Fluorescent carbon dots crosslinked cellulose Nanofibril/Chitosan interpenetrating hydrogel system for sensitive detection and efficient adsorption of Cu (II) and Cr (VI)

Abstract

• One-pot synthesis of carbon dots cross-linked cellulose nanofibril hydrogel. • The introduction of chitosan by solvent displacement forms IPN hydrogel. • Carbon dots provide visual detection during Cu (II) and Cr (VI) adsorption. • Amphoteric biomass and carbon dots provide adsorption sites for Cu (II) and Cr (VI). • The mechanism of Cu (II) and Cr (VI) sorption and sensing was determined. To address the pollution of heavy metal ions in water resources, a novel self-assembled nitrogen-doped carbon dots (NCDs) crosslinked, cellulose nanofibril (CNF) and chitosan (CS) based interpenetrating polymer network (IPN) hydrogel (NCDs-CNF/CSgel) was prepared for simultaneous fluorescent detection and adsorption of Cu (II) cation and Cr (VI) anion. The NCDs cross-linked CNF hydrogel network was synthesized by an environmentally friendly low-temperature hydrothermal process and subsequently, solvent replacement was used to form the second layer of CS network. The morphology, chemical structure, fluorescent properties, and adsorption behaviors of NCDs-CNF/CSgel were analyzed. The results showed that NCDs-CNF/CSgel exhibited a wide linear range of fluorescence response for Cu (II) (50–1000 mg/L, detection limit of 40.3398 mg/L) and superior sensitivity and selectivity of fluorescence response for Cr (VI) (linear range of 1–50 mg/L, detection limit of 0.7093 mg/L). NCDs-CNF/CSgel showed high adsorption capacities of 148.30 mg/g and 294.46 mg/g for Cu (II) and Cr (VI), respectively, and fitted well to the pseudo-second-order model and the Langmuir model. The detection of Cu (II) and Cr (VI) and their adsorption mechanisms onto NCDs-CNF/CSgel were further determined. Hence, this work provides a green and sustainable approach for the synthesis of a functional material which can be applied for the detection and adsorption of heavy metal ions.