Produção de nanopartícula magnética de ferrita de manganês modificada com poliestireno sulfonado na adsorção de íons de cádmio em solução aquosa

Abstract

Environmental pollution by heavy metals represents an enormous risk to living beings due to its characteristics of non-biodegradability and bioaccumulation in the food chain. Adsorption is an efficient treatment for removing heavy metals from wastewater. The use of magnetic nanosorbents allows simple removal from the aqueous medium by magnetism. This study aims to study the adsorption of cadmium by magnetic nanoparticles of pure manganese ferrite (NPM) and magnetic nanoparticles of manganese ferrite modified with sulfonated polystyrene (NPMPSS). NPM were synthesized by coprecipitation and sulfonated polystyrene by homogeneous sulfonation with acetylsulfate. The sulfonated polystyrene (PSS) was soluble in N, N – dimethylformamide and not soluble in water. Fourier transform infrared spectroscopy and X-ray energy dispersive spectroscopy confirmed sulfonic groups in NPMPSS. The pH of the point of zero charge were 4.37; 7.06 and 6.89 for PSS, NPM and NPMPSS, respectively. Scanning electron microscopy showed nanoparticles with uniform spherical shape, smooth texture and diameters ranging from 86 nm to 328 nm. X-ray diffraction confirmed the magnetic core composed of MnFe2O4 in the nanoparticles and determined an average crystallite size of 34.71 nm and 32.05 nm for NPM and NPMPSS, respectively. Thermogravimetric analysis estimated the presence of 14% polymer in NPMPSS. From the elemental analysis data a degree of sulfonation of 17.18% for PSS was obtained. The synthesized nanoparticles are mesoporous, with a reduction in the specific area from 12.18 m² g-1 to 6.61 m² g-1 after modification with PSS. The adsorption experiments were carried out in batch and in triplicate. The initial pH of the solution did not influence the removal of cadmium. Adsorption kinetics followed the pseudo first order model for NPM and the pseudo second order model for NPMPSS. The NPMPSS data were better fitted to the Freundlich isotherm model, while it was not possible to define an isotherm for the NPM. NPM and NPMPSS reached maximum cadmium removal of 58% and 86% and maximum adsorption capacity of 1.9 mg g-1 and 4.5 mg g-1, respectively. The sulfonic groups significantly increased the cadmium removal efficiency by the nanoparticles. However, future studies are needed to overcome the limitation regarding the dispersibility of NPMPSS.