A method for preparation of a composite comprising an anthocyanidin (aglycone of anthocyanin) dye and HMS-type mesoporous silica under neutral conditions was developed and the colorant properties of the composite as a red pigment were investigated.
HMS containing a small amount of Al in the synthesis step (Al-HMS) effectively adsorbed anthocyanidin dye to generate a red composite. However, the color of the composite shifted from red to purple as the Al content of Al-HMS increased. This phenomenon was not observed for the composite comprising Al and MCM-41-type mesoporous silica (Al-MCM-41) synthesized under strongly basic conditions. Washing with dilute NaOH
(aq) was effective for resolving this issue. Superficial Al species external to the silica framework were removed, and the resulting composite exhibited a vivid red color, even when the Al concentration was high.
Minimal elution of the dye from the Al-HMS composite was observed in water and the composite exhibited higher photo-stability than the Al-MCM-41 composite.
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