Synthesis of novel RuO2/NaBi(MoO4)2 nanosheets composite and its gas sensing performances towards ethanol

A novel NaBi(MoO4)2 nanosheets were synthesized by a two step method which included a solvent thermal and a hydrothermal treatments. The RuO2/NaBi(MoO4)2 composite was prepared by mixed NaBi(MoO4)2 nanosheets with RuCl3 ethanol solution and sequent heat treatment. Characterizations by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller analysis indicated that the NaBi(MoO4)2 nanosheets were tetragonal scheelite phase with the thickness of 10–15 nm, their agglomerates were porous material with specific surface area of 14.2 m2/g. The sensors based on as-prepared NaBi(MoO4)2 and RuO2/NaBi(MoO4)2 nanosheets showed a high gas response, fast response (less than 10 s), trace detection capacity (1 ppm), and selectivity to ethanol with no cross-sensitivity towards moisture and acetone etc. A new gas-sensing mechanism for NaBi(MoO4)2 is proposed, which is different to the adsorbed oxygen sensing mechanism for SnO2 and ZnO. Here, the ethanol molecules are catalytically oxidized by MoO42− tetrahedron, and the electrons transfer to Bi3+ which reduced into Bi0 metal. The results of X-ray photoelectron spectroscopy prove bismuth metal existence. The conductivity change comes from Bi quantum dots and free electrons resulting from oxygen vacancies formation in gas-sensing process. The gas sensing response of RuO2/NaBi(MoO4)2 increases two times higher than that of as-prepared NaBi(MoO4)2 nanosheets. Therefore, the RuO2/NaBi(MoO4)2 sensor is a promising candidate for fast, sensitive and selective detection of ethanol.