Controllable Acid Activation of Sulfur-Doped Carbon Nitride Enables Enhancement in Photocatalytic Indigo Carmine Degradation Performance

Herein, we introduce a controllable acid activation method of sulfur-doped carbon nitride (CNT) to enhance its photodegradation efficiency for indigo carmine. We establish that the surface functionalization of sulfur-doped carbon nitride using a diluted H2SO4/H2O2 aqueous solution treatment extends visible light absorption, promotes charge separation, and enables improvement in photocatalytic activity. More specifically, the optimal sample (E1-CNT) exhibits a remarkable indigo carmine degradation performance of 96.27% (at 25 ppm) within 40 min under UV light irradiation, comparable to the top-performing photocatalysts reported in the literature. The apparent first-order rate constants of E1-CNT are 2× and 3.6× higher than those of unmodified CNT and bulk CN from melamine, respectively. This work provides new insights into designing simple, affordable, highly active, and metal-free materials toward sustainable environmental remediation.