Method of rapid assessment of photocatalytic activities of self-cleaning films

A. Mills, J. Wang, M.A.S. McGrady

Research output: Contribution to journalArticle

68 Citations (Scopus)

Abstract

An ink, comprising the redox dye resazurin (Rz) and the sacrificial electron donor glycerol, is shown to be capable of the rapid assessment of the photocatalytic activities of self-cleaning films. In the key initial stage of photocatalysis the ink changes from blue to pink. Prolonged irradiation bleaches the ink and eventually mineralizes it. The kinetics of the initial photoinduced color change is studied as a function of UV irradiance, [glycerol], [Rz], and temperature. The results reveal an apparent approximate quantum yield of 3.5 × 10-3 and an initial rate, ri, which increases with [glycerol] and decreases with [Rz]. It is proposed that the reduction of Rz, dispersed throughout the thick (ca. 590 nm) indicator film, may take place either via the diffusion of the dye molecules in the ink film to the surface of the underlying semiconductor layer and their subsequent reaction with photogenerated electrons and/or via the diffusion of α-hydroxyalkyl radicals, produced by the oxidation of the glycerol by photogenerated holes, or hydroxy radicals, away from the surface of the semiconductor into the ink film and their subsequent reaction with the dye molecules therein. The decrease in ri with [Rz] appears to be due to dimer formation, with the latter impeding the reduction process. The activation energy for the initial color-change process is low, ca. 9.1 ± 0.1 kJ mol-1 and not unlike many other photocatalytic processes. The initial rate of dye reduction appears to be directly related to the rate of destruction of stearic acid. The ink can be applied by spin-coating, stamping, or writing, using a felt-tip pen. The efficacy of such an ink for assessing the photocatalytic activity of any photocatalytic film, including those employed on commercial self-cleaning glasses, tiles, and paving stones, is discussed briefly.
LanguageEnglish
Pages18324-18331
Number of pages8
JournalJournal of Physical Chemistry B
Volume110
DOIs
Publication statusPublished - 2006

Fingerprint

inks
Ink
cleaning
Cleaning
glycerols
Glycerol
Coloring Agents
Dyes
dyes
Semiconductor materials
Color
color
stamping
pens
Molecules
Stearic acid
Electrons
Photocatalysis
Stamping
tiles

Keywords

  • photocatalytic activities

Cite this

Mills, A. ; Wang, J. ; McGrady, M.A.S. / Method of rapid assessment of photocatalytic activities of self-cleaning films. In: Journal of Physical Chemistry B. 2006 ; Vol. 110. pp. 18324-18331.
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Method of rapid assessment of photocatalytic activities of self-cleaning films. / Mills, A.; Wang, J.; McGrady, M.A.S.

In: Journal of Physical Chemistry B, Vol. 110, 2006, p. 18324-18331.

Research output: Contribution to journalArticle

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AU - Wang, J.

AU - McGrady, M.A.S.

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N2 - An ink, comprising the redox dye resazurin (Rz) and the sacrificial electron donor glycerol, is shown to be capable of the rapid assessment of the photocatalytic activities of self-cleaning films. In the key initial stage of photocatalysis the ink changes from blue to pink. Prolonged irradiation bleaches the ink and eventually mineralizes it. The kinetics of the initial photoinduced color change is studied as a function of UV irradiance, [glycerol], [Rz], and temperature. The results reveal an apparent approximate quantum yield of 3.5 × 10-3 and an initial rate, ri, which increases with [glycerol] and decreases with [Rz]. It is proposed that the reduction of Rz, dispersed throughout the thick (ca. 590 nm) indicator film, may take place either via the diffusion of the dye molecules in the ink film to the surface of the underlying semiconductor layer and their subsequent reaction with photogenerated electrons and/or via the diffusion of α-hydroxyalkyl radicals, produced by the oxidation of the glycerol by photogenerated holes, or hydroxy radicals, away from the surface of the semiconductor into the ink film and their subsequent reaction with the dye molecules therein. The decrease in ri with [Rz] appears to be due to dimer formation, with the latter impeding the reduction process. The activation energy for the initial color-change process is low, ca. 9.1 ± 0.1 kJ mol-1 and not unlike many other photocatalytic processes. The initial rate of dye reduction appears to be directly related to the rate of destruction of stearic acid. The ink can be applied by spin-coating, stamping, or writing, using a felt-tip pen. The efficacy of such an ink for assessing the photocatalytic activity of any photocatalytic film, including those employed on commercial self-cleaning glasses, tiles, and paving stones, is discussed briefly.

AB - An ink, comprising the redox dye resazurin (Rz) and the sacrificial electron donor glycerol, is shown to be capable of the rapid assessment of the photocatalytic activities of self-cleaning films. In the key initial stage of photocatalysis the ink changes from blue to pink. Prolonged irradiation bleaches the ink and eventually mineralizes it. The kinetics of the initial photoinduced color change is studied as a function of UV irradiance, [glycerol], [Rz], and temperature. The results reveal an apparent approximate quantum yield of 3.5 × 10-3 and an initial rate, ri, which increases with [glycerol] and decreases with [Rz]. It is proposed that the reduction of Rz, dispersed throughout the thick (ca. 590 nm) indicator film, may take place either via the diffusion of the dye molecules in the ink film to the surface of the underlying semiconductor layer and their subsequent reaction with photogenerated electrons and/or via the diffusion of α-hydroxyalkyl radicals, produced by the oxidation of the glycerol by photogenerated holes, or hydroxy radicals, away from the surface of the semiconductor into the ink film and their subsequent reaction with the dye molecules therein. The decrease in ri with [Rz] appears to be due to dimer formation, with the latter impeding the reduction process. The activation energy for the initial color-change process is low, ca. 9.1 ± 0.1 kJ mol-1 and not unlike many other photocatalytic processes. The initial rate of dye reduction appears to be directly related to the rate of destruction of stearic acid. The ink can be applied by spin-coating, stamping, or writing, using a felt-tip pen. The efficacy of such an ink for assessing the photocatalytic activity of any photocatalytic film, including those employed on commercial self-cleaning glasses, tiles, and paving stones, is discussed briefly.

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