Preparation and Applications of High Surface Area Activated Carbons from Corncob Waste by the KOH Chemical Activation Method
Date Issued
2006
Date
2006
Author(s)
Tseng, Ru-Ling
DOI
zh-TW
Abstract
Two methods, KOH activation and a combination KOH plus CO2 activation, were employed to prepare of corncob derived activated carbon with high surface area in this study. Physical properties of activated carbon including specific surface area, pore volume, pore size distribution, and morphologies were evaluated with the BET surface area analysis and SEM observation. Through the investigations on the variations of physical and chemical properties of activated carbon, as the KOH/char ratios from 0.5 to 2, both physical pyrolysis and KOH etching coexisted during activation; as the KOH/char ratios from 3 to 6, only chemical KOH etching existed. At the KOH/char ratio equal to 6, BET surface area reached 2595 m2/g. The relationships between activated carbon characteristics and CO2 gasification time were investigated at the KOH/char ratios of 1 and 4 for studying the effect of the combined activation process. At the low KOH/char ratio, long CO2 gasification time significantly increased the specific surface area and mesopores volume ratio. At KOH/char equal to 4 and CO2 gasification time equal to 30 minutes, the highest surface area of 2844 m2/g was obtained. Elemental analysis and temperature programmed desorption were employed to measure the variations of chemical properties and functional groups of activated carbon. The results supported the above proposals. Cyclic voltammetry was employed to measure the carbon electrode. Capacitive-like curves with a maximum specific capacitance of 127 F/g (0.5 M H2SO4) was obtained at KOH/char ratio equal to 3. Furthermore, from the variation of surface resistivity, KOH activation for preparing the high surface area activated carbon caused discontinuities of electrical conductivity in carbon, affecting the applicability in electrochemical field. Both Langmuir and Freundlich equations were employed to analyze the adsorption isotherms of dyes and chlorinated phenols in solutions on activated carbons. Adsorbate coverage on activated carbon surface and unit area contribution was calculated. Adsorption kinetics was employed to investigate mass transfer within pores. Method of t50 was employed to calculate the effective diffusion coefficients of particles to understand the adsorption performance of the activated carbons studied in this work, and explained the application potential in various fields of new technology.
Subjects
活性碳
KOH活化法
物化性質
吸附
電化學
activated carbon
KOH activation
physical and chemical properties
adsorption
electrochemical
Type
thesis