Controllable\nAcid Activation of Sulfur-Doped Carbon\nNitride Enables Enhancement in Photocatalytic Indigo Carmine Degradation\nPerformance

Herein, we introduce a controllable acid activation method\nof sulfur-doped\ncarbon nitride (CN<sub>T</sub>) to enhance its photodegradation efficiency\nfor indigo carmine. We establish that the surface functionalization\nof sulfur-doped carbon nitride using a diluted H<sub>2</sub>SO<sub>4</sub>/H<sub>2</sub>O<sub>2</sub> aqueous solution treatment extends\nvisible light absorption, promotes charge separation, and enables\nimprovement in photocatalytic activity. More specifically, the optimal\nsample (E<sub>1</sub>-CN<sub>T</sub>) exhibits a remarkable indigo\ncarmine degradation performance of 96.27% (at 25 ppm) within 40 min\nunder UV light irradiation, comparable to the top-performing photocatalysts\nreported in the literature. The apparent first-order rate constants\nof E<sub>1</sub>-CN<sub>T</sub> are 2× and 3.6× higher than\nthose of unmodified CN<sub>T</sub> and bulk CN from melamine, respectively.\nThis work provides new insights into designing simple, affordable,\nhighly active, and metal-free materials toward sustainable environmental\nremediation.