This research has studied the optimisation of activated carbon production from corn cub, using microwave heating techniques. A comparative study was conducted on the results obtained from both production methods to provide information on the characteristics, advantages and disadvantages of each production technique from a physical and chemical perspective. The microwave production method was studied using a combination of RSM and the traditional single-factor-at-a-time experimental design. The production methods showed that at a particular degrees of carbon burnoff, much lower pore volume and internal surface area was achieved for the microwave produced samples. The highest BET surface area produced with the conventional production method was 1777 m2 /g, obtained from the activation of carbonised char with 0.67 ml/min water for 4 hours at 900°C. This value was nearly 2.5 times larger than the maximum BET surface area achieved from the microwave production method (715 m2 /g) (50 min at 1000W). Similar results were also obtained for the aqueous phase adsorption of phenol and methylene blue; 2.2x and 2.3x larger adsorption capacity for thermal sample, respectively. In general, the microwave production method was found to be less effective in the production of highly microporous carbon. While the rate of micropore development with carbon burn-off in microwave heating was much lower than the conventional method, mesopore volume was found to be close and even comparable with that achieved with the conventional method. Considering that the microwave heating resulted in lower energy consumption per unit carbon burn-off, this heating system can be energy efficient in the production of mesoporous adsorbents. The energy efficiency could be of great importance when a two step carbonization activation is to be employed, since it could considerably reduce the heating time to the final activation temperature.
1.1 BACKGROUND OF STUDY
Activated carbon, also widely known as activated charcoal or activated coal is a form of carbon which has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions (Mattson et al., 1971). The word active is sometimes used in place of activated. It is characterized by high degree of micro porosity. A gram of activated carbon can have a surface area in excess of 500 m2. Sufficient activation for useful applications may come solely from the high surface area, though further chemical treatment generally enhances the adsorbing properties of the material. Activated carbon is most commonly derived from charcoal.
Waste biomass is getting increasing attention all over the world for activated carbon development as it is renewable, widely available, cheap and environmentally friendly resource. The common method of development is the rmochemical (Kumar et al., 2005). The main concern is the removal of chemical component by adsorption from the liquid or gas phase (Bansal et al., 1988). Today, activated carbon has been produced from various biomass such as corncob, rice husk, cherry stones, coconut shells, palm shells, to mention but a few.
Preparation of activated carbon with ultra-high specific surface area from biomass such as lignin, corncob, cornstalk, dates, etc., has attracted much attention. Among these carbon sources, corncob is a good precursor for preparing carbon with ultrahigh specific surface area (Li, 2007). The carbons prepared from corncob have been used in wastewater treatment such as removal of organic pollutants (Sun et al., 2006).
However, a comprehensive study of activating corncob with different activation strategies to prepare carbon with ultra-high specific surface area and pore volumes, and their subsequent performance in water purification as the impurity adsorption has not to our knowledge been reported. Therefore, in this study we report the synthesis of ultra-high surface area carbon materials using two preparation strategies namely, chemical activation procedure using a chemical activator such as ammonium sulphate ((NH4)2SO4) and microwave-synthesized activation procedure. We also report the adsorption capacity of those carbons for water purification.