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To arrive to sustainable hydrogen-based energy solutions, the understanding of water-splitting catalysts plays the most crucial role. Herein, state-of-the-art hypotheses are combined on electrocatalytic active metal sites toward the oxygen evolution reaction (OER) to develop a highly efficient catalyst based on Earth-abundant cobalt and zinc oxides.
The precursor catalyst Zn0.35Co0.65O is synthesized via a fast microwaveassisted approach at low temperatures. Subsequently, it transforms in situ from the wurtzite structure to the layered γ-Co(O)OH, while most of its zinc leaches out. This material shows outstanding catalytic Performance and stability toward the OER in 1 m KOH (overpotential at 10 mA cm−2 ηinitial = 306 mV, η98 h = 318 mV). By comparing the electrochemical results and ex situ analyses to today’s literature, clear structureactivity correlations are able to be identified. The findings suggest that coordinately unsaturated cobalt octahedra on the surface are indeed the active centers for the OER.
The mechanism of action of zirconium permanent modifiers on graphite surfaces was investigated in order to understand its influence on the analytical signal in atomic and molecular absorption spectrometry (AAS/MAS). For this, the molecule formation of CaF was studied, which is used for the indirect analytical determination of fluorine in high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GFMAS). The kinetics of this reaction was established by monitoring its molecular spectrum at different atomisation temperatures. An Arrhenius plot showed a pseudo-first order reaction with respect to fluorine (n = 1). An intermediate state was isolated, and its structure was elucidated by spectroscopic methods: scanning electron microscopy with energy dispersive X-ray spectroscopy (SEMEDX), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XANES and EXAFS), and Raman microspectroscopy. We propose here a mechanism, where ZrO2 acts as a heterogeneous catalyst: after a pyrolytic step, an intermediate state of ZrO(OCaF) is activated, and at higher temperatures, CaF(g) is released from the zirconium-coated graphite surface. No evidence of the formation of zirconium carbide was found. Consequently, as the CaF formation is catalysed by a heterogeneous catalyst, surface modifications with ZrO2 nanoparticles and ZrO xerogels were investigated in order to increase the surface area. Their influence was evaluated in the molecule formation of CaF, CaCl, CaBr, and CaI. Graphite furnace modification with zirconium oxide nanoparticles proves to be the best choice for fluorine analysis with a signal enhancement of more than eleven times with respect a non-coated graphite furnace. However, the influence of zirconium modifications in the analytical signals of Cl, and I is lower than the F signals or even negative in case of the Br. Understanding zirconium modifiers as heterogeneous catalysts offers a new perspective to AAS and MAS, and reveals the potential of surface analytical methods for development of improved permanent modifiers and graphite furnace coatings.
This paper reports the formation of zinc phosphate nanoparticles from the artificial digestion of zinc chloride. Initially, the formation of amorphous primary particles with a mean radius of 1.1 nm is observed, alongside the formation of larger, protein stabilized aggregates. These aggregates, with a radius of gyration of 37 nm, are observed after 5 minutes of exposure to artificial saliva and are shown to be colloidally stable for a minimum time of two weeks. The initially formed primary particles are thought to consist of amorphous zinc phosphate, which is then transformed into crystalline Zn3(PO4)2·4H2O over the course of two weeks. Our results demonstrate that the interaction of inorganic salts with bodily fluids can induce the formation of de novo nanoparticles, which in turn, provides insights into how zinc‐enriched foods may also facilitate the formation of nanoparticles upon contact with saliva. As such, this may be considered as an undesirable (bio)mineralization.
X‑ray emission during the ablative processing of biological materials by ultrashort laser pulses
(2023)
The ablative laser processing with ultrashort pulsed laser beams may cause secondary emission of hazardous X-rays. While the effect has recently been proven to be considered in working safety regulations when processing technical materials, such as metals, the X-ray emission rates during the ablative processing of biological tissue materials are widely unexplored yet.
Therefore, biological materials like water, isotonic saline solution, pig eyes, and human teeth were ablated with ultrashort laser pulses of 1030 nm wavelength, 600 fs pulse duration and 5 kHz pulse repetition rate, aiming to mimic typical surgery situations. Simultaneously, in-situ X-ray dose rate measurements were performed at a short distance from the plasma to display potential X-ray emission. For all four studied biological materials, our measurements prove the secondary emission of laser-induced X-rays.
Direct Laser Writing (DLW) and X-ray computed tomography (XCT) both offer unique possibilities in their respective fields. DLW produces full three-dimensional (3D) polymer structures on the microscale with resolutions below 100 nm. The fabricated structures can be analysed by XCT or X-ray microscopy (XRM), which incorporates additional X-ray lenses, in three dimensions down to a minimal basic spatial resolution of about 500 nm or 50 nm, respectively. In this work, two different DLW structures are analysed via XCT. Internal defects are detected and analysed for the purpose of quality control. Defects and structures with sizes down to 1.5 µm are successfully analysed. A 3D reconstruction and internal, hidden features of the fabricated structures are shown and discussed. In a first-of-its-kind study, we demonstrate the detectability of a single-voxel line inside a fabricated structure that would not be detectable with SEM or light microscopy. Furthermore, the direct fabrication on a PET substrate is shown to overcome the high X-ray absorbance of commonly used glass substrates. Attenuation spectra of SZ2080 and glass substrates are compared to a fabrication route direct on a 170 µm PET foil. The practical aspects of XCT measurements for DLW structures on different substrates will be discussed.
Ultrashort pulse laser processing of materials allows for precise machining with high accuracy. By increasing the repetition rate to several 100 kHz, laser machining becomes quick and cost-effective. Ultrafast laser processing at high repetition rates and peak intensities above 10^13 W/cm^2 can cause a potential hazard by generation of unwanted x-ray radiation. Therefore, radiation protection must be considered. For 925 fs pulse duration at a center wavelength of 1030 nm, the x-ray emission in air at a repetition rate of 400 kHz was investigated up to a
peak intensity of 2.6 × 10^14 W/cm^2. Based on the presented measurements, the properties of potential shielding materials will be discussed. By extending our previous works, a scaling of the x-ray radiation emission to higher peak intensities up to 10^15 W/cm^2 is described, and emitted x-ray doses are predicted.
X-ray emission hazards from ultrashort pulsed laser material processing in an industrial setting
(2021)
Interactions between ultrashort laser pulses with intensities larger than 10^13 W/cm^2 and solids during material processing can lead to the emission of X-rays with photon energies above 5 keV, causing radiation hazards to operators. A framework for inspecting X-ray emission hazards during laser material processing has yet to be developed. One requirement for conducting radiation protection inspections is using a reference scenario, i.e., laser settings and process parameters that will lead to an almost constant and high level of X-ray emissions. To study the feasibility of setting up a reference scenario in practice, ambient dose rates and photon energies were measured using traceable measurement equipment in an industrial setting at SCHOTT AG. Ultrashort pulsed (USP) lasers with a maximum average power of 220 W provided the opportunity to measure X-ray emissions at laser peak intensities of up to 3.3 × 10^15 W/cm^2 at pulse durations of ~1 ps. The results indicate that increasing the laser peak intensity is insufficient to generate high dose rates. The investigations were affected by various constraints which prevented measuring high ambient dose rates. In this work, a list of issues which may be encountered when performing measurements at USP-laser machines in industrial settings is identified.
In laser machining with ultrashort laser pulses unwanted X-ray radiation in the keV range can be generated when a critical laser intensity is exceeded. Even if the emitted X-ray dose per pulse is low, high laser repetition rates can lead to an accumulation of X-ray doses beyond exposure safety limits. For 925 fs pulse duration at a center wavelength of 1030 nm, the X-ray emission was investigated up to an intensity of 2.6 × 10^14 W/cm2. The experiments were performed in air with a thin disk laser at a repetition rate of 400 kHz. X-ray spectra and doses were measured for various planar target materials covering a wide range of the periodic table from aluminum to tungsten. Without radiation shielding, the measured radiation doses at this high repetition rate clearly exceed the regulatory limits. Estimations for an adequate radiation shielding are provided.
Ultrashort pulse laser processing can result in the secondary generation of unwanted X-rays if a critical laser irradiance of about 10^13 W/cm^2 is exceeded. Spectral X-ray emissions were investigated during the processing of tungsten and steel using three complementary spectrometers (based on CdTe and silicon drift detectors) simultaneously for the identification of a worst-case spectral scenario. Therefore, maximum X-ray photon energies were determined, and corresponding dose equivalent rates were calculated. An ultrashort pulse laser workstation with a pulse duration of 274 fs, a center wavelength of 1030 nm, pulse repetition rates between 50 kHz and 200 kHz, and a Gaussian laser beam focused to a spot diameter of 33 µm was employed in a single pulse and burst laser operation mode. Different combinations of laser pulse energy and repetition rate were utilized, keeping the average laser power constant close to the maximum power of 20 W. Peak irradiances ranging from 7.3 × 10^13 W/cm^2 up to 3.0 × 10^14 W/cm^2 were used. The X-ray dose equivalent rate increases for lower repetition rates and higher pulse energy if a constant average power is used. Laser processing with burst mode significantly increases the dose rates and the X-ray photon energies. A maximum X-ray photon energy of about 40 keV was observed for burst mode processing of tungsten with a repetition rate of 50 kHz and a peak irradiance of 3 × 10^14 W/cm^2.
We present a workflow for obtaining fully trained artificial neural networks that can perform automatic particle segmentations of agglomerated, non-spherical nanoparticles from scanning electron microscopy images “from scratch”, without the need for large training data sets of manually annotated images. The whole process only requires about 15 minutes of hands-on time by a user and can typically be finished within less than 12 hours when training on a single graphics card (GPU). After training, SEM image analysis can be carried out by the artificial neural network within seconds. This is achieved by using unsupervised learning for most of the training dataset generation, making heavy use of generative adversarial networks and especially unpaired image-to-image translation via cycle-consistent adversarial networks. We compare the segmentation masks obtained with our suggested workflow qualitatively and quantitatively to state-of-the-art methods using various metrics. Finally, we used the segmentation masks for automatically extracting particle size distributions from the SEM images of TiO2 particles, which were in excellent agreement with particle size distributions obtained manually but could be obtained in a fraction of the time.
An artificial digestion of silver nitrate is reported. It is shown that AgSCN nanoparticles emerge from ionic silver in saliva and remain present during the entire digestion process. The particles were characterized by infrared spectroscopy and small- and wide-angle X-ray scattering (SAXS/WAXS) regarding their composition and size distribution.
The definition of the term “conversion” is discussed for a variety of polymer syntheses. It is demonstrated that in contrast to organic and inorganic chemistry several different definitions are needed in polymer science. The influence of increasing conversion on structure and topology of homo- and Copolymers is illustrated. Chain-growth polymerizations, such as radical polymerization or living anionic polymerizations of vinyl monomers, condensative chain polymerization, two and three-dimensional step-growth polymerizations, ring–ring or chain–chain equilibration and chemical modification of polymers are considered.
The coherent exchange of optical near fields between two neighbouring dipoles plays an essential role in the optical properties, quantum dynamics and thus the function of many naturally occurring and artificial nanosystems. These interactions are challenging to quantify experimentally. They extend over only a few nanometres and depend sensitively on the detuning, dephasing and relative orientation (that is, the vectorial properties) of the coupled dipoles. Here, we introduce plasmonic nanofocusing spectroscopy to record coherent light scattering spectra with 5 nm spatial resolution from the apex of a conical gold nanotaper.
The apex is excited solely by evanescent fields and coupled to plasmon resonances in a single gold nanorod. We resolve resonance energy shifts and line broadenings as a function of dipole distance and relative orientation. We demonstrate how These phenomena arise from mode couplings between different vectorial components of the interacting optical near fields, specifically from the coupling of the nanorod to both transverse and longitudinal polarizabilities of the taper apex.
Due to the extremely high specific surface area of nanoparticles and corresponding potential for adsorption, the results of surface analysis can be highly dependent on the history of the particles, particularly regarding sample preparation and storage. The sample preparation method has, therefore, the potential to have a significant influence on the results. This report describes an interlaboratory comparison (ILC) with the aim of assessing which sample preparation methods for ToF-SIMS analysis of nanoparticles provided the most intra- and interlaboratory consistency and the least amount of sample contamination. The BAM reference material BAM-P110 (TiO2 nanoparticles with a mean Feret diameter of 19 nm) was used as a sample representing typical nanoparticles. A total of 11 participants returned ToF-SIMS data,in positive and (optionally) negative polarity, using sample preparation methods of “stick-and-go” as well as optionally “drop-dry” and “spin-coat.” The results showed that the largest sources of variation within the entire data set were caused by adventitious hydrocarbon contamination or insufficient sample coverage, with the spin-coating protocol applied in this ILC showing a tendency toward insufficient sample coverage; the sample preparation method or the participant had a lesser influence on results.
Using solid catalysts in disulfide-based dynamic combinatorial solution- and mechano-chemistry
(2022)
We here show for the first time that solid amines can act as catalysts for disulfide-based dynamic combinatorial chemistry by ball mill grinding. The mechanochemical Equilibrium for the two disulfide reactions studied is reached within one to three hours using ten different amine catalysts. This contrasts with the weeks to months to achieve solution equilibrium for most solid amine catalysts at 2%M at 2mM concentration in a suitable solvent. The final mechanochemical equilibrium is independent of the catalyst used, but varies with other ball mill grinding factors such as the presence of traces of solvent. The different efficiencies of the amines tested are discussed.
Uptake and molecular impact of aluminum-containing nanomaterials on human intestinal caco-2 cells
(2018)
Aluminum (Al) is one of the most common elements in the earth crust and increasingly used in food, consumer products and packaging. Its hazard potential for humans is still not completely understood. Besides the metallic form, Al also exists as mineral, including the insoluble oxide, and in soluble ionic forms. Representatives of these three species, namely a metallic and an oxidic species of Al-containing nanoparticles and soluble aluminum chloride, were applied to human intestinal cell lines as models for the intestinal barrier. We characterized physicochemical particle parameters, protein corona composition, ion release and cellular uptake. Different in vitro assays were performed to determine potential effects and molecular modes of Action related to the individual chemical species. For a deeper insight into signaling processes, microarray transcriptome analyses followed by bioinformatic data analysis were employed. The particulate Al species showed different solubility in biological media. Metallic Al nanoparticles released more ions than Al2O3 nanoparticles, while AlCl3 showed a mixture of dissolved and agglomerated particulate entities in biological media. The protein corona composition differed between both nanoparticle species. Cellular uptake, investigated in transwell experiments, occurred predominantly in particulate form, whereas ionic Al was not taken up by intestinal cell lines. Transcellular transport was not observed. None of the Al species showed cytotoxic effects up to 200 mg Al/mL. The transcriptome analysis indicated mainly effects on oxidative stress pathways, xenobiotic metabolism and metal homeostasis. We have shown for the first time that intestinal cellular uptake of Al occurs preferably in the particle form, while toxicological effects appear to be ion-related.
Zielsetzung des vom Bundesministerium für Bildung und Forschung geförderten Projektes RUSEKU war es, repräsentative Untersuchungsstrategien für die Detektion von Mikroplastik mittels TED GC/MS in wässerigen Medien zu ermitteln. Dabei wurden verschiedene Probenahmekonzepte und – verfahren für unterschiedliche Fallgestaltungen und Fragestellungen untersucht, sowie neue Filtersysteme entwickelt. Bei der Detektion der Partikel lag der Fokus auf der Anwendung und Weiterentwicklung der ThermoExtraktion/Desorption-Gaschromatographie-Massenspektrometrie (TED-GC/MS) zur Bestimmung von Mikroplastikgehalten. Anwendung fanden die Methoden bei der Beprobung von Flaschenwasser, Waschmaschinenabläufen, dem urbanen Abwassersystem der Stadt Kaiserslautern, sowie in Oberflächengewässer.
Ligand based modification has been performed to synthesize a pair of
mixed ligands d10 MOF based materials related to a previously published compound as a base material. The previous compound was a Zn(II)-MOF, {[Zn(4-bpdh)(H2dht)](MeOH)(H2O)}n (1) [N,N′-bis(1-pyridin-4-yl-ethylidene)hydrazine = 4-bpdh and 2,5-dihydroxyterephthalic acid = H4dht], which is a five-fold interpenetrated framework and highly dynamic in nature. In the first synthetic modification, the central metal is replaced by Cd(II), which has the same framework formula as the base material, but this is a rigid compound and also there is no interpenetration in the framework. In the second modification, along with the metal center, the 4,4′- coordinating N,N′-donor ligand is replaced by an isomeric 3,3′-coordinating N,N′- donor linker. In this compound, the dynamism is regenerated. The dynamic nature can be realized by the extensive PXRD studies and characteristic “step-shaped” gas/solvent adsorption behavior for CO2, water, and ethanol. Furthermore, all these 3D MOFs show excited-state intramolecular proton transfer phenomena and water sensing properties in different organic solvents. Here excitingly, the ease of water sensing property is directly related to the dynamic behavior of the framework which has been studied thoroughly in terms of structural correlation.
Unintended Rate Enhancement in Mechanochemical Kinetics by Using Poly(methyl methacrylate) Jars
(2022)
Time-resolved in situ (TRIS) X-ray diffraction has changed how mechanochemical transformations are studied but requires the use of X-ray transparent jars often made from poly(methyl methacrylate) (PMMA). However, using PMMA jars can alter the apparent kinetics of mechanochemical polymorphism by an order of magnitude, questioning the interpretability of established TRIS methods. Our results suggest that rate enhancement in PMMA jars may not be dominated by chemical effects of the polymer, but rather a result of different equilibrium temperatures within the jar. These features must be better understood before control over mechanochemical reactions can be achieved.