Probing the activities of UV and visible-light absorbing photocatalyst powders using a resazurin-based photocatalyst activity indicator ink (Rz Paii )

Determining The Presence of Photocatalytic Titanium White Pigments via Embedded Paint Sample Staining: A Proof of Principle

“…An accurate classification of photocatalytic materials can be made after five minutes of irradiation. This result confirms the speed benefit of this test as reported by Mills et al (2005Mills et al ( -2017) on a microscopic system such as a paint sample. Generally, the rate of color change can be empirically divided into four categories after five minutes: the paints causing no change or a negative change (A); the paints causing an immediate but minor visually perceptible change (B); the paints causing a well noticeable change (C); and the paints causing a major change (D).…”

“…The one sample which was based solely on ZnO (R8) shows much less photocatalytic discoloration than expected, based on previous artificial aging studies under UV, where it showed similar oil degradation rates to uncoated anatase. This unexpected behavior may be caused by the difference between irradiation under a broad or narrow UV source (Kobayashi and Kalriess 1997;Sakthivel et al 2003;;van Driel et al 2018b); by inhibiting the reaction of the photogenerated election with atmospheric oxygen (Mills, Wells, and O'Rourke 2017); or by the electronic structure of ZnO, which dictates the recombination processes (Artesani et al 2016). On the other hand, organically coated anatase (CA(org), R2) was expected to display less discoloration than uncoated anatase (van Driel et al 2018b) but it falls into the same category.…”

“…It has been demonstrated that the inks, in the absence of glycerol, show no color change. PAII color change curves have been demonstrated, on multiple occasions, to relate directly to the photocatalyzed oxidation of several pollutants (Mills et al, 2005(Mills et al, -2017, proving its reliability as a method to assess photocatalytic activity. Even though the inks are a good indicator for real degradation processes, the test is based on the alternative reactions of photo-reduction and hole scavenging and may therefore be influenced differently by environmental factors.…”

“…Furthermore, several methods of monitoring color change such as change of absorbance (UV-VIS), diffuse reflectance spectroscopy, and digital photography (RGB (ΔR) or Lab (Δa) color space) have also been shown to have good correlation. Recent work in the field of PAII (Mills and Wells 2015;Mills, Wells, and O'Rourke 2017) is concerned with the development of PAII labels and the application of PAII on powdered materials and semiconductors other than titanium dioxide.…”

“…While the techniques lost popularity with the introduction of new, non-invasive techniques, microscopy analysis remains the first step of micro-invasive analysis. Hence, it is in this scope that we propose the application of PAII, developed by Mills et al (2005Mills et al ( -2017, by staining paint samples from modern paintings.…”