Under visible light irradiation, CdSe-nanoribbons photocatalyze H 2 evolution from aqueous sodium sulfite/ sulfide solution with a quantum efficiency of 9.2% at 440 nm, whereas bulk CdSe is not active for the reaction. Photoelectrochemical measurements show that the activity of nano-CdSe is caused by a raised flatband potential (-0.55 V, NHE) which follows from the increased bandgap (2.7 eV) of this quantum confined material. In the presence of a sulfide ion, the flatband potential is fixed to -0.43 V (NHE), slightly below the sulfide redox potential (-0.48 V, NHE). When the nanoribbons are chemically linked to MoS 2 nanoplates that were obtained by exfoliation and ultrasonication of bulk MoS 2 , the activity increases almost four times, depending on the mass percentage of MoS 2 . Cyclic voltammetry reveals that the enhancement from the MoS 2 nanoplates is due to a reduction of the H 2 evolution overpotential. In contrast, chemical linkage of Pt nanoparticles to the nanoribbons does not affect the photocatalytic activity.

Rutile IrO(2) is known as being among the best electrocatalysts for water oxidation. Here we report on the unexpected photocatalytic water oxidation activity of 1.98 nm ± 0.11 nm succinic acid-stabilized IrO(2) nanocrystals. From aqueous persulfate and silver nitrate solution the nonsensitized particles evolve oxygen with initial rates up to 0.96 μmol min(-1), and with a quantum efficiency of at least 0.19% (measured at 530 nm). The catalytic process is driven by visible excitations from the Ir-d(t(2g)) to the Ir-d(e(g)) band (1.5-2.75 eV) and by ultraviolet excitations from the O-p band to the Ir-d(e(g)) (>3.0 eV) band. The formation of the photogenerated charge carriers can be directly observed with surface photovoltage spectroscopy. The results shed new light on the role of IrO(2) in dye- and semiconductor-sensitized water splitting systems.

The photocatalytic H2O splitting activities of CdSe and CdSe/CdS core/shell quantum dots are contrasted. CdSe/CdS core/shell quantum dots constructed from 4.0 nm CdSe quantum dots are shown to be strongly active for visible-light-driven photocatalytic H2 evolution in 0.1 M Na2S/Na2SO3 solution with a turnover number of 9.94 after 5 h at 103.9 μmol/h. CdSe quantum dots themselves are only marginally active in 0.1 M Na2S/Na2SO3 solution with a turnover number of 1.10 after 5 h at 11.53 μmol/h, while CdSe quantum dots in pure H2O are found to be completely inactive. Broad-band transient absorption spectroscopy is used to elucidate the mechanisms that facilitate the enhancement in the CdSe core/shell quantum dots, which is attributed to passivation of surface-deep trap states with energies lying below the reduction potential necessary for H2O reduction. Thus, surface trapping dynamics and energetics can be manipulated to dictate the photocatalytic activities of novel CdSe quantum dot based photocatalytic materials.

CdSe nanoribbons show catalytic activity for photochemical hydrogen evolution from aqueous Na2S/Na2SO3 solution under irradiation with ultraviolet and visible light.

The two-dimensional structures formed by monolayers and submonolayers of p-sexiphenyl (p-6P) molecules evaporated onto the Au(111) surface are investigated using ultrahigh vacuum scanning tunneling microscopy (UHV-STM). Five different 2D structures corresponding to different surface coverages are discovered and their 2D structures solved. The trends in the molecular alignment with respect to the underlying gold lattice are discussed. An unusual structure that consists of paired rows of p-6P molecules was discovered. A surface structure with alternating domains of slightly differently packed p-6P molecules was also found. The boundary between these two domains contains systematic molecular vacancies.