Functionalization of graphitic carbon nitride/ZnO heterojunctions with zinc cyanamide groups: A powerful approach for photocatalytic degradation of anticancer drugs

• Developed cost-effective CN/ZnO photocatalysts with tunable zinc cyanamide content. • Highest photocatalytic activity obtained using the composite with zinc cyanamide. • Composite with 75 wt% of zinc chloride and treated at 550 °C is the most active. • Remarkable stability across catalytic cycles ensured by Zn–N bond stabilization. • Reaction intermediates of 5-fluorouracil degradation identified. Graphitic carbon nitride/zinc oxide composites (CN/ZnO) were innovatively synthesized via a one-pot thermal treatment of a mixture of melamine and different zinc salts (zinc acetate, zinc nitrate, zinc sulfate, and zinc chloride) as the precursor of CN and ZnO, respectively. Composites derived from acetate, nitrate or sulfate showcased hexagonal ZnO wurtzite phase, while those prepared with zinc chloride revealed a unique secondary phase identified as tetragonal zinc cyanamide (ZnNCN). This novel phase formation was fine-tuned by optimizing synthesis conditions, including temperature ranging from 450 to 650 °C and metal salt loading between 25 and 75 wt%. Photocatalytic testing for the degradation of cyclophosphamide (CP) and 5-fluorouracil (5-FU) under near UV–Vis irradiation, highlighted the standout performance of the composite synthesized with 75 wt% zinc chloride at 550 °C, labelled C-75–550. This composite delivered superior activity, attributed to enhanced pollutant adsorption and the suppression of electron-hole recombination due to the synergistic interplay of CN, ZnO, and ZnNCN. Furthermore, C-75–550 exhibited remarkable stability across multiple cycles, bolstered by Zn–N bond stabilization. Advanced analysis using UHPLC-MS, coupled with reactive species scavenger studies, allow to propose several pathways for the photodegradation of 5-FU, underscoring the composite transformative potential in environmental remediation.