Deconstruction of sisal lignocellulosic fibers by cupriethylenediamine hydroxide: creating hydrogels from cellulose, hemicelluloses, and lignin to assess their potential for heavy metal sorption.

Developing bio-based hydrogels offers a sustainable alternative to traditional fossil-based materials in wastewater treatment, particularly for absorbing heavy metals. This study focused on creating hydrogels from the components of sisal fibers, specifically cellulose (around 59 %), hemicelluloses (29 %), and lignin (12 %), through a deconstruction process using cupriethylenediamine hydroxide (CUEN) as the solvent and water as the coagulation medium. CUEN deconstructed 1 g and 2 g of sisal fibers; in total mass, the dissolution efficiency achieved was 73.7 % (cellulose and hemicelluloses) and 52.4 %, respectively. Lignin remained suspended in the medium alongside fractions of hemicelluloses and cellulose. Macromolecules dissolved and suspended in the medium were incorporated into the hydrogels. The hydrogel made from 1 g of sisal showed a higher water sorption capacity (5076.4 %). Meanwhile, the one created using 2 g of sisal demonstrated superior crystallinity, compression, and rheological properties, with a compressive elastic modulus of 62.4 kPa and a shear storage modulus of 416.8 kPa. Sisal_2_hydro also presented higher BET surface area and pore volume, enabling them to reach sorption capacities of up to 0.41 mmol/g for heavy metals, specifically Cu(II), Ni(II), Zn(II), Cd(II), Mn(II), and Cr(VI). The deconstruction of sisal fibers successfully produced hydrogels that demonstrated potential for sorbing heavy metals.