Development of g-C3N4/BiVO4 Binary Component Heterojunction as an Advanced Visible Light-Responded Photocatalyst for Polluted Antibiotics Degradation

Type II Heterojunction Formed between {010} or {012} Facets Dominated Bismuth Vanadium Oxide and Carbon Nitride to Enhance the Photocatalytic Degradation of Tetracycline

Both type II and Z schemes can explain the charge transfer behavior of the heterojunction structure well, but the type of heterojunction structure formed between bismuth vanadium oxide and carbon nitride still has not been clarified. Herein, we rationally prepared bismuth vanadium oxide with {010} and {012} facets predominantly and carbon nitride as a decoration to construct a core-shell structure with bismuth vanadium oxide wrapped in carbon nitride to ensure the same photocatalytic reaction interface. Through energy band establishment and radical species investigation, both {010} and {012} facets dominated bismuth vanadium oxide/carbon nitride composites exhibit the type II heterojunction structures rather than the Z-scheme heterojunctions. Furthermore, to investigate the effect of type II heterojunction, the photocatalytic tetracycline degradations were performed, finding that {010} facets dominated bismuth vanadium oxide/carbon nitride composite demonstrated the higher degradation efficiency than that of {012} facets, due to the higher conduction band energy. Additionally, through the free radical trapping experiments and intermediate detection of degradation products, the superoxide radical was proven to be the main active radical to decompose the tetracycline molecules. Therein, the tetracycline molecules were degraded to water and carbon dioxide by dihydroxylation-demethylation-ring opening reactions. This work investigates the effect of crystal planes on heterojunction types through two different exposed crystal planes of bismuth vanadate oxide, which can provide some basic research and theoretical support for the progressive and controlled synthesis of photocatalysts with heterojunction structures.

Synchronous removal of tetracycline and copper (II) over Z‑scheme BiVO4/rGO/g-C3N4 photocatalyst under visible-light irradiation

The combined pollution of heavy metals and organic pollutants in water body has become one of vital environmental issues. Herein, a series of BiVO₄/rGO/g-C₃N₄ nanocomposites were synthesized for concurrent removals of organic pollutant and heavy metal. Results showed that using the optimized photocatalyst BiVO₄/rGO/g-C₃N₄-28, tetracycline (TC) removal of 87.3% and copper (Cu (II)) removal of 90.6% were achieved under visible-light irradiation within 3 h, respectively; much higher than those using BiVO₄ and g-C₃N₄. More importantly, synergistic effect of TC and Cu (II) removals occurred on the surface of BiVO₄/rGO/g-C₃N₄ in the TC-Cu (II) coexistence condition. Additionally, the ·OH and ·O₂- were the most important active species for TC oxidation, while photogenerated electrons were the most responsible for Cu (II) reduction. Results of various characterizations and electron spin resonance test demonstrated that BiVO₄/rGO/g-C₃N₄ was a Z-scheme photocatalyst. Based on the identified intermediates, possible degradation pathways and mechanisms for photocatalytic degradation of TC were proposed. This study advances the development and mechanism of photocatalysts for collaborative removal of pollutants.

Enhanced photocatalytic degradation of paraben preservative over designed g-C3N4/BiVO4 S-scheme system and toxicity assessment

Paraben preservatives have been listed as emerging pollutants due to their ubiquity in various environmental matrices, especially the water bodies. How to efficiently and practically eliminate these paraben pollutants is therefore of great importance. Herein, a designed S-scheme heterojunction photocatalyst, consisting of graphitic carbon nitride (g-C₃N₄) and monoclinic bismuth vanadate (BiVO₄), was fabricated by a facile hydrothermal synthesis and employed to treat benzyl-paraben (BzP). TEM and XPS analysis testified the intimate interaction between g-C₃N₄ and BiVO₄, and the consequently smoothed interfacial charge transfer rendered the feasible recombination of the photoexcited electrons (from BiVO₄) and holes (from g-C₃N₄). The as-established S-scheme system enabled the left g-C₃N₄ electrons and BiVO₄ holes to maintain the high redox abilities and accelerated the charge separation concurrently. In particular, the g-C₃N₄/BiVO₄ composite generated much higher photocurrent response as compared with pure g-C₃N₄ and BiVO₄, highlighting the improved separation of photoinduced charges. Therefore, under visible light and natural solar light irradiation, the g-C₃N₄/BiVO₄ composite showed the significantly enhanced photocatalytic degradation of BzP, which was further optimized with 5 wt% g-C₃N₄ in the composite. According to the Mott-Schottky plots and identified active species, the mechanism of the g-C₃N₄/BiVO₄ S-scheme heterojunction system was illustrated. In addition, during the photocatalytic degradation process, the acute toxicity of the reaction solutions on zebrafish embryos was notably reduced. In conclusion, the demonstrated strategy to enhance the photocatalytic performance by designing S-scheme heterostructure may provide more insights into the development of high-efficiency photocatalyst towards the solar energy utilization and environmental treatment. Furthermore, photocatalytic degradation had been proved to be an efficient method for eliminating the ecological risk of paraben pollutants, warranting more attention in future work.