Preparation of Nanoporous Carbon from Rice Husk through Alkali Activation Treatment: a Detailed Mechanistic Investigation

Reaction processes that occur in preparation of porous carbon materials from pure carbon material through alkali activation treatment can be explained by the reaction of carbon to potassium hydroxide (KOH). The surface layer of carbonized rice husk (CRH) contains lots of silica (SiO2) which can create an alkali fusion reaction when interacted with KOH. The alkali fusion reaction of CRH is composed of two steps which are the elimination of SiO2 and the KOH activation. The elimination of SiO2 through alkali boiling increased the specific surface area (SBET) of CRH from 220 to 676 m2/g. After the alkali fusion, the amorphous carbon was covered by K2CO3, KHCO3 and K2SiO3.These byproducts were removed by neutralizing them with dilution water. The SBET of CRH increased from 220 to 2400 m2/g after removing these byproducts. Furthermore, the molar quantity of K that is needed in removing SiO2 is 6 mol while 9 mol of K is needed in the KOH activation by Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis. From estimation, the loss amount of C is 8 mol with 60% of the loss is contribute to the development of micro pores and 40% of the loss is contributed to the development of macro-meso pores.