Advanced activation of persulfate by polymeric g-C₃N₄ based photocatalysts for environmental remediation: A review

Photocatalytic materials for photocatalysis is recently proposed as a promising strategy to address environmental remediation. Metal-free graphitic carbon nitride (g-C₃N₄), is an emerging photocatalyst in sulfate radical based advanced oxidation processes. The solar-driven electronic excitations in g-C₃N₄ are capable of peroxo (O‒O) bond dissociation in peroxymonosulfate/peroxydisulfate (PMS/PDS) and oxidants to generate reactive free radicals, namely SO₄^•− and OH^• in addition to O₂^•− radical. The synergistic mechanism of g-C₃N₄ mediated PMS/PDS photocatalytic activation, could ensure the generation of OH^• radicals to overcome the low reductive potential of g-C₃N₄ and fastens the degradation reaction rate. This article reviews recent work on heterojunction formation (type-II heterojunction and direct Z-scheme) to achieve the bandgap for extended visible light absorption and improved charge carrier separation for efficient photocatalytic efficiency. Focus is placed on the fundamental mechanistic routes followed for PMS/PDS photocatalytic activation over g-C₃N₄-based photocatalysts. A particular emphasis is given to the factors influencing the PMS/PDS photocatalytic activation mechanism and the contribution of SO₄^•− and OH^• radicals that are not thoroughly investigated and require further studies. Concluding perspectives on the challenges and opportunities to design highly efficient persulfate-activated g-C₃N₄ based photocatalysts toward environmental remediation are also intensively highlighted.