One-step deposition of Au nanoparticles onto chemically modified ceramic hollow spheres via self-assembly

A concentrated citrate-stabilised Au nanoparticle (NP) colloid has been prepared using a modified Frens procedure, and characterised using transmission electron microscopy (TEM) and UV-Vis absorption spectroscopy. The average diameter determined from TEM images of concentrated Au NPs (16.57 +/- 0.65 nm) is similar to the diameter reported by Frens (16 nm). The surface plasmon band of the concentrated Au NPs UV-Vis spectrum has a lambda(max) at 522 nm. Bare silica ('Si') and iron-'Si' hollow microsphere surfaces have been functionalised with amino groups using the surfactant 3-aminopropyltrimethoxysilane (APTMS). The Au NPs have been assembled onto the APTMS-treated hollow spheres by dispersing a colloid of Au NPs into a suspension of hollow spheres at pH 4.5 (2 h). The volume ratio of Au NPs: hollow spheres was adjusted until maximum deposition could be achieved in a single step. TEM micrographs of ultrathin (80-100 nm) ultramicrotome sections through the Au NP-coated hollow spheres reveal that a single layer of Au NPs is mainly distributed on (1) the external side of the shell wall for 'Si' and (2) both sides of the shell wall for iron-'Si'. UV-Vis absorption spectra of the Au NP-coated hollow spheres show that the surface plasmon band shifts (524-613 nm) and broadens as the density of Au NPs is increased on the shell surface.