Deep-eutectic-solvothermal synthesis of cerium-iron bimetallic oxides (Ce:Fe-DES) for the removal of arsenic from water

Abstract

This research focuses on the development of innovative adsorbent materials for the removal of arsenic (As) from contaminated waters, a critical challenge for public health worldwide. Given the growing concern about environmental impacts, there is a need to explore sustainable methods in the synthesis of these materials, replacing conventional organic solvents. In this context, deep eutectic solvents (DES) have emerged as a promising and green alternative, allowing the fabrication of metal oxides with highly specialized chemical structures and properties. In this study, the synthesis of bimetallic cerium and iron oxyhydroxides has been achieved using a choline chloride:urea DES medium, by a microwave-assisted methodology, allowing a green and more sustainable methodology, avoiding the use of toxic solvents and reducing reaction temperatures.. The resulting materials, Ce:Fe-DES, were physiochemically characterized by various techniques, and multiple parameters were evaluated. The Ce:Fe-DES adsorbent material has an As(V) adsorption capacity of 22.87 mg/g at an equilibrium concentration of 2.3 mg/l, and this decreases only 25 % in the presence of a mixture of anions with a concentration of 25 mg/l of each of the competing anions ($F^{-}$, ${\mathrm{Cl}}^{-}$, ${\mathrm{SO}}_4^{2-}$, ${\mathrm{NO}}_3^{-}$, ${\mathrm{PO}}_4^{3-}$ and ${\mathrm{CO}}_3^{2-}$). Moreover, Ce:Fe-DES has an acceptable arsenic adsorption capacity with the advantage that it was synthesized using a green methodology that does not generate toxic waste. Also, the Ce:Fe-DES As removal remains almost constant after the second adsorption cycle and has proven to be a promising As(V) adsorbent materials because factors such as solution pH and the concentration of coexisting anions have little interference in the As(V) adsorption process.