###### Abstract  
Cadmium is one of the many toxic elements for humans even at low concentrations, and it could exist in the environment for a long time. The ion imprinting technique has gained much attention due to its selective recognition performance. In this study, a cadmium ion imprinted maleic acid-co-acrylonitrile polymeric microsphere (Cd-I-MA-co-AN) was synthesized via precipitation polymerization using Cd(II) as a template ion, acrylonitrile and maleic acid as functional monomers, divinylbenzene as a cross-linker, and potassium persulfate as an initiator. UV-vis, SEM and FTIR were used for characterization, and the adsorption conditions were observed and optimized. The adsorption capacity and selectivity of Cd-I-MA-co-AN for Cd(II) were analyzed by flame atomic absorption spectrometry (FAAS). The results documented that the optimal pH, flow rate and eluent were 6, 2 mL min\({}^{-1}\) and 1 mol L\({}^{-1}\) nitric acid, respectively. Compared with the non-ion imprinted maleic acid-co-acrylonitrile polymeric microsphere (NI-MA-co-AN), Cd-I-MA-co-AN had a higher adsorption capacity. The saturated adsorption capacities of Cd-I-MA-co-AN and NI-MA-co-AN were 20.46 mg g\({}^{-1}\) and 7.64 mg g\({}^{-1}\), respectively. The adsorption behavior of Cd-I-MA-co-AN fitted with the Freundlich isotherm model. The relative selectivity coefficients of Cd-I-MA-co-AN for Cd(II) in the presence of Cu(II), Mn(II), Ni(II) and Pb(II) were 3.79, 3.39, 3.90 and 3.31, respectively. The Cd-I-MA-co-AN showed good selectivity for Cd(II). In addition, a reusability study showed that Cd-I-MA-co-AN can be recycled ten times and has high recovery in natural water samples. cadmium ion; polymeric microsphere; precipitation polymerization; FAAS; selectivity 2022121083390/coatings1  
good selectivity [8]. Molecular imprinting technology supplies a wide range of applications in many fields, such as sensors, catalysis and sorbents. [PERSON] et al. [9] reported a molecularly imprinting electrochemical paraoxon sensor based on MoS\({}_{2}\)NPs@MWCNTs nanocomposite for the detection of organophosphorus pesticides. [PERSON] et al. [10] reported a novel SiO\({}_{2}\)-coated molecularly imprinted sensor based on Si quantum dots for selective detection of catechol in river water samples. [PERSON] et al. [11] reported molecularly imprinted MOFs for the degradation of sulfamethoxazole in wastewater. [PERSON] et al. [12] prepared molecularly imprinted polymers for the removal of kitasamycin from the environment. Ion-imprinted polymers are developed on the basis of molecular imprinting technology. Compared with the molecular-imprinted polymers, ion-imprinted polymers are prepared by metal coordination, using ion as the template ion. Ion imprinted polymers have excellent adsorption properties, due to the synergistic effect of functional groups and imprinted holes, which selectively recognizes metal ions and does not interfer with other elements in the sample. The advantages of ion-imprinted polymers include their adsorption capacity, recognition, reapplication, and stability [13; 14; 15; 16; 17; 18; 19; 20; 21]. Although great strides have been made in the use of degrading cadmium ion in the environment using the ion-imprinting technique, there are few previously published papers on the preparation and application of Cd(II) ion imprinted polymers for the extraction and separation of cadmium ions. [PERSON] et al. [22] synthesized cadmium(II)-imprinted poly (1-allyl-2-thiourea-co-ethylene glycol dimethacrylate) particles using the bulk polymerization technique. In this work, cadmium nitrate was used as the template. They selected the following four different functional monomers: viz. allyurea, 1-vinylimidazole, acrylamide and 1-allyl-2-thiourea. Ethylene glycol dimethacrylate was applied as a cross-linker. [PERSON] and co-workers [23] employed a surface-imprinting technique to prepare a Cd(II) ion-imprinted polymer. Cadmium chloride and allyl thiourea were applied as a template metal ion and functional monomer, respectively.