Investigation on the structure-performance of phthalic acid carboxyl position and carbon nitride towards efficient photocatalytic degradation of organic pollutants

Polymeric carbon nitride as photocatalysts to address environmental issues attract broad interest. Anchoring aromatic ring on CN surface can improve its charge pair separation, but the effect of functional group position of aromatic ring on its performance is ignored. Herein, we used three isomers of phthalic acid (phthalic acid, isophthalic acid and terephthalic acid) and urea to synthesize modified carbon nitride as a photocatalyst to remove sulfamethazine (SMZ). The phthalic acid may act as group modification and enhanced the absorption of longer wavelengths of carbon nitride, while part of isophthalic acid and terephthalic acid may enter the framework of carbon nitride as benzene ring and the others may act as the amorphous carbon in carbon nitride. Consequently, the phthalic acid modified carbon nitride (PA-CN) exhibited the optimal degradation performance for SMZ removal (0.0737 min−1). It was further revealed that the O2− and h+ played the significant role in the photocatalytic process. This study reveals the effect of the position of organic acid functional groups on the performance of carbon nitride, and points out that PA-CN can be applied to the purification of wastewater containing refractory pollutants.