Elsevier

Physica B: Condensed Matter

Volume 405, Issue 15, 1 August 2010, Pages 3096-3100
Physica B: Condensed Matter

Sonochemical synthesis, characterization and thermal and optical analysis of CuO nanoparticles

https://doi.org/10.1016/j.physb.2010.04.021Get rights and content

Abstract

Nanoparticles of CuO were prepared by a novel sonochemistry route from copper acetate and sodium hydroxide in the presence of polyethylene glycol (PEG), polypropylene glycol (PPG) and polyvinyl alcohol (PVA). Variations in several parameters and their effects on the structural properties of nanoparticles (particle size and morphology) were investigated. 0.05 M solution of copper acetate in the presence of PEG gave the best results. The characterizations were carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), IR spectroscopy, thermal gravimetry analysis and differential thermal analysis (TGA/DTA).

Introduction

Ultrasonic irradiation has proven to be a versatile and promising tool for the development of new processes in the chemical industry [1], [2]. Its unique character predominantly arises from acoustic cavitations, i.e. the growth and subsequent adiabatic collapse of a microscopic cavity in a liquid, leading to a momentary increase in temperature and pressure. These extreme local conditions can cause bond breakage and free radical formation, thereby providing an alternative route for inducing chemical reactions (sonochemistry).

It seems evident to increase the sound field intensity to enhance sonochemical reaction rates. The intensity can be increased either by reducing the radiating surface area or by increasing the power supplied to the system. In case of an existing experimental set-up, the power input is generally used to adjust the acoustic intensity. It has been reported that the sonochemical decomposition of organic solutes and the oxidation of potassium iodide increase linearly with increase in acoustic intensity, using low-frequency ultrasound (20–60 kHz) of relatively low intensity. At high intensities, however, an increase in intensity leads to a relatively small increase or even a decrease in the sonochemical efficiency [3], [4], [5], [6], [7]. Wu et al. have even demonstrated that in a single experimental set-up, the dependency on acoustic intensity can vary for different reactions [8]. Several explanations have been proposed in the literature to account for the remarkable effect of intensity. Increasing the power input, the sound field penetrates further into the liquid and, consequently, the sonochemical active zone covers a larger region. This effect has been confirmed by previously reported sonogenerated chemiluminescence studies [9], [10], [11]. On the contrary, the increased number of cavitation bubbles can absorb and scatter the sound wave, consequently weaken the acoustic field substantially (shielding) [12], [13].

On the other hand, in recent years, cupric oxide (CuO) has been received extensive investigations for its prospective applications in many fields. CuO is a p-type semiconductor with a narrow band gap of 1.4 eV [11]. It has similar properties with high-Tc super-conducting cuprates but consists of Cu–O bonding only, so it has been used as a basic material in high-Tc superconductors [13], [14]. It also can be used potentially in gas sensors, solar cells, FE emitters, electronic cathode materials and catalysts in organic reactions [15], [16], [17], [18], [19].

Many methods have been developed to prepare CuO with various morphologies. Zhang et al. synthesized nano-dendrite like CuO via hydrothermal route [20]. CuO nano-shuttle was also prepared under surfactant assisted conditions using the same method [21]. CuO nano-rods and nano-ribbons were synthesized by wet chemical methods [7]. In addition, the nanofibers of CuO were prepared by thermal oxidation on Cu substrate through importing the polycarbonate membrane template for initial deposition of Cu nuclei [22]. The above-mentioned methods cannot be departed from complex chemical reactions or processes. Thermal oxidation may assist the production of catalysts, semiconductor devices or functional oxide films under controlled conditions [23]. A direct and simple thermal oxidation method was employed to synthesize CuO nano-wires and nano-rods. Using this convenient route, with no catalyst and template assisted, many research teams prepared CuO nano-wires successfully by oxidizing copper foils under different conditions such as different annealing temperatures, time or atmosphere [24], [25], [26], [27].

In the present work, we found that ultrasonic irradiation can greatly enhance the conversion rate of precursor to nanometer-sized CuO particles in the presence of polyethylene glycol (PEG), polypropylene glycol (PPG) and polyvinyl alcohol (PVA). Also the role of calcinations, time, concentration of copper acetate solution and power of ultrasound wave on the size, morphology and chemical composition of nanoparticles was investigated. For the precursor, we used copper acetate dissolved in ethanol/water/(PEG or PPG or PVA). Then CuO nanoparticles were directly obtained by addition of a solution of sodium hydroxide. The influence of several parameters on the size and morphology of CuO particles was reported. The powder was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), IR spectroscopy, thermal gravimetry analysis and differential thermal analysis (TGA/DTA).

Section snippets

Experimental

Different amounts of NaOH solution with a concentration of 0.1 M were added to the 0.1, 0.05, 0.025 M solutions of Cu(CH3COO)2·2 H2O in ethanol/water. The obtained mixtures were sonicated for 30–60 min with different ultrasound powers. To investigate the role of surfactants on the size and morphology of nanoparticles, we used 0.5 g of polyethylene glycol (PEG) in the reactions with optimized conditions. Table 1 shows the conditions of reactions in detail. A multiwave ultrasonic generator (Bandlin

Results and discussion

The reaction between copper acetate and sodium hydroxide to form CuO nanoparticles is shown in Scheme 1. Various conditions such as concentration of sodium hydroxide solution, different sonicating times, ultrasound power and different templates for preparation of Cuo nanoparticles were examined (Table 1).

In sample nos. 1–12, 13–24 and 25–36, the reactions were studied in PEG, PPG and PVA template, respectively. Our investigation indicated that sample no. 2 is the best in terms of size,

Conclusion

A simple sonochemical method was presented by direct transformation of Cu(OAc)2·2H2O precursor to create CuO nanoparticles on PEG, PPG and PVA templates. The properties of nanoparticles were studied by SEM, XRD, solid state florecente, TG and DTA. SEM analysis showed that CuO nanoparticles have an average diameter of 35–103 nm, which varied by different factors. Comparing with other methods such as solvothermal, hydrothermal and sol–gel methods (which requires high temperature, expensive

Acknowledgement

Supporting of this investigation by Vali-E-Asr University (Rafsanjan, Iran) is gratefully acknowledged.

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