Innovative pectin-based composite membranes: preparation, characterization and color pollutant separation from water

Abstract

The aim of the present study was to synthesise and characterise innovative pectin/pine sawdust/magnetite composite membranes as potential sorbents for the purification of water contaminated with color pollutants. Methylene blue (MB) was employed as the pollutant model for sorption. Fourier-transform infrared spectroscopy (FTIR) was performed to analyse the formation of crosslinked membrane chains and confirm the sorption processes of the dye molecules. Thermogravimetry (TGA) and derivative thermogravimetry (DTG) indicated that the polymer matrix is stable at low temperatures and begins to degrade at temperatures above 250 °C, whereas X-Ray diffraction (XRD) patterns confirmed crystalline and amorphous regions. Mechanical assays confirmed an increase in the modulus of elasticity and tensile strength of the biopolymer membranes after incorporating PS. Moreover, a reduction in mechanical deformation was found after the incorporation of Fe₃O₄. Pollutant separation experiments were performed in a pH range from 3.0 to 10.0 with initial pollutant concentrations of 5 to 25 mg L⁻¹ and separation times from 1 to 3050 min. Higher sorption capacity was found after 1800 min with an initial pollutant concentration of 20 mg L⁻¹ and pH 10.0. The best isotherm fit was found using the Redlich-Peterson model, with fits using the Langmuir model depending on the experimental conditions. The best kinetic fit was found using the pseudo-first-order or pseudo-second-order models at pH 3.0, with differences in more alkaline solutions. The pectin-based composite membranes proved to be viable options for the purification of wastewater from industry using dye and could also be tested for the photodegradation of organic pollutants in water due to the presence of Fe₃O₄.