CHAPTER ONE
INTRODUCTION
1.0 DEFINITION OF PHOTOCATALYST
A photocatalyst is defined as a substance which is activated by adsorbing a photon and is capable of accelerating a reaction without being consumed (Kluwer,1988). These substances are invariably semiconductors. Semiconducting oxide photocatalysts have been increasingly focused in recent years due to their potential applications in solar energy conversion and environmental purification.
There are two types of photocatalysis, namely homogeneous andheterogeneous photocatalysis.Heterogeneous photocatalysis is a discipline which includes a large variety of reactions; mild or total oxidation, dehydrogenation, hydrogen transfer and deuterium alkane isotopic exchange metal decomposition, water detoxification, gaseous pollutant removal etc. It can be considered as one of the new advanced oxidation technology (AOT) for air and water purification treatment.
Semiconductor heterogeneous photocatalysis has enormous potential to treat organic contaminants in water and air. This process is known as advanced oxidation process (AOP) and is suitable for the oxidation of a wide range of organic compounds.
Among advanced oxidation process (AOPs), heterogeneousphotocatalysis has been proven to be of interest due to its efficiency in degrading recalcitrant organic compounds. Developed in the 1970s, heterogeneous photocatalytic oxidation has been given considerable attention and in the past two decades, numerous studies have been carried out on the application of heterogeneous photocatalytic oxidation process with a view to decompose and mineralize recalcitrant organic compounds. It involves the acceleration of photoreaction in the presence of a semiconductor catalyst (Gaya & Abdullah, 2008).
Several semiconductors (TiO2, ZnO, Fe2O3, CdS, ZnS) can act as photocatalysts but TiO2 has been most commonly studied due to its ability to break down organic pollutants and even achieve complete mineralization. Photocatalytic and hydrophilic properties of TiO2 makes it close to an ideal catalyst due to its high reactivity, reduced toxicity, chemical stability and lower costs (Fujishima et al, 2000). Fujishima and Honda in 1972 pioneered the concept of titaniaphotocatalysis (also known as “Honda-Fujishima effect”). Their work showed the possibility of water splitting in a photo electrochemical cell containing an inert cathode and rutile titania anode.
The applications of Titaniaphoto electrolysis has since been greatly focused in environmental applications including water and wastewater treatment. This chapter provides insight into the fundamentals of the TiO2photocatalysis, discusses the effect of variables affecting the performance of degradation of organic pollutants in water with a view to current state of knowledge and future needs.
1.1 STATEMENT OF PROBLEM
TiO2 exhibits photo catalytic ability on exposure to sunlight. However, a correlation of the degradation to the type of organic compound as well as the mechanism of the photo degradation as specific to the type of organic compound is still to be determine for several organic compounds.
1.2 AIM OF THE STUDY
The aims of the study were;
To employ the photo catalytic property of TiO2 to degrade stearic acid.
To evaluate the effect process condition such as exposure time and amount of TiO2 on the extent of the photo degradation.
To study in detail, the rate of the photo degradation from UV spectroscopic analysis as well as the mechanism of breakdown of the organicacid components through the liquid chromatographic method.
1.3 JUSTIFICATION
There is a need to improve the degradation of organic compound in order to create clean and safe environment. Therefore, the study of the photo degradation of organic compounds using TiO2nano particles is important. Through such study factors like the amount of TiO2nano particles for optimum photo degradation will be established.
