Reusable Sulfur-Doped g-C₃N₄ Hydrogel Beads for Sustainable Antibiotic Removal from Water under Visible-Light Irradiation

Abstract

The continuous discharge of pharmaceutical contaminants into aquatic environments has emerged as a significant environmental challenge due to their persistence and ecological risks. Among these pollutants, tetracycline is frequently detected in wastewater and conventional treatment systems often fail to achieve its complete removal. This study aimed to develop a reusable sulfur-doped graphitic carbon nitride (S-gC3N4) hydrogel photocatalyst for efficient antibiotic degradation under visible-light irradiation and to evaluate its potential for sustainable wastewater treatment. Sulfur-doped g-C3N4 was synthesized through thermal modification and immobilized within a carboxymethyl cellulose (CMC)-based hydrogel matrix to improve catalyst stability, handling, and recovery. The prepared material was characterized using XRD, FTIR, SEM–EDX, UV– DRS, PL and XPS analyses to examine its structural and optical properties. Photocatalytic degradation experiments were performed using tetracycline as a model contaminant under visible-light exposure. The hydrogel-immobilized S-g-C3N4 exhibited enhanced visible-light absorption and reduced charge recombination compared with pristine g-C3N4. Under optimized operating conditions, the system achieved nearly 98% tetracycline degradation, demonstrating high photocatalytic efficiency and operational stability. The hydrogel matrix facilitated catalyst recovery and maintained photocatalytic activity during repeated use. The developed S-g-C3N4 hydrogel system offers a sustainable and reusable platform for antibiotic-contaminated wastewater treatment and highlights the potential of hydrogel assisted photocatalysis for environmentally relevant water purification application.