Fluorescent biopolymer hydrogels crosslinked with carbon quantum dots for selective detection of heavy iron (III) ions

In this study, carbon quantum dots (CQDs) were synthesized using glycerol and citric acid under microwave radiation, achieving an 83 % quantum yield (QY) and 1.59 nm particle size. These CQDs were employed as softeners and crosslinkers for the production of fluorescent granular and film hydrogels, in combination with biopolymers such as starch, chitosan (Ch), and gelatin (Ge). The resulting biopolymer-CQD composites were evaluated for their ability to selectively detect heavy metal ions, such as iron (III), as well as for their water vapor permeability (WVP), water solubility (WS), and swelling properties. Various analyses confirmed the formation of fluorescence bio-nanocomposites and improvements in their properties. Notably, a hydrogel film containing 50% wt CQDs exhibited the highest mechanical strength, with a tensile strength of 6.28 MPa and an elongation at fracture of 91.2%. Additionally, a strongly crosslinked fluorescent granular hydrogel with a ratio of Ge 25%: Ch 75% and a fixed amount of CQDs was able to absorb 136 times its own weight in water and exhibited increased water vapor permeability with higher CQD content. Overall, the fabricated materials show potential for the detection of iron (II), iron (III), and mercury (II) in aqueous media.