Thin-film photoreactor with hydrogel-immobilized carbon dot-functionalized graphitic carbon nitride for pollutant degradation

This study reports the development of a sustainable, metal-free photocatalytic system for degrading emerging pollutants in water. A novel photocatalyst based on graphitic carbon nitride modified with carbon dots and amine-functionalized (GCN@CD-A) was synthesized to enhance visible-light absorption and charge separation, resulting in improved photocatalytic activity. The GCN@CD-A composite was immobilized within biopolymer hydrogels composed of carboxymethylcellulose (CMC) and sodium alginate (SA) to address the recovery and reuse limitations associated with powdered catalysts. Different CMC:SA ratios were tested to optimize the mechanical stability and photocatalytic performance of the hydrogel matrix. Among them, ratio 1:1 provided the best balance between structural integrity and catalytic efficiency, maintaining degradation performance comparable to the powdered catalyst toward model pollutants such as Rhodamine B, paracetamol, and acebutolol. Comprehensive material characterization confirmed successful composite formation and effective catalyst immobilization, while scavenger experiments identified superoxide radicals as the dominant reactive radical. The optimized hydrogel was subsequently integrated into a 3D-printed inclined thin-film photoreactor designed to enhance light exposure and mass transfer under laminar flow conditions. Photocatalytic performance was evaluated in recirculation mode using different water matrices, including ultrapure water, tap water, and secondary effluent. Complete degradation of the target pollutants was achieved under visible light irradiation, although reaction efficiency was influenced by water matrix complexity. Overall, this integrated approach demonstrates a scalable, eco-friendly solution for advanced water treatment, combining efficient pollutant degradation with improved catalyst reusability and practical applicability.