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 NaBH 4 was investigated. The catalyst showed both a highly catalytic activity  with a good recyclability.