Porous Structure and Characterization of Activated Carbons from the Grape Stalks

This study investigated the production and characterization of activated carbons (ACs) derived from grape stalks using CO2 and HNO3 as activating agents. Thermogravimetric analysis (TG-DTG) revealed three distinct stages of thermal decomposition, with mass losses attributed to water removal and the pyrolysis of hemicellulose, cellulose, and lignin. The AC yield varied depending on the activating agent, temperature, and number of cycles, with CO2 leading to lower yields but greater micropore development. Textural characterization revealed that HNO3-activated samples exhibited S(BET) specific surface areas of up to 741 m2/g, along with a higher proportion of mesopores compared to CO2-activated samples. FTIR analysis identified similar oxygenated functional groups across activation methods, with varying intensities. The point of zero charge (pHPZC) analysis indicated an acidic surface for HNO3 activated carbons (pHPZC between 5.2 and 5.5) and a basic surface for CO2 activated carbons (pHPZC ≈ 7.6). SEM images revealed that the fibrous structure of the grape stalks was preserved after activation, with the development of internal channels and macropores. This fibrous morphology gives the material added versatility, allowing it to be shaped into forms such as tows, fabrics, or felts, which is advantageous for a wide range of industrial and environmental applications.