Ca2+induced 3D porous MXene gel for continuous removal of phosphate and uranium

Three-dimensional (3D) porous MXene gel (MXene-Ca) was synthesized through a fast gelation of Ti3C2Tx MXene nanosheets initiated by calcium ions. The MXene-Ca showed efficient phosphate adsorption ability through the strong chemical reaction between Ca2+ and phosphate with a fast adsorption equilibrium (within 2 min). Furthermore, the recovered P/MXene-Ca gel after phosphate sorption could be used for adsorption of uranium in aqueous solution. Various analysis including SEM, TEM, XRD, XPS, FT-IR, BET surface area and zeta potential were carried out to fully characterize the materials. Increased specific surface area of the 3D porous structure and the formation of newly active adsorption sites of hydroxyapatite in P/MXene-Ca gel, are two main factors promoting the removal of U(VI). The maximum adsorption capacity was 823.6 mg/g at 298 K by Langmuir isotherm model. Kinetic studies disclosed that the of U(VI) followed the major chemical adsorption process. Overall results from batch experiments, leaching experiments, and characterizations demonstrated that the main mechanisms of the U(VI) removal by P/MXene-Ca including chemical adsorption on hydroxyapatite via dissolution precipitation and surface complexation with the oxygen-containing functional groups of MXene.