Novel applications of colourimetric gas sensors

This thesis is focused on developing new applications of existing and novel colourimetric indicators, primarily for the detection of carbon dioxide (CO₂). <br><br>The Introduction chapter gives a short history of CO₂ indicators from aqueous solutions, to ‘dry’ ink-based indicators, and the onset of plastic films. Some existing applications of colourimetric CO₂ indicators are discussed. <br><br>The Experimental chapter outlines the most important instrumentation and methods used throughout this PhD, to include UV-Vis spectroscopy, photography and digital colour analysis (DCA), lifetime O₂monitoring, microbiological techniques, general plastic film CO₂ indicator preparation, and gas mixing.<br><br>In Chapter 3, two commercial colourimetric CO₂ indicators are replicated in the lab- one for monitoring the level of dissolved CO₂ in an aquarium, and another for monitoring the level of CO₂ in breath.

Photography and DCA are used to convert the colour data from the indicators into a quantitative measure of CO₂.<br><br>In Chapter 4 the preparation of a plastic film indicator for the measurement of CO₂ in aquaria is described, based on extrusion of low-density polyethylene (LDPE) mixed with a small amount of a CO₂ sensitive pigment. The pigment comprises a mixture of a pH-indicator dye, xylenol blue (XB), with a base, coated onto silica.