BiO 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, BiO nanosheets in-situ decorated on carbon cloth (BiO-CC) was synthesized and it showed larger surface area and higher electrical conductivity than those of dropped BiO nanosheets onto carbon cloth (BiO/CC). Experimental results show that the nitrate removal efficiency of BiO-CC increased by 12.7% than that of BiO/CC at the same condition. Besides, the presence of Cl benefits the NITRR process since the reaction of BiO and Cl in acidic conditions can accelerate the conversion of Bi to Bi. 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 BiO-CC was applied to actual garbage fly ash wastewater, most nitrates were converted to ammonia. The designed BiO-CC is a high-potential material for converting nitrate in industrial wastewater to valuable feedstock chemical ammonia with high efficiency.