Nano/nanocomposite systems: in situ growth of particles and clusters of semiconductor metal sulfides in porous silica-pillared layered phosphates

Abstract

Silica-pillared metal(IV) hydrogen phosphates formed by the intercalation of octameric aminoalkyl or aryl species from solution into layered zirconium or tin phosphates, followed by thermal degradation of the organic moieties, are crosslinked microporous, nanocomposite materials with surface areas up to 230 m^–2 g^–1. Their use as templates for size-quantization of metal sulfide particles is described via, the sorption of Zn^–2+ and Cd^–2+ ions from aqueous solution, followed by reaction with H₂S in acetone. Band gaps obtained from optical absorption spectra for occluded ZnS and CdS are significantly increased from those of the corresponding bulk-metal sulfides. These data, and those of X-ray absorption spectroscopic measurements at the zinc and cadmium K edges, allow the metal sulfide aggregates to be described in terms of ‘superclusters’, where discrete ‘molecule-like’ Zn(Cd)S semiconductors confined in the micropores interconnect through windows in the pillar network to form more extended structures of diameter ca. 25 Å.