Photocatalytic Degradation of Organic Pollutants in Water

Abstract

A photocatalyst is defined as a substance which is activated by adsorbing a photon and is capable of accelerating a reaction without being consumed [1]. These substances are invaria‐ bly semiconductors. Semiconducting oxide photocatalysts have been increasingly focused in recent years due to their potential applications in solar energy conversion and environmen‐ tal purification. 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 AOPs, heterogeneous photocatalysis have been proven to be of interest due to its efficiency in degrading recalcitrant organic compounds. Developed in the 1970s, heteroge‐ neous photocatalytic oxidation has been given considerable attention and in the past two decades numerous studies have been carried out on the application of heterogeneous photo‐ catalytic 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 [2]. 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 pollu‐ tants 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, chemi‐ cal stability and lower costs [3]. Fujishima and Honda [4] pioneered the concept of titania photocatalysis (also known as “Honda-Fujishima effect”). Their work showed the possibility of water splitting in a photoelectrochemical cell containing an inert cathode and rutile titania anode. The applications of titania photoelectrolysis has since been greatly focused in envi‐ ronmental applications including water and wastewater treatment. This chapter provides insight into the fundamentals of the TiO2 photocatalysis, discusses the effect of variables af‐