A Crucial Role of Rh Substituent Ion in Photoinduced Internal Electron Transfer and Enhanced Photocatalytic Activity of CdS-Ti_(5.2-x)/6Rh_x/2O₂ Nanohybrids

The photocatalytic activity and photostability of CdS quantum dot (QD) can be remarkably enhanced by hybridization with Rh-substituted layered titanate nanosheet even at very low Rh substitution rate (<1%). Mesoporous CdS-Ti_(5.2-x)/6Rh_x/2O₂ nanohybrids are synthesized by a self-assembly of exfoliated Ti_(5.2-x)/6Rh_x/2O₂ nanosheets with CdS QDs. The partial substitution of Rh³⁺/Rh⁴⁺ ions for Ti⁴⁺ ions in layered titanate is quite effective in enhancing an electronic coupling between hybridized CdS and titanate components via the formation of interband Rh 4d states. A crucial role of Rh substituent ion in the internal electron transfer is obviously evidenced from in situ X-ray absorption spectroscopy showing the elongation of (RhO) bond under visible light irradiation. This is the first spectroscopic evidence for the important role of substituent ion in the photoinduced electron transfer of hybrid-type photocatalyst. The CdS-Ti_(5.2-x)/6Rh_x/2O₂ nanohybrids show much higher photocatalytic activity for H₂ production and better photostability than do CdS and unsubstituted CdS-TiO₂ nanohybrid. This result is ascribable to the enhancement of visible light absorptivity, the depression of electron-hole recombination, and the enhanced hole curing of CdS upon Rh substitution. The present study underscores that the hybridization with composition-controlled inorganic nanosheet provides a novel efficient methodology to optimize the photo-related functionalities of semiconductor nanocrystal.