DSpace at EWHA: Remarkable enhancement of photocatalytic hydrogen evolution efficiency utilizing an internal cavity of supramolecular porphyrin hexagonal nanocylinders under visible-light irradiation

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Remarkable enhancement of photocatalytic hydrogen evolution efficiency utilizing an internal cavity of supramolecular porphyrin hexagonal nanocylinders under visible-light irradiation

Title: Remarkable enhancement of photocatalytic hydrogen evolution efficiency utilizing an internal cavity of supramolecular porphyrin hexagonal nanocylinders under visible-light irradiation

Authors: Hasobe T.; Sakai H.; Mase K.; Ohkubo K.; Fukuzumi S.

Ewha Authors: Shunichi Fukuzumi

SCOPUS Author ID: Shunichi Fukuzumi

Issue Date: 2013

Journal Title: Journal of Physical Chemistry C

ISSN: 1932-7447

Citation: vol. 117, no. 9, pp. 4441 - 4449

Indexed: SCI; SCIE; SCOPUS

Abstract: An efficient visible light-induced hydrogen evolution system has been developed by using supramolecular porphyrin hexagonal nanocylinders that encapsulate Pt-colloids-deposited TiO2 nanoparticles (Pt/TiO 2) in the internal cavity. First, porphyrin nanocylinders structurally controlled by encapsulated Pt/TiO2 are prepared via a solvent mixture technique. The bar-shaped structure composed of Pt/TiO 2 and zinc meso-tetra(4-pyridyl)porphyrin [ZnP(Py)4] is formed with the aid of a surfactant: cetyltrimethylammonium bromide (CTAB) in a DMF/H2O mixture solution [denoted as Pt/TiO2-ZnP(Py) 4 nanorods]. In scanning electron microscopy (SEM) measurements, ZnP(Py)4 pristine hexagonal nanocylinder with a large hollow structure [denoted as ZnP(Py)4 nanocylinder] was observed, whereas the hollow hole was completely closed in case of Pt/TiO2-ZnP(Py) 4 nanorods. X-ray diffraction (XRD) analyses also revealed that ZnP(Py)4 alignment in the nanorod was based on the stacked-assemblies of ZnP(Py)4 coordinated hexagonal formations. These results clearly indicate that Pt colloids-deposited TiO2 nanoparticles (Pt/TiO 2) were successfully encapsulated within a ZnP(Py)4 hexagonal nanocylinder. Pt/TiO2-ZnP(Py)4 also shows a broadened absorption in the visible region because of aggregation of ZnP(Py)4. Then, Pt/TiO2-ZnP(Py)4 exhibited efficient hydrogen evolution under visible light irradiation, whereas no hydrogen was evolved in the case of Pt/TiO2 without ZnP(Py) 4. In addition, the hydrogen evolution efficiency of Pt/TiO 2-ZnP(Py)4 nanorods per unit weight of Pt was two orders magnitude greater than that of the nonencapsulated system: Pt/TiO2 and ZnP(Py)4 nanocylinder composites [Pt/TiO2 + ZnP(Py)4 composites]. Finally, the photodynamics of the excited state of Pt/TiO2-ZnP(Py)4 nanorods was examined by femtosecond time-resolved transient absorption spectroscopy to clarify the photocatalytic mechanism. © 2013 American Chemical Society.