Template controlled synthesis of monometallic zerovalent metal nanoclusters inside cross-linked polymer frameworks: the effect of a single matrix on the size of different metal nanoparticles

Starting from the gel-type, cross-linked copolymer co-poly-{(N,N-dimethethylacrylamide/4-vinylpyridine/N,N'-methylenebisacrylamide} (DV44) we prepared nanoclusters of several noble metals (Ru, Rh, Pd, Pt, Ag, Au) inside its polymer framework through the so-called "template-controlled synthesis'' approach. This procedure involves the immobilization of the relevant metal centers inside the polymer framework, followed by their reduction to M(0) nanoclusters (in our case, uptake from solutions of suitable precursors and reduction with aqueous solutions of NaBH(4), respectively). In this way, a set of monometallic polymer supported nanoclusters (M/DV44, M = Ru, Rh, Pd, Pt, Ag, Au) were obtained. The experimental conditions were set so as to generally obtain a homogeneous radial distribution of the metal throughout the particles of the materials. The latter were characterized by means of transmission electron microscopy for the assessment of the metal nanocluster sizes. The diameter of the nanoclusters generated by reduction inside water-swollen DV44 were compared with the size of the nanopores of the water-swollen polymer framework that had previously been determined by means of inverse steric exclusion chromatography. The diameter of the prevailing pore fractions in water-swollen DV44 was 3.2-4.3 nm and the largest available pores observed had a diameter of 8.1 nm. Nanoclusters with diameters larger than this value were observed in no cases, and in all cases the average diameter of the nanoclusters never exceeded the diameter of the prevailing pore fraction. For Pd/DV44, Ag/DV44 and Au/DV44, the average nanocluster diameter compared very well with the diameter of the prevailing pore fraction.