Dye adsorption performance of nanocellulose beads with different carboxyl group content

The problems caused by water pollution are increasingly serious, wastewater contains a lot of heavy metal ions, textile dyes, medicines, etc. However, most adsorption materials usually face problems such as inefficient recycling, high cost, and secondary pollution. As a natural polymer, cellulose has low cost, degradability and good biocompatibility. In this work, by changing the addition amount of sodium hypochlorite during 2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO) oxidation, nanocellulose with different carboxyl content could be prepared, which is expected to be a good high-efficiency cationic adsorbent due to its rich in hydroxyl groups on the surface and negatively charged. Then the calcium chloride solution was used as the cross-linking agent to prepare TEMPO-oxidized cellulose nanofibril beads (TOCNB) by the dropping solidification method. As the content of carboxyl groups increases, the Zeta potential value of the nanocellulose dispersion became increasingly negative. The nanocellulose beads all presented a good three-dimensional network porous structure. With the increase of carboxyl group content, the specific surface area increases from 173 to 367 m² g⁻¹, and the adsorption capacity for methylene blue (MB) also gradually strengthened. The saturated adsorption capacity of TOCNB on MB was calculated as high as 925.93 mg g⁻¹. The nanocellulose bead was a cationic adsorbent with highly efficient adsorption and adjustable specific surface area, and the preparation method was simple, fast, efficient and green.