A comparative study of functional monomer and crosslinker ratios in the synthesis of catechin-selective MIPs via suspension polymerisation

Abstract

Catechin contamination in food and environmental samples presents challenges for selective extraction and analysis, requiring advanced polymeric materials with high specificity and capacity. This study investigates the synthesis of catechin-selective molecularly imprinted polymers (MIPs) using suspension polymerisation, with a systematic evaluation of crosslinker-to-monomer (CL:M) and template-to-monomer (T:M) ratios. Polymers were prepared with CL:M ratios ranging from 1:1 to 4:1 and T:M ratios from 0 to 0.5, and characterised by particle size analysis, BET surface area and pore measurements, and scanning electron microscopy (SEM). Adsorption experiments were conducted at initial catechin concentrations of 2.5–10 mg/L, and binding isotherm models were applied to interpret the adsorption mechanisms. Polymers synthesised at CL:M ratios of 1:1 and 2:1 with T:M = 0.125 exhibited the highest adsorption capacities, consistently achieving values above 0.080 mg/g at 10 mg/L catechin. These optimal conditions also produced polymers with yields up to 94.7%, median particle diameters between 1100–1500 μm, and average pore radii approaching 10 Å. In addition, SEM analysis revealed that optimal samples displayed uniform, spherical morphology with well-developed surface porosity, whereas non-optimal samples showed increased aggregation and denser, less accessible surfaces. Notably, the Temkin isotherm provided the best fit for the adsorption data (R² = 0.9807), indicating heterogeneous binding sites and significant adsorbate–adsorbate interactions. In contrast, higher crosslinker (CL:M= 4:1 and 3:1) or template ratios (T:M= 0.375 and 0.5) led to reduced adsorption capacity and, in some cases, persistent template leaching. These results indicate that extraction conditions must be carefully optimised, such as by increasing Soxhlet extraction time or adjusting solvent parameters, to ensure complete template removal and improve polymer performance in practical applications. Overall, these findings establish suspension polymerisation, combined with carefully optimised synthesis and extraction conditions, as an effective strategy for producing catechin-selective MIPs with enhanced selectivity, capacity, and reproducibility.