| Pickering emulsions are stable dispersion system, whose oil/water interface was stabilized by solid particles. In contrast to conventional surfactant stabilized emulsions, Pickering emulsions are extremely stable in both thermodynamics and dynamics as well as low-toxic and less emulsifier consumption. Pickering emulsions has found many potential important applications in biomedicine, food products, fine chemistry, wastewater treatment, nanomaterials, interfacial catalysis and oil recovery etc. Up to now, a large class of inorganic nanoparticles and organic polymer(including naturally occurring polymers and synthetic polymers with different topological structure) have been successfully applied to the stabilized Pickering emulsions.However, the high stability also brings forth many obstacles in some application fields of Pickering emulsion. Therefore, achieving Pickering emulsion with both high stability and facile demulsification is an important issue in the process of practical application. In our present study, the emphasis was laid on the synthesis of high stable Pickering emulsions with controlled demulsification and its application in oil-water interfacial catalysis and new material synthesis. The main research contents were summarized as following:(1) Synthesis of Pickering emulsions with p H-induced demulsification and its application in oil-water interfacial catalysis. Firstly, Au@PEO-b-P4 VP hybrid nanoparticles were synthesized by cross-linking the poly(4-vinylpyridine)(P4VP)block of poly(ethylene oxide)-b-poly(4-vinylpyridine)(PEO113-b-P4VP119) in methanol using chloroauric acid(HAu Cl4) and Na BH4 as cross-link agent and reduction agent, respectively. The structure and morphology of the obtained“core-shell” star Au@PEO-b-P4 VP hybrid nanoparticles could be verified by TEM observation. Then n-decanol in water Pickering emulsion was prepared employing Au@PEO-b-P4 VP hybrid nanoparticles as stabilizer. The synthesized hybrid nanoparticles showed a high emulsifying performance, highly stable Pickering emulsion could be generated at an extremely low particles content. Lowering p H of water phase to less than 4 by adding HCl aqueous solution, n-decanol in water Pickering emulsion showed a rapid demulsification. For the broken emulsion, the separated oil and water could be reemulsified to stabilized Pickering emulsion upon increasing p H to above 4 by adding Na OH aqueous solution. Our extensive experiments revealed that this p H-induced emulsification/demulsification couldundergo successive six cycles with only a slight reduction in emulsion layer thickness.DLS, zeta potentials measurements and interfacial tension measurements as well as TEM characterization all showed this reversible cycle was the result of the tunable wettabilities of the core cross-linked hybrid micelles with the p H 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 p H-responsible reversible emulsification/demulsification cycle, the generated Pickering emulsion could be used as an ideal microcapsule for the interfacial catalytic reaction. As a proof of the concept, the catalytic reduction reaction of p-nitroanisole by Na BH4 has been efficiently carried out at the oil-water interface with a good recyclability and a facile separation.(2) Preparation and catalytic application of hollow porous Au/Si O2 hybrid microspheres. Firstly, mixed oil(TEOS/n-decanol) in water Pickering emulsions stabilized by Au@PEO-b-P4 VP hybrid nanoparticles were generated. Then hollow Au/Si O2 hybrid microspheres with nano-/submicro-sized protrusions on their shells,termed as massage ball-like microspheres, were successfully synthesized using the generated Pickering emulsion as template, in which the P4 VP catalyzed hydrolysis and condensation of TEOS in the TEOS/n-decanol mixed oil phase occurred at the oil/water interface. As a result, a continuous Si O2 shell was formed. The uneven adsorption of polydisperse hybrid nanoparticles at the oil/water interface as well as the volume shrinkage of the oil phase during the early hydrolysis and condensation of TEOS facilitated the formation of protrusions on the shell surface. After further removal of the polymer components embedded in the shell by calcination, hollow Au/Si O2 hybrid microspheres with micropore/mesopore bimodal porous shells were produced. The as-prepared Au/Si O2 hybrid microspheres were applied as catalysts for the reduction of p-nitrophenol with Na BH4, showing a high catalytic activity with a good recyclability owing to the large specific areas, the easily accessible Au active centres and the enhanced mass transportation. |
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