Template-assisted modified g-C3N4 for visible-light-driven degradation of emerging organic pollutants: Mechanistic pathways and toxicity assessment revealed by LC-MS and DFT.

This study presents a comprehensive mechanistic and toxicological investigation into the visible-light-driven degradation of bisphenol A (BPA), 4-bromophenol (4-BP), and sulfamethoxazole (SMX) using template-assisted modified graphitic carbon nitride (MCN) photocatalysts under visible light irradiation. The photocatalysts were synthesized via a one-pot polymerization process using homemade calcium cyanamide (CaCN2) as a template. The prepared MCN nanosheets exhibited significantly enhanced photocatalytic performance, with improved charge separation, reduced sheet grain size, and increased activity, attributed to template-assisted synthesis. The degradation efficiencies of BPA, 4-BP, and SMX were systematically evaluated, demonstrating superior degradation performance. Integrated analytical techniques, including LC-MS/MS, elucidated the degradation pathways, whereas Density Functional Theory (DFT) calculations provided detailed insights into the adsorption mechanisms and molecular descriptors of the pollutants on the photocatalyst surface. Theoretical calculations indicated significant differences in adsorption energy and interaction between the pollutants and MCN, with SMX showing the strongest adsorption but slower degradation kinetics, attributed to its complex structure. Additionally, ecotoxicological assessments using Ecological Structure-Activity Relationship (ECOSAR) predicted a reduction in the toxicity of degradation intermediates, underscoring the broad applicability of MCN in environmental remediation. These findings provide valuable guidance for the rational design of efficient photocatalysts for the degradation of emerging organic pollutants.