Surface engineering and local electron structure modulation to accelerate electroreduction of low-concentration nitrate

Abstract

Electroreduction of low-concentration nitrate is constrained due to the competitive hydrogen evolution side reaction and sluggish reaction dynamics. Herein, we present a NiFe-layered double hydroxide featuring hydrophobicity and oxygen vacancies formed by in situ electrochemical intercalation of sodium dodecylbenzene sulphonate (V_O-NiFe-LDH/CF). Different from traditional intercalation by the ion-exchange method, V_O-NiFe-LDH/CF retains the hydrophobic properties of the alkyl chains in sodium dodecylbenzene sulphonate, while the sulfonic acid functional groups inhibit the formation of surface hydroxyl groups. The introduction of oxygen vacancies induces local electron redistribution and d-band center optimization, thereby enhancing nitrate adsorption capacity and reducing the energy barrier for the rate-determining step (*NO → *NOH). In situ FTIR measurement confirms the electrochemical hydrogenation route of nitrate. The optimized V_O-NiFe-LDH/CF can realize 96.8% nitrate removal efficiency and 96% ammonia selectivity at an initial NO₃⁻-N concentration of 50 mg L⁻¹. The NO₃⁻-N removal rate of V_O-NiFe-LDH/CF is 2.1-fold higher than that of NiFe-LDH/CF. Furthermore, V_O-NiFe-LDH/CF has excellent practicality for practical industrial nitrate-wastewater; the total nitrogen was reduced from 114.7 mg L⁻¹ to 7 mg L⁻¹. V_O-NiFe-LDH/CF shows outstanding stability and robust anti-interference performance during the long-term experiments.