Uniform core–shell molecularly imprinted polymers: a correlation study between shell thickness and binding capacity†
Core–shell molecularly imprinted polymers (CS-MIPs) have aroused increasing interest owing to their easy accessibility and favorable mass transfer. Herein, we explore the correlation between shell thickness and binding capacity by using Sudan I as template molecule to prepare different CS-MIPs at the surface of carboxyl polystyrene through emulsion polymerization with a two-step temperature-rising process. Extensive characterization was performed using techniques such as SEM/TEM, FT-IR, BET, and TGA. Main factors were systematically studied such as the amount of prepolymer solution, the amount of SDS, and the temperature step. Under the optimized conditions, CS-MIPs with a shell thickness of 2.60 μm presented the highest binding capacity of 30.1 μmol g−1 and the most rapid mass transfer rate. A uniform sphere model was constructed, and it was found that template molecules located in the spherical MIPs with a diameter of 5.20 μm will be completely eluted, thereby attaining the maximum binding capacity. The static adsorption isotherm followed the Langmuir–Freundlich adsorption model, and the fast kinetics obeyed the pseudo-second-order kinetics model. High recognition specificity for Sudan I with respect to its analogues was displayed, with an imprinting factor of 2.7. The establishment of a critical value of shell thickness provides new insights into the preparation methodology and molecular recognition mechanism of core–shell imprinted polymers.