Polyethyleneimine modified cellulose nanofiber microgel for rapid and efficient Cr(VI) removal

Balancing the adsorption rate and efficiency is crucial for the removal of hazardous chemicals such as Cr(VI) in water, especially when the adsorbent could be easily separated from system. To address this challenge, polyethyleneimine (PEI) modified cellulose nanofiber (CNF) microgels (PCM) were prepared using an emulsion template method, where glutaraldehyde (GA) served as the crosslinking agent between the amino group in PEI and hydroxyl group in CNFs. The resulting PCM materials exhibited an ellipsoidal shape with an average size of approximately 500 μm, which allowed these adsorbents to be easily separated by Nylon filter mesh. Furthermore, the optimal sample PCM3 reached adsorption equilibrium within 20–240 min, which was shorter than most cellulose based aerogels or bead adsorbents. This sample also demonstrated a high adsorption capacity for Cr(VI) (410.0 mg g⁻¹), higher than the macroscopic PEI/CNF aerogel (16.9 mg g⁻¹). After five recycling cycles, the removal quantity remained at 122.9 mg g⁻¹, indicating good reusability. The adsorption of Cr(VI) in aqueous solution was primarily driven by electrostatic interactions, due to the protonation of amino group, and some Cr(VI) ions were reduced into Cr(III) by amino group during the adsorption process. This study provides a novel strategy for developing CNF-based microgels that can efficiently and rapidly adsorb Cr(VI).