Hexavalent Chromium Sorption by Modified Cellulose Macro and Nanofibers Obtained from Eucalyptus Residues

Exposure to potentially toxic metallic elements (PTME) released in watercourses by industries results in irreversible damage to living beings or even death. The removal of a PTME, such as hexavalent chromium (Cr(VI)) in industrial wastewater aligned with the reuse/modification of natural adsorbents, is a promising alternative to remedy this problem. This paper presents cellulose from eucalyptus by-products at the macro (CMS) and nanoscale (CNS), obtained through a ball-milling process, which were also modified with zirconium oxide, providing MCMS and MCNS, respectively. The samples were characterized by FTIR, TGA, DRX, and adsorption tests. The cellulose chemical structure was maintained after milling and modification, but Zr-O bands’ inclusion indicated the fiber modification. The nanostructure presented a higher modification degree, highlighted by a considerable increase in thermal stability associated with the modified cellulose surface by zirconium. This result was corroborated by XRD analysis that presented new peaks for MCNS and reduced crystallinity. The adsorption test showed that the hydroxyl groups from the cellulose structure could remove Cr(VI) from water. However, this behavior was considerably enhanced by zirconium that increased the available binding sites, especially for the modified nanostructure, which presented the removal of 54% of Cr(VI). These results highlight the potential revaluation of eucalyptus residue and the modification treatment to attain a material with great adsorption properties that could reduce water contamination. Graphical Abstract