Síntese e modificação química de resinas magnéticas de poli(divinilbenzeno) para adsorção de herbicidas triazínicos

Abstract

Triazines are organic compounds widely used as herbicides in various crops due to their effectiveness. However, their high stability and ability to migrate into water bodies make them major contaminants of surface and groundwater globally. Recent studies indicate that they may be endocrine disruptors and carcinogenic, threatening the environment and human health. This has increased the demand for new technologies and materials for the extraction or pre-concentration of these pollutants in complex environments. In this work, chemically modified magnetic microspheres were synthesized for the adsorption of triazines. The magnetic material was synthesized using the coprecipitation method. Subsequently, the magnetic material was treated with oleic acid for use in the synthesis of polymeric microspheres with magnetic properties. Poly(divinylbenzene) (PDVB) microspheres with and without magnetic properties were produced by suspension polymerization. n-heptane (100 and 150% dilution degree) and toluene (100% dilution degree) were used as diluents to obtain resins with different morphologies. The resulting microspheres were then chemically modified to obtain carboxylic groups capable of adsorbing triazine molecules. The resins obtained had carboxylic group counts between 0.82 and 1.50 mmol/g. The magnetic material and its modification with oleic acid were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), vibrating sample magnetometry (VSM), and thermogravimetric analysis (TG). The magnetic material composed of maghemite and/or magnetite exhibited superparamagnetic behavior with a saturation magnetization of 45 emu/g and an average particle size of around 18nm. The polymeric resins and their modifications were also characterized by the aforementioned techniques. Additionally, their morphologies were identified by optical microscopy and scanning electron microscopy (SEM). Functionalized and non-functionalized polymeric resins with and without magnetic properties were obtained with different morphologies, which varied according to the diluent and dilution degree used. The resins maintained their thermal resistance and morphology after chemical modifications. Furthermore, their superparamagnetic properties and magnetic separation capability remained unchanged. Adsorption tests were performed using atrazine as the adsorbate. Both carboxyl-functionalized and non-functionalized resins fit better to the pseudo-second-order model. Non-functionalized resins achieved atrazine removal efficiency between 93 and 97%, with rate constant values between 0.2 and 0.6 (g.mg-1.min-1) and maximum calculated capacity between 0.9 and 1.0 (mg/g). The functionalization of the resins did not result in improved adsorption capacity or adsorption rate.