Tin oxide-based substrate catalyzed formation of MoO2 under microwave irradiation

Abstract

Heterogeneous catalysis on metal oxide surfaces for organic conversion reactions and electrocatalysis is well known and finds extensive applications in industry. This pioneering work on substrate (SnO₂ derived) induced synthesis provides an environment friendly method for the rapid synthesis of foam-like MoO₂(15 minutes, ~90% yield) by microwave method. The method involves irradiating a mixture of molybdenum precursor and citric acid in aqueous medium, in the presence of tin oxide substrates, at a microwave power of 240 W for 15-30 min. The effect of all the reactants is systematically analysed by using various molybdenum precursors, different carboxylic acids as surfactants and SnO ₂ (or its doped forms) as substrates by energy efficient microwave method. Substrate catalyzed reaction yields foam-like, porous and metallic MoO₂ with a resistivity of 0.87 Ωm that could be obtained as powder and films on substrates. X-ray diffraction and high-resolution electron microscopy shows MoO₂ lattice while Raman spectra and X-ray photoelectron spectroscopy indicate the presence of higher oxides on the surface. The MoO₂ formation is tested in the presence of other substrates such as SiO₂, Si, TiO₂, ZnO, CuO and glass under microwave irradiation, hardly yielding any product. Density functional theory calculations reveal optimum stabilization of the intermediate MoO₄H₂ on SnO₂ surface compared to other substrates, facilitating the possibility for the formation of extended nanolayers of MoO₂ on former surface. The unique substrate-induced growth mechanisms offer a promising pathway for the scalable, cost-effective, and green synthesis of inorganic nanomaterials.