Efficient electrocatalytic reduction of nitrate in a three-dimensional system via zirconium-based metal-organic framework-modified Zn-Fe layered double hydroxide.

This study reports the first development of a zirconium-based metal-organic framework (UiO-66)-modified Zn-Fe layered double hydroxide (LDH) particle electrode (U6/ZF-LDH) for efficient electrocatalytic nitrate reduction in a three-dimensional electrochemical reaction system (3D-ERS). By anchoring UiO-66 onto LDH via coprecipitation, this work overcomes the limitations of conventional LDH, including low surface area and insufficient active sites. Under the optimal preparation conditions (Zn/Fe molar ratio of 3:1, UiO-66 mass of 2 g, preparation pH of 10, and hydrothermal treatment of 60 °C) and operating parameters (room temperature, neutral environment, 2 g/L of catalyst dosage, and 0.20 A of applied current), U6/ZF-LDH achieved >90 % of nitrate removal and >70 % of selectivity for N2 within 4 h for nitrate concentrations of 25-150 mg/L. Characterization results indicated that the introduction of UiO-66 significantly increased the specific surface area of LDH and optimized its pore structure, accelerating interfacial electron transfer. Finally, a possible mechanism for the nitrate reduction in the 3D-ERS through the utilization of U6/ZF-LDH as a catalyst is proposed. Mechanistic studies revealed that the U6/ZF-LDH interface promoted the enrichment of the key intermediate (NO), enhancing selectivity for N2 via the N-N coupling pathway. This study provides a novel strategy for designing highly active and stable nitrate electrocatalytic materials.