Nanocarbon eco-hydrogel kit: on-site visual metal ion sensing and dye cleanup, advancing the circular economy in environmental remediation

The naked-eye detection of hazardous pollutants through simple and cost-effective techniques is of great interest to the scientific community and related stakeholders in analytical science. The present study emphases the development of a stimuli-responsive probe by encountering sophisticated techniques for the detection of environmental pollutants. Herein, highly swellable and fluorescent-WTR-CDs-loaded HB-Alg/Gel@WTR-CDs was fabricated through a simple extrusion dripping method. The fluorescent WTR-CDs-loaded composite hydrogel showed rapid (within 10-15 min) naked-eye detection with high selectivity and sensitivity towards Cr⁶⁺ and Mn⁷⁺ ions over other metal ions. The developed probe had a linear detection range of 0-10 μg mL^-1 with a detection limit of 0.28 μg mL^-1 and 0.30 μg mL^-1 for Cr⁶⁺ and Mn⁷⁺ ions, respectively. Interestingly, the hydrogel-based fluorescent sensor enabled on-site naked-eye detection of real water samples with good recovery. Additionally, the recyclability and reusability approach were employed for the removal of model pollutant dyes with Alg/Gel-carbon, which was synthesized using spent hydrogel beads after sensing. The present study demonstrates the tremendous potential applications of HB-Alg/Gel@WTR-CDs for simple, low-cost and fast visual detection of environmental pollutants. According to the analytical greenness evaluation (AGREE), the developed analytical method is green with an AGREE score of 0.81 and an ecofriendly circular-economy approach.