Accepted Manuscript Green synthesis of iron nanoparticles by various tea extracts: Comparative study of the reactivity Lanlan Huang, Xiulan Weng, Zuliang Chen, Mallavarapu Megharaj, Ravendra Naidu PII: DOI: Reference:
S1386-1425(14)00610-6 http://dx.doi.org/10.1016/j.saa.2014.04.037 SAA 12001
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received Date: Revised Date: Accepted Date:
26 February 2014 1 April 2014 7 April 2014
Please cite this article as: L. Huang, X. Weng, Z. Chen, M. Megharaj, R. Naidu, Green synthesis of iron nanoparticles by various tea extracts: Comparative study of the reactivity, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.04.037
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
1
Green synthesis of iron nanoparticles by various tea extracts:
2
Comparative study of the reactivity
3 4
Lanlan Huang1, Xiulan Weng1, Zuliang Chen1,2,3*, Mallavarapu Megharaj2,3,
5
Ravendra Naidu2,3
6 7
1. School of Environmental Science and Engineering, Fujian Normal University,
8
Fuzhou 350007, Fujian Province, China
9
2.Centre for Environmental Risk Assessment and Remediation, University of South
10
Australia, Mawson Lakes, SA 5095, Australia
11
3. Cooperative Research Centre for Contamination Assessment and Remediation of
12
Environments, Mawson Lakes, SA 5095, Australia
13 14 15 16 17 18 19 20 21 22 23 24 25
*Corresponding author. Fax: 61-08-83025057; E-mail: Zuliang.chen@unisae,du,au
2
26 27
Abstract
28
Iron nanoparticles (Fe NPs) are often synthesized using sodium borohydride with
29
aggregation, which is a high cost process and environmentally toxic. To address these
30
issues, Fe NPs were synthesized using green methods based on tea extracts, including
31
green, oolong and black teas. The best method for degrading malachite green (MG)
32
was Fe NPs synthesized by green tea extracts because it contains a high concentration
33
of caffeine/polyphenols which act as both reducing and capping agents in the
34
synthesis of Fe NPs. These characteristics were confirmed by a scanning electron
35
microscope (SEM), UV-visible (UV-vis) and specific surface area (BET). To
36
understand the formation of Fe NPs using various tea extracts, the synthesized Fe NPs
37
were characterized by SEM, X-ray energy-dispersive spectrometer (EDS), and X-ray
38
diffraction (XRD). What emerged were different sizes and concentrations of Fe NPs
39
being synthesized by tea extracts, leading to various degradations of MG. Furthermore,
40
kinetics for the degradation of MG using these Fe NPs fitted well to the pseudo
41
first-order reaction kinetics model with more than 20 kJ/mol activation energy,
42
suggesting a chemically diffusion-controlled reaction. The degradation mechanism
43
using these Fe NPs included adsorption of MG to Fe NPs, oxidation of iron, and
44
cleaving the bond that was connected to the benzene ring.
45 46 47 48 49 50
Keywords: Green synthesis; Fe NPs; Malachite green; Characterization; Degradation.
3
51
1. Introduction
52
Malachite green (MG) is a cationic triphenylmethane dye widely used in the dyeing of
53
cotton, silk, paper, leather and in the manufacture of paints and inks and aquaculture
54
as a biocide [1, 2]. MG is toxic and therefore has to be removed from wastewater prior
55
to its discharge into aquatic environments. Various conventional methods such as
56
adsorption [1], photo-catalytic degradation [3, 4] and biological degradation [5, 6] are
57
often employed to remove MG from wastewater [3, 4]. While to some extent these
58
approaches have succeeded, the high cost and low efficiency of these processes limit
59
their applicability [7]. Therefore, the development of innovative remediation
60
techniques is required.
61 62
In recent years, zero-valent iron (nZVI) has received great attention from researchers
63
examining groundwater treatment and site remediation due to the higher intrinsic
64
reactivity of its surface sites [7]. Various physical and chemical methods have been
65
developed for the synthesis of nZVI. Physical methods are thermal decomposition [8]
66
and ultraviolet radiation and aerosol [9], but they are limited by the energy
67
consumption required to maintain high pressure and temperature. Sodium borohydride
68
(NaBH4) as a reducing agent is often used in chemical synthesis of nZVI [10, 11]. The
69
drawbacks include chemical substances such as NaBH4, organic solvents, stabilizing
70
and dispersing agents being toxic and very expensive. Furthermore while the
71
electrochemical method has been used to compose iron nanoparticles, its disadvantage
72
lies in the fact that aggregation of nanoparticles often occurs in the cathode’s motor
73
[12].
74 75
The green synthesis of nZVI has been recently proposed as a cost effective,
4
76
environmental friendly alternative to chemical and physical methods since a variety of
77
materials from biorenewable natural sources can be employed [13-15]. The
78
components in the synthesis of nZVI such as polyphenols from coffee and tea, protein,
79
vitamins and wine polyphenols are available [13-15]. Consequently, these components
80
have emerged as replacements for the established chemical synthesis of nZVI.
81
Furthermore, these components are extracted from natural sources that are non-toxic,
82
biodegradable and the green material acts as both a dispersive and capping agent,
83
helping to minimize the oxidation and agglomeration of nZVI [14]. The synthesis of
84
nZVI using tea polyphenols has been recently examined in the context of in vitro
85
biocompatibility [11], and used for degrading bromothymol blue by Fenton oxidation
86
[16]. More recently, the synthesis of the membrane Fe/Pd using a green tea extract has
87
been used to degrade trichloroethylene (TCE) [14]. The green synthesis of iron
88
nanoparticles (Fe NPs) using the extract of green tea leaves a Fenton-like catalyst.
89
This has been also reported in the degradation of aqueous cationic and anionic dyes
90
[15]. The size and reactivity of the synthesized Fe NPs depend on significant factors
91
such the reducing and capping agents [17], and different tea extracts indicate
92
differences in the reducing and capping agents. From this it can be concluded that the
93
size and reactivity, as well as the concentration of the synthesized Fe NPs, refer to
94
different tea extracts. However, to date, few studies have been published on the
95
synthesis of iron nanoparticles using different tea extracts.
96 97
In our previous studies, oolong tea extract has been used to synthesize iron
98
nanoparticles [18]. To determine whether other tea extracts could be acted as reducing
99
agent to synthesize Fe NPs, green tea extract, oolong tea extract and black tea extract
100
were acted as the reducing agent to synthesize Fe NPs and used for Fenton-like
5
101
oxidation of monochlorobenzene (MCB), where 69%, 59% and 39% of MCB were
102
removed [19]. As a reductive degradation, the different degradations of MG are
103
obtained using Fe NPs since the Fe NPs are synthesized by various extracts. Therefore,
104
in this study, the synthesis of Fe NPs employs extracts from green tea, oolong tea and
105
black tea as reducing and capping agents. These can determine whether the
106
synthesized Fe NPs can be used to degrade MG, as well as to examine why differences
107
in using these Fe NPs emerge when the degradation of MG is being considered. To
108
achieve these aims, the following issues are investigated: (1) the synthesis of Fe NPs
109
utilizing various tea extracts and characterization of these Fe NPs by SEM, EDS,
110
XRD, and BET-N2; (2) evaluating the degradation of MG by Fe NPs synthesized from
111
various tea extracts, including their degradation kinetics; (3) the mechanism of
112
degradation of MG being proposed; and (4) demonstrating the application of Fe NPs
113
to remove MG from wastewater.
114 115
2. Experimental procedure
116
2.1 Preparation of Fe NPs using tea extracts
117
The synthesis of Fe NPs using green tea extracts has been described previously [15,
118
16]. The initial concentrations of 60.0 g/L green tea, oolong tea and black tea extracts
119
were prepared by heating them at 800C for 1 h. These extracts were then
120
vacuum-filtered and 0.10 mol/L FeSO4 solution was added to the tea extracts at a ratio
121
of 1:2 respectively. The Fe NPs were synthesized from green tea, oolong and black tea
122
extracts in the form of GT-Fe, OT-Fe and BT-Fe, respectively. The stock solution of
123
MG with a 100.0 mg/L was first prepared, and the required MG concentration in our
124
experiments was diluted using deionized water.
125
6
126
2.2 Characterization
127
The synthesized Fe NPs using tea extracts were characterized using Uv-vis, SEM,
128
EDS, BET-N2 and XRD techniques. Morphology and distribution of Fe NPs were
129
characterized using a scanning electron microscope (SEM) (JSM 7500F, Japan).
130
Images of samples were recorded at different magnifications using an operating
131
voltage of 10 kV. Localized elemental information of Fe NPs was determined by
132
INCA EDS (Oxford Instruments, UK) in conjunction with SEM.
133
X-ray diffraction (XRD) patterns of Fe NPs before and after reaction with MG were
134
obtained using a Philips-X’Pert Pro MPD (Netherlands) with a high-power Cu-Kα
135
radioactive source (λ = 0.154 nm) at 40 kV/40 mA. All samples were scanned from
136
10° to 80° 2θ at a scanning rate of 3° 2θ per minute.
137 138
The specific surface areas (SSA) of Fe NPs were measured using the BET-N2
139
adsorption method (Brunauer-Emmett-Teller isotherm), specifically Micromeritics’
140
ASAP 2020 Accelerated Surface Area and Porosimetry Analyzer (Micromeritics
141
Instrument Corp., Georgia, USA).
142 143
2.3 Degradation of malachite green
144
To compare the removal efficiency of MG using various synthesized Fe NPs, batch
145
experiments were carried out using GT-Fe (0.01 g), OT-Fe (0.01 g) and BT-Fe (0.01 g)
146
added to a solution containing 50.0 mg/L MG (8 mL). These were then placed on a
147
rotary shaker at 298 K and 250 r/min. The degraded solutions were then filtered
148
through 0.45 µm membranes to determine the concentration of MG. This
149
concentration was measured using a UV-Spectrophotometer (752N, Shanghai, China)
150
at 617 nm. The removal efficiency of MG using various nanomaterials was calculated
7
151
using the following equation [17]: η=
152
C0 − Ce × 100% C0
(1)
153
Where η (%) = the MG removal efficiency, C0 = the initial MG concentration in the
154
solution (mg L-1), Ce = the MG concentration after reaction (mg L-1). All experiments
155
were undertaken in duplicate.
156 157
3. Results and discussion
158
3.1 The synthesis of Fe NPs employing tea extracts to degrade malachite green
159
Fig. 1(a) and (b) shows the UV spectra changes between tea extracts and after their
160
reaction with Fe2+. Fig. 1(a) shows that the peaks at 205 and 275 nm in tea extracts
161
correspond to the tea polyphenols and caffeine, which were recently confirmed by a
162
HPLC-UV analysis of the green tea extracts [20, 21], and the polyphenols and
163
caffeine of GTE was highest, then was OTE, BTE. As shown in Fig.1 (b), the
164
intensity of peaks at 205 and 272 nm declined after reacting with Fe2+ when the
165
reaction between FeSO4 and tea extracts led to the reaction mixture’s color changing
166
rapidly from yellow to dark. This indicates that it was that the tea polyphenols and
167
caffeine acted as reducing agent in the process of synthesis iron nanoparticles and iron
168
nanoparticles produced by tea extracts. In addition, the reduction potential of
169
polyphenols/caffeine is in the 0.3 -0.8 V range and the reduction potential of Fe was
170
only -0.44 V, which supported the reaction was feasible [16]. In contrast to the
171
absorption band of FeSO4 solution, the formation of Fe NPS was observed in broad
172
absorption at wavelength (500 nm-700 nm), which confirmed the formation of iron
173
nanoparticles [16, 22, 23]. More importantly, the strong absorption peak of the Fe NPs
174
synthesized by green tea was observed, indicating the reactivity of GT-Fe was higher
8
175
that of OT-Fe, BT-Fe, which supports the result of Fig.1c.
176 177
To evaluate the reactivity of the Fe NPs synthesized using tea extracts, the
178
degradation of MG in aqueous solution with an initial concentration of 50 mg/L is
179
shown in Fig. 1(c). After reacting for 10 min, decoloration using various Fe NPs
180
increased as contact time also increased. The removal efficiency of MG was 81.6%,
181
75.6% and 67.1% after reacting with GT-Fe, OT-Fe and BT-Fe for 60 min,
182
respectively, when the corresponding degradation rate was 0.052 min-1 for GT-Fe,
183
0.045 min-1 for OT-Fe and 0.031 min-1 for BT-Fe. This indicates that MG can be
184
removed when employing various synthesized Fe NPs using tea extracts, but a high
185
degradation rate and better efficiency were obtained using GT-Fe. This can be
186
attributed the fact that caffeine and polyphenols in green tea extract not only served as
187
capping agents that reduced the aggregation of Fe NPs, but also served as the reducing
188
agents for the synthesis of Fe NPs. This is explained by the green tea extract
189
containing a number of polyphenols and caffeine [14-16]. Consequently, the stability
190
and reactivity of GT-Fe was enhanced, which was confirmed by the subsequent SEM
191
images and EDS analysis. This was consistent with a previous study on green tea
192
extract used for the synthesis of membranes containing Fe and Fe/Pd immobilized in a
193
polymer, where the degradation of trichloroethylene (TCE) indicated a high
194
nanoparticle longevity and resistance to oxidation [14]. Compared to the green tea
195
extract, both oolong tea extract and black tea extract acted as both reducing and
196
capping agents, which were able to synthesize larger Fe NPs and Fe NPs with less
197
content, as well as indicate more aggregation of Fe NPs according to the SEM images
198
and EDS analysis. It can therefore be concluded that reducing and capping agents
199
such as caffeine and polyphenols in oolong tea and black tea extracts have less
9
200
content [22].
201 202
3.2 Characterization
203
The SEM images of Fe NPs synthesized using tea extracts are shown in Fig. 2, which
204
depicts the morphology and distribution of GT-Fe (Fig. 2(a)), OT-Fe (Fig. 2(c)) and
205
BT-Fe (Fig. 2(e)), respectively. It can clearly be seen that the Fe NPs with a spherical
206
shape and diameter in the range of 40-50 nm were dispersed on the component
207
existing in tea extracts. Additionally, a decrease in aggregation of Fe NPs and more
208
singular spherical nanoparticles appearing on the tea extract were observed. These
209
were consistent with the results of synthesized Fe NPs using the green tea extracts
210
[15]. Moreover, compared to OT-Fe and BT-Fe, the Fe NPs synthesized using green
211
tea extracts yielded only small amounts of Fe NPs having a uniform distribution,
212
whereas oolong and black tea extracts yielded large nanoparticles; slight aggregation
213
of Fe NPs was observed. These outcomes can be explained by the fact that the
214
polyphenols/caffeine concentrations in tea extracts play a key role in the formation of
215
the final structures and size of the Fe NPs since polyphenols/caffeine are important for
216
reducing and capping behaviors [15, 16]. These results support the contention that the
217
highest degradation of MG was obtained using Fe NPs synthesized by green tea
218
extracts as shown in Fig. 1(c).
219 220
To further confirm the role of tea extracts in synthesizing Fe NPs, the localized
221
elemental information of Fe NPs using tea extracts was determined by EDS, which
222
presented the important elements of GT-Fe (Fig. 2(b)), OT-Fe (Fig. 2(d)) and BT-Fe
223
(Fig. 2(f)), respectively. The main compositions in the tea extracts used to synthesize
224
them consisted of O, C, S and Fe. However, a high Al content was detected in both
10
225
oolong and black tea extracts as shown Table 1. Nonetheless this clearly demonstrates
226
that the Fe peak using green tea extract was much higher than those of oolong and
227
black tea extracts, where the percentage of Fe is 16.8% for green tea extract, 10.6%
228
for oolong tea extract and 7.7% for black tea extract, respectively. This evidence
229
supported the fact that more degradation of MG occurred using GT-Fe and Fe NPs,
230
particularly when they were well dispersed on the green tea extract. This is explained
231
by higher polyphenols/caffeine concentrations in the green tea extract causing a
232
decrease in particle size [14].
233 234
The XRD pattern of Fe NPs synthesized using tea extracts is shown in Fig. 3. The
235
characteristic peaks at 2θ=44.9°, 35.68°, 35.45° and 20.35° corresponded to
236
zero-valent iron (α-Fe), maghemite (γ-Fe2O3) , magnetite (Fe3O4) and iron hydroxides
237
[16]. However, since the Fe NPs synthesized by tea extracts are amorphous in nature,
238
iron oxide and iron oxohydroxide were observed [15, 16]. These matched well with
239
the XRD patterns of Fe NPs synthesized using green tea extract [15, 16]. Nevertheless,
240
hexagonal Fe0 in Fe NPs synthesized with green tea extract was also observed in other
241
studies on highly concentrated tea extract for synthesizing Fe NPs [15, 16]. Intensity
242
peak at 2θ=17.56° in Fig. 3 (a), (b) and (c) was identified as the ingredient in
243
polyphenols/caffeine, which was confirmed in a prior study [15], where Fe NPs were
244
synthesized at room temperature using aqueous sorghum bran extracts. It is consistent
245
with our previous UV-vis and SEM analysis, where UV-vis adsorption of
246
polyphenols/caffeine and O, C elements was observed.
247 248
The specific surface area of GT-Fe, OT-Fe and BT-Fe found using the BET was 5.8
249
m2/g, 5.0 m2/g and 2.6 m2/g, respectively. Furthermore in each case the average
11
250
equivalent particle size was 40-50 nm. This clearly indicates that high degradation of
251
MG using GT-Fe can be attributed to its higher SSA, resulting in a high concentration
252
of polyphenols/caffeine in green tea extracts acting as both reducing and capping
253
agents that diminished the aggregation of Fe NPs [15,16]. The outcome was an
254
increase in the SSA and hence the reactivity of GT-Fe was enhanced [17, 24].
255
However, the SSA of Fe NPs synthesized by tea extracts is smaller than that of the Fe
256
NPs synthesized utilizing chemical methods [17], which is likely to occur due to the
257
surface of Fe NPs being enveloped in organics existing in tea extracts as shown in
258
previous SEM images. Nevertheless, the OT-Fe and BT-Fe indicated a state of high
259
reactivity with MG. Equally important is the SSA of the GT-Fe being larger than that
260
of OT-Fe and BT-Fe, which is consistent with the results obtained from SEM and EDS.
261
Here the Fe NPs dispersion and Fe content used various tea extracts.
262 263
3.3 Degradation of malachite green and its kinetics
264
Fig. 4 illustrates the degradation of MG using Fe NPs synthesized by tea extracts,
265
which was measured by UV-vis spectra. The characteristic peak of MG stood at 428
266
nm and 617 nm, and it can been seen that the peak of MG was obviously reduced or in
267
fact disappeared after Fe NPs synthesized by tea extracts reacted with MG for 30 min.
268
These degraded products at 200-220 nm could be related to the aromatic ring [20, 21,
269
24]. However, the MG peak did rapidly abate using GT-Fe due to its higher reactivity,
270
and this is consistent with the result described in the previous section. It further
271
indicated that MG could be effectively removed using Fe NPs synthesized by tea
272
extracts by cleaving the -C=C- and =C=N- [24]. In addition, the distinct peak of 272
273
nm did agree with the composition of the polyphenols/caffeine in tea extracts and they
274
took on the role of reducing and capping agents in the green synthesis of Fe NPs [15,
12
275
16].
276 277
The reaction temperature ranging from 288 - 308 K was tested for batch experiments
278
to evaluate the influence of temperature on the degradation of MG using Fe NPs
279
synthesized by tea (see Fig. 5). Generally, the removal efficiency of MG using Fe NPs
280
synthesized by tea extracts increases when temperature also increases, thereby
281
indicating that the degraded process of MG when employing Fe NPs synthesized by
282
tea extracts is endothermic in character. This is explained by the dye molecules
283
increasing the tendency to transfer from the solution phase to the B-nZVI particle
284
surface [17]. However, higher removal efficiency was obtained using GT-Fe in all
285
cases, for example, 81.6%, 75.6% and 67.1% of MG at 298 K was removed when
286
using GT-Fe, OT-Fe and BT-Fe, respectively.
287 288
In order to understand the degradation of MG when employing Fe NPs synthesized by
289
tea extracts, the pseudo first-order kinetics model was generally used to test the
290
degradation of malachite green utilizing iron nanoparticles. This can be expressed as
291
the following equation [17, 25]:
292
v=−
293
ln
dc = kSA as ρm c = kobs c dt
c = − k obs t c0
(2)
(3)
294
295
Where c is the concentration (mg/L) of MG in solution, kobs is the observed rate
296
constant of a pseudo-first-order reaction (min-1) and can be calculated from the slope
297
of the line by plotting ln(c/c0) versus time; kSA is the specific reaction rate constant
298
bounded to the SSA of the materials (L/(h m2)); as is the specific surface area (m2/g);
13
299
and ρm is the mass concentration (g/L).
300 301
As shown in Fig. 5, plots of ln (c/c0) versus time were linear with high correlation
302
coefficients (R2)>0.910 at 288 K, 298 K, and 308 K, indicating that the degradation of
303
MG with Fe NPs synthesized by tea extracts was well described using a pseudo
304
first-order model. The rate constant for GT-Fe was 0.030, 0.052 and 0.057 min-1 at
305
288 K, 298 K and 308 K, respectively, while the rate constant for OT-Fe and BT-Fe
306
were 0.028, and 0.045, 0.050 and 0.026, 0.031 and 0.044 min-1, respectively. In
307
addition, apparent activation energy can be obtained from the following Arrhenius
308
formula [17, 25]:
309
lnK obs = −
310
Where Ea (kJ/mol) is the apparent activation energy and A0 is pre-exponential factor
311
with the same dimension as kobs.
Ea + InA0 RT
(4)
312 313
A line can be drawn by plotting lnK against 1/T. Activation energy (Ea) and factor (A0)
314
can be calculated through the slope and intercept of this linear regression equation,
315
respectively. The degradation of MG using GT-Fe, OT-Fe and BT-Fe was calculated to
316
be 23.86 kJ/mol, 21.53 kJ/mol and 20.29 kJ/mol, respectively. Diffusion-controlled
317
reactions in solution had relatively low activation energies (8-21 kJ/mol), thus
318
confirming that chemically diffusion-controlled reaction in the degradation of MG
319
using Fe NPs synthesized by tea extracts did occur [17, 25].
320 321
The pathway for the degradation of MG in aqueous solution using Fe NPs synthesized
322
by tea extracts is described in eqs (5-9). Firstly, the adsorption of MG onto the surface
323
of Fe NPs and components of tea extract and iron oxide is proposed. Secondly, the
14
324
corrosion of NPs dispersed on tea polyphenols in solution is suggested, leading to
325
causing the electrons to be released. Finally, the electrons accepted by MG and the
326
-C=C- and =C=N- bond linked to the benzene ring were broken down. These
327
processes can be explained as follows:
328 329
(1) Adsorption process:
330
MG + GTE → MG - GTE
(5)
331
MG + Fe2O3/Fe3O4 → MG - Fe2O3/Fe3O4
(6)
332 333
(2) The corrosion of Fe in solution
334
Fe0 + 2H2O → Fe2+ +2OH- + H2 (in basic solution)
(7)
335
Fe0 + 2H+ → Fe2+ + H2 (in basic solution)
(8)
336
(3) Cleaving the bond that was connected to the benzene ring
337
338
(9)
339 340
4. Conclusion
341
In this study the green synthesis of Fe NPs using tea extracts was attempted to assess
342
their ability to degrade MG. The major outcome was that polyphenols/caffeine in tea
343
extracts acted as both reducing and capping agents that reduced the aggregation of Fe
15
344
NPs, and improved the stability and in turn reactivity of Fe NPs. However, the high
345
degradation of MG (81.56%) using Fe NPs synthesized by green tea extracts was
346
obtained due to the high polyphenols/caffeine content in green tea extracts. This
347
resulted in the production of small sized but highly concentrated Fe NPs, which was
348
confirmed by SEM, EDS, XRD, BET and UV-vis. Kinetics data showed that the
349
degradation of MG by Fe NPs fitted with a pseudo first-order model and was
350
dominated by a chemically diffusion-controlled reaction. To sum up, the possible
351
mechanism for removing MG involved two processes. The first involved adsorption
352
on the Fe NPs and iron oxide, while the second consisted of reduction, where Fe0
353
acted as a reducing agent. Here the degradation of MG was thought to cleave the
354
C=C- and =C=N- bond linked to the benzene ring.
355 356
Acknowledgements
357
This research was supported by a Fujian “Minjiang Fellowship” Grant from Fujian
358
Normal University.
359 360
References
361
[1] F. Ding, X. Li, J. Diao, Y. Sun, L.Zhang, L. Ma, X. L.Yang, Y. Sun, Potential
362
toxicity and affinity of triphenylmethane dye malachite green to lysozyme, Ecotoxicol.
363
Environ. Saf., 78 (2012) 41-49.
364
[2] S. Shivaji, S. Ranjana, D. Roy, Toxicological effects of malachite green, Aquat.
365
Toxicol. 66 (2004) 319-329.
366
[3] K.Wu, Y.D. Xie, J.C. Zhao, H. Hidaka, Photo-Fenton degradation of a dye under
367
visible light irradiation, J. Mol. Catal., A: Chem. 144 (1999) 77-84.
368
[4] C. Hachem, F. Bocquillon, O. Zahraa, M. Bouchy, Decolourization of textile
16
369
industry wastewater by the photocatalytic degradation process, Dyes Pigments. 49
370
(2001) 117-125.
371
[5] C. Yatome, S. Yamada, T. Ogawa, Degradation of crystal violet by Nocardia
372
corullina, Appl. Microbiol. Biotechnol. 38 (1993) 565-569.
373
[6] W.Tsai, H.Chen, Removal of malachite green from aqueous solution using
374
low-cost chlorella-based biomass, J. Hazard. Mater., 175 (2010) 844-849.
375
[7] S. Iravani, Green synthesis of metal nanoparticles using plants, Green Chem. 13
376
(2011) 2638-2650.
377
[8] Y. Wang, S. Maksimuk, R. Shen, H Yang, Synthesis of iron oxide nanoparticles
378
using a freshly-made or recycled imidazolium-based ionic liquid, Green Chem. 9
379
(2007) 1051-1056.
380
[9] J.G. Parsons, J.R. Peralt-Videa, J.L.Gar dea-Tor resdey, Use of plants in
381
biotechnology: Synthesis of metal nanoparticles by inactivated plant tissues, plant
382
extracts, and living plant, Developments in Environmental Science. 5 (2007) 463-485.
383
[10] Y. Sun, X. Li, J. Cao, W. Zhang, H. Wang, Characterization of zero-valent iron
384
nanoparticles, Colloid Interface Sci. 120 (2006) 47-56.
385
[11] M.N. Nadagouda, A.B. Castle, R.C. Murdock, S.M. Hussain, R.S. Varma, In vitro
386
biocompatibility of nanoscale zero valent iron particles (NZVI) synthesized using tea
387
polyphenols, Green Chem. 10 (2010) 114-122.
388
[12] R. A. Crane, T.B. Scott, Nanoscale zero-valent iron: Future prospects for an
389
emerging water treatment technology，J. Hazard. Mater. 211–212 (2012) 112–125.
390
[13] E. C. Njagi, H. Huang, L. Stafford, H. Genuino, H. M. Galindo, J. B. Collins, G.
391
E. Hoag, S. L. Suib, Biosynthesis of iron and silver nanoparticles at room temperature
392
using aqueous sorghum bran extracts, Langmuir. 27 (2011) 264-271.
393
[14] V. Smuleac, R. Varma, S. Sikdar, D. Bhattacharyyaa, Green synthesis of Fe and
17
394
Fe/Pd bimetallic nanoparticles in membranes for reductive degradation of chlorinated
395
organics, J. Membr. Sci. 379 (2011) 131-137.
396
[15] T. Shahwan, S. AbuSirriah, M. Nairat, E. Boyac, A.E. Ero ˘glu, T.B. Scott, K.R.
397
Hallam, Green synthesis of iron nanoparticles and their application as a Fenton-like
398
catalyst for the degradation of aqueous cationic and anionic dyes, Chem. Eng. J. 172,
399
(2011) 258-266.
400
[16] G.E. Hoag, J. B. Collins, J. L. Holcomb, J. R. Hoag, M.N. Nadagouda, R. S.
401
Varma, Degradation of bromothymol blue by‘greener’ nano-scale zero-valent iron
402
synthesized using tea polyphenols , J. Mater. Chem. 19 (2009) 8671-8677.
403
[17] Z. Chen, X. Jin, Z. Chen, M. Megharaj, R. Naidu, Removal of methyl orange
404
from aqueous solution using bentonite-supported nanoscale zero-valent iron, J.
405
Colloid Interface Sci. 363 (2011) 601-607.
406
[18] Lanlan Huang, Xiulan Weng, Zuliang Chen, Mallavarapu Megharaj, Ravendra
407
Naidu. Synthesis of iron-based nanoparticles using oolong tea extract for the
408
degradation of malachite green, Spectrochim. Acta, Part A, 117, 3(2014)801-804.
409
[19] Ye Kuang, Qingping Wanga, Zuliang Chen Mallavarapu Megharaj, Ravendra
410
Naidu, Heterogeneous Fenton-like oxidation of monochlorobenzene using green
411
synthesis of iron nanoparticles. J. Colloid Interface Sci., 410(2013) 67-73.
412
[20] M.S. El-Shahawi, A. Hamza, S.O. Bahaffi, A.A. Al-Sibaai, T.N. Abduljabbar
413
Analysis of some selected catechins and caffeine in green tea by high performance
414
liquid chromatography, Food Chem. 134 (2012) 2268–2275
415
[21] M. Colon, C. Nerin, Role of Catechins in the Antioxidant Capacity of an Active
416
Film Containing Green Tea, Green Coffee, and Grapefruit Extracts, J. Agric. Food
417
Chem. 60 (2012) 9842−9849.
418
[22] M. N. Nadagouda and R. S. Varma, Green synthesis of silver and palladium
18
419
nanoparticles at room temperature using coffee and tea extract, Green Chem. 10 10
420
(2008) 859-862.
421
[23] Kesarla Mohan Kumar, Badal Kumar Mandal, Koppala Siva Kumar, Pamanji
422
Sreedhara Reddy, Bojja Sreedhar, Biobased green method to synthesise palladium and
423
iron nanoparticles using Terminalia chebulaaqueous extract, Spectrochim. Acta, Part
424
A, 102 (2013) 128-133.
425
[24] Y. Ju, J. Qiao, X. Peng, Z. Xu, J. Fang, S. Yang, C. Sun, Photodegradation of
426
malachite green using UV–vis light from two microwave-powered electrodeless
427
discharge lamps (MPEDL-2): further investigation on products, dominant routes and
428
mechanism, Chem. Eng. J. (2012), doi: http://dx.doi.org/10.1016/j.cej.2012.06.055.
429
[25] J. Su, S. Lin, Z.Chen, M. Megharaj, R. Naidu, Decolourination of p-chlorophenol
430
from aqueous solution using bentonite-supported Fe/Pd nanoparticles: synthesis,
431
characterization and kinetics, Desalination. 280 (2011) 167-173.
432 433 434 435 436 437 438 439 440 441 442 443
19
444 445
Figure caption
446
Fig. 1 (a) UV-vis spectra of GTE, OTE, BTE.
447
Condition: 0.1mL GTE, OTE, BTE, diluted 50 times
448
Fig. 1 (b) UV-vis spectra of FeSO4, GT-Fe NPs, OT-Fe NPs, BT-Fe NPs.
449
Condition: 0.1 mL FeSO4, GT-Fe, OT-Fe, BT-Fe, diluted 50 times
450
Fig. 1 (c) Degradation of malachite green using different teas
451
Dose: 0.01 g/L GT-Fe, OT-Fe and BT-Fe respectively; initial concentration: 8ml 50
452
mg/L malachite green
453 454
Fig. 2 SEM scanning images of GT-Fe (a) and a typical EDS spectrum of GT-Fe (b);
455
SEM scanning images of OT-Fe (c) and a typical EDS spectrum of GT-Fe (d); SEM
456
scanning images of BT-Fe (e) and a typical EDS spectrum of BT-Fe (f)
457 458
Fig. 3 XRD patterns of GT-Fe (a) OT-Fe (b) and BT-Fe (c)
459 460
Fig. 4 UV-vis scanning images of degradation of malachite green using various
461
materials
462 463
Fig. 5 Degradation of malachite green using GT-Fe (a),OT-Fe (b) and BT-Fe (c) in
464
different temperature.
465
Does: 0.01g/L GT-Fe, OT-Fe and BT-Fe respectively; 8mL 50 mg/L malachite green;
466
rotary speed: 250 rpm; temperature: 283 K, 293 K, 303 K
467 468
20
469 470
0.75
Absorbance (a.u)
a 0.50
GTE OTE BTE
0.25
0.00 200
300
400
500
600
700
800
Wavelength (nm) 0.75
Absorbance (a.u)
b 0.50
FeSO4 GT-Fe NPs OT-Fe NPs BT-Fe NPs
0.25
0.00 200
300
400
500
600
700
800
Removal Efficiency (%)
Wavelength (nm)
c
80
60
40 GT-Fe NPs OT-Fe NPs BT-Fe NPs
20
0 0
10
20
30
40
Time (min)
471 472 473 474
Fig. 1
50
60
21
475 476
477 478 479 480 481 482 483 484
Fig. 2
22
485 486
FeOOH Fe2O3
c FeOOH
Intensity
Fe2O3
Fe3O4
0
Fe
b
FeOOH Fe2O3 Fe3O4
10
20
30
40
0
Fe
a 50
60
70
80
2Theta(degree) 487 488
Fig. 3
3.0
Absorbance (a.u)
2.5 2.0 MG GT-Fe NPs OT-Fe NPs BT-Fe NPs
1.5 1.0 0.5 0.0 200
490
492
400
500
600
Wavelength (nm)
489
491
300
Fig. 4
700
800
23
493 494
a
0.0 -0.1
ln (C/C0)
-0.2 -0.3 -0.4 -0.5
2
288K K=0.028 R =0.929 2 298K K=0.045 R =0.948 2 308K K=0.050 R =0.913
-0.6 0
2
4
6
8
10
T (min)
b
0.0 -0.1
ln (C/C0)
-0.2 -0.3 -0.4 -0.5
288K K=0.030 R2=0.925 298K K=0.057 R2=0.973 308K K=0.052 R2=0.933
-0.6 0
2
4
6
8
10
T (min)
c
0.0 -0.1
ln (C/C0)
-0.2 -0.3 -0.4 2
288K K=0.026 R =0.910 2 298k K=0.031 R =0.941 2 308k K=0.044 R =0.986
-0.5 -0.6 0
2
4
T (min)
495 496 497 498 499 500
Fig. 5
6
8
10
24
501 502 503 504
Table 1 The percentage of various elements in GT-Fe NPs, OT-Fe NPs, BT-Fe NPs examined
505
through EDS
Fe
C
O
S
Al
GT-Fe NPs
16.80
30.65
34.76
3.56
14.23
OT-Fe NPs
10.63
30.86
38.45
4.98
15.09
BT-Fe NPs
7.65
39.16
32.13
3.46
17.60
Percentage (%)
Materials
506 507
25
508 509
510 511 512
Graphical abstract UV-vis images of degradation of malachite green using various Fe NPs
3.0
Absorbance (a.u)
2.5 2.0 MG GT-Fe NPs OT-Fe NPs BT-Fe NPs
1.5 1.0 0.5 0.0 200
513 514
300
400
500
600
Wavelength (nm)
700
800
26
515 516
517
Research highlights 518 519
► Iron nanoparticles (Fe NPs) were synthesized by 3 tea extracts. ► Differences in Fe NPs synthesized were observed by characterization.
520
► The removal of malachite green was 81.2%, 75.6% and 67.1%.
521
► Degradation mechanism of MG using Fe NPs were proposed.
522
S1386-1425(14)00610-6 http://dx.doi.org/10.1016/j.saa.2014.04.037 SAA 12001
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received Date: Revised Date: Accepted Date:
26 February 2014 1 April 2014 7 April 2014
Please cite this article as: L. Huang, X. Weng, Z. Chen, M. Megharaj, R. Naidu, Green synthesis of iron nanoparticles by various tea extracts: Comparative study of the reactivity, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.04.037
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
1
Green synthesis of iron nanoparticles by various tea extracts:
2
Comparative study of the reactivity
3 4
Lanlan Huang1, Xiulan Weng1, Zuliang Chen1,2,3*, Mallavarapu Megharaj2,3,
5
Ravendra Naidu2,3
6 7
1. School of Environmental Science and Engineering, Fujian Normal University,
8
Fuzhou 350007, Fujian Province, China
9
2.Centre for Environmental Risk Assessment and Remediation, University of South
10
Australia, Mawson Lakes, SA 5095, Australia
11
3. Cooperative Research Centre for Contamination Assessment and Remediation of
12
Environments, Mawson Lakes, SA 5095, Australia
13 14 15 16 17 18 19 20 21 22 23 24 25
*Corresponding author. Fax: 61-08-83025057; E-mail: Zuliang.chen@unisae,du,au
2
26 27
Abstract
28
Iron nanoparticles (Fe NPs) are often synthesized using sodium borohydride with
29
aggregation, which is a high cost process and environmentally toxic. To address these
30
issues, Fe NPs were synthesized using green methods based on tea extracts, including
31
green, oolong and black teas. The best method for degrading malachite green (MG)
32
was Fe NPs synthesized by green tea extracts because it contains a high concentration
33
of caffeine/polyphenols which act as both reducing and capping agents in the
34
synthesis of Fe NPs. These characteristics were confirmed by a scanning electron
35
microscope (SEM), UV-visible (UV-vis) and specific surface area (BET). To
36
understand the formation of Fe NPs using various tea extracts, the synthesized Fe NPs
37
were characterized by SEM, X-ray energy-dispersive spectrometer (EDS), and X-ray
38
diffraction (XRD). What emerged were different sizes and concentrations of Fe NPs
39
being synthesized by tea extracts, leading to various degradations of MG. Furthermore,
40
kinetics for the degradation of MG using these Fe NPs fitted well to the pseudo
41
first-order reaction kinetics model with more than 20 kJ/mol activation energy,
42
suggesting a chemically diffusion-controlled reaction. The degradation mechanism
43
using these Fe NPs included adsorption of MG to Fe NPs, oxidation of iron, and
44
cleaving the bond that was connected to the benzene ring.
45 46 47 48 49 50
Keywords: Green synthesis; Fe NPs; Malachite green; Characterization; Degradation.
3
51
1. Introduction
52
Malachite green (MG) is a cationic triphenylmethane dye widely used in the dyeing of
53
cotton, silk, paper, leather and in the manufacture of paints and inks and aquaculture
54
as a biocide [1, 2]. MG is toxic and therefore has to be removed from wastewater prior
55
to its discharge into aquatic environments. Various conventional methods such as
56
adsorption [1], photo-catalytic degradation [3, 4] and biological degradation [5, 6] are
57
often employed to remove MG from wastewater [3, 4]. While to some extent these
58
approaches have succeeded, the high cost and low efficiency of these processes limit
59
their applicability [7]. Therefore, the development of innovative remediation
60
techniques is required.
61 62
In recent years, zero-valent iron (nZVI) has received great attention from researchers
63
examining groundwater treatment and site remediation due to the higher intrinsic
64
reactivity of its surface sites [7]. Various physical and chemical methods have been
65
developed for the synthesis of nZVI. Physical methods are thermal decomposition [8]
66
and ultraviolet radiation and aerosol [9], but they are limited by the energy
67
consumption required to maintain high pressure and temperature. Sodium borohydride
68
(NaBH4) as a reducing agent is often used in chemical synthesis of nZVI [10, 11]. The
69
drawbacks include chemical substances such as NaBH4, organic solvents, stabilizing
70
and dispersing agents being toxic and very expensive. Furthermore while the
71
electrochemical method has been used to compose iron nanoparticles, its disadvantage
72
lies in the fact that aggregation of nanoparticles often occurs in the cathode’s motor
73
[12].
74 75
The green synthesis of nZVI has been recently proposed as a cost effective,
4
76
environmental friendly alternative to chemical and physical methods since a variety of
77
materials from biorenewable natural sources can be employed [13-15]. The
78
components in the synthesis of nZVI such as polyphenols from coffee and tea, protein,
79
vitamins and wine polyphenols are available [13-15]. Consequently, these components
80
have emerged as replacements for the established chemical synthesis of nZVI.
81
Furthermore, these components are extracted from natural sources that are non-toxic,
82
biodegradable and the green material acts as both a dispersive and capping agent,
83
helping to minimize the oxidation and agglomeration of nZVI [14]. The synthesis of
84
nZVI using tea polyphenols has been recently examined in the context of in vitro
85
biocompatibility [11], and used for degrading bromothymol blue by Fenton oxidation
86
[16]. More recently, the synthesis of the membrane Fe/Pd using a green tea extract has
87
been used to degrade trichloroethylene (TCE) [14]. The green synthesis of iron
88
nanoparticles (Fe NPs) using the extract of green tea leaves a Fenton-like catalyst.
89
This has been also reported in the degradation of aqueous cationic and anionic dyes
90
[15]. The size and reactivity of the synthesized Fe NPs depend on significant factors
91
such the reducing and capping agents [17], and different tea extracts indicate
92
differences in the reducing and capping agents. From this it can be concluded that the
93
size and reactivity, as well as the concentration of the synthesized Fe NPs, refer to
94
different tea extracts. However, to date, few studies have been published on the
95
synthesis of iron nanoparticles using different tea extracts.
96 97
In our previous studies, oolong tea extract has been used to synthesize iron
98
nanoparticles [18]. To determine whether other tea extracts could be acted as reducing
99
agent to synthesize Fe NPs, green tea extract, oolong tea extract and black tea extract
100
were acted as the reducing agent to synthesize Fe NPs and used for Fenton-like
5
101
oxidation of monochlorobenzene (MCB), where 69%, 59% and 39% of MCB were
102
removed [19]. As a reductive degradation, the different degradations of MG are
103
obtained using Fe NPs since the Fe NPs are synthesized by various extracts. Therefore,
104
in this study, the synthesis of Fe NPs employs extracts from green tea, oolong tea and
105
black tea as reducing and capping agents. These can determine whether the
106
synthesized Fe NPs can be used to degrade MG, as well as to examine why differences
107
in using these Fe NPs emerge when the degradation of MG is being considered. To
108
achieve these aims, the following issues are investigated: (1) the synthesis of Fe NPs
109
utilizing various tea extracts and characterization of these Fe NPs by SEM, EDS,
110
XRD, and BET-N2; (2) evaluating the degradation of MG by Fe NPs synthesized from
111
various tea extracts, including their degradation kinetics; (3) the mechanism of
112
degradation of MG being proposed; and (4) demonstrating the application of Fe NPs
113
to remove MG from wastewater.
114 115
2. Experimental procedure
116
2.1 Preparation of Fe NPs using tea extracts
117
The synthesis of Fe NPs using green tea extracts has been described previously [15,
118
16]. The initial concentrations of 60.0 g/L green tea, oolong tea and black tea extracts
119
were prepared by heating them at 800C for 1 h. These extracts were then
120
vacuum-filtered and 0.10 mol/L FeSO4 solution was added to the tea extracts at a ratio
121
of 1:2 respectively. The Fe NPs were synthesized from green tea, oolong and black tea
122
extracts in the form of GT-Fe, OT-Fe and BT-Fe, respectively. The stock solution of
123
MG with a 100.0 mg/L was first prepared, and the required MG concentration in our
124
experiments was diluted using deionized water.
125
6
126
2.2 Characterization
127
The synthesized Fe NPs using tea extracts were characterized using Uv-vis, SEM,
128
EDS, BET-N2 and XRD techniques. Morphology and distribution of Fe NPs were
129
characterized using a scanning electron microscope (SEM) (JSM 7500F, Japan).
130
Images of samples were recorded at different magnifications using an operating
131
voltage of 10 kV. Localized elemental information of Fe NPs was determined by
132
INCA EDS (Oxford Instruments, UK) in conjunction with SEM.
133
X-ray diffraction (XRD) patterns of Fe NPs before and after reaction with MG were
134
obtained using a Philips-X’Pert Pro MPD (Netherlands) with a high-power Cu-Kα
135
radioactive source (λ = 0.154 nm) at 40 kV/40 mA. All samples were scanned from
136
10° to 80° 2θ at a scanning rate of 3° 2θ per minute.
137 138
The specific surface areas (SSA) of Fe NPs were measured using the BET-N2
139
adsorption method (Brunauer-Emmett-Teller isotherm), specifically Micromeritics’
140
ASAP 2020 Accelerated Surface Area and Porosimetry Analyzer (Micromeritics
141
Instrument Corp., Georgia, USA).
142 143
2.3 Degradation of malachite green
144
To compare the removal efficiency of MG using various synthesized Fe NPs, batch
145
experiments were carried out using GT-Fe (0.01 g), OT-Fe (0.01 g) and BT-Fe (0.01 g)
146
added to a solution containing 50.0 mg/L MG (8 mL). These were then placed on a
147
rotary shaker at 298 K and 250 r/min. The degraded solutions were then filtered
148
through 0.45 µm membranes to determine the concentration of MG. This
149
concentration was measured using a UV-Spectrophotometer (752N, Shanghai, China)
150
at 617 nm. The removal efficiency of MG using various nanomaterials was calculated
7
151
using the following equation [17]: η=
152
C0 − Ce × 100% C0
(1)
153
Where η (%) = the MG removal efficiency, C0 = the initial MG concentration in the
154
solution (mg L-1), Ce = the MG concentration after reaction (mg L-1). All experiments
155
were undertaken in duplicate.
156 157
3. Results and discussion
158
3.1 The synthesis of Fe NPs employing tea extracts to degrade malachite green
159
Fig. 1(a) and (b) shows the UV spectra changes between tea extracts and after their
160
reaction with Fe2+. Fig. 1(a) shows that the peaks at 205 and 275 nm in tea extracts
161
correspond to the tea polyphenols and caffeine, which were recently confirmed by a
162
HPLC-UV analysis of the green tea extracts [20, 21], and the polyphenols and
163
caffeine of GTE was highest, then was OTE, BTE. As shown in Fig.1 (b), the
164
intensity of peaks at 205 and 272 nm declined after reacting with Fe2+ when the
165
reaction between FeSO4 and tea extracts led to the reaction mixture’s color changing
166
rapidly from yellow to dark. This indicates that it was that the tea polyphenols and
167
caffeine acted as reducing agent in the process of synthesis iron nanoparticles and iron
168
nanoparticles produced by tea extracts. In addition, the reduction potential of
169
polyphenols/caffeine is in the 0.3 -0.8 V range and the reduction potential of Fe was
170
only -0.44 V, which supported the reaction was feasible [16]. In contrast to the
171
absorption band of FeSO4 solution, the formation of Fe NPS was observed in broad
172
absorption at wavelength (500 nm-700 nm), which confirmed the formation of iron
173
nanoparticles [16, 22, 23]. More importantly, the strong absorption peak of the Fe NPs
174
synthesized by green tea was observed, indicating the reactivity of GT-Fe was higher
8
175
that of OT-Fe, BT-Fe, which supports the result of Fig.1c.
176 177
To evaluate the reactivity of the Fe NPs synthesized using tea extracts, the
178
degradation of MG in aqueous solution with an initial concentration of 50 mg/L is
179
shown in Fig. 1(c). After reacting for 10 min, decoloration using various Fe NPs
180
increased as contact time also increased. The removal efficiency of MG was 81.6%,
181
75.6% and 67.1% after reacting with GT-Fe, OT-Fe and BT-Fe for 60 min,
182
respectively, when the corresponding degradation rate was 0.052 min-1 for GT-Fe,
183
0.045 min-1 for OT-Fe and 0.031 min-1 for BT-Fe. This indicates that MG can be
184
removed when employing various synthesized Fe NPs using tea extracts, but a high
185
degradation rate and better efficiency were obtained using GT-Fe. This can be
186
attributed the fact that caffeine and polyphenols in green tea extract not only served as
187
capping agents that reduced the aggregation of Fe NPs, but also served as the reducing
188
agents for the synthesis of Fe NPs. This is explained by the green tea extract
189
containing a number of polyphenols and caffeine [14-16]. Consequently, the stability
190
and reactivity of GT-Fe was enhanced, which was confirmed by the subsequent SEM
191
images and EDS analysis. This was consistent with a previous study on green tea
192
extract used for the synthesis of membranes containing Fe and Fe/Pd immobilized in a
193
polymer, where the degradation of trichloroethylene (TCE) indicated a high
194
nanoparticle longevity and resistance to oxidation [14]. Compared to the green tea
195
extract, both oolong tea extract and black tea extract acted as both reducing and
196
capping agents, which were able to synthesize larger Fe NPs and Fe NPs with less
197
content, as well as indicate more aggregation of Fe NPs according to the SEM images
198
and EDS analysis. It can therefore be concluded that reducing and capping agents
199
such as caffeine and polyphenols in oolong tea and black tea extracts have less
9
200
content [22].
201 202
3.2 Characterization
203
The SEM images of Fe NPs synthesized using tea extracts are shown in Fig. 2, which
204
depicts the morphology and distribution of GT-Fe (Fig. 2(a)), OT-Fe (Fig. 2(c)) and
205
BT-Fe (Fig. 2(e)), respectively. It can clearly be seen that the Fe NPs with a spherical
206
shape and diameter in the range of 40-50 nm were dispersed on the component
207
existing in tea extracts. Additionally, a decrease in aggregation of Fe NPs and more
208
singular spherical nanoparticles appearing on the tea extract were observed. These
209
were consistent with the results of synthesized Fe NPs using the green tea extracts
210
[15]. Moreover, compared to OT-Fe and BT-Fe, the Fe NPs synthesized using green
211
tea extracts yielded only small amounts of Fe NPs having a uniform distribution,
212
whereas oolong and black tea extracts yielded large nanoparticles; slight aggregation
213
of Fe NPs was observed. These outcomes can be explained by the fact that the
214
polyphenols/caffeine concentrations in tea extracts play a key role in the formation of
215
the final structures and size of the Fe NPs since polyphenols/caffeine are important for
216
reducing and capping behaviors [15, 16]. These results support the contention that the
217
highest degradation of MG was obtained using Fe NPs synthesized by green tea
218
extracts as shown in Fig. 1(c).
219 220
To further confirm the role of tea extracts in synthesizing Fe NPs, the localized
221
elemental information of Fe NPs using tea extracts was determined by EDS, which
222
presented the important elements of GT-Fe (Fig. 2(b)), OT-Fe (Fig. 2(d)) and BT-Fe
223
(Fig. 2(f)), respectively. The main compositions in the tea extracts used to synthesize
224
them consisted of O, C, S and Fe. However, a high Al content was detected in both
10
225
oolong and black tea extracts as shown Table 1. Nonetheless this clearly demonstrates
226
that the Fe peak using green tea extract was much higher than those of oolong and
227
black tea extracts, where the percentage of Fe is 16.8% for green tea extract, 10.6%
228
for oolong tea extract and 7.7% for black tea extract, respectively. This evidence
229
supported the fact that more degradation of MG occurred using GT-Fe and Fe NPs,
230
particularly when they were well dispersed on the green tea extract. This is explained
231
by higher polyphenols/caffeine concentrations in the green tea extract causing a
232
decrease in particle size [14].
233 234
The XRD pattern of Fe NPs synthesized using tea extracts is shown in Fig. 3. The
235
characteristic peaks at 2θ=44.9°, 35.68°, 35.45° and 20.35° corresponded to
236
zero-valent iron (α-Fe), maghemite (γ-Fe2O3) , magnetite (Fe3O4) and iron hydroxides
237
[16]. However, since the Fe NPs synthesized by tea extracts are amorphous in nature,
238
iron oxide and iron oxohydroxide were observed [15, 16]. These matched well with
239
the XRD patterns of Fe NPs synthesized using green tea extract [15, 16]. Nevertheless,
240
hexagonal Fe0 in Fe NPs synthesized with green tea extract was also observed in other
241
studies on highly concentrated tea extract for synthesizing Fe NPs [15, 16]. Intensity
242
peak at 2θ=17.56° in Fig. 3 (a), (b) and (c) was identified as the ingredient in
243
polyphenols/caffeine, which was confirmed in a prior study [15], where Fe NPs were
244
synthesized at room temperature using aqueous sorghum bran extracts. It is consistent
245
with our previous UV-vis and SEM analysis, where UV-vis adsorption of
246
polyphenols/caffeine and O, C elements was observed.
247 248
The specific surface area of GT-Fe, OT-Fe and BT-Fe found using the BET was 5.8
249
m2/g, 5.0 m2/g and 2.6 m2/g, respectively. Furthermore in each case the average
11
250
equivalent particle size was 40-50 nm. This clearly indicates that high degradation of
251
MG using GT-Fe can be attributed to its higher SSA, resulting in a high concentration
252
of polyphenols/caffeine in green tea extracts acting as both reducing and capping
253
agents that diminished the aggregation of Fe NPs [15,16]. The outcome was an
254
increase in the SSA and hence the reactivity of GT-Fe was enhanced [17, 24].
255
However, the SSA of Fe NPs synthesized by tea extracts is smaller than that of the Fe
256
NPs synthesized utilizing chemical methods [17], which is likely to occur due to the
257
surface of Fe NPs being enveloped in organics existing in tea extracts as shown in
258
previous SEM images. Nevertheless, the OT-Fe and BT-Fe indicated a state of high
259
reactivity with MG. Equally important is the SSA of the GT-Fe being larger than that
260
of OT-Fe and BT-Fe, which is consistent with the results obtained from SEM and EDS.
261
Here the Fe NPs dispersion and Fe content used various tea extracts.
262 263
3.3 Degradation of malachite green and its kinetics
264
Fig. 4 illustrates the degradation of MG using Fe NPs synthesized by tea extracts,
265
which was measured by UV-vis spectra. The characteristic peak of MG stood at 428
266
nm and 617 nm, and it can been seen that the peak of MG was obviously reduced or in
267
fact disappeared after Fe NPs synthesized by tea extracts reacted with MG for 30 min.
268
These degraded products at 200-220 nm could be related to the aromatic ring [20, 21,
269
24]. However, the MG peak did rapidly abate using GT-Fe due to its higher reactivity,
270
and this is consistent with the result described in the previous section. It further
271
indicated that MG could be effectively removed using Fe NPs synthesized by tea
272
extracts by cleaving the -C=C- and =C=N- [24]. In addition, the distinct peak of 272
273
nm did agree with the composition of the polyphenols/caffeine in tea extracts and they
274
took on the role of reducing and capping agents in the green synthesis of Fe NPs [15,
12
275
16].
276 277
The reaction temperature ranging from 288 - 308 K was tested for batch experiments
278
to evaluate the influence of temperature on the degradation of MG using Fe NPs
279
synthesized by tea (see Fig. 5). Generally, the removal efficiency of MG using Fe NPs
280
synthesized by tea extracts increases when temperature also increases, thereby
281
indicating that the degraded process of MG when employing Fe NPs synthesized by
282
tea extracts is endothermic in character. This is explained by the dye molecules
283
increasing the tendency to transfer from the solution phase to the B-nZVI particle
284
surface [17]. However, higher removal efficiency was obtained using GT-Fe in all
285
cases, for example, 81.6%, 75.6% and 67.1% of MG at 298 K was removed when
286
using GT-Fe, OT-Fe and BT-Fe, respectively.
287 288
In order to understand the degradation of MG when employing Fe NPs synthesized by
289
tea extracts, the pseudo first-order kinetics model was generally used to test the
290
degradation of malachite green utilizing iron nanoparticles. This can be expressed as
291
the following equation [17, 25]:
292
v=−
293
ln
dc = kSA as ρm c = kobs c dt
c = − k obs t c0
(2)
(3)
294
295
Where c is the concentration (mg/L) of MG in solution, kobs is the observed rate
296
constant of a pseudo-first-order reaction (min-1) and can be calculated from the slope
297
of the line by plotting ln(c/c0) versus time; kSA is the specific reaction rate constant
298
bounded to the SSA of the materials (L/(h m2)); as is the specific surface area (m2/g);
13
299
and ρm is the mass concentration (g/L).
300 301
As shown in Fig. 5, plots of ln (c/c0) versus time were linear with high correlation
302
coefficients (R2)>0.910 at 288 K, 298 K, and 308 K, indicating that the degradation of
303
MG with Fe NPs synthesized by tea extracts was well described using a pseudo
304
first-order model. The rate constant for GT-Fe was 0.030, 0.052 and 0.057 min-1 at
305
288 K, 298 K and 308 K, respectively, while the rate constant for OT-Fe and BT-Fe
306
were 0.028, and 0.045, 0.050 and 0.026, 0.031 and 0.044 min-1, respectively. In
307
addition, apparent activation energy can be obtained from the following Arrhenius
308
formula [17, 25]:
309
lnK obs = −
310
Where Ea (kJ/mol) is the apparent activation energy and A0 is pre-exponential factor
311
with the same dimension as kobs.
Ea + InA0 RT
(4)
312 313
A line can be drawn by plotting lnK against 1/T. Activation energy (Ea) and factor (A0)
314
can be calculated through the slope and intercept of this linear regression equation,
315
respectively. The degradation of MG using GT-Fe, OT-Fe and BT-Fe was calculated to
316
be 23.86 kJ/mol, 21.53 kJ/mol and 20.29 kJ/mol, respectively. Diffusion-controlled
317
reactions in solution had relatively low activation energies (8-21 kJ/mol), thus
318
confirming that chemically diffusion-controlled reaction in the degradation of MG
319
using Fe NPs synthesized by tea extracts did occur [17, 25].
320 321
The pathway for the degradation of MG in aqueous solution using Fe NPs synthesized
322
by tea extracts is described in eqs (5-9). Firstly, the adsorption of MG onto the surface
323
of Fe NPs and components of tea extract and iron oxide is proposed. Secondly, the
14
324
corrosion of NPs dispersed on tea polyphenols in solution is suggested, leading to
325
causing the electrons to be released. Finally, the electrons accepted by MG and the
326
-C=C- and =C=N- bond linked to the benzene ring were broken down. These
327
processes can be explained as follows:
328 329
(1) Adsorption process:
330
MG + GTE → MG - GTE
(5)
331
MG + Fe2O3/Fe3O4 → MG - Fe2O3/Fe3O4
(6)
332 333
(2) The corrosion of Fe in solution
334
Fe0 + 2H2O → Fe2+ +2OH- + H2 (in basic solution)
(7)
335
Fe0 + 2H+ → Fe2+ + H2 (in basic solution)
(8)
336
(3) Cleaving the bond that was connected to the benzene ring
337
338
(9)
339 340
4. Conclusion
341
In this study the green synthesis of Fe NPs using tea extracts was attempted to assess
342
their ability to degrade MG. The major outcome was that polyphenols/caffeine in tea
343
extracts acted as both reducing and capping agents that reduced the aggregation of Fe
15
344
NPs, and improved the stability and in turn reactivity of Fe NPs. However, the high
345
degradation of MG (81.56%) using Fe NPs synthesized by green tea extracts was
346
obtained due to the high polyphenols/caffeine content in green tea extracts. This
347
resulted in the production of small sized but highly concentrated Fe NPs, which was
348
confirmed by SEM, EDS, XRD, BET and UV-vis. Kinetics data showed that the
349
degradation of MG by Fe NPs fitted with a pseudo first-order model and was
350
dominated by a chemically diffusion-controlled reaction. To sum up, the possible
351
mechanism for removing MG involved two processes. The first involved adsorption
352
on the Fe NPs and iron oxide, while the second consisted of reduction, where Fe0
353
acted as a reducing agent. Here the degradation of MG was thought to cleave the
354
C=C- and =C=N- bond linked to the benzene ring.
355 356
Acknowledgements
357
This research was supported by a Fujian “Minjiang Fellowship” Grant from Fujian
358
Normal University.
359 360
References
361
[1] F. Ding, X. Li, J. Diao, Y. Sun, L.Zhang, L. Ma, X. L.Yang, Y. Sun, Potential
362
toxicity and affinity of triphenylmethane dye malachite green to lysozyme, Ecotoxicol.
363
Environ. Saf., 78 (2012) 41-49.
364
[2] S. Shivaji, S. Ranjana, D. Roy, Toxicological effects of malachite green, Aquat.
365
Toxicol. 66 (2004) 319-329.
366
[3] K.Wu, Y.D. Xie, J.C. Zhao, H. Hidaka, Photo-Fenton degradation of a dye under
367
visible light irradiation, J. Mol. Catal., A: Chem. 144 (1999) 77-84.
368
[4] C. Hachem, F. Bocquillon, O. Zahraa, M. Bouchy, Decolourization of textile
16
369
industry wastewater by the photocatalytic degradation process, Dyes Pigments. 49
370
(2001) 117-125.
371
[5] C. Yatome, S. Yamada, T. Ogawa, Degradation of crystal violet by Nocardia
372
corullina, Appl. Microbiol. Biotechnol. 38 (1993) 565-569.
373
[6] W.Tsai, H.Chen, Removal of malachite green from aqueous solution using
374
low-cost chlorella-based biomass, J. Hazard. Mater., 175 (2010) 844-849.
375
[7] S. Iravani, Green synthesis of metal nanoparticles using plants, Green Chem. 13
376
(2011) 2638-2650.
377
[8] Y. Wang, S. Maksimuk, R. Shen, H Yang, Synthesis of iron oxide nanoparticles
378
using a freshly-made or recycled imidazolium-based ionic liquid, Green Chem. 9
379
(2007) 1051-1056.
380
[9] J.G. Parsons, J.R. Peralt-Videa, J.L.Gar dea-Tor resdey, Use of plants in
381
biotechnology: Synthesis of metal nanoparticles by inactivated plant tissues, plant
382
extracts, and living plant, Developments in Environmental Science. 5 (2007) 463-485.
383
[10] Y. Sun, X. Li, J. Cao, W. Zhang, H. Wang, Characterization of zero-valent iron
384
nanoparticles, Colloid Interface Sci. 120 (2006) 47-56.
385
[11] M.N. Nadagouda, A.B. Castle, R.C. Murdock, S.M. Hussain, R.S. Varma, In vitro
386
biocompatibility of nanoscale zero valent iron particles (NZVI) synthesized using tea
387
polyphenols, Green Chem. 10 (2010) 114-122.
388
[12] R. A. Crane, T.B. Scott, Nanoscale zero-valent iron: Future prospects for an
389
emerging water treatment technology，J. Hazard. Mater. 211–212 (2012) 112–125.
390
[13] E. C. Njagi, H. Huang, L. Stafford, H. Genuino, H. M. Galindo, J. B. Collins, G.
391
E. Hoag, S. L. Suib, Biosynthesis of iron and silver nanoparticles at room temperature
392
using aqueous sorghum bran extracts, Langmuir. 27 (2011) 264-271.
393
[14] V. Smuleac, R. Varma, S. Sikdar, D. Bhattacharyyaa, Green synthesis of Fe and
17
394
Fe/Pd bimetallic nanoparticles in membranes for reductive degradation of chlorinated
395
organics, J. Membr. Sci. 379 (2011) 131-137.
396
[15] T. Shahwan, S. AbuSirriah, M. Nairat, E. Boyac, A.E. Ero ˘glu, T.B. Scott, K.R.
397
Hallam, Green synthesis of iron nanoparticles and their application as a Fenton-like
398
catalyst for the degradation of aqueous cationic and anionic dyes, Chem. Eng. J. 172,
399
(2011) 258-266.
400
[16] G.E. Hoag, J. B. Collins, J. L. Holcomb, J. R. Hoag, M.N. Nadagouda, R. S.
401
Varma, Degradation of bromothymol blue by‘greener’ nano-scale zero-valent iron
402
synthesized using tea polyphenols , J. Mater. Chem. 19 (2009) 8671-8677.
403
[17] Z. Chen, X. Jin, Z. Chen, M. Megharaj, R. Naidu, Removal of methyl orange
404
from aqueous solution using bentonite-supported nanoscale zero-valent iron, J.
405
Colloid Interface Sci. 363 (2011) 601-607.
406
[18] Lanlan Huang, Xiulan Weng, Zuliang Chen, Mallavarapu Megharaj, Ravendra
407
Naidu. Synthesis of iron-based nanoparticles using oolong tea extract for the
408
degradation of malachite green, Spectrochim. Acta, Part A, 117, 3(2014)801-804.
409
[19] Ye Kuang, Qingping Wanga, Zuliang Chen Mallavarapu Megharaj, Ravendra
410
Naidu, Heterogeneous Fenton-like oxidation of monochlorobenzene using green
411
synthesis of iron nanoparticles. J. Colloid Interface Sci., 410(2013) 67-73.
412
[20] M.S. El-Shahawi, A. Hamza, S.O. Bahaffi, A.A. Al-Sibaai, T.N. Abduljabbar
413
Analysis of some selected catechins and caffeine in green tea by high performance
414
liquid chromatography, Food Chem. 134 (2012) 2268–2275
415
[21] M. Colon, C. Nerin, Role of Catechins in the Antioxidant Capacity of an Active
416
Film Containing Green Tea, Green Coffee, and Grapefruit Extracts, J. Agric. Food
417
Chem. 60 (2012) 9842−9849.
418
[22] M. N. Nadagouda and R. S. Varma, Green synthesis of silver and palladium
18
419
nanoparticles at room temperature using coffee and tea extract, Green Chem. 10 10
420
(2008) 859-862.
421
[23] Kesarla Mohan Kumar, Badal Kumar Mandal, Koppala Siva Kumar, Pamanji
422
Sreedhara Reddy, Bojja Sreedhar, Biobased green method to synthesise palladium and
423
iron nanoparticles using Terminalia chebulaaqueous extract, Spectrochim. Acta, Part
424
A, 102 (2013) 128-133.
425
[24] Y. Ju, J. Qiao, X. Peng, Z. Xu, J. Fang, S. Yang, C. Sun, Photodegradation of
426
malachite green using UV–vis light from two microwave-powered electrodeless
427
discharge lamps (MPEDL-2): further investigation on products, dominant routes and
428
mechanism, Chem. Eng. J. (2012), doi: http://dx.doi.org/10.1016/j.cej.2012.06.055.
429
[25] J. Su, S. Lin, Z.Chen, M. Megharaj, R. Naidu, Decolourination of p-chlorophenol
430
from aqueous solution using bentonite-supported Fe/Pd nanoparticles: synthesis,
431
characterization and kinetics, Desalination. 280 (2011) 167-173.
432 433 434 435 436 437 438 439 440 441 442 443
19
444 445
Figure caption
446
Fig. 1 (a) UV-vis spectra of GTE, OTE, BTE.
447
Condition: 0.1mL GTE, OTE, BTE, diluted 50 times
448
Fig. 1 (b) UV-vis spectra of FeSO4, GT-Fe NPs, OT-Fe NPs, BT-Fe NPs.
449
Condition: 0.1 mL FeSO4, GT-Fe, OT-Fe, BT-Fe, diluted 50 times
450
Fig. 1 (c) Degradation of malachite green using different teas
451
Dose: 0.01 g/L GT-Fe, OT-Fe and BT-Fe respectively; initial concentration: 8ml 50
452
mg/L malachite green
453 454
Fig. 2 SEM scanning images of GT-Fe (a) and a typical EDS spectrum of GT-Fe (b);
455
SEM scanning images of OT-Fe (c) and a typical EDS spectrum of GT-Fe (d); SEM
456
scanning images of BT-Fe (e) and a typical EDS spectrum of BT-Fe (f)
457 458
Fig. 3 XRD patterns of GT-Fe (a) OT-Fe (b) and BT-Fe (c)
459 460
Fig. 4 UV-vis scanning images of degradation of malachite green using various
461
materials
462 463
Fig. 5 Degradation of malachite green using GT-Fe (a),OT-Fe (b) and BT-Fe (c) in
464
different temperature.
465
Does: 0.01g/L GT-Fe, OT-Fe and BT-Fe respectively; 8mL 50 mg/L malachite green;
466
rotary speed: 250 rpm; temperature: 283 K, 293 K, 303 K
467 468
20
469 470
0.75
Absorbance (a.u)
a 0.50
GTE OTE BTE
0.25
0.00 200
300
400
500
600
700
800
Wavelength (nm) 0.75
Absorbance (a.u)
b 0.50
FeSO4 GT-Fe NPs OT-Fe NPs BT-Fe NPs
0.25
0.00 200
300
400
500
600
700
800
Removal Efficiency (%)
Wavelength (nm)
c
80
60
40 GT-Fe NPs OT-Fe NPs BT-Fe NPs
20
0 0
10
20
30
40
Time (min)
471 472 473 474
Fig. 1
50
60
21
475 476
477 478 479 480 481 482 483 484
Fig. 2
22
485 486
FeOOH Fe2O3
c FeOOH
Intensity
Fe2O3
Fe3O4
0
Fe
b
FeOOH Fe2O3 Fe3O4
10
20
30
40
0
Fe
a 50
60
70
80
2Theta(degree) 487 488
Fig. 3
3.0
Absorbance (a.u)
2.5 2.0 MG GT-Fe NPs OT-Fe NPs BT-Fe NPs
1.5 1.0 0.5 0.0 200
490
492
400
500
600
Wavelength (nm)
489
491
300
Fig. 4
700
800
23
493 494
a
0.0 -0.1
ln (C/C0)
-0.2 -0.3 -0.4 -0.5
2
288K K=0.028 R =0.929 2 298K K=0.045 R =0.948 2 308K K=0.050 R =0.913
-0.6 0
2
4
6
8
10
T (min)
b
0.0 -0.1
ln (C/C0)
-0.2 -0.3 -0.4 -0.5
288K K=0.030 R2=0.925 298K K=0.057 R2=0.973 308K K=0.052 R2=0.933
-0.6 0
2
4
6
8
10
T (min)
c
0.0 -0.1
ln (C/C0)
-0.2 -0.3 -0.4 2
288K K=0.026 R =0.910 2 298k K=0.031 R =0.941 2 308k K=0.044 R =0.986
-0.5 -0.6 0
2
4
T (min)
495 496 497 498 499 500
Fig. 5
6
8
10
24
501 502 503 504
Table 1 The percentage of various elements in GT-Fe NPs, OT-Fe NPs, BT-Fe NPs examined
505
through EDS
Fe
C
O
S
Al
GT-Fe NPs
16.80
30.65
34.76
3.56
14.23
OT-Fe NPs
10.63
30.86
38.45
4.98
15.09
BT-Fe NPs
7.65
39.16
32.13
3.46
17.60
Percentage (%)
Materials
506 507
25
508 509
510 511 512
Graphical abstract UV-vis images of degradation of malachite green using various Fe NPs
3.0
Absorbance (a.u)
2.5 2.0 MG GT-Fe NPs OT-Fe NPs BT-Fe NPs
1.5 1.0 0.5 0.0 200
513 514
300
400
500
600
Wavelength (nm)
700
800
26
515 516
517
Research highlights 518 519
► Iron nanoparticles (Fe NPs) were synthesized by 3 tea extracts. ► Differences in Fe NPs synthesized were observed by characterization.
520
► The removal of malachite green was 81.2%, 75.6% and 67.1%.
521
► Degradation mechanism of MG using Fe NPs were proposed.
522
