- Email: [email protected]
Facile Green synthesis and characterization of copper nanoparticles by aconitic acid for catalytic reduction of nitrophenols
Journal Pre-proof Facile Green Synthesis and Characterization of Copper Nanoparticles by Aconitic Acid for Catalytic Reduction of Nitrophenols Ke Zhao, Jingyu Wang, Weiteng Kong, Peizhi Zhu
PII:
S2213-3437(19)30640-2
DOI:
https://doi.org/10.1016/j.jece.2019.103517
Reference:
JECE 103517
To appear in:
Journal of Environmental Chemical Engineering
Received Date:
13 October 2019
Revised Date:
30 October 2019
Accepted Date:
2 November 2019
Please cite this article as: Zhao K, Wang J, Kong W, Zhu P, Facile Green Synthesis and Characterization of Copper Nanoparticles by Aconitic Acid for Catalytic Reduction of Nitrophenols, Journal of Environmental Chemical Engineering (2019), doi: https://doi.org/10.1016/j.jece.2019.103517
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier.
Facile Green Synthesis and Characterization of Copper Nanoparticles by Aconitic Acid for Catalytic Reduction of Nitrophenols
Ke Zhao1, Jingyu Wang1, Weiteng Kong1, Peizhi Zhu1,*
1
*
ro of
School of Chemistry and Chemical Engineering, Yangzhou University, 225009 Jiangsu, China
Corresponding author: [email protected]
-p
Abstract：In this study, a simple one-pot green synthesis of stable copper nanoparticles
(CuNPs) using copper (II) chloride (CuCl2, 8.542 g/ L) as copper precursor, aconitic
re
acid (17.411 g/ L) as a reducing agent and pluronic (0.5 g/ L)as a stabilizer was reported. The size, shape, and morphology of the synthesized CuNPs were characterized by high-
lP
resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). HRTEM images revealed that the
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synthesized spherical CuNPs ranged in the size of 3 to 4 nm. These CuNPs were stable and evenly dispersed in aqueous solutions. XRD characterization confirmed the formation of CuNPs. Catalytic degradation activity of these CuNPs were evaluated by the reduction reaction of three nitrophenols (NPs), including 2-nitrophenol (2-NP), 3nitrophenol (3-NP) and 4-nitrophenol (4-NP). CuNPs showed very high catalytic
Jo
efficiency in the reduction for NPs. The mechanism of these catalytic reactions were also discussed.
Keywords: Green synthesis; Copper nanoparticles; Catalytic reduction; Nitrophenol; Kinetics
1. Introduction As a chemical reagent, nitrophenol compounds are widely used in explosives, dyes, pharmaceuticals, indicators, analytical reagents, etc. Most of them are considerably toxic and can penetrate the human body through the skin and then retain, accumulate, ultimately even cause a variety of serious conditions. However, in the presence of catalyst, nitrophenols (NPs) can be reduced to aminophenols (APs), which shows lower toxicity than NPs [1]. Recently, metal/ metal oxide nanoparticles have been found to be excellent materials for catalytic degradation of phenolic compounds (incliding
ro of
nitrophenols), dyes and antibiotics [2-9]. Due to their ultra-fine particle size, copper nanoparticles (CuNPs) have better ductility, higher heat resistance, larger specific surface area, better conductivity and many other superior properties, which had
attracted the attention from researchers in many fields [10, 11]. Currently, chemical
-p
treatment, electrochemical synthesis, photochemical techniques, sonochemical
methods, and thermal treatmenta, are five types of methods for synthesizing CuNPs
re
[12]. Among them, the wet chemical method is a classical chemical treatment, which uses a reducing substance such as sodium borohydride [13], hydrazine [14], 1, 2-
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hexadecanediol [15] and ascorbic acid [16] etc. to reduce copper ions in the solution to obtain size-selectable CuNPs [12].
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In this paper, a convenient chemical reduction method to synthesize CuNPs with low cost, high stability, even distribution and high catalytic activity using aconitic acid as a reducing agent and pluronic as a stabilizer was introduced. 2. Materials and methods
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2.1 Preparation of copper nanoparticles (CuNPs) After 0.8524 g of copper (II) chloride was dissolved in 50 mL deionized water to
form 0.1 mol/L solution, pluronic (0.5 g) was added as a stabilizer. With magnetic stirring at 80oC, 50 mL aconitic acid (1 mol/L) was placed in a constant pressure dropping funnel and then dripped and mixed into the solution. The initial pH of this mixed solution was 1.89, after 9 h of reaction, the pH changed into 1.97, dialysis bags
(MW: 300) was used to dialysis the solution. Finally, the product was centrifuged at 8000 rpm for 10 min to remove precipitate. 2.2 Characterization of CuNPs HRTEM (Tecnai G2 F30 S-TWIN, FEI, US) was choose to characterize the particle distribution, size and morphology of CuNPs. Selected area electron diffraction (SEAD) and energy dispersive X-ray (EDX) detector were used to further characterize the prepared CuNPs. The crystalline phase of the samples was examined by X-ray diffraction
(XRD,
D8
ADVANCE,
Bruker-AXS,
Germany)
with
graphite
ro of
monochromatized Cu Kα radiation operating with 40 kV and 40 mA at room
temperature. Inductive Coupled Plasma Emission Spectrometer ICP-OES, (Optima
7300 DV, PerkinElmer, US) was used to separately analyze the concentrations. And the
-p
absorbance of NPs solutions was recorded by UV-Vis spectrophotometer (Cary 60, Agilent, US), and the differences in concentration could be analyzed accordingly.
re
2.3 Catalytic activity of CuNPs
The concentration of nano-copper colloidal solution in the prepared samples was
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determined by ICP-OES. After that, the colloidal solution was diluted for further utilization. In order to make the UV-vis absorbance in the appropriate range, different concentrations of NPs and CuNPs were used. The actual amount of other reagent for
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each experiment are listed in Table. 1. UV-Vis was used to record the absorbance every 2 min. All of these experiments were carried out at room temperature. Table. 1. The actual amount of reagent for each experiment. C NPs
VNPs
CNaBH4
VNaBH4
CCuNPs
VCuNPs
2-NP 3-NP 4-NP
10 mM 40 mM 2 mM
0.1 mL 0.1 mL 0.1 mL
0.1 M 0.1 M 0.1 M
2 mL 2 mL 2 mL
20 µg/mL 20 µg/mL 1 µg/mL
0.1 mL 0.1 mL 0.1 mL
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NPs
3. Results and discussion As shown by Fig. 1 (a), the HRTEM figures shows that the synthesized CuNPs (the black dots) were well dispersed, after amplification (Fig 1. b), they are clearly observed to have an average diameter of 3-4 nm. The polycrystalline SEAD pattern corresponds to (111), (200), (220) and (311) of the FCC crystal structures of Cu (0).The EDS
spectrum of the CuNPs is presented in Fig. 1 (c). This spectrum exhibited mainly Cu peaks, which provided further evidence for the successful synthesis of the CuNPs. Fig. 1 (d). shows the XRD pattern of CuNPs and all the peaks of CuNPs well matched with the standard copper (PDF 04-0836).The diffraction peaks of the sample were consistent with those of pure copper at 2θ values of 43, 50 and 74, which are indexed to (111), (200) and (220) planes, respectively [17]. The average crystallite size of CuNPs samples calculated using the Debye-Scherrer equation is approximately 3.7 nm, which matched with HRTEM result. The XRD pattern, EDS and SEAD analysis confirmed that the
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synthesized nanoparticles are Cu (0). In addition, since Cu (0) NPs are easily oxidized to Cu+/ Cu2+, and agglomerate into large particles, these characterizations also
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demonstrate that pluronic provides good dispersion and antioxidant protection [18, 19].
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Fig. 1. TEM (a), EDS (b), SEAD images (c), and XRD pattern (d) of synthesized CuNPs. The catalytic reduction of NPs in the presence of an excessive reducing agent can
be easily monitored by UV–Vis spectrophotometry. As NaBH4 was in a greatly excessive concentration which could be considered as constant during the reaction process, the reduction of NPs could be assumed to follow pseudo-first-order kinetics [20-22]. The kinetic equation of this catalytic reaction (including all the following reactions) is given as follows [23, 24]:
ln(𝐶𝑡 ⁄𝐶0 ) = ln(𝐴𝑡 ⁄𝐴0 ) = − 𝑘𝑡
(1)
Where, Ct and C0 are the concentrations of NPs at time t and initial state (t = 0), respectively, and k is the rate constant. The results for the reduction of NPs to APs with CuNPs as catalyst are shown in Fig. 2. The reduction of NPs progressed over time can be monitored by decreasing intensity of absorption peak (415 nm for 2-NP, 390 nm for 3-NP and 400 nm for 4-NP). After the induction time was drawn, three linear graphs were obtained, which showed a good linearity. Therefore, the reduction reaction follows pseudo-first-order rate model, the calculated apparent rate constants (kapp) for the
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reduction of 2-NP, 3-NP and 4-NP are 9.7 ×10-3 min-1, 8.8 × 10-3 min-1 and 9.15 × 10-2 min-1, respectively. A brief comparison with a noble metal catalyst is shown in Table. 2. after converting its data, the Kapp of 4-NP reduction is similar when the amount of
-p
CuNPs are less than one in twenty thousandth of AuNPs. When the amount of CuNPs
are less than one ten thousandth of AgNPs, Kapps of 2-NP and 3-NP reductions
re
catalyzed by AgNPs are only less than 500 times of them catalyzed by CuNPs. Table. 2. Catalytic activity of NPs reduction of other catalysts. CNPs
VNPs
CNaBH4
2-NP
0.1mM
0.5ml
6mM
0.5 ml
AuNPs (0.0145mmol ≈2.86mg)[25]
3.22×10-1min-1
3-NP
0.1mM
0.5ml
6mM
0.5 ml
AuNPs (0.0145mmol ≈2.86mg)[25]
4.4×10-1min-1
0.1mM
0.5ml
6mM
0.5 ml
AuNPs (0.0145mmol ≈2.86mg)[25]
9×10-2min-1
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4-NP
VNaBH4
Catalyst
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NPs
Kapp
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Fig. 2. UV-Vis absorption of 2-NP (a), 3-NP (b) and 4-NP (c) versus time with CuNPs and variation of ln (A/ A0) versus time with linear equation. It was observed that before the reduction reactions, the induction time only existed in 2-NP and 4-NP, but not in 3-NP. A possible mechanism (Langmuir-Hinshelwood mechanism) for metal nanoparticles catalytic degradation of NPs was proposed by Fig.
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3. Wunder et al. [26] and Zhou et al. [27] found out that the time scale of minute magnitude might be related to the dynamic reconstitution process of nanoparticles. It was believed this so-called ‘dynamic reconstitution process’ is the reduction process of nitro group to amino group on the surface of nano-copper. It was well known that the breakage and formation of chemical bonds take much longer time than the adsorption and desorption, and thus the rate-determining step is the breakage and formation of chemical bonds. Therefore, the effect of pushing electron of hydroxyl group increases
the electron density of nitro group on 2-NP and 4-NP, makes it more difficult for negative hydrogen ions to attack the nitro groups, resulting in longer induction time
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than that for 3-NP.
Fig 3. Possible mechanism for catalytic degradation of NPs by CuNPs.
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Good catalytic efficiency can be benefited from the small size and high specific
surface area of CuNPs [28]. The presence of stabilizer allows the nano-copper particles
re
to be disperse evenly in the solution, reduce their aggregation and expose more active sites for NPs adsorption, which also leads to a better catalytic efficiency. It is also worth
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mentioning that the newly synthesized product solution (without dialysis) has higher concentration of CuNPs (about 300mg/L), which can be used as catalyzer directly. The solution can be stored stably for more than 1 month in the case of air isolation. After
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being used as catalyst, CuNPs can be oxidized by air gradually to form precipitate and leave the solution. After being filtered, it can be reused as raw material.
4. Conclusions
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In this work, an environmental-friendly and cost-effective chemical reduction
method was developed to synthesize CuNPs for the first time by using copper (II) chloride and aconitic acid as raw materials and water as an environmental-friendly solvent. HRTEM images showed that the synthesized CuNPs had uniform particle size and high dispersion with particle size of about 3-4 nm.These CuNPs also showed superior catalytic activities for the reduction of NPs, even at an extreme low concentration.
Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
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Acknowledgements
This research was funded by Technology Support Program of Science and
Technology Department of Jiangsu Province (BE2017689), Technology Support
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Program of Science and Technology Department of Yangzhou City (YZ2018084).
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[24] F.L. Xia, X.Y. Xu, X.C. Li, L. Zhang, L. Zhang, H.X. Qiu, W. Wang, Y. Liu, J.P. Gao, Preparation of Bismuth Nanoparticles in Aqueous Solution and Its Catalytic Performance for the Reduction of 4-Nitrophenol, Ind Eng Chem Res 53(26) (2014) 10576-10582.doi:10.1021/ie501142a. [25] W. Shen, Y. Qu, X. Pei, X. Zhang, Q. Ma, Z. Zhang, S. Li, J. Zhou, Green synthesis of gold nanoparticles by a newly isolated strain Trichosporon montevideense for catalytic hydrogenation of nitroaromatics, Biotechnology Letters 38(9) (2016) 1503-1508.doi:10.1007/s10529-016-2120-5. [26] A.D. Verma, R.K. Mandal, I. Sinha, Kinetics of p-Nitrophenol Reduction Catalyzed by PVP Stabilized Copper Nanoparticles, Catal Lett 145(10) (2015) 1885-1892.doi:10.1007/s10562-015-1605-5.
[27] X.C. Zhou, W.L. Xu, G.K. Liu, D. Panda, P. Chen, Size-Dependent Catalytic Activity and Dynamics of Gold Nanoparticles at the Single-Molecule Level, J Am Chem Soc 132(1) (2010) 138146.doi:10.1021/ja904307n. [28] G.W. Zhan, Synthetic architecture of integrated nanocatalysts with controlled spatial distribution of
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PII:
S2213-3437(19)30640-2
DOI:
https://doi.org/10.1016/j.jece.2019.103517
Reference:
JECE 103517
To appear in:
Journal of Environmental Chemical Engineering
Received Date:
13 October 2019
Revised Date:
30 October 2019
Accepted Date:
2 November 2019
Please cite this article as: Zhao K, Wang J, Kong W, Zhu P, Facile Green Synthesis and Characterization of Copper Nanoparticles by Aconitic Acid for Catalytic Reduction of Nitrophenols, Journal of Environmental Chemical Engineering (2019), doi: https://doi.org/10.1016/j.jece.2019.103517
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier.
Facile Green Synthesis and Characterization of Copper Nanoparticles by Aconitic Acid for Catalytic Reduction of Nitrophenols
Ke Zhao1, Jingyu Wang1, Weiteng Kong1, Peizhi Zhu1,*
1
*
ro of
School of Chemistry and Chemical Engineering, Yangzhou University, 225009 Jiangsu, China
Corresponding author: [email protected]
-p
Abstract：In this study, a simple one-pot green synthesis of stable copper nanoparticles
(CuNPs) using copper (II) chloride (CuCl2, 8.542 g/ L) as copper precursor, aconitic
re
acid (17.411 g/ L) as a reducing agent and pluronic (0.5 g/ L)as a stabilizer was reported. The size, shape, and morphology of the synthesized CuNPs were characterized by high-
lP
resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). HRTEM images revealed that the
ur na
synthesized spherical CuNPs ranged in the size of 3 to 4 nm. These CuNPs were stable and evenly dispersed in aqueous solutions. XRD characterization confirmed the formation of CuNPs. Catalytic degradation activity of these CuNPs were evaluated by the reduction reaction of three nitrophenols (NPs), including 2-nitrophenol (2-NP), 3nitrophenol (3-NP) and 4-nitrophenol (4-NP). CuNPs showed very high catalytic
Jo
efficiency in the reduction for NPs. The mechanism of these catalytic reactions were also discussed.
Keywords: Green synthesis; Copper nanoparticles; Catalytic reduction; Nitrophenol; Kinetics
1. Introduction As a chemical reagent, nitrophenol compounds are widely used in explosives, dyes, pharmaceuticals, indicators, analytical reagents, etc. Most of them are considerably toxic and can penetrate the human body through the skin and then retain, accumulate, ultimately even cause a variety of serious conditions. However, in the presence of catalyst, nitrophenols (NPs) can be reduced to aminophenols (APs), which shows lower toxicity than NPs [1]. Recently, metal/ metal oxide nanoparticles have been found to be excellent materials for catalytic degradation of phenolic compounds (incliding
ro of
nitrophenols), dyes and antibiotics [2-9]. Due to their ultra-fine particle size, copper nanoparticles (CuNPs) have better ductility, higher heat resistance, larger specific surface area, better conductivity and many other superior properties, which had
attracted the attention from researchers in many fields [10, 11]. Currently, chemical
-p
treatment, electrochemical synthesis, photochemical techniques, sonochemical
methods, and thermal treatmenta, are five types of methods for synthesizing CuNPs
re
[12]. Among them, the wet chemical method is a classical chemical treatment, which uses a reducing substance such as sodium borohydride [13], hydrazine [14], 1, 2-
lP
hexadecanediol [15] and ascorbic acid [16] etc. to reduce copper ions in the solution to obtain size-selectable CuNPs [12].
ur na
In this paper, a convenient chemical reduction method to synthesize CuNPs with low cost, high stability, even distribution and high catalytic activity using aconitic acid as a reducing agent and pluronic as a stabilizer was introduced. 2. Materials and methods
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2.1 Preparation of copper nanoparticles (CuNPs) After 0.8524 g of copper (II) chloride was dissolved in 50 mL deionized water to
form 0.1 mol/L solution, pluronic (0.5 g) was added as a stabilizer. With magnetic stirring at 80oC, 50 mL aconitic acid (1 mol/L) was placed in a constant pressure dropping funnel and then dripped and mixed into the solution. The initial pH of this mixed solution was 1.89, after 9 h of reaction, the pH changed into 1.97, dialysis bags
(MW: 300) was used to dialysis the solution. Finally, the product was centrifuged at 8000 rpm for 10 min to remove precipitate. 2.2 Characterization of CuNPs HRTEM (Tecnai G2 F30 S-TWIN, FEI, US) was choose to characterize the particle distribution, size and morphology of CuNPs. Selected area electron diffraction (SEAD) and energy dispersive X-ray (EDX) detector were used to further characterize the prepared CuNPs. The crystalline phase of the samples was examined by X-ray diffraction
(XRD,
D8
ADVANCE,
Bruker-AXS,
Germany)
with
graphite
ro of
monochromatized Cu Kα radiation operating with 40 kV and 40 mA at room
temperature. Inductive Coupled Plasma Emission Spectrometer ICP-OES, (Optima
7300 DV, PerkinElmer, US) was used to separately analyze the concentrations. And the
-p
absorbance of NPs solutions was recorded by UV-Vis spectrophotometer (Cary 60, Agilent, US), and the differences in concentration could be analyzed accordingly.
re
2.3 Catalytic activity of CuNPs
The concentration of nano-copper colloidal solution in the prepared samples was
lP
determined by ICP-OES. After that, the colloidal solution was diluted for further utilization. In order to make the UV-vis absorbance in the appropriate range, different concentrations of NPs and CuNPs were used. The actual amount of other reagent for
ur na
each experiment are listed in Table. 1. UV-Vis was used to record the absorbance every 2 min. All of these experiments were carried out at room temperature. Table. 1. The actual amount of reagent for each experiment. C NPs
VNPs
CNaBH4
VNaBH4
CCuNPs
VCuNPs
2-NP 3-NP 4-NP
10 mM 40 mM 2 mM
0.1 mL 0.1 mL 0.1 mL
0.1 M 0.1 M 0.1 M
2 mL 2 mL 2 mL
20 µg/mL 20 µg/mL 1 µg/mL
0.1 mL 0.1 mL 0.1 mL
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NPs
3. Results and discussion As shown by Fig. 1 (a), the HRTEM figures shows that the synthesized CuNPs (the black dots) were well dispersed, after amplification (Fig 1. b), they are clearly observed to have an average diameter of 3-4 nm. The polycrystalline SEAD pattern corresponds to (111), (200), (220) and (311) of the FCC crystal structures of Cu (0).The EDS
spectrum of the CuNPs is presented in Fig. 1 (c). This spectrum exhibited mainly Cu peaks, which provided further evidence for the successful synthesis of the CuNPs. Fig. 1 (d). shows the XRD pattern of CuNPs and all the peaks of CuNPs well matched with the standard copper (PDF 04-0836).The diffraction peaks of the sample were consistent with those of pure copper at 2θ values of 43, 50 and 74, which are indexed to (111), (200) and (220) planes, respectively [17]. The average crystallite size of CuNPs samples calculated using the Debye-Scherrer equation is approximately 3.7 nm, which matched with HRTEM result. The XRD pattern, EDS and SEAD analysis confirmed that the
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synthesized nanoparticles are Cu (0). In addition, since Cu (0) NPs are easily oxidized to Cu+/ Cu2+, and agglomerate into large particles, these characterizations also
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demonstrate that pluronic provides good dispersion and antioxidant protection [18, 19].
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Fig. 1. TEM (a), EDS (b), SEAD images (c), and XRD pattern (d) of synthesized CuNPs. The catalytic reduction of NPs in the presence of an excessive reducing agent can
be easily monitored by UV–Vis spectrophotometry. As NaBH4 was in a greatly excessive concentration which could be considered as constant during the reaction process, the reduction of NPs could be assumed to follow pseudo-first-order kinetics [20-22]. The kinetic equation of this catalytic reaction (including all the following reactions) is given as follows [23, 24]:
ln(𝐶𝑡 ⁄𝐶0 ) = ln(𝐴𝑡 ⁄𝐴0 ) = − 𝑘𝑡
(1)
Where, Ct and C0 are the concentrations of NPs at time t and initial state (t = 0), respectively, and k is the rate constant. The results for the reduction of NPs to APs with CuNPs as catalyst are shown in Fig. 2. The reduction of NPs progressed over time can be monitored by decreasing intensity of absorption peak (415 nm for 2-NP, 390 nm for 3-NP and 400 nm for 4-NP). After the induction time was drawn, three linear graphs were obtained, which showed a good linearity. Therefore, the reduction reaction follows pseudo-first-order rate model, the calculated apparent rate constants (kapp) for the
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reduction of 2-NP, 3-NP and 4-NP are 9.7 ×10-3 min-1, 8.8 × 10-3 min-1 and 9.15 × 10-2 min-1, respectively. A brief comparison with a noble metal catalyst is shown in Table. 2. after converting its data, the Kapp of 4-NP reduction is similar when the amount of
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CuNPs are less than one in twenty thousandth of AuNPs. When the amount of CuNPs
are less than one ten thousandth of AgNPs, Kapps of 2-NP and 3-NP reductions
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catalyzed by AgNPs are only less than 500 times of them catalyzed by CuNPs. Table. 2. Catalytic activity of NPs reduction of other catalysts. CNPs
VNPs
CNaBH4
2-NP
0.1mM
0.5ml
6mM
0.5 ml
AuNPs (0.0145mmol ≈2.86mg)[25]
3.22×10-1min-1
3-NP
0.1mM
0.5ml
6mM
0.5 ml
AuNPs (0.0145mmol ≈2.86mg)[25]
4.4×10-1min-1
0.1mM
0.5ml
6mM
0.5 ml
AuNPs (0.0145mmol ≈2.86mg)[25]
9×10-2min-1
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4-NP
VNaBH4
Catalyst
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NPs
Kapp
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Fig. 2. UV-Vis absorption of 2-NP (a), 3-NP (b) and 4-NP (c) versus time with CuNPs and variation of ln (A/ A0) versus time with linear equation. It was observed that before the reduction reactions, the induction time only existed in 2-NP and 4-NP, but not in 3-NP. A possible mechanism (Langmuir-Hinshelwood mechanism) for metal nanoparticles catalytic degradation of NPs was proposed by Fig.
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3. Wunder et al. [26] and Zhou et al. [27] found out that the time scale of minute magnitude might be related to the dynamic reconstitution process of nanoparticles. It was believed this so-called ‘dynamic reconstitution process’ is the reduction process of nitro group to amino group on the surface of nano-copper. It was well known that the breakage and formation of chemical bonds take much longer time than the adsorption and desorption, and thus the rate-determining step is the breakage and formation of chemical bonds. Therefore, the effect of pushing electron of hydroxyl group increases
the electron density of nitro group on 2-NP and 4-NP, makes it more difficult for negative hydrogen ions to attack the nitro groups, resulting in longer induction time
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than that for 3-NP.
Fig 3. Possible mechanism for catalytic degradation of NPs by CuNPs.
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Good catalytic efficiency can be benefited from the small size and high specific
surface area of CuNPs [28]. The presence of stabilizer allows the nano-copper particles
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to be disperse evenly in the solution, reduce their aggregation and expose more active sites for NPs adsorption, which also leads to a better catalytic efficiency. It is also worth
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mentioning that the newly synthesized product solution (without dialysis) has higher concentration of CuNPs (about 300mg/L), which can be used as catalyzer directly. The solution can be stored stably for more than 1 month in the case of air isolation. After
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being used as catalyst, CuNPs can be oxidized by air gradually to form precipitate and leave the solution. After being filtered, it can be reused as raw material.
4. Conclusions
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In this work, an environmental-friendly and cost-effective chemical reduction
method was developed to synthesize CuNPs for the first time by using copper (II) chloride and aconitic acid as raw materials and water as an environmental-friendly solvent. HRTEM images showed that the synthesized CuNPs had uniform particle size and high dispersion with particle size of about 3-4 nm.These CuNPs also showed superior catalytic activities for the reduction of NPs, even at an extreme low concentration.
Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
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Acknowledgements
This research was funded by Technology Support Program of Science and
Technology Department of Jiangsu Province (BE2017689), Technology Support
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Program of Science and Technology Department of Yangzhou City (YZ2018084).
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