In this research, pure lemon juice was used to synthesize carbon-based quantum dots (CQDs) using hydrothermal method. Heated at 120C for a period of 3 hours, CQDs were successfully synthesized. The properties of CQDs were investigated by both FTIR and fluorescence spectrophotometer. Successful results show satisfactory optical properties and good water solubility from the CQDs. To further increase the quantum yield percentage of CQDs, onion juice was added to pure lemon juice at lemon-onion ratio of 8:2. The CQDs synthesized showed improved results with unexpected optical properties, strong water solubility as well as higher quantum yield percentage of 1.349%. Further investigation was done to find the optimal lemon-onion ratio for best quantum yield percentage results with different lemon-onion ratio. Results proves lemon-onion ratio of 8:2 is the optimal ratio. The CQDs synthesized are non-toxic due to the use of natural resources as its main materials as well as zero addition of chemicals throughout the synthesis process. Its zero-toxicity could benefit consumers in terms of consumables, such as toiletries, and water quality monitoring industry, such as heavy metal sensing and free chlorine sensing, as well as in medical field, such as bio-imaging and nanomedicine. Moreover, the by-products after synthesis are degradable, thus it would not create any long-lasting wastes. This could benefit the zero waste direction the world is heading towards.
