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, Fourier-transform 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.

Siderite Formation by Mechanochemical and High Pressure–High Temperature Processes for CO2 Capture Using Iron Ore as the Initial Sorbent

Iron ore was studied as a CO2 absorbent. Carbonation was carried out by mechanochemical and high temperature–high pressure (HTHP) reactions. Kinetics of the carbonation reactions was studied for the two methods. In the mechanochemical process, it was analyzed as a function of the CO2 pressure and the rotation speed of the planetary ball mill, while in the HTHP process, the kinetics was studied as a function of pressure and temperature. The highest CO2 capture capacities achieved were 3.7341 mmol of CO2/g of sorbent in ball milling (30 bar of CO2 pressure, 400 rpm, 20 h) and 5.4392 mmol of CO2/g of absorbent in HTHP (50 bar of CO2 pressure, 100 °C and 4 h). To overcome the kinetics limitations, water was introduced to all carbonation experiments. The calcination reactions were studied in Argon atmosphere using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis. Siderite can be decomposed at the same temperature range (100 °C to 420 °C) for the samples produced by both methods. This range reaches higher temperatures compared with pure iron oxides due to decomposition temperature increase with decreasing purity. Calcination reactions yield magnetite and carbon. A comparison of recyclability (use of the same material in several cycles of carbonation–calcination), kinetics, spent energy, and the amounts of initial material needed to capture 1 ton of CO2, revealed the advantages of the mechanochemical process compared with HTHP.