Preparation of Biomass Waste-Derived Carbon Dots by the Thermal Degradation Process

Agricultural and food industry waste biomass is a material with diverse origins and a resulting variety of physicochemical characteristics and compositions. Because of its source, it is characterized by a high carbon content, and so it has been considered a worthwhile substrate for the synthesis of carbon dots (CDs). Therefore, waste biomass with high availability in Central Europe was selected as substrates for CDs synthesis: apple pomace, rapeseed pomace, and potato peelings. These materials are characterized by varying the composition and nitrogen content. The synthesis of CDs by thermolysis was investigated. The obtained CDs were examined by UV-vis spectrophotometry, spectrofluorimetry, Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, and X-ray diffraction. The CDs synthesis yield (SY) and fluorescence quantum yield (QY) were determined. This paper proves that CDs can be synthesized efficiently by thermal degradation in a solvent-free process using plant waste biomass. Despite the varying compositions of the substrates, CDs with similar emission characteristics were achieved. CDs obtained from apple pomace and potato peelings have a crystalline structure and size of 4-5 nm, while CDs obtained from rapeseed pomace have an amorphous structure and size of 11 nm. CDs derived at 260 °C from potato peelings are characterized by the strongest fluorescence among synthesized materials, a QY of 14.5%, with 12.3% SY. The potential of the obtained CDs as an optical biosensor was investigated against a variety of metal ions and water pollutants. The CDs obtained from potato peelings can be effectively used in the detection of Fe³⁺ ions (linearity range 12.5-1250 μM) and ibuprofen (linearity range 0.25-5 mM).