Kayiwa R, Kasedde H, Lubwama M, Kirabira J B
Department of Mechanical Engineering, College of Engineering, Design, Art and Technology, Makerere University, P.O. Box 7062, Kampala, Uganda.
Bioresour Bioprocess. 2021 Jun 24;8(1):53. doi: 10.1186/s40643-021-00407-0.
The search for alternatives to fossil-based commercial activated carbon (AC) continues to reveal new eco-friendly potential precursors, among which is agricultural waste. The key research aspect in all these endeavors is empirical ascertainment of the core properties of the resultant AC to suit a particular purpose. These properties include: yield, surface area, pore volume, and the active surface groups. It is therefore pertinent to have process conditions controlled and tailored towards these properties for the required resultant AC. Pre-leaching cassava peels with NaOH followed by KOH activation and carbonization at holding temperatures (780 °C) above the melting point of K (760 °C) yielded mesoporous activated carbon with the highest surface area ever reported for cassava peel-based AC. The carbonization temperatures were between 480 and 780 °C in an activation-carbonization stepwise process using KOH as the activator at a KOH:peel ratio of 5:2 (mass basis). A 42% maximum yield of AC was realized along with a total pore volume of 0.756 cmg and BET surface area of 1684 mg. The AC was dominantly microporous for carbonization temperatures below 780 °C, but a remarkable increase in mesopore volume (0.471 cmg) relative to the micropore volume (0.281 cmg) was observed at 780 °C. The Fourier transform infrared (FTIR) spectroscopy for the pre-treated cassava peels showed distortion in the C-H bonding depicting possible elaboration of more lignin from cellulose disruption by NaOH. A carboxylate stretch was also observed owing to the reaction of Na ions with the carboxyl group in the raw peels. FTIR showed possible absorption bands for the AC between 1425 and 1712 cm wave numbers. Besides the botanical qualities of the cassava peel genotype used, pre-leaching the peels and also increasing holding activation temperature above the boiling point of potassium enabled the modified process of producing highly porous AC from cassava peel. The scanning electron microscope (SEM) and transmission electron microscope (TEM) imaging showed well-developed hexagonal pores in the resultant AC and intercalated K profile in the carbon matrices, respectively.
对基于化石的商业活性炭（AC）替代品的探索不断揭示出新的环保潜在前驱体，其中包括农业废弃物。所有这些研究的关键方面是通过实验确定所得AC的核心特性，以满足特定用途。这些特性包括：产率、表面积、孔体积和活性表面基团。因此，有必要控制工艺条件并针对这些特性进行调整，以获得所需的AC。用NaOH对木薯皮进行预浸提，然后用KOH活化，并在高于K熔点（760°C）的保温温度（780°C）下碳化，得到了具有中孔结构的活性炭，其表面积是有史以来基于木薯皮的AC中报道的最高值。在以KOH为活化剂、KOH与木薯皮比例为5:2（质量比）的活化-碳化分步过程中，碳化温度在480至780°C之间。AC的最大产率为42%，总孔体积为0.756 cmg，BET表面积为1684 mg。对于碳化温度低于780°C的情况，AC主要为微孔结构，但在780°C时，观察到中孔体积（0.471 cmg）相对于微孔体积（0.281 cmg）有显著增加。预处理木薯皮的傅里叶变换红外（FTIR）光谱显示C-H键发生畸变，表明NaOH可能使纤维素分解产生了更多木质素。由于Na离子与生木薯皮中的羧基反应，还观察到了羧酸盐伸缩振动。FTIR显示AC在1425至1712 cm波数之间可能存在吸收带。除了所用木薯皮基因型的植物学特性外，对木薯皮进行预浸提以及将保温活化温度提高到钾的沸点以上，使得从木薯皮生产高孔隙率AC的改性工艺成为可能。扫描电子显微镜（SEM）和透射电子显微镜（TEM）成像分别显示所得AC中发育良好的六边形孔和碳基质中嵌入的K分布。
