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Lanthanide Nanocrystals as Authentication and Security Tags and Reporters for Optical Sensors
(2023)
Counterfeiting of goods has serious economic implications worldwide and can present a considerable threat to human health and national security, rendering product authentication more and more important. This led to an increasing interest in simple tags for anticounterfeiting and authentication applications for the integration into different materials and matrices that are robust enough to survive the respective production processes and can be read out in-situ with simple instrumentation.
Here we present a platform of chemically inert, multi-color luminescent lanthanide nanocrystals (LnNC) consisting of a NaYF4 matrix doped with Yb, Er, Tm, or Ho as promising candidates for such applications.
LnNC with characteristic multi-color emission patterns, composed of narrow bands of varying intensity in the ultraviolet, visible, near-infrared, and short-wave were synthesized via a thermal decomposition approach under inert conditions[1]. The tailor-made design of different emission pattern was achieved by tuning particle size, material composition, and particle surface chemistry in upscaleable syntheses.[2] Particle size and morphology were determined by dynamic light scattering and transmission electron microscopy and the optical properties were characterized by absorption and fluorescence spectroscopy as well as fluorescence lifetime measurements.
The particles were then incorporated into security inks and consumer products. In addition, microenvironment-specific changes in the emission properties of the LnNC tag were utilized to study and sense changes of physico-chemical parameters in different matrices.
Counterfeiting of goods has serious economic implications worldwide and can be a threat to human health and safety. Upconversion nanoparticles (UCNPs)are ideal candidates for optical encoding of various materials. Particles with tailor-made emission patterns can be used as anti-counterfeiting markers and luminophores in security inks and to track material flows. Microenvironment-specific changes in the emission properties of the UCNP tags can be used to study, signal, and sense changes of physico-chemical parameters in different environments, e.g., building
materials.
Use of the solvent-free mechanochemical method for a sustainable preparation of pharmaceuticals
(2023)
With the growing interest in environmental issues on the part of governments and institutions, pharmaceutical industries are asked to reduce their environmental footprint. Given the major impact related to the use of solvents, the development of methodologies less solvent demanding is nowadays even more urgent. In light of that, mechanochemistry would be a suitable solvent-free technology since it promotes the activation of the chemical reactions between (generally) solid materials via inputs of mechanical energy. Since such reactions may occur outside the kinetic and thermodynamic rules of conventional solution chemistry, the main limit of mechanochemistry is the poor mechanistic understanding of the solid-state transformations involved, which is still hindering a widespread use of the method, as well a scale-up to the industrial level. However, the development of methods for real-time monitoring of the mechanochemical reactions enables obtaining (in)accessible information on reaction intermediates, new products, or reaction time, thus getting closer to a better understanding of the mechanistic behaviour. With the rules of this chemistry becoming increasingly clear, the new reaction pathways of mechanochemistry wouldn’t represent a limit anymore, but an asset, that may lead to lot of opportunities for the pharmaceutical industry.
Safety is a key parameter for the design and construction of buildings. The most widely used construction material to date is concrete that consists of about 15-20 wt.-% cement, which is responsible for the main concrete properties, i.e., strength and durability. Despite many standards regulating the quality of cement, at present, there exists no viable method to track the cement life cycle “from cradle to grave”. This led to an increasing interest in simple and robust methods for studying the processes and changes occurring during the life cycle of cement. In this context, we explored the applicability of fluorescence measurements which can be performed with relatively inexpensive and miniaturized instrumentation yet require robust optical probes which survive the harsh cement environment. Therefore, we developed a platform of lanthanide-based upconversion nanoparticles (UCNPs), consisting of a NaYF4 matrix doped with Yb3+ and Er3+ with sizes between 20 nm and 55 nm, which show characteristic multi-color emission patterns, composed of narrow bands of varying intensity in the ultraviolet, visible, near-infrared, and short-wave spectral region and examined their potential for cement probing and the non-invasive monitoring of the hydration processes occurring during cement formation.
UCNPs of different size and chemical composition were synthesized via a thermal decomposition approach under inert conditions. The tailor-made design of different emission patterns was achieved by tuning particle size and morphology, material composition, and particle surface chemistry in upscaleable syntheses. For cement probing, different types of UCNPs were added to cement and the evolution of the UCNP emission pattern was used to probe in-situ changes of physico-chemical parameters in the cementitious environment during hydration, utilizing a simple and portable custom-designed optical setup. The observed changes in the UCNP emission patterns are characteristic for a given particle size, surface chemistry, and cement composition. In addition to fluorescence measurements, conventional isothermal heat flow calorimetry was used to study the influence of UCNP addition on cement hydration kinetics. Subsequently, both sets of measurements were correlated. Our results underline the potential of our optical approach ad UCNPs for the non-invasive probing of cementitious systems and cement hydration. This can be also exploited for cutting-edge applications of construction materials such as 3D concrete printing.
Mechanochemistry provides polymorphs that are difficult to obtain by conventional solution-based methods. Based on the nicotinamide and pimelic acid cocrystal, we demonstrated that the ball size, frequency, and temperature are essential parameters. Our results indicate that fine-tuning the energy input during a mechanochemical reaction can provide control over polymorphism.
Benchtop 1H-NMR and FTIR have both been successfully developed for size-exclusion chromatography (SEC) applications. The latest implementations of these methods by Wilhelm and collaborators[1-3] have taken advantage of commerically available low-cost equipment, and a provide a means to obtain slice-by-slice spectra for the monitoring of functional groups in polymer separations. Demonstrated applications include the detection of highly diluted chains in a polymer blend (e.g., PS/PMMA), copolymer content determination (e.g., styrene-methyl methacrylate), and butadiene isomer detection. To synthesize and characterize an end-labelled low molecular wt. poly(ethylene glycol) as a model polymer to aid in the development and validation of spectroscopic detection (FTIR and 1H-NMR) for SEC applications. A particular focus is to improve quantitation and/or detection of highly diluted funtional groups (e.g., polymer chain ends or sparsely functionalized chains) In the first approach, an isocyanate with IR- and NMR-active functional groups was reacted with PEG (4000 and 10000 g/mol) to form end-functionalized chains by means of an addition reaction. The functionalization of the 10000 g/mol PEG was found to be non-homogeneous (not discussed further). The 4000 g/mol PEG was successfully functionalized to 100%, found to be homogeneous across the molecular weight distribution and could therefore serve as a model polymer for analysis by the coupled methods.
Nanoparticles (NPs) have become important materials for a variety of chemical technologies, including catalysis. One of the main challenges is the reduction of green house gases, such as CO2. One opportunity besides the capturing is the conversion to synthesis gas via the reverse water-gas shift reaction.
A facile and efficient method is described for the solvothermal synthesis of size-tunable, stable, and uniform NiCu core-shell NPs. The diameter of the NPs can be tuned in a range from 6 nm to 30 nm and the Ni:Cu ratio from 30:1 to 1:1. The NPs are structurally characterized with combination of transmission electron microscopy, anomalous small-angle X-ray scattering, X-ray photoelectron spectroscopy, and X-ray absorption fine structure. Using these analytical methods, a core-shell-shell structure their chemical composition is elucidated. A depletion from the core to the shell is observed, with the core consisting of NiCu alloy, surrounded by an inner Ni-rich shell and an outer NiO shell. The SiO2-supported NiCu core-shell NPs show pronounced selectivity of >99% for CO in the catalytic reduction of CO2 to CO using hydrogen as reactant (reverse water–gas shift reaction).
With the online coupling (or hyphenation) of chemically-resolved spectroscopy detection with classical size-exclusion chromatography (SEC) it is possible to correlate polymer molecular size with chemical structure in a single in-situ or on-flow measurement. Medium-resolution 1H-NMR (60 MHz) spectroscopy (i.e., “desktop NMR”) and Fouriertransform Infrared Spectroscopy (FTIR) have both been developed as coupled methods (SEC-MR-NMR, SEC-FTIR) for the detection of polymer analytes by monitoring e.g. alkene or carbonyl functionality.1,2 Here, we have investigated the potential for the detection of polymer end groups, using a slightly higher field-strength spectrometer (80 MHz 1H Larmor frequency) and taking advantage of a columnless injection method that provides bulk spectra for reference. End-functionalized polymers were synthesized by reaction of PEG with toluene isocyanate, yielding ,-functionalized polymers with exactly 2 IR- and NMR-detectable functional groups per chain, as proven by MALD-TOF mass spectrometry. We have investigated the sensitivity (limit of detection) and spectral resolution for these functional groups in chloroform, THF, and water. Results have demonstrated a good feasibility for the simultaneous online detection of PEG backbone (M~4000 g/mol) and these end groups at the level of ca. 2 mol%.
Mechanochemistry offers a unique opportunity to modify or synthesize new crystal forms. Although the method is very promising, little is known about the mechanochemical means to control the synthesis of a solid form. Using an polymorphic organic cocrystal system, we show here that mechanochemistry can be used to obtain a polymorph transformation under the apparently conventional (thermal) transition point.
Our aim is to develop a simple and inexpensive method for full field X-ray fluorescence imaging.We combine an energydispersive array detector with a coded aperture to obtain high resolut ion images. To obtain the information from the recorded image a reconstruction step is necessary. The reconstruction methods we have developed, were tested on simulated data and then applied to experimental data. The first tests were carried out at the BAMline @BESSY II. This method enables the simultaneous detection of multiple elements,which is important e.g. in the field of catalysis.
Compositionally complex alloys (CCAs) are a new class of alloys containing at least 5 elements with concentrations between 5 and 35 atomic percent. Due to their adjustable composition, which enables modifications of mechanical properties (such as hardness, strength and ductility etc) and their stability at high temperatures, CCAs have been the focus of various studies [1,2]. Especially the corrosion behavior of CCAs has been a wide research interest.
However, there are only few studies that deals with the degradation process on such materials, which is highly relevant for the safety aspect for future component design. To thoroughly investigate the corrosion processes and to determine oxidation states of metal components within the reaction products, we need special analytical tools. Since the grazing exit X-ray fluorescence (GEXRF) offers a non-destructive way to collect notable information regarding the high temperature oxidation, we consider it as a useful method to investigate how CCAs behave in corrosive environments.
The main idea of grazing geometry is to enhance the fluorescence signal of the surface. This enables highly sensitive surface analyses of thin protective film on surface in sub-micrometer scale [3]. When compared to a conventional CCD-based camera, the advantage and most important feature of the detector system (Color X-Ray Camera (CXC)) is that each pixel is an energy sensitive detector. The position and area sensitive detector, with 264x264 pixel detector area, provides information regarding the signal emitted from the sample as a function of the emission angle and thus allows depth-sensitive analysis. Furthermore, the data collected from samples of an incidence energy which can be controlled with a resolution of 0.5 eV provides XANES data to determine oxidation states.
In this contribution, we address the feasibility of our setup and new optimization procedure (Bayesian Optimization and Gaussian Regression). The results of a conceptual study regarding layer properties of the reference sample (Cr-Oxide layer (300nm) on Cr layer (500nm) on Si wafer) and CrCoNi (Cr-Oxide (>1µm) layer on CrCoNi substrate) medium entropy alloy.
Getting more efficient – The use of Bayesian optimization and Gaussian processes at the BAMline
(2022)
For more than 20 years, BAM is operating the BAMline at the synchrotron BESSY II in Berlin Adlershof. During this time, the complexity of the setup and the amount of data generated have multiplied. To increase the effectiveness and in preparation for BESSY III, algorithms from the field of machine learning are increasingly used.
After a short introduction to BO and GP, the first example is the automatic alignment of our double multilayer monochromator (DMM).
The second example is the optimization of measurement time in XRF scanning.
Confocal Micro X-ray fluorescence analysis (μXRF) is a powerful method for the destruction-free investigation of the elemental composition of various samples in three dimensions. Quantitative results rely heavily on the transmission properties of polycapillary optics, used in confocal setups.
Different models for the functional correlation between energy and transmission of a polycapillary half-lens are compared with experimental data, established with a monochromatic confocal laboratory setup [1], as well as Monte-Carlo-Simulations [2]. The effect of the different approaches on quantitative results are compared using well known SRMs, ranging from thick samples to thin layers and structured materials.
Along with this the basic principles for quantitative evaluations of XRF spectra taken with confocal setups are presented, and compared with experimental results.
High entropy alloys (HEAs) are considered as a new class of alloys containing at least 5 elements with concentrations between 5 and 35 atomic percent. There has been a growing interest in HEAs in the material research field in recent years. Due to their adjustable composition, which enables the modifications of mechanical properties (such as hardness, strength and ductility etc) and their stability at high temperatures, HEAs have been the focus of various studies.
Especially the corrosion behavior of HEAs has been a wide research interest. Since the grazing exit X-ray fluorescence (GEXRF) offers a non-destructive way to collect notable information regarding the high temperature oxidation, we consider it as a useful method to investigate how HEAs behave in corrosive environments.
The main idea of grazing geometry is to enhance the fluorescence signal of the surface. This enables highly sensitive surface analyses of thin protective film on surface in sub-micrometer scale. Position-sensitive area detectors provide information regarding the signal emitted from the sample as a function of emission angle and thus allow depth-sensitive analysis. Furthermore, the data collected from samples of an incidence energy which lays within a specific energy range provides XANES data to determine oxidation states. Moreover, since GEXRF profiles can also be simulated through physical models (Urbach 1999), they enable us to determine the layer thickness of a given sample in a non-destructive way.
In this contribution, we present the preliminary results of a conceptual study regarding layer properties of CrCoNi medium entropy alloy. The successful implementation of such methodological concept will pave the way for the investigation of more complex alloys with multiple layers, which is planned for the later phases of the project.
This work aims to investigate the role of F-F and F-π interactions in dictating structural and mechanical properties, through a combination of X-ray powder diffraction and dispersion-corrected density functional. As no benchmarking data exist for F-dominating organic system, we first assess how different functionals affect the mechanical properties of the material.
Coordination polymers can be used as sacrificial templates to prepare nitrogen- and metal doped carbons (NMCs), which are promising catalysts for the oxygen reduction reaction. We at BAM employ mechanochemistry as a "green" synthetic approach to coordiantion polymers, which are throroughly characterized by methods such as XRD, XPS and sorption studies. Our collaborators can prepare NMCs from our coordination polymers and assess the catalytic activity thereof.
The oxygen reduction reaction (ORR) is a common process in a variety of electrochemical devices, like fuel cells
and metal air batteries. The sluggish kinetics of the ORR require an electrocatalyst to pass this bottleneck.[1]
Currently, the most used catalytical systems are platinum-based, with several drawbacks, such as the high cost,
low availability, and deactivation by CO poisoning.[2] Efforts are made to develop efficient, durable and low cost
catalysts to promote the commercialization of fuel cells.
Non-precious metal catalysts are promising candidates for efficient ORR catalysis. It has been shown that
pyrolyzing metal organic frameworks (MOFs) under inert conditions yields carbon-rich materials, with evenly
distributed metal sites, which possess promising electrocatalytic activity.[3] One widely used type of MOF as ORR
catalyst precursors is the zeolitic imidazole framework (ZIF) where metal cations are linked through imidazolebased ligands.
Herein we report the mechanochemical synthesis, structural analysis and of Co-doped ZIF-8 (Zn), as well as its
fluorinated counterpart Co-doped CF3
-ZIF-8 (Zn). The samples showed electrochemical performance comparable
to platinum after carbonization for 1h at temperatures ranging between 850 – 1000°C.
The oxygen reduction reaction (ORR) is a common process in a variety of electrochemical devices, like fuel cells and metal air batteries. The sluggish kinetics of the ORR require an electrocatalyst to pass this bottleneck.[1] Currently, the most used catalytical systems are platinum-based, with several drawbacks, such as the high cost, low availability, and deactivation by CO poisoning.[2] Efforts are made to develop efficient, durable and low cost catalysts to promote the commercialization of fuel cells.
Non-precious metal catalysts are promising candidates for efficient ORR catalysis. It has been shown that pyrolyzing metal organic frameworks (MOFs) under inert conditions yields carbon-rich materials, with evenly distributed metal sites, which possess promising electrocatalytic activity.[3] One widely used type of MOF as ORR catalyst precursors is the zeolitic imidazole framework (ZIF) where metal cations are linked through imidazole-based ligands. Their porous nature is partially retained after carbonization, making MOFs very suitable precursor materials.
Herein we report the mechanochemical synthesis and structural analysis of Co-doped ZIF-8 (Zn), as well as two polymorphs (dense and prorous) of fluorinated Co-doped CF3-ZIF-8 (Zn). The samples showed electrochemical performance comparable to platinum after carbonization for 1 h at temperatures ranging between 850 – 1000°C.
The oxygen reduction reaction (ORR) – an important reaction in electrochemical devices, such as fuel cells - is characterized by its sluggish kinetics and therefore requires catalysis. The industry currently relies on platinum as a catalyst, although it is scarce and expensive, hindering the commercial breakthrough of fuel cells in automotive applications. Platinum-free catalysts on basis of nitrogen- and metal doped carbons (NMCs) and fluorinated carbons are promising materials to replace platinum-based catalysts for the ORR. In this work we prepared six metal-organic frameworks (MOFs) by mechanical ball mill grinding and studied their formation by in-situ powder X-ray diffraction. Furthermore, the samples were carbonized under controlled conditions (900°C, 1h, N2-atmosphere) to yield carbon materials, that were employed in ORR-electrocatalysis. The effect of Co-doping and fluorination was systematically studied and outstanding ORR activity was found for the catalyst prepared from the Co-doped fluorinated ZIF-8.
The recycling of critical elements has crucial importance to maintain sustainable use of raw materials. Phosphorus(P) is a sought-after limited natural resource due to its wide use in modern agriculture mainly as P-fertilizers. But it causes major problems for the environment such as eutrophication of ecosystems. In the future it could be depleted due to the high demand and declining natural phosphorite ore deposits. Therefore, the phosphorus recovery from mine and agricultural waste waters will be an important factor in preservation of the global consumption. The precipitation of M-struvite (NH4MPO4·6H2O, M2+= Mg2+, Ni2+, Co2+) from waste waters is a promising P-recovery route. Besides avoidance of eutrophication due to extraction of excess phosphates and the restoration of the phosphorus resources the recovered M-struvites may be potentially be up-cycled for industrial applications e.g. Co and Ni-phosphate show excellent electrochemical properties for batteries or supercapacitors.
The precipitation process of M-struvites is strongly dependent on the degree of supersaturation, pH and on the exchange ions M2+.The influence of these precipitation parameters on the crystal morphology and size of transition metal struvite has been investigated only to a limited extent. An optimization of the reaction conditions could lead to more efficient M-struvite precipitation and significantly improved P-recovery method.
We reveal the effect of different reaction conditions on the crystal shape and crystallite size of M-struvites (NH4MPO4∙6H2O, M = Mg2+, Ni2+, Co2+). Furthermore, we characterize the coordination environment of the crystalline end products and their related phases [Co-dittmarite (COD) NH4CoPO4∙H2O and Co(II)phosphate octahydrate (CPO) Co3(PO4)2∙8H2O]. Due to the presence of various amorphous phases pH is changing significantly in the different systems. Mg- and Ni-struvite are stable in multiple concentrations of the educts and metal/phosphorus (M/P) ratios in contrast to Co-struvite which forms below M/P ratios of 0.4. A high M/P ratio with high concentrations of the educts decrease the crystallite size and idiomorphism of the crystals while low M/P ratios with low concentrations of the educts increase the crystallite size and the euhedral formation of the crystal planes. In the (Ni, Co)-solid solutions Ni and Co are homogenously distributed in the crystals with similar Ni# as in the aqueous solutions indicating no elemental fractionation in crystallization. Ni and Co-struvite exhibit a more centrosymmetric coordination environment compared to their related phases of COD and CPO determined by EXAFS. The CoO6 octahedron expands slightly the ideal size of the struvite structure and decomposes to Co-dittmarite. From TEM analysis and pH measurements it is suggested that the crystallization of Ni- and Co-struvite follows a non-classical crystallization theory which consists of multiple nanophases, crystalline or amorphous, on the way to the final crystalline product.