Metal single-atom modified TiO2 or g-C3N4: reaction mechanism and research progress as semiconductor photocatalysts

Abstract

As photocatalytic materials, TiO₂ and g-C₃N₄ are widely used in the degradation of organic pollutants, removal of volatile organic compounds or nitrogen oxides, and photocatalytic reduction of CO₂, among other applications, and have excellent prospects for use. However, due to the large band gap of TiO₂, its absorption of visible light is limited, and the electron–hole pair is easy to recombine, resulting in poor photocatalytic performance. Although g-C₃N₄ can absorb visible light, its limited absorption range and insufficient utilization of long-wavelength light also restrict its photocatalytic performance. Single-atom modified TiO₂ or g-C₃N₄ has become a new strategy to overcome these challenges. TiO₂ and g-C₃N₄ are widely used as ideal carriers for single-atom photocatalysts, benefiting from their strong metal–support interactions (SMSIs), high coordination flexibility, excellent chemical stability, defect tolerance, and scalability. Single-atom modified TiO₂ or g-C₃N₄ can precisely tailor the electronic structure, introduce crystalline defects, and optimize light absorption characteristics. They effectively address key limitations in photocatalysis, including rapid charge recombination, a narrow visible light response range, and low atomic utilization efficiency, thereby enhancing overall performance. In this paper, we summarize the research progress on single-atom modified TiO₂ or g-C₃N₄ photocatalysts, including those modified with Cu, Fe, Pt, Ag, and Au, and analyze their excellent photocatalytic performance and possible reaction mechanisms in detail. Finally, a brief perspective has been proposed to improve the photocatalytic activity by single-atom modified TiO₂ or g-C₃N₄ in solving energy and environmental problems.