Efficiency and synergy of MnO2@LDO for arsenic and fluoride simultaneous sorption from water

Abstract

High levels of groundwater containing both arsenic and fluorine are prevalent, resulting in serious health problems when consumed as drinking water. This co-pollution phenomenon is widespread and requires urgent attention. The multiple forms of arsenic and arsenic–fluorine co-contamination pose a significant challenge to efficiently co-remove both substances. This research utilized a green and stable synthesis approach to create MgLaFe layered double oxide (LDO) heterostructures, which were anchored on α-MnO2 nanowires. The materials comprise magnesium and lanthanum elements with a powerful attraction toward fluoride ions; elemental iron, which can establish stable compounds with arsenate; and MnO2, which can effectively oxidize arsenous acid, thereby enabling efficient co-removal of arsenic and fluorine. The efficient oxidation process of the MnO2 nanowire and the prompt ion adsorption process of the LDO work together synergistically. The adsorption performance was assessed through isotherms and kinetic fitting. Chemisorption was found to be the process for As(Ⅲ), As(V), and F− adsorption, with As(Ⅲ) going through monolayer adsorption on the surface of MnO2 nanowires, while As(V) and F− were mainly adsorbed by multilayer process on LDO. The maximum adsorption capacities were 111.76, 230.51, and 765.10 mg/g for As(Ⅲ), As(V), and F−, respectively. The x-ray photo-electronic spectroscopy analysis provided further elucidation on the adsorption mechanism of the MnO2@LDO heterostructure, detailing each component's role in the process. The results confirm the successful construction of the heterostructure and the efficient coupling of oxidation and adsorption.