One‐Step Microwave Solid‐State Synthesis of N, S Co‐Doped Carbon Dots and Their Multifunctional Applications

ABSTRACT Nitrogen and sulfur co‐doped yellow‐green fluorescent carbon dots (N,SCDs) were synthesized using thiourea and 5‐sulfo salicylic acid as raw materials through a one‐step microwave solid‐phase method. A series of characterizations, including transmission electron microscope (TEM), X‐ray photoelectron spectroscopy (XPS), Fourier‐transform infrared (FT‐IR), UV–Vis spectrum, and fluorescent spectrum, were conducted, revealing that N,SCDs are carbon dots with an average size of approximately 5.65 nm. These dots were found to possess a surface rich in hydroxyl, amino, carbonyl, and sulfhydryl groups, along with excellent solid‐state luminescent properties. N,SCDs were combined with starch to form N,SCDs‐starch composite, which was successfully utilized for high‐quality fingerprint development. Additionally, the solid‐state N,SCDs were dissolved in DMSO to produce the liquid form, L‐N,SCDs, which was effectively applied for the analysis and detection of Fe 3+ and OH − . The limits of detection (LODs) for Fe 3+ were determined to be 0.73 and 2.65 μM in the concentration ranges of 0–100 and 100–237.5 μM, respectively. Similarly, the LODs for OH − were found to be 0.027 and 0.66 μM in the ranges of 0–225and 225–525 μM, respectively. Furthermore, L‐N,SCDs configured as fluorescent inks were demonstrated to exhibit significant potential in applications related to information anticounterfeiting.