Ferroelectric Barium Titanate For Semiconductor Photocatalytic Application

Abstract

Semiconductor photocatalysis has received extensive attention due to its wide applications in water and indoor air purification, solar fuel production, etc. Charge carrier separation is a crucial step in semiconductor photocatalysis and influences the overall efficiency. It has been demonstrated that internal depolarisiation field of ferroelectric materials can drive spatial separation of charge carriers, which results in spatial separation of reduction and oxidation reactions, and improved charge carrier separation. In this thesis, ferroelectric barium titanate was chosen and its photocatalytic performance in decolourisation of organic dye molecules was investigated. Photodeposition method was adopted to deposite silver nanoparticles on the surface of barium titanate. Silver modified barium titanate showed increased photodecolourisation rate compared with bare barium titanate due to its role of electron traps and hindered charge carrier recombination. A simple thermal treatment was used to alter the phase composition of the as-received barium titanate. Samples which contained more ferroelectric tetragonal phase were found to possess higher photocatalytic activity compared with non-ferroelectric samples. This was associated with stronger ferroelectricity after thermal treatment, which enhanced dye molecule adsorption and aid charge carrier separation. The mechanism and intermediates generated in photodegradation of Rhodamine B with silver modified ferroelectric barium titanate were studied. Cleavage of chromophore was demonstrated to dominate in the initial process. Benzoic acid was identified as the main intermediate and no siginificant discrepancy in intermediates distribution between ferroelectric photocatalytic system and non-ferroelectric system was observed. The influence of ferroelectric dipole of barium titanate on photocatalytic activity of heterostructured barium titanate/hematite was also studied. The synthesised heterostructured barium titanate/hematite showed higher photodcolourisation rate than both barium titanate and hematite. This phenomenon was attributed to the improved charge carrier separation and extended charge carrier lifetime arising from heterojunction and an interaction between the ferroelectric dipole and the carriers in the hematite.