Synthesis of temperature-sensitive ion-imprinted polymer based on chitosan for selective separation of La³⁺ from aqueous solution: Effect of different salt anions in the template

Temperature-sensitive chitosan-based ion-imprinted polymer (TCIIP) is a promising adsorption material due to its ability to recycle only by rinsing with cold deionized water. However, little attention has been paid to the role of salt anions in the template. Herein, lanthanum ion-imprinted polymers ([La3+-anions]-CS-IIPs) were synthesized using different lanthanum salts containing anions (NO3-, Cl- and CH3COO-) as template, CS and NIPIM as functional monomer, BIS as crosslinker, APS as initiator. The adsorption performance of La3+ in aqueous solution on the [La3+-anions]-CS-IIPs have been studied. SEM, BET, XPS and FTIR were performed to characterize the synthesized materials. The results showed that the disparities in adsorption capacity and selectivity of the three [La3+-anions]-CS-IIPs could be attributed to the template effect and various affinities for rare earth ions, arising from salt anions with different geometric shapes, ionic radii and rare earth ion complexing capacities. The adsorption capacity of these [La3+-anions]-CS-IIPs is [La3+-NO3-]-CS-IIPs > [La3+-CH3COO-]-CS-IIPs degrees [La3+-Cl-]-CS-IIPs. Three kinetic and isothermal adsorption models in each were used to investigate the adsorption mechanism of La3+ on [La3+-anion]-CS-IIPs. The adsorption capability of three [La3+-anions]-CS-IIPs retained above 92% in the 4 times adsorption-desorption process. Meanwhile, three [La3+-anions]-CS-IIPs clearly have higher adsorption affinities for La3+ than Ce3+, Nd3+, Y3+. The adsorption selectivity of [La3+-anions]-CS-IIPs is [La3+-CH3COO-]-CS-IIP > [La3+-Cl-]-CS-IIP > [La3+-NO3-]-CS-IIP. The findings of this work provide an idea for regulating the selective adsorption behavior of rare earth ion imprinted polymers by utilizing the anions effect.