Valorization of Sunflower Seed Husks into Cellulose Nanofibrils and Nanocrystals for Sustainable Hydrogel Adsorbents in Heavy Metal Removal

The application of cellulose-based nanocomposite sorbents as environmentally friendly materials for water purification has emerged as an important and rapidly developing research area. In this context, cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) were successfully extracted from microcrystalline cellulose (MCC) derived from sunflower seed husks (SFHs) and comprehensively characterized. The obtained nanocellulosic materials were subsequently utilized to fabricate nanocomposite hydrogels, designated as HGCNF and HGCNC. The results revealed distinct structural and physicochemical characteristics of CNFs and CNCs, which significantly affected the morphology, swelling behavior, and stability of the resulting hydrogels. Swelling experiments conducted under various environmental conditions demonstrated that HGCNF exhibited higher water uptake and swelling capacity than HGCNC. Both hydrogels showed maximum swelling under near-neutral conditions (pH ≈ 6.5) and exhibited pronounced sensitivity to changes in ionic strength and solvent polarity. Furthermore, adsorption studies confirmed the effective removal of Cu2+ ions by both hydrogels, with HGCNC exhibiting a slightly higher adsorption capacity than HGCNF; the degree of sorption was 51.5%. These findings demonstrate that nanocellulose-based hydrogels possess tunable physicochemical properties and considerable potential as sustainable sorbent materials for water treatment, while also offering promising applications in environmental remediation, controlled drug delivery, and biomedical engineering.