Surface protection of an organic pigment based on a modification using a mixed-micelle system

•Organic pigment particles were successfully covered by a thin layer of silica.•Appropriate mixture of surfactants maximized the stability of the pigment dispersion.•The same mixture provided nucleation sites for the formation of a dense silica shell.•A silica layer protected the pigment against photocatalytically induced degradation.•The procedure allows further improvements in chemical protection of organic pigments.

The surface of a model red organic pigment, 3,6-bis(4-chlorophenyl)pyrrolo[3,4-c]pyrrole-1,4-dione, was modified using a mixed-micelle system containing different surfactants and polymers to improve the dispersibility of the pigment. It is shown that modifying the surface using a non-ionic surfactant and a mixed-micelle solution leads to good dispersibility of the pigment. The surface-modified pigment particles were additionally encapsulated with a SiO2 shell to improve the UV/TiO2 fastness. The influence of the synthesis parameters, such as the temperature and the pH, on the formation of the SiO2 protective layer around the pigment particles and, consequently, on the UV/TiO2 protection were investigated. The conditions leading to a compact and uniform protective silica layer over the majority of the pigment particles are discussed in detail.

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