Pickering Emulsions Prepared by Layered Niobate K₄Nb₆O₁₇ Intercalated with Organic Cations and Photocatalytic Dye Decomposition in the Emulsions

We investigated emulsions stabilized with particles of layered hexaniobate, known as a semiconductor photocatalyst, and photocatalytic degradation of dyes in the emulsions. Hydrophobicity of the niobate particles was adjusted with the intercalation of alkylammonium ions into the interlayer spaces to enable emulsification in a toluene–water system. After the modification of interlayer space with hexylammonium ions, the niobate stabilized water-in-oil (w/o) emulsions in a broad composition range. Optical microscopy showed that the niobate particles covered the surfaces of emulsion droplets and played a role of emulsifying agents. The niobate particles also enabled the generation of oil-in-water (o/w) emulsions in a limited composition range. Modification with dodecylammonium ions, which turned the niobate particles more hydrophobic, only gave w/o emulsions, and the particles were located not only at the toluene–water interface but also inside the toluene continuous phase. On the other hand, interlayer modification with butylammonium ions led to the formation of o/w emulsions. When porphyrin dyes were added to the system, the cationic dye was adsorbed on niobate particles at the emulsion droplets whereas the lipophilic dye was dissolved in toluene. Upon UV irradiation, both of the dyes were degraded photocatalytically. When the cationic and lipophilic porphyrin molecules were simultaneously added to the emulsions, both of the dyes were photodecomposed nonselectively

pH-Sensitive Adsorption Behavior of Polymer Particles at the Air–Water Interface

pH-Sensitive adsorption of polymer particles bearing poly­[2-(dimethylamino)­ethyl methacrylate] hairs at the air–water interface was investigated using a surface tensiometer, a Langmuir–Blodgett trough, and an X-ray reflectometer. We clarified that the particles are adsorbed at the interface at basic pH; by contrast, at acidic pH, only a small number of particles are adsorbed, whereas the majority are dispersed in the water phase. X-ray reflectometry analysis revealed that a particle monolayer was formed at the air–water interface, which was packed densely under increasing surface pressure, as determined by the electron density profile change. The contact angles of the particles at the air–water interface were estimated to be 29° and 34° at pH 3 and 10, respectively, by direct visualization of the air–water interface position of the particles using a polycyanoacrylate trapping method