David Havlíček

Sol-gel titanium dioxide blocking layers for dye-sensitized solar cells: electrochemical characterization.

Compact, thin TiO2 films are grown on F-doped SnO2 (FTO) by dip-coating from precursor solutions containing poly(hexafluorobutyl methacrylate) or hexafluorobutyl methacrylate as the structure-directing agents. The films are quasi-amorphous, but crystallize to TiO2 (anatase) upon heat treatment at 500 °C in air. Cyclic voltammetry experiments performed using Fe(CN)6(3-/4-) or spiro-OMeTAD as model redox probes selectively indicate the pinholes, if any, in the layer. The pinhole-free films on FTO represent an excellent rectifying interface at which no anodic faradaic reactions occur in the depletion state. The flat-band potentials of the as-grown films are upshifted by 0.2-0.4 V against the values predicted for a perfect anatase single-crystal surface, but they still follow the Nernstian pH dependence. The optimized buffer layer is characterized by a combination of quasi-amorphous morphology (which is responsible for the blocking function) and calcination-induced crystallinity (which leads to fast electron injection and electron transport in the conduction band). The latter manifests itself by a reversible charging of the chemical capacitance of TiO2 in its accumulation state. The capacitive-charging capability and pinhole formation significantly depend on the post-deposition heat treatment.

The chemical and mineralogical composition of the water-soluble fraction of power-plant ash and its effect on the process of crystallization of water

The content of the water-soluble fraction of power-plant fly ash from nine power plants burning brown and black coal varied in the range 0.43–1.34%. It was found, on the basis of chemical analysis and X-ray diffraction measurements, that the soluble fraction consists mostly of anhydrous CaSO4, 3MgSO4.CaSO4, Na2Ca(SO4)2 and other double sulphates. The sample from one power plant burning black coal also contained CaCO3, CaO and K2CO3. The nucleation activity of the original ash sample, the ash without the water-soluble fraction and the separated fraction was found by the methods of nucleation deposition and the freezing of water drops. These measurements demonstrated that the soluble components, which, by themselves, exhibit low nucleation activity, considerably increase the nucleation activity of the ash when associated with the ash particles.

Content of quartz and mullite in some selected power-plant fly ash in Czechoslovakia

Abstract This study was performed primarily to account for the differences between ice forming activity of fly ashes from different sources. Ten samples of fly ash from ten various power plants on our territory were examined by X-ray powder diffraction to determine the contents of quartz, mullite and hematite. The quartz content varied in the range 5–17% depending on the type of coal and mullite contents varied from 0 to 22%. The amounts of crystalline phases were compared with data about composition of ashes obtained by elemental chemical analysis. The distribution of silica and aluminia between crystalline phases and amorphous phase is discussed in connection with the origin of fly ash and with the differences observed in the ice forming activity. A direct relationship between the freezing temperatures and the contents of crystalline fractions in the samples does not exist but the presence of mullite and/or hematite in the concentrations found in samples could account for the observed freezing temperatures of droplets containing some of the samples.

A mixture of nitrogen dioxide and oxygen as a Lux acid in nitrate melts

Abstract The effect of an NO2+O2 gaseous mixture on a melt of sodium and potassium nitrates and the acid-base reactions of this mixture with some Lux bases were studied, measuring the potential of an oxygen electrode at a temperature of 260°C. It has been found that the NO2+O2 mixture acts as a Lux acid conjugated with NO−3 anion as the base, even under the atmospheric pressure. The strengths of the NO2 +O2 acid and the NO−3 base related to other studied conjugated acids and bases were qualitatively estimated from the shape of potentiometric curves of the acid—base reactions.

Synthesis and characterization of metallo-supramolecular polymers from thiophene-based unimers bearing pybox ligands

A series of novel metallo-supramolecular polymers was successfully prepared, based on 2,6-bis(2-oxazolinyl)pyridine building blocks consisting of pyridine flanked by two oxazoline rings as a tridentate binding site bridged with thiophene, bithiophene and thienothiophene as a linker, beginning from a cheap and commercially available 1,4-dihydro-4-oxo-2,6-pyridinedicarboxylic (chelidamic) acid. Metallo-supramolecular polymers were obtained and spectroscopically characterized upon treatment of the synthesized building blocks, also known as unimers, with the following metal ions: Fe2+, Zn2+, Ni2+, Cu2+. During the self-assembly process of the prepared unimers with a Cu2+ ion coupler, UV/vis investigation showed the highest shift of absorption maxima to lower energies, contrary to the Fe2+ ion couplers where the lowest value of shift was detected, compared to the free unimer. Upon the complexation of the Fe2+ ion coupler with selected unimers, the appearance was observed of new absorption bands around 600 nm ascribable to metal-to-ligand charge-transfer transitions. The luminescence study of the complexation of the synthesized unimers with Zn2+ exhibited a high fluorescence increase with an increase of metal ion concentration. Adversely, all of the other metals only showed fluorescence quenching.

Preparation of quaternary pyridinium salts as possible proton conductors

On basis of earlier experimental experience, the transfer of protons in salts of the organic cation-inorganic anion type occurs primarily through directional arrangement of the anion-anion type short hydrogen bonds. The submitted work presents the preparation of quaternary pyridinium salts of inorganic hydrogen anions in the absence of solvent molecules in their crystal structure. These substances can form only the above-described anion-anion type hydrogen bonds; in addition, the absence of solvate anions increases the stability of the prepared compounds. A total of six substituted pyridinium salts were prepared, four of which have not been described yet: 1,2,4,6-tetraphenylpyridinium perchlorate, 1-benzyl-2,4,6-trimethylpyridinium perchlorate, 1,4-dimethylpyridinium hydrogen sulphate, 1,4-dimethylpyridinium dihydrogen phosphate, 1,4-dimethylpyridinium hydrogen sulphate, and 1,2-dimethyl-5-ethylpyridinium dihydrogen phosphate. Three of these substances were characterised by X-ray structural analysis: 1,2,4,6-tetraphenylpyridinium perchlorate crystallises in the orthorhombic system, space group Pbca; 1-benzyl-2,4,6-trimethylpyridinium perchlorate crystallises in the monoclinic system, space group P21/c; and 1,4-dimethylpyridinium dihydrogen phosphate crystallises in the monoclinic system, space group C2/c. This structure contains an oriented anion network bond by short anion-anion type hydrogen bonds with the donor acceptor lengths of 2.567(3) Å and 2.557(3) Å and thus fulfils the requirements of a good proton conductor.

The acid-base reactions of mixtures of nitrogen dioxide and oxygen with polyacid lux bases

Abstract The dissolution of lux bases and acids and the acid-base reactions of solutions of polyacidic bases with a gaseous mixture of NO 2 + O 2 acting as a lux acid were studied by measuring the potential of an oxygen electrode at a temperature of 260°C. The strength of the conjugate pairs of acids and bases was compared qualitatively with respect to the nitrate system using the shapes of the potentiometric curves for the acid-base reactions. Some effects that were found for the first time on poteniometric curves were explained on the basis of theoretical treatment of acid-base reactions in systems where the poorly soluble acid is precipitated from the melt.

Calculation of the solubility curves in ternary salt systems with compound formation

Abstract A new method for the calculation of solubility curves in solubility diagrams of ternary salt systems with compound formation is described. The method is based on the assumption that every physico-chemical process (the formation of a solid phase, formation of complex species in solution) in a given system is characterized by an interaction constant value. The relative magnitudes of these constants determine the type and shape of the diagram. The derivation does not include any empirical or adjustable parameters. The work also contains an explanation for the incongruent solubility of compounds with salt character. The conclusion contains extensive comparison of experimental data with the theoretical results.