Electrocatalytic reduction of diethyl oximinomalonate at a Ti/nanoporous TiO2 electrode

A “green” method for production of diethyl aminomalonate was presented by electrocatalytic reduction of diethyl oximinomalonate (DEOM) to diethyl aminomalonate in the acetic acid and sodium acetate medium at the surface of Ti/nanoporous TiO₂ electrode. The heterogeneous catalytic redox behaviour of a nanoporous TiO₂ film electrode surface was investigated by cyclic voltammetry (CV). A comparison of the CV recorded in the absence and in the presence of DEOM confirmed the catalytic reduction of DEOM by Ti(IV)/Ti(III) redox system on the nanoporous TiO₂ film surface.     

Colloidal crystal-derived nanoporous electrode materials of Cut SWNTs-assembly and TiO2/SWNTs nanocomposite

Relatively ordered macroporous films of a cut single-walled carbon nanotubes (c-SWNTs) assembly and a TiO 2/c-SWNTs nanocomposite were successfully fabricated by colloidal crystal template processes using polystyrene particles. The macroporous TiO2/c-SWNTs nanocomposite film showed excellent rate capability of Li-insertion/extraction. The rate-dependent Li-insertion/extraction capacities were close to theoretical values expected from Li-diffusion in anatase--TiO2 thin layer without blocking electrolyte-ion and electron access.     

Characterization of photoinduced self-exchange reactions at molecule-semiconductor interfaces by transient polarization spectroscopy: lateral intermolecular energy and hole transfer across sensitized TiO2 thin films

Transient anisotropy measurements are reported as a new spectroscopic tool for mechanistic characterization of photoinduced charge-transfer and energy-transfer self-exchange reactions at molecule-semiconductor interfaces. An anisotropic molecular subpopulation was generated by photoselection of randomly oriented Ru(II)-polypyridyl compounds, anchored to mesoscopic nanocrystalline TiO(2) or ZrO(2) thin films, with linearly polarized light. Subsequent characterization of the photoinduced dichromism change by visible absorption and photoluminescence spectroscopies on the nano- to millisecond time scale enabled the direct comparison of competitive processes: excited-state decay vs self-exchange energy transfer, or interfacial charge recombination vs self-exchange hole transfer. Self-exchange energy transfer was found to be many orders-of-magnitude faster than hole transfer at the sensitized TiO(2) interfaces; for [Ru(dtb)(2)(dcb)](PF(6))(2), where dtb is 4,4'-(C(CH(3))(3))(2)-2,2'-bipyridine and dcb is 4,4'-(COOH)(2)-2,2'-bipyridine, anchored to TiO(2), the energy-transfer correlation time was θ(ent) = 3.3 μs while the average hole-transfer correlation time was <θ(h+)> = 110 ms, under identical experimental conditions. Monte Carlo simulations successfully modeled the anisotropy decays associated with lateral energy transfer. These mesoscopic, nanocrystalline TiO(2) thin films developed for regenerative solar cells thus function as active "antennae", harvesting sunlight and transferring energy across their surface. For the dicationic sensitizer, [Ru(dtb)(2)(dcb)](PF(6))(2), anisotropy changes indicative of self-exchange hole transfer were observed only when ions were present in the acetonitrile solution. In contrast, evidence for lateral hole transfer was observed in neat acetonitrile for a neutral sensitizer, cis-Ru(dnb)(dcb)(NCS)(2), where dnb is 4,4'-(CH(3)(CH(2))(8))(2)-2,2'-bipyridine, anchored to TiO(2). The results indicate that mechanistic models of interfacial charge recombination between electrons in TiO(2) and oxidized sensitizers must take into account diffusion of the injected electron and the oxidized sensitizer. The phenomena presented herein represent two means of concentrating potential energy derived from visible light that could be used to funnel energy to molecular catalysts for multiple-charge-transfer reactions, such as the generation of solar fuels.     

Internal structure of nanoporous TiO2/polyion thin films prepared by layer-by-layer deposition

The internal structure of porous TiO2 films prepared by electrostatic layer-by-layer deposition was investigated. The films were prepared by alternate dipping of solid substrates into dispersions of TiO2 nanoparticles and polycations, polyanions, or pure buffer solution, respectively. The surface charge of the amphoteric TiO2 particles was controlled by the pH of the aqueous dispersions. The morphology of the film surface was investigated by means of scanning electron microscopy. It was found that the surface roughness strongly depends on the polymeric material used for the deposition process but is independent of the ionic strength of the solution or the molecular weight of the polyions. The samples with rough surfaces feature strong light scattering. The porosity and internal structure of the TiO2/polyelectrolyte films were investigated by adsorption/desorption of dye molecules. A crude estimate yields an internal surface that is up to 160 times the plane surface of the substrate for a film thickness of 1 microm. The composition of the films was investigated by X-ray photoelectron spectroscopy (XPS). Detection of the XPS signal after each deposition step of the first three dipping cycles shows a significant increase of the relative surface coverage of Ti after the TiO2 deposition step and of PSS after the PSS deposition step. For later dipping cycles, such an increase was also detectable but less prominent.     

Hydrazine sensors development based on a glassy carbon electrode modified with a nanostructured TiO2 films by electrochemical approach

Microchimica Acta - The authors describe a selective hydrazine sensor that is based on the use of a film of TiO2 nanoparticles faceted predominantly at the 101 and 001 sides. The hydrazine (Hyd)...     

Preparation of a nanoporous CaCO3-coated TiO2 electrode and its application to a dye-sensitized solar cell

A nanoporous CaCO3 overlayer-coated TiO2 thick film was prepared by the topotactic thermal decomposition of Ca(OH)2, and its performance as an electrode of a dye-sensitized solar cell was investigated. As compared to bare TiO2, nanoporous CaCO3-coated TiO2 provided higher specific surface area and, subsequently, a larger amount of dye adsorption; this in turn increased short-circuit current (Jsc). Furthermore, the CaCO3 coating demonstrated increased impedance at the TiO2/dye/electrolyte interface and increased the lifetime of the photoelectrons, indicating the improved retardation of the back electron transfer, which increases Jsc, open-circuit voltage (Voc), and fill factor (ff). Thereby, the energy conversion efficiency (eta) of the solar cell improved from 7.8 to 9.7% (an improvement of 24.4%) as the nanoporous CaCO3 layer was coated onto TiO2 thick films.     

Effect of organic passivation on photoinduced electron transfer across the quantum dot/TiO2 interface

We report a study of the internal quantum efficiency (IQE) of CdSe quantum-dot (QD)-sensitized solar cells prepared by direct adsorption of pre-synthesized QDs, passivated with either tri-n-octylphosphine oxide (TOPO) or n-butylamine (BA), onto a nanocrystalline TiO(2) film.     

Photocatalytic single electron transfer reactions on TiO2 semiconductor

The use of inorganic semiconductor particles such as titanium dioxide(TiO_2) has received relatively less attention in organic chemistry, although semiconductor particles have been widely used as a single electron transfer photocatalyst in waterpurification, air-cleaning, and self-cleaning. In recent years, the photocatalysis on semiconductor particles has become an active area of research even in organic chemistry, since the heterogeneous semiconductor photocatalysis leads to the unique redox organic reactions. In an early stage, the semiconductor photocatalysis was applied to the oxidation of organic molecules.Semiconductor particles have also the potential to induce the reductive chemical transformations in the absence of oxygen(O_2),by using the suitable sacrificial hole scavenger. In this review, we summarize the representative examples of the reductive and oxidative organic reactions using semiconductor particles and the recent applications to the stereoselective reactions.     

导电高聚物修饰纳米尺度TiO~2多孔膜电极的光电化学研究

用光电化学方法研究了用导电高聚物修饰的纳米晶TiO~2多孔膜电极在不含氧化还原对和含不同氧化还原对体系电解质溶液中的光电转换过程。TiO~2/导电高聚物多孔膜电极为双层n型半导体结构,内层TiO~2多孔膜的禁带宽度为3.26eV,外层聚吡咯(PPy)膜的禁带宽度为2.23eV,而聚苯胺(PAn)膜的禁带宽度为2.88eV。用导电高聚物修饰半导体电极能使其在可见光区的光吸收增加,光电流增强,且起始波长红移至>600nm,使宽禁带半导体电极的光电转换效率得到明显改善。     

Preparation of nanoporous MgO-coated TiO2 nanoparticles and their application to the electrode of dye-sensitized solar cells

Sol-gel-derived Mg(OH)(2) gel was coated onto TiO(2) nanoparticles, and the subsequent thermal topotactic decomposition of the gel formed a highly nanoporous MgO crystalline coating. The specific surface area of the electrode that was prepared from the core-shell-structured TiO(2) nanoparticles significantly increased compared with that of the uncoated TiO(2) electrode. The increase in the specific surface area of the MgO-coated TiO(2) electrode was attributed to the highly nanoporous MgO coating layer that resulted from the topotactic reaction. Dye adsorption behavior and solar cell performance were significantly enhanced by employing the MgO-coated TiO(2) electrode. Optimized coating of a MgO layer on TiO(2) nanoparticles enhanced the energy conversion efficiency as much as 45% compared to that of the uncoated TiO(2) electrode. This indicates that controlling the extrinsic parameters such as the specific surface area is very important to improve the energy conversion efficiency of TiO(2)-based solar cells.     

Electrochemical studies of novel chitosan/TiO2 bioactive electrode for biosensing application

Bioactive electrode of uniformly dispersed TiO₂ in Chitoan (CS) was fabricated on ITO substrate for immobilization of horseradish peroxidase (HRP). Enhanced surface porosity and decrease in relative proportion of carbonyl functionality of CS in CS/TiO₂ matrix was observed. Current voltage characteristic of CS/TiO₂ matrix was enhanced by a factor of four possibly due to covalent and hydrogen binding of Ti atoms with hydroxyl and amino groups of CS. The immobilization of HRP on CS/TiO₂ had increased resistance for charge transfer. This is possibly due to strongly binding of HRP with CS/TiO₂ matrix and controlling transport of the ions of the supporting electrolyte.     

Absorption spectra related to heterogeneous electron transfer reactions: the perylene TiO2 system

Linear absorption spectra of dye-semiconductor systems (perylene attached to nanostructured TiO2) are studied theoretically and experimentally. The systems show ultrafast photoinduced heterogeneous electron transfer (HET). By applying a time-dependent formulation of the absorbance, the theoretical analysis of the measured data is carried out. The respective electron-vibrational wave packet propagation fully accounts for the electronic coupling to the conduction band continuum of TiO2 and is based on a single-reaction-coordinate model (corresponding to a perylene in-plane C-C stretching vibration with a quantum energy of 1370 cm(-1)). By the insertion of different bridge-anchor groups, the electronic coupling responsible for HET is varied. The dye absorbance in a solvent and the trends in the line broadening of the vibrational progression due to the coupling to the conduction band continuum are reproduced for all investigated types of bridge-anchor groups. HET rates deduced from the calculations on the absorbance displaying line broadenings follow the qualitative trend obtained from transient absorption spectra.     

Double-layer coating of SrCO3/TiO2 on nanoporous TiO2 for efficient dye-sensitized solar cells

Surface modification plays a crucial role in improving the efficiency of dye-sensitized solar cells (DSSCs), but the reported surface treatments are in general superior to the untreated TiO(2) but inferior to the typical TiCl(4)-treated TiO(2) in terms of solar cell performance. This work demonstrates a two-step treatment of the nanoporous titania surface with strontium acetate [Sr(OAc)(2)] and TiCl(4) in order, each step followed by sintering. An electronically insulating layer of SrCO(3) is formed on the TiO(2) surface via the Sr(OAc)(2) treatment and then a fresh TiO(2) layer is deposited on top of the SrCO(3) layer via the TiCl(4) treatment, corresponding to a double layer of Sr(OAc)(2)/TiO(2) coated on the TiO(2) surface. As compared to the typical TiCl(4)-treated DSSC, the Sr(OAc)(2)-TiCl(4) treated DSSC improves short-circuit photocurrent (J(sc)) by 17%, open-circuit photovoltage (V(oc)) by 2%, and power conversion efficiency by 20%. These results indicate that the Sr(OAc)(2)-TiCl(4) treatment is better than the often used TiCl(4) treatment for fabrication of efficient DSSCs. Charge density at open circuit and controlled intensity modulated photocurrent/photovoltage spectroscopy reveal that the two electrodes show almost same conduction band level but different electron diffusion coefficient and charge recombination rate constant. Owing to the blocking effect of the SrCO(3) layer on electron recombination with I(3)(-) ions, the charge recombination rate constant of the Sr(OAc)(2)-TiCl(4) treated DSSC is half that of the TiCl(4)-treated DSSC, accounting well for the difference of their V(oc). The improved J(sc) is also attributed to the middle SrCO(3) layer, which increases dye adsorption and may improve charge separation efficiency due to the blocking effect of SrCO(3) on charge recombination.     

Multistep electron transfer processes on dye co-sensitized nanocrystalline TiO2 films

We report a method for achieving multilayer co-sensitization of nanocrystalline TiO2 films. The method is based upon an aluminum isopropoxide treatment of the monosensitized film prior to deposition of a second sensitizer. Appropriate selection of sensitizer dyes allows vectorial, multistep, electron transfer processes, resulting in a suppression of interfacial charge recombination and a significantly improved photovoltaic device performance relative to single-layer co-sensitization devices.     

Solvent isotope effects on interfacial protein electron transfer in crystals and electrode films

D(2)O-grown crystals of yeast zinc porphyrin substituted cytochrome c peroxidase (ZnCcP) in complex with yeast iso-1-cytochrome c (yCc) diffract to higher resolution (1.7 A) and pack differently than H(2)O-grown crystals (2.4-3.0 A). Two ZnCcP's bind the same yCc (porphyrin-to-porphyrin separations of 19 and 29 A), with one ZnCcP interacting through the same interface found in the H(2)O crystals. The triplet excited-state of at least one of the two unique ZnCcP's is quenched by electron transfer (ET) to Fe(III)yCc (k(e) = 220 s(-1)). Measurement of thermal recombination ET between Fe(II)yCc and ZnCcP+ in the D(2)O-treated crystals has both slow and fast components that differ by 2 orders of magnitude (k(eb)(1) = 2200 s(-1), k(eb)(2) = 30 s(-1)). Back ET in H(2)O-grown crystals is too fast for observation, but soaking H(2)O-grown crystals in D(2)O for hours generates slower back ET, with kinetics similar to those of the D(2)O-grown crystals (k(eb)(1) = 7000 s(-1), k(eb)(2) = 100 s(-1)). Protein-film voltammetry of yCc adsorbed to mixed alkanethiol monolayers on gold electrodes shows slower ET for D(2)O-grown yCc films than for H(2)O-grown films (k(H) = 800 s(-1); k(D) = 540 s(-1) at 20 degrees C). Soaking H(2)O- or D(2)O-grown films in the counter solvent produces an immediate inverse isotope effect that diminishes over hours until the ET rate reaches that found in the counter solvent. Thus, D(2)O substitution perturbs interactions and ET between yCc and either CcP or electrode films. The effects derive from slow exchanging protons or solvent molecules that in the crystal produce only small structural changes.     

Site-dependent electron-stimulated reactions in water films on TiO2(110)

Electron-stimulated reactions in thin [<3 ML (monolayer)] water films adsorbed on TiO(2)(110) are investigated. Irradiation with 100 eV electrons results in electron-stimulated dissociation and electron-stimulated desorption (ESD) of adsorbed water molecules. The molecular water ESD yield increases linearly with water coverage theta for 0< or =theta< or =1 ML and 11 ML, the water ESD yield per additional water molecule adsorbed (i.e., the slope of the ESD yield versus coverage) is 3.5 times larger than for theta<1 ML. In contrast, the number of water molecules dissociated per incident electron increases linearly for theta< or =2 ML without changing slope at theta=1 ML. The total electron-stimulated sputtering rate, as measured by postirradiation temperature programmed desorption of the remaining water, is larger for theta>1 ML due to the increased water ESD for those coverages. The water ESD yields versus electron energy (for 5-50 eV) are qualitatively similar for 1, 2, and 40 ML water films. In each case, the observed ESD threshold is at approximately 10 eV and the yield increases monotonically with increasing electron energy. The results indicate that excitations in the adsorbed water layer are primarily responsible for the ESD in thin water films on TiO(2)(110). Experiments on "isotopically layered" films with D(2)O adsorbed on the Ti(4+) sites (D(2)O(Ti)) and H(2)O adsorbed on the bridging oxygen atoms (H(2)O(BBO)) demonstrate that increasing the water coverage above 1 ML rapidly suppresses the electron-stimulated desorption of D(2)O(Ti) and D atoms, despite the fact that the total water ESD and atomic hydrogen ESD yields increase with increasing coverage. The coverage dependence of the electron-stimulated reactions is probably related to the different bonding geometries for H(2)O(Ti) and H(2)O(BBO) and its influence on the desorption probability of the reaction products.     

Highly selective and sensitive fluorescent turn-on chemosensor for Al3+ based on a novel photoinduced electron transfer approach

A photoinduced electron transfer (PET)-based chemosensor possessing dual PET processes by simultaneously introducing both nitrogen and sulfur donors was achieved. The fluorescence signal of the free chemosensor is in a normal-off state due to the sulfur donor being insensitive to environmental pH stimuli. As a result, the device can be used over a wide pH span of 3-11. Upon binding Al(3+), a significant fluorescence enhancement with a turn-on ratio over 110-fold was triggered by the inhibition of PET processes from both the sulfur and the nitrogen donors to the fluorophore.     

Protein dynamics studies on a wheat type 2 lipid transfer protein

Plant non specific lipid transfer proteins form a superfamily of related proteins composed of type 1 and type 2 LTPs. Type 2 LTPs have been less extensively studied than type 1 and differ in term of primary sequence, molecular mass and transfer efficiency. We have undertaken NMR studies of the wheat 7 kDa type 2 LTP. Whilst the 3D structure determination is in progress, we have studied the protein dynamics. Two zones have been defined within the protein. One remains unperturbed, the LTP being liganded or not; the other one exists in different states, depending on the ligandation, and on the kind of lipid interacting with the protein. S² determination showed a rigid backbone. Multifield analysis allowed the calculation of the chemical exchange rate for each residue.     

纳米尺度TiO2聚苯胺多孔膜电极光电化学研究

用光电流作用谱，光电流－电势图等光电化学方法研究了ＴｉＯ２／聚本胺复合多孔膜电极在不含氧化还原和含有没氧化还原对体系中的光电转换过程。结果说明，ＴｉＯ２／聚苯胺复合多孔膜电极为双层ｍ－型半导体结构，ＴｉＯ２多孔膜的禁带宽度为３．２ｅＶ，外层聚苯胺膜的禁带宽度为２．８８ｅＶ。     

H2 adsorption on Fe/ZSM-5 zeolite: a theoretical approach

The hydrogen reduction of the red-ox Fe/ZSM-5 zeolite is an essential step for catalyst preparation. In this letter, various adsorption modes of the H(2) molecules on the Fe(III)/ZSM-5 zeolite were first explored by density functional theory, with their exact configurations provided. The adsorption energies revealed that the two configurations with Fe(III) at the sextet states are the main ones, consistent with the results of inelastic neutron scattering (INS) experiments. On such basis, the vibrational and orbital analyses were made, which will be valuable for the future studies on the Fe/ZSM-5 systems.