Cellulose hydrogel and its derivatives: A review of application in heavy metal adsorption

Adsorption of heavy metals is a promising technique for heavy metal recycling as well as effluent treatment. Due to their high functionality, swelling characteristics, bio-compatibility, non-toxic nature and high adsorption capacity, hydrogels are strong contenders for a practical solution aimed at heavy metal adsorption. Studies aiming at the regeneration potential of hydrogel have reported only 10–15% loss of adsorption capacity for three to five cycles of reuse. For the past decade, hydrogels have been the focus of research as a green absorbent. Cellulose, being the most abundant natural polymer, is an obvious choice for hydrogel base. Additionally, the hydroxyl groups on cellulose provide feasibility for synthesis of multiple structures of hydrogels. This review discusses the chemistry of cellulose, various plant-based sources for cellulose hydrogel, structure of hydrogel, synthesis routes followed by adsorption mechanism, theoretical study of cellulose-metal adsorption using density functional theory, kinetics and isotherms specific to heavy metal adsorption on cellulose hydrogel.