Bi₁₂SiO₂₀/g-C₃N₄ heterojunctions: Synthesis, characterization, photocatalytic activity for organic pollutant degradation, and mechanism

This work reports the synthesis of new and efficient composite photocatalysts (Bi₁₂SiO₂₀/g-C₃N₄) via the controlled hydrothermal method. The Bi₁₂SiO₂₀/g-C₃N₄ composites were characterized by XRD, SEM-EDS, HRTEM, FT-IR, XPS, DRS, BET, PL, and EPR. In comparison to pure Bi₁₂SiO₂₀ and g-C₃N₄, the Bi₁₂SiO₂₀/g-C₃N₄ materials showed significantly higher photocatalytic activity for degradation of crystal violet (CV) under visible-light irradiation (99% in 48 h). The 5 wt% Bi₁₂SiO₂₀/g-C₃N₄ composite revealed the highest rate constant of CV degradation (0.078 h⁻¹); 15 and 2 times larger than the constants obtained with individual Bi₁₂SiO₂₀ and g-C₃N₄, respectively. Further investigation of the photocatalytic activity of the 5 wt% Bi₁₂SiO₂₀/g-C₃N₄ materials were performed on other organic pollutants. 98% degradation of 2-hydroxybenzoic acid (2-HBA) and 99.5% degradation of rhodamine-B (RhB) were achieved upon exposure to visible-light irradiation for 72 h with 5 wt% Bi₁₂SiO₂₀/g-C₃N₄. Bi₁₂SiO₂₀/GO (graphene oxide) composites were also synthesized to compare the photocatalytic activities of different Bi heterojunctions. It was found that Bi₁₂SiO₂₀/g-C₃N₄ photocatalysts had enhanced photocatalytic activity in degradation of CV and 2-HBA and were considerably more stable in recycling experiments in comparison to Bi₁₂SiO₂₀/GO photocatalysts. Lastly, the plausible photocatalytic mechanism for the Bi₁₂SiO₂₀/g-C₃N₄ composite material was proposed and the principal active species involved in the photodegradation of CV were investigated using scavenger and ESR experiments. The Bi₁₂SiO₂₀/g-C₃N₄ composite demonstrates good photocatalytic activity, stability and reusability, demonstrating its prospective use in photodegradation applications under visible-light irradiation.