The molecularly imprinted polymers (MIPs) synthesized by conventional bulky imprinting methods suffer from several limitations, such as time-consuming preparation process, poor site accessibility to the target molecules and the lower binding capacity for the target molecules. To overcome these problems in bulking imprinting, in this work, a novel surface-ion imprinting method that not only is simple but also highly effective, is put forward and found. The coupling agent γ-aminopropyltrimethoxysilane (AMPS) was bond onto the surface of silica gel particles, and amino groups were introduced onto the surfaces of silica gel particles, obtaining the modified particles AMPS-SiO₂. In aqueous solution, the molecules of the cationic monomer methacryloxyethyltrimethyl ammonium chloride (DMC) were first combined around the template ion, phosphate ion, by right of ion exchange action. A redox initiating system was constructed by the amino groups on AMPS-SiO₂ and ammonium persulphate in the solution, and free radicals were produced on the surfaces of silica gel particles. These free radicals initiated the monomer DMC and the crosslinker N,N'-methylene bisacrylamide (MBA) to be graft-copolymerized and crosslinked, and the surface-imprinting of phosphate ion was realized. After removing the template ions, PO₄^3- ion surface-imprinted material IIP-PDMC/SiO₂ was obtained. Both permanganate ion, MnO₄^- ion, and PO₄^3- ion are isoelectronic bodies. Their chemical structures are similar and their configurations are the same, but their sizes are different. In this work, MnO₄^- ion was used as contrast ion, and both static and dynamic methods were adopted to study the binding properties and ion recognition character of IIP-PDMC/SiO₂ for PO₄^3- ion. The experiment results show that IIP-PDMC/SiO₂ have specific recognition selectivity and excellent binding affinity for PO₄^3- ion, and its selectivity selectivity coefficients for PO₄^3- ion with respect of MnO₄^- ion is 9.58. Besides, IIP-PDMC/SiO₂ has excellent elution property, with NaCl solution as eluent, the desorption ratio of PO₄^3- ion reach 99.53% in 20 BV.

Key words: ion exchange, surface-initiated graft-polymerization, surface ion-imprinting, silica gel, phosphate ion, ion recognition