Efficient Removal of Heavy Metals from Aqueous Solution Using Licorice Residue-Based Hydrogel Adsorbent

Abstract

The removal of heavy metals through adsorption represents a highly promising method. This study focuses on the utilization of an abundant cellulose-rich solid waste, licorice residue (LR), as a natural material for hydrogel synthesis. To this end, LR-EPI hydrogels, namely, LR-EPI-5, LR-EPI-6 and LR-EPI-8, were developed by crosslinking LR with epichlorohydrin (EPI), specifically targeting the removal of Pb, Cu, and Cr from aqueous solutions. Thorough characterizations employing Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy confirmed the successful crosslinking of LR-EPIs by EPI, resulting in the formation of porous and loosely structured hydrogels. Batch studies demonstrated the high efficacy of LR-EPI hydrogels in removing the three heavy metal ions from aqueous solutions. Notably, LR-EPI-8 exhibited the highest adsorption capacity, with maximum capacities of 591.8 mg/g, 458.3 mg/g, and 121.4 mg/g for Pb2+, Cr3+, and Cu2+, respectively. The adsorption processes for Pb2+ and Cu2+ were well described by pseudo-second-order kinetics and the Langmuir model. The adsorption mechanism of LR-EPI-8 onto heavy metal ions was found to involve a combination of ion-exchange and electrostatic interactions, as inferred from the results obtained through X-ray photoelectron spectroscopy and FTIR. This research establishes LR-EPI-8 as a promising adsorbent for the effective removal of heavy metal ions from aqueous solutions, offering an eco-friendly approach for heavy metal removal and providing an environmentally sustainable method for the reutilization of Chinese herb residues. It contributes to the goal of “from waste, treats waste” while also addressing the broader need for heavy metal remediation.

Efficient and Selective Removal of Heavy Metals and Dyes from Aqueous Solutions Using Guipi Residue-Based Hydrogel

“…To thoroughly explore the adsorption kinetics, we employed the pseudo-first-order and pseudo-second-order kinetic models, as outlined by [22]. The pseudo-first-order The influence of contact time on the absorption of the RhB and MO dyes in the hydrogel samples within a time range of 15 to 240 min was investigated.…”

“…To thoroughly explore the adsorption kinetics, we employed the pseudo-first-order and pseudo-second-order kinetic models, as outlined by [22]. The pseudo-first-order model posits that the adsorption pace is predominantly governed by diffusion and mass transfer, whereas the pseudo-second-order model contends that the rate-determining step is driven by chemical adsorption.…”

“…The GP material underwent pretreatment according to the methodology reported in our previous works [22]. The GP sample was initially rinsed with distilled water and subjected to three successive boiling cycles to eliminate the active constituents.…”

“…These adsorbents also effectively remove dye pollutants from aqueous solutions [19,20]. Therefore, adsorption is an efficient and friendly method for the removal of heavy metals and dyes from aqueous solutions, and substantial attention has been directed towards advancing adsorption materials, encompassing carbon-based hydrogels [21,22].…”

“…The utilization of Chinese herb residue has been suggested as a potential method for the production of cellulose-based hydrogels [22]. However, cellulose extraction for environmentally sustainable conversion purposes presents inherent difficulties.…”