Effective Modified Walnut Shell Adsorbent: Synthesis and Adsorption BehaⅥor for Pb~(~(2+)) and Ni~(~(2+)) from Aqueous Solution

摘要

A highly effective modified walnut shell (MWNS) adsorbent was prepared by reacting walnut shell with maleic anhydride, and was characterized through Fourier transform infrared, X-ray photoelectron spectroscopy, and point of zero charge analysis. Adsorption behavior of metal ions (Pb2+ and Ni2+) onto MWNS was studied. Adsorption kinetics were fitted with pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models. Isotherms data were analyzed using Langmuir, Freundlich, and Dubinin-Radushkevich models, and the feature concentration (C-eD) for Pb2+ was determined. Results showed that the maximum monolayer adsorption capacity for Pb2+ of MWNS is 383.50 mg/g at 318 K obtained from Langmuir model. Also, the Pb2+ adsorption onto MWNS is monolayer chemisorption at C-e < C-eD, and multilayer physisorption at C-e > C-eD, while the Ni2+ adsorption onto MWNS belongs to heterogeneous multilayer physisorption. Competitive adsorption experiment of Pb2+ and Ni2+ in binary system was carried out. Material Studio (Adsorption Locator) was applied to determine the adsorption location between MWNS and metal ions, and the results can explain the priority adsorption of Pb2+.