Exploring barley bran as a precursor for carbon quantum dots with enhanced fluorescence characteristics

The research described in this article deals with the synthesis of carbon quantum dots (CQDs) from barley bran including husk (BB) enriched with nitrogen by a hydrothermal-microwave method. Barley bran, as a raw material, is distinguished by its high carbon content and the presence of chemical compounds such as polysaccharides, proteins, fatty acids, and triglycerides, which contribute to the significant presence of oxygen atoms. The BB material was characterized using techniques such as Roentgen diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), dry weight analysis, scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and CHNOS elemental analysis. The results of XRD and FT-IR analysis were compared with those for dried CQDs, which show significant structural changes. Transmission Electron Microscopy (TEM) was used to analyze the size and structure of CQDs. The particles with a crystalline structure were characterized by an average size of 5.5 nm and a distance between crystal planes in the range of 0.19–0.28 nm. The optical properties of the CQDs particles were checked by UV–Vis spectroscopy analysis and their ability to emit light by spectrofluorimetry. The suspensions were characterized by absorption at 280 nm and fluorescence at 380 nm excitation with an emission peak base of about 200 nm and a peak maximum of 464 nm. The analysis showed that process parameters such as temperature, synthesis time, and filtrate volume significantly affect the properties of the obtained CQDs. The best fluorescence results were obtained for samples synthesized at 235 °C or 250 °C with larger filtrate volumes. Analysis of the optimization of the synthesis process showed that the best optical properties were obtained for samples prepared at 250 °C for 1 h from a filtrate volume of 40 mL. The study also underscores the need to further improve product purification procedures and reduce particle aggregation in aqueous solutions, which is an important element in improving the stability and performance of CQDs. • Novel use of barley bran for the synthesis of CQDs. • Energy-efficient hydrothermal-microwave synthesis yielded CQDs with high fluorescence (464 nm) from plant material. • Confirmation of structural changes of CQDs by XRD and FT-IR analyses. • Key effects of process parameters on CQDs properties. • Possible use of CQDs as biomolecule sensors in biomedical and environmental applications.