Metal nanoparticle-loaded porous carbon hollow spheres by twin polymerization

The formation of silver and gold nanoparticle-encapsulated hollow carbon spheres (HCS) by twin polymerization is reported. Therefore, silica spheres with different diameters (Aerosil(A (R)) AS90, d = 20 nm; Aerosil(A (R)) OX50, d = 40 nm; Stober particles, d = 200 nm) were coated with the metal carboxylates [AgO2C(CH2OCH2)(3)H] (1) or [(PPh3)AuO2C(CH2OCH2)(3)H] (2). Thermal treatment of the as-produced templates gave the respective metal nanoparticle-functionalized systems, which were characterized by powder X-ray diffraction (PXRD) and transmission electron microscopy. The plasmon resonance of the surface-bonded particles was determined by using UV-Vis spectroscopy showing absorptions at 412 nm for silver and 524 nm for gold. The metal nanoparticle-modified templates were then coated with a twin polymer layer as result of the acid-catalyzed twin polymerization of 2,2'-spiro-bi[4H-1,3,2-benzodioxasiline] (3). This coating consists of a phenolic resin and in situ formed silicon dioxide nanoclusters. After carbonization and removal of the SiO2 phase by refluxing with a NaOH solution, the appropriate metal-loaded HCS were obtained. The thus prepared carbon materials were characterized by PXRD, electron microscopy and nitrogen adsorption-desorption isotherms. Mainly micro-porous materials (IUPAC type I) were obtained with a surface area between 910 and 1110 m(2)/g. These HCS materials were used for the catalytic reduction of methylene blue and 4-nitrophenol proving the accessibility of the incorporated M-NPs. A size-dependent influence of the used carbon hull was found.