Sustainable starch-microcellulose composite hydrogels for efficient removal of heavy metals from water

This work investigates the development of sustainable composite hydrogels based on corn starch and microfibrillated cellulose (MFC) derived from eucalyptus sawdust for the removal of copper from aqueous environments. The incorporation of MFC into the starch matrix reduced solubility from 55.2 % to 36.4 %, increased true density from 1.466 to 1.525 g/cm³, and decreased surface area with increasing MFC content (from 4.010 to 1.814 m²/g). The MFC presented the following metallic affinity order: Cu²⁺ > Mn³⁺ > Ni²⁺ > Zn²⁺ > Cd²⁺ > Cr⁶⁺. Adsorption experiments showed enhanced Cu²⁺ removal with increasing MFC content, with the Starch/MFC-5 % hydrogel achieving a maximum removal efficiency of 52.4 % and sorption capacity of 0.258 mmol/g. Langmuir isotherms provided the best fit to the equilibrium data (R² = 0.998), and the Dubinin-Radushkevich analysis indicated a shift from physisorption (E = 2.42 kJ/mol) to chemisorption (E = 8.11 kJ/mol). Kinetics equilibrium time was reached between 480 and 780 min, with best description by pseudo second-order model. The reuse of hydrogel was achieved for up to four sorption/desorption cycles. The mechanisms of Cu²⁺ sorption involved interactions with the functional groups present on the materials and cation exchange. These results confirm that starch/MFC hydrogels are promising, low-cost, and biodegradable materials for the efficient removal of metal ions from contaminated water.