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The direct in-situ stabilization of an anatase-based nanocrystalline photocatalyst (Degussa P25) was obtained by sintering the catalyst powder in presence of Zr 4+ organic salts. This approach allows the doping of an already-formed nanocrystalline photocatalyst instead of introducing the dopant in the crystal lattice during the catalyst synthesis. The procedure was demonstrated by the production of thick ceramic layers using the screen printing technique. This new method allows to easily stabilize the anatase phase 200 °C higher than the undoped P25 maintaining the same photocatalytic activity. The process was studied using specifically formulated screen-printing inks added with Zr 4+ organic salt at 1% and 2% Zr/Ti molar ratio. The anatase phase stability was investigated in the 500–900 °C temperature range analysing the resulting catalysts with XRD, TEM and (S)TEM-EDS. The catalytic activity of the screen-printed layers was assessed by measuring the degradation of toluene in air at ambient concentration (500 nmol m −3 ) and low UV-A irradiance (180 μW cm −2 ). The described in-situ stabilization method could be potentially applied to any deposition process involving already formed anatase photocatalyst, allowing higher sintering temperature and then an improved mechanical stability of the active layers without photocatalytic activity degradation. [ABSTRACT FROM AUTHOR]

Abstract: Screen-printed titania photocatalytic layers made from Degussa P25 were studied in order to assess the potential of this deposition technology for the production of catalytic surfaces for airborne pollutant degradation. The deposited catalytic TiO2 layers were characterized by a low density (about 25% of the titania bulk crystal) typical of very porous films. The study was carried out using toluene at low concentration (12ppb) as model pollutant and with a low UV-A irradiance level on the sample surface (200μWcm−2). The catalyst layers were deposited on alumina and quartz substrates demonstrating a good catalytic depollution activity. The relationship between the layer thickness and the catalytic activity was studied in the 1 to 6.8μm range indicating an optimal 3–4μm film thickness. Thicker layers do not show significant increases in the catalytic activity. The optical transmittance was studied using quartz substrate samples, showing a severely reduced photon flux for layers deeper than 5μm. The effect of post-printing thermal treatment was studied in the 500–900°C range, demonstrating good catalytic activity for processing temperatures≤700°C. These results indicate that the screen-printing process can be a promising technology for the realization of high efficiency photocatalytic materials for air depollution applications at low UV-A irradiance. [Copyright &y& Elsevier]

Three new D-A-π-A organic dyes (1a-c) containing a 2,3-diphenylquinoxaline core as the main chromophore were designed to act as sensitizers for the TiO 2 -based photoanode of dye-sensitized photoelectrochemical cells (DS-PEC) for water splitting. The dyes structures featured a cyanoacrylic acid group as the terminal acceptor/anchoring moiety and three different donor groups of moderate strength, namely mono- and dialkoxy-substituted benzenes, which were introduced to modulate the energies of the respective HOMO levels and enable the electron transfer from a Ru-based molecular water oxidation catalyst (WOC). Dyes 1a-c were synthesized following a C–H activation strategy and fully characterized. In addition, the previously known catalyst Ru(bda)(PyP) 2 (bda = 2,2′-bipyridine-6,6′-dicarboxylate; PyP = pyridin-4-methyl phosphonic acid) was also prepared by modification of a reported procedure. The dynamics of charge transfer processes involving the dyes adsorbed on nanocrystalline TiO 2 films were investigated by means of transient absorption spectroscopy. Photo-electrochemical experiments carried out on photoanodes functionalized with 1a-c and Ru(bda)(PyP) 2 in 0.1 M aq. Na 2 SO 4 electrolyte showed the production of photocurrents up to ca. 0.15 mA cm−2 at + 0.5 V vs. NHE, and highlighted how modifications of the TiO 2 staining procedure can lead to significant differences in cell performances. [Display omitted] [ABSTRACT FROM AUTHOR]

This work deeply investigated the effect of water in terpineol-based TiO 2 screen-printing inks, commonly used for the deposition of photoanodes for dye-sensitized solar cells. The study involved all the different phases necessary for the photoanode production and the final device characterization. Firstly, inks modified with different amounts of water were produced and analyzed considering particle dispersion (DLS) and rheological behavior, while the deposited layers were analyzed in terms of morphology (FE–SEM), roughness (profilometry) transmittance (UV–Vis spectroscopy) and dye adsorption capability. Finally, the observed properties were correlated to the performance and the electrochemical behavior (EIS) of a complete DSC. The extensive study allowed to understand the real role played by the water in the ink formulation and, as a consequence, the identification of the optimal amount to be introduced in the system. Water was showed to increase the dispersion and time stability of the particle suspensions, leading to an optimized flow behavior of the inks. The ceramic films so obtained exhibited improved morphologies and enhanced optical properties and dye uptake. However, the optimal concentration for DSC application was found to be not the one that allows the best dispersability of the ceramic particles but the one that best compromised the homogeneity of the film with the highest dye uptake. This key result could not be obtained analyzing just the film morphology but necessitate a thorough analyses of all the different properties (morphological, electrochemical and photovoltaic) related to the final application. The best-performing device recorded an increase in efficiency of the 12% compared to the un-modified system. [ABSTRACT FROM AUTHOR]

In this study, a novel procedure for the production of Zr-doped TiO 2 ceramic layers, deposited by screen-printing technique, is presented. A suitable Zr precursor (Zr(IV) 2,4-pentanedionate) was added to the formulation of a standard TiO 2 ink, in order to promote the diffusion of Zr ions directly during the sintering of the deposited layers. In order to evaluate the impact of this process on the properties of the ink, thermal and rheological analysis were done; a significant effect on the flow behavior was found, related to a relevant dispersing action of the precursor. The efficacy of the method was proved by XRD analyses, that showed the stabilization of anatase phase and crystal size at high temperature (700 °C), due to Zr doping. The properties of the films were then analyzed in order to evaluate their application as photoanodes for Dye-Sensitized Solar Cells (DSCs). The use of the Zr precursor resulted to improve the film morphology, whereas it did not affect the dye adsorption capability of the TiO 2 . Electrochemical characterization pointed out increased flat band potential and density of states (DOS), the latter being potentially beneficial even for photocatalytic applications. Doped photoanodes resulted to induce a slight deterioration of the performance, pointing out the need of a more accurate optimization of the process for this application. Finally, the proposed doping method resulted effective and potentially adaptable to other dopant-semiconductor systems. [ABSTRACT FROM AUTHOR]

Abstract: A thin compact layer of TiO2 deposited on the conductive transparent substrate of a dye-sensitized solar cell photoanode, (blocking layer, BL) can enhance the performances of the entire device. In this paper, an optimized spin coating process using an alcoholic TiCl4 solution was developed and correlated to the final properties of the layer. The physicochemical characteristics of the precursor solution and the spin coating parameters were optimised to obtain a uniform layer. XRD, FE-SEM, UV–Vis spectroscopy, AFM, cyclic voltammetry and electrochemical impedance spectroscopy were used to evaluate the influence of the number of deposition cycles on the TiO2 layer. The results were compared with those obtained using a conventional dip coating technique, showing that the newly developed spin coating process produces blocking layers with superior properties. Finally, analyses of the photovoltaic performances of the complete cell confirmed that an optimized blocking layer can lead to an improvement of the solar conversion efficiency of about 84%. [Copyright &y& Elsevier]