Z-scheme heterojunction with spatially separated dual redox-active sites for coupled carbon dioxide photoreduction and tetracycline photooxidation

Coupling solar-powered CO 2 conversion with pollutant removal via Z -scheme heterojunctions offers a promising strategy to simultaneously address energy and environmental challenges. However, achieving efficient charge separation and optimizing active sites for both reduction and oxidation reactions are still significant challenges. Herein, a Z -scheme heterojunction photocatalyst with spatially separated dual active sites (hydroxyl-functionalized red phosphorus (HRP) and amino-functionalized graphitic carbon nitride (ACN)) was developed to enable the concurrent photoreduction of CO 2 and photooxidation of tetracycline (TC). The optimized heterojunction, incorporating 1.25 wt% HRP, achieved a 4.96-fold increase in CO yield and 1.09-fold improvement in TC degradation compared with a red phosphorus/graphitic carbon nitride (RP/CN) system without surface functionalization. Density functional theory calculations and experimental analyses confirmed a Z -scheme charge transfer mechanism wherein hydroxyl groups facilitated hole-mediated TC oxidation and amino groups promoted electron-driven CO 2 reduction. The 1.25HRP/ACN photocatalyst demonstrated an electron transfer efficiency of 87.8 %, significantly surpassing the 64.9 % observed for 1.25RP/CN, highlighting the synergistic benefits of dual-site engineering. This study provides detailed insights into dual-functionalized Z -scheme heterojunctions with spatially separated redox-active sites, advancing the design of integrated systems for solar fuel generation and environmental remediation.