Effect of Surface Coating on the Photocatalytic Function of Hybrid CdS-Au Nanorods

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 11; no. 4; pp. 462 - 471
• Main Authors: Ben-Shahar, Yuval, Scotognella, Francesco, Waiskopf, Nir, Kriegel, Ilka, Dal Conte, Stefano, Cerullo, Giulio, Banin, Uri
• Format: Journal Article
• Language: English
• Published: Germany Blackwell Publishing Ltd 2015; Wiley Subscription Services, Inc
• Subjects: Charge; charge transfer dynamics; Coatings; hybrid nanoparticles; Hydrogen evolution; Ligands; Mathematical models; Nanoparticles; Nanorods; Nanotechnology; Photocatalysis; surface coatings; hydrogen evolution; surface coatings; photocatalysis; charge transfer dynamics; hybrid nanoparticles
• ISSN: 1613-6810; 1613-6829; 1613-6829
• DOI: 10.1002/smll.201402262

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. Surface coating effects on the photocatalytic properties of hybrid CdS‐Au nanorods are studied by comparing the hydrogen evolution rate and efficiencies in the water splitting reaction. Thiolated‐alkyl ligands show low yields, while polymer coatings with polyethyleneimine provide a significant increase in the apparent quantum yield due to the improved surface passivation reducing the competing surface trapping of charge carriers.