Rapid Communication Synthesis and characterization of nano ZnO rods via microwave assisted chemical precipitation method N. Uma Sangari n , S. Chitra Devi Department of Chemistry, The S.F.R. College for Women, Sivakasi 626123, India article info Article history: Received 9 May 2012 Received in revised form 24 July 2012 Accepted 5 August 2012 Available online 14 August 2012 Keywords: Chemica precipitation Nano rods Aspect ratio SEM Band gap DRS abstract A microwave assisted chemical precipitation method has been employed for the synthesis of nano zinc oxide rods by reacting zinc nitrate and potassium hydroxide. The amount of potassium hydroxide was adjusted for three different pHs to achieve ZnO nano rods with varying aspect ratio. The mechanism of growth of nano rods is explained briefly. The average crystallite size of the as synthesized samples was analyzed by means of powder XRD pattern and estimated to vary from 25.6 nm to 43.1 nm. The existence of rods was confirmed using scanning electron microscopy (SEM). The samples were also analyzed using FT-IR. The optical properties of the samples were also studied by means of UV– visible spectra and Room Temperature Photo Luminescence studies. The band gap of the samples was determined from the DRS spectrum. A strong near band emission peaks due to surface defects are observed in the PL spectrum. & 2012 Elsevier Inc. All rights reserved. 1. Introduction Zinc oxide, an n-type, II–IV semiconductor, is a commercially important material used in solar cells [1], rubber [2], sensors [3], varistors [4], etc. Also it is a self-activated crystal of a hexagonal wurtzite structure with direct band gap energy  3.37 eV and relatively high exciton binding energy (60 meV) at room tem- perature [5], displays excellent piezoelectric [6], catalysis [7] and novel optical properties [8]. Recently, a wide range of research on synthesizing metal oxides with one dimensional nano structures such as nano rods, fibers, tubes, wires, ribbons, nano needles and nano sheets have gained much importance due to their potential applications in various fields [9]. Among these metal oxides, zinc oxide attracted the scientists as it is low cost, environmentally benign and efficient semiconductor. In recent years, ZnO rods have been synthesized by many methods such as solvothermal process [10], surfactant assisted synthesis [11,12], gel casting method [13], sonochemical method [14], chemical vapor deposi- tion method [15] and thermal evaporation method [16]. Such methods to prepare these types of nano structures of ZnO require high temperature and are sometimes complicated. Hence a simple and inexpensive synthetic process is required. Herein, we report a simple and effective approach using a solvent and surfactant free microwave assisted wet chemical precipitation method. We also investigated the effect of pH on the particle size, morphology and optical properties of the samples. 2. Experimental procedure 2.1. Materials The following chemicals zinc nitrate (99% purity, Merck), potassium hydroxide (85% purity, Merck), lead acetate and phenolphthalein were procured from Merck and used without further purification. 2.2. Microwave assisted synthesis procedure All the chemicals and reagents used in this experiment were of analytical grade and used without further purification. Prepara- tion process of nano ZnO rods in our study is as follows: 29.749 g of zinc nitrate was dissolved in 200 ml of double distilled water. Then 1 M KOH prepared in DD water was added dropwise very slowly into the zinc nitrate aqueous solution at a stirring rate of 500–520 rpm till the required pH of 13, 11 and 9 was attained. Also, when the viscosity of the mixture increases, the revolution of the Teflon was so adjusted to maintain the stirring rate of 500– 520 rpm throughout the experiment. After the addition was completed, the stirring was continued for another 30 min at 60 1C. During stirring a milky white suspension of Zn(OH) 2 was obtained. The above solution was kept overnight at room tem- perature and the precipitate was filtered, washed thoroughly with Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jssc Journal of Solid State Chemistry 0022-4596/$ - see front matter & 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jssc.2012.08.011 n Corresponding author. E-mail addresses: umasangariselvakumar@gmail.com, umaselvakumar@yahoo.co.in (N. Uma Sangari). Journal of Solid State Chemistry 197 (2013) 483–488