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Reasonable design of a corn stalk cellulose-based adsorbent for adsorption of Cd(II) and Ni(II): adsorption behaviors and mechanisms

A corn stalk cellulose-based adsorbent was reasonably designed and synthesized by two steps of modification to effectively remove Cd(II) and Ni(II) from wastewater of nickel–cadmium (Ni–Cd) and nickel-metal hydride (Ni-MH) batteries. Glycidyl methacrylate (GMA), N,N-methylene-bisacrylamide (MBA), and potassium persulfate (KSP) was selected as the grafting monomer, cross-linking agent and initiator, respectively, in the first step to introduce enough epoxy groups and generate three dimensional (3D) network structures on the cellulose (Cell) surface. Under the optimum conditions of weight ratio of GMA: Cell = 3:1, 20 mmol L–1 KSP, 5.0 wt.% of MBA to Cell and 60°C for 2 h, the maximum grafting efficiency and the amount of epoxy groups could reach 93.69% and 4.96 mmol g–1, respectively. Then this grafted and cross-linked product (Cell-g-GMA-c-MBA) was further reacted with diethylenetriamine (DETA) to introduce amino groups on the adsorbent. The final adsorbent (Cell-g-GMA-c-MBA-DETA) with the maximum amount of 7.20 mmol g–1 amino groups was obtained under the optimized amination conditions. The experiment results showed that the maximum adsorption capacity of Cd(II) and Ni(II) on Cell-g-GMA-c-MBA-DETA could reach 367.3 and 295.9 mg g–1, respectively at 45°C and pH = 4.5. The detailed investigation on relationships between microstructures and adsorption performances of Cell-g-GMA-c-MBA-DETA proved that the introduced sufficient amino groups were the major adsorption sites to adsorb Cd(II) and Ni(II). Cd(II) was inclined to be adsorbed by forming chelation complexes with 2–3 mmol N atoms from amino groups while the adsorption of Ni(II) would require at least 1 mmol N atom from amino groups by accepting lone-pair electrons and forming coordinate bonds. This modified cellulose also displayed a good reproducibility, whose regeneration efficiency for adsorbing Cd(II) and Ni(II) after sixth cycles were still 80% and 82%, respectively. It could be considered as a promising material for effective removal of Cd(II) and Ni(II) from batteries wastewater.