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 TiO 2 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-TiO 2 composites to promote multielectron transfer, such as in CO 2 reduction. In this work, we assembled oxygen-defected TiO 2 -Keggin POM microspheres by ultrasonic spray pyrolysis technique for multielectron transferred reactions including mineralization of gaseous acetaldehyde and CO 2 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%) H 3 PW 12 O 40 (HPW)-TiO 2 displays the highest activity among composites of HPW-TiO 2 , H 4 SiW 12 O 40 (HSiW)-TiO 2 , and H 3 PMo 12 O 40 (HPMo)-TiO 2 , which is consistent with the best energy level match between defective TiO 2 and H 3 PW 12 O 40 . The strategy of assembly of POM-TiO 2 microspheres provides a facile and promising solution to promote multielectron reaction for environmental purification and solar-to-fuel conversion.