title: Effect of surface coating on the photocatalytic function of hybrid CdS-Au nanorods.
abstract: Hybrid semiconductor-metal nanoparticles are interesting materials for use as photocatalysts due to their tunable properties and chemical processibility. Their function in the evolution of hydrogen in photocatalytic water splitting is the subject of intense current investigation. Here, the effects of the surface coatings on the photocatalytic function are studied, with Au-tipped CdS nanorods as a model hybrid nanoparticle system. Kinetic measurements of the hydrogen evolution rate following photocatalytic water reduction are performed on similar nanoparticles but with different surface coatings, including various types of thiolated alkyl ligands and different polymer coatings. The apparent hydrogen evolution quantum yields are found to strongly depend on the surface coating. The lowest yields are observed for thiolated alkyl ligands. Intermediate values are obtained with L-glutathione and poly(styrene-co-maleic anhydride) polymer coatings. The highest efficiency is obtained for polyethylenimine (PEI) polymer coating. These pronounced differences in the photocatalytic efficiencies are correlated with ultrafast transient absorption spectroscopy measurements, which show a faster bleach recovery for the PEI-coated hybrid nanoparticles, consistent with faster and more efficient charge separation. These differences are primarily attributed to the effects of surface passivation by the different coatings affecting the surface trapping of charge carriers that compete with effective charge separation required for the photocatalysis. Further support of this assignment is provided from steady-state emission and time-resolved spectral measurements, performed on related strongly fluorescing CdSe/CdS nanorods. The control and understanding of the effect of the surface coating of the hybrid nanosystems on the photocatalytic processes is of importance for the potential application of hybrid nanoparticles as photocatalysts.
authors.affiliation: The Institute of Chemistry and Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel.
authors.forename: Yuval
authors.initials: Y
authors.lastname: Ben-Shahar
authors.forename: Francesco
authors.initials: F
authors.lastname: Scotognella
authors.forename: Nir
authors.initials: N
authors.lastname: Waiskopf
authors.forename: Ilka
authors.initials: I
authors.lastname: Kriegel
authors.forename: Stefano
authors.initials: S
authors.lastname: Dal Conte
authors.forename: Giulio
authors.initials: G
authors.lastname: Cerullo
authors.forename: Uri
authors.initials: U
authors.lastname: Banin
keywords: charge transfer dynamics.; hybrid nanoparticles; hydrogen evolution; photocatalysis; surface coatings