Adsorption characteristics and pore structure of activated carbons prepared from sorghum distillery residue

Sorghum distillery residue (SDR), one type of fermentation waste, was used as the precursor to prepare activated carbon (AC) using the method of physics activation with steam-or CO₂-activation. The yield and iodine value of sorghum distillery residue activated carbon (SDRAC) was 15.74 to 29.24% and 113 to 684 mg/g using CO₂-activation, as well as 10.63 to 26.07% and 548 to 770 mg/g using steam-activation. As the iodine value of SDRAC was above 700 mg/g, the methylene blue adsorption value was 143.56 to 344.87 mg/g, the BET specific surface area was 502.7 to 530.1 m²/g, the average pore diameter ranged from 2.89 to 3.18 nm and the true density was 1.86 to 1.97 g/cm³. The nitrogen adsorption-desorption isotherms of the SDRAC were classified as Type IV, indicating the presence of microporous and mesoporous structures, according to the Bruauer, Deming, Deming and Teller (BDDT) Classification, and were H3 type hysteresis loops for most of the mesoporous structures in accordance with the International Union of Pure and Applied Chemistry (IUPAC). SDR, with a suitable activation condition, can serve as an excellent precursor for preparing AC because the iodine value and the BET specific surface area of the resulting SDRAC can be reached at the commercial value. SDRAC is able to be applied to liquid absorption, such as water purification, due to its mesoporous structure.