Mercaptoalkyl Groups Anchored on the Layer Surface of New α-Zirconium Phosphate Phosphonates for the Stabilization of Gold Nanoparticles

Layered zirconium phosphate mercaptoalkylphosphonates, with general composition Zr(O3POH)2-x(O3P(CH2)11SH)x, where x=0.4-1.4, are prepared according to two procedures: direct reaction between a zirconyl salt and a mixture of phosphoric/phosphonic acid in propanol, or topotactic ion exchange reaction of phosphate groups of nanocrystalline & alpha;-Zr(O3POH)2 with mercaptoundecylphosphonate groups. FT-IR analysis and XPS proves the presence of the mercapto groups and, according to X-Ray diffraction analysis, they result randomly distributed on the layer surface. The solids are used as supports for gold nanoparticles synthesized according to three different methods: reaction of HAuCl4 with NaBH4, added after 24 hours (Procedure A), or concomitantly (Procedure B) to the addition of the Au(III) salt to the solid suspension, or by mixing the solid suspension with a colloidal dispersion of gold nanoparticles prepared according to the Turkevich method (Procedure C). The best results were obtained with Procedure B, that provided composites with gold nanoparticles having an average size of (6 & PLUSMN;2) nm.Layered zirconium phosphate mercaptoundecylphosphonates were prepared and employed as supports for gold nanoparticles. According to the procedure, different gold species are stabilized by the support: Au ionic species and/or small gold clusters, Au(0) nanoparticles with an average size of 6 nm, or larger Au(0) nanoparticles with an average size of 20 nm.image