The synthesis and characterization of high purity mixed microporous/mesoporous activated carbon from rice husk using chemical activation with NaOH and KOH

Potassium hydroxide activation of activated carbon: a commentary

“…Chemical activation is a single step process, as both carbonization and activation occur simultaneously at temperatures ranging between 400 o C and 700 o C, which is lower than that of physical activation [9]. However, in some cases, additional carbonization or a pre-carbonization step is performed to produce char prior to chemical impregnation and activation [5,4,[10][11][12][13]. Thus, potassium hydroxide activation can be achieved through either direct chemical activation or char-impregnated chemical activation.…”

“…The grape seed activated carbon is mainly microporous with a surface area of 1222 m 2 /g [6], while the rice husk activated carbon (2696 m 2 /g) is mainly mesoporous [12]. The mesoporous char-impregnated chemical activation is more favourable in the manufacture of activated carbon as compared to direct chemical activation.…”

“…The mesoporous char-impregnated chemical activation is more favourable in the manufacture of activated carbon as compared to direct chemical activation. Pre-carbonization, executed in some studies [12,14], produces some advantages in the textural properties of the activated carbon, although KOH is a strong base which supports single step activation.…”

“…From Table 1, it is generally found that an activation temperature above 800 o C and an activation time of more than 30 min will produce activated carbon with a specific surface area greater than 900 m 2 /g [6,[10][11][12]15,16]. However, some studies have revealed a lower product yield of 17% to 31% when a temperature above 800 o C was used [6,12,17].…”

“…However, some studies have revealed a lower product yield of 17% to 31% when a temperature above 800 o C was used [6,12,17]. In other words, higher activation temperature and longer retention time could promote the further development of pores, which consequently leads to a greater surface area of up to 2696 m 2 /g, and at the same time suffers a lower carbon yield [12]. The pyrolysis with KOH reduces the amount of carbon due to the intercalation of potassium ions into the carbon matrix, which accelerates the carbon liberation.…”