Biochar-templated g-C3N4/Bi2O2CO3/CoFe2O4 nano-assembly for visible and solar assisted photo-degradation of paraquat, nitrophenol reduction and CO2 conversion

The development of novel visible powered nano-heterojunctions with multi-pronged capabilities for environmental and catalytic applications has been gaining importance for persistent pollutant degradation & clean energy production. A magnetically recoverable biochar supported ternary g-C3N4/Bi2O2CO3/CoFe2O4 heterojunction (BCBF) was fabricated which shows a high visible photoactivity. The heterojunction was used for degradation of pesticide paraquat under visible radiation (Xe lamp), natural sunlight, photo-ozonation, peroxymonosulphate, and coupled conditions. A high degradation of 99.3% was achieved under visible radiation in 90 min and 92.1% under solar light in 120 min. Biochar supported ternary junction performs manifold faster than Bi2O2CO3/CoFe2O4, g-C3N4/CoFe2O4, g-C3N4/CoFe2O4, Bi2O2CO3 (BOC), CoFe2O4 (CF) and g-C3N4 (CN). The effect of operational parameters as effect of pH, H2O2, anions, ozone and peroxymonosulphate (PMS) was also studied. In BCBF + PMS + O-3 + Vis protocol a spectacular complete degradation was observed in less than 30 min. Ternary band structure efficiently reduces the charge recombination rate and promotes spectral activity which was confirmed by photoluminescence, photocurrent response and EIS analysis. By LC-MS, scavenging experiments and ESR studies a possible mechanism was also proposed. Cyto-toxicity studies of degraded products on human peripheral blood cells revealed almost 99% cell viability affirming the complete mineralization. The junction was also used for reduction of 4-nitrophenol into 4-aminophenol with complete conversion in less than 5 min with rate constant 13.05 x 10(-3) s(-1). In addition the ternary junction shows a high visible powered conversion of CO2 (p)roducing CH4 (similar to 119 mu mol g(-1)), CO (similar to 131 mu mol g(-1)) and O-2 (similar to 242 mu mol g(-1)) with a high rate constant of 13.05 x 10(-3) s(-1).