Synergistic effect and mechanism of nZVI/LDH composites adsorption coupled reduction of nitrate in micro-polluted water

In this study, nZVI/LDH composites were prepared by loading nano zero-valent iron (nZVI) on layered double hydroxide (LDH) surface for adsorption coupled reduction of nitrate (NO3--N). The results showed that the removal of NO3--N and total nitrogen (TN) by the nZVI/LDH composites was 88.64% and 77.63%, respectively, with a selectivity of 55.21% for N2 and only 1.86% for ammonia nitrogen (NH4+-N) within 180 min. The valence states of various N forms during the adsorption-reduction process were investigated. The mechanism of synergistic adsorption-reduction degradation of NO3--N was proposed by measuring the contents of NO3--N, nitrite (NO2--N), and NH4+-N in the aqueous and adsorbed phases in the reaction process, including rapid adsorption of initial NO3--N, chemical reduction of adsorbed NO3--N and resorption of the final product. The nZVI/LDH also maintained up to 82.56% NO3--N removal in natural water, with aging experiments proved that the composites maintained 60.48% NO3--N removal after 15 days. Therefore, the composites may have great application prospects for NO3--N removal in micro-polluted water.