Sustainable conversion of lemon biomass into carbon quantum dots/TiO₂ composites for photocatalytic degradation of tetracycline under visible light

This study explores the synthesis of carbon quantum dots (CQDs) from natural lemon sources and evaluates their potential for photocatalytic applications from various perspectives. CQDs were successfully synthesized from natural lemon juice and lemon peel via a simple hydrothermal process. Furthermore, CQDs/TiO₂ composites were fabricated through a facile mixing process at room temperature. The hydrophilic functional groups and surface characteristics of the synthesized CQDs significantly enhanced the photocatalytic properties of the composites for removing organic pollutants in aqueous systems. The composites exhibited improved optical properties and band edge structures, facilitating effective operation under visible light irradiation. Enhanced charge carrier separation, mediated by the CQDs, facilitated the generation of superoxide radicals, which promoted a 97 % degradation of tetracycline. The degradation process resulted in the formation of 10 distinct intermediates and its mineralization within 2 h under optimal conditions. Both CQDs/TiO₂ demonstrated excellent structural stability and photocatalytic efficiency over repeated cycles, confirming their recyclability. Moreover, their robust performance across various water quality indices and environmental conditions highlights their potential as sustainable and eco-friendly water treatment technologies derived from natural materials.