Evaluation of Carbon Dots from Arabica, Liberica, and Robusta Spent Coffee Grounds as Fluorescent Agents

Well-known as a popular food and beverage product worldwide, most people consume coffee. Besides coffee's strong and good taste, it contains many bioactive compounds beneficial for our health. High coffee consumption also results in so much organic waste from the by-products of the coffee industry, such as husks, parchment, and spent coffee grounds. Utilization of coffee by-products is highly possible due to their beneficial content, such as fibers, phenolics, minerals, carbohydrates, proteins, and lipids. Spent coffee grounds are known to have high carbon content, which is more than 50%, so they have good potential to be used as sustainable carbon dots precursors. Coffee has many types, such as Arabica, Robusta, and Liberica, with different characteristics and compounds. Carbon dots synthesized from Arabica, Robusta, and Liberica spent coffee grounds are studied, and their fluorescent properties are evaluated. The synthesis of the spent coffee grounds into carbon dots used a hydrothermal method with hydrazine hydrate as a reagent. Synthesized carbon dots were then characterized using TEM to evaluate particle size and morphology. The fluorescent properties of the carbon dots samples were also evaluated using a spectrofluorometer instrument. The results show that spent coffee grounds, especially Liberica, are a good candidate to replace the potentially harmful precursor chemicals for carbon dots synthesis. Carbon dots synthesized from spent coffee grounds also show the potential to be applied as fluorescent nanomaterials for sensing, imaging, and optoelectronic devices.