Green acid-free hydrolysis of wasted pomelo peel to produce carboxylated cellulose nanofibers with super absorption/flocculation ability for environmental remediation materials

• Cellulose nanofiber-based environmental repairing materials were prepared by hydrogen peroxide. • POCNF-PEI has excellent Cu(Ⅱ) adsorption properties with maximum adsorption capacity of 74 mg/g. • POCNF-PEI has excellent MG adsorption ability with maximum adsorption capacity of 530 mg/g. • POCNF-PEI can be recycled four times with larger adsorption capacity of 65–72 mg/g. Carboxylated nanocellulose hold great application potential and research value in environmental remediation owing to its eco-friendly nature, high specific surface area, high density of functional groups and abundant reserves properties. In present work, a new type of cellulose nanofibers (CNF) with high aspect ratio and high density of carboxyl groups were prepared by directly thermo-oxidizing natural wasted pomelo peel with H 2 O 2 . The effects of reaction time on the content of carboxyl groups, morphology, and thermal stability of CNF were investigated. It is found that pomelo-CNF (POCNF) with larger aspect ratio of 169 and carboxyl group contents of 1.711 ± 0.173 mmol/g was fabricated by reacting at 60 °C for 6 h. Furthermore, the high density of carboxyl groups of POCNF allowed it to graft functional polyetherimide (PEI) on the surface of nanocellulose, and the resulting PNOCNF-PEI showed excellent adsorption performance to pollutants, such as malachite green (MG) and Cu(II), with adsorption capacity of 530 mg/g to MG and 74.2 mg/g to Cu(II). Moreover, the adsorbent showed excellent reusability. Besides, the possible adsorption kinetics/mechanism of nanocelluloses to various pollutants has been provided. The simple preparation process and excellent properties of POCNF made it become a viable candidate as environmental remediation material.