Synthesis of an iso-type graphitic carbon nitride heterojunction derived from oxamide and urea in molten salt for high-performance visible-light driven photocatalysis

Abstract

This research focuses on a straightforward method for synthesising thrice-modified g-C₃N₄ (carbon nitride; CN) with cyano groups and an asymmetric planar heptazine/triazine-based iso-type structure. The thermal polymerisation of urea in the presence of molten salt (KCl + LiCl) and oxamide easily produced an effective photocatalyst featuring the desired modifications to the CN framework (hereafter referred to as MOCN). Various characterisation techniques were performed to evaluate the properties of the synthesised MOCN. Compared with pristine CN, MOCN exhibited considerably greater activity toward bisphenol A (BPA) degradation. The triple chemical structural modification of g-C₃N₄ resulted in an 11.6-fold increase in rate constant for BPA degradation compared with that obtained when pristine CN was used. The improved photocatalytic performance of MOCN could be attributed to its enhanced specific surface area, changes in its energy band structure/bandgap, sub-gap formation, efficient charge separation/transfer, and low electron–hole (e⁻/h⁺) recombination rate. The cyano groups, which are strong e⁻-withdrawing groups, of MOCN promoted the rapid separation and transport of photogenerated e⁻/h⁺ pairs on its surface. MOCN exhibited high stability during repeated photocatalytic reactions and successfully mineralised BPA to CO₂ and H₂O. This research supplements the current understanding of the in situ modification of g-C₃N₄ and presents MOCN as a remarkably effective, visible-light sensitive, stable, and reusable photocatalyst with potential use in environmental purification.