稻壳质介孔炭的制备与成孔机制

Preparation and activation mechanism of rice husk based mesoporous carbon

以稻壳为原料、KOH为活化剂,采用炭化和活化两步法制备了介孔炭。采用比表面积测定仪测定介孔炭的N2吸附脱附等温线,采用扫描电子显微镜(SEM)、X射线衍射分析仪(XRD)、小角X射线衍射分析仪(SAXRD)表征介孔炭形成过程中的物相变化与显微结构,由同步热分析质谱联用仪(TG-MS)分析生成的气体成分并推测成孔机制。结果表明:稻壳在420℃下炭化4 h,再将KOH与炭化稻壳按质量比3∶1混合均匀后,在750℃下活化1h,所制备的活性炭平均孔径为2.3 nm,最可几孔径4.5 nm,比表面积高达2175 m2/g,介孔率达到78.57%;同时,炭化稻壳在KOH的活化过程中生成的气体成分含有CO、CO2和H2O,炭化稻壳中SiO2与KOH的高温分解物K2O反应生成K2Si4O9。

Mesoporous carbon has been prepared by a combination of carbonization and activation processes,in which rice husk and KOH were used as carbon source and activator,respectively. N2 adsorption and desorption isotherms were measured,and the phase change and changes in microstructure during the formation of the mesoporous carbon were characterized by scanning electron microscopy( SEM),X-ray diffraction( XRD),and small angle Xray diffraction( SAXRD). Simultaneous thermal analysis- mass spectrometry( TG- MS) was used to analyze the composition of the gas generated and a mechanism for the pore production proposed. The results show that the mesoporous carbon prepared under the protection of nitrogen,carbonized at 420 ℃ for 4 h,with a mass ratio of KOH and carbonized rice husk of 3∶ 1 and activated at 750 ℃ for 1 h,had an average pore size of 2. 3 nm and a modal pore size of 4. 5 nm,with a specific surface area and mesopore ratio as high as 2175 m2/ g and 78. 57%,respectively. The gas emitted during KOH activation of the rice husks contained CO,CO2,and H2O. Furthermore,SiO2 in the carbonized rice husk reacted with the K2O produced by high-temperature decomposition of KOH to form K2Si4O9.