Carbon Quantum Dot (CQD)-Based Composite Fluorescent Hydrogel for the Isolation and Determination of Iron (III)

Carbon quantum dots (CQDs) were derived from saponin and introduced into polyacrylamide hydrogel to prepare a novel bifunctional material (CQDs@HG). This hydrogel emitted strong blue fluorescence under ultraviolet light (365 nm) and exhibited stable adsorption and detection of iron(III) in water samples. The morphological characteristics, chemical composition, Fe3+ adsorption performance, and optical properties of CQDs@HG were characterized. Depending upon the Fe3+ concentration, CQDs@HG exhibited different quenching effects to allow Fe3+ determination. The limit of detection was 0.115 μM, and the adsorption was as high as 12.13 mg/g. The mechanism was due to both static and dynamic quenching. Notably, the sensor based on CQDs@HG successfully determined Fe3+ in water samples, with spiked recoveries between 95.32% and 103.11%. When combined with software image analysis, the sensor semi-quantitatively determined Fe3+ in the field. This fluorescent hydrogel provides a reference for constructing portable sensors for monitoring hazardous substances in water.