Ligand exchange on CdSe nanoplatelets for the solar light sensitization of TiO2 and ZnO nanorod arrays

In quantum dot (QD) solar cells, the ex situ sensitization of wide band gap semiconductors (WBSCs) makes it possible to control the shape and the passivation of the nanosized sensitizer. Hence, ex situ techniques can be used to investigate how the band gap of the sensitizers affects the performance of quantum dot solar cells. The latter can be precisely controlled in 1D confined structures such as quasi-2D nanoplatelets (NPLs), the thickness of which is defined with an atomic precision. In this work, we tested and thoroughly characterized the attachment of 7, 9 and 11 monolayers thick CdSe NPLs (as well as QDs for the sake of comparison) to ZnO and to TiO2 nanorods. A crucial point of the ex situ techniques is the choice of bifunctional ligands that link the nanosized sensitizers to the WBSCs. Besides the well-known mercaptopropionic acid, we also studied two ‘atomic linkers’ (OH− and SH−) to minimize the distance between the sensitizer and the oxide. The as-prepared systems have been analyzed by UV/VIS absorption and Raman spectroscopy. Among them, SH− was found to be the most versatile linker that enabled the efficient attachment of all types of CdSe nanocrystals on ZnO and TiO2 nanorods.Fil: Szemjonov, A.. PSL Research University; Francia. Centre National de la Recherche Scientifique; FranciaFil: Tasso, Mariana Patricia. Laboratoire de Physique Et D'etude Des Materiaux; Francia. Centre National de la Recherche Scientifique; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Ithurria, S.. Laboratoire de Physique Et D'etude Des Materiaux; FranciaFil: Ciofini, I.. PSL Research University; Francia. Centre National de la Recherche Scientifique; FranciaFil: Labat, F.. PSL Research University; Francia. Centre National de la Recherche Scientifique; FranciaFil: Pauporté, T.. PSL Research University; Francia. Centre National de la Recherche Scientifique; Franci

Novel Trinuclear Single-Site Titanosilicate with Targeted Connectivity: Synthesis, Characterization and Catalytic Properties in Selective Oxidation of Olefins

Catalysts are an essential component in the chemical industry converting raw materials into essential products. Transition metal catalysts, more specifically titanosilicates, are effective in the selective oxidation of olefins producing monomers and chemical intermediates used in many industrial applications. A major challenge in the catalysis community is developing synthetic methodologies that produce robust heterogeneous catalysts with isolated, single type of active sites with targeted connectivities to the support matrix. The Barnes’ research group has developed a building block synthetic methodology that produces a single-site heterogeneous catalyst. This methodology uses a molecular building block and titanium (IV) precursors to create site isolated, atomically dispersed titanium actives sites with identical connectivities to a porous silicate matrix. The primary focus of this family of catalysts has been synthesizing mononuclear titanium (IV) active sites supported within a silicate matrix. The goals of this dissertation aim at extending the building block methodology to synthesizing and characterizing a trinuclear titanosilicate single-site heterogeneous catalyst with targeted connectivities to the support matrix. The highly active trinuclear catalysts synthesized in this work have a Ti3O2 core containing bridging carboxylate and oxo ligands between titanium centers with a well-defined number of connections to the silica building block matrix. Characterization techniques determined the connectivity of the active site to the silicate matrix as well as the surface area and porosity of the resulting materials. Gravimetric analysis, 1 HNMR, and infrared spectroscopy were used as frontline techniques to determine the initial connectivity of the active site to the support. XAS and DRUV conclusively showed that the titanium atoms in the Ti3O2-core contain higher coordination geometries (5- and 6-coordinate centers), with EXAFS results clearly supporting the existence of a single type of Ti3O2-core. Catalytic test reactions involving the selective oxidation of cyclohexene to cyclohexene oxide was extensively studied. The catalysts synthesized in this work exhibit excellent activity and selectivity to the targeted product and are better than several leading candidates described in the literature. Furthermore, these Ti3O2-based titanosilicates possess a superior chemical robustness capable of turn-over numbers exceeding 7500 with turn-over frequencies ~95 min-1, with respect to oxide formation

Integrated Wireless Backhaul Over Optical Access Networks

Recent technological advances and deployments are creating a new landscape in access networks, with an integration of wireless and fiber technologies a key supporting technology. In the past, a separation between those with fiber in the access networks and those with wireless networks, the relatively low data-rate requirements of backhaul and the relatively large cell sites, have all combined to keep fiber deployment low in wireless backhaul. As fiber has penetrated the access network and the latest wireless standards have demanded smaller, higher bandwidth cells, fiber connectivity has become key. Choices remain as to where the demarcation between key elements should be in the network and whether fiber should be used as just a high data-rate backhaul path or if a transition to radio-over-fiber techniques can afford benefits. This paper will explore the network options available in particular those demonstrated in recent European Union (EU) projects, how they can be integrated with existing access networks and how techniques such as radio-over-fiber can be deployed to offer increased functionality

Novel Single-Site Titanosilicates with Targeted Connectivity and Nuclearity of Titanium(IV): Synthesis, Characterization and Catalytic Properties in Alkylphenol Oxidation

Titanosilicates are a family of porous materials that have shown excellent catalytic activity in olefin epoxidation and many other selective oxidation reactions. These materials have been extensively studied in the past few decades. One of the central questions in these investigations has been to define the catalytically active centers. The traditional synthesis of wet impregnation followed by calcination often produces more than one type of catalytic center within the same matrix, i.e. different coordination, connectivity and nuclearity. Each type potentially possesses unique catalytic activity. Co-existence of multiple catalytic centers makes it impossible to establish the relationship between the structure of titanium center and catalytic activity. The goal of this research was to establish a structure-function relationship in titanosilicate materials through targeted synthesis of single-site nanostructured catalysts, in which titanium centers are isolated from one another while possessing the uniform structure. A building block synthetic methodology was utilized to prepare a series of catalysts, namely 2-connected (2C), 3-connected (3C), 4-connected (4C) and tetranuclear (Ti4 [subscript 4]) titanium catalysts. These materials were characterized in detail via gravimetric analysis, solid state NMR, diffuse reflectance UV spectroscopy, infrared spectroscopy, BET surface area and X-ray absorption spectroscopy (XANES and EXAFS). Catalytic activity of each catalyst was examined in the oxidation of 2, 3, 6-trimethylphenol with aqueous hydrogen peroxide to give the corresponding benzoquinone. Under identical conditions, high to mediocre catalytic activity has been observed in a sequence of Ti4 [subscript 4] \u3e 2C \u3e 3C ≈ 4C, in terms of both conversion and selectivity. All synthesized catalysts showed excellent stability and recyclability with aqueous hydrogen peroxide at elevated temperature. A structure-function relationship was therefore developed through targeted synthesis of novel single-site titanosilicate catalysts

Establishment of a Structure-Activity Relationship in Heterogeneous Titanosilicate Catalysts for Olefin Epoxidation via a Building Block Method

The non-aqueous building block (NABB) method is a synthetic method that has the goal of producing atomically dispersed, well-defined, single-site heterogeneous catalysts. The active sites of these catalysts are able to be structured on the nanometer scale using the process of sequential additions. The method is designed in such a manner that it should be able to produce a series of catalysts each with a unique, well-defined, single active site. This series of catalysts can then be used to elucidate the structure-activity relationship for the active site in a particular chemical reaction. In this dissertation a new building block, butyltin cube, is developed for the NABB method. The preparation of the butyltin cube uses reagents that are less toxic and costly than the reagents used to prepare the previous methyltin cube starting material. A series of titanium NABB materials containing different active sites was prepared. The local structure around the active site of these materials was then probed using quantitative NMR, FT-IR, Raman, XANES, and EXAFS. The activity and selectivity of these materials in the epoxidation of cyclohexene with tert-butylhydroperoxide was then measured. The information was then used to propose a structure-activity relationship for olefin epoxidation and comparisons were made with structure-activity relationships noted in the literature

Changing availability of TV white space in the UK

The UK regulator Ofcom has held a Pilot of TV white space (TVWS) technology in the UK. On the basis of the results of this Pilot, Ofcom has varied its calculations of allowed white space device equivalent isotropically radiated powers (EIRP). Further, the World Radiocommunication Conference (WRC) 2015 has assigned 694-790 MHz to mobile broadband on a co-primary basis, in International Telecommunication Union (ITU) Region 1 (which includes the UK/EU). Fundamental observations on the effects of these changes on TVWS availability in the UK are provided.</p