Progress in the modification of cellulose-based adsorbents for the removal of toxic heavy metal ions

Pollution caused by heavy metals poses a global threat to both human health and ecosystems. While there are existing methods to address this issue, it is essential to acknowledge their drawbacks: high cost, substantial energy requirements, and the generation of toxic waste. Consequently, the scientific community is strongly dedicated to developing more efficient, cost-effective, and environmentally friendly approaches. Among these, adsorption has emerged as a powerful, green, and sustainable method for water purification. Specifically, nontoxic biomaterials like cellulose-based adsorbents have garnered significant interest in the field. The surface of cellulose is enriched with numerous hydroxyl groups, enabling the incorporation of chemical moieties that enhance adsorption capabilities for toxic metal cations. Cellulose's high chemical versatility allows for its modification through various synthetic approaches, enabling fine-tuning of its structural properties. Combined with its intrinsic properties, such as porosity, surface area, and chemical stability, this makes cellulose an excellent substrate for developing adsorbents with enhanced capabilities for metal cation removal. Modifying cellulose-based adsorbents can improve and tailor their adsorption capacity and selectivity towards specific toxic metal cations, as well as their robustness, allowing for recovery, regeneration, and reusability. Additionally, the widespread availability of cellulose in nature enhances the cost-effectiveness and reduces the environmental impact of developing novel adsorbent materials. In this paper, we present a comprehensive and up-to-date literature review that highlights the remarkable progress on synthetic strategies used to obtain cellulose-based adsorbents and their application in wastewater treatment, particularly focusing on the removal of heavy metal ions.