Thesis Abstract

Abstract
Activated carbon, a widely used adsorbent in various industries, can be synthesized using different methods, such as chemical activation and microwave activation. In this study, we conducted a comparative analysis of activated carbon derived from corn cob using these two synthesis techniques. The corn cob was chosen as the precursor due to its abundance, low cost, and renewable nature, making it a sustainable option for activated carbon production. The chemical activation method involved impregnating the corn cob with a chemical activating agent, such as potassium hydroxide, followed by carbonization at high temperatures. On the other hand, the microwave activation process utilized microwave irradiation to heat the corn cob directly, leading to its activation. The resulting activated carbons were characterized using various techniques, including scanning electron microscopy, Brunauer-Emmett-Teller surface area analysis, and Fourier-transform infrared spectroscopy. The comparative study focused on evaluating the physical and chemical properties of the activated carbons obtained from the two methods. The results indicated that the microwave-synthesized activated carbon exhibited higher surface area and pore volume compared to the chemically synthesized activated carbon. This can be attributed to the rapid and uniform heating provided by microwave irradiation, which promotes better activation of the precursor material. Furthermore, the microwave-synthesized activated carbon showed superior adsorption performance for methylene blue dye compared to the chemical-synthesized activated carbon. This enhanced adsorption capacity can be attributed to the larger surface area and pore volume of the microwave-synthesized material, providing more active sites for adsorption. Overall, this comparative study demonstrates that microwave synthesis is a promising method for the production of activated carbon from corn cob, offering advantages such as higher surface area, larger pore volume, and enhanced adsorption performance. The sustainable nature of corn cob as a precursor further highlights the potential of microwave activation as an efficient and environmentally friendly approach for activated carbon production.

Thesis Overview

INTRODUCTION

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 thermochemical (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.2Preparation 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 ultra-high 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.

To prepare activated carbon, conventional heating method is usually adopted, in which the heat is produced by electrical furnace. However, in some cases, the thermal process may take several hours, even up to a week to reach the desired level of activation (Yuen et al., 2009). Another problem related to the furnace is that the surface heating does not ensure a uniform temperature for different shapes3and sizes of samples. This generates a thermal gradient from the hot surface to the kernel of the sample particle, blocks the effective diffusions of gaseous products to its surroundings and finally results in activated carbon quality decrease (Peng et al., 2008). Furthermore, there is a considerable risk of overheating or even thermal runaway (exothermic process) of portion of sample, leading to the complete combustion of the carbon (Williams et al., 2008).Recently, microwave has been widely used in preparation and regeneration of activated carbon. The main difference between microwave devices and conventional heating systems is heating pattern. In microwave device, the energy is directly supplied to the carbon bed. The conversion of microwave energy is not by conduction or convection as in conventional heating, but by dipole rotation and ionic conduction inside the particles (Jones, 2002). Therefore, the treatment time can be significantly reduced through microwave heating.

1.2 STATEMENT OF PROBLEM

In recent years, increasing awareness of environmental impact of organic and inorganic compounds has prompted the purification of waste water prior to discharge into natural waters. A number of conventional treatment technologies have been considered for treatment of waste water contaminated with organic substance. Among them, the adsorption process has been found to be the most4effective method while activated carbon is regarded as the most effective material for controlling this organic load. Common active carbons available are usually developed by thermochemical means using activating agents and heating ovens, thus producing activated carbons which take a longer time with limited pore structures. With the advent of microwave technology, a better and efficient activated carbon can be produced within a short period and a cheaper cost.

1.3 OBJECTIVE OF THE RESEARCH

The aim of this research project is to determine and compare the performance of chemically and microwave synthesized activated carbon from corn cob. 1.4 SIGNIFICANCE OF THE RESEARCH When this research project is successfully completed, it will provide the following benefits: i. Corn cobs are abundant in Nigeria. ii. Encourage the establishment of industries that will use Agricultural waste materials to produce activated carbon. iii. It will create job opportunities, thereby reducing unemployment in the country.5iv. It will attract foreign exchange for Nigeria as activated carbon has very wide industrial applications.

1.5 SCOPE OF RESEARCH

This research work focuses on the following: i. Preparation of activated carbon from corn cob by thermal and microwave means ii. Comparative study of the adsorption capacities of chemically and microwave synthesized activated carbon.