Abstract
The historical knowledge inherited from house paint documents and the experimental research on synthetic pigments show that production methods have an important role in the performance of paint. In this regard, this work investigates the links existing between the optical emission, crystal defects and photocatalytic activity of zinc white pigment from different contemporary factories, with the aim of elucidating the effects of these characteristics onto the tendency of the pigment to induce paint failures. The analysed samples display highly similar crystallite structure, domain size, and specific surface area, whilst white pigments differ from pure ZnO in regards to the presence of zinc carbonate hydrate that is found as a foreign compound. In contrast, the photoluminescence measurements categorize the analysed samples into two groups, which display different trap-assisted emissions ascribed to point crystal defects introduced during the synthesis process, and associated to Zn or O displacement. The photocatalytic degradation tests infer that the emerged defective structure and specific surface area of ZnO-based samples influence their tendency to oxidize organic molecules under light irradiation. In particular, the results indicate that the zinc interstitial defects may be able to promote the photogenerated electron-hole couples separation with a consequent increase of the overall ZnO photocatalytic activity, negatively affecting the binding medium stability. This groundwork paves the way for further studies on the link between the photoluminescence emission of the zinc white pigment and its tendency to decompose organic components contained in the binding medium.
Highlights
Zinc oxide was widely employed as a white pigment in modern oil paintings, and it was appreciated by the master artists of the 19th century for its intense whiteness and elevated ductility [1].Since the second half of the 1800, the pigment was produced from zinc metal extracted from mines all over the World and derived according to three main processes
The ofchemical this study highlight tiny zincallwhite pigments and pure zinc oxides in results terms of composition anddifference crystallinebetween structure: samples are characterised by oxides in terms of chemical composition and crystalline structure: all samples are characterised by hexagonal structure with similar crystallite size, while the specific surface area is found around a few m2g-1, except for ZnO2 with a value higher than 10 m2g−1
The presence of this compound has been associated with the conversion of the metal oxide hexagonal structure with similar crystallite size, while the specific surface area is found around a few m2 g−1, except for ZnO2 with a value higher than 10 m2 g−1
Summary
Zinc oxide was widely employed as a white pigment in modern oil paintings, and it was appreciated by the master artists of the 19th century for its intense whiteness and elevated ductility [1].Since the second half of the 1800, the pigment was produced from zinc metal extracted from mines all over the World and derived according to three main processes. Morley-Smith mentioned the detection of two different fluorescent emissions in samples synthetized via the indirect process under high magnification microscope: One emission was bright green and the other purple-blue, and this difference was not directly associated to different particle sizes Based on this observation and on other experiments, he deduced that (i) the blue fluorescent emission of zinc oxide depends on the presence of hydrogen proxide at the pigment surface particles; (ii) pigment particles displaying the blue emission are less stable than the ones emitting in the green, especially in the presence of water. He concluded that the rapid chalking observed in samples synthetized via the indirect process was correlated with the presence of higher proportion of blue emitting particles, which were more reactive in oil paint
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