Springback effect and structural features during the drying of silica aerogels tracked by in-situ synchrotron X-ray scattering

The springback effect during ambient pressure drying of aerogels is an interesting structural phenomenon, consisting of a severe shrinkage followed by almost complete re-expansion. The drying of gels causes shrinkage, whereas re-expansion is believed to be linked to repelling forces on the nanoscale. A multi-scale structural characterization of this significant volume change is key in controlling aerogel processing and properties. In this work, hydrophobic, monolithic silica aerogels with high specific surface areas were synthesized by modification with trimethylchlorosilane and ambient pressure drying. Here, we report a multi-method approach focusing on in-situ X-ray scattering to observe alterations of the nanostructured material during the drying of surface-modified and unmodified silica gels. Both show a porous fractal nanostructure, which partially collapses during drying and only recovers in surface-modified samples during the springback effect. Distinct changes of the X-ray scattering data were reproducibly associated with the shrinkage, re-expansion and drying of the gel network. Our findings may contribute to tailor aerogels with specific functionality, as the springback effect has a direct influence on properties (e.g., porosity, pore size distribution), which is directly affected by the degree of re-expansion

Grafting and stabilization of ordered mesoporous silica COK-12 with graphene oxide for enhanced removal of methylene blue

Large-pore ordered mesoporous silica (OMS) COK-12, analogous to the well-known SBA-15, but synthesized in a more environmentally friendly way and exhibiting a shorter plate-like structure, was grafted with different amounts of graphene oxide (GO) for the first time in an inexpensive and rapid process, that was successfully upscaled. Samples were examined with nitrogen sorption analysis, SAXS, Raman spectroscopy, XPS, and zeta potential analysis. Adsorption experiments with the cationic dye methylene blue (MB) were conducted on the grafted materials and on pure COK-12, taking into account the influence of initial dye concentration (30–600 mg L−1), adsorbent dosage (0.2–14 g L−1), contact time (0.3–300 min), solution pH (4–10), and influence of salts and temperature (0–1 M NaCl, 80 °C) to simulate industrial dye effluent. The adsorption process was found to be represented best by the Langmuir isotherm model, i.e., adsorption is a monolayer process. The calculated maximum adsorption capacities were found to be 20.2 and 197.5 mg g−1 at dosages of 5 and 0.5 g L−1 for pure COK-12 and COK-12 grafted with 50 wt% GO, respectively, at pH 5.65 and MB concentration of 100 mg L−1. Adsorption kinetics were found to follow the pseudo-second order model, i.e., chemisorption is the rate controlling step. The adsorption performances could be well preserved at simulated dye effluent. Desorption was found to be most effective with hydrochloric acid. The COK-12 grafted with GO presented in this work shows superior adsorption properties in comparison to other grafted OMS materials. In addition, grafting with GO remarkably improved the stability of COK-12 in aqueous solution.TU Berlin, Open-Access-Mittel - 201

The contrasting effect of the Ta/Nb ratio in (111)-layered B-site deficient hexagonal perovskite Ba5Nb4-xTaxO15 crystals on visible-light-induced photocatalytic water oxidation activity of their oxynitride derivatives

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The effect of the Ta/Nb ratio in the (111)-layered B-site deficient hexagonal perovskite Ba5Nb4-xTaxO15 (0 <= x <= 4) crystals grown by a KCl flux method on visible-light-induced photocatalytic water oxidation activity of their oxynitride derivatives BaNb1-xTaxO2N (0 <= x <= 1) was investigated. The Rietveld refinement of X-ray data revealed that all Ba5Nb4-xTaxO15 samples were well crystallized in the space group P (3) over bar m1 (no. 164). Phase-pure BaNb1-xTaxO2N (0 <= x <= 1) porous structures were obtained by nitridation of the flux-grown oxide crystals at 950 degrees C for 20, 25, 30, 35, and 40 h, respectively. The absorption edge of BaNb1-xTaxO2N (0 <= x <= 1) was slightly shifted from 720 to 690 nm with the increasing Ta/Nb ratio. The O-2 evolution rate gradually progressed and reached the highest value (127.24 mu mol in the first 2 h) with the Ta content up to 50 mol% but decreased at 75 and 100 mol% presumably due to the reduced specific surface area and high density of structural defects, such as grain boundaries acting as recombination centers, originated from high-temperature nitridation for prolonged periods. Transient absorption spectroscopy provided evidence for the effect of the Ta/Nb ratio on the behavior and energy states of photogenerated charge carriers, indicating a direct correlation with photocatalytic water oxidation activity of BaNb1-xTaxO2N

Effect of fomes fomentarius cultivation conditions on its adsorption performance for anionic and cationic dyes

Lab-cultivated mycelia of Fomes fomentarius (FF), grown on a solid lignocellulose medium (FF-SM) and a liquid glucose medium (FF-LM), and naturally grown fruiting bodies (FF-FB) were studied as biosorbents for the removal of organic dyes methylene blue and Congo red (CR). Both the chemical and microstructural differences were revealed using X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, zeta potential analysis, and scanning electron microscopy, illuminating the superiority of FF-LM and FF-SM over FF-FB in dye adsorption. The adsorption process of CR on FF-LM and FF-SM is best described by the Redlich–Peterson model with β constants close to 1, that is, approaching the monolayer Langmuir model, which reach maximum adsorption capacities of 48.8 and 13.4 mg g–1, respectively, in neutral solutions. Adsorption kinetics follow the pseudo-second-order model where chemisorption is the rate-controlling step. While the desorption efficiencies were low, adsorption performances were preserved and even enhanced under simulated dye effluent conditions. The results suggest that F. fomentarius can be considered an attractive biosorbent in industrial wastewater treatment and that its cultivation conditions can be specifically tailored to tune its cell wall composition and adsorption performance.DFG, 414044773, Open Access Publizieren 2021 - 2022 / Technische Universität Berli

Pbca-Type In2O3: the high-pressure post-corundum phase at room temperature

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/jp5061599High-pressure powder X-ray diffraction and Raman scattering measurements in cubic bixbyite-type indium oxide (c-In2O3) have been performed at room temperature. On increasing pressure c-In2O3 undergoes a transition to the Rh2O3-II structure but on decreasing pressure Rh2O3-II-type In2O3 undergoes a transition to a previously unknown phase with Pbca space group which is isostructural to Rh2O3-III. On further decrease of pressure, we observed a phase transition to the metastable corundum-type In2O3 near room conditions. Recompression of the metastable corundum-type In2O3 at room temperature leads to a transition to the Rh2O3-III phase, thus showing that the Rh2O3-III phase is the post-corundum phase at room temperature. Our results are supported by theoretical ab initio calculations. Furthermore, they show that the Rh2O3-III phase could be present in other sesquioxides, thus prompting to a revision of the pressure-temperature phase diagrams of sesquioxidesFinancial support by the Spanish MEC under Grant No. MAT2010-21270-C04-01/03/04, MAT2013-46649-C4-1/2/3-P, by MALTA Consolider Ingenio 2010 project (CSD2007-00045) and by Generalitat Valenciana (GVA-ACOMP-2013-012). Red Espanola de Supercomputacion (RES) and ALBA Synchrotron Light Source are also acknowledged. B.G.-D. and J.A.S. acknowledge financial support through the FPI program and Juan de la Cierva fellowship, respectively. We also thank J. L. Jorda for fruitful discussions. A.L.J.P. acknowledges financial support through Brazilian CNPq. A.S. expresses thanks to FEDER Grant UNLV10-3E-1253 for financial support.García-Domene, B.; Sans Tresserras, JÁ.; Gomis, O.; Manjón Herrera, FJ.; Ortiz, HM.; Errandonea, D.; Santamaría Pérez, D.... (2014). Pbca-Type In2O3: the high-pressure post-corundum phase at room temperature. Journal of Physical Chemistry C. 118(35):20545-20552. https://doi.org/10.1021/jp5061599S20545205521183

Synergistic NGF/B27 Gradients Position Synapses Heterogeneously in 3D Micropatterned Neural Cultures

Native functional brain circuits show different numbers of synapses (synaptic densities) in the cerebral cortex. Until now, different synaptic densities could not be studied in vitro using current cell culture methods for primary neurons. Herein, we present a novel microfluidic based cell culture method that combines 3D micropatterning of hydrogel layers with linear chemical gradient formation. Micropatterned hydrogels were used to encapsulate dissociated cortical neurons in laminar cell layers and neurotrophic factors NGF and B27 were added to influence the formation of synapses. Neurotrophic gradients allowed for the positioning of distinguishable synaptic densities throughout a 3D micropatterned neural culture. NGF and B27 gradients were maintained in the microfluidic device for over two weeks without perfusion pumps by utilizing a refilling procedure. Spatial distribution of synapses was examined with a pre-synaptic marker to determine synaptic densities. From our experiments, we observed that (1) cortical neurons responded only to synergistic NGF/B27 gradients, (2) synaptic density increased proportionally to synergistic NGF/B27 gradients; (3) homogeneous distribution of B27 disturbed cortical neurons in sensing NGF gradients and (4) the cell layer position significantly impacted spatial distribution of synapses

Optical properties of CdI

The transmittance (T) of thin films of CdI2, prepared by thermal evaporation technique on quartz substrates, have been measured over the wavelength range 200−900 nm. From analysis of the transmittance data, the optical constants, the refractive index (n) and the extinction coefficient (k), have been studied. Analysis of the refractive index (n) yields a low frequency dielectric constant, average oscillator strength and average oscillator energy. From analysis of the absorption coefficient (α), the fundamental absorption edge can be determined. Both allowed direct transitions and allowed indirect transitions are observed. The composition of films is checked using energy dispersive X-ray (EDX) spectroscopy technique. X-ray diffraction (XRD) measurements showed that the CdI2 films evaporated at room temperature substrates were characterized by a polycrystalline form. At large thicknesses the films indicated the inhomogeneity. The effect of annealing temperature (up to 523 K) on the film properties has been studied

Band gap and electronic structure of cubic, rhombohedral, and orthorhombicIn2O3polymorphs: Experiment and theory

Recent studies on In2O3 have revealed a rich phase diagram and have led to the discovery of new In2O3 polymorphs, including the synthesis and ambient recovery of Pbcn In2O3. The electronic properties of this new phase are studied together with other better-known polymorphs (Ia ¯ 3 and R¯3c) using soft x-ray absorption and emission spectroscopy, directly probing the partial density of states and transition matrix elements. Together with complementary full-potential all-electron density functional theory calculations, this allows important material parameters, such as the electronic band gap and partial density of states, to be elucidated. Excellent agreement between experiment and theory is obtained, with band gaps of 3.2±0.3,3.1±0.3, and 2.9±0.3 eV determined for the Ia¯3, R¯3c, and Pbcn In2O3 polymorphs, respectively. The effective mass of carriers in Pbcn In2O3 is predicted to be 12% less than in the widely used Ia3 polymorph while having a similar effective optical band gap