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Synthesis of iron-based nanoparticles using oolong tea extract for the degradation of malachite green
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 801–804
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Short Communication
Synthesis of iron-based nanoparticles using oolong tea extract for the degradation of malachite green Lanlan Huang a, Xiulan Weng a, Zuliang Chen a,b,c,⇑, Mallavarapu Megharaj b,c, Ravendra Naidu b,c a
School of Environmental Science and Engineering, Fujian Normal University, Fuzhou 350007, Fujian, China Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia c Cooperative Research Centre for Contamination Assessment and Remediation of Environments, Mawson Lakes, SA 5095, Australia b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Iron nanoparticles (Fe NPs, 40–
Degradation of malachite green using iron nanoparticles synthesized by oolong tea extract.
50 nm) were synthesized using oolong tea extracts. 75.5% MG was removed by Fe NPs. The formation of Fe NPs were confirmed by various techniques.
a r t i c l e
i n f o
Article history: Received 30 July 2013 Received in revised form 3 September 2013 Accepted 7 September 2013 Available online 24 September 2013 Keywords: Green synthesis OT-FeNP Malachite green Characterization Degradation
a b s t r a c t Iron-based nanoparticles (OT-FeNP) were synthesized using oolong tea extracts. Their morphology, structure and size were confirmed by scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), UV–visible (UV–vis) and Fourier Transform Infrared spectroscopy (FTIR). Formation of FeNP results in mostly spherical particles with diameters ranging from 40 to 50 nm. Degradation of malachite green (MG) using OT-FeNP demonstrated that kinetics fitted well to the pseudo first-order reaction by removing 75.5% of MG (50 mg/L). This indicated that OT-FeNP has the potential to serve as a green nanomaterial for environmental remediation. Ó 2013 Elsevier B.V. All rights reserved.
Introduction In recent years, iron-based nanoparticles (FeNP) due to the high intrinsic reactivity of their surface sites have been used in ⇑ Corresponding author at: Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia. Tel.: +61 8 82025057; fax: +61 8 83025057. E-mail address: [email protected] (Z. Chen). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.09.054
groundwater treatment and site remediation [1]. FeNP can be readily synthesized with chemical and physical methods, but the drawbacks of these methods are the consumption of high energy and use of toxic chemical substances such as NaBH4, organic solvents, stabilizing and dispersing agents [2–4]. The green synthesis of FeNP has received more attention because it is cost effective and environmentally friendly [4–7]. To date, FeNP synthesized by green tea extract has been used as a Fenton catalyst for oxidizing cationic and anionic dyes [7]. However, few studies have been published on
802
L. Huang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 801–804
the green synthesis of FeNP using tea extract for the reductive degradation of dye such as malachite green (MG), which is difficult to degrade from aqueous solutions. Previous studies have reported that zero-valent iron (nZVI) can be used to degrade azo dye [8], where the removal rate of azo dye decreased with the aggregation and oxidation of nanoparticles. It can be concluded that size and reactivity played an important role in degrading dyes. In this study, the synthesis of FeNP using oolong tea extracts (OTE) was investigated when a large amount of oolong tea became available in Fujian, China. In this investigation of whether synthesized FeNP can be used to degrade organic contaminants or otherwise, the following conclusions were made: (1) we confirmed OT-FeNP was nano-sized and OT-FeNP was synthesized as expected; and (2) OT-FeNP was efficient in the degradation of MG.
covered with a thin, electric conductive gold film. Images of samples were recorded at different magnifications at an operating voltage of 10 kV. OT-FeNP from the chosen region was obtained by INCA EDS (Oxford Instruments, UK) in conjunction with SEM [1,8]. XRD pattern of OT-FeNP was obtained using a Philips-X’Pert Pro MPD (Netherlands) with a high-power Cu Ka radioactive source (k = 0.154 nm) at 40 kV/40 mA. FTIR (FTIR Nicolet 5700, Thermo Corp., USA) assisted in detecting the tea extract and OT-FeNP. Samples for determination were prepared by mixing 1% (w/w) specimens with 100 mg of KBr powder and pressing the mixture into a sheer slice. Following this the average over 9 scan was collected for each measurement with a resolution of 2 cm 1 [1,8].
Experimental
The synthesis of FeNP used to degrade malachite green
Materials and methods
Fig. 1a shows the UV spectra of FeSO4, oolong tea extract and OT-FeNP. Fig. 1a illustrates that the peaks at 272 nm in tea extract correspond to the tea polyphenols and caffeine, as recently confirmed by a HPLC-UV analysis of the tea extracts [9]. However, the intensity of peaks 272 nm declined after reaction with Fe2+ and the formation of OT-FeNP was observed in broad absorption at a higher wavelength [10,11]. This further explained that the reaction mixture’s color changed rapidly from yellow to dark after the reaction between FeSO4 and tea extracts. To evaluate the reactivity of the FeNP synthesized using oolong tea extract, the degradation of MG in aqueous solution with an initial concentration of 50 mg/L is shown in Fig. 1b, where 12.3% of MG removed by the capping agent in tea extract was observed, while the removal efficiency of MG using OT-FeNP was 61.9% after 10 min. In addition, removal efficiency of MG using OT-FeNP improved as contact time increased, and it reached equilibrium (75.5%) within 60 min with a corresponding degradation rate of 0.045 min 1. This can be attributed the fact that caffeine and polyphenols in oolong tea extract not only served as capping agents that reduced the aggregation of FeNP, but also served as reducing agents for the synthesis of FeNP due to the oolong tea extract containing a number of polyphenols and caffeine [6,7,11]. Consequently, the stability and reactivity of OT-FeNP were enhanced, as confirmed by the subsequent SEM images, EDS analysis and FTIR. The degradation of MG using OT-FeNP was fitted well to pseudo first-order kinetics with high correlation coefficients (R2) > 0.980 [8]. Activation energy of degradation of MG using OT-FeNP was 23.86 kJ/mol, suggesting that chemically diffusioncontrolled reaction did occur [8].
Ferrous sulfate (FeSO47H2O, purity over 99%) was purchased from Xilong Chemical Co., Ltd. (China) and used directly without pretreatment. Oolong tea was purchased from the Fuzhou Blue Better Tea Factory (China). Preparation of OT-FeNP and batch experiment The synthesis of FeNP using tea extracts has been described previously [5,6]. An initial concentration of 60.0 g/L oolong tea extract was prepared by heating it at 80 °C for 1 h. Then the extract was vacuum-filtered and a solution of 0.10 mol/L of FeSO4 added to the tea extracts at a ratio of 1:2. The stock solution of MG with 100.0 mg/L was prepared, and the required MG concentration in batch experiments was 50 mg/L. Batch experiments were carried out using OT-FeNP (0.01 g) added to a solution containing 50.0 mg/L MG (8 mL), which was then placed on a rotary shaker at 298 K and 250 r/min. The degraded solution was then filtered through a 0.45 lm filter paper to determine the standard curve information of MG. This absorbance of solution was measured using a UV-Spectrophotometer (752N, Shanghai, China) at 617 nm. Characterization Morphology and distribution of OT-FeNP were characterized using SEM (JSM 7500F, Japan). The powdered samples were first affixed onto adhesive tapes supported on metallic disks and then
Results and discussion
Fig. 1. (a) UV–vis spectra of OTEeSO4 and OT-FeNP. Condition: 0.1 mL OTE.1 mL FeSO4 and OT-FeNP, diluted 50 times and (b) degradation of malachite green using OT-FeNP and OTE. Dose: 0.01 g/L OT-FeNP; initial concentration: 8 ml 50 mg/L malachite green.
L. Huang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 801–804
803
Fig. 2. (a). SEM scanning images of OT-FeNP, (b) typical EDS spectrum of OT-FeNP, and (c) XRD patterns of OT-FeNP.
Fig. 3. (a) UV–vis scanning images of MG and the degradation of MG; (b)-a The FTIR image of MG and (b)-b the FTIR image of OT-FeNP.
Characterization The SEM image of FeNP synthesized using oolong tea extracts is shown in Fig. 2a. It can be clearly seen that the OT-FeNP with a spherical shape has a diameter of 40–50 nm. Synthesized OT-FeNP was dispersed and capped by tea extract. This may well be the component existing in oolong tea extract, thereby indicating that the polyphenols/caffeine concentrations in tea extracts play a key role in the formation of the final structures and size of the FeNP [6,11]. The elemental compositions of oolong tea extract and OT-FeNP were determined by EDS. The main compositions in the oolong tea extract were O (20.34%), C (49.51%), S (5.05%) and K (15.10%), respectively, where C and O are attributed to the polyphenols and other C-containing molecules in the tea extracts [5,7]. Nonetheless this clearly demonstrates that a Fe peak was observed in OT-FeNP, where the percentage of Fe is 11.63% as shown in Fig. 2b. This confirmed the elemental Fe on the surface of OT-FeNP. However, FeNP was probably dispersed and capped in the oolong tea extract, indicating that some part of FeNP was not detected by EDS [6,7]. In addition, SEM, XRD and FTIR techniques identified the existence of capping agents from tea extract. The XRD pattern of a synthesized OT-FeNP using oolong tea extract is depicted in Fig. 2c. The characteristic peaks at 2h = 44.9°, 35.68°, 35.45° and 20–35° corresponded to zero-valent iron (a-Fe), maghemite (c-Fe2O3), magnetite (Fe3O4) and iron hydroxides [11]. However, since the FeNP synthesized by tea extract was poorly crystalline in nature, only iron oxide and iron oxohydroxide were observed [7,11]. These matched well with the XRD patterns of FeNPs synthesized using green tea extract [7,11]. The
intense peak at 2h = 20.56° in Fig. 2c was identified as the ingredient in polyphenols/caffeine [7]. Fig. 3a illustrates the degradation of MG using an OT-FeNP measured by UV–vis spectra. The peaks of MG stood at 428 nm and 617 nm and these peaks clearly decreased after 30 min reaction. It further indicated that MG could be effectively removed using FeNP by cleaving the AC@CA and @C@NA [11,12]. In addition, the distinct peak of 272 nm correlated with the composition of the polyphenols/caffeine in tea extracts as reducing and capping agents in the green synthesis of FeNP [7,11]. FTIR analysis was employed to evaluate the possible biomolecules responsible for the reduction of the metal precursors and functional group changes in the spectral range 400–4000 [7]. The FTIR spectra of tea extracts and OT-FeNP are presented in Fig. 3b. As seen from Fig. 3(b)-a, the FTIR bands of oolong tea extracts displaying bands at 3388 cm 1, 1636 cm 1, and 1039 cm 1 refer to OAH, C@C, CAOAC stretching vibrations, respectively [13], with the polyphenol and reducing sugar in the oolong tea extract being responsible for the reduction of the Fe-NPs. In Fig. 3(b)-b the FTIR bands for OT-FeNP demonstrate that the Fe0 surface was capped by the oolong tea extracts because they matched well with Fig. 3(b)-a, where AOH and CAOAC groups are capping ligands for the FeNPs. Furthermore, adsorption bands around 460 cm 1 and 546 cm 1 corresponded to FeAO stretches of Fe2O3 and Fe3O4 [14], which was consistent with the results obtained from the XRD. Conclusion This study showed that the green synthesis of OT-FeNP using oolong tea extract was confirmed by SEM, EDS, XRD, UV–vis and
804
L. Huang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 801–804
FTIR, which can be used for the degradation of MG. The results show that: firstly, OT-FeNP was nano-sized and OT-FeNP was synthesized as expected, and polyphenols/caffeine in oolong tea extract acted as both reducing and capping agents, leading to reduced aggregation and to increased reactivity of OT-FeNP. Secondly, OT-FeNP proved to be efficient in the degradation of MG, resulting in 75.5% of MG (50 mg/L) being removed. Future research should aim to understand the formation of OT-FeNP and the degradation mechanism of MG using OT-FeNP. Acknowledgements This research was supported by a Fujian ‘‘Minjiang Fellowship’’ Grant from Fujian Normal University. References [1] L.N. Shi, X. Zhang, Z.L. Chen, Water Res. 45 (2011) 886–892.
[2] R.A. Crane, T.B. Scott, J. Hazard. Mater. 211–212 (2012) 112–125. [3] S. Iravani, Green Chem. 3 (2011) 2638–2650. [4] Y.P. Sun, X.Q. Li, W.Z. Zhang, H.P. Wang, Colloid Surf. A: Physicochem. Eng. Aspects 308 (2007) 60–66. [5] E.C. Njagi, H. Huang, L. Stafford, H. Genuino, H.M. Galindo, J.B. Collins, G.E. Hoag, S.L. Suib, Langmuir 27 (2011) 264–271. [6] V. Smuleac, R. Varma, S. Sikdar, D. Bhattacharyyaa, J. Membr. Sci. 379 (2011) 131–137. [7] T. Shahwan, S. AbuSirriah, M. Nairat, E. Boyac, A.E. Eroglu, T.B. Scott, K.R. Hallam, Chem. Eng. J. 172 (2011) 258–266. [8] Z.X. Chen, X.Y. Jin, Z.L. Chen ZL, M. Megharaj, R. Naidu, J. Colloid Interface Sci. 363 (2011) 601–607. [9] M.S. El-Shahaw, A. Hamza, S.O. Bahaffi, A.A. Al-Sibaai, T.N. Abduljabbar, Food Chem. 134 (2012) 2268–2275. [10] M.N. Nadagouda, R.S. Varma, Green Chem. 10 (2008) 859–862. [11] C.E. Hoag, J.B. Collins, J.L. Holcomb, J.R. Hoag, M.N. Nadagouda, R.S. Varm, J. Mater. Chem. 19 (2009) 8671–8677. [12] Y. Ju, J. Qiao, X. Peng, Z. Xu, J. Fang, S. Yang, C. Sun, Chem. Eng. J. (2012). http:// dx.doi.org/10.1016/j.cej.2012.06.055. [13] W.R. Cai, L.L. Xie, Y. Chen, H. Zhang, Purif. Carbohydr. Polym. 92 (2013) 1086– 1090. [14] M. Iram, C. Guo, Y.P. Guan, A. Ishfaq, H.Z. Liu, J. Hazard. Mater. 181 (2010) 1039–1050.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Short Communication
Synthesis of iron-based nanoparticles using oolong tea extract for the degradation of malachite green Lanlan Huang a, Xiulan Weng a, Zuliang Chen a,b,c,⇑, Mallavarapu Megharaj b,c, Ravendra Naidu b,c a
School of Environmental Science and Engineering, Fujian Normal University, Fuzhou 350007, Fujian, China Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia c Cooperative Research Centre for Contamination Assessment and Remediation of Environments, Mawson Lakes, SA 5095, Australia b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Iron nanoparticles (Fe NPs, 40–
Degradation of malachite green using iron nanoparticles synthesized by oolong tea extract.
50 nm) were synthesized using oolong tea extracts. 75.5% MG was removed by Fe NPs. The formation of Fe NPs were confirmed by various techniques.
a r t i c l e
i n f o
Article history: Received 30 July 2013 Received in revised form 3 September 2013 Accepted 7 September 2013 Available online 24 September 2013 Keywords: Green synthesis OT-FeNP Malachite green Characterization Degradation
a b s t r a c t Iron-based nanoparticles (OT-FeNP) were synthesized using oolong tea extracts. Their morphology, structure and size were confirmed by scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), UV–visible (UV–vis) and Fourier Transform Infrared spectroscopy (FTIR). Formation of FeNP results in mostly spherical particles with diameters ranging from 40 to 50 nm. Degradation of malachite green (MG) using OT-FeNP demonstrated that kinetics fitted well to the pseudo first-order reaction by removing 75.5% of MG (50 mg/L). This indicated that OT-FeNP has the potential to serve as a green nanomaterial for environmental remediation. Ó 2013 Elsevier B.V. All rights reserved.
Introduction In recent years, iron-based nanoparticles (FeNP) due to the high intrinsic reactivity of their surface sites have been used in ⇑ Corresponding author at: Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia. Tel.: +61 8 82025057; fax: +61 8 83025057. E-mail address: [email protected] (Z. Chen). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.09.054
groundwater treatment and site remediation [1]. FeNP can be readily synthesized with chemical and physical methods, but the drawbacks of these methods are the consumption of high energy and use of toxic chemical substances such as NaBH4, organic solvents, stabilizing and dispersing agents [2–4]. The green synthesis of FeNP has received more attention because it is cost effective and environmentally friendly [4–7]. To date, FeNP synthesized by green tea extract has been used as a Fenton catalyst for oxidizing cationic and anionic dyes [7]. However, few studies have been published on
802
L. Huang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 801–804
the green synthesis of FeNP using tea extract for the reductive degradation of dye such as malachite green (MG), which is difficult to degrade from aqueous solutions. Previous studies have reported that zero-valent iron (nZVI) can be used to degrade azo dye [8], where the removal rate of azo dye decreased with the aggregation and oxidation of nanoparticles. It can be concluded that size and reactivity played an important role in degrading dyes. In this study, the synthesis of FeNP using oolong tea extracts (OTE) was investigated when a large amount of oolong tea became available in Fujian, China. In this investigation of whether synthesized FeNP can be used to degrade organic contaminants or otherwise, the following conclusions were made: (1) we confirmed OT-FeNP was nano-sized and OT-FeNP was synthesized as expected; and (2) OT-FeNP was efficient in the degradation of MG.
covered with a thin, electric conductive gold film. Images of samples were recorded at different magnifications at an operating voltage of 10 kV. OT-FeNP from the chosen region was obtained by INCA EDS (Oxford Instruments, UK) in conjunction with SEM [1,8]. XRD pattern of OT-FeNP was obtained using a Philips-X’Pert Pro MPD (Netherlands) with a high-power Cu Ka radioactive source (k = 0.154 nm) at 40 kV/40 mA. FTIR (FTIR Nicolet 5700, Thermo Corp., USA) assisted in detecting the tea extract and OT-FeNP. Samples for determination were prepared by mixing 1% (w/w) specimens with 100 mg of KBr powder and pressing the mixture into a sheer slice. Following this the average over 9 scan was collected for each measurement with a resolution of 2 cm 1 [1,8].
Experimental
The synthesis of FeNP used to degrade malachite green
Materials and methods
Fig. 1a shows the UV spectra of FeSO4, oolong tea extract and OT-FeNP. Fig. 1a illustrates that the peaks at 272 nm in tea extract correspond to the tea polyphenols and caffeine, as recently confirmed by a HPLC-UV analysis of the tea extracts [9]. However, the intensity of peaks 272 nm declined after reaction with Fe2+ and the formation of OT-FeNP was observed in broad absorption at a higher wavelength [10,11]. This further explained that the reaction mixture’s color changed rapidly from yellow to dark after the reaction between FeSO4 and tea extracts. To evaluate the reactivity of the FeNP synthesized using oolong tea extract, the degradation of MG in aqueous solution with an initial concentration of 50 mg/L is shown in Fig. 1b, where 12.3% of MG removed by the capping agent in tea extract was observed, while the removal efficiency of MG using OT-FeNP was 61.9% after 10 min. In addition, removal efficiency of MG using OT-FeNP improved as contact time increased, and it reached equilibrium (75.5%) within 60 min with a corresponding degradation rate of 0.045 min 1. This can be attributed the fact that caffeine and polyphenols in oolong tea extract not only served as capping agents that reduced the aggregation of FeNP, but also served as reducing agents for the synthesis of FeNP due to the oolong tea extract containing a number of polyphenols and caffeine [6,7,11]. Consequently, the stability and reactivity of OT-FeNP were enhanced, as confirmed by the subsequent SEM images, EDS analysis and FTIR. The degradation of MG using OT-FeNP was fitted well to pseudo first-order kinetics with high correlation coefficients (R2) > 0.980 [8]. Activation energy of degradation of MG using OT-FeNP was 23.86 kJ/mol, suggesting that chemically diffusioncontrolled reaction did occur [8].
Ferrous sulfate (FeSO47H2O, purity over 99%) was purchased from Xilong Chemical Co., Ltd. (China) and used directly without pretreatment. Oolong tea was purchased from the Fuzhou Blue Better Tea Factory (China). Preparation of OT-FeNP and batch experiment The synthesis of FeNP using tea extracts has been described previously [5,6]. An initial concentration of 60.0 g/L oolong tea extract was prepared by heating it at 80 °C for 1 h. Then the extract was vacuum-filtered and a solution of 0.10 mol/L of FeSO4 added to the tea extracts at a ratio of 1:2. The stock solution of MG with 100.0 mg/L was prepared, and the required MG concentration in batch experiments was 50 mg/L. Batch experiments were carried out using OT-FeNP (0.01 g) added to a solution containing 50.0 mg/L MG (8 mL), which was then placed on a rotary shaker at 298 K and 250 r/min. The degraded solution was then filtered through a 0.45 lm filter paper to determine the standard curve information of MG. This absorbance of solution was measured using a UV-Spectrophotometer (752N, Shanghai, China) at 617 nm. Characterization Morphology and distribution of OT-FeNP were characterized using SEM (JSM 7500F, Japan). The powdered samples were first affixed onto adhesive tapes supported on metallic disks and then
Results and discussion
Fig. 1. (a) UV–vis spectra of OTEeSO4 and OT-FeNP. Condition: 0.1 mL OTE.1 mL FeSO4 and OT-FeNP, diluted 50 times and (b) degradation of malachite green using OT-FeNP and OTE. Dose: 0.01 g/L OT-FeNP; initial concentration: 8 ml 50 mg/L malachite green.
L. Huang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 801–804
803
Fig. 2. (a). SEM scanning images of OT-FeNP, (b) typical EDS spectrum of OT-FeNP, and (c) XRD patterns of OT-FeNP.
Fig. 3. (a) UV–vis scanning images of MG and the degradation of MG; (b)-a The FTIR image of MG and (b)-b the FTIR image of OT-FeNP.
Characterization The SEM image of FeNP synthesized using oolong tea extracts is shown in Fig. 2a. It can be clearly seen that the OT-FeNP with a spherical shape has a diameter of 40–50 nm. Synthesized OT-FeNP was dispersed and capped by tea extract. This may well be the component existing in oolong tea extract, thereby indicating that the polyphenols/caffeine concentrations in tea extracts play a key role in the formation of the final structures and size of the FeNP [6,11]. The elemental compositions of oolong tea extract and OT-FeNP were determined by EDS. The main compositions in the oolong tea extract were O (20.34%), C (49.51%), S (5.05%) and K (15.10%), respectively, where C and O are attributed to the polyphenols and other C-containing molecules in the tea extracts [5,7]. Nonetheless this clearly demonstrates that a Fe peak was observed in OT-FeNP, where the percentage of Fe is 11.63% as shown in Fig. 2b. This confirmed the elemental Fe on the surface of OT-FeNP. However, FeNP was probably dispersed and capped in the oolong tea extract, indicating that some part of FeNP was not detected by EDS [6,7]. In addition, SEM, XRD and FTIR techniques identified the existence of capping agents from tea extract. The XRD pattern of a synthesized OT-FeNP using oolong tea extract is depicted in Fig. 2c. The characteristic peaks at 2h = 44.9°, 35.68°, 35.45° and 20–35° corresponded to zero-valent iron (a-Fe), maghemite (c-Fe2O3), magnetite (Fe3O4) and iron hydroxides [11]. However, since the FeNP synthesized by tea extract was poorly crystalline in nature, only iron oxide and iron oxohydroxide were observed [7,11]. These matched well with the XRD patterns of FeNPs synthesized using green tea extract [7,11]. The
intense peak at 2h = 20.56° in Fig. 2c was identified as the ingredient in polyphenols/caffeine [7]. Fig. 3a illustrates the degradation of MG using an OT-FeNP measured by UV–vis spectra. The peaks of MG stood at 428 nm and 617 nm and these peaks clearly decreased after 30 min reaction. It further indicated that MG could be effectively removed using FeNP by cleaving the AC@CA and @C@NA [11,12]. In addition, the distinct peak of 272 nm correlated with the composition of the polyphenols/caffeine in tea extracts as reducing and capping agents in the green synthesis of FeNP [7,11]. FTIR analysis was employed to evaluate the possible biomolecules responsible for the reduction of the metal precursors and functional group changes in the spectral range 400–4000 [7]. The FTIR spectra of tea extracts and OT-FeNP are presented in Fig. 3b. As seen from Fig. 3(b)-a, the FTIR bands of oolong tea extracts displaying bands at 3388 cm 1, 1636 cm 1, and 1039 cm 1 refer to OAH, C@C, CAOAC stretching vibrations, respectively [13], with the polyphenol and reducing sugar in the oolong tea extract being responsible for the reduction of the Fe-NPs. In Fig. 3(b)-b the FTIR bands for OT-FeNP demonstrate that the Fe0 surface was capped by the oolong tea extracts because they matched well with Fig. 3(b)-a, where AOH and CAOAC groups are capping ligands for the FeNPs. Furthermore, adsorption bands around 460 cm 1 and 546 cm 1 corresponded to FeAO stretches of Fe2O3 and Fe3O4 [14], which was consistent with the results obtained from the XRD. Conclusion This study showed that the green synthesis of OT-FeNP using oolong tea extract was confirmed by SEM, EDS, XRD, UV–vis and
804
L. Huang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 801–804
FTIR, which can be used for the degradation of MG. The results show that: firstly, OT-FeNP was nano-sized and OT-FeNP was synthesized as expected, and polyphenols/caffeine in oolong tea extract acted as both reducing and capping agents, leading to reduced aggregation and to increased reactivity of OT-FeNP. Secondly, OT-FeNP proved to be efficient in the degradation of MG, resulting in 75.5% of MG (50 mg/L) being removed. Future research should aim to understand the formation of OT-FeNP and the degradation mechanism of MG using OT-FeNP. Acknowledgements This research was supported by a Fujian ‘‘Minjiang Fellowship’’ Grant from Fujian Normal University. References [1] L.N. Shi, X. Zhang, Z.L. Chen, Water Res. 45 (2011) 886–892.
[2] R.A. Crane, T.B. Scott, J. Hazard. Mater. 211–212 (2012) 112–125. [3] S. Iravani, Green Chem. 3 (2011) 2638–2650. [4] Y.P. Sun, X.Q. Li, W.Z. Zhang, H.P. Wang, Colloid Surf. A: Physicochem. Eng. Aspects 308 (2007) 60–66. [5] E.C. Njagi, H. Huang, L. Stafford, H. Genuino, H.M. Galindo, J.B. Collins, G.E. Hoag, S.L. Suib, Langmuir 27 (2011) 264–271. [6] V. Smuleac, R. Varma, S. Sikdar, D. Bhattacharyyaa, J. Membr. Sci. 379 (2011) 131–137. [7] T. Shahwan, S. AbuSirriah, M. Nairat, E. Boyac, A.E. Eroglu, T.B. Scott, K.R. Hallam, Chem. Eng. J. 172 (2011) 258–266. [8] Z.X. Chen, X.Y. Jin, Z.L. Chen ZL, M. Megharaj, R. Naidu, J. Colloid Interface Sci. 363 (2011) 601–607. [9] M.S. El-Shahaw, A. Hamza, S.O. Bahaffi, A.A. Al-Sibaai, T.N. Abduljabbar, Food Chem. 134 (2012) 2268–2275. [10] M.N. Nadagouda, R.S. Varma, Green Chem. 10 (2008) 859–862. [11] C.E. Hoag, J.B. Collins, J.L. Holcomb, J.R. Hoag, M.N. Nadagouda, R.S. Varm, J. Mater. Chem. 19 (2009) 8671–8677. [12] Y. Ju, J. Qiao, X. Peng, Z. Xu, J. Fang, S. Yang, C. Sun, Chem. Eng. J. (2012). http:// dx.doi.org/10.1016/j.cej.2012.06.055. [13] W.R. Cai, L.L. Xie, Y. Chen, H. Zhang, Purif. Carbohydr. Polym. 92 (2013) 1086– 1090. [14] M. Iram, C. Guo, Y.P. Guan, A. Ishfaq, H.Z. Liu, J. Hazard. Mater. 181 (2010) 1039–1050.