Activation of peroxymonosulfate by S-scheme Bi2S3/doped gCN heterostructure photocatalyst for highly efficient visible light driven tetracycline degradation: Insights into reaction mechanisms

A solid state microwave (MW) assisted hydrothermal method was used to prepare S-scheme heterojunction composite Bi2S3@doped gCN (BS@CN). TC was degraded upto 99.9 % under 20 min visible light, with synergistic action of 0.2 g/L catalyst having 10 wt% Bi2S3 (BS(10)@CN) and 1.5 g/L PMS, for initial TC concentration of 50 mg/L, exhibiting first order rate constant (kapp): 0.215 min 1. The modulation of band-structure due to the generation of heterojunction, coupled with different surface-bound redox cycles, i. e.,Co2 + /Co3 +|(surf),Ce-3 + /Ce-4 +|(surf). andBi(3) + /Bi-4 +... surf., helped the charge migration, separation of excited e-/h+ and production of reactive species, like,SO4 center dot- , (OH)-O-center dot,O-2(center dot),O-2(1), etc., that played important roles towards TC degradation. Band-structure determination, XPS analysis and other characterizations revealed the formation of Sscheme configuration and corresponding surface-bound metastable complexes towards self-regeneration and excellent catalytic activity of the composite, even in the contaminated real-life surface water sources. Extensive intermediate analysis was carried out to develop a detailed TC degradation pathway. The BS@CN photocatalyst can be recycled multiple times, without significant loss of photocatalytic activity (similar to 88 % TC degradation after 5 cycles). This study demonstrated the design and fabrication of metal oxide doped gCN/metal chalcogenide-based heterojunction photocatalysts that have potential applications towards the removal of refractory contaminants in aqueous medium.