UV sensors Based on Photocatalytic Properties of Titanium Dioxide

Abstract

In Australia skin cancer from sun exposure is a major issue. However, for individuals to know when they are at risk of receiving too much sun exposure is difficult to determine. The goal of this thesis is to develop new types of UV wearable sensors for monitoring personal UV radiation exposure. The aim would be to make these wearable sensors cheap and easy to use. This will hopefully lead to decreased skin cancer incidence, which kills around 1600 Australian each year. In this regard, a simple and novel idea is proposed. This is to exploit the reducing power of photoexcited titanium dioxide (TiO2) in two different paths to fabricate wearable sensor for monitoring sun exposure. TiO2 is a photocatalyst that is only sensitive to UV irradiation and is already being used in sunscreens to block UV radiation of sun. Therefore, here this photocatalyst is utilized to fabricate two different types of wearable UV sensors. The first proposed wearable sensor is fabricated by ink-jet printing of a suspension containing TiO2, an FDA approved food dye (e.g. brilliant blue FCF) and a polymer, polyvinylpyrrolidone (PVP) as a binder on paper. Exposure to UV radiation led to the decomposition of the dye by the TiO2 that resulted in a colour change. This discoloration time was optimised to correspond with the time required to sunburn for a range of different skin colours protected with sunscreens with varying sun protection factors (SPF). The mechanism behind this discolouration is studied by MALDI and LC-MS, respectively. The results revealed that the degradation products found in MALDI are among the ones obtained from LC-MS and are products of successive loose of methyl benzene sulfonic acid groups. Furthermore, it was found that the triarylmethane backbone of the dye is the most stable part of the dye and stays unbreakable until the last steps of photodegradation of the dye. The second wearable device is a UV sensor based on the photoreduction of graphene oxide to graphene by TiO2. This process is accompanied by a significant change in resistivity as a result of converting the semiconductor (graphene oxide) to a highly conductive material (graphene).