Simple synthesis of spent coffee ground-based microporous carbons using K₂CO₃ as an activation agent and their application to CO₂ capture

Microporous carbons were prepared from spent coffee grounds via solid-state K₂CO₃ activation. Activation temperature and time were changed to manipulate the properties and CO₂ adsorption performance of porous carbons. As the activation temperature and time increased, textural properties such as specific surface area and total pore volume increased, reaching 2337 m² g⁻¹ and 1.15 cm³ g⁻¹, respectively. Among the prepared samples, the highest CO₂ uptake (4.54 mmol g⁻¹) at 25 °C and 1 atm was obtained in the porous carbon activated at 700 °C for 5 h. Depending on adsorption temperature and pressure, a dominant factor for CO₂ uptake was different. Nitrogen content and narrow microporosity were crucial at the low-pressure, 0.15 atm, and the narrow micropore volume was decisive but the significant pore size range was different depending on the adsorption temperature at atmospheric pressure. In addition to high CO₂ uptake, the developed porous carbons showed excellent cyclic stability and good selectivity for CO₂ over N₂. The high value-added porous carbons prepared from spent coffee grounds using the simple and less hazardous method have a potential of industrial application for CO₂ capture.