Influence of oxygen vacancies on the performance of ZnO nanoparticles towards CO2 photoreduction in different aqueous solutions

CO2 photoreduction is a promising technique for fuel production using semiconductors as photocatalysts. However, introducing defects on the crystal structure of the photocatalysts affects greatly on its photocatalytic activity. In this regard, defected ZnO nanoparticles were synthesized at 300, 350, and 400 degrees C by thermal decomposition method. XPS data revealed the presence of oxygen vacancies for ZnO samples. These results were furtherly confirmed by Raman, FTIR, and SEM analysis. It was pointed out that Methanol was the major attainable product through the photochemical reduction of CO2 under UV-light. Importantly, the created oxygen vacancies have played a dynamic role in facilitating the charge transfer rather than recombination sites, hence improving the catalytic activity. The highest efficiency was detected over ZnO sample prepared at 350 degrees C using HCO3- anion in aqueous solution with about 113 umol/g maximum yield of methanol. Different scenarios were discussed implying the synergic effect of anion type and oxygen vacancies. A hypothesis investigation of the reaction mechanism of CO2 photoreduction over ZnO was proposed.