Pavel Dytrych

Ultrathin functional films of titanium(IV) oxide

Chemistry and physics of thin semiconducting layers of various types are subjects of intense research. Especially when nanotechnology methods such as self-assembly are involved, amazing structural and/or functional properties may appear. Also modern physical methods using variously organized plasma arrangements are able to produce uniform structures with distinctive functionality. In this review, based virtually on our own work, discussions on the preparation, structure, morphology, and function of titanium(IV) oxide nanoscopic thin films are presented. It was shown that structurally and functionally similar titanium(IV) oxide films can be prepared via completely different preparation techniques. Function tests were arranged as “primary”, covering the assessment of the light induced charge separation efficiency, and “secondary”, based on photocatalytic surface oxidations.

Theoretical interpretation of the role of the ionic liquid phase in the (R)-Ru-BINAP catalyzed hydrogenation of methylacetoacetate

Recently, the work focusing on the role of alkyl chain length in the N[R,222][Tf2N] ionic liquids and its reflection in the kinetic parameters of stereoselective hydrogenation of methylacetoacetate over (R)-[RuCl(binap)(p-cymene)]Cl complex was reported. Irregular trends in the principle parameter of enantioselectivity were observed. Here, a possible theoretical explanation of such irregular trends elucidated with the help of molecular simulations methods is presented. A stepwise approach is proposed for evaluating the energetically most stable conformers of a series of individual N[R,222][Tf2N] for the interpretation of selectivity-structure effects observed experimentally. Initially, Monte Carlo molecular mechanics was used followed by a semi-empirical PM3 method to elucidate also the characteristic thermodynamic functions of state and theoretical molecular spectra. The density functional theory was finally applied. The specific absolute entropy data revealed that due to the partition of the cation and anion twisted closer approach the ionic liquids N[8,222][Tf2N] and N[12,222][Tf2N] may stabilize the structures of the (R)-[RuCl(binap)(p-cymene)]Cl complex.

Interactions of the (R) Ru-BINAP catalytic complex with an inorganic matrix in stereoselective hydrogenation of methylacetoacetate: kinetic, XPS and DRIFT studies

Stereoselective hydrogenation of methyl acetoacetate to optical isomers of methyl-3-hydroxybutanoate over various forms of supported [RuCl((R)-BINAP)(p-cymene)]Cl is reported. The catalysts were prepared via two alternative methods: direct immobilization, and surface anchorage with heteropolyacids. The kinetic data (rate constants, optical yields, overall selectivity to methyl-3-hydroxybutanoate) were discussed and interpreted with help of XPS and DRIFT to assess bonding surface interactions. In all cases montmorillonite as a model support was employed. It was shown that the stereoselective course was dependent on the mode of [RuCl((R)-BINAP)(p-cymene)]Cl immobilization. The procedure based on the commonly used impregnation did not provide a catalyst with a stable anchorage of the active complex. Strong surface anchorage was found for a catalystproduced with help of H4SiMo12O40 heteropolyacid, but due to structural changes upon the reaction the catalyst performance in the reaction was poor. When H3PW12O40 was employed, the immobilization provided a catalyst with a very good performance. The two-step immobilization via the dimer [RuCl2(p-cymene)]2 instead of the one-step with [RuCl((R)-BINAP)(p-cymene)]Cl yielded a catalyst with the performance parameters comparable to the homogeneous experiments with [RuCl((R)-BINAP)(p-cymene)]Cl dissolved in the reaction mixture. It was due to breaking up the original dimer structure and accomplishing the surface interaction through the adsorbed monomeric units.

The influence of rutile particles on photo-induced activity of the sol–gel TiO2/ITO photo-anode

The rutile effect on structural and photo-electrochemical properties and photo-induced activity were studied. Thin TiO2 layers were prepared by the sol–gel method using a reverse micelles system as a molecular template and deposited on the conductive ITO substrate by a dip-coating technique. Pure anatase or mixed anatase/rutile phase were obtained during the calcination step as a result of the selected temperature. The crystallographic structure was determined by Raman spectroscopy and XRD analysis. The positive influence of the presence of rutile particles in the thin layer on the photo-induced properties was verified. It was found that the mixed crystallographic phase of anatase and rutile can exhibit much higher photo-induced activity than pure anatase or the pure rutile form. The reason for this is that the excited electrons can easily transfer from the anatase surface states to rutile as well as from the anatase conduction band to rutile, which improves the electron-transfer rate. The electron transport between connected anatase and rutile particles can support the photo-excited charge separation and thus reduce the recombination rate.

Elimination of dissolved Fe3+ ions from water by electrocoagulation

AbstractElectrocoagulation (EC) was applied for elimination of dissolved Fe3+ ions from model contaminated water. Electrochemical experiments were performed using a coagulation set-up with the volume of storage tank of 50 L. To represent inorganic contamination, FeCl3·6H2O was chosen as a model pollutant; its concentration was equal to 50 mg/L. Experiments were carried out by circulating model effluent (1 pass) through the cell at a flow rate (40 L/h) whilst operating the power supply in galvanostatic mode. Dosing concentration was varying by changing the input current between set points and holding for sufficient time for steady state to be reached and for a sample to be collected. The process using the steel electrode reached removal efficiency up to 99%, depending on pH, and proved to be very suitable for elimination of dissolved Fe3+ ions from water. However, electrochemical experiments using the aluminum electrode reached removal efficiency only up to 25%. The different efficiency of two anodes is probably due to lower adsorption capacity of hydrous aluminum oxide for iron ions in comparison to hydrous ferric oxides. Produced nanostructured flocs were subsequently filtered, dried, and characterized by N2 physisorption, X-ray photoelectron spectroscopy, and scanning electron microscopy. Obtained characteristics synchronously demonstrate different tendencies of Al and Fe nanostructured flocs.

The role of titania layers in decomposition of endocrine disruptors under UV Light

AbstractDegradation of three different endocrine disruptors (EDs) was thoroughly studied on prepared durable thin layers of titanium dioxide with an anatase crystalline structure. Specially constructed laboratory reactors bringing information on all individual processes (photolysis, photocatalysis, sorption) involved in decomposition of the studied EDs (17α-ethynylestradiol, bisphenol A and 4-nonylphenol) were applied. It was found that photolytic removal of EDs is the fastest degradation process; nevertheless, this method may be less effective regarding all indicators including toxicity. It was verified that individual degradation processes (photolysis and photocatalysis) showed a significantly different influence on toxicity of resulting solutions. During the photolytic process, EDs degradation caused increasing toxicity contrary to the photocatalytic process. Obtained results were corroborated by a mathematical model, which showed that a limitation step for photocatalysis is a sorption and for photolysis a toxicity of resulting products.