Catalytic Behaviour of Mesoporous Cobalt-Aluminum Oxides for CO Oxidation

Ordered mesoporous materials are promising catalyst supports due to their uniform pore size distribution, high specific surface area and pore volume, tunable pore sizes, and long-range ordering of the pore packing. The evaporation-induced self-assembly (EISA) process was applied to synthesize mesoporous mixed oxides, which consist of cobalt ions highly dispersed in an alumina matrix. The characterization of the mesoporous mixed cobalt-aluminum oxides with cobalt loadings in the range from 5 to 15 wt% and calcination temperatures of 673, 973, and 1073 K indicates that Co2+ is homogeneously distributed in the mesoporous alumina matrix. As a function of the Co loading, different phases are present comprising poorly crystalline alumina and mixed cobalt aluminum oxides of the spinel type. The mixed cobalt-aluminum oxides were applied as catalysts in CO oxidation and turned out to be highly active.Fil: Bordoloi, Ankur. Indian Institute of Petroleum; IndiaFil: Sanchez, Miguel Dario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Noei, Heshmat. Research Group X-Ray Physics and Nanoscience Deutsches Elektronen-Synchrotron; AlemaniaFil: Kaluza, Stefan. Fraunhofer Institute of Environmental, Safety, and Energy Technology; AlemaniaFil: Großmann, Dennis. Ruhr Universität Bochum; AlemaniaFil: Wang, Yuemin. Ruhr Universität Bochum; AlemaniaFil: Grünert, Wolfgang. Ruhr Universität Bochum; AlemaniaFil: Muhler, Martin. Ruhr Universität Bochum; Alemani

DESY NanoLab

The DESY NanoLab is a facility providing access to nano-characterization, nano-structuring and nano-synthesis techniques which are complementary to the advanced X-ray techniques available at DESY’s light sources. It comprises state-of-the art scanning probe microscopy and focused ion beam manufacturing, as well as surface sensitive spectroscopy techniques for chemical analysis. Specialized laboratory x-ray diffraction setups are available for a successful sample pre-characterization before the precious synchrotron beamtimes. Future upgrades will include as well characterization of magnetic properties

A New Synthesis Approach for Carbon Nitrides: Poly(triazine imide) and Its Photocatalytic Properties

Poly (triazine imide) (PTI) is a material belonging to the group of carbon nitrides and has shown to have competitive properties compared to melon or g-C3N4, especially in photocatalysis. As most of the carbon nitrides PTI is usually synthesized by thermal or hydrothermal approaches. We present and discuss an alternative synthesis for PTI which exhibits a pH dependent solubility in aqueous solutions. This synthesis is based on the formation of radicals during electrolysis of an aqueous melamine solution, coupling of resulting melamine radicals and the final formation of PTI. We applied different characterization techniques to identify PTI as the product of this reaction and report the first liquid state NMR experiments on a triazine-based carbon nitride. We show that PTI has a relatively high specific surface area and a pH dependent adsorption of charged molecules. This tunable adsorption has a significant influence on the photocatalytic properties of PTI which we investigated in dye degradation experiments

High‐Performance n‐ and p‐Type Field‐Effect Transistors Based on Hybridly Surface‐Passivated Colloidal PbS Nanosheets

Colloidally synthesized nanomaterials are among the promising candidates for future electronic devices due to their simplicity and the inexpensiveness of their production. Specifically, colloidal nanosheets are of great interest since they are conveniently producible through the colloidal approach while having the advantages of two-dimensionality. In order to employ these materials, according transistor behavior should be adjustable and of high performance. We show that the transistor performance of colloidal lead sulfide nanosheets is tunable by altering the surface passivation, the contact metal, or by exposing them to air. We found that adding halide ions to the synthesis leads to an improvement of the conductivity, the field-effect mobility, and the on/off ratio of these transistors by passivating their surface defects. Superior n-type behavior with a field-effect mobility of 248 cm^2V^-1s^-1 and an on/off ratio of 4×10^6 is achieved. The conductivity of these stripes can be changed from n-type to p-type by altering the contact metal and by adding oxygen to the working environment. As a possible solution for the post-Moore era, realizing new high quality semiconductors such as colloidal materials is crucial. In this respect, our results can provide new insights which helps to accelerate their optimization for potential applications

Function Follows Form: From Semiconducting to Metallic toward Superconducting PbS Nanowires by Faceting the Crystal

In the realm of colloidal nanostructures, with its immense capacity for shape and dimensionality control, the form is undoubtedly a driving factor for the tunability of optical and electrical properties in semiconducting or metallic materials. However, influencing the fundamental properties is still challenging and requires sophisticated surface or dimensionality manipulation. In this work, we present such a modification for the example of colloidal lead sulphide nanowires. We show that the electrical properties of lead sulphide nanostructures can be altered from semiconducting to metallic with indications of superconductivity, by exploiting the flexibility of the colloidal synthesis to sculpt the crystal and to form different surface facets. A particular morphology of lead sulphide nanowires has been synthesized through the formation of {111} surface facets, which shows metallic and superconducting properties in contrast to other forms of this semiconducting crystal, which contain other surface facets ({100} and {110}). This effect, which has been investigated with several experimental and theoretical approaches, is attributed to the presence of lead rich {111} facets. The insights promote new strategies for tuning the properties of crystals as well as new applications for lead sulphide nanostructures.Comment: 23 pages, 6 figure

Elucidating the Defect-Induced Changes in the Photocatalytic Activity of TiO2TiO_{2}

The adsorption and subsequent photo-oxidation ofcarbon monoxide on the anatase TiO2(101) and rutile TiO2(110)single crystal surfaces was investigated using low temperature X-rayphotoelectron spectroscopy. Anatase was shown to significantlyoutperform rutile in terms of the rate of carbon dioxide yield onthe stoichiometric surface, and further to this, the presence ofdefects was shown to heavily influence the photocatalyticefficiency. The oxidation rate was reduced on anatase but increasedon rutile. This change is attributed to the location of defects withinthe crystal structure and is further discussed in this work. Thesefindings are of significant importance and demonstrate the possibilities of defect engineering in photocatalysis

Gold Nanoparticle-Based Chemiresistors: Recognition of Volatile Organic Compounds Using Tunable Response Kinetics

The development of sensors enabling the identification of volatile organic compounds (VOCs) and their mixtures is an ongoing challenge driven by many potential applications, such as breath analysis in medical diagnosis, food quality control, and environmental monitoring. In this context, hybrid materials of organically stabilized or cross-linked metal nanoparticles show great potential for the chemiresistive detection of VOCs. Here, we show that the unique nanostructure of these materials induces analyte-dependent response kinetics, which can be tuned and employed for analyte recognition. First, the response kinetics of different α,ω-alkanedithiol (ADT) cross-linked GNP film chemiresistors were measured by exposing them to vapors of toluene, 1-butanol, 1-propanol, 2-propanol, ethanol, water, 4-methylpentan-2-one, and different homologous alkanes. The t80 response times and the integrated area below the response transients were used as characteristic features of the response kinetics. The response times depended strongly on the molecular volume of the analyte as opposed to the maximum sensor response, which was governed by the analytes’ polarity and vapor pressure. We attribute the variation in response time to molecular transport of the analyte molecules entering the sensor film. Second, using different-sized cross-linkers, different film thicknesses, or by preexposing the sensors to deep ultraviolet radiation, it is possible to tune the kinetics of the sensors’ responses to different analytes. Third, by employing linear discriminant analysis on data sets containing the maximum responses and kinetic response features of a GNP/ADT sensor array with adjusted response kinetics, it was possible to differentiate between very similar analytes over a broad range of concentrations (100–4000 ppm). Hence, the methods described herein will be very useful for various applications of nanoparticle-based chemiresistor arrays

Interaction of Water with Graphene/Ir(111) Studied by Vibrational Spectroscopy

Water in confinement exhibits altered properties in molecular arrangement, bonding, and interaction with its neighboring environment, as compared to its bulk counterpart. In this work, periodically arranged D2O nano droplets of ∼1 nm size on top of a graphene/iridium moiré superstructure were investigated by Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) under ultrahigh vacuum conditions at ∼120 K. The IR bands of D2O clusters differ significantly from those observed for bulk D2O amorphous solid water or crystalline ice phases. Blue-shifted symmetric and asymmetric stretching bands with narrower band widths and modified band intensity ratios were observed, pointing to an enhanced internal order and a reduced nearest neighbor distance. Furthermore, two IR bands of “dangling” deuterium atoms were detected originating from threefold coordinated water molecules at the surface of the clusters and at their interface to the graphene layer. The latter arose only with the transition from the water clusters to an amorphous solid water layer. We propose that upon coalescence, opposing local dipoles trigger a hydrogen bond rearrangement at the interface. Our results represent a first step toward an atomistic understanding of water in confinement

Mild yet phase-selective preparation of TiO2TiO_{2} nanoparticles from ionic liquids – a critical study

The phase selective synthesis of nanocrystalline TiO2, titania, in ionic liquids (ILs) is explored. The influence not only of the IL but also of the Ti-precursor, pH, and temperature is investigated. Sonochemical synthesis, microwave synthesis and conventional heating are compared. In the case of Ti(OiPr)4 (OiPr = isopropyl) as the Ti-source the ILs [C4mim][Tf2N] (1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide), [C3mimOH][Tf2N] (1-(3-hydroxypropyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)amide), [C4Py][Tf2N] (butylpyridinium bis(trifluoromethanesulfonyl)amide), [N1888][Tf2N] (methyltrioctylammonium bis(trifluoromethanesulfonyl)amide), and [P66614][Tf2N] (tetradecyltrihexyl phosphonium bis(trifluoromethanesulfonyl)amide) led at ambient temperature to TiO2 in the form of anatase. The morphology of nano-anatase is controlled by the IL cation. Anatase nanospheres with a crystal size below 10 nm are obtained in [C3mimOH][Tf2N], [P66614][Tf2N] and [C4Py][Tf2N], whilst nanorods with a length and diameter of [similar]10 to 20 and 5 nm are formed in [N1888][Tf2N] and spindle-shaped particles with an average length of 10–25 nm are formed in [C4mim][Tf2N]. Calcination at temperatures above 730 °C leads to rutile. When using TiCl4 as the Ti-precursor an anatase–rutile mixture forms under ambient conditions. Pure rutile can be obtained under ambient conditions in the presence of an appropriate volume of aqueous HCl. At moderate to high pH values pure anatase can be obtained even from TiCl4. The photocatalytic activity of the obtained TiO2 materials has been assessed by the photodegradation of an aqueous methyl orange solution under UV light. The results indicate that the photocatalytic activity of anatase–brookite mixtures obtained in [C4mim][Tf2N], [N1888][Tf2N] and [P66614][Tf2N] is higher than that of pure anatase which is formed in [C3mimOH][Tf2N] and [C4Py][Tf2N] and competitive with commercially available catalysts