Comparison of Four Adsorption Isotherm Models for Characterizing Molecular Recognition of Individual Phenolic Compounds in Porous Tailor-Made Molecularly Imprinted Polymer Films

A molecularly imprinted polymer (MIP) film using catechol as the template was designed for adsorption of a range of phenols from water. Four different isotherm models (Langmuir (LI), Freundlich (FI), Langmuir-Freundlich (L-FI), and Brunauer, Emmett, and Teller (BET)) were used to study the MIP adsorption of five phenolic compounds: phenol (Ph), 2-methylphenol (2-MP), 3-methylphenol (3-MP), 2-chlorophenol (2-CP), and 4-teroctylphenol (4-OP). Each model was evaluated for its fit with the experimental data, and key parameters, including a number of binding sites and binding site energies, were compared. Though the LI, L-FI, and BET models showed good agreement for estimation of the number of binding sites and affinity for most adsorbates, no single model was suitable for all. The LI and L-FI models gave the best fitting statistics for the Ph, 2-MP, 3-MP, and 2-CP. The recognition of 4-OP, which has much higher binding affinities than the smaller phenolic compounds not attributable to hydrophobicity alone, was explained only by the BET model, which indicates the formation of multilayers. The BET model failed only with phenol. MIPs also showed higher adsorption capacities and improved homogeneity over the analogous non-imprinted polymers.