Insights into enhanced elimination of U(VI) and Eu(III) by amidoxime-functionalized Ti3C2Tx MXenes

Abstract

Although two-dimensional transition metal carbides and carbonitrides (MXenes) are becoming increasingly popular in contaminant remediation field, the preparation of MXene nanosheets that can efficiently eliminate the target pollutants still deserves in-depth investigation. Here we produced amidoxime Ti3C2Tx nanosheets (TC-AO), which were efficient radionuclide adsorbents with high stability and positive affinity, by introducing the amidoxime group into the Ti3C2Tx MXene surface through grafting by diazonium salt. The high stability and abundant functional groups of TC-AO were demonstrated by different characterization techniques such as scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analyzer (TGA), and X-ray photoelectron spectroscopy (XPS). Multiple factors affecting the radionuclide removal performance were explored, including reaction time, temperature, pH, ionic strength, anions and cations. The experimental results demonstrated that the radionuclide uptake by TC-AO was a heat-absorbing, spontaneous single-molecule chemisorption process and was consistent with the pseudo-secondary and Langmuir models. When pH < 6, the mechanism of uranium removal was inner complexation, and as the pH continued to increase, uranium removal shifted to outer complexation. Furthermore, the results certificated that TC-AO exhibited fast reaction kinetics (reaching equilibrium in about 20 min), excellent removal efficiency (279.57 mg U·g−1 and 73.99 mg Eu·g−1), outstanding selectivity and good stability. The studies showed that TC-AO had good stability and functionality, which was not only valuable for the design of MXene based adsorbents, but also provided a meaningful option for the extraction of radioactive pollutants from wastewater.