Manufacturing sulfated cellulose nanofibers using a unique combined DES-based pretreatment-functionalization protocol for metal ion decontamination through porous adsorbents

This study confirms the efficacy of a unique combined pretreatment-functionalization protocol based on the use of deep eutectic solvent (DES) to obtain sulfated lignocellulose and cellulose nanofibers (SLNF or SNF) hydrogels, which have been successfully shaped as sponge-based adsorbents and fruitfully assessed for the removal of heavy metals from water. A comprehensive characterization study was conducted, demonstrating an excellent degree of sulfation (0.62) in DES-treated wheat straw-derived nanofibers. The direct use of SLNF or SNF hydrogels and their application as porous sponges exhibited highly favorable characteristics for successful ion decontamination. Cu²⁺ removal was up to 70 % higher using DES-sulfated nanocellulose hydrogels compared to conventional treated-nanocellulose. Various isotherm models were studied, and the analysis of the kinetic and diffusion studies confirmed the influence of the sample format in the removal behavior. SLNF and SNF-sponges proved to be the most effective in adsorption, achieving Cu²⁺ removal rates of up to 60 %. More profitable decontamination processes with lower run times could be guessed when the application of nanocellulose is led through the processing of advanced formats. The easy handling of sponges would avoid the extra costs of the downstream unit operations which are sometimes needed to separate the hydrogel of the decontaminated media.