Synthesis of high surface area monoclinic WO3 particles using organic ligands and emulsion based methods

Abstract

Several synthetic approaches have been used to obtain nano-sized monoclinic WO₃ (m-WO₃) powders. All of these methods begin with a standard preparative method where H₂WO₄ is first generated by passing a Na₂WO₄ solution through a cation-exchange resin. It is shown that high surface area particles are produced by dripping the H₂WO₄ exiting from the ion-exchange column into a solution containing oxalate and acetate exchange ligands or alternatively, into a water-in-oil (w/o) based emulsion. In comparison to commercial WO₃ powders, the surface area of the m-WO₃ powders were higher by factors of 10 and 20 times when prepared in the presence of acetate/oxalate chelating agents and w/o emulsions, respectively. The much higher surface areas enable infrared spectroscopic identification of surface sites along with detection and monitoring of gaseous reactions and adsorbed species on the surface of this metal oxide. This is demonstrated with the adsorption of a nerve agent simulant, dimethyl methyl phosphonate. In general, little is known about the reactions of gaseous molecules on m-WO₃ surfaces and the fabrication of high surface area m-WO₃ particles will aid in gaining an understanding of the chemical processes occurring in WO₃ based sensors.