Photocatalyst testing and development

A supersensitive test (SST) for photocatalytic activity was developed to assess the activities of materials that show little, if any activity when tested using the NO ISO. An expression is derived which relates rate, thereby photocatalytic activity, directly to the average %NO removed, measured under either standard ISO or SST conditions, where the latter value is directly related to the photocatalytic area, A, and the reciprocal of the flow rate, 1/f.

This relationship allows all %NOrem values < 25%, measured using either standard ISO or SST conditions, to be combined to create a universal scale of photocatalytic activity. This work identified commercial photocatalytic materials, such as tiles, that were of such low activity that even this test was unable to measure the activity leading to the development of a new silver ion photocatalytic activity indicator ink, paii that can probe even very low activity photocatalytic materials via a striking colour change from colourless to brown-black upon illumination with UV light.

During this work, it became apparent that the photodeposition of Ag metal onto commercial photocatalytic films such as that on self-cleaning glass, could be used to produce highly conducting wires, investigated initially for demisting purposes. A study of Ag-particle growth on sol-gel TiO2 films demonstrated the necessity of overlapping island growth of the Ag-particles to enable conduction.