Crosslinked hydrogel based on Polyvinyl alcohol/chitosan/glyoxal for the removal of Crom(VI) ions from aqueous solution

Abstract

This article describes an effective method to remove pollutants from wastewater using crosslinked hydrogels based on polyvinyl alcohol and chitosan. Glyoxal was used as the crosslinker for the hydrogels. The reaction between glyoxal and PVA as well as chitosan was conducted at 80oC for 90 minutes, contributing to the formation of the hydrogels which act as absorbents for removing Cr(VI) ions from the aqueous solution. The adsorption process was progressed at about 32oC and pH 7, in which the hydrogel samples were soaked in the Cr(VI) solution until the adsorption reached equilibrium state. The characterization of hydrogels was discovered with using various analytical techniques, including scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), UV–visible spectrophotometry (UV-Vis), and energy dispersive X-rays (EDX). The equilibrium adsorption isotherm analysis for Cr(VI) ions was researched by using Langmuir and Freundlich equilibrium isotherm models. The pseudo-first and pseudo-second-order kinetic models were studied for investigating adsorption kinetics. The microstructural surface of the hydrogel with the pores of 10 – 50 m was revealed by SEM images. EDX analysis confirmed the existence of Cr(VI) ions on the hydrogel surface after adsorption. The adsorption capacity and removal efficiency were studied with the various initial concentrations of Cr(VI) solutions, from 10 - 50 (mg.L-1). The maximum adsorption capacity was about 344 (mg.g-1) and the removal efficiency was from 82.35 % to 89.99 %. About adsorption isotherm and kinetics, the experimental data were consistent with Langmuir isotherm model and agreed with the pseudo-second-order kinetics. These results showed the presence of the Cr(VI) ions monolayer on the hydrogels and existence of chemical interaction between metal ions and the hydrogels during the adsorption process. Therefore, the PVA/chitosan/glyoxal hydrogels could be effectively used as an application in removing Cr(VI) from wastewater.