Development of a novel UV indicator and dosimeter film

Abstract

A novel UV indicator is described, comprising nanocrystalline particles of titania dispersed in a film of a polymer, hydroxyl ethyl cellulose (HEC), containing: a mild reducing agent, triethanolamine (TEOA) and a redox indicator, methylene blue (MB). The UV indicator film is blue-coloured in the absence of UV light and loses colour upon exposure to UV light, attaining within a few min a steady-state degree of bleaching that can provide a measure of the irradiance of the incident light. The original blue colour of the film returns once the source of UV light is removed. The spectral characteristics of a typical UV indicator film, and its components, are discussed and the UV-absorbing action of the titania particles highlighted. From the measured %bleaching undergone by a typical UV indicator as a function of light irradiance the indicator appears fully bleached, within 7 min, by a UV irradiance of 3 mW cm(-2) or greater. The mechanism by which the UV indicator works is described. The reversible nature of the UV indicator is removed by covering a typical UV indicator with a thin, largely oxygen impermeable, polymer film, such as the regenerated cellulose found in Sellotape. The product is a UV dosimeter, the response of which is related to the intensity and duration of the incident UV light, as well as the amount of titania in the film. A typical UV dosimeter film is fully bleached by 250 mJ cm(-2) of UV light. The possible use of these novel indicators to measure UV exposure levels, irradiance and dose, is discussed.

UV dosimetry for solar water disinfection (SODIS) carried out in different plastic bottles and bags

“…The use of titania and SnO 2 as photocatalysts for sunburn indicators which absorb UVA and UVB light [38] and the UVB component only [39], respectively, have been previously reported. The latter system is much less solar UV sensitive due to the higher band-gap of SnO 2 which does not respond to the highly abundant UVA component in the solar spectrum.…”

“…Since these UV dosimeters [38,39] are designed for sunburn warning they are far too UV sensitive to be appropriate as UV dosimeters for SODIS. The use of titania and SnO 2 as photocatalysts for sunburn indicators which absorb UVA and UVB light [38] and the UVB component only [39], respectively, have been previously reported.…”

“…In recent papers colorimetric UV dosimeters that utilise a semiconductor photocatalyst for use as sunburn warning indicators [38,39] have been reported. The UVA indicators comprised a polymer film containing: a redox dye (D), SED and SC photocatalyst.…”

Photocatalytic Enhancement for Solar Disinfection of Water: A Review

“…the University of Strathclyde has been investigating the use of photocatalytic systems as intelligent inks [42,43]. As titanium dioxide (TiO 2 ) is excited by UVA light, these systems may be used as UVA dosimetric indicators.…”

“…As titanium dioxide (TiO 2 ) is excited by UVA light, these systems may be used as UVA dosimetric indicators. At the University of Ulster, we have tested a simple prototype system to measure UVA dose utilising the photocatalytic reduction of methylene blue (MB) to leuco-Methylene Blue (LMB) (method adopted from Mills, Lee, and Sheridan [43]).…”