Pore size and surface charge control in mesoporous TiO(2) using post-grafted SAMs.

Two types of TiO(2) are used as mesoporous scaffolds, one (i) randomly sintered yielding an average pore size of 15-20 nm including bottlenecks of 1-3 nm (s-TiO(2)), the other (ii) prepared by evaporation-induced self-assembly with a pore size of 7-9 nm (t-TiO(2)). The pore walls of these materials were post-grafted with phosphonic acids bearing one or two pyridinium or sulfonate head groups via 6, 10 or 14 methylene groups, in order to tune the free pore diameter and the surface charge over a broad range. The modification was characterized by FTIR spectroscopy. Charge transport through the modified pores was investigated by cyclic voltammetry using [Fe(CN)(6)](4-/3-), [IrCl(6)](2-/3-) [Ru(NH(3))(6)](3+/2+), and (ferrocenylmethyl)trimethylammonium as electroactive tracer ions and La(3+) or naphthalene trisulfonate as non-electroactive species. The Faradaic current through the pores is controlled by the combination of surface charge, tracer ion charge, charge of the non-electroactive ions present, as well as the pore diameter. High currents due to strong preconcentration are observed, e.g. a partitioning coefficient value of 7 x 10(3) for [Fe(CN)(6)](4-/3-) on a modified electrode making it a candidate for ion-exchange voltammetry. Other phenomena presented are: (i) electrostatic closure of the porous system due to overlapping Debye layers, (ii) charge inversion of the pore walls, and (iii) the mode of charge propagation along the pore walls. Interestingly s-TiO(2) is more effective at building up an electrostatic barrier compared to t-TiO(2), probably because of narrow bottlenecks which interconnect the pores in s-TiO(2) only.

Phototriggered NO and CN release from [Fe(CN)5NO]2- molecules electrostatically attached to TiO2 surfaces.

Phototriggered NO and CN release from [Fe(CN)(5)NO](2-) (NP) molecular monolayers is studied by a combination of electrochemistry, infrared spectroscopy, and mass spectrometry under light irradiation at temperatures of 80 K and 294 K. The NP molecular monolayers were electrostatically attached to thin films of mesoporous TiO(2) deposited on silicon. Irradiation of the surfaces results in NO and CN release, which is verified using mass spectrometry. The kinetic trace of the light driven NO release of the [Fe(CN)(5)NO](2-) is determined by inspection of the nu(NO) stretching mode as a function of exposure to light in the violet/green spectral range. The decrease of the nu(NO)-amplitude can be modeled considering the NO release as a two-step process with an intermediate state between the attached and the released state. According to literature, the intermediate state may be related to the light-induced linkage NO isomerization of the NP.

Tailor-made oxide architectures attained by molecularly permeable metal-oxide organic hybrid thin films.

Tailor-made metal oxide (MO) thin films with controlled compositions, electronic structures, and architectures are obtained via molecular layer deposition (MLD) and solution treatment. Step-wise formation of permeable hybrid films by MLD followed by chemical modification in solution benefits from the versatility of gas phase reactivity on surfaces while maintaining flexibility which is more common at the liquid phase.

Transformation of organic-inorganic hybrid films obtained by molecular layer deposition to photocatalytic layers with enhanced activity.

We present the transformation of organic-inorganic hybrid titanicone films formed by TiCl(4) as metal precursor and ethylene glycol (EG) using solvent-free MLD to highly active photocatalytic films. The photocatalytic activities of the films were investigated using hydroxyl-functionalized porphyrin as a spectroscopic marker. TEM imaging and electron diffraction, XPS, UV-vis spectroscopy, and spectroscsopic ellipsometry were employed for structural and composition analyses of the films. The photocatalytic activity of Ti-EG films was investigated for different anneal temperatures and compared to TiO(2) films prepared by ALD using TiCl(4) as metal precursor and H(2)O (TiO(2) films). Overall, our results indicate that the photocatalytic activity of the thermally annealed Ti-EG film is about 5-fold increased compared to that of the TiO(2) film prepared by ALD for optimal process conditions. The combined results indicate that the structural and photocatalytic properties can be assigned to three states: (I) amorphous state, intermediate dye loading, low photocatalytic activity, (II) intermediate film state with both crystalline and amorphous regions, high dye loading, high catalytic activity, and (III) highly crystalline film with low dye loading and low photocatalytic activity. The formation of photocatalytic nanotubes (NTs) is demonstrated using sacrificial Ge nanowires (NWs) scaffolds to yield Ti-EG NT structures with controllable wall thickness structures and enhanced dye loading capacity. Our results demonstrate the feasibility and high potential of MLD to form metal oxides with high photocatalytic activity.