- Nano Express
- Open Access
Effect of Gelatin-Stabilized Copper Nanoparticles on Catalytic Reduction of Methylene Blue
© The Author(s). 2016
- Received: 29 July 2016
- Accepted: 22 September 2016
- Published: 1 October 2016
The synthesis of copper nanoparticles was carried out with gelatin as a stabilizer by reducing CuSO4.5H2O ions using hydrazine. Ascorbic acid and aqueous NaOH were also used as an antioxidant and pH controller, respectively. The effects of NaOH, hydrazine, and concentration of gelatin as stabilizer were studied. The synthesized copper nanoparticles were characterized by UV-vis spectroscopy, XRD, zeta potential measurements, FTIR, EDX, FESEM, and TEM. The formation of CuNPs@Gelatin is initially confirmed by UV-vis spectroscopic analysis with the characteristic band at 583 nm. XRD and TEM reports revealed that CuNPs@Gelatin (0.75 wt.%) is highly crystalline and spherical in shape with optimum average size of 4.21 ± 0.95 nm. FTIR studies indicated the presence of amide group on the surface of the CuNPs indicating the stability of CuNPs which is further supported by zeta potential measurements with the negative optimum value of −37.90 ± 0.6 mV. The CuNPs@G4 showed a good catalytic activity against methylene blue (MB) reduction using NaBH4 as a reducing agent in an aqueous solution. The best enhanced properties of CuNPs@G4 were found for the 0.75 wt.% gelatin concentration. Thermodynamic parameters (ΔH and ΔS) indicate that under the studied temperature, the reduction of MB by CuNPs@G4 is not feasible and had endothermic in nature.
- Catalytic reduction
- Methylene blue
- Copper nanoparticles
Copper nanoparticles are a less expensive other option to different precious metal nanoparticles with a range of prospective users in the area of nanoscience and technology . However, the preparation of CuNPs has been broadly concentrated on for a long time as it is an essential industrial material because of its unique physicochemical properties. Likewise, in the area of electronics, copper is the most widely recognized as a result of its excellent electrical conductivity and additionally low cost . Similarly, CuNPs have engrossed great attention in catalytic applications. In any case, CuNPs have significant impediments, which incorporate quick oxidation on subjection to atmospheric air. Copper oxidizes to Cu2O and CuO and convert to Cu2+ during preparation and storage, so it is hard to prepare CuNPs without an inert environment . Along these lines, another method has been developed to prepare CuNPs in the presence of polymer and surfactants as stabilizers and to form covers on the surface of nanoparticles. These stabilizers are mostly from non-renewable materials, finding eco-friendly stabilizing material is needed.
Gelatin is an animal protein obtained by a controlled hydrolysis of the fibrous insoluble collagen present in the bones and the skin produced as waste during animal slaughtering and processing . It possesses an important properties, such as flexibility, adhesiveness, and low cost, which make it suitable for practical application in various fields of research . Similarly, gelatin contains free carboxyl groups on its backbone and has the potential for chelating and reducing noble metals. Few works on the preparation of gelatin-stabilized CuNPs have been reported [6, 7]. However, the preparation of CuNPs has become a subject of interest in material research, several synthesis methods of CuNPs with controlled size and shape have been reported, including sonochemical reduction [8, 9], laser ablation , microemulsion , thermal deposition , chemical reduction , microwave , and green method . Among the methods, chemical reduction is the most extensively applied methods for its simplicity, low cost, and ease of size and shape control over CuNPs. CuNPs have also been reported as a suitable catalyst for chemical reduction of various organic pollutants in wastewater [16–18]. Besides, many researchers have reported the reduction of dyes using various metal nanoparticles [19–27]. However, the use of CuNPs for the reduction of aromatic dyes has remained an unexplored area.
However, to the best of our knowledge, no work on CuNPs@Gelatin catalyst for the reduction of methylene blue dye has been reported. In an effort to develop a green and cost-effective catalyst to address the said environmental issue, in this work, we report a simple method for the preparation of CuNPs stabilized with gelatin, using copper sulfate, NaOH solution, and hydrazine hydrate and ascorbic acid as copper precursor, pH controller, reducing agent, and to prevent the oxidation of CuNPs, respectively, without any inert atmosphere at a temperature of 80 °C. The effect of gelatin concentrations on the catalytic activity of CuNPs against the chemical reduction of methylene blue using NaBH4 as a hydrogen donor was studied. Likewise, the thermodynamic parameters for reduction reaction has been looked into.
CuSO4.5H2O (99 %) was used as copper ions precursor and was provided by Bendosen Laboratory Chemicals, ascorbic acid (90 %) was provided by Hamburg, NaOH (99 %) and hydrazine hydrate (35 % hydrazine) were purchased from MERCK (Germany), and gelatin (type B), ethanol, methylene blue and NaBH4 (98.5 %) were purchased from Sigma-Aldrich (USA). In this, all the preparation of solutions, chemical of analytical reagent grade, and deionized water were used.
Synthesis of Copper Nanoparticles in Gelatin
For the synthesis of copper nanoparticles (CuNPs) in gelatin, five different gelatin suspensions were first prepared by dissolving 0.5, 0.38, 0.25, 0.13, and 0.05 g of the gelatin in five different flasks containing 50 mL warm distilled water each at 40 °C to achieve 1, 0.75, 0.5, 0.25, and 0.1 % (w/v) suspensions. After that, 15 mL of CuSO4.5H2O (0.1 M) were added to 35 mL each of 1, 0.75, 0.5, 0.25, and 0.1 % (w/v) of gelatin suspensions to get the final concentration of 0.03 M. Then, 2.5 mL of 0.02 M ascorbic acid was added with constant stirring at 80 °C for 20 min. This was followed by the addition of 5 ml of NaOH solution, after further mixing for another 20 min, until a light green solution was obtained. Finally, 2.5 mL of 35 wt.% hydrazine was added for reduction of copper ions during which the solution mixture change from dark to reddish brown within 30 min of the reaction time with constant stirring. The CuNPs@Gelatin was secluded by centrifugation at 14,000 rpm for 10 min and dried in a vacuum overnight at 60 °C.
Catalytic Activity of CuNPs@Gelatin
An investigation of the catalytic activity of the prepared copper nanoparticles supported in different percentages of gelatin was carried out according to a previous work by , using the reduction of methylene blue dye by NaBH4 as a model reaction. Briefly, 10 mg of the prepared samples were added to 18 mL of methylene blue aqueous solution (1 × 10−5 M). Subsequently, the above solution was mixed with 2 mL fresh NaBH4 solution (1 × 10−2 M). The reaction was done in the given temperature with continuous stirring. The progress of the degradation reaction was then monitored by recording the absorbance value at 664 nm at different time interval using UV-vis spectrophotometer. The concentration of the methylene blue was calculated based on a calibration curve of the absorbance values versus dye concentrations. Also, blank experiments were carried out to show that the reactions do not proceed without catalysts only in the presence of NaBH4. The influence of the temperature and recyclability of the optimum samples were studied.
Characterization of the Synthesized CuNPs@Gelatin
The initial characterization was carried out by UV-vis spectroscopic study using a UV 1650 PC-Shimazu B UV-visible spectrophotometer (Shimazu, Osaka, Japan). The XRD analysis of the prepared CuNPs@Gelatin was carried out by Philip X’pert PXRD (Cu Kα radiation; PANalytical, Almedo, The Netherlands). The prepared CuNPs@Gelatin was also subjected to zeta potential measurements using a dynamic laser light scattering method in a Malvern zeta instrument 3000 (Malvern Instrument, UK). FTIR spectra of the samples were obtained at ambient temperature using the KBr disk method. A disk containing 1 mg of sample was recorded within the wavenumber range of 200 to 4000 cm−1 using a series 100 Perkin Elmer (USA) FT-IR 1650 spectrophotometer. The components of the samples were measured by the energy dispersive x-ray spectroscopy (EDX). The morphology and size of the prepared CuNPs@Gelatin were examined using FESEM and TEM. The FESEM with EDX analysis was performed with a JEOL JSM-7600F instrument. The transmission electron microscopy (TEM) observation was carried out using TEM, Philips CM-12, and the particle size distribution was measured using UTHSCSA Image Tool version 3.0. Also, the histograms were created using IBM-SPSS software, and the graph fitting was created using Microsoft Excel program.
Optimization of Synthesis Method for the Preparation of CuNPs@Gelatin
To prepare a stable small size CuNPs, different parameters such as concentrations of gelatin, concentrations of CuSO4, volume of NaOH, and volume of hydrazine were investigated. The optimum values were found to be 0.75 wt.% of gelatin, 0.03 M concentration of Cu2+ ions, 4 mL of 0.5 M NaOH, and 2 mL of 35 wt.% hydrazine concentration, respectively. These values were required to obtain a stable small CuNPs in an aqueous solution.
Zeta potential of gelatin and CuNPs@Gelatin at various concentrations of gelatin [0.1, 0.25, 0.5, 0.75, and 1 wt.% (b–f)]
Zeta potential (mV)
−25.4 ± 2.0
−28.7 ± 1.4
−30.4 ± 0.8
−34.8 ± 1.1
−37.9 ± 0.6
−39.7 ± 0.9
Fourier Transform Infrared Spectroscopy
Energy Dispersive X-ray Spectroscopy
Catalytic Activity of CuNPs@Gelatin
Completion time and rate constants of CuNPs (G0) and CuNPs@Gelatin at different concentrations of gelatin [G1,G2, G3, G4, and G5 (0.1, 0.25, 0.5, 0.75, and 1 wt.%)] catalyzed reduction reaction of MB
Completion time (min)
Rate constant (k app) (min−1)
Thermodynamic Parameters of CuNPs@G4
The thermodynamic parameters ΔH and ΔS were determined from (Eq. 6), respectively. Figure 12a shows increase in reaction rate constant as a function of temperature. Figure 12b shows an Arrhenius plot, in which the activation energy was calculated from its slope. However, Fig. 12c shows Eyring plots in which ΔH and ΔS were determined from its slope and intercept for ΔH and ΔS, respectively. The values for E a , ΔH, ΔS, and ΔG 298 for the methylene blue reduction catalyzed by CuNPs@G4 were found to be 43.61 kJ/mol, 41.05 kJ/mol, −111.86 J/mol, and 74.38 kJ/mol, respectively.
The CuNPs@Gelatin was also successfully prepared in gelatin biopolymer as stabilizer in an aqueous solution, with the variation of the gelatin concentration in the range of 0.1, 0.25, 0.5, 0.75, and 1 wt.%. The prepared CuNPs@Gelatin were initially confirmed by using UV-vis spectroscopy and XRD study. The UV-vis spectral profile generated for gelatin-stabilized CuNPs revealed the formation of CuNPs@Gelatin with a maximum wavelength around 583 nm. According to the XRD and TEM analyses revealed that with increasing concentration of the gelatin, the mean diameters of the CuNPs gradually decrease. The CuNPs@Gelatin showed a good catalytic activity against MB reduction using NaBH4 as reducing agent in an aqueous solution. The best enhanced properties of CuNPs@Gelatin were found for the 0.75 wt.% gelatin concentration.
The authors are grateful to the staff of the Department of Chemistry UPM, Institute of Advanced Technology (ITMA) for their help in this research and the Institute of Bioscience (IBS/UPM) for technical assistance.
AM carried out the experimental work. MBA, MZH, SMI and HAS conceived of the study and coordinated the project. AM and MBA drafted the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
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