A comparative study of TiO2 preparation method on their photocatalytic activity for CO2 reduction

Abstract

In this work, we aimed to correlate the structural properties of different TiO2 with their photocatalytic performance and selectivity during CO2 photocatalytic reduction at different pH. We prepared two types of TiO2 photocatalysts and characterized them in detail using X-ray powder diffraction, field emission scanning electron microscope, nitrogen adsorption, UV-Vis spectroscopy, photoelectrochemical measurements and X-ray photoelectron spectroscopy techniques. The prepared photocatalysts demonstrated significantly higher selectivity to CO2 reduction (CH4 and CO yields), than a commercial P25. Among them, the photocatalysts TiSG, which had the lowest portion of hydroxyl oxygen species, had the highest photoreduction efficiency. Therefore, the key factors in photocatalytic CO2 reduction with TiO2 are not only the phase composition but also the portion of different types of surface oxygen species, which strongly affects their efficiency and selectivity. Another objective was to investigate the effect of pH on the efficiency and especially the selectivity of photocatalytic CO2 reduction. While methane is mainly formed in basic environments, carbon monoxide is formed in more acidic environments. Also, hydrogen production is twice as high in more acidic environment compared to the basic environment.