- Email: [email protected]
Green synthesis of 2D CuO nanoleaves (NLs) and its application for the reduction of p-nitrophenol
Author’s Accepted Manuscript Green synthesis of 2D CuO nanoleaves (NLs) and its application for the reduction of p-nitrophenol Archita Bhattacharjee, M. Ahmaruzzaman
www.elsevier.com
PII: DOI: Reference:
S0167-577X(15)30417-1 http://dx.doi.org/10.1016/j.matlet.2015.08.061 MLBLUE19422
To appear in: Materials Letters Received date: 23 May 2015 Accepted date: 12 August 2015 Cite this article as: Archita Bhattacharjee and M. Ahmaruzzaman, Green synthesis of 2D CuO nanoleaves (NLs) and its application for the reduction of pnitrophenol, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2015.08.061 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 galley proof before it is published in its final citable 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.
Green Synthesis of 2D CuO nanoleaves (NLs) and its application for the reduction of pnitrophenol Archita Bhattacharjee, M. Ahmaruzzaman* Department of Chemistry National Institute of Technology, Silchar-788010, Assam, India ABSTRACT This article reports green synthesis of 2D CuO nanoleaves (NLs) using the amino acid serine and NaOH by microwave heating method. The aminoacid acts as a complexing/capping agent in the synthesis of CuO NLs. This method results in the formation of self assembled 2D CuO NLs having an average length and width of ~400nm and ~86nm respectively. 2D CuO NLs are composed of CuO primary single crystal nanoparticles. CuO NLs were characterized by XRD, TEM, SAED and FTIR and UV-visible spectroscopy. The CuO NLs act as an efficient catalyst in the conversion of 4-nitrophenol to 4aminophenol in aqueous medium. Keywords: CuO NLs, nanoparticles, microwave, nanocrystalline materials, X-ray techniques, Spectroscopy. * Corresponding author: [email protected] (M. Ahmaruzzaman) 1. INTRODUCTION CuO is a p-type semiconductor with a narrow band gap of ~1.2eV [1]. CuO nanoparticles are of great interest due to their potential applications in wide range of areas including semiconductors, catalysis, field emitters, and batteries [1-3]. Numerous methods were used to synthesize CuO nanostructures [1, 4-6] and many efforts were devoted for the fabrication of CuO nanostructures with different morphologies to enhance their existing applications. Among the various methods, microwave heating method provides a more convenient, energy saving, environmentally benign route because of shorter reaction time, good control over particle size and uniform nucleation of powders in suspension. This article reports a green microwave synthesis of CuO NLs using environmentally benign reactants namely serine and NaOH in aqueous medium. Herein, we developed a green synthesis of CuO NLs using NaOH and serine, which acts as a good complexing and capping agent. The presence of aminoacid also influences the size and morphology of CuO nanoparticles. Nanoparticles were employed as a catalyst in the synthesis of essential organic compounds and it converts hazardous compounds into useful, non-toxic compounds. 4-AP is an important intermediate in the synthesis of various analgesic and antipyretic drugs, such as paracetamol, acetanilide and phenacitin. It has enormous applications in the synthesis of various 1
dyes, as photographic-developer, corrosion inhibitor [7-8]. Hence, synthesis of 4-AP from 4-NP by a cheaper and effective method is always desirable. Hence, we design the conversion of 4-NP to 4-AP using metal-oxide nanoparticles (CuO NLs) as catalyst in presence of NaBH4 as reducing agent in aqueous medium. 2. EXPERIMENTAL Materials and Method: All the reagents, CuSO4.5H2O, NaOH, serine, 4-nitrophenol and NaBH4 were procured from Merck and analytical grade (AR). The reaction was carried out in a domestic microwave oven. CuO NLs were synthesized using aqueous solution of CuSO4.5H2O, serine and NaOH. A total of 50ml of 0.01M aqueous solution of serine was added slowly to 50ml, 0.01M solution of CuSO4.5H2O under vigorous stirring. To the above mixture, 50ml of 0.05M NaOH solution was added under constant stirring. The reaction mixture was then kept in a microwave oven and irradiated with thirty 10s shots. This resulted in the formation of black precipitate. The precipitate obtained was centrifuged and washed five times with distilled water. The final product was dried at 100oC and collected for characterization. CuO NLs were characterized by powder XRD method using Phillips X’Pert PRO diffractometer with CuKα radiation of wavelength 1.5418Å. The size, morphology and diffracted ring pattern of CuO nanoleaves were determined by JEM-2100 Transmission Electron Microscope. Infrared spectrum was recorded by Bruker Hyperion 3000 FTIR spectrometer. Absorption spectra were recorded on Cary 100 BIO UV-visible spectrophotometer. Catalytic activity of synthesized CuO NLs in the reduction of 4-nitro phenol: The conversion of 4-nitrophenol (4-NP) to 4-amino phenol (4-AP) was carried out in a standard quartz cuvette using aqueous solution of NaBH4 at room temperature in presence of CuO NLs as catalyst. The progress of the reaction was monitored by UV-visible spectroscopy. In the cuvette, 2.6ml of water and 60µl of 0.006M 4-NP were taken separately and the absorbance was recorded using UV-visible spectrometer. To the above solution, 300µl of 0.1M aqueous solution of NaBH4 was added and the absorbance was recorded. Now, 300µl aqueous solution of CuO NLs (0.001g) was added to the reaction mixture and UV-visible absorption spectra were recorded till the peak due to the presence of nitro group disappeared completely. 3. RESULTS AND DISCUSSION In this experiment, serine acts as a complexing as well as capping agent in the synthesis of CuO NLs. Initially, serine forms complex with Cu2+ ions. On treatment with NaOH, the complex breaks down to form Cu(OH)2 which on further heat
2
treatment (100oC) decomposes to form CuO NLs. After the decomposition of Cu2+-serine complex, some molecules of serine gets adsorbed on the surface of CuO NLs and thereby acts as a capping agent [9].
CuSO4 + Serine
[Cu2+- serine]
NaOH
Formationof deep blue coloured complex
Immediate formation of Cu(OH)2 nuclei Formation of individual leaf-like structure on heating at 100oC
Formation of 2D CuO nanoleaves
Fig. 1a represents the FTIR spectrum of CuO NLs. The peaks at 426, 546 and 597cm-1 correspond to characteristic stretching vibration of Cu-O bond in monoclinic CuO [3, 6]. FTIR spectrum was recorded not only to detect the formation of CuO NLs but also to perceive the presence of capping agent. The bands around 3424 and 1600cm-1 indicate the presence of N-H and – COO group of serine adsorbed on the surface of CuO NLs. The peaks around 2924 and 2855cm-1 is due to C-H asymmetric and symmetric stretch which further confirms that serine acts as a capping agent in the synthesis of CuO NLs. The crystal structure, purity and crystalline nature of CuO nanoparticles were investigated by XRD pattern (Fig. 1b). The peaks obtained were well indexed to the single-phase CuO with a monoclinic structure. The diffraction pattern was in good agreement with the JCPDS card of CuO (JCPDS 05-0661) [1]. No peaks of impurity were detected in the XRD pattern. The XRD pattern also depicts the highly crystalline nature of CuO NLs. To investigate the optical properties of CuO NLs absorption spectrum was recorded (Fig. 1c). UV-visible spectra of synthesized CuO NLs showed a broad absorption band around 385nm because of surface plasmon absorption of metal oxide [10, 3]. The optical band gap of CuO NLs can be obtained by using the equation: α(ν) hν = K (hν-Eg)n, where K is a constant and Eg is the band gap energy. The exponent ‘n’ depends on the type of transition. In this case, value of n is ½ for allowed direct transition [1, 3]. The Fig. 1(c) depicts the plot of (αhν)2 versus (hν) for CuO NLs. From this figure, band gap energy is calculated by extrapolating the curve to zero absorption co-efficient and found to be 2.3eV. A significant blue shift was observed in the band gap energy of synthesized CuO NLs from bulk CuO (1.2eV) due to quantum confinement effect.
3
The morphology and size distribution of synthesized CuO nanoparticles were analyzed by TEM and HRTEM images (Fig. 2a, 2b). TEM image (Fig. 2a) showed the 2D leaf-like morphology of synthesized CuO nanoparticles with dimensions of ~400nm in length and and ~86nm in width. The Fig. 2a represents the magnified TEM image of CuO NLs. The primary crystals of CuO self assembled to form the 2D leaf–like structure. The spacing between two adjacent lattice planes obtained from HRTEM image (Fig. 2b) is 0.18 nm which corresponds to interplanar separation of (
) lattice plane of standard
CuO nanoparticles. The SAED pattern (Fig. 2c) of synthesized CuO NLs depicts the monoclinic structure of CuO (JCPDS 05-0661) and resemblance with the XRD pattern of the synthesized CuO NLs [1]. The SAED pattern reveals that the particles resemble to a certain degree with that of single crystal. The elongated spots indicate the near perfect alignment of primary crystals within each particle. The catalytic efficiency of CuO NLs were investigated by carrying out reduction of 4-NP to 4-AP in aqueous medium using NaBH4. It is evident from UV-visible spectra that 4-NP has a maximum absorbance at 317nm in aqueous medium (Fig. A1; Supporting Information). The subsequent addition of freshly prepared NaBH4 solution to 4-NP leads to a red shift from 317 to 403nm (Fig. A2; Supporting Information). It is also observed that light yellow color of 4-NP solution changes to intense yellow due to the formation of 4-nitrophenolate ions under alkaline condition [7]. The peak obtained at 403nm is unaltered after a couple of days in absence of any catalyst. The yellow color of 4-NP solution slowly faded after the addition of 300µl of 0.001g of CuO NLs and finally disappeared on complete reduction of 4-NP. This decolorization was monitored by UV-visible spectroscopy at a regular interval of time. Fig. 3(a) shows the UV-visible spectra for the reduction of 4-NP. From Fig. 3(a) it is evident that with an increase in time the characteristic peak for 4-NP decreases with simultaneous appearance of a new peak centered at 297nm. This is due to the reduction of 4-NP to 4-AP. The peak at 297nm increases gradually with time due to the formation of 4-AP [7]. The complete reduction of 4-NP takes place within 15min. Hence, CuO NPs act as an efficient catalyst in the reduction of 4-NP in presence of NaBH4. The rate constant (k) has been determined following first order kinetics [7] from linear plot of ln[At] versus reduction time and found to be 2.2×10-2 min-1 (Fig. 3b). About 97% of 4-NP get reduced to 4-AP within 15min. 4. CONCLUSION This communication briefly describes a facile, cost-effective, green synthesis of CuO NLs using serine and NaOH by microwave heating method. TEM images reveal the formation of self assembled 2D CuO NLs having dimension of ~400nm in length and ~86nm in width. The SAED pattern of CuO NLs depicts the monoclinic structure of CuO which is also in resemblance with the XRD pattern of CuO NLs. The SAED pattern indicates that the particles resemble to a certain degree
4
with that of single crystal. A significant blue shift was observed in the band gap of CuO NLs (2.3eV) due to quantum effect. The synthesized CuO NLs also act as an efficient catalyst in the conversion of 4-NP to 4-AP in aqueous medium. • Supplementary Information: Mechanism of reduction of 4-NP is provided in Supplementary Information. References: 1.
Chen H, Jhao G, Liu Y. Mater Lett 2013; 93:60-3
2.
Hong ZS, Cao Y, Deng JF. Mater Lett 2002;52:34-8
3.
Wang TX, Xu SH, Yang FX. Powder Technol 2012;228:128-30
4.
Cheng Z, Xu J, Zhong H, Chu X, Song J. Mater Lett 2011;65:2047-50
5.
Qin H, Zhang Z, Liu X, Zhang Y, Hu J. J Magn Magn Mater 2010;322:1994-8
6.
Yang C, Su X, Wang J, Cao X, Wang S, Zhang L. Sens Actuators B 2013;185:159-65
7.
Mandlimath TR, Gopal B. J Mol Catal A: Chem 2011;350:9-15
8.
Saha S, Pal A, Kundu S, Basu S, Pal T. Langmuir 2010;26:2885-93
9.
Srestha KM, Sorensen CM, Klabunde KJ. J Phys Chem. C 2010;114:14368-76
10. Das D, Nath BC, Phukon P, Dolui SK. Colloids Surf. B 2013;101:430-3 Figures: 1. Figure 1. (a) FT-IR spectrum of CuO NLs; (b) XRD pattern of CuO NLs; (c) Absorption spectrum of CuO NLs (upper right inset represents the corresponding plot of (αhν)2 versus photon energy, hν) 2. Figure 2. (a) TEM microphotograph of CuO NLs (upper right inset represents the magnified TEM image of CuO NLs), (b) HRTEM image of CuO NPs, (c) SAED pattern of CuO NLs 3. Figure 3. (a) Absorption spectra of conversion of 4-NP to 4-AP using CuO NLs as catalyst in presence of NaBH4 in aqueous medium, (b) Plot of ln[At] versus reduction time.
(a)
5
0.8
Absorbance (a.u.)
Intensity (a.u.)
(202) (110)
(113) (220) (202) (311) (311)
1.00E+009
0.6
8.00E+008 6.00E+008 4.00E+008
0.5
2.00E+008 0.00E+000 0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
hν
0.4
(112) (222)
(112) 30
1.20E+009
0.7
(020)
20
1.40E+009
(c)
(111) (111) (002) (200)
(α h ν ) 2
(b)
40
50
60
70
0.3 80
200
o
2θ ( )
300
400
500
600
700
800
Wavelength (nm)
Figure 1. (a) FT-IR spectrum, (b) XRD pattern, (c) Absorption spectrum of CuO NLs (upper right inset represents the corresponding plot of (αhν)2 versus photon energy (hν)
Figure 2. (a) TEM microphotograph of CuO NLs (upper right inset represents the magnified TEM image of CuO NLs)
Figure 2. (b) HRTEM image, (c) SAED pattern of CuO NLs 6
2.5
0m 3m 6m 9m 12 m 15 m
Absorption (a.u.)
2.0
1.5
1.0
0.5
0.0 200
300
400
500
600
Wavelength (nm)
Figure 3. (a) Absorption spectra of conversion of 4-NP to 4-AP using CuO NLs as catalyst in presence of NaBH4 in aqueous medium
1.0 0.5
ln At
0.0 -0.5 -1.0 -1.5 -2.0 -2.5 -2
0
2
4
6
8
10
12
14
16
Time (min)
Figure 3(b) Plot of ln[At] versus time required for the reduction of 4-NP
7
Highlights: 1. Development of a facile, cost-effective, green synthesis of 2D CuO nanoleaves 2. Design of microwave heating method using serine acting as complexing/capping agent 3. Formation of single crystalline 2D CuO NLs having 400nm length and 86nm width 4. 2D CuO NLs act as an efficient catalyst in the conversion of 4-NP to 4-AP
8
www.elsevier.com
PII: DOI: Reference:
S0167-577X(15)30417-1 http://dx.doi.org/10.1016/j.matlet.2015.08.061 MLBLUE19422
To appear in: Materials Letters Received date: 23 May 2015 Accepted date: 12 August 2015 Cite this article as: Archita Bhattacharjee and M. Ahmaruzzaman, Green synthesis of 2D CuO nanoleaves (NLs) and its application for the reduction of pnitrophenol, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2015.08.061 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 galley proof before it is published in its final citable 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.
Green Synthesis of 2D CuO nanoleaves (NLs) and its application for the reduction of pnitrophenol Archita Bhattacharjee, M. Ahmaruzzaman* Department of Chemistry National Institute of Technology, Silchar-788010, Assam, India ABSTRACT This article reports green synthesis of 2D CuO nanoleaves (NLs) using the amino acid serine and NaOH by microwave heating method. The aminoacid acts as a complexing/capping agent in the synthesis of CuO NLs. This method results in the formation of self assembled 2D CuO NLs having an average length and width of ~400nm and ~86nm respectively. 2D CuO NLs are composed of CuO primary single crystal nanoparticles. CuO NLs were characterized by XRD, TEM, SAED and FTIR and UV-visible spectroscopy. The CuO NLs act as an efficient catalyst in the conversion of 4-nitrophenol to 4aminophenol in aqueous medium. Keywords: CuO NLs, nanoparticles, microwave, nanocrystalline materials, X-ray techniques, Spectroscopy. * Corresponding author: [email protected] (M. Ahmaruzzaman) 1. INTRODUCTION CuO is a p-type semiconductor with a narrow band gap of ~1.2eV [1]. CuO nanoparticles are of great interest due to their potential applications in wide range of areas including semiconductors, catalysis, field emitters, and batteries [1-3]. Numerous methods were used to synthesize CuO nanostructures [1, 4-6] and many efforts were devoted for the fabrication of CuO nanostructures with different morphologies to enhance their existing applications. Among the various methods, microwave heating method provides a more convenient, energy saving, environmentally benign route because of shorter reaction time, good control over particle size and uniform nucleation of powders in suspension. This article reports a green microwave synthesis of CuO NLs using environmentally benign reactants namely serine and NaOH in aqueous medium. Herein, we developed a green synthesis of CuO NLs using NaOH and serine, which acts as a good complexing and capping agent. The presence of aminoacid also influences the size and morphology of CuO nanoparticles. Nanoparticles were employed as a catalyst in the synthesis of essential organic compounds and it converts hazardous compounds into useful, non-toxic compounds. 4-AP is an important intermediate in the synthesis of various analgesic and antipyretic drugs, such as paracetamol, acetanilide and phenacitin. It has enormous applications in the synthesis of various 1
dyes, as photographic-developer, corrosion inhibitor [7-8]. Hence, synthesis of 4-AP from 4-NP by a cheaper and effective method is always desirable. Hence, we design the conversion of 4-NP to 4-AP using metal-oxide nanoparticles (CuO NLs) as catalyst in presence of NaBH4 as reducing agent in aqueous medium. 2. EXPERIMENTAL Materials and Method: All the reagents, CuSO4.5H2O, NaOH, serine, 4-nitrophenol and NaBH4 were procured from Merck and analytical grade (AR). The reaction was carried out in a domestic microwave oven. CuO NLs were synthesized using aqueous solution of CuSO4.5H2O, serine and NaOH. A total of 50ml of 0.01M aqueous solution of serine was added slowly to 50ml, 0.01M solution of CuSO4.5H2O under vigorous stirring. To the above mixture, 50ml of 0.05M NaOH solution was added under constant stirring. The reaction mixture was then kept in a microwave oven and irradiated with thirty 10s shots. This resulted in the formation of black precipitate. The precipitate obtained was centrifuged and washed five times with distilled water. The final product was dried at 100oC and collected for characterization. CuO NLs were characterized by powder XRD method using Phillips X’Pert PRO diffractometer with CuKα radiation of wavelength 1.5418Å. The size, morphology and diffracted ring pattern of CuO nanoleaves were determined by JEM-2100 Transmission Electron Microscope. Infrared spectrum was recorded by Bruker Hyperion 3000 FTIR spectrometer. Absorption spectra were recorded on Cary 100 BIO UV-visible spectrophotometer. Catalytic activity of synthesized CuO NLs in the reduction of 4-nitro phenol: The conversion of 4-nitrophenol (4-NP) to 4-amino phenol (4-AP) was carried out in a standard quartz cuvette using aqueous solution of NaBH4 at room temperature in presence of CuO NLs as catalyst. The progress of the reaction was monitored by UV-visible spectroscopy. In the cuvette, 2.6ml of water and 60µl of 0.006M 4-NP were taken separately and the absorbance was recorded using UV-visible spectrometer. To the above solution, 300µl of 0.1M aqueous solution of NaBH4 was added and the absorbance was recorded. Now, 300µl aqueous solution of CuO NLs (0.001g) was added to the reaction mixture and UV-visible absorption spectra were recorded till the peak due to the presence of nitro group disappeared completely. 3. RESULTS AND DISCUSSION In this experiment, serine acts as a complexing as well as capping agent in the synthesis of CuO NLs. Initially, serine forms complex with Cu2+ ions. On treatment with NaOH, the complex breaks down to form Cu(OH)2 which on further heat
2
treatment (100oC) decomposes to form CuO NLs. After the decomposition of Cu2+-serine complex, some molecules of serine gets adsorbed on the surface of CuO NLs and thereby acts as a capping agent [9].
CuSO4 + Serine
[Cu2+- serine]
NaOH
Formationof deep blue coloured complex
Immediate formation of Cu(OH)2 nuclei Formation of individual leaf-like structure on heating at 100oC
Formation of 2D CuO nanoleaves
Fig. 1a represents the FTIR spectrum of CuO NLs. The peaks at 426, 546 and 597cm-1 correspond to characteristic stretching vibration of Cu-O bond in monoclinic CuO [3, 6]. FTIR spectrum was recorded not only to detect the formation of CuO NLs but also to perceive the presence of capping agent. The bands around 3424 and 1600cm-1 indicate the presence of N-H and – COO group of serine adsorbed on the surface of CuO NLs. The peaks around 2924 and 2855cm-1 is due to C-H asymmetric and symmetric stretch which further confirms that serine acts as a capping agent in the synthesis of CuO NLs. The crystal structure, purity and crystalline nature of CuO nanoparticles were investigated by XRD pattern (Fig. 1b). The peaks obtained were well indexed to the single-phase CuO with a monoclinic structure. The diffraction pattern was in good agreement with the JCPDS card of CuO (JCPDS 05-0661) [1]. No peaks of impurity were detected in the XRD pattern. The XRD pattern also depicts the highly crystalline nature of CuO NLs. To investigate the optical properties of CuO NLs absorption spectrum was recorded (Fig. 1c). UV-visible spectra of synthesized CuO NLs showed a broad absorption band around 385nm because of surface plasmon absorption of metal oxide [10, 3]. The optical band gap of CuO NLs can be obtained by using the equation: α(ν) hν = K (hν-Eg)n, where K is a constant and Eg is the band gap energy. The exponent ‘n’ depends on the type of transition. In this case, value of n is ½ for allowed direct transition [1, 3]. The Fig. 1(c) depicts the plot of (αhν)2 versus (hν) for CuO NLs. From this figure, band gap energy is calculated by extrapolating the curve to zero absorption co-efficient and found to be 2.3eV. A significant blue shift was observed in the band gap energy of synthesized CuO NLs from bulk CuO (1.2eV) due to quantum confinement effect.
3
The morphology and size distribution of synthesized CuO nanoparticles were analyzed by TEM and HRTEM images (Fig. 2a, 2b). TEM image (Fig. 2a) showed the 2D leaf-like morphology of synthesized CuO nanoparticles with dimensions of ~400nm in length and and ~86nm in width. The Fig. 2a represents the magnified TEM image of CuO NLs. The primary crystals of CuO self assembled to form the 2D leaf–like structure. The spacing between two adjacent lattice planes obtained from HRTEM image (Fig. 2b) is 0.18 nm which corresponds to interplanar separation of (
) lattice plane of standard
CuO nanoparticles. The SAED pattern (Fig. 2c) of synthesized CuO NLs depicts the monoclinic structure of CuO (JCPDS 05-0661) and resemblance with the XRD pattern of the synthesized CuO NLs [1]. The SAED pattern reveals that the particles resemble to a certain degree with that of single crystal. The elongated spots indicate the near perfect alignment of primary crystals within each particle. The catalytic efficiency of CuO NLs were investigated by carrying out reduction of 4-NP to 4-AP in aqueous medium using NaBH4. It is evident from UV-visible spectra that 4-NP has a maximum absorbance at 317nm in aqueous medium (Fig. A1; Supporting Information). The subsequent addition of freshly prepared NaBH4 solution to 4-NP leads to a red shift from 317 to 403nm (Fig. A2; Supporting Information). It is also observed that light yellow color of 4-NP solution changes to intense yellow due to the formation of 4-nitrophenolate ions under alkaline condition [7]. The peak obtained at 403nm is unaltered after a couple of days in absence of any catalyst. The yellow color of 4-NP solution slowly faded after the addition of 300µl of 0.001g of CuO NLs and finally disappeared on complete reduction of 4-NP. This decolorization was monitored by UV-visible spectroscopy at a regular interval of time. Fig. 3(a) shows the UV-visible spectra for the reduction of 4-NP. From Fig. 3(a) it is evident that with an increase in time the characteristic peak for 4-NP decreases with simultaneous appearance of a new peak centered at 297nm. This is due to the reduction of 4-NP to 4-AP. The peak at 297nm increases gradually with time due to the formation of 4-AP [7]. The complete reduction of 4-NP takes place within 15min. Hence, CuO NPs act as an efficient catalyst in the reduction of 4-NP in presence of NaBH4. The rate constant (k) has been determined following first order kinetics [7] from linear plot of ln[At] versus reduction time and found to be 2.2×10-2 min-1 (Fig. 3b). About 97% of 4-NP get reduced to 4-AP within 15min. 4. CONCLUSION This communication briefly describes a facile, cost-effective, green synthesis of CuO NLs using serine and NaOH by microwave heating method. TEM images reveal the formation of self assembled 2D CuO NLs having dimension of ~400nm in length and ~86nm in width. The SAED pattern of CuO NLs depicts the monoclinic structure of CuO which is also in resemblance with the XRD pattern of CuO NLs. The SAED pattern indicates that the particles resemble to a certain degree
4
with that of single crystal. A significant blue shift was observed in the band gap of CuO NLs (2.3eV) due to quantum effect. The synthesized CuO NLs also act as an efficient catalyst in the conversion of 4-NP to 4-AP in aqueous medium. • Supplementary Information: Mechanism of reduction of 4-NP is provided in Supplementary Information. References: 1.
Chen H, Jhao G, Liu Y. Mater Lett 2013; 93:60-3
2.
Hong ZS, Cao Y, Deng JF. Mater Lett 2002;52:34-8
3.
Wang TX, Xu SH, Yang FX. Powder Technol 2012;228:128-30
4.
Cheng Z, Xu J, Zhong H, Chu X, Song J. Mater Lett 2011;65:2047-50
5.
Qin H, Zhang Z, Liu X, Zhang Y, Hu J. J Magn Magn Mater 2010;322:1994-8
6.
Yang C, Su X, Wang J, Cao X, Wang S, Zhang L. Sens Actuators B 2013;185:159-65
7.
Mandlimath TR, Gopal B. J Mol Catal A: Chem 2011;350:9-15
8.
Saha S, Pal A, Kundu S, Basu S, Pal T. Langmuir 2010;26:2885-93
9.
Srestha KM, Sorensen CM, Klabunde KJ. J Phys Chem. C 2010;114:14368-76
10. Das D, Nath BC, Phukon P, Dolui SK. Colloids Surf. B 2013;101:430-3 Figures: 1. Figure 1. (a) FT-IR spectrum of CuO NLs; (b) XRD pattern of CuO NLs; (c) Absorption spectrum of CuO NLs (upper right inset represents the corresponding plot of (αhν)2 versus photon energy, hν) 2. Figure 2. (a) TEM microphotograph of CuO NLs (upper right inset represents the magnified TEM image of CuO NLs), (b) HRTEM image of CuO NPs, (c) SAED pattern of CuO NLs 3. Figure 3. (a) Absorption spectra of conversion of 4-NP to 4-AP using CuO NLs as catalyst in presence of NaBH4 in aqueous medium, (b) Plot of ln[At] versus reduction time.
(a)
5
0.8
Absorbance (a.u.)
Intensity (a.u.)
(202) (110)
(113) (220) (202) (311) (311)
1.00E+009
0.6
8.00E+008 6.00E+008 4.00E+008
0.5
2.00E+008 0.00E+000 0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
hν
0.4
(112) (222)
(112) 30
1.20E+009
0.7
(020)
20
1.40E+009
(c)
(111) (111) (002) (200)
(α h ν ) 2
(b)
40
50
60
70
0.3 80
200
o
2θ ( )
300
400
500
600
700
800
Wavelength (nm)
Figure 1. (a) FT-IR spectrum, (b) XRD pattern, (c) Absorption spectrum of CuO NLs (upper right inset represents the corresponding plot of (αhν)2 versus photon energy (hν)
Figure 2. (a) TEM microphotograph of CuO NLs (upper right inset represents the magnified TEM image of CuO NLs)
Figure 2. (b) HRTEM image, (c) SAED pattern of CuO NLs 6
2.5
0m 3m 6m 9m 12 m 15 m
Absorption (a.u.)
2.0
1.5
1.0
0.5
0.0 200
300
400
500
600
Wavelength (nm)
Figure 3. (a) Absorption spectra of conversion of 4-NP to 4-AP using CuO NLs as catalyst in presence of NaBH4 in aqueous medium
1.0 0.5
ln At
0.0 -0.5 -1.0 -1.5 -2.0 -2.5 -2
0
2
4
6
8
10
12
14
16
Time (min)
Figure 3(b) Plot of ln[At] versus time required for the reduction of 4-NP
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Highlights: 1. Development of a facile, cost-effective, green synthesis of 2D CuO nanoleaves 2. Design of microwave heating method using serine acting as complexing/capping agent 3. Formation of single crystalline 2D CuO NLs having 400nm length and 86nm width 4. 2D CuO NLs act as an efficient catalyst in the conversion of 4-NP to 4-AP
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