Efficient adsorption and reduction of Cr(VI) and U(VI) by nanoscale zero-valent iron supported on polydopamine-decorated SBA-15

Highlights: • nZVI@SBA-15-PDA/PEI composites were developed via a facile method. • nZVI@SBA-15-PDA/PEI exhibited better performance of stability than nZVI. • Adsorption conditions played a vital role in the elimination of Cr(VI) and U(VI). • Removal of Cr(VI) and U(VI) was an adsorption and reduction process. Herein, a composite material (nZVI@SBA-15-PDA/PEI) was developed by loading nanoscale zero-valent iron (nZVI) on polydopamine-decorated SBA-15 for Cr(VI) and U(VI) removal. The structure, morphology and composition of the as-prepared composites were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffractometer (XRD) and fourier transform infrared spectroscopy (FT-IR) techniques. The experimental results demonstrated that the water environmental conditions played an important role in elimination of Cr(VI) and U(VI), such as pH values, pollutant concentrations and equilibrium time. Meanwhile, the fitted data displayed that the elimination process could be more accurately explained by the Langmuir and pseudo-second-order kinetic models, and the maximum removal capacities for Cr(VI) and U(VI) were 44.05 mg/g (pH = 3.0) and 57.78 mg/g (pH = 6.0) at 298 K, respectively. The characterization analysis conformed that the elimination mechanisms were proposed as a two-step interaction. Namely, both Cr(VI) and U(VI) were firstly attached onto the surface of composite materials via electrostatic interaction or surface complex reaction, and subsequently about 47.1% of U(VI) and 55.7% Cr(VI) were reduced to U(IV) and Cr(III) by nZVI. Thus, this nZVI composites exhibited a high potential to eliminate Cr(VI) and U(VI) from polluted water environment.