Facile preparation and formation mechanism of three low valent transition metal oxides in supercritical methanol
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Zhe Zhang, Shengnan Jiang, Xin Ge, and Jie Zhang College of Chemical Engineering, Shenyang University of Chemical Technology, Shenyang 110142, China
Wenxiu Li Key Laboratory of Chemical Separation Technology of Liaoning Province, Shenyang University of Chemical Technology, Shenyang 110142, China
Sansan Yua) College of Chemical Engineering, Shenyang University of Chemical Technology, Shenyang 110142, China; and Key Laboratory of Chemical Separation Technology of Liaoning Province, Shenyang University of Chemical Technology, Shenyang 110142, China (Received 25 January 2016; accepted 23 March 2016)
Three important low valent transition metal oxides were synthesized in supercritical methanol by using inorganic metal salts as precursors. X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and x-ray photoelectron spectroscopy were applied to analyze the composition, structure, and morphology of the products. Results showed that Cu2O, MoO2, and V2O3 were obtained successfully under a supercritical condition of 240 °C and 9.0 MPa. MoO2 and V2O3 displayed sphere-like morphology with average particle sizes of 20–40 and 20–50 nm, respectively. Cu2O particles displayed edge-truncated cubic morphology with a particle size of 2.5 lm. Formation mechanism proposed that high valent metal oxides (CuO, MoO3, and V2O5) were formed firstly in supercritical methanol by the decomposing of precursors and then reduced to target products by free hydroxyl anions. In addition, methanol performed important roles not only as a reaction medium but also as a reducing agent under supercritical fluid conditions.
I. INTRODUCTION
In recent years, low valent transition metal oxide (LVTMO) materials, e.g., Cu2O, MoO2, V2O3, and so on, have attracted much interest due to their enhanced catalytic abilities, novel electrical, and conduction properties and unique magnetic properties.1–4 These materials have been applied in various fields, including catalysis, sensors, batteries, high density magnetic recording materials, and electrochemistry.5–9 Some methods of preparing transition metal oxides have been reported over the past few years including wet chemical, solvothermal, thermal decomposition, reverse micelle, and chemical deposition method.10–15 Cu2O, for example, has been prepared mainly by wet chemical technique.1,16–19 This method, however, requires complex synthesis systems composed of solvents, precursors, Contributing Editor: Edson Roberto Leite a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.149 1440
J. Mater. Res., Vol. 31, No. 10, May 28, 2016
http://journals.cambridge.org
Downloaded: 30 Jul 2016
reducing agents, surfactants, stabilizers, and other additives, which increase the operation complexities and the subsequent separation difficulties. Furthermore, the method is not environmentally friendly due to the usage of toxic reducing agents and the production of hazardous chemical wastes. There are some very different methods for the synthesis of MoO2 and V
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