Light assisted room-temperature NO2 sensors with enhanced performance based on black SnO1-alpha@ZnO1-beta@SnO2-gamma nanocomposite coatings deposited by solution precursor plasma spray

The development of room-temperature gas sensors with high performance for nitrogen dioxide gases is of great importance and appealing. Our previous works show that visible light illumination is an effective method to replace heating. In this paper, solution precursor plasma spray (SPPS) process is used to prepare black SnO1-alpha@ ZnO1-beta@SnO2-gamma, sensitive coatings. Stoichiometric ZnO, SnO2 and SnO are in white color. The introduced highly concentrated donor defects provided by SPPS process make them turn to black. The light absorption range of the black coatings was extended from ultraviolet area to yellow light region. Raman spectroscopy, photoluminescence spectroscopy and X-ray photoelectron spectroscopy were used to characterize the chemical compositions and oxidation states of SPPS coatings. Donor defects formed deep donor levels between the valence band and conduction band, which can be excited under visible light illumination. FE-SEM and HRTEM images exhibited a highly porous nanostructure, and n-n heterojunctions were formed between SnO1-alpha,ZnO1-beta and SnO2-gamma The SPPS coatings exhibited an obvious response towards 1.0 ppm NO2 gas under visible light illumination at room temperature. The enhanced sensing performance was mainly attributed to the presence of donor defects and homogenous heterojunctions.