Recent advances on small molecule doped carbon nitride photocatalysts: Application in environmental water remediation and clean energy production

Sustainable photocatalytic clean energy production and environmental water remediation technologies represent effective strategies for mitigating energy and environmental crises. The key to successful implementation of photocatalysis lies in the choice of a suitable photocatalyst. Carbon nitride (CN or g-C 3 N 4 ), as a metal -free semiconductor, has been extensively utilized in photocatalytic energy conversion and environmental purification due to its stable physicochemical properties, cost-effective materials, straightforward preparation method and tuneability of structure/band-gap. However, CN faces challenges such as limited visible -light absorption, insufficient exposure of active sites, and high recombination rate of photogenerated carriers. Doping has emerged as an efficient strategy to enhance the photocatalytic activity of CN, particularly through small molecule doping, and numerous research reports have been reported in recent years, while there is no specialized reviews to summarize them. This paper provides a comprehensive summary of the research progress on small molecule doping for improving the catalytic activity of CN including the formation of CN skeleton (e.g., benzene ring, heterocyclic ring, small molecule bonding), via doping elements from small molecules (B, S, O, C, Cl, P) as well as defect formation induced by small molecule doping. At last, the current challenges and future prospects in this field are discussed.