Covalent attachment of catalyst molecules to conductive diamond: CO2 reduction using "smart" electrodes.

We report here covalent attachment of a catalytically active cobalt complex onto boron-doped, p-type conductive diamond. Peripheral acetylene groups were appended on a cobalt porphyrin complex, and azide-alkyne cycloaddition was used for covalent linking to a diamond surface decorated with alkyl azides. The functionalized surface was characterized by X-ray photoelectron spectroscopy and Fourier transform IR spectroscopy, and the catalytic activity was characterized using cyclic voltammetry and FTIR. The catalyst-modified diamond surfaces were used as "smart" electrodes exhibiting good stability and electrocatalytic activity for electrochemical reduction of CO(2) to CO in acetonitrile solution.

Transient 2D IR spectroscopy of charge injection in dye-sensitized nanocrystalline thin films.

We use nonlinear 2D IR spectroscopy to study TiO(2) nanocrystalline thin films sensitized with a Re dye. We find that the free electron signal, which often obscures the vibrational features in the transient absorption spectrum, is not observed in the 2D IR spectra. Its absence allows the vibrational features of the dye to be much better resolved than with the typical IR absorption probe. We observe multiple absorption bands but no cross peaks in the 2D IR spectra, which indicates that the dyes have at least three conformations. Furthermore, by using a pulse sequence in which we initiate electron transfer in the middle of the infrared pulse train, we are able to assign the excited state features by correlating them to the ground state vibrational modes and determine that the three conformations have different time scales and cross sections for electron injection. 2D IR spectroscopy is proving to be very useful in disentangling overlapping structural distributions in biological and chemical physics processes. These experiments demonstrate that nonlinear infrared probes are also a powerful new tool for studying charge transfer at interfaces.

Highly stable molecular layers on nanocrystalline anatase TiO2 through photochemical grafting.

Well-defined molecular layers can be formed on the surface of nanocrystalline anatase TiO2 by photochemically grafting organic molecules bearing a terminal vinyl group. The molecular layers produced are shown to have minimal oxidation and are able to be patterned and uniformly grafted through optically thick nanocrystalline films. Stability tests show that the layers have excellent stability in deionized water at 80 degrees C, aqueous solutions at pH=1.0 and pH=10.3 at 65 degrees C, and acetonitrile for time scales approaching 1200 h. Degradation of the films in deionized water occurs using a AM1.5 full-spectrum solar simulator as an illumination source but is partially suppressed by filtering with a 400 nm UV blocking filter which blocks the above-bandgap light. A mechanism is proposed for the grafting reaction in which the surface hydroxyl groups trap photoexcited holes, facilitating reaction with the vinyl group.