 5 min. The reaction mixture immediately showed a light pinkish red shade which implied the complete reduction of chaoroaurate ions. The colloids C2–C6 were obtained by varying the diluted multiples of the extracts stock solution as 50%, 20%, 10%, 5%, and 1% respectively. Appropriate choice of different volumes of the stock solution and diluted solution is made through repeated
J. Yu et al. / Materials Letters 166 (2016) 110–112
111
Fig. 1. UV–visible spectra of gold colloids (C1–C6) at 298 K (A) and the TEM image of gold colloid C2 (B); the inset in (A) shows the corresponding real pictures of gold colloids C1, C2 and C5; inset image in B shows the size distribution of gold colloid C2.
Fig. 2. X-ray diffraction pattern recorded from drop coated films of the colloid C2 deposited on glass substrates (A) and FT-IR spectra of C. maxima fruit extracts and the C. maxima mediated colloid C2 (B).
Fig. 3. Time dependent UV–vis spectra for the reduction of 4-NP with NaBH4 catalyzed by C. maxima mediated gold colloid C2 at the concentration 1 mmol/L (A); and the corresponding plot of ln(C/C0) vs. time.
experiments. To evaluate the catalytic activity of synthesized AuNPs, the reduction of 4-Nitrophenol (4-NP) to 4-Aminophenol (4-AP) by NaBH4 is selected as a probe reaction. The effect of concentration of AuNPs on the speed of catalytic reduction was investigated by using different quantities of AuNPs colloids. After the addition of gold colloids, reduction is ascertained by recording the UV–visible spectra.
3. Results and discussion As shown in Fig. 1A, the UV–vis spectra of AuNPs formation at constant concentration of HAuCl4 with varying quantity of C. maxima fruit extracts 100%, 50%, 20%, 10%, 5%, and 1% stock solution (C1–C6). The gradual color change from purplish red (C1) to wine red (C2) to pink red (C5) was observed during reaction with varying concentration of C. maxima fruit extracts which are
112
J. Yu et al. / Materials Letters 166 (2016) 110–112
characteristic of the Surface Plasmon Resonance of different size of AuNPs in solution (inset image of Fig. 1A). From the spectra it is clear that when the concentration of C. maxima fruit extracts decreased from 50% to 1% (C2–C6), the SPR band is shifted towards the longer wavelength region from 535 nm to 585 nm which shows an increase in a particle size. It is interesting to note that in Fig. 1A, only for C2–C4 (50–10%) of the maximum plasmon absorption wavelength of AuNPs was obtained for the least value (535–540 nm) without another absorption band in the longitudinal plasmon resonance. Moreover, absorption spectra of gold nanoparticles synthesized using 100%, 5% and 1% C. maxima fruit extracts stock shifted to longer wave length region. Most researchers believed that the as-prepared nanoparticles exhibit a size dependent catalytic property, the smaller nanoparticles showing faster activity. When the size of gold nanoparticles decreases, there is an increase in the number of low-coordinated Au atoms which promote the absorption of the reactants on the catalyst surface and facilitates the reduction [1,15]. The SPR band can give useful information about the size and the shape of the synthesized nanoparticles. The increase in particle size causes the increase in the maximum wavelength (red shift), and the reduction in particle size leads to the decrease in the maximum wavelength (blue shift) [2,16]. In order to obtain the smaller size of particle, we chose 50% concentration of C. maxima fruit extracts to prepare AuNPs (C2) according to this theoretical analysis. Typical TEM images obtained for AuNPs colloids C2 shown in Fig. 1B. It can be seen that the morphology consist of a mixture of rod and spherical like particles. The average particle size measured for the AuNPs colloids C2 are observed to be 25.77 10 nm. Dynamic light scattering (DLS) measurements showed that polydispersity of the particles was lower than 0.1. The XRD patterns of the products prepared by 50% of C. maxima fruit extracts stock solution (gold colloid C2) are seen in Fig. 2A. It shows intensive characteristic peaks of metallic Au. The diffraction peaks at 2θ 38.56°, 44.67°, 64.50° and 77.58° correspond to the (111), (200), (220) and (311) Bragg planes of fcc gold lattice, respectively, which are in agreement with the diffraction standard of gold (JCPDS 80-3697) [17]. In this case, the peak due to (111) reflection is more intense than those owed to (200), (220) and (311) reflections. This clearly shows that AuNPs are predominantly oriented along the (111) plane utilizing C. maxima fruit extracts. Fig. 2B shows the FTIR spectrum of the gold nanoparticles synthesized using C. maxima fruit extracts, which exhibited bands at 617, 1125, 1376, 1658 and 3278 cm 1. The peak at 3278 cm 1 was assigned to O–H stretching vibrations, which can be found in flavonoids, terpene and ascorbic acids extracts [1]. In case of AuNPs synthesized using C. maxima fruit extracts strong bands at 1658 and 1376 cm 1 are observed. The two bands correspond to the amide I and II bands of polypeptides/proteins respectively and agree with those reported in the literature [17]. The absorption band at 1125 cm 1 was assigned as the amide III band of polypeptide present in the fruit [6,10,11]. The polypeptides or proteins had rich amino and thiol groups, which strongly bind the Au(0), forming a polypeptides/proteins–Au complex. The reduction function of the amino acid residues was activated to trigger the nucleation and growth of AuNPs in the scaffolds between amino acid molecules. These structural changes have confirmed the fact that the polypeptides or proteins could possibly form a layer covering the nanoparticles to prevent agglomeration and thereby stabilize the medium. The peak at 1658 cm 1 could be assigned to
the vibrational modes of C ¼C double bones of biomolecules. The band located at 1376 cm 1 was due to the C–N stretching vibrations. Herein, the flavonoids, terpenes and vitamins present in C. maxima fruit are powerful reducing agents which may be responsible for the reduction of choroauric acid. The proteins and polypeptides can act as surfactant to attach on the surface of AuNPs and it stabilizes AuNPs through electrostatic stabilization. When AuNPs were added to the reaction system, the intensity of the peak at 400 nm due to 4-NP gradually decreased with time and a new peak appeared at 302 nm due to the formation of 4-AP (Fig. 3A). In this context, pseudo-first-order kinetics could be used to evaluate the kinetic reaction rate of the current catalytic reaction [11]. The kinetic rate constant kapp can be calculated from the rate equation ln (C/C0)¼ -kappt, where C0 is the initial concentration of 4-NP with a constant value of 0.25 10 3 mol/L and C represents the concentration of 4-NP at the time t. As expected, a good linear correlation of ln(C/C0) versus time was obtained, and AuNPs synthesized using C. maxima fruit extracts exhibit a high activity with an estimated kapp value of 0.08977 min 1 (Fig. 3B).
4. Conclusions We have reported a simple single step eco-friendly method to produce AuNPs surrounded by plant matrix which acts as a reducing or stabilizing agent. Such a method for synthesizing AuNPs will be an added advantage, and other food materials rich in vitamins, terpenes and flavonoids can be potentially converted into a high value nanoproductive. These particles are expected to have extensive applications in semiconductors, spectroscopy, drug delivery, tissue imaging and cancer therapy.
Acknowledgments This work was supported by the National Natural Science Foundation of China (Nos. J1210053 and 51408168), the Science and Technology Support Project of China (No. 2012BAD19B0704) and China Postdoctoral Science Foundation (No. 2014T70304).
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
S.A. Aromal, D. Philip, Spectrochim. Acta Part A 97 (2012) 1–5. M. Noruzi, Bioprocess Biosyst. Eng. 38 (2015) 1–14. R.K. Das, B.B. Borthakur, U. Bora, Mater. Lett. 64 (2010) 1445–1447. T.K. Sau, A.L. Rogach, F. Jäckel, T.A. Klar, J. Feldmann, Adv. Mater. 22 (2010) 1805–1825. M.M. Kumari, D. Philip, Spectrochim. Acta Part A 111 (2013) 154–160. P. Khademi-Azandehi, J. Moghaddam, Particuology 19 (2015) 22–26. Y. Mikami, A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Catal. Sci. Technol. 3 (2013) 58–69. C. Dipankar, S. Murugan, Colloids Surf. B 98 (2012) 112–119. D. Philip, Spectrochim. Acta Part A 77 (2010) 807–810. M.H.K. Mostafa, H.I. Eman, F. El-Magdoub, Arab. J. Chem. 5 (2012) 431–437. M.V. Sujitha, S. Kannan, Spectrochim. Acta Part A 102 (2013) 15–23. G.S. Ghodake, N.G. Deshpande, Y.P. Lee, E.S. Jin, Colloids Surf. B 75 (2010) 584–589. K. Gopinath, K.S. Venkatesh, R. Ilangovan, K. Sankaranarayanan, A. Arumugam, Ind. Crops Prod. 50 (2013) 737–742. M. Noruzi, D. Zare, D. Davoodi, Spectrochim. Acta Part A 94 (2012) 84–88. R.K. Sharma, S. Gulati, S. Mehta, J. Chem. Educ. 89 (2012) 1316–1318. M.M. Byranvand, A.N. Kharat, Mater. Lett. 134 (2014) 64–66. P.P. Gan, S.H. Ng, Y. Huang, Li SFY, Bioresour. Technol. 113 (2012) 132–135.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Facile one-step green synthesis of gold nanoparticles using Citrus maxima aqueous extracts and its catalytic activity Jia Yu a, Di Xu b, Hua Nan Guan a,c, Chao Wang b, Li Kun Huang c, De Fu Chi a,n a
College of Forestry, Northeast Forestry University, Harbin 150040, People's Republic of China College of life and Science, Northeast Forestry University, Harbin 150040, People's Republic of China c College of Food Engineering, Harbin University of Commerce, Harbin 150076, People's Republic of China b
art ic l e i nf o
a b s t r a c t
Article history: Received 14 July 2015 Received in revised form 20 October 2015 Accepted 6 December 2015 Available online 8 December 2015
A low cost eco-friendly method for the synthesis of gold nanoparticles (AuNPs) using Citrus maxima (C. maxima) fruit extracts was reported. The nanoparticles obtained were characterized by UV–vis spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform-infrared spectroscopies (FTIR) analysis. The synthesized AuNPs using 50% concentration of C. maxima fruit extracts were characterized by a peak at 535 nm in the UV–vis spectrum. The mean particle size for AuNPs was observed to be 25.77 10 nm. FTIR spectrum indicated that C. maxima fruit had the ability to perform dual functions of reduction and stabilization of AuNPs. The synthesized AuNPs also showed the good catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol by excess NaBH4. & 2015 Elsevier B.V. All rights reserved.
Keywords: Gold nanoparticles Green synthesis Catalysis Citrus maxima
1. Introduction Gold nanoparticles (AuNPs) have attracted wide attention due to their potential applications in catalysis, electrical conductivity, optical properties, etc. [1]. These can be readily synthesized and display high chemical as well as thermal stability [2]. Although various physical and chemical routes have been approved for the synthesis of AuNPs, such methods are not considered environmentally friendly which limited their applications in food and medical fields [3–5]. In recent years, the development of efficient green chemistry methods for the synthesis of AuNPs has become a major focus of researchers. One of the methods is the production of AuNPs using biological system such as microbes, fungi and plant extracts [6–8]. Plant mediated synthesis of AuNPs are noteworthy due to its simplicity, rapid rate of synthesis, ecofriendliness and it can potentially render more biocompatibility with biomolecules [9]. Green synthesis of AuNPs by plants such as Olive leaf, Citrus sinensis, Pear fruit, Trigonella foenum-graecum, Edible coconut oil, black tea leaves and Cypress leaves, have been reported earlier [10–14]. In the present work, we report the green synthesis of AuNPs using the extracts of Citrus maxima (C. maxima) fruit as reducing and capping agents. This method is simple, efficient, economic and environmentally benign. Moreover, the catalytic activity in reduction of 4-nitrophenol to 4-aminophenol in n
Correspondence to: No. 26, He Xing Road, Harbin, People's Republic of China. E-mail address: [email protected] (D.F. Chi).
http://dx.doi.org/10.1016/j.matlet.2015.12.031 0167-577X/& 2015 Elsevier B.V. All rights reserved.
the presence of NaBH4 and its rate constant was also evaluated. To the best of our knowledge, this is the first report for the synthesis of AuNPs using C. maxima fruit extracts.
2. Experimental Chloroauric acid tetrahydrate (HAuCl4 4H2O) was purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China, http://sinoreagent.cn.alibaba.com/). Sodium borohydride (NaBH4) and 4-nitrophenol were obtained from Huanwei Fine Chemical Co., Ltd., (Tianjin, China). First, C. maxima were cleaned with deionized water, and then finely cut into small pieces. These pieces were squeezed to extracts the juice which was later strained through a fine pore nylon mesh. Obtained extraction was centrifuged at 12,000 rpm for 5 min to remove any undesired impurities. The extraction was considered as a stock solution and other concentrations of the extracts were prepared using this. The AuNPs colloids (C1) was prepared at room temperature (298 K) by adding 2 mL of stock solution to vigorously stirred 10 mL aqueous solution of HAuCl4 4H2O (1%,W/V) and stirring continued for 5 min. The reaction mixture immediately showed a light pinkish red shade which implied the complete reduction of chaoroaurate ions. The colloids C2–C6 were obtained by varying the diluted multiples of the extracts stock solution as 50%, 20%, 10%, 5%, and 1% respectively. Appropriate choice of different volumes of the stock solution and diluted solution is made through repeated
J. Yu et al. / Materials Letters 166 (2016) 110–112
111
Fig. 1. UV–visible spectra of gold colloids (C1–C6) at 298 K (A) and the TEM image of gold colloid C2 (B); the inset in (A) shows the corresponding real pictures of gold colloids C1, C2 and C5; inset image in B shows the size distribution of gold colloid C2.
Fig. 2. X-ray diffraction pattern recorded from drop coated films of the colloid C2 deposited on glass substrates (A) and FT-IR spectra of C. maxima fruit extracts and the C. maxima mediated colloid C2 (B).
Fig. 3. Time dependent UV–vis spectra for the reduction of 4-NP with NaBH4 catalyzed by C. maxima mediated gold colloid C2 at the concentration 1 mmol/L (A); and the corresponding plot of ln(C/C0) vs. time.
experiments. To evaluate the catalytic activity of synthesized AuNPs, the reduction of 4-Nitrophenol (4-NP) to 4-Aminophenol (4-AP) by NaBH4 is selected as a probe reaction. The effect of concentration of AuNPs on the speed of catalytic reduction was investigated by using different quantities of AuNPs colloids. After the addition of gold colloids, reduction is ascertained by recording the UV–visible spectra.
3. Results and discussion As shown in Fig. 1A, the UV–vis spectra of AuNPs formation at constant concentration of HAuCl4 with varying quantity of C. maxima fruit extracts 100%, 50%, 20%, 10%, 5%, and 1% stock solution (C1–C6). The gradual color change from purplish red (C1) to wine red (C2) to pink red (C5) was observed during reaction with varying concentration of C. maxima fruit extracts which are
112
J. Yu et al. / Materials Letters 166 (2016) 110–112
characteristic of the Surface Plasmon Resonance of different size of AuNPs in solution (inset image of Fig. 1A). From the spectra it is clear that when the concentration of C. maxima fruit extracts decreased from 50% to 1% (C2–C6), the SPR band is shifted towards the longer wavelength region from 535 nm to 585 nm which shows an increase in a particle size. It is interesting to note that in Fig. 1A, only for C2–C4 (50–10%) of the maximum plasmon absorption wavelength of AuNPs was obtained for the least value (535–540 nm) without another absorption band in the longitudinal plasmon resonance. Moreover, absorption spectra of gold nanoparticles synthesized using 100%, 5% and 1% C. maxima fruit extracts stock shifted to longer wave length region. Most researchers believed that the as-prepared nanoparticles exhibit a size dependent catalytic property, the smaller nanoparticles showing faster activity. When the size of gold nanoparticles decreases, there is an increase in the number of low-coordinated Au atoms which promote the absorption of the reactants on the catalyst surface and facilitates the reduction [1,15]. The SPR band can give useful information about the size and the shape of the synthesized nanoparticles. The increase in particle size causes the increase in the maximum wavelength (red shift), and the reduction in particle size leads to the decrease in the maximum wavelength (blue shift) [2,16]. In order to obtain the smaller size of particle, we chose 50% concentration of C. maxima fruit extracts to prepare AuNPs (C2) according to this theoretical analysis. Typical TEM images obtained for AuNPs colloids C2 shown in Fig. 1B. It can be seen that the morphology consist of a mixture of rod and spherical like particles. The average particle size measured for the AuNPs colloids C2 are observed to be 25.77 10 nm. Dynamic light scattering (DLS) measurements showed that polydispersity of the particles was lower than 0.1. The XRD patterns of the products prepared by 50% of C. maxima fruit extracts stock solution (gold colloid C2) are seen in Fig. 2A. It shows intensive characteristic peaks of metallic Au. The diffraction peaks at 2θ 38.56°, 44.67°, 64.50° and 77.58° correspond to the (111), (200), (220) and (311) Bragg planes of fcc gold lattice, respectively, which are in agreement with the diffraction standard of gold (JCPDS 80-3697) [17]. In this case, the peak due to (111) reflection is more intense than those owed to (200), (220) and (311) reflections. This clearly shows that AuNPs are predominantly oriented along the (111) plane utilizing C. maxima fruit extracts. Fig. 2B shows the FTIR spectrum of the gold nanoparticles synthesized using C. maxima fruit extracts, which exhibited bands at 617, 1125, 1376, 1658 and 3278 cm 1. The peak at 3278 cm 1 was assigned to O–H stretching vibrations, which can be found in flavonoids, terpene and ascorbic acids extracts [1]. In case of AuNPs synthesized using C. maxima fruit extracts strong bands at 1658 and 1376 cm 1 are observed. The two bands correspond to the amide I and II bands of polypeptides/proteins respectively and agree with those reported in the literature [17]. The absorption band at 1125 cm 1 was assigned as the amide III band of polypeptide present in the fruit [6,10,11]. The polypeptides or proteins had rich amino and thiol groups, which strongly bind the Au(0), forming a polypeptides/proteins–Au complex. The reduction function of the amino acid residues was activated to trigger the nucleation and growth of AuNPs in the scaffolds between amino acid molecules. These structural changes have confirmed the fact that the polypeptides or proteins could possibly form a layer covering the nanoparticles to prevent agglomeration and thereby stabilize the medium. The peak at 1658 cm 1 could be assigned to
the vibrational modes of C ¼C double bones of biomolecules. The band located at 1376 cm 1 was due to the C–N stretching vibrations. Herein, the flavonoids, terpenes and vitamins present in C. maxima fruit are powerful reducing agents which may be responsible for the reduction of choroauric acid. The proteins and polypeptides can act as surfactant to attach on the surface of AuNPs and it stabilizes AuNPs through electrostatic stabilization. When AuNPs were added to the reaction system, the intensity of the peak at 400 nm due to 4-NP gradually decreased with time and a new peak appeared at 302 nm due to the formation of 4-AP (Fig. 3A). In this context, pseudo-first-order kinetics could be used to evaluate the kinetic reaction rate of the current catalytic reaction [11]. The kinetic rate constant kapp can be calculated from the rate equation ln (C/C0)¼ -kappt, where C0 is the initial concentration of 4-NP with a constant value of 0.25 10 3 mol/L and C represents the concentration of 4-NP at the time t. As expected, a good linear correlation of ln(C/C0) versus time was obtained, and AuNPs synthesized using C. maxima fruit extracts exhibit a high activity with an estimated kapp value of 0.08977 min 1 (Fig. 3B).
4. Conclusions We have reported a simple single step eco-friendly method to produce AuNPs surrounded by plant matrix which acts as a reducing or stabilizing agent. Such a method for synthesizing AuNPs will be an added advantage, and other food materials rich in vitamins, terpenes and flavonoids can be potentially converted into a high value nanoproductive. These particles are expected to have extensive applications in semiconductors, spectroscopy, drug delivery, tissue imaging and cancer therapy.
Acknowledgments This work was supported by the National Natural Science Foundation of China (Nos. J1210053 and 51408168), the Science and Technology Support Project of China (No. 2012BAD19B0704) and China Postdoctoral Science Foundation (No. 2014T70304).
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
S.A. Aromal, D. Philip, Spectrochim. Acta Part A 97 (2012) 1–5. M. Noruzi, Bioprocess Biosyst. Eng. 38 (2015) 1–14. R.K. Das, B.B. Borthakur, U. Bora, Mater. Lett. 64 (2010) 1445–1447. T.K. Sau, A.L. Rogach, F. Jäckel, T.A. Klar, J. Feldmann, Adv. Mater. 22 (2010) 1805–1825. M.M. Kumari, D. Philip, Spectrochim. Acta Part A 111 (2013) 154–160. P. Khademi-Azandehi, J. Moghaddam, Particuology 19 (2015) 22–26. Y. Mikami, A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Catal. Sci. Technol. 3 (2013) 58–69. C. Dipankar, S. Murugan, Colloids Surf. B 98 (2012) 112–119. D. Philip, Spectrochim. Acta Part A 77 (2010) 807–810. M.H.K. Mostafa, H.I. Eman, F. El-Magdoub, Arab. J. Chem. 5 (2012) 431–437. M.V. Sujitha, S. Kannan, Spectrochim. Acta Part A 102 (2013) 15–23. G.S. Ghodake, N.G. Deshpande, Y.P. Lee, E.S. Jin, Colloids Surf. B 75 (2010) 584–589. K. Gopinath, K.S. Venkatesh, R. Ilangovan, K. Sankaranarayanan, A. Arumugam, Ind. Crops Prod. 50 (2013) 737–742. M. Noruzi, D. Zare, D. Davoodi, Spectrochim. Acta Part A 94 (2012) 84–88. R.K. Sharma, S. Gulati, S. Mehta, J. Chem. Educ. 89 (2012) 1316–1318. M.M. Byranvand, A.N. Kharat, Mater. Lett. 134 (2014) 64–66. P.P. Gan, S.H. Ng, Y. Huang, Li SFY, Bioresour. Technol. 113 (2012) 132–135.