Highly-efficient Pb2+ removal from water by novel K2W4O13 nanowires: Performance, mechanisms and DFT calculation

Abstract

As one of the most toxic heavy metals, lead ions (Pb2+) contamination arouses increasing public concern for high carcinogenicity and neurotoxicity. In this study, a modified hydrothermal method was designed to fabricate novel hexagonal K2W4O13 nanowires to achieve highly-efficient Pb2+ removal from water. Attractively, the as-prepared K2W4O13 exhibited large uptake capacity (228.83 mg/g), fast kinetic (141.67 mg/g in 30 min), superior acid-resistance (75% of removal at pH = 2) and excellent reusability (over 95% of removal after 5 runs) toward Pb2+ adsorption. The Langmuir isotherm and pseudo-second-order kinetic model gave a better fit to the adsorption experimental data. The Pb2+ adsorption process on K2W4O13 was revealed to be a spontaneous, exothermic, film diffusion limited chemisorption reaction. The mechanism studied elucidated that both ion-exchange and complexation were involved in Pb2+ adsorption, with each accounting for approximate 50% of Pb2+ elimination. Through density functional theory (DFT) calculation, the equatorial oxygen was found to be more accessible for Pb attachment than the axial corner oxygen from [WO6] octahedra. Electron pairs from the adjacent O atoms would transfer to the empty orbitals of Pb atoms after adsorption, causing the Pb2+ removal via metal-ligand complexation.