Sorption of emerging contaminants in magnetic composites and chitosan particles
water pollution; textile industry; medication disposal; drug adsorption; dyes
The pollution of water resources caused by the textile industry and the improper disposal of medicines are serious environmental problems that require immediate attention. Dyes used in the textile industry are highly soluble in water, contaminating water resources and making removal difficult. On the other hand, improper disposal of medicines can contaminate soil and water, representing a significant risk to public health and the environment. These emerging contaminants are being detected at increasing levels in the environment and which still do not have regulations or established control standards. It is crucial that the population is aware of the risks associated with the inappropriate disposal of medicines and that they take steps for their safe and responsible disposal, and through programs to collect expired or unused medications. In this context, this thesis proposes the study of the sorption of drugs sodium cromoglycate and tetracycline hydrochloride on magnetic composites, and the development of a numerical method applied to the adsorption of dyes, acid blue 260 (AA), and methyl orange (AM), on crosslinked chitosan to individually and simultaneously identify the concentration of these dyes in aqueous solutions. For this purpose, techniques such as thermogravimetric analysis, molecular absorption spectroscopy in the ultraviolet and visible region, infrared absorption spectroscopy, X-ray diffraction, and adsorption equilibrium studies were employed. The study on drugs revealed that sorption occurred in multiple layers, reaching saturation at concentrations of 0.2 mmol of drug per gram of composite for tetracycline hydrochloride (HTCCl) in both positive and negative magnetic composites. The anionic drug was adsorbed with similar intensity in both composites, with saturation in the negatively charged composite achieved at a value of approximately 0.05 mmol per gram of composite. The Gibbs free energy of adsorption was estimated under dilute solution conditions, ranging from ‒17 to ‒3 kJ/mol. The analysis of thermal degradation kinetics using the isoconversional approach revealed that the presence of magnetite in the magnetic composites reduced the apparent activation energy. Values obtained reached up to 400 kJ/mol for the degradation of the organic phase. This phenomenon demonstrated that magnetite increased the surface area available for drug adsorption. As for the developed method applied to the dyes, it demonstrated more effective sorption for AA, which could be characterized by determining different isothermic parameters, estimation of the Gibbs free energy of adsorption as well as competitive sorption by itself.