Abstract
In this study, a series of molecularly imprinted polymers (MIPs) have been synthesized using separately diclofenac, naproxen, and ibuprofen as templates with three different polymerization approaches. Two functional monomers, methacrylic acid (MAA) and 2-vinylpyridine (2-VP), were tested and ethylene glycol dimethacrylate (EGDMA) was used as crosslinker; also, template-free polymers (NIPs) were synthesized. It was found that the MIP with the highest retention percentage for diclofenac was the one prepared by the emulsion approach and with MAA (98.3%); for naproxen, the one prepared by the bulk polymerization with MAA (99%); and for ibuprofen, the one synthesized by bulk with 2-VP (97.7%). These three MIPs were characterized by scanning electron microscopy, thermogravimetric test, Fourier transform infrared, specific area measurements, and surface charge. It was found that the emulsion method allowed particle size control, while the bulk method gave heterogeneous particles. The three evaluated MIPs exhibited thermal stability up to 300 °C, and it was observed that 2-VP confers greater stability to the material. From the BET analysis, it was demonstrated that the MIPs and NIPs evaluated are mesoporous materials with a pore size between 10 and 20 nm. In addition, the monomer influenced the surface charge of the material, since the MAA conferred an acidic point of zero charge (PZC), while the 2-VP conferred a PZC of basic character. Through adsorption isotherms, it was determined that there is a higher adsorption capacity of the MIPs at acidic pH following a pseudo-second-order kinetic model. Finally, the MIPs were used to determine the non-steroidal anti-inflammatory drugs (NSAIDs) understudy in San Luis Potosí, México, wastewater, finding concentrations of 0.642, 0.985, and 0.403 mg L-1 for DCF, NPX, and IBP, respectively.