Preparation and properties of high-content carbon dots hydrogel based on amination modification

In order to solve the problem of reduced fluorescence intensity caused by aggregation of carbon dots (CDs) in solution, this study successfully optimized the synthesis conditions for amination-modified carbon dots (N-CDs) by adjusting factors such as nitrogen source, reaction temperature, and time, making the fluorescence stable and easy combination with natural polymers. Additionally, the semi-dissolution acidification sol–gel transition (SD-A-SGT) method was used to prepare the carboxymethylcellulose (CMC) and chitosan (CS) composite hydrogels, achieving a high content of CDs with a straightforward process. Fluorescence properties, chemical composition, and morphological characteristics of CD fluorescent hydrogels were analyzed. The results showed that the fluorescent hydrogels revealed distinct absorption bands in the FT-IR spectra (1601 cm⁻¹, 1395 cm⁻¹, and 1632 cm⁻¹), indicating the formation of intermolecular complexes. CS and CMC in N-CDs/CMC/CS composite hydrogels formed intermolecular complexes through strong electrostatic and hydrogen-bonding interactions between NH₃⁺ and COO⁻ groups, exhibiting an interconnected porous network structure that provided space for the uniform dispersion of N-CDs. Compared to the aqueous N-CDs solution, the fluorescence curve of the N-CDs/CMC composite was slightly enhanced (1.82%) and broadened, and N-CDs achieved ideal immobilization at high content in the gel system without quenching. This work develops an environmentally friendly composite hydrogel with strong fluorescence, holding promising applications in metal detection.