Carbon nanodots from watermelon peel as CO2 absorbents in biogas

We report the synthesis of carbon nanodots (Cdots) from watermelon peel waste. The Cdots obtained were characterized using ultraviolet-visible, photoluminescence, Fouriertransform infrared spectroscopies, and transmission electron microscopy. The Cdots exhibited green luminescence. The average diameter of the Cdots was 4 nm and the C=C functional groups were dominant. The Cdots were then utilized as CO2 absorbent in biogas. The result showed that the concentration of CO2 was reduced by up to 40% based on the gas chromatography test. The higher the Cdots concentration, the higher is the amount of CO2 that can be reduced in the biogas. Based on the heat performance test, higher concentration of Cdots produced higher heat energy of the biogas.