Highly selective nitrate reduction to N₂ by Cu-nZVI/LDH bimetallic composite: Mechanism, reaction pathway and...

Due to the highly reductive capacity of nano zero-valent iron (nZVI), the reduction of nitrate (NO₃^--N) is prone to produce ammonia (NH₄⁺-N) as a by-product and has low selectivity for nitrogen gas (N₂). Selective conversion of NO₃^--N to harmless N₂ by regulating reaction pathway is the key to improve the reduction and nitrogen removal performance of nZVI-based materials. In this study, metal copper (Cu) was added to nZVI to prepare Cu-nZVI/LDH bimetallic composites. Cu was used as a catalyst to form a galvanic coupling with nZVI to accelerate electron transfer and improve the electron utilization efficiency. Synergism of adsorption and reduction of NO₃^--N was achieved through adsorption of layered bimetallic hydroxide (LDH) and reduction of nZVI. The results showed that the NO₃^--N removal and N₂ product selectivity by Cu-nZVI/LDH was as high as 95.6 % and 80.3 %, respectively. The critical reaction pathway of N₂ generation on the Cu surface of Cu-nZVI/LDH composite was further revealed by DFT theoretical calculations. Experiments on actual micro-polluted water showed that the removal of NO₃^--N by Cu-nZVI/LDH reached 85.2 %. The NO₃^--N removal of the composite material slightly decreased to 78.6 % after 15 d of aging, verifying that the composite material had good potential for practical applications.