Thesis Abstract

Abstract
Activated carbon is a versatile material widely used in various environmental and industrial applications due to its high surface area and adsorption capacity. In this study, activated carbon was produced from corn cob through two different methods chemical activation with phosphoric acid and microwave-assisted activation. The aim of the research was to compare the characteristics and performance of activated carbon produced by these two methods. The chemical activation process involved impregnation of corn cob with phosphoric acid followed by carbonization at 500°C. The microwave-assisted activation process included the same impregnation step but utilized microwave irradiation for the carbonization process. The resulting activated carbons were then characterized using various analytical techniques including scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The results showed that the microwave-assisted activated carbon exhibited a higher surface area compared to the chemically activated carbon. The BET surface area of the microwave-assisted activated carbon was measured to be 1128 m2/g, while the chemically activated carbon had a surface area of 892 m2/g. This difference in surface area can be attributed to the rapid and uniform heating of the precursor material by microwave irradiation, resulting in better activation and development of porosity in the final product. Furthermore, the FTIR analysis indicated differences in the functional groups present on the surface of the two activated carbons. The microwave-assisted activated carbon showed a higher abundance of oxygen-containing functional groups, which can enhance its adsorption properties for polar compounds. TGA analysis revealed that both activated carbons exhibited good thermal stability, with the microwave-assisted activated carbon showing slightly higher thermal resistance. Overall, the comparative study highlighted the potential of microwave-assisted activation for producing activated carbon with superior properties compared to traditional chemical activation methods. The microwave-assisted activated carbon showed higher surface area, different surface functionalities, and comparable thermal stability, suggesting its suitability for various adsorption applications in environmental remediation and industrial processes. Further research could focus on optimizing the microwave-assisted activation process parameters to tailor the properties of activated carbon for specific applications.

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.