The aim of this study is the improvement of the photostability of several natural anionic dyes, carmine (CM), carthamus yellow (CY), and annatto dye (ANA), by complexation with hydrotalcite. The composite of the dyes and hydrotalcite is prepared by the coprecipitation method. CM is successfully intercalated in the hydrotalcite layer when the amount of introduced CM is large. The photostability of CM in CM/HT composites is superior to the CM adsorbed on silica surface. The effect of the stability enhancement is larger when the amount of introduced CM exceeds 0.23 g/g-host, or when the layer charge density of the hydrotalcite is larger. CY is also stabilized by complexation with hydrotalcite, whereas ANA is not stabilized by complexation with hydrotalcite. The photostability of an anionic natural dye can be improved by intercalation into the hydrotalcite layer, if the dye has a hydrophilic nature and a rather planar structure. The intercalated dye is stabilized by the protection from the attack of the atmospheric oxygen. In addition, contribution of the electrostatic interaction between the positively charged hydrotalcite layer and the intercalated anionic dye is also proposed.
Current doubling effects in the photoanodic reactions of
HCOOH
or
normalHCOONa
on n‐type semiconductor electrodes (
normalZnO
,
normalCdS
, and
TiO2
) and the photocathodic reaction of
false(NH4)2S2O8
on a p‐type semiconductor
false(normalGaPfalse)
were studied by the measurement of the temperature change of a semiconductor electrode surface. The results of the temperature change measurements show that these photoelectrode reactions proceed with quantum efficiencies greater than 1 but less than 2. The temperature changes are interpreted in terms of the current doubling process.
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