Remarkable formaldehyde photo-oxidation efficiency of Zn2SnO4 co-modified by Mo doping and oxygen vacancies

[Display omitted] •Zn2SnO4 with Mo doping and oxygen vacancies was obtained by a hydrothermal method.•Dual active sites in Zn2SnO4 for HCHO photooxidation were identified.•The complete HCHO mineralization with ultra-high activity was achieved.•The mechanism of deep HCHO photooxidation was proposed. Formaldehyde (HCHO) is one of the major volatile organic compounds (VOCs) contributing to both urban and indoor air pollution. It is emitted from several industrial activities and construction materials. Photocatalytic oxidation is a green promising technology aiming at HCHO removal. However, it still has some scientific challenges not fully addressed, like insufficient reaction active sites and not enough active species. This results in low HCHO removal efficiency, several toxic intermediates and poor stability. Therefore, the design of photocatalysis with surface-active sites, improved mineralization activity and recycling stability is of crucial importance. Herein, we report a facile one-pot hydrothermal method to prepare Zn2SnO4 (ZSO) with transition metal Mo doping (using Na2MoO4·2H2O as molybdenum source). Our experiments show that Mo is successfully incorporated into the ZSO lattice and contributes to the generation of oxygen vacancies (OVs). Moreover, the introduction of Mo enhances the separation and migration of photogenerated carriers and hinders their recombination. Furthermore, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations reveal that switching the active sites from O terminals to Mo ones effectively improves adsorption and activation of the target molecules (O2, H2O, and HCHO), and promotes conversion of the reaction intermediates. Thus, ZSO co-modified by Mo doping and oxygen vacancies allows to achieve an efficient HCHO removal activity of 96%, which is much higher than pristine ZSO (21%) and other previously reported photocatalysts.