Preparation of sodium acrylate-corncobs graft copolymers and its adsorption mechanism for Ni²⁺

In order to explore the feasibility of preparing high-efficiency adsorption material with agricultural waste corncobs as raw material to remove heavy metal ions from aqueous solution, a large number of carboxyl groups with strong affinity for heavy metal ions were grafted onto the surface of corncobs using atom transfer radical polymerization (ATRP) technology to obtain the sodium acrylate-corncobs graft copolymers (MC-g-PGMA-g-PAA-Na). Thermogravimetry, fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray energy spectrum (EDS) and X-ray photoelectron spectroscopy (XPS) were used to characterize MC-g-PGMA-g-PAA-Na before and after adsorption of Ni²⁺ for studying its adsorption mechanism. The results show that MC-g-PGMA-g-PAA-Na can effectively remove Ni²⁺ in aqueous solution. The carboxyl content in MC-g-PGMA-g-PAA-Na reaches 6.02 mmol·g⁻¹ and is 35.4 times that before modification. It is proved that when MC-g-PGMA-g-PAA-Na is contacted with a solution containing Ni²⁺, the carboxyl groups contained in MC-g-PGMA-g-PAA-Na act on Ni²⁺ to adsorb Ni²⁺ in the solution and form carboxylic acid nickel. The valence of Ni²⁺ do not change before and after adsorption. The coordination mode of carboxyl and Ni²⁺ is mainly a bidentate bridge. At the same time, all Na⁺ contained in MC-g-PGMA-g-PAA-Na are released into the solution, indicating that the process of adsorption of Ni²⁺ in the solution is accompanied by cation exchange between Na⁺ and Ni²⁺.