Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Eingeladener Vortrag
- nein (7)
Nanoforms with at least one dimension below 100 nm have an important part to play in more and more areas of our daily life. Therefore, risk assessment of these materials is becoming increasingly important. In this context, the European Chemical Agency (ECHA) considered eleven physico-chemical properties as relevant, of which the following six are essential for the registration: chemical composition, crystallinity, particle size, particle shape, surface chemistry and specific surface area. Four of these priority properties can be obtained with electron microscopy and surface analytics like XPS and ToF-SIMS. The reliability of this data must be ensured, especially for their use for grouping and read across approaches. On the other hand, the “reproducibility” crisis has revealed major shortcomings in the reliability of published data.
In a case study, we show how the quality of the data can be ensured by using existing standards and protocols of each step in the workflow of sample characterization. As exemplary samples, two Al-coated TiO2 samples as nanopowders were selected from the JRC repository, capped either with a hydrophilic or a hydrophobic organic ultrathin shell. SEM results provided the size and shape of the nanoparticles, a first overview about the composition was obtained with EDS. XPS and ToF-SIMS supplied the surface chemistry, especially information about the shell and the coating of the particles. Standards and protocols of all steps of the analytical workflow including preparation and data reduction are discussed regarding reliable and reproducible data. Additionally, uncertainties for the different steps are specified.
Only such a detailed description of all these factors allows a comprehensive physico-chemical characterization of the nanoparticles with understanding of their potential risk assessment.
Morpho-Chemical Characterisation of Me-TiO2 Nanoparticles for Enhanced Photocatalytical Activity
(2022)
The conversion of solar energy into electricity and solar fuels is of crucial importance for a green and sustainable future. Water splitting using semiconductor photo-catalysts is considered a sustainable method to produce clean hydrogen (H2) fuel. Nevertheless, H2 photo-production efficiency remains still low, although extensive research works to understand better the mechanisms of the Hydrogen Evolution Reaction (HER) and the Oxygen Evolution Reaction (OER) are being carried out. In this respect, TiO2 is a key photoactive material, usually employed with a co-catalyst deposited onto the surface to enhance charge carriers’ separation and catalyze surface charge transfer reactions. The deposition of a co-catalyst on the TiO2 nanoparticle surface represents one successful way to enhance the activity of the photocatalyst through a modification of its surface and redox properties. In this context, high-resolution scanning electron microscopy coupled with elemental analysis by energy-dispersive X-ray spectroscopy (EDS) is fundamental for studying and understanding the effect of the nanoparticle morphology on the functional properties of shape-controlled TiO2 crystals (bipyramides, platelets, and elongated particles). Different types of metal-semiconductor combinations, TiO2 shapes and dopant metals (Ag, Pt, etc) and metal concentrations will be discussed.
Recent developments of X-ray photoelectron spectroscopy using excitation energies different from the usual lab-sources Mg Kα and Al Kα, thus covering larger and different kinetic energy ranges, require more flexible approaches for determining the transmission function than the well-established ones using reference spectra. Therefore, the approach using quantified peak areas (QPA) was refined allowing a more precise estimation of the transmission function. This refinement was tested by comparing the results obtained with the new version with former calculations. Furthermore, the obtained transmission function was validated by comparing the results with a transmission function using the reference spectrum of polyethylene. Additionally, an ionic liquid was used as reference for estimating the transmission function at the energy resolved HE-SGM beamline at BESSY II. Comparison between the measured and stoichiometric composition shows that a transmission function was determined, which allows a reasonable quantification.
Inspired by the chemistry of mussel adhesive proteins, polydopamine (PDA) exhibits strong adhesion to nearly any kind of organic or inorganic surface and shows high ability for surface post-modification and secondary reactions. As a result, PDA has been widely used as a base adlayer to enable versatile surface chemistry and functionalization. It has shown great potential in wide range of applications including biomedical field (e.g., drug delivery, adhesives, photothermal therapy, bone and tissue engineering, cell adhesion, biosensing). However, implementation of PDA in microdevices is still hindered by insufficient spatial and temporal control of excited deposition methods.
In this work we present a novel approach to fabricate tunable micropatterned substrates where mussel-inspired chemistry provides base for various surface modification [2]. Current approach applies Multiphoton Lithography (MPL) to initiate local PDA formation, and, therefore, does not require use of microstamp or photomask. As a result, the microstructures of complex designs can be produced with the spatial resolution down to 0.8 μm (Figure 1). The desired design can be easily altered by adjusting the stl model or the fabrication code. Unlike the conventional deposition of PDA based on dopamine auto-oxidation, our method does not require presence of strong oxidants, metal ions or alkaline pH. Herein-demonstrated deposition approach will significantly facilitate applications of polydopamine and other mussel-inspired materials in microdevices and high-resolution active microcomponents (e.g., in MEMS and microfluidics).
Adjustment of MPL parameters revealed that the morphology and thickness of resulted PDA microstructures can be controlled by altering the laser power and its scanning velocity. As a result, it also enables the production of micropatterns with structural gradient. Apart from the glass substrate, we performed PDA patterning at surfaces of different nature such as polychlorotrifluoroethylene, polydimethylsiloxane, polyethylene terephthalate, silicon wafers, and fluorinated glass coverslips. We tested different composition of dopamine solution for its ability of PDA buildup. Solutions containing Tris buffer, phosphate buffer or DI water only as well as different pH (6.0, 7.0 and 8.5) could be successfully applied for high-precision PDA micropatterning. Moreover, the effect of antioxidants and purging of the solution with oxygen and nitrogen was investigated. In all cases, no decrease of deposition efficiency was observed. The chemical nature of PDA was confirmed by locally recorded vibrational and x-ray photoelectron spectra. To ensure post-modification potential of MPL deposited PDA we demonstrated one-step deposition of micropatterns with trypsin. Obtained bio-functionalised surface can be further applied as a protein sensing active microelement.
Gold films coated with a graphene sheet are being widely used as sensors for the detection of label-free binding interactions using surface plasmon resonance (SPR). During the preparation of such sensors, it is often essential to subject the sensor chips to a high-temperature treatment in order to ensure a clean graphene surface. However, sensor chips used currently, which often use chromium as an adhesion promoter, cannot be subjected to temperatures above 250 °C, because under such conditions, chromium is found to reorganize and diffuse to the surface, where it is easily oxidized, impairing the quality of SPR spectra. Here we present an optimized preparation strategy involving a three-cycle tempering coupled with chromium (oxide) etching, which allows the graphene-coated SPR chips to be annealed up to 500 °C with little deterioration of the surface morphology. In addition, the treatment delivers a surface that shows a clear enhancement in spectral response together with a good refractive index sensitivity. We demonstrate the applicability of our sensors by studying the kinetics of avidin–biotin binding at different pH repeatedly on the same chip. The possibility to anneal can be exploited to recover the original surface after sensing trials, which allowed us to reuse the sensor for at least six cycles of biomolecule adsorption.
XPS of GR2M
(2022)
Core–shell nanoparticles have attracted much attention in recent years due to their unique properties and their increasing importance in many technological and consumer products. However, the chemistry of nanoparticles is still rarely investigated in comparison to their size and morphology. In this review, the possibilities, limits, and challenges of X-ray photoelectron spectroscopy (XPS) for obtaining more insights into the composition, thickness, and homogeneity of nanoparticle coatings are discussed with four examples: CdSe/CdS quantum dots with a thick coating and a small core; NaYF4-based upconverting nanoparticles with a large Yb-doped core and a thin Er-doped coating; and two types of polymer nanoparticles with a poly(tetrafluoroethylene) core with either a poly(methyl methacrylate) or polystyrene coating. Different approaches for calculating the thickness of the coating are presented, like a simple numerical modelling or a more complex simulation of the photoelectron peaks. Additionally, modelling of the XPS background for the investigation of coating is discussed. Furthermore, the new possibilities to measure with varying excitation energies or with hard-energy X-ray sources (hard-energy X-ray photoelectron spectroscopy) are described. A discussion about the sources of uncertainty for the determination of the thickness of the coating completes this review.
VAMAS-Enabling international standardisation for increasing the take up of Emerging Materials
(2022)
VAMAS (Versailles Project on Advanced Materials and Standards) supports world trade in products dependent on advanced materials technologies by providing technical basis for harmonized measurements, testing, specification, reference materials and standards. The major tools for fulfilling this task are interlaboratory comparisons (ILC). The organisation structure of VAMAS is presented. It is discussed, how a new technical activity can initiate.
Mussel-inspired polydopamine (PDA) initiated a multifunctional modification route that leads to the generation of novel advanced materials and their applications. However, existing PDA deposition techniques still exhibit poor spatial control, have a very limited capability of micropatterning and do not allow to locally tune PDA topography. Herein, we demonstrate PDA deposition based on Multiphoton Lithography (MPL) that enables full spatial and temporal control with nearly total freedom of patterning design. Using MPL, we achieve 2D microstructures of complex design with pattern precision of 0.8 μm without the need of a photomask or stamp. Moreover, this approach permits adjusting the morphology and thickness of the fabricated microstructure within one deposition step, resulting in a unique tunability of materials properties. The chemical composition of PDA is confirmed and its ability for protein enzyme immobilization is demonstrated. This work presents a new methodology for high precision and complete control of PDA deposition, enabling PDA incorporation in applications where fine and precise local surface functionalization is required. Possible applications include multicomponent functional elements and devices in microfluidics or lab-on-a-chip systems.
Catalysts derived from pyrolysis of metal organic frameworks (MOFs) are promising candidates to replace expensive and scarce platinum-based electrocatalysts commonly used in polymer electrolyte membrane fuel cells. MOFs contain ordered connections between metal centers and organic ligands. They can be pyrolyzed into metal- and nitrogen-doped carbons, which show electrocatalytic activity toward the oxygen reduction reaction (ORR). Furthermore, metal-free heteroatom-doped carbons, such as N-F-Cs, are known for being active as well. Thus, a carbon material with Co-N-F doping could possibly be even more promising as ORR electrocatalyst. Herein, we report the mechanochemical synthesis of two polymorphs of a zeolitic imidazole framework, Co-doped zinc 2-trifluoromethyl-1H-imidazolate (Zn0.9Co0.1(CF3-Im)2). Time-resolved in situ X-ray diffraction studies of the mechanochemical formation revealed a direct conversion of starting materials to the products. Both polymorphs of Zn0.9Co0.1(CF3-Im)2 were pyrolyzed, yielding Co-N-F containing carbons, which are active toward electrochemical ORR.
Whereas the characterization of nanomaterials using different analytical techniques is often highly automated and standardized, the sample preparation that precedes it causes a bottleneck in nanomaterial analysis as it is performed manually. Usually, this pretreatment depends on the skills and experience of the analysts. Furthermore, adequate reporting of the sample preparation is often missing. In this overview, some solutions for techniques widely used in nano-analytics to overcome this problem are discussed. Two examples of sample preparation optimization by au-tomation are presented, which demonstrate that this approach is leading to increased analytical confidence. Our first example is motivated by the need to exclude human bias and focuses on the development of automation in sample introduction. To this end, a robotic system has been de-veloped, which can prepare stable and homogeneous nanomaterial suspensions amenable to a variety of well-established analytical methods, such as dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), field-flow fractionation (FFF) or single-particle inductively coupled mass spectrometry (sp-ICP-MS). Our second example addresses biological samples, such as cells exposed to nanomaterials, which are still challenging for reliable analysis. An air–liquid interface has been developed for the exposure of biological samples to nanomaterial-containing aerosols. The system exposes transmission electron microscopy (TEM) grids under reproducible conditions, whilst also allowing characterization of aerosol composition with mass spectrometry. Such an approach enables correlative measurements combining biological with physicochemical analysis. These case studies demonstrate that standardization and automation of sample preparation setups, combined with appropriate measurement processes and data reduction are crucial steps towards more reliable and reproducible data.
A facile and efficient methodology is described for the solvothermal synthesis of size-tunable, stable, and uniform NiCu core–shell nanoparticles (NPs) for application in catalysis. The diameter of the NPs is tuned in a range from 6 nm to 30 nm and to adjust the Ni:Cu ratio from 30:1 to 1:1. Furthermore, the influence of different reaction parameters on the final NPs is studied. The NPs are structurally characterized by a method combination of transmission electron microscopy, anomalous small-angle X-ray scattering, X-ray absorption fine structure, and X-ray photoelectron spectroscopy. Using these analytical methods, it is possible to elucidate a core–shell–shell structure of all particles and their chemical composition. In all cases, 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) independent of size and Ni:Cu ratio.
The Competence Centre nano@BAM is presenting a new X-ray Photoelectron Spectrometer – the HAXPES (XPS at hard energy) – for researching advanced materials at the nanoscale. With HAXPES detailed chemical information can now be gained not only from the first outermost nanometres of the sample surface, but also from deeper regions.
Top international experts will share their knowledge and key findings on how to utilise HAXPES for exploring the surface of various advanced materials. Following the lectures, we will show you a short demo of the new instrument and answer your questions.
In order to bridge the gap between lab-scale and industrial-scale production of graphene it is necessary to develop processes, equipment and measurement procedures to control the material features. One of the crucial reasons of graphene’s limited commercialization is the lack of standard procedures to properly characterize and define the material chemical and structural properties down to the nanometer level. This leads to many issues regarding material synthesis repeatability, inappropriateness choice of measurands and measurement reproducibility which heavily affect the consistency of the material performance.
In our study, a comparative analysis is performed on two different series (G5 and G6) of industrial graphene powders, each series produced with four types of functionalization: raw graphene, oxygen-functionalized, nitrogen-functionalized and fluorine-functionalized. All the 8 sample variants were analyzed from a chemical and morphological point of view in the form of powders prepared as slightly pressed in metallic sample holders.
The results of the comparative chemical analyses XPS and EDS show a good agreement in the concentration values for all the elements present in the samples, despite the different analysis volumes addressed by the two techniques. For this reason, the samples can be considered homogeneous in both lateral and vertical direction.
A clear influence of the morphology on the composition is evident. Therefore, such correlative measurements of morphology and composition are necessary for a comprehensive characterization of industrial graphene flakes.
This work presents the determination of the corrosion characteristics of CrCoNi (medium entropy alloy) and CrMnFeCoNi (high entropy alloy) in 0.1 M NaCl and 0.1 M H2SO4. The morphology and chemical composition of the oxide layers formed on CrCoNi and CrMnFeCoNi were comparatively analyzed by scanning Kelvin probe microscopy (SKPFM) and scanning electron microscopy (SEM) and supported with chemical analysis by means of inductively coupled plasma mass spectrometry (ICP-MS) and X-Ray photoelectron spectroscopy (XPS). The analysis of the 3p core level peaks showed that the oxide layer (native and after anodic passivation) on CrCoNi consisted mainly of Cr oxides, while the oxide layer on CrMnFeCoNi was primarily composed of a mixture of Cr and Fe oxides. In addition, XPS was utilized to assess the oxide layer thicknesses. These results were compared to the thicknesses obtained by means of electrochemical impedance spectroscopy (EIS), with both approaches yielding values up to about 4 nm depending on the electrolyte and the alloy. Cyclic polarization measurements indicated superior corrosion resistance of CrCoNi in both aqueous environments compared to CrMnFeCoNi, as well as to AISI 304 stainless steel.
Nanosafety is becoming increasingly important as nanomaterials are widely used in industrial processes and consumer products. For nanotoxicity measurements prior sterilization of the samples is necessary, but as structure activity relationships are made with properties of pristine particles, the question arises, if the sterilization process has an impact on the physico-chemical properties of nanoparticles and thus on the biological behavior.
This question will be addressed in this talk. For this purpose, results from SEM and EDS measurements are combined with those of a novel lab-based HAXPES spectrometer in order to obtain a more complete picture. At the end, an influence of sterilization will be evident, which indicates a restructuring of the nanoparticles owing to sterilization.