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S.J. Ahmadi Jaber Ebne Hayyan Research Laboratory, NSTRI, Tehran, Iran

T. Mousavand Department of Mechanical Engineering, McGill University, Montre´al, Que´bec H3A 2K6, Canada

M. Outokesha) School of Energy Engineering, Sharif University of Technology, Tehran, Iran (Received 19 April 2010; accepted 12 July 2010)

Ultra fine CuO nanoparticles in the range of 2
0.2 nm were synthesized by the supercritical hydrothermal method in a batch reactor. It was demonstrated that elevating the pH of the Cu2þ precursor solution to around 6 (neutral condition) not only does not lead to excessive agglomeration of the particles, but also reduces particle size and in general promotes their nanoscale characteristics. Prepared nanoparticles were immobilized in the biopolymeric matrix of barium alginate and calcined at different temperatures resulting in microspherical granules of high porosity and elevated mechanical strength. The fabricated samples were characterized using x-ray diffractometry (XRD), transmission and scanning electron microscopy (TEM and SEM), nitrogen adsorption analysis (BET), mechanical testing, and temperature programmed reduction (TPR). It was found that topochemical models based on a nucleation growth mechanism fail in proper fitting of the TPR data. Instead, a generalized Sestak model in which different physicochemical mechanisms such as the mass action law are taken into account gives a satisfactory regression of the kinetics behavior.

I. INTRODUCTION

Metal oxide nanoparticles have special physicochemical properties arising from the quantum size effect and a high specific surface area which may be different from their bulk counterparts.1 One of the most investigated nano metal oxides is CuO, an advanced material with wide potential applications as high Tc superconductors,2 gas sensors,3 catalysts for the water-gas shift reaction,4 steam reforming,5 and CO oxidation at low temperature for the treatment of automobile exhaust gases.6 In addition, the applicability of CuO nanopowder for heat transfer in nanofluids has also been reported.7 The past few years witnessed a great deal of effort to develop efficient techniques for the preparation of CuO nanoparticles. Reported approaches include the metalorganic chemical vapor deposition (MOCVD) template method,8 the wet chemistry route,9 sonochemical preparation,10 the alkoxide-based method,11 solid-state reaction in the presence of polyethylene glycol (PEG),12 and eventually supercritical hydrothermal synthesis.13–15 a)

Address all correspondence to this author. e-mail: [email protected]; [email protected] DOI: 10.1557/JMR.2010.0262 J. Mater. Res., Vol. 25, No. 10, Oct 2010

http://journals.cambridge.org

Downloaded: 11 Mar 2015

Supercritical hydrothermal synthesis (SCHS) is a relatively simple and environmentally benign process that is carried out in both batch and continuous schemes. Advantages of this method over previous synthesis approaches16–21 are shorter reaction time (> RGrowth. The above-mentioned previous investigation revealed that thes