Red 33 dye co-encapsulated with cetyltrimethylammonium in mesoporous silica materials

•In situ encapsulation of the Red 33 dye inside mesoporous silica.•High loading (25 wt%) of an azodye inside mesoporous silica.•Stable immobilization of a hydrophilic dye in water and oil media.•Interactions between the Red 33 and the silica host matrix.•Electrostatic interactions between the surfactant and the Red 33.

A water soluble dye, the Red 33, used in cosmetic industry was immobilized into mesoporous silica by a one-step method which consists in the introduction of the dye molecules in the precursor medium of the mesoporous silica i.e. containing surfactant and silica source.A high loading rate of 25 wt% was achieved. The resulting Red 33-silica pigment is stable in water and oil media. The characterizations carried out on this material have shown that the encapsulation is effective and that the presence of Red 33 has an effect on the structure and texture of the material. The material exhibits an excellent stability in water due to the interactions between the Red 33 molecules, the silicate species and the surfactant molecules. It has been shown that the dye molecules interact with both the silica host matrix through the NH2 and phenyl groups, as well as with the surfactant molecules, via electrostatic interactions between the polar head of the surfactant and the sulfonate group of Red 33 which undergoes no steric hindrance.

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