Synthesis and characterization of carbon-dots from tofu solid waste for future food packaging biosensor applications using a circular economy approach

Environmental impacts can be minimized by converting agro-industrial waste into value added products based on the principle of a circular economy. Therefore, this study aims to investigate an green synthesis method for the production of carbon dots (C-dots) using tofu solid waste through two environmentally friendly methods. The synthesis process was carried out using a hydrothermal autoclave at 200°C and a microwave-assisted method at a power of 600 W. The resulting C-dots were characterized based on yield, photoluminescence, UV-Vis spectroscopy, FTIR, zeta potential, color, crystallinity, crystal size, morphology, and particle size. The results showed that the highest yield of 63.77% was obtained from the autoclave hydrothermal method. The fluorescence of C-dots was orange, yellow, reddish, greenish, and bluish, which was strong under UV light. The UV-Vis spectrum showed an absorbance peak range at 261–368 nm, indicating the presence of π–π* and n–π* transitions. The FTIR spectrum showed the presence of hydroxyl groups and aromatic structures with 2 main peaks, namely wavenumber 1624–1628 cm −1 and 3351–3353 cm −1 . In addition, the negative zeta potential value was −3.47 mV to −3.83 mV, with the highest value obtained in the autoclave hydrothermal method. The crystallinity index was 92.52%, while the crystal size was 65.8 nm. An average particle size of 3.71 nm was obtained from the autoclave hydrothermal method, while 43.86 nm was recorded from the microwave method. These results contribute to the development of tofu waste-based biomaterial technology and support the application of circular economy principles in the management of renewable resources.