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?0.65nm) is similar to the diameter reported by Frens (16 nm). The surface plasmon band of the concentrated Au NPs UV-Vis spectrum has a !max at 522nm. 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 (80–100nm) 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 (524–613nm) and broadens as the density of Au NPs is increased on the shell surface.