From La2O3 to LaCoO3: XPS analysis

Nanostructured LaCoO3 powder was prepared by a new approach: cobalt oxide nanoparticles were deposited, by wet impregnation, on the La2O3surface. The La2O3 support was prepared byprecipitation from a basic solution of La(NO3)3\ub76H2O. The precipitate was dried at 353 K for 2 h and calcined at 923 K for 6h in air. Nanostructured LaCoO3 was obtained by wet impregnation of La2O3 with aqueous solutions of Co(NO3)2\ub76H2O:Co/La nomimal 1.0 nominal atomic ratio is obtained from the precursors weighed quantities. The obtained suspension was maintained under stirring for two days and then kept in rest for one day. Water was evaporated in air and the obtained solid was dried at 353 K for2h and at 923K for 6h in air.The thermal treatment in air promotes a solid state reaction between La-O and Co-O and then the formation of LaCoO3

Large-Scale MOCVD Deposition of Nanostructured TiO2 on Stainless Steel Woven: A Systematic Investigation of Photoactivity as a Function of Film Thickness

Heterogeneous photocatalysis is considered as one of the most appealing options for the treatment of organic pollutants in water. However, its definitive translation into industrial practice is still very limited because of both the complexity of large-scale production of catalysts and the problems involved in handling the powder-based photocatalysts in the industrial plants. Here, we demonstrate that the MOCVD approach can be successfully used to prepare large-scale supported catalysts with a good photocatalytic activity towards dye degradation. The photocatalyst consisted of nanostructured TiO2 thin film deposited on a stainless steel mesh substrate. The film thickness, the morphological features, and the crystallographic properties of the different portions of the sample were correlated to the position in the reactor chamber and the reaction conditions. The photocatalytic activity was evaluated according to the international standard test ISO 10678:2010 based on methylene blue degradation. The photocatalytic activity is essentially constant (PMB over 40 µmol·m−2·h−1) throughout the film, except for the portion of sample placed at the very end of the reactor chamber, where the TiO2 film is too thin to react properly. It was assessed that a minimum film thickness of 250–300 nm is necessary to reach the maximum photocatalytic performance

La0.6Sr0.4Co1-yFeyO3- \u3b4 Powders Studied by X-ray Photoelectron Spectroscopy

Perovskite-type oxides are known to be very good oxidation catalysts. The redox properties of the TM cation, the availability of weakly bonded oxygen at the Surface and the presence of lattice defects have been often claimed as responsible for their catalytic activity. Moreover, their performances can be improved if they are nanodimensioned. The present stud focuses on the development of new LaCoO3-based catalysts for alcohol (methanol, ethanol) steam reforming. Several La0.6Sr0.4Co1-yFeyO3 (y=0.2, 0.5, 0.8) were prepared by the citrte gel method and calcined at 1073K for 5h in air. Herein the influence of the cobalt/iron ration on the surface properties was investigated

CVD techniques for surface functionalization: ALD potentiality for long-range periodic structures

The surface of a solid material and the regions closest to it represent the 'element of dialogue' with the surrounding environment, so conditioning the physical and chemical properties of the material itself. In this context, Material Science is fundamental to properly functionalize the material surface through a suitable bottom-up approach in order to induce a targeted behavior. Chemical Vapor Deposition (CVD) is an attractive technique for the synthesis of opportunely designed nanostructured thin films. The possibility to modify several physical and chemical growth parameters makes CVD a challenging process to tailor material composition, microstructure, and morphology, so influencing the final functional properties. In particular, Atomic Layer Deposition (ALD), a recent variant of CVD process, is a powerful and unique technique which allows the deposition of high quality thin films with atomic level control of composition and thickness. The capability to produce periodic metal oxide structures with both a long range order and a good control of dimension at micro- and nano-metric level is of great scientific interest. These surfaces, thanks to their high surface-to-volume ratio, may find wide application in processes based on surface reactions, such as heterogeneous catalysis, sensors and photovoltaics. In fact, although structuring micro- and nano-materials may also be obtained with conventional templating and lithographic techniques, an alternative and strategic approach is found exploiting the self-assembly of polymeric materials (to set the template patterns up) combined with the ALD process (to conformally cover the polymeric templates). Here, a case study is reported in order to show the ALD potentiality by focusing the attention on the optimization of hybrid organic-inorganic methodology to prepare 2D-microporous TiO2 with honey-comb (HC) morphology. The hybrid methodology first employs the preparation of a polystyrene template with a specific pattern, which is later used for the subsequent deposition of TiO2 via ALD at low temperature. Finally, high temperature post-deposition thermal treatments on PS/TiO2 composite material is carried on in order to decompose and extract the PS templates and in the meantime to crystallize TiO2 in anatase phase, maintaining the HC structure

Au/CeO<SUB>2</SUB> Supported Nanocatalysts: Interaction with Methanol

The effect of preparation procedure (Direct Anionic Exchange, DAE, Deposition-Precipitation, DP, and wet Impregnation, IMP) and Au/Ce atomic ratio (0.018 and 0.066) on Au/CeO(2) supported nanocatalysts was investigated with respect to reactivity. XPS data suggest the presence of traces of Ce(III). Usually, gold is present as Au(0) but in the DAE sample with high Au content, traces of oxidized species are observed. The Au/Ce XPS atomic ratio is lower than the expected value. Au deposition decreases surface interaction with atmospheric moisture and carbon dioxide. Methanol interacts molecularly and dissociatively with the samples; methoxy groups are observed to be mono-coordinated at Ce(IV) at room temperature and bi-coordinated to Ce(IV) and Ce(III) at increasing temperature. Oxidation products (formates, carbonates, carbon dioxide) form at temperatures higher than 373-423 K; activity and selectivity in methanol oxidation reaction are influenced by the metal content and the preparation procedure

Osteointegrative functionalization of dental implants: a new synergic approach

Titanium and its alloys have been widely used for dental implants due to their excellent combination of strength-to-weight ratio, excellent corrosion resistance and biocompatibility [1]. In order to improve osseointegration, the titanium surface is generally functionalised. A typical methodology of surface modification, able to efficiently change the surface chemistry of a metallic implant, is the coating of the titanium substrates with layers of bioactive calcium phosphate ceramics (CPCs) [2]. Moreover, titanium implants are usually processed in order to increase the surface roughness in a controlled way: sandblasting and/or chemical etching are approaches commonly used. With the aim of improving the adhesion strength between the Ti substrate and the CPC layer, the insertion of dense and compact ceramic interlayers is reported to be useful [1]. Indeed, they improve the film to implant adhesion both reducing the thermal mismatch between the metal and the calcium layer and increasing the amount of -OH sites available. Among various ceramics, crystalline titania (TiO2) has been extensively used as an inter-layer thanks to its well-known biocompatibility and bioactivity [1]. In this work, three types of Ti substrates (machined, sandblasted, and sandblasted/acid etched) were initially coated with a crystalline, dense and compact TiO2 inter-layer via MOCVD. Then, a discontinuous and homogenously spread CPC top-layer was obtained by means of spray pyrolysis technique. Finally, a thermal treatment at high temperature was carried out in order to crystallize the final composite material. Preliminary investigation on the influence of the pristine substrate morphology on TiO2 crystalline structure, morphology, surface wettability and in vitro acellular bioactivity is here presented. Moreover, the CPC/TiO2 composite material was also characterized by means XRD, SEM and release tests

Effective and Low-Cost Synthesis of Sulphur-Modified TiO2Nanopowder with Improved Photocatalytic Performances in Water Treatment Applications

In the present paper, sulphur-modified titanium dioxide (S-TiO2) is prepared as nanopowder in mixed rutile-anatase phase by an unprecedented simple, reproducible and cheap synthetic procedure, directly employing elemental sulphur powder as sulphur source. TiO2 and several reference TiO2 samples obtained in pure rutile or anatase phase were also prepared with nanometric size and compared to S-TiO2 as well as Degussa P25. The prepared samples and the reference benchmark were characterised by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), UV-Vis Spectroscopy, Fourier Transform Infrared Spectroscopy (FT-IR), BET specific surface area and X-ray Photoelectron Spectroscopy (XPS) techniques, while their photoactivity was determined with respect to methyl red degradation as typical probe reaction. The results from the characterisation and photocatalytic measurements were discussed and inter-correlated, thus providing a complete and consistent analysis of the samples performances. The prepared sulphur modified titanium dioxide appeared as a very efficient and long-lasting photocatalyst with respect to the unmodified TiO2 and to the benchmark Degussa P25 (S-TiO2 appears to be two times faster than P25) for the methyl red removal under UV lighting, also in repeated cycles

Exploitation of ALD potentiality for the realization of long-range ordered structures

Atomic Layer Deposition (ALD) is a powerful and unique technique which allows the deposition of high quality thin films with atomic level control of composition and thickness, and with a high conformal coverage even on complex shaped surfaces. It can also work at low temperature (LT-ALD), so allowing the employment of temperature-sensitive substrates [1]. The capability to realize periodic metal oxides structures with both a long range order and a good control of dimension at micro- and nano-metric level is of great scientific interest. These surfaces, thanks to their high surface-to-volume ratio, may find wide application in processes based on surface reactions, such as heterogeneous catalysis, sensors and photovoltaics. In this regard, ALD is a key technology for the surface modification of complex nanostructured materials [2]. In fact, although structuring micro- and nano-materials may also be possible with conventional templating and lithographic techniques, an alternative and strategic approach is based on the self-assembly of polymeric materials (to set the template patterns up) combined with the ALD process (to conformally cover the polymeric templates). The aim of this work is to investigate the potentiality of ALD process by focusing the attention on the optimization of hybrid organic-inorganic methodologies to prepare two different long-range ordered spatial organizations. In particular, 2D-microporous TiO2 with honey-comb (HC) morphology and 3D-anatase TiO2 hollow nanospheres with Direct Opal (DO) arrangement are here presented. The hybrid methodology first employs the preparation of polystyrene templates with a specific pattern, which are later used for the subsequent deposition of TiO2 via ALD at low temperature. Finally, high temperature post-deposition thermal treatments on PS/TiO2 composite materials are carried on in order to decompose and extract the PS templates and in the meantime to crystallize TiO2 in anatase phase, maintaining the HC and DO structures. Samples were characterized by SEM, XRD and UV-Vis analyses. As demonstrated by SEM analysis, the ALD growth produces films with optimal infiltration features and conformal coverage thus preserving the original structure of the starting templates