Synthesis of immobilized silver nanoparticles on ionic silicate clay and observed low-temperature melting

Silver nanoparticles (AgNPs) of narrow size distribution and low melting point were synthesized from the reduction of silver nitrate in the presence of inorganic silicate clays. The natural clays with a lamellar geometric shape provided a high surface area for immobilizing AgNPs with nanometer diameter in the range of 17-88 nm. At a 1/1 equivalent ratio of Ag+ to clay counter ions, the generated particles had a narrow size distribution (polydispersity of D-w/D-n 1.2 at 26 nm D-n by SEM) and a UV absorption at 420 cm(-1). Without organic dispersants, the colloidal clays could complex with Ag+ in the initial stage of mixing and subsequently stabilized the generated Ag-0 particles. It seems that the high surface area stabilizes the clay rather than the Ag metal intercalation into the layered structure since the basal spacing was only slightly enlarged (12.0 angstrom versus 13.9 angstrom by XRD). The resulting AgNPs were highly stable and maintained their particle size after several cycles of drying at 80 degrees C and re-dispersion in water. Moreover, the AgNPs on the clay surface melted at a low temperature (110 degrees C), observed by SEM. Such AgNPs may have potential applications for fabricating silver arrays or conductors at low temperature.