Adsorption-photoreduction behaviors and mechanisms of layered double hydroxide loaded on uranium(vi) removal

The synthesis and development of cost-effective and high-efficiency adsorption-photocatalysis bifunctional treatment agents for uranium-containing wastewater is of great importance. In this work, we successfully synthesized layered double hydroxides (LDHs, NiAl and ZnNiAl) with different nickel coordination environments and investigated the adsorption activity and photocatalytic removal performance of uranium (U(VI)) under visible light. The adsorption experimental results showed that the adsorption capacity of NiAl was about four times that of ZnNiAl, and the excellent adsorption properties of NiAl originated from its large surface area and surface Ni-OH groups, which had a high coordination ability toward U(VI). In addition, NiAl had a narrower band gap than ZnNiAls due to the electronegativity of Ni2+(1.91) being greater than Zn2+(1.65), and NiAl (0.055 h-1) exhibited a higher efficiency of U(VI) photoreduction than ZnNiAl (0.0138 h-1) under visible light. Thus, NiAl showed dual properties of adsorption and photoreduction. In the process of photocatalysis, the photogenerated electrons and generated ˙O2- radicals could reduce the absorbed U(VI) into insoluble UO2(s) and U3O8. Consequently, photocatalytic reduction could further improve the performance of NiAl in removing U(VI) from the solution. NiAl with its low cost and disposal simplicity could be exploited for the decontamination of U(VI), involving surface complexation and photocatalytic reduction.