Myrjam Mertens

Initial stages of few-layer graphene growth by microwave plasma-enhanced chemical vapour deposition.

A promising method for the production of few-layer graphene (FLG) is microwave plasma-enhanced chemical vapour deposition (MW PECVD). However, the growth mechanism of PECVD-synthesized FLG is not completely understood. The aim of this work was to investigate the initial stages of the growth process of FLG deposited by MW PECVD on several substrates (quartz, silicon, platinum). The deposited thin films were characterized by angle-resolved x-ray photoelectron spectroscopy (ARXPS), electron backscattered diffraction (EBSD), scanning electron microscopy (SEM) and x-ray diffraction (XRD). It was found that the initial stages of the deposition were different for the three chosen substrate materials. However, the fully grown FLG layers were similar for all substrates.

Photocatalytic removal of phenol and methylene-blue in aqueous media using TiO2@LDH clay nanocomposites

Abstract Herein, we report the formation of a series of nanocomposites composed of LDH structures and TiO 2 with anatase crystal phase. The structure of the LDH clay was modulated by the insertion of different di-, tri- or tetravalent cations, such as Zn 2+ , Cu 2+ , Al 3+ , Fe 3+ or Ti 4+ , within the brucite-like sheets. Afterwards, the anatase seeds were deposited onto the LDH clays, obtaining new nanocomposite systems with tailored photocatalytic activity. In this way, the photoresponsive properties of the final nanocomposites were shifted from the UV to the visible range of the solar spectrum. The obtained nanocomposites were tested for the degradation of different organic pollutants, like phenol and methylene blue, under UV and visible light in aqueous media with different pH. The kinetic study showed that the TiO 2 @LDH nanocomposites are efficient for the phenol (and its intermediary species catechol and hydroquinone) and methylene blue photocatalytic degradation under both UV and Vis light illumination.

Laser metal deposition of Inconel 625: Microstructure and mechanical properties

Laser metal deposition (LMD) is used in industry to coat, additive manufacture, and/or repair high value metal components through deposition and laser induced melting of powder delivered in a gas stream. This study relates to the production of three-dimensional Inconel 625 components by LMD. After LMD, a dense cellular – dendritic structure containing carbides of the type MC, M23C6, and M6C has been detected by x-ray diffraction. Parts with tensile yield strengths, ultimate strengths, and elongations in the range of, respectively, 480–656 MPa, 882–1000 MPa, and 24%–36% have been obtained. Compression testing along and perpendicular to the build direction reveals a slight anisotropy in fracture strength. This is attributed to the preferential orientation of the dendrites parallel to the build direction. Tensile test samples have been fabricated in “lying” and “standing” orientations. The tensile yield and ultimate strength are considerably lower and the elongation is larger for the samples built in standin...

Rapid microwave-assisted synthesis of benzene bridged periodic mesoporous organosilicas†

Following extended use in organic chemistry, microwave-assisted synthesis is gaining more importance in the field of inorganic chemistry, especially for the synthesis of nanoporous materials. It offers some major advantages such as a significant shortening of the synthesis time and an improved promotion of nucleation. In the research here reported, microwave technology is applied for the synthesis of benzene bridged PMOs (periodic mesoporous organosilicas). PMOs are one of the latest innovations in the field of hybrid ordered mesoporous materials and have attracted much attention because of their feasibility in electronics, catalysis, separation and sorption applications. The different synthesis steps (stirring, aging and extraction) of the classical PMO synthesis are replaced by microwave-assisted synthesis steps. The characteristics of the as-synthesized materials are evaluated by X-ray diffraction, N2-sorption, thermogravimetric analysis, scanning- and transmission electron microscopy. The microwave-assisted synthesis drastically reduces the synthesis time by more than 40 hours without any loss in structural properties, such as mesoscale and molecular ordering. The porosity of the PMO materials has even been improved by more than 25%. Moreover, the number of handling/transfer steps and amounts of chemicals and waste are drastically reduced. The study also shows that there is a clear time (1 to 3 hours) and temperature frame (373 K to 403 K) wherein synthesis of benzene bridged PMO is optimal. In conclusion, the microwave-assisted synthesis pathway allows an improved material to be obtained in a more economical way i.e. a much shorter time with fewer chemicals and less waste.

Immersion calorimetry as a tool to evaluate the catalytic performance of titanosilicate materials in the epoxidation of cyclohexene.

Different types of titanosilicates are synthesized, structurally characterized, and subsequently catalytically tested in the liquid-phase epoxidation of cyclohexene. The performance of three types of combined zeolitic/mesoporous materials is compared with that of widely studied Ti-grafted-MCM-41 molecular sieve and the TS-1 microporous titanosilicate. The catalytic test results are correlated with the structural characteristics of the different catalysts. Moreover, for the first time, immersion calorimetry with the same substrate molecule as in the catalytic test reaction is applied as an extra means to interpret the catalytic results. A good correlation between catalytic performance and immersion calorimetry results is found. This work points out that the combination of catalytic testing and immersion calorimetry can lead to important insights into the influence of the materials structural characteristics on catalysis. Moreover, the potential of using immersion calorimetry as a screening tool for catalysts in epoxidation reactions is shown.

Direct spectroscopic detection of framework-incorporated vanadium in mesoporous silica materials

Framework-incorporated vanadium mesoporous silica materials with different contents in vanadium were obtained by a facile, direct synthesis at room temperature, using VOSO4 x 5H2O as the vanadium precursor. The porous characteristics of the samples and the coordination environment of the vanadia in the structure were studied by a combination of techniques: X-ray diffraction, N2-adsorption/desorption, FT-Raman, FTIR-PAS and UV-Vis-DR, electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectroscopy. A structural comparison is made using pulsed EPR and ENDOR spectroscopic techniques between vanadia deposited on the surface of MCM-41 by the Molecular Designed Dispersion method and as-synthesised samples of vanadia incorporated in the mesoporous silica framework using the above-mentioned synthesis method. The EPR study on the non-calcined samples proves the incorporation of a high amount of vanadium in the silica framework by the observation of a strong hyperfine coupling of the unpaired electron with 29Si. It demonstrates the feasibility for EPR to reveal structural information on true incorporation of metal ions in framework positions leading to metal oxides.

Controlling pore size and uniformity of mesoporous titania by early stage low temperature stabilization.

The control of the formation process during and after self-assembly is of utmost importance to achieve well structured, controlled template-assisted mesoporous titania materials with the desired properties for various applications via the evaporation induced self-assembly method (EISA). The present paper reports on the large influence of the thermal stabilization and successive template removal on the pore structure of a mesostructured TiO(2) material using the diblock copolymer Brij 58 as surfactant. A controlled thermal stabilization (temperature and duration) allows one to tailor the final pore size and uniformity much more precise by influencing the self-assembly of the template. Moreover, also the successive thermal template removal needs to be controlled in order to avoid a structural collapse. N(2)-sorption, TGA, TEM, FT-Raman spectroscopy, and small angle & wide angle XRD have been used to follow the crystal growth and mesostructure organization after thermal stabilization and after thermal template removal, revealing its effect on the final pore structure.

Post-synthesis deposition of V-zeolitic nanoparticles in SBA-15

A post-synthesis deposition of vanadium silicalite-1 zeolite nanoparticles in the pores of SBA-15 results in a highly ordered hexagonal templated silica material with V-silicalite zeolitic plugs, giving rise to an increased crystallinity of the amorphous mesoporous walls.

Formation of a Ti-siliceous trimodal material with macroholes, mesopores and zeolitic features via a one-pot templating synthesis

Based on a facile one-pot templating synthesis, using a TS-1 zeolite recipe whereby part of the zeolite structure directing agent is replaced by a mesopore templating agent, a trimodal material is formed. The resulting meso-TSM material combines mesoporosity (Ti-MCM-41) with zeolitic features (TS-1) and a unique sheet-like morphology with uniform macroporous voids (macroholes). Moreover, the macrohole formation, mesoporosity and zeolitic properties of the meso-TSM material can be controlled in a straightforward way by adjusting the length of the hydrothermal treatment. This newly developed material may imply great potential for catalytic redox applications and diffusion limitated processes because of its highly tunable character in all three dimensions (micro-, meso- and macroporous scale).

Novel magnetic nanocomposites containing quaternary ferrites systems Co_{0.5}Zn_{0.25}M_{0.25}Fe_{2}O_{4} (M = Ni, Cu, Mn, Mg) and TiO_{2} -anatase phase as photocatalysts for wastewater remediation under solar light irradiation

Abstract In this study smart-removal magnetic nanocomposites are developed in an attempt to decrease the band gap energy of the catalyst and to enable separation of the catalyst from the wastewater after the process. Ferrite magnetic nanoparticles Co0.5Zn0.25M0.25Fe2O4 (M = Ni, Cu, Mn, Mg) (MNPs) are obtained by the co-precipitation method using carboxymethyl cellulose (CMC) as surfactant and NaOH as precipitation agent. Further, the magnetic nanocomposites Co0.5Zn0.25M0.25Fe2O4-TiO2 (anatase) (MNPs-TiO2) are obtained by the TiO2 deposition onto the MNPs using Pluronic P123 as template and tetra butyl titanate (TBOT) as titanium source. This type of photocatalyst can be used under solar light irradiation because of the activation of TiO2 with MNPs in visible light range and can be very easily recovered due to their strong magnetic properties. The MNPs-TiO2 have proven to be very active for the degradation of different dyes, such as methyl orange and methylene blue, under solar light irradiation.