Surface CN bonds mediate photocatalytic CO₂ reduction into efficient CH₄ production in TiO₂-decorated g-C₃N₄ nanosheets

Graphitic carbon nitride (g-C3N4, CN) has garnered considerable attention in the field of photocatalysis due to its favorable band gap and high specific surface area. However, its primary practical limitation lies in the strong radiative recombination of lone pair (LP) electronic states, leading to limited efficiency in separating photogenerated carriers and subsequently diminishing photocatalytic performance. In this study, we devised and synthesized a heterojunction photocatalytic system comprising TiO2 nanosheets supported on modified g-C3N4 (MCN), designated as MCN/TiO2. The presence of C equivalent to N functional groups on the tri-s-triazine nitrogen captures photogenerated electrons by modifying LP electronic states, resulting in a reduction in the fluorescence emission intensity of g-C3N4. Simultaneously, it forms chemical bonds with the supported TiO2 nanosheets, creating an efficient electron transfer pathway for the accumulation of photogenerated electrons at the active Ti sites. Experimentally, the MCN/TiO2 photocatalytic system exhibited optimal performance in CO2 reduction. The CH4 production rate reached 26.59 mu mol g(-1) h(-1), surpassing that of TiO2 and CN/TiO2 by approximately 8 and 3 times, respectively. Furthermore, this photocatalytic system demonstrated exceptional photostability over five cycles, each lasting 4 h. This research offers a valuable approach for the efficient separation and transfer of photogenerated carriers in composite materials based on g-C3N4.