Green Hydrothermal Synthesis of Highly Fluorescent Thyme-Derived Carbon Quantum Dots as Potent Broad-Spectrum Antibacterial Agents


Chiayee Salih Ajaj, Wasfiya A. Muneer, Diyar Sadiq, Chinar Mustafa Mohammed, Briyar Mustafa, Abubaker Hassan Hamad

https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/slct.202506817

Carbon quantum dots (CQDs) formed by Thyme were synthesized by a single-step green hydrothermal process using Thyme extract as the carbon source. Subsequently, they evaluated their effectiveness as an antibacterial versus several microbes. The synthesized CQDs exhibited a quasi-spherical morphology, with an average diameter of around 6.4 nm, and had a broad (002) x-ray diffraction (XRD) peak indicative of graphitic carbon. Fourier transform infrared (FTIR) and energy-dispersive x-ray spectroscopy (EDX) tests demonstrated the existence of several hydroxyl, carboxyl, and carbonyl groups on the surface, thus enhancing hydrophilicity and stability. Optical analyses demonstrated strong π–π* and n–π* transitions, accompanied by excitation-sensitive photoluminescence (PL) at 512 nm, yielding a significant quantum efficiency of 36%. The Thyme-CQDs demonstrated significant antibacterial activity versus E. coli, S. aureus, and P. aeruginosa, with S. aureus showing the highest sensitivity. The antibacterial effects are ascribed to the generation of reactive oxygen substances (ROS), breakdown of membranes, and the combined properties of thyme-derived phenolics, such as thymol and carvacrol. The results show that thyme can serve as a renewable carbon preparation for high-performance CQDs suitable for antibacterial, environmental, and bioimaging applications.