Uranium extraction from wastewater by heteroatom-doped carbon microspheres derived from polyphosphazene loading with zinc oxide

Abstract

The effective management of uranium-contaminated wastewater is crucial for environmental protection and public health safety. In this context, a novel composite was synthesized involving the intergration of zinc oxide into heteroatom-doped polyphosphazene carbon microspheres (TAC/ZnO) by hydrothermal method. The incorporation of ZnO into TAC significantly enhanced the porosity, offering more adsorption sites and improving the uranium adsorption performance. The optimal adsorption experiment achieved a remarkable adsorption capacity of 513.9 mg.g−1 for U(VI) at a pH of 5.5 within just 80 min. Additionally, the adsorption process was found to be endothermic and spontaneous, following both the Langmuir isothermal adsorption model and the pseudo-second-order kinetic model. Moreover, the TAC/ZnO presented higher selectivity for U(VI) in the presence of other cations. Even after 8 cycles, TAC/ZnO maintained a good removal rate for U(VI), decreasing from 97.54 % to 81.95 %. Furthermore, the findings from X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations indicated that the adsorption mechanism of U(VI) on TAC/ZnO may involve the coordinated interaction between oxygen atoms in Zn-O and nitrogen atoms in pyridinie-N-oxide with uranyl ions. Overall, this study presents an easily prepared, cost-effective, and highly efficient adsorbent that offers potential for large-scale production and practical application in purifying radioactive wastewater.