Preparation and chelation adsorption property of composite chelating material poly(amidoxime)/SiO2 towards heavy metal ions

Micron-sized silica gel particles were first surface-modified with coupling agent, γ-methacryloylpropyl trimethoxysilane (MPS), introducing polymerizable double bonds into the surfaces of silica gel particles, and then acrylonitrile (AN) was graft-polymerized in the manner of “grafting from”, resulting in the grafted particles PAN/SiO2. In succession, the grafted PAN was transformed into the grafted poly(amidoxime) (PAO) via amidoximation transformation reaction with hydroxylamine hydrochloride as reaction reagent, and the composite chelating particles PAO/SiO2 were obtained. In this work, the chelating adsorption property and mechanism of PAO/SiO2 particles towards heavy metal ions were mainly investigated, and the adsorption thermodynamics was also researched. The experiment results show that PAO/SiO2 particles possess strong chelating adsorption ability for heavy metal ions, for example, the saturated adsorption amounts of Pb2+ and Cu2+ ions on PAO/SiO2 particles can get up to 12 and 10 g/100 g, respectively. The adsorption of PAO/SiO2 towards heavy metal ions is an endothermic chemical adsorption process driven by entropy, and the adsorption capacity increases with raising temperature. The adsorption property of PAO/SiO2 is dependent on the pH value of the medium, and in a certain pH range, the adsorption ability is strengthened with increasing pH value. The adsorption of PAO/SiO2 for heavy metal ions is selective, and the adsorption capacity is in the order of Cu2+ ≫ Ni2+ > Pb2+ > Cd2+.