Hybrid MnFe-LDO-biochar nanopowders for degradation of metronidazole via UV-light-driven photocatalysis: Characterization and mechanism studies

Abstract

A cost-competitive MnFe-LDO-biochar hybrid catalyst was successfully synthesized via a simple yet efficient technique for the decomposition of metronidazole (MZ). MnFe-LDO-biochar was characterized by various techniques and the results revealed that it has a bandgap of 2.85 eV, high photocurrent response of 3.8 μA cm^-2 and can be separated rapidly from the bulk solution by an external magnet due to its saturation magnetization of 28.5 emu g^-1. Initially, in the dark condition, 20% of MZ was removed after 30 min when 20 mg L^-1 MZ solution was treated with 50 mg MnFe-LDO-biochar in the presence of 6 mM H₂O₂. The MZ degradation increased remarkably to ∼98% upon exposure to a UV light for 60 min. Under various processes, UV/MnFe-LDO-biochar/H₂O₂ presented high degradation rate constant of 0.226 min^-1 and lowest energy consumption cost of 0.38$ at 7.56 kWh m^-3 which is ∼13 times lower than the degradation of MZ by the photolytic process under similar conditions. The MZ photocatalytic decomposition trend revealed a multiprocess mechanism influenced majorly by ^•OH and partly by h⁺ and ^•O₂^-. Note that in MnFe-LDO-biochar/UV system; 5% of MZ degradation was observed after 120 min and reached 13% after 300 min. MnFe-LDO-biochar maintained ∼88% reuse efficiency after three consecutive recycling tests.

Keywords: Biochar; Emerging pollutants; Hybrid magnetic recyclable catalyst; Metronidazole degradation; Mn–Fe LDO; Photocatalysis.