Study on the cross-linked molecularly imprinted poly(methacrylic acid) and poly(acrylic acid) towards selective adsorption of diuron

Abstract

In the present study new molecularly imprinted adsorbents based on poly(methacrylic acid) and poly(acrylic acid) have been synthesized, characterized and evaluated as selective materials for the adsorption of diuron. Morphological, textural data and the presence of functional groups in the polymer have been evaluated by means of SEM, nitrogen adsorption-desorption assays and FT-IR, respectively. Two functional monomers were evaluated for the MIP synthesis, methacrylic acid (MIPMAA) and acrylic acid (MIPAA), and the first one showed higher selectivity and better adsorption towards diuron in the presence of competitor molecules, carbofuran and 2,4-D. The experimental adsorption isotherm of diuron has been obtained at pH 7.0 in phosphate buffer (0.05 mol L-1):acetonitrile (1:2, v/v) medium and equilibrium time of 180 min. The respective maximum adsorption capacities (MAC) of MIPMAA and MIPAA were found to be 14.58 and 7.32 mg g-1. One should note that MAC of MIPAA and its respective blank polymer (NIPAA) was very similar to each other, while for the MIPMAA its MAC was significantly higher (14.58 mg g-1) than the MAC of NIPMAA (6.12 mg g-1). Such result demonstrates the great influence of monomer on the adsorption and selectivity of MIP. Adsorption kinetic data were well fitted to pseudo-first-order and intraparticle diffusion models, while the adsorption isotherms showed good fit to the isotherm of Langmuir-Freundlich for two sites (LF-2) and one site (LF-1), but the former one allowed insight into the adsorption mechanism with more details.