Photocatalyst activity indicator ink
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Photocatalyst activity indicator ink (paii) is a substance used to identify the presence of an underlying heterogeneous
Applications
A photocatalyst activity indicator ink quickly and easily identifies the presence of an underlying heterogeneous photocatalyst and provides a measure of its activity. A heterogeneous photocatalyst is a material that uses absorbed light energy (usually
Background
Water molecules—adsorbed to the photocatalyst—are also needed to generate the hydroxyl groups on the surface.[21]
The marketing of photocatalytic products and prevention of counterfeiting is made difficult because the photocatalytic coatings are usually and necessarily invisible to the eye.[20] One way to achieve a visual demonstration of photocatalysis is to use a dyestuff, like methylene blue, dissolved in water, as the organic species to be mineralised, since, as the photocatalytic process proceeds, the colour of the dye disappears as it is oxidised.[22] This approach forms the basis of a well-established ISO test for photocatalytic activity of films ISO.[23] However, most photocatalyst commercial products use only a thin layer of titania (e.g. ca. 15 nm thick in self-cleaning glass)[24] and ambient UV levels are often low (e.g. for a sunny day in the UK the UVA irradiance is only ca. 4 mW/cm2). As a consequence, the photocatalytic oxidative bleaching of methylene blue is usually very slow, taking many hours,[23] and so inappropriate for marketing at least.
Theory
Photocatalyst activity indicator inks are a recent advance in the visual demonstration of photocatalysis and the assessment of the activity of photocatalyst materials.[15][25] They are inexpensive, easy to use and provide a very quick route to demonstrating the presence of a photocatalytic film, even under low levels of UV light. Unlike the photo-oxidative bleaching of methylene blue,[22] they use the underlying semiconductor photocatalyst film to photoreduce the dye (Dox in figure 2), in the ink coating, to another (usually colourless) form, (Dred in figure 2) whilst simultaneously oxidising an easily oxidised organic species, a sacrificial electron donor (SED), such as glycerol, which is also present in the ink.[15][25][26] The kinetics of reduction of the dye in a paii have been studied in great detail.[27][28] Figure 2 illustrates the basic principles of operation of a paii when applied to a product that has a thin photocatalyst film coating.
Practice
The ink is applied to the photocatalyst coating, usually using either a felt-tipped pen, air-brush, rubber stamp, paint brush, or a drawdown bar, and then exposed it to sunlight or an alternative, appropriate light source. The ink identifies the presence of the photocatalyst coating by changing colour upon irradiation of the latter at a rate (usually < 10 min[15]) which provides a measure of the film's activity.
For example, it has been established that the rate of change in colour of an paii on commercial self-cleaning glass is directly related to the rate at which the glass is also able to photo-oxidatively mineralise, via reaction (1) the wax-like, natural fatty acid, stearic acid,[15][29][30][31] found in finger prints.[32] The rate of the rapid colour change associated with photocatalyst activity indicator inks has also been directly correlated with the photocatalytic oxidation of methylene blue [33][34] and NOx.[35][36] It has also been shown that digital colour analysis of photographs monitoring the colour change of a paii can be used to extract apparent absorbance data which correlates well with UV-vis absorption data for the same sample, without the need for expensive spectrophotometric instrumentation.[18]
By making the dyes in the ink increasing difficult to reduce chemically, for example by using: basic blue 66,[37] resazurin,[15] and acid violet 7,[35] respectively, it is possible to make paiis which are effective on photocatalyst coatings which exhibit, respectively: low (most self-cleaning tiles), moderate (self-cleaning glass) or high (self-cleaning paints) activities. paiis based on the dyes 2,6-dichloroindophenol (DCIP)[38] and methylene blue[28] have also been reported.
Dye | Colour (Dox) | Colour (Dred) | Reference |
---|---|---|---|
Resazurin (Rz) | Blue | Pink | [15] |
Basic Blue 66 (BB66) | Blue | Colourless | [37] |
Acid Violet 7 (AV7) | Pink | Colourless | [35] |
Methylene Blue (MB) | Blue | Colourless | [28] |
2,6-Dichloroindophenol (DCIP) | Blue | Colourless | [38] |
Applications
External videos | |
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Application of the new SunCatalyst Laboratories Paii Label |
Paiis can be used as quality control and marketing tools in commerce and as a quick and easy way to assess and/or map the activities of new photocatalytic materials in research.[15][25][39][26][16] In addition, it has also been demonstrated that such inks can be used on highly coloured and black surfaces, provided the oxidised and/or reduced form of the redox dye is luminescent,[40] and that they can be effectively used to demonstrate the activity of visible light photocatalysts.[41][42] In light of the need for in situ testing of commercial photocatalyst materials, paii labels have been developed that can be applied simply in the field on any surface to be tested, in both a non-reusable[43] and reusable[44] form. One noteworthy application of paiis is where a uniform film has been applied to a photocatalytic surface, and the variation in the rate of colour change across the surface has been monitored and used to generate a surface map of the photoactivity.[26][45] By this method the uniformity of the surface activity may be investigated, and any "hotspots" of photoactivity identified.[45] By varying the composition of a semiconductor photocatalyst surface across the surface itself, a paii photoactivity surface map may be used to determine the optimal composition which yields the greatest photocatalytic response.[26][46]
The rapid colour change of paiis makes them suitable for such applications as:
- Quality control (in laboratory, factory and on site);
- Marketing;
- Counterfeit identification;
- Research material assessment.
See also
References
- ^ ISO 21066:2018, 'Fine ceramics (advanced ceramics, advanced technical ceramics) — Qualitative and semiquantitative assessment of the photocatalytic activities of surfaces by the reduction of resazurin in a deposited ink film', ISO, Geneva, 2018.
- ^ a b "Activ, Pilkington". NSG group. Retrieved 2021-08-19.
- ^ a b "BIOCLEAN". Saint-Gobain. Retrieved 2021-08-19.
- ^ a b "Neat+ Glass". Cardinal Glass Industries Inc. Retrieved 2021-08-19.
- ^ a b "TOTO Hydrotect" (PDF). TOTO Ltd. Archived from the original (PDF) on 2021-08-18. Retrieved 2021-08-18.
- ^ a b "Hytect Technology". Agrob Buchtal, Deutsche Steinzeug AG. Retrieved 2021-08-18.
- ^ a b "Lotus Air". Erlus AG. Retrieved 2021-08-18.
- ^ a b "TioCem, Hanson". Heidelberg Cement Group. Retrieved 2021-08-19.
- ^ a b "TX Active, Italcementi". Heidelberg Cement group. Retrieved 2021-08-19.
- ^ a b Sto Ltd. "StoColor Photosan, StoColor Climasan". Sto Ltd. Retrieved 2021-08-19.
- ^ a b "BOYSEN KNOxOUT". BOYSEN. Retrieved 2021-08-19.
- ^ a b "SHEERFILL with EverClean". Saint-Gobain. Retrieved 2021-08-19.
- ^ a b "Air Purify fabric, Taiyo Europe". Taiyo Kogyo, MakMax. Retrieved 2021-08-19.
- ^ a b "GUNRID curtains". IKEA. Retrieved 2021-08-19.
- ^ a b c d e f g h Mills, A., Wang, J., Lee, S. & Simonsen, M. 2005, "An intelligence ink for photocatalytic films.", Chemical Communications (Cambridge, United Kingdom), no. 21, pp. 2721-2723.
- ^ a b "Home | The Intelligent Pen and Ink Company | Photocatalytic Testing Pens & EquipmentThe Intelligent Pen and Ink Company-Photocatalytic Testing Pens & Equipment". Inkintelligent.com. Retrieved 2014-06-02.
- .
- ^ S2CID 105384670.
- ^ Mills, A., Wells, N., Reductive photocatalysis and smart inks, Chem. Soc. Rev., 10 (2015) 2849-64.
- ^ a b V. Augugliaro, V. Loddo, M. Pagliaro, G. Palmisano, L. Palmisano, "Clean by Light Irradiation: Practical Applications of Supported TiO2", RSC Publishing, Cambridge, 2010.
- .
- ^ a b A. Mills, M. McFarlane “Current and possible future methods of assessing the activities of photocatalyst films”, Catalysis Today vol. 129, 2007, pp. 22–28.
- ^ a b ISO 10678: 2010, ‘Fine ceramics, advanced technical ceramics – determination of photocatalytic activity of surfaces in an aqueous medium by degradation of methylene blue’, ISO, Geneva, 2010.
- .
- ^ a b c Mills, A. & McGrady, M. 2008, "A study of new photocatalyst indicator inks.", Journal of Photochemistry and Photobiology, A: Chemistry, vol. 193, no. 2-3, pp. 228-236.
- ^ a b c d Kafizas, A., Crick, C. & Parkin, I.P. 2010, "The combinatorial atmospheric pressure chemical vapor deposition (cAPCVD) of a gradating substitutional/interstitial N-doped anatase TiO2 thin-film; UVA and visible light photocatalytic activities.", Journal of Photochemistry and Photobiology, A: Chemistry, vol. 216, no. 2-3, pp. 156-166.
- S2CID 55020872.
- ^ PMID 20355907.
- PMID 16970453.
- .
- .
- ^ B. Hartzell-Baguley, R. E. Hipp, N. R. Morgan, S. L. Morgan, “Chemical Composition of Latent Fingerprints by Gas Chromatography–Mass Spectrometry. An Experiment for an Instrumental Analysis Course”, Journal of Chemical Education, vol. 84 (4), 2007, pp. 689–691.
- S2CID 54929907.
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- ^ a b c A. Mills, C. O’Rourke, K. Lawrie, S. Elouali, Assessment of the activity of photocatalytic paint using a simple smart ink designed for high activity surfaces, ACS Appl. Mater. Inter., 6, 2014, 545−552.
- ^ ISO 22197-1:2016, 'Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for air-purification performance of semiconducting photocatalytic materials — Part 1: Removal of nitric oxide', ISO, Geneva, 2016.
- ^ a b A. Mills, C. O’Rourke, N. Wells, A smart ink for the assessment of low activity photocatalytic surfaces, Analyst, 139, 2014, 5409–5414.
- ^ ISSN 1110-662X.
- PMID 19756293.
- ^ Mills, A, Yusufu, D, Wells, N. & O’Rourke, C., Assessment of activity of ‘transparent and clear’ and ‘opaque and highly coloured’ photocatalytic samples using a fluorescent photocatalytic activity indicator ink, FPaii, J. Photochem. Photobiol., A, 330, 2016, 90–94.
- S2CID 55144404.
- .
- ^ Mills, A., Wells, N., Hawthorne, D., Hazafy, D., Photocatalyst activity indicating adhesive labels for use in the field, (2018) https://doi.org/10.1016/j.jphotochem.2018.01.005
- ^ A. Mills, N. Wells, Smart, reusable labels for assessing self-cleaning films, Chem. Commun., 51, 2015, 4161–4163.
- ^ S2CID 103813923.
- ISSN 0959-9428.