Temperature-Tuned ZnO/rGO/TiO2 Ternary All-solid-state Z-scheme Heterojunction for Enhanced Photocatalytic Degradation of Rhodamine B

The development of efficient photocatalyst with improved charge separation remains essential for enhancing the degradation of organic pollutants. In this study, ZnO/rGO/TiO 2 (ZrT) composites were successfully synthesized via a one-pot method, followed by calcination at 300, 500, and 700°C to investigate the influence of phase evolution on photocatalytic performance toward Rhodamine B (RhB) degradation. Phase analysis reveals a temperature-dependent transformation of TiO 2 from anatase (with minor brookite) to mixed anatase-rutile and finally rutile-dominant phases. The ZrT composite forms all-solid-state Z-scheme heterojunction, in which rGO acts as an efficient solid electron mediator. Among all samples, ZrT 500°C exhibits the lowest charge-transfer resistance and the highest photocatalytic activity, achieving 93% RhB degradation within 5 h with a first-order rate constant of 0.555 h -1 . The enhanced performance is attributed to the synergistic interaction between ZnO, mixed-phase TiO 2 , and rGO, which promotes efficient charge separation and reactive oxygen species generation. GC-MS analysis further confirmed the degradation of RhB into simpler organic compound through oxidative fragmentation pathways. These findings demonstrate that temperature-engineered ZnO/rGO/TiO 2 heterostructures are promising photocatalysts for efficient RhB degradation and wastewater treatment applications.