Simple one-pot synthesis of manganese dioxide modified bamboo-derived biochar composites for uranium(vi) removal

Abstract

Exploitation of bamboo-derived biochar offers a lucrative opportunity for using moso bamboo due to its short growth cycle, large quantity and universality. Novel MnO₂ modified bamboo-derived biochar composites (MnO₂@BBC) were successfully fabricated via a facile one-pot solvothermal reaction, and uranium(VI) adsorption experiments of MnO₂@BBC were systematically performed under different pH values, adsorbent dosages, contact times, initial uranium(VI) concentrations and temperatures. Characterization analysis via Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photo electron spectroscopy (XPS) techniques and batch experiments demonstrated that MnO₂ decoration could promote uranium(VI) adsorption by MnO₂@BBC because of the increasing BET surface area (from 10.56 m² g⁻¹ to 63.50 m² g⁻¹) and more abundant oxygen-containing functional groups on the surface. The adsorption processes of uranium(VI) by MnO₂@BBC were pH-dependent, endothermic (ΔH = 38.08 kJ mol⁻¹ for MnO₂@BBC-1) and spontaneous (ΔG < 0) in nature, and fitted to pseudo-second-order and Langmuir models. The maximum adsorption capacity of uranium(VI) by MnO₂@BBC-1 was 97.40 mg g⁻¹. As the primary mechanism of U(VI) adsorption by MnO₂@BBC, inner-sphere surface complexation of U(VI) with the Mn–O in MnO₂ or with the C–O and CO on the biochar surface was considered. Low-cost feedstock, simple preparation route and competitive adsorption capacity further highlighted the feasibility of MnO₂@BBC for treating uranium-containing wastewater in practical application.