Carbon dots (CDs) are a promising class of nanomaterials with attractive optical properties, offering a sustainable alternative to traditional inorganic quantum dots (QDs). This review focuses on the synthesis, function, and sustainability of CDs. CDs are synthesized from biomass and non-toxic materials, avoiding precious metals and critical raw materials. However, current methods often use non-sustainable solvents and energy, leading to waste and environmental concerns. The review highlights the need for future studies to consider the environmental impact of starting materials, solvents, and byproducts, and to provide quantitative data on energy and material usage for sustainability assessments. CDs have been synthesized from various biomass sources, including watermelon peels, soy milk, jasmine leaves, and egg white, demonstrating their versatility. Pretreatment steps such as washing, drying, size reduction, and extraction are crucial for efficient chemical conversion. Washing removes impurities, drying reduces moisture, size reduction increases surface area, and extraction isolates functional compounds. Chemical conversion methods include solvothermal, hydrothermal, reflux, pyrolysis, and microwave-assisted processes. Solvothermal and hydrothermal methods use solvents like ethanol and acetone, while pyrolysis and microwave-assisted methods are more energy-efficient. N-doping with ammonia or urea enhances emission properties, and the use of ionic liquids for biomass dissolution is also explored. Purification techniques such as filtration and centrifugation are essential for obtaining high-purity CDs. Filtration removes larger particles, while centrifugation separates precipitates from supernatants. The review emphasizes the importance of sustainable practices in CD synthesis, including energy-efficient methods and the use of environmentally benign solvents. Overall, CDs offer a sustainable alternative to QDs, with potential applications in lighting, sensors, and biomedical fields. However, further research is needed to optimize synthesis methods and ensure environmental sustainability.Carbon dots (CDs) are a promising class of nanomaterials with attractive optical properties, offering a sustainable alternative to traditional inorganic quantum dots (QDs). This review focuses on the synthesis, function, and sustainability of CDs. CDs are synthesized from biomass and non-toxic materials, avoiding precious metals and critical raw materials. However, current methods often use non-sustainable solvents and energy, leading to waste and environmental concerns. The review highlights the need for future studies to consider the environmental impact of starting materials, solvents, and byproducts, and to provide quantitative data on energy and material usage for sustainability assessments. CDs have been synthesized from various biomass sources, including watermelon peels, soy milk, jasmine leaves, and egg white, demonstrating their versatility. Pretreatment steps such as washing, drying, size reduction, and extraction are crucial for efficient chemical conversion. Washing removes impurities, drying reduces moisture, size reduction increases surface area, and extraction isolates functional compounds. Chemical conversion methods include solvothermal, hydrothermal, reflux, pyrolysis, and microwave-assisted processes. Solvothermal and hydrothermal methods use solvents like ethanol and acetone, while pyrolysis and microwave-assisted methods are more energy-efficient. N-doping with ammonia or urea enhances emission properties, and the use of ionic liquids for biomass dissolution is also explored. Purification techniques such as filtration and centrifugation are essential for obtaining high-purity CDs. Filtration removes larger particles, while centrifugation separates precipitates from supernatants. The review emphasizes the importance of sustainable practices in CD synthesis, including energy-efficient methods and the use of environmentally benign solvents. Overall, CDs offer a sustainable alternative to QDs, with potential applications in lighting, sensors, and biomedical fields. However, further research is needed to optimize synthesis methods and ensure environmental sustainability.