Bi2O3 nanosheets arrays in-situ decorated on carbon cloth for efficient electrochemical reduction of nitrate

Excessive nitrate in industrial wastewater is still an important environmental protection issue for human beings. As nitrate promoter metal, Sn has been extensively studied in nitrate reduction reaction (NITRR). However, it suffers from high selectivity of nitrite as the final product at times. As the same main group as Sn, bismuth-based materials have exhibited excellent performance in the field of electrochemical reduction reactions but were rarely investigated for NITRR. In this study, Bi2O3 nanosheets in-situ decorated on carbon cloth (Bi2O3-CC) was synthesized and it showed larger surface area and higher electrical conductivity than those of dropped Bi2O3 nanosheets onto carbon cloth (Bi2O3/CC). Experimental results show that the nitrate removal efficiency of Bi2O3-CC increased by 12.7% than that of Bi2O3/CC at the same condition. Besides, the presence of Cl− benefits the NITRR process since the reaction of Bi2O3 and Cl− in acidic conditions can accelerate the conversion of Bi3+ to Bi0. The mechanism of the NITRR process was proposed based on the electrochemical and scavenging experiments. It was found that both the direct electron transfer and atomic H∗ contribute to the electrochemical reduction of nitrate to ammonia. More importantly, when Bi2O3-CC was applied to actual garbage fly ash wastewater, most nitrates were converted to ammonia. The designed Bi2O3-CC is a high-potential material for converting nitrate in industrial wastewater to valuable feedstock chemical ammonia with high efficiency.