Jurnal Akademika Kimia, 12(2): 1-7, February 2023 ISSN (online) 2477-5185 | ISSN (print) 2302-6030 http://jurnal.fkip.untad.ac.id/index.php/jak/ OPEN ACCESS 1 Synthesis of Fluorescent Carbon Dots from Soybean Residuals Using Hydrothermal Method Dinda Gusti Ayu 1,2,3 , Saharman Gea* 2,3 , Andriayani 2 , & Ronn Goei 4 1 Postgraduate School, Department of chemistry/FMIPA, Universitas Sumatera Utara, Medan-Indonesia 20155 2 Department of chemistry/FMIPA, Universitas Sumatera Utara, Medan-Indonesia 20155 3 Cellulosic and Functional Materials Research Centre, Universitas Sumatera Utara, Medan-Indonesia 20155 4 School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798 Received 03 December 2022, Revised 08 January 2023, Accepted 14 February 2023 http://jurnal.fkip.untad.ac.id/index.php/jak/ Abstract Soybean residuals is biowaste that composed of carbon chains and amine groups bounded in peptide linkages. The component was identified through FTIR analysis which showed the vibration of the diamide bond (N=C=N) at the wave number 2132cm -1 . Owing to the existence of these components, soybean has the potential to be used as a precursor to synthesize carbon nano-material, such as Carbon Dots (C-Dots). In this study, the synthesis of C-Dots material from soybean residuals was carried out using the facile hydrothermal method at a temperature of 200 o C for 6 hours. Afterwards, the as-synthesized C-Dots were analyzed for its optical property, structure and morphology. Based on the analysis of the UV-Vis and photoluminescent spectra, C-Dots exhibited absorbance peaks of 292 nm and 301 nm in the UV light region, and fluorescence emission peaks of 468 nm, with blue luminescence characteristics. The observation was supported by the morphological analysis using the HR-TEM, C-Dots exist in a spherical shape with average particle size of 3.467 nm and a lattice distance of 0.363 nm. Besides, the C-Dots exhibited a good quantum yield of 28.15%. From the results of the analysis, it is known that the synthesis of C-Dots material has been successfully carried out with particle size <10 nm. Keywords: Soybean Residuals, Fluorescent, Carbon Dots, Quantum Yield. Introduction Carbon Dots (C-Dots) are zero-dimensional carbon materials with particle size smaller than 10 nm and several functional groups, such as hydroxyl, carboxyl, carbonyl and amine in their surface structure (Hu et al., 2021). With these characteristics, C-Dots have several advantages such as, light absorption over a wide range of electromagnetic, strong photoluminescent (PL), photostability, good water solubility, high biocompatibility, and low toxicity. Therefore, C- Dots are widely used in various fields such as biosensing, bioimaging, photocatalysts, and other applications (Ortega-gómez et al., 2015). The most challenges to the synthesis C-Dots are the source of precursors and the method of synthesis. Biomass is a good precursor sources for the synthesis of C-Dots. It has many advantages, including being environmentally friendly, easy to obtain, renewable, and low-cost (M. Abbas et al., 2018). In recent years, various biomass that has been used as the source of carbon in C-Dots synthesis were rice husks (Wongso et al., 2020), corn cobs (L. Zhang et al., 2019), bamboo leaves (Hasija et al., 2019). The approaches to the synthesis route of C- Dots (bottom-up vs top-down synthesis) give risk to another type of challenge. The processes involved in the bottom-up synthesis method is usually easier than top-down synthesis. The bottom- up method can be categorized into several process, such as solvothermal or hydrothermal, pyrolysis, and microwave irradiation (Xia et al., 2019). Among those methods, hydrothermal or solvothermal is considered as one of the most preferred type of C-Dots synthesis, considering its simple and low- cost process that does not require high energy and especially with its potential for a large scale synthesis (Z. Zhang et al., 2020). Hydrothermal method is the thermochemical degradation of biomass with ratio (water or solvent / biomass ranging from 5 : 1 to 75 : 1) at a certain temperature and pressure (A. Abbas et al., 2018). Considering the potential applications of C-Dots, in this study we synthesize bio-compatible C-Dots from soybean residuals. Soybean residuals is the main surplus material of soybean product and it is often regarded as waste. In Japan soybean residuals is burnt which will create carbon dioxide. Meanwhile soybean residuals as waste is potential environmental problem (Almaraz et al., 2009). Soybean residuals contains protein, fat/oil, crude fiber, carbohydrates, and ash, which are composed of carbon chains (Li et al., 2013). The presence of these substances makes soybean residuals have potentials precursor for the synthesis of C-Dots. In this study, C-Dots from soybean residuals was carried out by using facile hydrothermal method. The C-Dots was characterized to determine their structure, morphology, and optical properties.