Fluorescence ‘Turn-on’ Probe for Chromium Reduction, Adsorption and Detection Based on Cellulosic Nitrogen-Doped Carbon Quantum Dots Hydrogels

Abstract

This paper proposes a new, highly effective fluorescence test for Cr(VI) detection. This method utilizes a hydrogel composed of hydroxyethyl cellulose (HEC), nitrogen-doped carbon quantum dots (N–CQDs), and poly(co-acrylamido-2-methyl-1-propane sulfonic acid) (AMPS). The N–CQDs were successfully synthesized using a simple microwave method, and then conjugated with HEC and AMPS. The higher adsorption (99.41%) and higher reduction rate in H1 likely stems from both the presence of N–CQDs (absent in HB) and their increased free functional groups (compared to H2/H3, where N–CQDs block them). This facilitates the release (desorption) of Cr(VI) from the hydrogels, making it more available for reduction to the less toxic Cr(III). The fluorescent brightness of the HEC-N–CQDs-g-poly(AMPS) hydrogel increases gradually when Cr(VI) is added in amounts ranging from 15 to 120 mg/L. The fluorescent enhancement of the HEC-N–CQDs-g-poly(AMPS) hydrogel appeared to exhibit a good linear relationship with the 15–120 mg of the Cr(VI) concentration, with a detection limit of 0.0053 mg/L, which is lower than the standard value published by WHO. Our study found that the HEC-N–CQDs-g-poly(AMPS) hydrogel served effectively as a fluorescent probe for Cr(VI) detection in aqueous solutions, demonstrating high sensitivity.