Fluorescent cellulose nanofibrils hydrogels for sensitive detection and efficient adsorption of Cu²⁺ and Cr⁶

Increasing chromium and copper pollution poses a significant threat to the global environment and human health. It is crucial to detect and remove Cu (II) and Cr (VI) from water. Cellulose nanofibrils (CNF)-based hydrogels were a natural, abundant, and biocompatible material that has attracted great attention for bio adsorption applications. In this work, a new fluorescent CNF-based hydrogel (PAA-CNF-W) was prepared for the high-efficiency adsorption and sensitive detection of Cu (II) and Cr (VI). CNF was introduced as a natural backbone to construct a three-dimensional porous structure, which increased the specific surface area and provided additional active sites, exhibiting excellent adsorption properties for Cu (II) (159.24 mg/g) and Cr (VI) (173.87 mg/g). Moreover, the synthesized dansyl chloride derivatives with fluorescent properties were introduced to the hydrogel and formed chelates with the metals leading to fluorescence quenching. PAA-CNF-W hydrogels showed high sensitivity to the detection limit (LOD) of Cu (II) (28.70 mg/L) and Cr (VI) (1.45 mg/L). The kinetic study revealed that pseudo-second order kinetics was the best-fitting model. The Langmuir isotherm was the best adjustment model. The study provides a new idea for efficient detection and removal of Cu (II) and Cr (VI) from wastewater by cellulose materials.