Control over energy level match in Keggin polyoxometallate-TiO2 microspheres for multielectron photocatalytic reactions

Abstract

Recent years have witnessed that polyoxometallate (POM) is promising to mediate electron transfer on TiO2 for enhanced photocatalysis. Therein, significant progress is made on photooxidation process, which mainly involves single electron transfer. It still represents a major challenge to develop POM-TiO2 composites to promote multielectron transfer, such as in CO2 reduction. In this work, we assembled oxygen-defected TiO2-Keggin POM microspheres by ultrasonic spray pyrolysis technique for multielectron transferred reactions including mineralization of gaseous acetaldehyde and CO2 reduction. Comprehensive analysis including transient photovoltage, surface photovoltage, and photochromic phenomena reveal that oxygen defects could induce better energy level match and hence mediate multielectron transfer. With variation of loading amount and kind of POM, the (5 wt%) H3PW12O40 (HPW)-TiO2 displays the highest activity among composites of HPW-TiO2, H4SiW12O40 (HSiW)-TiO2, and H3PMo12O40 (HPMo)-TiO2, which is consistent with the best energy level match between defective TiO2 and H3PW12O40. The strategy of assembly of POM-TiO2 microspheres provides a facile and promising solution to promote multielectron reaction for environmental purification and solar-to-fuel conversion.