Excellent biosorption performance of novel alginate-based hydrogel beads crosslinked by lanthanum(III) for anionic azo-dyes from water

Abstract

A novel lanthanum-sodium alginate hydrogel (La-SA) biosorbent has been successfully prepared by the cross-linking reaction of sodium alginate (SA) with lanthanum(III) ions, and characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), Fourier Transform-Infrared (FTIR), UV visible diffuse reflectance spectroscopy (UV-Vis DRS), Thermogravimetric Analysis (TGA) and determination of point of zero charge (pHpzc), respectively. The adsorption experiments revealed that La-SA gel beads showed the excellent adsorption performance for the removal of anionic azo-dyes Direct Green 1 (DG 1) and Acid Blue 113 (AB 113) from aqueous solution at pH < 6.0, while the high-efficiency adsorption of DG could allow in a wider pH range of 2.0 ∼ 10.0. Langmuir and Freundlich models were used for dealing with the equilibrium data and it is found that the adsorption behaviors of DG 1 and AB 113 onto La-SA are perfectly in accordance with the Langmuir model, and the corresponding maximum adsorption capacities can reach 909 and 983 mg/g at 40 °C, respectively. The kinetics adsorption data fully conformed to the pseudo-second-order rate equation, and adsorption processes were mainly controlled by intraparticle diffusion. The thermodynamic studies and spectral characterization indicate the adsorption reactions of two dyes are of spontaneous and endothermic nature, and strongly depend on the the electrostatic interaction, hydrogen bonding and ligand exchange between dye anions and La-SA gel beads. La-SA biosorbent with low cost and high efficiency would have a good application prospect in the purification of high-concentration dye wastewater.