Tailoring cellulose-based hydrogels by phosphorylation of unbleached kraft pulps for adsorption applications

Industrialization and human activities have exacerbated water pollution, demanding effective pollutant removal methods. Bio-based hydrogels, with their high porosity and extensive surface area, hold promise for this purpose. Cellulose is a suitable biopolymer for gel fabrication; however, the adsorption capacity of unmodified raw cellulose fibers often falls short of performance expectations due to the lack of strong binding sites. Therefore, this study investigates how different cellulose fiber types, chemical treatments, and solvent systems influence hydrogel properties for adsorption applications. Hydrogels were prepared from phosphorylated and unphosphorylated unbleached kraft pulps (UKP) derived from eucalyptus and pine using NMMO and IL solvent systems. Phosphorylation increased the surface charge of UKP from similar to 0.05 to similar to 2.3 mmol/g. However, the surface charge of phosphorylated samples decreased to 0.5-0.72 mmol/g after coagulation into hydrogels. Hydrogels prepared from phosphorylated UKP exhibited superior properties compared to the unphosphorylated counterparts, including increased specific surface area (12-64 m(2)/g to 53-95 m(2)/g), swelling capacity (1930-2800% to 3400-4800%), and higher MB adsorption capacity (13-30 mg/g to 156-291 mg/g). When comparing solvent systems, the NMMO-based hydrogel showed enhanced surface area and pore characteristics, while the IL-based hydrogel exhibited increased MB adsorption capacity (291 mg/g vs. 233 mg/g). Although pine-derived hydrogels had lower MB adsorption than eucalyptus-derived ones (156 mg/g vs. 291 mg/g), both showed comparable adsorption performance for Cu2+ ions (similar to 40 mg/g). Overall, the IL-derived hydrogel from phosphorylated eucalyptus UKP proved most effective for removing MB and Cu2+ from aqueous solutions. These findings contribute to advancing cellulose-based hydrogels for efficient adsorption in wastewater treatment.