Effect of Cellulose Nanofibril Size on Adsorption Behavior of 3-D Cellulose Hydrogels

Abstract

With the development of cellulose nanofibril (CNF)-based adsorbents, the influence of particle size on adsorption capability has become increasingly recognized. In this study, endoglucanase FiberCare® was utilized to decrease fibril size of TEMPO-oxidized cellulose nanofibrils (TCNFs) without changing carboxyl groups content of the resulting TCNFs. Average fibril length decreased by 27.3% (from 508.7 nm to 369.4 nm) after enzymatic hydrolysis for 12 h and further decreased by 35.4% (to 328.2 nm) after 24 h. Meanwhile, the average fibril diameter decreased 20.2% (from 56.8±16.3 to 45.3±14.3) after 12 h of hydrolysis, further reduced by 32.6% (to 38.3±13.1 nm) after 24 h. Carboxyl group content remained unchanged. Zeta potential of the TCNFs was increased by 5.5 mV after 24 h hydrolysis due to the exposure of more hydroxyl groups as fibril size decreases. TCNF hydrogel (from 12 h hydrolyzed) showed 20.3% increase in adsorption of cationic methylene blue dyes (from 64 mg/g to 77 mg/g) compared to untreated samples. However, further fibril size reduction after 24 h hydrolysis did not improve adsorption capability. Kinetic analysis using pseudo-second-order kinetic model and intra-particle diffusion model revealed no change in the adsorption mechanism, though the overall adsorption rate increased. This study highlights that reducing fibril size can enhance both adsorption capacity and rate, offering guidance for the design of CNF-based adsorbents. Graphical Abstract

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