Abstract：Carbon quantum dots (CQDs) is a novel type of fluorescent carbon nanomaterials， highly regarded for their excellent biocompatibility and outstanding optical properties. However， the fluorescence quenching during their application have affected the monitoring effect. In this study CQDs were synthesized through hydrothermal method and the surface of CQDs was amino modificated using ammonia (NH3)， obtaining amino-functional carbon quantum dots (NH2-CQDs). A fluorescence quenching system comprising NH2-CQDs and polyacrylic acid (PAA) was constructed， and the fluorescence recovery was quantitatively investigated using sodium hydroxide (NaOH). The characterization of NH2-CQDs' size， composition， and fluorescence intensity was conducted using transmission electron microscopy (TEM)， Fourier transform infrared spectroscopy (FTIR)， ultraviolet-visible spectroscopy (UV-Vis)， and fluorescence spectroscopy (FL). The relationship between the molar ratios of NaOH and PAA and the effect of incubation time on the reaction system were examed primarily. The results indicated that NH2-CQDs had an average particle size of 4.8 nm， and their surfaces were rich in hydrophilic groups such as hydroxyl and nitrogen (N)-containing functional groups， offering excellent water solubility and stability in aqueous solutions. NH2-CQDs exhibited a distinct absorption peak at 332 nm， with the highest fluorescence intensity at an emission wavelength of 451 nm when excited at 378 nm， and their emission peak position varies with the excitation wavelength. Under the presence of PAA， the fluorescence of NH2-CQDs was effectively quenched； whereas under the presence of NaOH， the fluorescence recovered. The best fluorescence recovery was observed when 5.00×10－5 mol NaOH was added to the fluorescence quenching system containing 4.17×10－5 mol PAA (approximately mPAA∶mNaOH＝1∶1)， with relatively stronger stability and reversibility and demonstrating a clear overall contour of the polymer under the optimal conditions. This research potentially enables the online labeling of polymers with CQDs.
2025, Vol. 59 
