Periodic Mesoporous Silica - Synthesis and Surface Derivatization

Periodisch mesoporöse Materialien vom Typ MCM-n oder SBA-n sind in letzter Zeit zunehmend in den Brennpunkt des Wissenschaftsbereich „Katalyse“ und „Neue Materialien“ gerückt. In dieser Arbeit wurden periodisch mesoporöse Materialien vom Typ MCM-41, MCM-48 und SBA-15 mit variablen Porendurchmessern synthetisiert. Die Oberflächen dieser Materialien wurden mit metallorganischen Reagenzien modifiziert. Auf diese Weise wurden organische und metallorganische Oberflächen-Gruppen eingeführt sowie Monoschichten von Metalloxiden auf der Oberfläche erzeugt. Die Oberflächenspezies wurden mit Elementaranalyse, FTIR, MAS-NMR und Stickstoff-Physisorption charakterisiert.Periodic mesoporous silica materials have attracted much attention in the field of catalysis or material sciences. In this work periodic mesoporous materials such as MCM-41, MCM-48 and SBA-15 with adjustable pore sizes were synthesized. The materials were modified by surface grafting of organometallic compounds. Accordingly, organic and organometallic surface groups were introduced and also metal oxide monolayers were produced. The surface species were characterized by elemental analysis, FTIR, MAS NMR and nitrogen physisorption

Ag-only inner electrode Na₀.₅Bi₀.₅TiO₃-based X9R MLCC: achieving high performance and cost efficiency

The demand for high-power electronic applications is set to drive the necessity for robust components like multi-layer ceramic capacitors (MLCCs). These MLCCs must endure a broad temperature range and withstand high electric fields. Simultaneously, the production cost of these components is a crucial concern for manufacturers. The regularly used Ag/Pd inner electrodes constitute the most significant cost factor. Hence, this study showcases the fabrication of a sodium bismuth titanate (NBT)-based MLCC using only Ag inner electrodes. This could be achieved by reducing the sintering temperatures with the help of sintering aids, but still maintaining excellent dielectric properties of the ceramic. This MLCC demonstrates an exceptional operational temperature range (− 90 to 310 °C), high energy density (up to 5.1 J/cm³), higher efficiency (92%) at 217 kV/cm, and robust capacitance stability (variation less than 10%) even under high temperatures and electric fields

Recycling process development with integrated life cycle assessment - a case study on oxygen transport membrane material

The transformation towards a circular economy based on sustainable technologies requires future-oriented materials development, which considers materials recycling with a minimum environmental impact (EI). This demands a holistic approach towards materials design, including a combined assessment of functional and environmental performance. Scientific methods for environmental assessment, e.g., life cycle assessment (LCA), are well established but rarely integrated into the chemical process development at early stages. Consequently, sustainability claims often lack scientific verification. Here, we test the approach of integrating a screening LCA into the development of a chemical (recycling) process. As a relevant use case, we selected the recently developed oxygen transport membrane (OTM) material (La0.9Ca0.1)2Ni0.75Cu0.25O4±δ (LCNC). An initial LCA identified the consumption of primary metal nitrates as a major contributor to the EI of the primary synthesis. To address this issue, a Pechini-based chemical recycling process for LCNC was developed, which involves microwave-heated dissolution and subsequent re-gelation. Experimental results demonstrate the synthesis of recycled LCNC powder with primary-like properties, similar reaction behaviour, and >96% yield. Based on the LCA results, the EI of recycling is reduced by up to 76% compared to the primary synthesis in 12 of 14 impact categories. Measures for the simultaneous improvement of the process functionality and environmental performance were identified. The approach of integrating LCA in chemical process development is discussed critically based on the given use case. The results strongly encourage the integration of LCA as a standard method into the future development of sustainable chemical processes

Morphologically and compositionally controlled Cs2SbBr6 by Bi and Ag substitution

Morphology-controlled Cs2SbBr6 crystals are synthesized by Bi- and Ag-substitution of the precursor solution. X-ray diffraction (XRD) together with Raman spectroscopy confirms the lattice tilting and symmetry changes with the dominant appearance of higher index facets by Bi substitution. Ag substitution does not induce crystal symmetry changes in the Cs2BBr6 (B = Sb or Bi) phase, but results in highly defective structures hindering the formation of a smooth surface during the crystal growth. Successful substitution of Bi and limited substitution of Ag into Cs2SbBr6 is also confirmed by energy dispersive X-ray spectroscopy (EDX). This research provides design principles and practical examples of how to control the morphology of Cs2SbBr6 crystals with structural defects and multiphase formation

Tailoring the Anisotropic Oxygen Transport Properties in Bulk Ceramic Membranes Based on a Ruddlesden–Popper Oxide by Applying Magnetic Fields

Textured Nd2NiO4+δ bulk ceramic membranes are fabricated via slip casting in a 0.9 T magnetic field generated by neodymium magnets. This process aligns the oxide grains with their easy-magnetization c-axis parallel to the applied magnetic field. Depending on the magnetic field's direction relative to the slip casting, grains orient either with their a,b-plane or c-axis parallel to the normal direction of the disk-shaped ceramic, thus aligning with the oxygen permeation direction. Without the magnetic field, a non-textured bulk membrane is formed. The microstructure and texture of the ceramic membranes are meticulously analyzed using advanced techniques, including X-ray diffraction, scanning and transmission electron microscopy, as well as related methods. Evaluation of the texturing effect on the oxygen permeation performance shows that the a,b-plane textured Nd2NiO4+δ bulk membrane achieves the highest oxygen permeation fluxes between 1023–1223 K. Additionally, it demonstrates impressive CO₂ stability, maintaining effective performance for at least 140 h due to preferential oxygen transport along the a,b-plane. These characteristics make Nd2NiO4+δ an auspicious material for industrial applications as an oxygen transport membrane, outperforming more susceptible perovskite-based materials. Magnetic alignment thus proves to be an effective method for achieving membrane texturing, enabling precise regulation of oxygen transport properties

Tunable optical properties and the role of defects on the carrier lifetimes of Cs3Sb2I9 synthesized in various solvents

Pb-free halide perovskites have recently attracted immense attention due to the number of advantages in their optical and electronic properties. However, tuning the optical bandgap with minimized amounts of point defects is a particularly challenging task in photovoltaics. It is pivotal to clearly understand the detailed relationship between the bandgap change with defect generation and charge carrier lifetime. In this study, Cs3Sb2I9 crystals are synthesized by varied choice of solvents, namely, γ-butyrolactone, a mixture of dimethylformamide and dimethyl sulfoxide, and hydroiodic acid. Although the same principles of decreasing solubility and crystallization are applied, Cs3Sb2I9 crystals with different size and shape in microscopic and macroscopic scale are obtained during heating and cooling of the solution. The synthesized crystals are investigated using a combination of different spectroscopies including Raman, UV–visible, and time-resolved photoluminescence. In the results, it is suggested that there is a strong relationship between Urbach energy and the lifetime of charge carriers. In this research, readily applicable practical principles and examples of how to control the defects for the advancement in Pb-free perovskite photovoltaics are provided

Tailoring the structure and thermoelectric properties of BaTiO3via Eu2+ substitution

A series of Ba1_xEuxTiO3_d (0.1 < x < 0.9) phases with B40 nm particle size were synthesized via a Pechini method followed by annealing and sintering under a reducing atmosphere. The effects of Eu2+ substitution on the BaTiO3 crystal structure and the thermoelectric transport properties were systematically investigated. According to synchrotron X-ray diffraction data only cubic perovskite structures were observed. On the local scale below about 20 \uc5 (equal to B5 unit cells) deviations from the cubic structure model (Pm%3m) were detected by evaluation of the pair distribution function (PDF). These deviations cannot be explained by a simple symmetry breaking model like in EuTiO3_d. The best fit was achieved in the space group Amm2 allowing for a movement of Ti and Ba/Eu along h110i of the parent unit cell as observed for BaTiO3. Density functional calculations delivered an insight into the electronic structure of Ba1_xEuxTiO3_d. From the obtained density of states a significant reduction of the band gap by the presence of filled Eu2+ 4f states at the top of the valence band was observed. The physical property measurements revealed that barium\u2013europium titanates exhibit n-type semiconducting behavior and at high temperature the electrical conductivity strongly depended on the Eu2+ content. Activation energies calculated from the electrical conductivity and Seebeck coefficient data indicate that at high temperatures (800 K o T o 1123 K) the conduction mechanism of Ba1_xEuxTiO3_d (0.1 r x r 0.9) is a polaron hopping when 0 o x r 0.6 and is a thermally activated process when 0.6 o x o 1. Besides, the thermal conduc tivity increases with increasing Eu2+ concentration. Due to a remarkable improvement of the power factor, Ba0.1Eu0.9TiO3_d showed a ZT value of 0.24 at 1123 K

Site-selective substitution and resulting magnetism in arc-melted perovskite ATiO3-δ (A = Ca, Sr, Ba)

Magnetic properties in perovskite titanates ATiO3-δ (A = Ca, Sr, Ba) were investigated before and after arc melting. Crystal structure analysis was conducted by powder synchrotron X-ray diffraction with Rietveld refinements. Quantitative chemical element analysis was carried out by X-ray photoelectron spectroscopy. Magnetic measurements were conducted by vibrating sample magnetometer and X-ray magnetic circular dichroism (XMCD). The magnetic properties are found to be affected by impurities of 3d elements such as Fe, Co, and Ni. Depending on the composition and crystal structure, the occupation of the magnetic ions in perovskite titanates is selectively varied, which is interpreted to be the origin of the different magnetic behaviors in arc-melted perovskite titanates ATiO3-δ (A = Ca, Sr, Ba). In addition, both formation of oxygen vacancies and the reduction of Ti4+ to Ti3+ during arc-melting also play a role as proven by XMCD. Nevertheless, preferential site occupation of magnetic impurities is dominant in the magnetic properties of arc-melted perovskite ATiO3-δ (A = Ca, Sr, Ba)

Hydrogen-Tolerant La0.6Ca0.4Co0.2Fe0.8O3–d Oxygen Transport Membranes from Ultrasonic Spray Synthesis for Plasma-Assisted CO2 Conversion

La0.6Ca0.4Co1–xFexO3–d in its various compositions has proven to be an excellent CO2-resistant oxygen transport membrane that can be used in plasma-assisted CO2 conversion. With the goal of incorporating green hydrogen into the CO2 conversion process, this work takes a step further by investigating the compatibility of La0.6Ca0.4Co1–xFexO3–d membranes with hydrogen fed into the plasma. This will enable plasma-assisted conversion of the carbon monoxide produced in the CO2 reduction process into green fuels, like methanol. This requires the La0.6Ca0.4Co1–xFexO3–d membranes to be tolerant towards reducing conditions of hydrogen. The hydrogen tolerance of La0.6Ca0.4Co1–xFexO3–d (x = 0.8) was studied in detail. A faster and resource-efficient route based on ultrasonic spray synthesis was developed to synthesise the La0.6Ca0.4Co0.2Fe0.8O3–d membranes. The La0.6Ca0.4Co0.2Fe0.8O3–d membrane developed using ultrasonic spray synthesis showed similar performance in terms of its oxygen permeation when compared with the ones synthesised with conventional techniques, such as co-precipitation, sol–gel, etc., despite using 30% less cobalt

Synthesis and Characterization of 40 wt % Ce₀.₉Pr₀.₁O₂−δ−60 wt % NdxSr₁₋ₓFe₀.₉Cu₀.₁O₃−δ Dual-Phase Membranes for Efficient Oxygen Separation

Dense, H₂- and CO₂-resistant, oxygen-permeable 40 wt % Ce₀.₉Pr₀.₁O₂–δ–60 wt % NdₓSr₁₋ₓFe₀.₉Cu₀.₁O₃−δdual-phase membranes were prepared in a one-pot process. These Nd-containing dual-phase membranes have up to 60% lower material costs than many classically used dual-phase materials. The Ce₀.₉Pr₀.₁O₂−δ–Nd₀.₅Sr₀.₅Fe₀.₉Cu₀.₁O₃−δ sample demonstrates outstanding activity and a regenerative ability in the presence of different atmospheres, especially in a reducing atmosphere and pure CO₂ atmosphere in comparison with all investigated samples. The oxygen permeation fluxes across a Ce₀.₉Pr₀.₁O₂−δ–Nd₀.₅Sr₀.₅Fe₀.₉Cu₀.₁O₃−δ membrane reached up to 1.02 mL min⁻¹ cm⁻² and 0.63 mL min⁻¹ cm⁻² under an air/He and air/CO₂ gradient at T = 1223 K, respectively. In addition, a Ce₀.₉Pr₀.₁O₂–δ–Nd₀.₅Sr₀.₅Fe₀.₉Cu₀.₁O₃–δ membrane (0.65 mm thickness) shows excellent long-term self-healing stability for 125 h. The repeated membrane fabrication delivered oxygen permeation fluxes had a deviation of less than 5%. These results indicate that this highly renewable dual-phase membrane is a potential candidate for long lifetime, high temperature gas separation applications and coupled reaction–separation processes