Assembly of Nanoparticles in Zeolite Y for the Photocatalytic Generation of Hydrogen from Water

Abstract

Synthesis of nanoparticles of TiO2, Pt, CdS, and their binary and ternary combinations were made on zeolite Y starting from molecular precursors that are ion exchanged into the zeolite. Nanoclusters of TiO2 in the anatase form were formed from titanyl ions at low loadings of Ti (1 per 2.5 supercages). CdS (hexagonal form) and metallic Pt were formed from Cd2+ and Pt(NH3)42+ ion exchanged into the zeolite. Binary clusters of TiO2−Pt and TiO2−CdS were also synthesized. Electron microscopy and elemental analysis suggests colocalization of the distinct nanoparticles. Photocatalytic H2 evolution is the strongest indicator of colocalization, since improvements in H2 evolution rates of ∼100 for Pt/TiO2-zeolite over TiO2-zeolite and ∼18 for CDS/TiO2-zeolite Y over CdS-zeolite Y were observed. These improvements exceed colloidal binary systems reported in the literature. However, improvements in the H2 evolution rate of the ternary system Pt/CdS/TiO2 was not as marked, as compared to the best colloidal ternary systems reported in the literature. A model is proposed that explains the colocalization of nanoparticles, mediated by the zeolite via a self-assembly process. This model also explains why the ternary system is not optimal; since the Pt needs to be associated only with TiO2 for best H2 evolution, and the zeolite-based assembly promotes a statistical colocalization of the three nanoparticles.