Advances in Modified Wood-Based Adsorbents for Contaminant Removal: Valorization Methods, Modification Mechanisms, and Environmental Applications

Purpose of Review

Wood-based adsorbents are increasingly used for environmental applications. They demonstrate considerable advantages, including renewable feedstock, relatively simple preparation processes, and advantageous structural and surface properties. In short, they provide environmentally friendly, effective, and economical sources for contaminant removal. This review summarizes recent advances in the preparation and use of selected modified wood-based residues (biochar, ash, and cellulose) as adsorbents for environmental applications (water, air, and soil remediation).

Recent Findings

Although chemical modifications have produced better results for wood-based adsorbents, the inherent corrosion problems and safety issues have made physical modifications more feasible on an industrial scale. For environmental remediation, inorganic contaminants can be removed by raw and modified wood-based adsorbents, mainly via electrostatic interaction, surface complexation, pore filling, and ion exchange. Organic contaminants are removed via van der Waals forces between unsaturated polycyclic molecules, pore filling, and hydrogen bonding. Specific surface area and porosity are critical parameters for effective contaminant adsorption, mostly from water and air. A comparison of wood-based residues used for wastewater treatment ranked the efficiency as ash > cellulose > biochar versus cellulose > biochar > ash for air remediation. Adding modified wood residues to soil enhances the fertility and biological characteristics in addition to remediation. Moreover, spent wood-based adsorbents can be used in construction materials, soil fertilizers, and catalysts.

Summary

This review summarizes classical and new physical and chemical methods for modifying wood adsorbents and the impacts on physiochemical characteristics such as porosity, pore volume, surface area, and surface functional groups. Also addressed are the adsorption capacity and efficiency of raw and modified wood adsorbents for removing contaminants from synthetic effluents, mine water, air, and soil. Valorization methods for spent modified wood-based adsorbents are then outlined. Suggestions and prospects are given for future studies on environmental decontamination by wood residues.