Effect of Supercritical Ethanol Drying on the Properties of Zinc Oxide Nanoparticles Theresa Egbuchunam 1 and Devrim Balkose 2 1 Department of Chemistry, Federal University of Petroleum Resources, Effurun, Delta State, Nigeria 2 Chemical Engineering Department, Izmir Institute of Technology, Gulbahcekoyu, Urla, Izmir, Turkey The synthesis, characterization, and application as polymers and anti-wear additives of nanosized zinc oxide particles obtained by conventional and supercritical ethanol drying are reported in this study. The nanaoparticles of ZnO produced by the two different drying techniques were characterized using Fourier Transform Infrared (FT-IR) spectrophotometry, Scanning Electron Micro- scopy (SEM), X-ray Diffraction (XRD) and Thermogravimetric analysis (TGA) to elucidate the shape, size, composition, and stab- ility of the nanoparticles. ZnO nanoparticles were then applied to poly (vinyl chloride) (PVC) powder and light mineral oil to assess their effectiveness and suitability as additives in diverse areas. XRD analysis revealed ZnO crystalline structure with average particle size of 24.7 nm for zinc oxide nanoparticles prepared by supercritical ethanol drying while SEM showed well-isolated and monodisperse particles with average size of 61.08 nm. Keywords Mineral oil; Poly (vinyl chloride); Supercritical etha- nol drying; Zinc oxide nanoparticles INTRODUCTION Nanoparticles are of considerable importance in numerous technological applications. The development of advanced functional nanomaterials for various applica- tions, including catalysis, pigments, cosmetic sunscreens, textile materials, etc., [1–4] have received considerable interest in the last few years. Nanomaterials possess useful properties ranging from novel optical, electronic, and chemical properties [5,6] to sunscreens, paints, varnishes, plastics, cosmetics, [7] and lubricants. [8] Zinc oxide (ZnO) is an important material used for a variety of applications such as chemical sensors, varistors, thin-film luminescent devices, catalysts, and cosmetic materials. [9] Due to the diverse applications of ZnO, the generation of highly dispersible materials homogeneously distributed in applied systems is of great importance as materials having a structure with a grain size in the nano- meter range exhibit properties significantly different from those for the same material with larger grain size. Ultrafine zinc oxide particles show a high degree of transparency, making them useful, especially for broad UV-A and UV-B blocking. [7] During production, nanoparticles agglomerate owing to the influence of interfacial tension during conventional dry- ing. [9,10] In order to prevent particle agglomeration during production, a number of new synthetic strategies have been developed to generate well-defined nanoparticles having structures and properties suitable for applications in aque- ous and non-aqueous systems. Various methods for the preparation of metal oxide nanoparticles have been devel- oped with the ultimate goal to produce particles of control- lable properties including size distribution, morphology, and crystal structure. Amongst these methods is supercriti- cal fluid drying, where the solvent is removed above its critical temperature (T c ) and critical pressure (P c ). High temperatures have been shown to be necessary in obtaining very fine particles as the liquid-vapor interface and capil- lary pressure are eliminated and the resulting particles do not tend to stick to each other. [7,11–13] The unique properties of supercritical fluids, mainly water, carbon dioxide, organic solvents, usually alcohols, have been demonstrated as a route for the production of metal oxide particles as they allow controlled particle properties, such as morphology, structure, and particle size distribution. [14] Ethanol is a green fuel of the future, which can be regenerated from biomass through photosynthesis; therefore, ethanol can be used as a renewable bio-fuel. Ethanol has been used as an effective polar modifier for water and carbon dioxide in the supercritical fluid extrac- tion and in supercritical chromatography. [15] The synthesis of zinc oxide (ZnO) nanoparticles using various methods has been reported in the literature. [16–21] The use of supercritical fluid drying of ZnO has been investigated previously. Han et al. [22] prepared ZnO nano- particles in supercritical methanol and supercritical water and obtained particles down to 10 nm size. Gao et al. [23] dried alcoholic ZnO gels by supercritical carbon dioxide drying. Monolithic zinc oxide aerogels were prepared Correspondence: Theresa Egbuchunam, Department of Chemistry, Federal University of Petroleum Resources, Effurun, Delta State, Nigeria; E-mail: tessychunam@gmail.com Drying Technology, 30: 739–749, 2012 Copyright # 2012 Taylor & Francis Group, LLC ISSN: 0737-3937 print=1532-2300 online DOI: 10.1080/07373937.2012.661380 739