Bifunctional hierarchical WO3 nanorods@Br-doped g-C3N4 Z-scheme heterojunctions for efficient tetracycline photodegradation: Optimization of key parameters, toxicological assessment, and electrocatalytic hydrogen evolution reaction

In this study, graphitic carbon nitride (CN) and tungsten trioxide (WO₃) were successfully incorporated into bromine (Br)-doped graphitic carbon nitride (BCN) using an in-situ hydrothermal method. The photocatalytic efficiency of the resulting WO₃/Br-doped CN (WBCN) composites for the removal of tetracycline (TC) antibiotics under sunlight irradiation was evaluated. The mass ratio of WO₃ to Br-doped CN (BCN) significantly influenced TC adsorption and photocatalytic degradation, with an optimal ratio of 9:1. The synthesized catalyst exhibited exceptional performance, achieving 98% TC detoxification under sunlight, attributed to enhanced light absorption, efficient charge separation, and reduced electron-hole (e^-/h⁺) recombination facilitated by BCN doping. Trapping experiments and ESR analysis identified ^•O₂^- and ^•OH as the primary reactive species in TC decomposition, with h⁺ radicals playing a secondary role. Reusability tests further confirmed the high stability of the photocatalyst. The Z-scheme charge transfer mechanism was elucidated, highlighting the crucial role of Br doping in enhancing synergistic interactions between WO₃ and CN. Additionally, the nickel foam (NF) electrode supported by the WBCN-2 composite demonstrated remarkable electrocatalytic activity for hydrogen evolution, achieving a minimum overpotential of 99 mV and a Tafel slope of 108 mV/dec at a current density of 10 mA/cm². The WBCN-2@NF composite catalyst also achieved excellent performance, with a low cell voltage of 1.77 V at 10 mA/cm². Chronopotentiometry (CP) tests revealed remarkable long-term stability, with minimal current loss over 15 h of continuous operation. Overall, the WBCN composite exhibits excellent photocatalytic and electrocatalytic performance, making it a promising candidate for practical environmental remediation and sustainable energy production.