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Oxygen Vacancies Induced by Pd Doping in Ni-P2O5/MoO3 Hollow Polyhedral Heterostructures for Highly Efficient Diethylamine Gas Sensing.

Semiconductor metal-oxide materials have a high surface-to-volume ratio and many active sites, making them potentially useful for gas sensing. Dopants introduced into the lattice can improve the catalytic activity of oxides and promote the formation of oxygen vacancies, hence improving the sensing performance of the materials. However, the simple preparation of materials with high sensitivity, selectivity, and a low detection limit remains a challenge. Herein, we report on the synthesis of Ni-P2O5/MoO3 and Pd-doped Ni-P2O5/MoO3 hollow polyhedral heterostructures (HPHSs) and their application in diethylamine (DEA) sensing for the first time. The Pd-doped Ni-P2O5/MoO3 HPHS was synthesized by doping different proportions of palladium-containing precursors using hydrothermal and solid-state reaction techniques. The concentration of oxygen vacancies in the HPHS composite increased by increasing Pd doping from 2 to 6 weight percent (wt %) but later reduced, according to X-ray photoelectron spectroscopy (XPS) measurements. Pd6%Ni-P2O5/MoO3 has the highest sensitivity to DEA (Ra/Rg = 42.5) and is 5.0 times and 42.5 times more sensitive than the pure Ni-P2O5/MoO3 HPHS (Ra/Rg = 8.5) and commercial ammonium phosphomolybdate (Ra/Rg = 1) at 175 °C toward 10 ppm DEA. Moreover, the DEA sensor exhibits a low detection limit (Ra/Rg = 3.5@1 ppm) with a wide dynamic response (Ra/Rg = 145.5@50 ppm). The remarkable improvement in DEA sensitivity is attributed to the hollow polyhedral structure, heterostructures, and oxygen vacancies formed by Pd doping. This study confirms that developing Pd-doped Ni-P2O5/MoO3 HPHSs provides an innovative approach for DEA sensors.