Thesis Abstract

Activated carbons have been widely used for water purification due to their high surface area and adsorption properties. However, to improve their efficiency in removing contaminants from water, modifications of activated carbons have been explored. This research project focuses on the modification of surface, physical, and chemical properties of activated carbons to enhance their performance in water purification applications. Various methods have been investigated to modify the surface properties of activated carbons. These methods include physical techniques such as impregnation, heat treatment, and chemical methods such as oxidation, reduction, and functionalization. The goal of these modifications is to increase the surface area, introduce functional groups, and enhance the adsorption capacity of activated carbons for specific contaminants. Additionally, the modifications aim to improve the selectivity and efficiency of the adsorption process. Physical modifications such as heat treatment can enhance the pore structure of activated carbons, leading to increased adsorption capacity. Impregnation with metal oxides or nanoparticles can introduce catalytic properties to activated carbons, allowing for the degradation of organic pollutants in water. Chemical modifications such as oxidation with strong acids can create surface functional groups like carboxyl and hydroxyl groups, which can improve the affinity of activated carbons for certain contaminants. The modification of activated carbons also involves altering their physical properties such as particle size, surface morphology, and pore size distribution. By controlling these physical properties, the accessibility of contaminants to the active sites on the surface of activated carbons can be improved, leading to higher adsorption efficiency. Moreover, the modification of physical properties can also influence the kinetics of adsorption processes, making them faster and more effective. In addition to surface and physical modifications, the chemical properties of activated carbons can be tailored to enhance their performance in water purification. Functionalization of activated carbons with specific groups can impart selective adsorption properties, allowing for the removal of target contaminants while minimizing the adsorption of other substances. Furthermore, the modification of chemical properties can also improve the stability and reusability of activated carbons in water treatment processes. Overall, the modification of surface, physical, and chemical properties of activated carbons plays a crucial role in improving their efficiency and selectivity for water purification applications. By tailoring the properties of activated carbons to specific contaminants and water conditions, the performance of these materials can be optimized for sustainable and effective water treatment processes.

Thesis Overview

INTRODUCTION

1.1 ORIGIN AND NATURE OF ACTIVATED CARBON

Carbon is the fifteenth most abundant element in the earth’s crust and the fourth most abundant element in the universe by mass after hydrogen, helium and oxygen. Scientists, industries, and consumers use different forms of carbon and carbon containing compounds in many ways such as activated carbon or carbon in its active form which can be used to purify water, among others.Activated carbon is a form of carbon that has been produced to make it extremely porous and thus have a very large surface area available for adsorption or chemical reactions.It can be defined as a microcrystalline non-graphitic amorphous form of carbon which has been processed to develop a high internal porosity due to its network of inter-connecting pores.The history of activated carbon is dated since the fifteenth century, during the time of Columbus when sailors used to blacken the inside of wooden water barrels with fire, since they observed that the water would stay fresh much longer. It is likely that people at that time proceeded by intuition only without having anyCHE/2007/063 14insight into the mechanism of the effect. The mechanism was recognized beginning from the eighteenth century.In 1862, Lipscombe prepared a carbon material for purifying portable water. This development paved the way for the commercial application of activated carbon first for portable water and then in waste water sector.

1.2 METHODS OF MANUFACTURE OF ACTIVATED CARBON

The methods employed in the industrial manufacture of activated carbons are numerous but consist of three main methods namely; Chemical activation, Steam activation and thermal processing techniques.The raw materials or precursors used in the manufacture of activated carbon are as follows; Softwood, coconut shell, lignite, hardwood, grain and agro products, bituminous coal, anthracite, etc.Chemical activation is generally used for the production of activated carbon from sawdust, wood or peat and uses chemicals for activation. Chemical activation technique involves mixing an inorganic chemical compound with the carbonaceous raw materials and the most widely used activating agents are Phosphoric acid and Zinc Chloride.CHE/2007/063 15Steam activation technique is generally used for coal-based, coconut shell and grain-based activated carbons and uses gases, vapors or a mixture of both for its activation.Thermal processing technique is a separation process that removes unwanted materials from the carbonaceous precursor used under varying heat applications. This technique is at a lower cost compared to the two techniques above and meets all environmental standards, while others need expensive solutions to achieve the same results.

1.3 NEED FOR PRESENT INVESTIGATION

The need for present investigation of this material cannot be over emphasized. This is as a result of the pressing need for treatment of waste water emanating from domestic and industrial concerns.Activated carbon plays an important role in the purification of fluids (water), including vegetable oils used in domestic cooking and as a precursor in industrial manufacture of food products. The slow pace of technological development in the country has resulted to the expenditure of the nation’s resources on importation of activated carbons to meet the demand for local chemical and process industries, as well as the demand for municipal and industrial water treatment plants.CHE/2007/063 16Rapid industrialization, together with the increase in modern methods of agriculture and the increase in population, has contributed to the pollution of the ecosystem. Most of the pollutants are toxic to living organisms. It is therefore imperative that waste water has to be treated to remove the toxic materials before disposal to the environment. Most methods of treating water have some inherent shortfalls. Activated carbon treatment was therefore developed because of its effectiveness in pollutants removal, especially in water purification.

1.4 OBJECTIVES AND SCOPE OF THE STUDY

The primary objectives and scope of the present investigation include the following:i. Acquisition of the different types of activated carbons available to the nation’s chemical industry.ii. Modification of the surface physical and chemical properties of the carbon material, for their use in liquid phase applications.iii. Determination of the physical properties of the as-received and modified activated carbon materials.iv. Testing the adsorption capacity of the carbon materials in adsorption processes.v. Evaluation of the fractional surface coverage for each carbon material.CHE/2007/063 17vi. Proposal of a scheme for the optimal modification of activated carbon material for optimal application in liquid phase adsorption.CHE/2007/063 18