Self-tuning tetragonal zirconia-based bimetallic nano(hydr)oxides as superior and recyclable adsorbents in arsenic-tolerant environment: Template-free in and ex situ synthetic methods, stability, and mechanisms

In this study, we aimed to decorate nano-ZrO_2 on LaO_x to enhance the architectural stability of LaO_x for the uptake of both arsenate and arsenite in single solutions. LaO_x was obtained as lanthanum methanoate (LaMe) from a simple solvothermal reaction of lanthanum and benzoic acid. The leaving group of formic acid was used as a reducing agent to grow ZrO_2 over LaO_x, which resulted in a nanocomposite denoted as ZrO_2@x%LaMe. The de-arsenic behavior of this composite was compared with that of one-pot-synthesized La-ZrO_2 and ZrO_2@x%La(OH)_3, with La(OH)_3 being obtained commercially. Powder X-ray diffraction patterns showed that the ZrO_2 structure was transformed from monoclinic to tetragonal during the formation of ZrO_2@x%LaMe, La-ZrO_2, and ZrO_2@x%La(OH)_3. Among the synthesized nano-bimetallic composites, ZrO_2@50%LaMe exhibited the highest adsorption densities for both arsenate and arsenite due to the uniform distribution of ZrO_2 over the LaO_x surface resulted in a larger Brunauer–Emmett–Teller specific surface area and a higher zeta potential charge. The synthesized nanocomposites were reused several times with the aid of 0.1 M HNO_3 for maximizing the uptake of both arsenate and arsenite from water. Selectivity and the stability (pH) studies indicated that the nanocomposites were highly selective and showed zero-dissolution behavior, respectively. The results of this study suggested that these nanocomposites could be used as alternatives for many La-based adsorbent materials in practical applications.