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

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 Fe³⁺ and OH^-. The limits of detection (LODs) for Fe³⁺ 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.