US nanoparticles, prepared in reverse micellar systems, were immobilized onto two types of thiol-modified periodic mesoporous organosilicates (PMOS), t-PMOS(I) and t-PMOS(II) by a simple procedure via the addition of t-PMOS and mild stirring. A particle-sieving effect of the t-PMOS was observed, in that the immobilization of the US nanoparticles was decreased with increasing the nanoparticle size. The resulting CdS-PMOS(I) and CdS- PMOS(II) were then used as photocatalysts for the generation of H-2 from 2-propanol aqueous solution. CdS- PMOS(II), which was more stable against photoirradiation, showed higher photocatalytic activity, compared to CdS-PMOS(I). The quantity of H-2 generated on the PMOS-immobilized CdS nanoparticles was greater than that obtained from mesoporous silica (MCM-41)-immobilized CdS nanoparticles (CdS-L-FM41). (C) 2005 Elsevier Ltd. All rights reserved.