Synthesis and Investigation of Green Hydrogels for Simultaneous Removal of Mercuric Cations and Methylene Blue from Aqueous Solutions

Abstract

A green composite comprised of guar gum (GG)/chitosan (CH) cross-linked with glutaraldehyde was prepared and then enforced with different weight ratios (1, 2, and 3%) of talc powder (TP) as inorganic support. This group of green sorbent materials was introduced to remove methylene blue and toxic heavy metal cation (Hg+2) from aqueous solutions. The chemical modification was proved by the IR spectroscopy and the prepared hydrogels were investigated by X-ray diffraction (XRD) for their crystallinity. The thermal properties of the green sorbents were evaluated by the Thermal gravimetric analysis (TGA). Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) were used to investigate the surface features and surface topography of the optimum adsorbent before and after adsorption respectively. Adsorption experiments were conducted as functions versus the contact time and temperature. Moreover, isothermal, thermodynamic adsorption, and kinetic theoretical constants were calculated. Results revealed that guar gum/chitosan grafted nanocomposite GG/CH/GA/T2 enhanced the removal of methylene blue (MB) up to (79%) and metal ion discharge (92.11%). The maximum cationic dye MB and Hg+2 ions adsorption efficiencies were reached at temperature (318 K). For both MB dye and Hg+2 ions, the pseudo-2nd -order model has successfully defined the adsorption kinetics and the Langmuir model could exactly explain adsorption isotherms for both Hg+2 and MB dye. Hg+2 and MB dye have recorded the maximum removal performance of 277.4 and 57.992 mg/g respectively on GG/CH/GA/T2 at 25 °C; indicating an efficient separation of adsorbent from aqueous solutions for both cationic dyes and toxic heavy metals.