This paper presents a critical review of novel achievements in the modification of N–TiO₂ photocatalytic systems aimed at enhancing TiO₂ applications in the areas of energy conversion and environmental clean-up. Herein we studied the synthesis, physical properties, as well as synergism of modified N-doped TiO₂. Based on the studies reported in the literature, metal, nonmetal and metal oxide modified N–TiO₂ are very effective systems to extend the activating spectra to the visible range. Therefore, modified N–TiO₂ play an important role in the development of efficient photocatalysts for future perspectives.

Platinum nanoparticles (Pt NPs) are one of the most efficient cocatalysts in photocatalysis, and their size determines the activity and the selectivity of the catalytic reaction. Nevertheless, an in-depth understanding of the platinum’s size effect in the carbon dioxide photocatalytic reduction is still lacking. Through analyses of the geometric features and electronic properties with variable-sized Pt NPs, here we show a prominent size effect of Pt NPs in both the activity and selectivity of carbon dioxide photocatalytic reduction. Decreasing the size of Pt NPs promotes the charge transfer efficiency, and thus enhances both the carbon dioxide photocatalytic reduction and hydrogen evolution reaction (HER) activity, but leads to higher selectivity towards hydrogen over methane. Combining experimental results and theoretical calculations, in Pt NPs, the terrace sites are revealed as the active sites for methane generation; meanwhile, the low-coordinated sites are more favorable in the competing HER.