Bismuth-based heterojunction photocatalysts for antibiotic remediation: A review of tetracycline degradation and mechanistic insights.

The present review focuses on the bismuth-based heterojunction photocatalysts for the degradation of tetracycline (TC) antibiotic. The frequent usage of antibiotics causes several environmental and health concerns due to their widespread occurrence and persistence in aquatic ecosystems. In this context, bismuth-based photocatalysts have extended noteworthy interest for their tunable structures, visible-light activity, suitable band gap energies, and unique physicochemical properties. However, their distinct use is limited by inadequate charge separation and reduced conduction band potentials. To address these limitations, the development of Type-II, Z-scheme, p-n heterojunctions, and more recently, S-scheme heterojunctions has been studied and reviewed to improve the charge carrier dynamics and light absorption. In this review, various bismuth-based heterojunctions, detailing their synthesis methods, structural properties, and mechanism involve therein. Notably, few of bismuth-based heterojunction photocatalysts stand out as the most efficient, owing to their strong visible-light absorption, multistep charge transfer channels, and active surface chemistry. The heterojunction photocatalysts exhibit significant enhancements in photocatalytic efficiency by expediting the separation of photogenerated charges and reducing recombination rates but have certain limitations. The degradation of TC reached over 90 % in short time period, highlighting the efficacy of the photocatalysts reported over time. The synergistic roles of reactive species, including hydroxyl radicals (•OH), superoxide radicals (•O), and photogenerated holes (h), in the degradation of TC are discussed. Further, this review highlights the limitations and prospects of the conventional mechanisms and S-scheme heterojunction based-mechanism, respectively. Theoretical aspects were reviewed to enhance bismuth-based photocatalysis and what important major steps need to be taken for a strong heterojunction formation. The review highlights the design of bismuth-based photocatalysts with anticipated extended light response, strong heterojunction formation, stability, scalability, development of thin-film designs, and degradation of other pollutants.