pH-responsible Pickering emulsion and its catalytic application for reaction at water-oil interface

In this work, pH-responsible Pickering emulsion stabilized by polymer-metal hybrid micelles and its catalytic application for reaction at oil-water interface were presented. Employing Au@poly(ethylene oxide)-b-poly(4-vinylpyridine) polymer-metal hybrid micelles as emulsifier, n-decanol in water Pickering emulsion was first generated. The produced Pickering emulsion displayed reversible emulsification/demulsification with pH variation of the water phase, and this pH-induced emulsification/demulsification could undergo multiple cycles with only a slight reduction in emulsion performance. Dynamic light scattering, zeta potential measurement, and interfacial tension measurement, as well as transmission electron microscopy characterization, all showed that this reversible emulsification/demulsification cycle was the result of the tunable wettabilities of the core cross-linked hybrid emulsifier micelles with pH variation. Benefited from the excellent catalytic performances of the implanted Au nanoparticles at the oil-water interface and the large interfacial area of the emulsion droplets together with the pH-responsible reversible emulsification/demulsification cycle, the generated Pickering emulsion could readily applied as a catalytic microreactor for a broad of organic reactions occurred in water medium. As a proof of the concept, Au catalyzed reduction reaction of p-nitroanisole by NaBH4 was investigated. The catalyst showed both a highly catalytic activity with a good recyclability.