Engineering a carbon quantum dot-bridged CuInS₂/MnFe-BTC/g-C₃N₄ Z-scheme photocatalyst for efficient removal of organic pollutants from water

Developing efficient, eco-friendly photocatalysts is essential to address water pollution by persistent organic contaminants like antibiotics and synthetic dyes. This study introduces a novel Z-scheme photocatalyst, CuInS₂/ MnFe-BTC/g-C₃N₄ (“CMG”) integrated with carbon quantum dots (CQD-CMG), synthesized through a green, microwave-assisted hydrothermal method, for visible-light-driven degradation of tetracycline (TC) and Reactive Yellow 145 (RY-145) dye. The resulting photocatalyst exhibited a high surface area (1031.5 m²/g), nanoparticle size (20–40 nm), broad visible-light absorption, and excellent charge separation efficiency (0.342 µA/cm²). The integration of carbon quantum dots significantly enhanced charge transfer and suppressed electron–hole recombination, as evidenced by electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) measurements. Under visible-light irradiation, CQD-15 %CMG achieved outstanding degradation efficiencies of 98.2 % for TC and 98.6 % for RY-145. Operational factors such as pH, pollutant concentration, catalyst dosage, coexisting anions, humic substances, and material reusability were thoroughly evaluated. Radical scavenging experiments and electron spin resonance (ESR) analysis identified ^•OH and ^•O₂^– as the dominant reactive species. Band structure analysis via UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS) and Mott–Schottky analysis confirmed that the photocatalytic mechanism followed an efficient Z-scheme charge transfer pathway. This work highlights the potential of CQD-CMG as a high-performance, sustainable photocatalyst for the remediation of contaminated water, offering a promising solution for advanced water purification technologies.