Pickering Emulsions Stabilized By SiO₂/Ag Composite Nanoparticles And Application In Catalytic Research

Solid-stabilized emulsions (Pickering emulsions), which is a thermodynamic stability and dynamic instability system, is stabilized by solid particles as emulsifier instead of the traditional surfactant. Stability of emulsion is crucially dependent on the wettability of the particles. At present, the solid particle's wettability is mainly adjusted on molecule scale. However, there are rare reports on adjusting the wettability of solid particle by attaching nanoparticles at their surface. In the paper, the effect of emulsion stability by the particles'wettability turned on the nano-scale was investigated and the effect of mixed solid particles on the stability of Pickering emulsions was discussed. The prepared Pickering emulsions were used as template to prepare the inorganic / organic composite material, which was useful to analyze the particles'behavior in the interface of Pickering emulsion. Meanwhile the photocatalysis in the stable Pickering emulsion was studied.Using ammonia as catalyzer, mono-dispersed nano-SiO2 spherical particles were prepared by hydrolysis of tetraethoxy-silicane (TEOS) in alcohol-water mixed solvents. The silica nanoparticles were modified by attaching the silver nanaparticles to their surface. The hydrophobic of silica particles could be adjusted by attaching silver nanoparticles of different sizes to their surfaces through the mount of Ag(NH3)2+ solution. The hydrophobicity of Ag/SiO2 composite nanoparticles was characterized. Different Ag/SiO2 nanoparticle-stabilized emulsions and mixed Ag/SiO2 nanoparticle-stabilized emulsions were prepared. The stability of the emulsions was observed by optical microscope. As a result, the stability of single particle-stabilized emulsions was connected with the particles'wettability, namely the stable Pickering emulsion stabilized by the solid particles with higher or lower silver attached couldn't be obtained; the stability of Pickering emulsion stabilized by two kinds of mixed particles could be improved and decreased With increasing the oil/water volume ratio. Through the way of polymerization, the assembly of Ag/SiO2/polystyrene third-class composite materials was prepared in the stable Pickering emulsion. The products were characterized by Scan Electrical Microscope (SEM), which is an useful way to learn the behavior of the Ag/SiO2 composite nanoparticles on the surface of polymer. The results show that adsorption of Ag/SiO2 nanoparticles with moderate wettability could be more on the interface of polymer; there were certain flocculate activities between Ag/SiO2 nanoparticles, which enhanced the strength of the interfacial film to increase the stability of the Pickering emulsion.The photocatalytic degradation of methyl orange in Pickering emulsion was investigated. The results showed that the photocatalytic activity of the Ag/SiO2 composite nanoparticles and the dissolving action of oil had cooperative effect on the Pickering emulsion catalysis.