Using natural antioxidant Rhubarb extracts in PVA/chitosan bio-adsorbent films for efficient removal of cationic and anionic dyes from polluted water

Abstract

In this research, sustainable membrane films were developed for removal of cationic and anionic dyes from wastewater based on polyvinyl alcohol/chitosan (PVA/CS) incorporated with natural antioxidant Rhubarb dye (Rh) extracts. Rh dye was extracted from Rhubarb roots by a green method. Three different quantities of Rh dye extracts (i.e., 2.5, 5, and 10 %) were used to fabricate crosslinked PVA/CS films by solvent-casting approach. The fabricated films subjected to different techniques such as X-ray diffraction (XRD), scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX), dynamic mechanical analysis (DMA), as well as antioxidant activity. In all cases, the incorporation of Rh dye extracts inside the composite improved the crystallinity, biocompatibility, stress–strain properties, besides the DPPH scavenging activity reached 42.50 % for PVA/CS-10 % Rh membrane compared to PVA/CS blank (i.e., ∼ 2.10 %). Dyes adsorption including different cationic and anionic dyes implemented for all selected membranes. The data revealed that the membrane containing 10 % Rh dye was the optimum for removal of malachite green oxide (MG, 93 %) as cationic dye and methyl orange (MO, 95.70 %) as anionic dye. Moreover, the kinetics of the removal process exhibited that this process followed the Langmuir, Freundlich, Temkin, Dubinin-Radushkevich models, and the pseudo-1st order kinetic model, with an R² of 0.998 and 0.943 for MG and MG, respectively. Whereas, the adsorption process corresponded to the Freundlich isotherm model, with coefficients R² was of 0.989 and 0.988 for MO and MG, respectively. Other parameters including dye concentration, contacting time, pH media, and kinetic studies were also applied on PVA/CS-10 % Rh membrane.