High-performance yellow ceramic pigments Zr(Ti1-x-ySnx-yVyMy)O4 (M = Al, In, Y): crystal structure, colouring mechanism and technological properties

Zirconium titanate-stannate doped with V with co-dopants Al, In or Y was synthesised by solid state reaction and its structural (XRD, SEM), optical (DRS) and technological properties were determined to assess its potential use as ceramic pigment. These compounds have a srilankite-type, disordered orthorhombic structure, implying a random distribution of Zr, Ti, Sn and dopants in a single, strongly distorted octahedral site. Doping caused an increase of unit-cell dimensions, metal-oxygen distances and octahedron distortion. Optical spectra show crystal field electronic transitions of V4+ as well as intense bands in the blue-UV range due to V4+-V5+ intervalence charge transfer and/or to V-O charge transfer. The formation of oxygen vacancies is supposed to compensate the occurrence of V4+ ensuring the lattice charge neutrality. These srilankite-type oxides develop a deep and brilliant yellow shade with colourimetric parameters close to those of industrial ceramic pigments. Technological tests in several ceramic applications proved that zirconium titanate-stannate is very stable at high temperature, exhibiting an excellent performance in the 1200-1250?C range, even better than praseodymium-doped zircon

Heterocoagulation-spray drying process for the inclusion of ceramic pigments

The improvement of the physico-chemical resistance of hematite pigment in ceramic bodies has been pursued through its inclusion into a transparent and refractory matrix of silica or zirconia. The inclusion process was accomplished by heterocoagulation followed by spray-drying. The heterocoagulation process was optimised through an electrokinetic technique, that measured the potential of both matrix and pigment as a function of pH and of different amounts of dispersing agents. Suspensions of pigment and matrix were designed in order to achieve the maximum surface charges. The heterocoagulated mix was then spray-dried in order to avoid any separated coagulation of pigment and matrix and to obtain a well granulated powder suitable for application in ceramic bodies. A stable red-coloured ceramic pigment for low firing applications was obtained starting from amorphous silica as matrix and hematite as colorant

Novel Preparation Method of TiO2-Nanorod-Based Photoelectrodes for Dye-Sensitized Solar Cells with Improved Light-Harvesting Efficiency

We present a novel, facile, and cost-effective method to prepare highly transparent mesoporous films made by anatase TiO2 nanorods that have been synthesized by a single-step solvothermal process. Such nanorods have been conveniently used as prepared-without completely removing the residual organics-to obtain suitable screen-printable paste by means of the use of proper polymeric binders. This method has been successfully implemented to fabricate highly efficient nanorod-based photoelectrodes for dye-sensitized solar cells. They showed an increment of the overall quantum conversion efficiency comprised between 34% and 58% with respect to cells based oil commercial P25 titanium dioxide nanoparticles. In particular, a maximum photocurrent density and solar conversion efficiency of 16.9 mA/cm(2) and 7.9% have been obtained, respectively

NOVEL FLUORINATED METAL COMPLEXES

The present invention relates to novel fluorinated metal complexes effective as charge transfer photosensitizers, with utility as components of dye-sensitized solar cells (DSSC) and similar devices

Evaluation of N719 amount in TiO2 films for DSSC by thermogravimetric analysis

The aim of this work is to evaluate the amount of N719 dye in TiO2 films for DSSCs by thermogravimetric analysis coupled with mass spectrometry (TG-MS) in comparison with the traditional method based on the dye extraction in NaOH solutions. The characterization was carried out on TiO2 films applied on FTO glasses by automatic screen printing method. For all the samples, TG-MS showed three well defined steps. The first, below 100 °C and coupled to an endothermic signal was due to water release. From 200 to about 300 °C, there was the release of CO2 coming from decarboxylation reaction of N719. The last exothermic step was due to the combustion of organic residues. As the decarboxylation reaction occurs with release of 4 moles of CO2 per mole of N719, it was used to determine the dye loading of the samples that resulted in the range 7−15 wt% well agreeing the relevant content of dye obtained by desorption with NaOH

Fluorinated imidazolium salts having liquid crystal characteristics

A family of fluorinated imidazolium salts showing liquid–crystalline properties in a wide temperature range was developed. These fluorinated ionic liquid crystals, due to their intrinsic hydrophobicity, high thermal stability and good conductivity, are suitable candidates to be used as electrolytes in electrochemical devices such as Dye Sensitized Solar Cell (DSSC) or lithium batteries

Limited crystallite growth upon isothermal annealing of nanocrystalline anatase

The crystalline growth kinetics during isothermal sintering of two nanotitania powders synthesized by similar routes, but with and without the presence of chlorine in the synthesis batch, were studied by X-ray powder diffraction and modeled by several grain growth models. Both nanopowders contained anatase as the initial titania phase with similar crystallite dimension. Crystal growth curves at three isotherms per sample were sampled over a period of time up to 40 h. Temperature steps within different ranges (375, 425, and 475 °C for Cl-free sample; 500, 550, and 600 °C for Cl-containing sample) were chosen. The XRD analysis of samples heated at 900 °C revealed that, while the entire Cl-free sample was converted to rutile, only 10% of the Cl-containing sample had transformed to rutile with a very limited crystal growth. Direct comparison of the crystal growth curves showed different behavior which was modeled by different grain growth kinetic equations including a growth limiting factor. Although the generalized parabolic grain growth model with time exponent (so-called “Hofler-Averback equation” ) provided good fi ts for both the Cl-free and Cl-containing nanopowders at all temperatures, only the isothermal curve at 500 °C of the Cl-containing sample was satisfactorily fitted with a modified KJMA equation. The activation energy values of the grain growth are very similar and in line with the previously reported values. We conclude that the crystal size locking phenomenon observed for Cl-bearing anatase can be ascribed to the effects of chlorine ions adsorbed on grain surface as previously suggested. The blocked crystal growth of nanoanatase obtained by the reflux synthesis of organic solvents in the presence of hydrochloric acid as catalyst makes this material very appealing for devices that require a given nanosize and for the anatase phase in spite of the high temperature processing

DSSC anode: tailoring crystal shape/phase stability of anatase nanopowders and their use in paste formulation

Among these, anatase nano-rods are used as photo-anode in the Dye Sensitized Solar Cells (DSSC) which have been demonstrated to be a promising, cost-effective alternative to conventional solid semiconducting solar cells for production of electrical energy [2]. Parameters such as shape, size and phase type of titania nanocrystals, that can be optimized recurring to different synthesis methods [3], influence the surface area of the nanoTiO2 and therefore the amount of sensitizing dye absorbed [4,5] that is strictly connected to the DSSC performance. Anyhow, despite the large number of studies on the anatase-to-rutile transformation (A-R) [6] and ab-initio calculations of the effects of crystal shape on anatase stability relative to rutile [7] the role of nanoparticle shape in DSSC are still to be clarified. The present study reports the synthesis of shape- and size-controlled anatase nanorods, their characterization as a function of thermal treatment and their use for preparation of a photo-anode paste. Anatase nanorods (Figure 1) were synthesized by a procedure encompassing hydrolysis of a TiO2 precursor, dispersion in high boiling organic solvent and suitable workup. By only changing the hydrolysis of titanium dioxide precursor, anatase nanorods with two different aspect ratios were obtained. These samples were then subjected to stepwise heating in the range form RT to 1000°C, and the variation of crystal shape, size and titania phase were monitored by powder X-ray diffraction and Rietveld refinements. A paste was made starting from a sample of anatase powder (labeled “SF”) having a surface area higher than the commercial nanotitania products (e.g. Degussa P25®). Each paste was prepared with an amount of TiO2 content of about 10-20% wt/wt. The starting raw material was obtained from a nanosuspension washed with a controlled pH value aqueous solution dried by spray drying. The powder was then mixed with a solvent (terpineol), a co-solvent (2-ethyl-1-hexanol), a binder and a dispersant, under mechanical stirring at room temperature. Such a prepared material was further added with ethanol and mixed for a time needed to ensure the best homogeneity. The paste so obtained was then dried under vacuum to eliminate the low boiling solvents. A strong milling of the paste by a three roll mill (EXAKT) was performed to ensure the grip of the TiO2 thick layer to the conductive glass (FTO) even after heat treatment in the sintering furnace. The adhesion of the fired paste to the support glass was checked by scanning electron microscopy. The paste applied in DSSC devices has been irradiated with solar lamp to allow the calculation of current values of the closed circuit. The values compared with paste made with the commercial nanotitania powder, show an improvement from 20% to 50% in terms of photo-current generated by the cell. Reference: [1] U. Diebold, Surface Science Reports, 2003, 48, 53-229. [2] B. O’Regan, M. Grätzel, Nature, 1991, 353, 737. [3] M. Fernandez-Garcıa, X. Wang, C. Belver, J.C. Hanson, J.A. Rodriguez, J. Phys. Chem. C, 2007, 111, 674-682. [4] Md. K. Nazeeruddin, S. M. Zakeeruddin, R. Humphry-Baker, M. Jirousek, P. Liska, N. Vlachopoulos, V. Shklover, C.-H. Fischer, and M. Grätzel, Inorg. Chem, 1999, 38, 6298-6305. [5] S. Ito, P. Chen, P. Comte, M. K. Nazeeruddin, P. Liska, P. Péchy, and M. Grätzel, Progress in Photovoltaics, 2007, 15, 603- 612. [6] H. Zhang, J.F. Banfield, Chem. Mater., 2005, 17, 3421-3425. [7] A. S. Barnard, L. A. Curtiss, NanoLetters, 2005, 5, 1261-126