D-Sorbitol Xanthate-Based Hydrogel Polymer for Cost-Effective and Efficient Removal of Potentially Toxic Elements from Aqueous Solutions

Abstract

Three grades of D-sorbitol xanthate-based hydrogel (DSXHs-1, DSXHs-2, and DSXHs-3) were synthesized using the free radical solution copolymerization technique, with acrylic acid and acrylamide as a monomer, KPS as an initiator, and methylene bisacrylamide (MBA) as a cross-linker. The DSXHs hydrogels were characterized using Fourier transform-infrared (FTIR) spectroscopy, UV–Vis spectroscopy, point of zero charge (ΔpH_PZC) analysis, thermogravimetric analysis (TGA), and scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS). The synthesized DSXHs hydrogels were employed for the removal of Cu²⁺ and Co²⁺ ions from wastewater. The percentage swelling ratio (%SR) of DSXHs-3 was found to be 25,145% in distilled water, 21,148% in tap water, and 18,652% in grey wastewater in 840 min. The percentage water retention ratio (%WRR) was seen as 81.85% in distilled water, 79.47% in tap water, and 77.67% in grey water in 24 h. The extreme removal of metal ions was detected as 95.25% for Cu²⁺ and 93.67% for Co²⁺ ions using the DSXHs-3 hydrogel under optimal conditions. The adsorption data fit well with Langmuir isotherm (LI) model, exhibiting a maximum adsorption capacity of 531.91 mg/g for Cu²⁺ and 515.46 mg/g for Co²⁺ ions using DSXHs-3 hydrogel. The adsorption kinetics data was better explained with the help of pseudo-second-order (PSO) kinetic model, with rate constants of 1.4 × 10^–4 g/(mg min) for Cu²⁺ and 1.5 × 10^–4 g/(mg min) for Co²⁺ ions. Additionally, DSXHs-3 hydrogel demonstrated good reusability. After the fourth cycle, the removal efficiency remained at 84.27% for Cu²⁺ and 82.44% for Co²⁺ ions.