One-pot synthesis of Ag@SiO2@Ag sandwich nanostructures

Abstract

Ag@SiO2@Ag sandwich nanostructures were prepared by a facile one-pot synthesis method. The Ag core,SiO2 shell and Ag nanoparticle shell were all synthesized with polyvinylpyrrolidone, catalysed by ammonia,in the one-pot reaction. The polyvinylpyrrolidone, acting as a smart reducing agent, reduced theAg + to Ag cores and Ag shells separately. Furthermore, the polyvinylpyrrolidoneserved as a protective agent to prevent the silver cores from aggregating. TheSiO2 shell and outer layer Ag nanoparticles were obtained when tetraethyl orthosilicateand ammonia were added to the silver core solution. Ammonia, acting asthe catalyst, accelerated the hydrolysis of the tetraethyl orthosilicate toSiO2, which coated the silvercores. Furthermore, Ag(NH3)2 + ions were formed when aqueous ammonia was added to the solution, whichincreased the reduction capability. Then the polyvinylpyrrolidone reduced theAg(NH3)2 + ions to small Ag nanoparticles on the surface of theAg@SiO2 andformed Ag@SiO2@Ag sandwich structures with a standard deviation of less than 4%. This structure effectivelyprevented the Ag nanoparticles on the silica surface from aggregating. Furthermore, theAg@SiO2@Ag sandwich structures showed good catalysis properties due to the large surfacearea/volume value and activity of surface atoms of Ag particles.