Rapid synthesis of nanocrystalline ZnO by a microwave-assisted combustion method L.C. Nehru a , V. Swaminathan b , C. Sanjeeviraja a, ⁎ a School of Physics, Alagappa University, Karaikudi 630 002, India b School of Materials Science and Engineering, Nanyang Technological University, 639798, Singapore abstract article info Article history: Received 22 December 2011 Received in revised form 9 March 2012 Accepted 24 March 2012 Available online 30 March 2012 Keywords: ZnO Nanocrystalline Combustion Microwave Synthesis A facile and rapid microwave-assisted combustion method (MWAC) was developed to synthesis to produce nanocrystalline ZnO powder using dissolution of zinc nitrate (as the oxidant) and urea (as fuel) as the starting materials and water as solvent, then heating the resulting solution in a microwave oven. The study suggested that application of microwave heating to produce the homogeneous porous ZnO was achieved in a few minutes. The structure and morphology of the as-prepared combustion products were investigated by means of X-ray powder diffraction (XRD), Fourier transform infrared spectra (FTIR), Raman spectra, UV–Vis absorbance spectra and Scanning electron microscopy (SEM). The XRD, FTIR and Raman spectra confirmed the formation of hexagonal wurtzite structural ZnO and the SEM results indicated the porous surface characteristic of the products. The as-prepared powders have larger band gap energy (3.06 eV) and are described here. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. 1. Introduction The fabrication of transition metal oxides with nano structure has been the target of scientific interests in recent years because of their unique properties and fascinating applications in optoelectronics, devices and biomedical science [1]. Among these oxides, zinc oxide nanostructure has attracted considerable interest in many areas of chemistry, physics and material science. It's having attracted extra attention due to their broad range of applications in sensors [2], catalysts [3], solar cells [4], transparent conductive oxides [5], optoelectronic devices [6] piezoelectric devices [7] antibacterial treatment [8] and additive in many industrial products. So the researchers exert much effort in continuing to focus on investigating them for technological applications due to their unusual physical and chemical properties, which differ significantly from those of conven- tional bulk materials from the standpoint of their extremely small size or large specific surface area. Generally nanoscale particles possess different physical, chemical properties, better sinter ability, and larger catalytic activity and other unique properties may be expected because their nano-sized crystallites are high surface area with different surface defect properties etc. So the technological importance of ZnO has motivated several studies on the synthesis of this material using various methods, such as pulse laser deposition [9], vapor phase transparent process [10], thermal evaporation [11], aqueous solution deposition [12], template-based growth [13], combustion synthesis [14], sol–gel [15], chemical vapor deposition [16] and vapor transparent deposition have been developed for the preparation of nano ZnO [17]. However, these methods require specific apparatus, vacuum conditions and chemical costs, respec- tively. Microwave irradiation as a heating method has found a number of applications in chemistry. The utilization of microwave irradiation in the preparation of nano particles has been reported in recent years [18]. Compared to the conventional methods, the microwave synthesis has the advantages of producing small particle size metal oxides with high purity owing to short reaction time [19–23]. Microwave-assisted synthesis is a novel method to produce materials, since microwave heating is an in situ mode of energy conversion and the microwave heating process is fundamentally different from conventional heating processes. Heat will be generated internally within the material, instead of originating from external sources. By means of this method, many functional materials and compounds with novel structures and properties have been obtained [24]. In the recent studies, it has been shown that nanoparticles such as Co 3 O 4 [25], LiMn 2 - x Cr x O 4 [26], SnO 2 [27] Ce 1-x Gd x O 2-1/2x [28], MgO [29], ZnO [30] and Ni x Co 1 - x Fe 2 O 4 [31], can be prepared by the microwave synthesis process. In this paper, we report a simple method for the preparation of hexagonal ZnO nanoparticles by using microwave-assisted combus- tion synthesis process to fast, mild, energy-efficient and environmen- tally friendly rout to produce ZnO nano particles using urea as fuel. 2. Experimental All the reagents used in the experiments were analytically pure and were purchased from MERCK Company, and were used as Powder Technology 226 (2012) 29–33 ⁎ Corresponding author. E-mail address: sanjeeviraja@rediffmail.com (C. Sanjeeviraja). 0032-5910/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2012.03.042 Contents lists available at SciVerse ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec