Synthesis of the inorganic-organic hybrid of two-dimensional polydopamine-functionalized titanate nanosheets and its efficient extraction of U(VI) from aqueous solution

Abstract

The novel functional composites of two-dimensional polydopamine@titanate nanosheets (PDA@TNSs) with the increased affinity and capacity were successfully synthesized by non-covalent self-assembly and covalent oxidative polymerization. The batch experiments were employed to systematically investigate the U(VI) adsorption performance of PDA@TNSs. Compared with TNSs, PDA@TNSs represented excellent adsorption efficiency and selectively. The optimal pH values were determined to be 4.0-6.0 (PDA@TNSs) and 3.0-4.0 (TNSs), respectively, suggesting that PDA@TNSs maintained satisfactory adsorption efficiency over a wider range of pH than TNSs. The adsorption profiles were well-expressed by Langmuir isotherm model, and the monolayer maximum capacity of PDA@TNSs increased to 284.90 mg/g as compared with TNSs (241.43 mg/g). Pseudo-second-order model was more tallied with the adsorption process of TNSs and PDA@TNSs, and corroborated that U(VI) adsorption was controlled by chemical interaction. The nature of a spontaneous and exothermic process was identified by thermodynamic analysis. Competing cations had a certain inhibition effect on U(VI) removal at the order of Ca2+>Mg2+>Na+>K+. By XRD, FT-IR and XPS analysis, it was confirmed that cation exchange between Na+/H+ and U(VI) as well as coordination interaction played a primary role for U(VI) removal. This study not only developed a novel efficient adsorbent, but also provided a platform technique for enhancing adsorption of inorganic materials for the cleanup of radioactive waste.