Development and testing of thin photocatalyst films

Abstract

This thesis details the development of surface-exposed nanoparticle (SEN) films made from titanium dioxide (TiO₂) and cadmium sulfide (CdS) nanoparticles, as well as their characterisation and testing for photocatalytic activity by using a variety of known photocatalytic reactions and techniques.

A TiO₂-SEN film is detailed, based on the formation of ion-pairs formed between TiO₂ P25 nanoparticles in an acidic dispersion, and an anionic lipophilic promoter, which find themselves most stable in a water-organic interface. These interfacial films are then captured in situ by polymer film formation as the solvent evaporates. The photoactivity of the film is then quantified using the oxidations of 4-chlorophenol and methylene blue, as well as the reductions of methylene blue and resazurin, in solution and ink forms. The photoactivity of TiO₂-SEN film is measured against Pilkington Activ™ glass for each of these reactions, which is a commercial product that has a TiO₂ film analogous to the films made in this work.

A SEN film from a synthesised CdS colloid is also described, highlighting the ease and versatility of the film synthesis method. These films are found to perform well in photocatalytic reactions suitable for CdS, including the reduction of dissolved oxygen, methyl orange, crystal violet and methyl viologen, as well as the reduction of water to create hydrogen when in the presence of a platinum co-catalyst. Methods devised to improve robustness of these films are described, including the 3D-printing of a transparent backing layer and ironing on the films to various plastics and fabrics, both using heat transfer. These methods vastly improve the ease of handling of the SEN films without being at the cost of photoactivity.

The development of a photoinduced absorption spectroscopy (PIAS) setup is described, as well as its use to investigate the photoreduction of oxygen by monitoring the formation and decay of transients associated with photogeneration of electrons in CdS paste films, TiO₂ paste films and TiO₂-SEN films. These results are also compared against results of steady-state oxygen photoreduction by extracting constants to describe the dependence of formation and decay rate of electrons on the level of oxygen in solution.

Date of Award	Jul 2021
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Andrew Mills (Supervisor) & Steven Bell (Supervisor)