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Reliable measurement of the size of polydisperse, complex-shaped commercial nanopowders is a difficult but necessary task, e.g., for regulatory requirements and toxicity risk assessment. Suitable methods exist for the accurate characterization of the size of non-aggregated, stabilized, spherical and monodisperse nanoparticles. In contrast, industrial nanoscale powders usually require dedicated sample preparation procedures developed for the analysis method of choice. These nano-powders tend to agglomerate and/or aggregate, a behavior which in combination with an innate broad particle size distribution and irregular shape often significantly alters the achievable accuracy of the measured size parameters. The present study systematically tests two commercially available nanoscale powders using different sample preparation methods for correlative analysis by scanning electron microscopy, dynamic light scattering, Brunauer–Emmet–Teller method and differential mobility analysis. One focus was set on the sample preparation by embedding nanoparticles in carbon-based hot-mounting resin. Literature on this topic is scarce and the accuracy of the data extracted from cross sections of these particles is unclearly stated. In this paper systematic simulations on the deviation of the size parameters of well-defined series of nanoparticles with different shapes from the nominal value were carried out and the contributing factors are discussed.
The ISO 16000-6 standard gives directions to adapt the analysis of volatile organic compounds (VOCs) in indoor and test chamber air to very volatile organic compounds (VVOCs). The same techniques with sorbent-based active sampling, thermal desorption and gas chromatography coupled with mass spectrometry (TD-GC/MS) should be used. However, VVOCs require gaseous standards, an adapted GC column and a reliable sampling adsorbent. This work presents experimental results to tackle those three experimental gaps. A stable standard gas mixture containing 47 VVOCs, 13 VOCs and an internal standard was successfully generated. It was employed to study the suitability of seven types of chromatography columns. The use of PLOT (Porous Layer Open Tubular) columns such as PoraBOND Q is well suitable for VVOC analysis. The recoveries of the 60 analytes on a total of 16 adsorbents and their combinations were determined: A combination of the graphitized carbon black Carbograph 5TD 40/60 and the carbon molecular sieve CarbosieveTM SII showed great recoveries for all analytes. Carbon molecular sieves adsorb water which can impair the analysis. A dry purge of the multi-sorbent in the sampling direction led to a complete water removal and promising recoveries of the analytes.
We present how mesoporosity can be engineered in transition metal phosphate (TMPs) materials in a template-free manner. The method involves the transformation of a precursor metal phosphate phase, called M-struvite (NH4MPO4·6H2O, M = Mg2+, Ni2+, Co2+, NixCo1−x2+). It relies on the thermal decomposition of crystalline M-struvite precursors to an amorphous and simultaneously mesoporous phase, which forms during degassing of NH3 and H2O. The temporal evolution of mesoporous frameworks and the response of the metal coordination environment were followed by in situ and ex situ scattering and diffraction, as well as X-ray spectroscopy. Despite sharing the same precursor struvite structure, different amorphous and mesoporous structures were obtained depending on the involved transition metal. We highlight the systematic differences in absolute surface area, pore shape, pore size, and phase transitions depending on the metal cation present in the analogous M-struvites. The amorphous structures of thermally decomposed Mg-, Ni- and NixCo1−x-struvites exhibit high surface areas and pore volumes (240 m2 g−1 and 0.32 cm−3 g−1 for Mg and 90 m2 g−1 and 0.13 cm−3 g−1 for Ni). We propose that the low-cost, environmentally friendly M-struvites could be obtained as recycling products from industrial and agricultural wastewaters. These waste products could be then upcycled into mesoporous TMPs through a simple thermal treatment for further application, for instance in (electro)catalysis.
Industrial and agricultural waste streams (waste water, sludges, tailings, etc.) which contain high concentrations of NH4+, PO43–, and transition metals are environmentally harmful and toxic pollutants. At the same time, phosphorous and transition metals constitute highly valuable resources. Typically, separate pathways have been considered to extract hazardous transition metals or phosphate independently from each other. Investigations on the simultaneous removal of multiple components have been carried out only to a limited extent. Here, we report the synthesis routes for Ni- and Co-struvites (NH4MPO4·6H2O, M = Ni2+ and Co2+), which allow for P, ammonia, and metal co-precipitation. By evaluating different reaction parameters, the phase and stability of transition metal struvites as well as their crystal morphologies and sizes could be optimized. Ni-struvite is stable in a wide reactant concentration range and at different metal/phosphorus (M/P) ratios, whereas Co-struvite only forms at low M/P ratios. Detailed investigations of the precipitation process using ex situ and in situ techniques provided insights into the crystallization mechanisms/crystal engineering of these materials. M-struvites crystallize via intermediate colloidal amorphous nanophases, which subsequently aggregate and condense to final crystals after extended reaction times. However, the exact reaction kinetics of the formation of a final crystalline product varies significantly depending on the involved metal cation in the precipitation process: several seconds (Mg) to minutes (Ni) to hours (Co). The achieved level of control over the morphology and size makes precipitation of transition metal struvites a promising method for direct metal recovery and binding them in the form of valuable phosphate raw materials. Under this paradigm, the crystals can be potentially up-cycled as precursor powders for electrochemical or (electro)catalytic applications, which require transition metal phosphates.
Electron microscopy (EM) is the gold standard for the characterisation of the morphology (size and shape) of nanoparticles. Visual observation of objects under examination is always a necessary first step in the characterisation process. Several questions arise when undertaking to identify and count particles to measure their size and shape distribution. In addition to challenges with the dispersion and identification of the particles, more than one protocol for counting particles is in use. This paper focuses on precise rules for the counting of particles in EM micrographs, as this influences the measurement accuracy of the number of particles, thus implicitly affecting the size values of the counted particles. We review and compare four different, commonly used methods for counting, which we then apply in case studies. The impact of the selected counting rule on the obtained final particle size distribution is highlighted. One main aim of this analysis is to support the application of a specific, well-defined counting approach in accordance with regulatory
requirements to contribute to achieving more reliable and reproducible results. It is also useful for the new harmonised measurement procedures for determining the particle size and particle size distribution of nanomaterials.
Herein we report the synthesis of a zeolitic imidazolate framework (ZIF-8) by an easy “mix and wait” procedure. In a closed vial, without any interference, the mixture of 2-methylimidazole and basic zinc carbonate assembles into the crystalline product with approx. 90% conversion after 70 h. The reaction exhibits sigmoidal kinetics due to the self-generated water which accelerates the reaction.
For more than 110 years, BAM has been producing reference materials for a wide range of application fields. With the development of new analytical methods and new applications as well as continuously emerging more stringent requirements of laboratory accreditation with regard to quality control and metrological traceability, the demand and requirements for reference materials are increasing. This trend article gives an overview of general developments in the field of reference materials as well as developments in selected fields of application in which BAM is active. This includes inorganic and metal analysis, gas analysis, food and consumer products, and geological samples. In addition to these more traditional fields of application, developments in the areas of optical spectroscopy, particulary fluorescence methods, and nanomaterials are considered.
Cellulose ethers, like methyl cellulose (MC) or hydroxypropyl cellulose (HPC), are widely used in conservation. They also occur as additives and rheology modifiers in various products like dispersions or gels. Do such products release harmful volatile organic compounds (VOC) during their accelerated aging? A mass testing series utilizing the Oddy test of 60 commercial cellulose ethers ranks the products in safe for permanent use (P, no corrosion), only for temporary use (T, slight corrosion), and unsuitable at all (F, heavy corrosion). Results show that 55% of the products passed the test whereas 33% are for temporary use as slight corrosion occurred on at least one metal coupon and only 11% failed the Oddy test. Raman measurements of the corrosion products identified oxides like massicot, litharge, cuprite, and tenorite among carbonates (hydrocerussite, plumbonacrite), and acetates like basic lead acetate, lead acetate trihydrate as well as lead formate as main phases. For example, commercial, industrial Klucel® G (HPC) scored a T rating through slight corrosion on the lead coupon. Basic lead acetate among other phases indicates the presence of acetic acid. Additional measurements of the sample with thermal desorption GC–MS utilizing the BEMMA scheme confirm the high acetic acid outgassing and reveal the presence of a small amount of formaldehyde.
The diversity of fused filament fabrication (FFF) filaments continues to grow rapidly as the popularity of FFF-3D desktop printers for the use as home fabrication devices has been greatly increased in the past decade. Potential harmful emissions and associated health risks when operating indoors have induced many emission studies. However, the lack of standardization of measurements impeded an objectifiable comparison of research findings. Therefore, we designed a chamber-based standard method, i.e., the strand printing method (SPM), which provides a standardized printing procedure and quantifies systematically the particle emission released from individual FFF-3D filaments under controlled conditions. Forty-four marketable filament products were tested. The total number of emitted particles (TP) varied by approximately four orders of magnitude (1E9 ≤ TP ≤ 1E13), indicating that origin of polymers, manufacturer-specific additives, and undeclared impurities have a strong influence. Our results suggest that TP characterizes an individual filament product and particle emissions cannot be categorized by the polymer type (e.g., PLA or ABS) alone. The user's choice of a filament product is therefore decisive for the exposure to released particles during operation. Thus, choosing a filament product awarded for low emissions seems to be an easily achievable preemptive measure to prevent health hazards.
The development of traceable new methodologies to quantify elemental air pollutants in particulate matter (PM) supports modernization of methods used in air quality monitoring networks in Europe. In the framework of the EURAMET EMPIR AEROMET II project, the combination of cascade impactor aerosol sampling and total reflection X-ray fluorescence elemental spectroscopy (TXRF) was investigated. This technique requires a traceable calibration based on reference samples. This paper describes a new, simple and effective method to produce such reference samples using flexible, reusable, and low-cost parylene C shadow masks, fabricated by photolithographic steps. These shadow masks can be used to produce reference samples that mimic the Dekati cascade impactor’s deposition patterns by applying as-prepared micro stencils to 30 mm acrylic substrates and evaporating a reference material (Ti) in arrangements of thin circular dots. The highly flexible direct patterning of acrylic discs with reference material, otherwise impossible with conventional photolithography, allows multiple reusing of the same micro stencils. The aspect ratios of the dots could be repeated with an error less than 4 %. A first set of standard reference samples for the 13 stages of the Dekati cascade impactor was produced and preliminary TXRF measurements of the deposited Ti masses were performed. The centricity of the deposition patterns turned out to be an important parameter for the quality of the TXRF results. The parylene mask technology for the production of reference samples turns out to be a promising new approach for the traceable calibration of TXRF spectrometers for the quantification of element concentrations in environmental aerosol samples but, due to its great versatility, it could be used for several other micropatterning applications on conventional and unconventional substrates.
Nonporous corundum powder, known as an abrasive material in the industry, was functionalized covalently with protein binders to isolate and enrich specific proteins from complex matrices. The materials based on corundum were characterized by TEM, ESEM, BET, DLS, EDS, and zeta potential measurements. The strong Al-O-P bonds between the corundum surface and amino phosphonic acids were used to introduce functional groups for further conjugations. The common crosslinker glutaraldehyde was compared with a hyperbranched polyglycerol (PG) of around 10 kDa. The latter was oxidized with periodate to generate aldehyde groups that can covalently react with the amines of the surface and the amino groups from the protein via a reductive amination process. The amount of bound protein was quantified via aromatic amino acid analysis (AAAA). This work shows that oxidized polyglycerol can be used as an alternative to glutaraldehyde. With polyglycerol, more of the model protein bovine serum albumin (BSA) could be attached to the surface under the same conditions, and lower non-specific binding (NSB) was observed. As a proof of concept, IgG was extracted with protein A from crude human plasma. The purity of the product was examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A binding capacity of 1.8 mg IgG per gram of corundum powder was achieved. The advantages of corundum include the very low price, extremely high physical and chemical stability, pressure resistance, favorable binding kinetics, convenient handling, and flexible application.
The roles extracellular polymeric substances (EPS) play in mineral attachment and weathering were studied using genetically modified biofilms of the rock-inhabiting fungus Knufia petricola strain A95. Mutants deficient in melanin and/or carotenoid synthesis were grown as air-exposed biofilms. Extracted EPS were quantified and characterised using a combination of analytical techniques. The absence of melanin affected the quantity and composition of the produced EPS: mutants no longer able to form melanin synthesised more EPS containing fewer pullulan-related glycosidic linkages. Moreover, the melanin-producing strains attached more strongly to the mineral olivine and dissolved it at a higher rate. We hypothesise that the pullulan-related linkages, with their known adhesion functionality, enable fungal attachment and weathering. The released phenolic intermediates of melanin synthesis in the Δsdh1 mutant might play a role similar to Fe-chelating siderophores, driving olivine dissolution even further. These data demonstrate the need for careful compositional and quantitative analyses of biofilm-created microenvironments.
Metagenomic datasets of air samples collected during episodes of severe smoke-haze in Malaysia
(2021)
Transboundary emissions of smoke-haze from land and forest fires have recurred annually during the dry period (June to October, over the past few decades) in South East Asia. Hazardous air quality has been recorded in Malaysia during these episodes. Agricultural practices such as slash-and-burn of biomass and peat fires particularly in Sumatera and Kalimantan, Indonesia, have been implicated as the major causes of the haze. Past findings have shown that a diversity of microbes can thrive in air including in smoke-haze polluted air. In this study, metagenomic data were generated to reveal the diversity of microorganisms in air during days with and without haze. Air samples were collected during non-haze (2013A01) and two haze (2013A04 and 2013A05) periods in the month of June 2013. DNA was extracted from the samples, subjected to Multiple Displacement Amplification and whole genome sequencing (Next Generation Sequencing) using the HiSeq 2000 Platform. Extensive bio-informatic analyses of the raw sequence data then followed. Raw reads from these six air samples were deposited in the NCBI SRA databases under Bioproject PRJNA662021 with accession numbers SRX9087478, SRX9087479 and SRX9087480.
The ISO 16000-6 standard describes a method for the determination of volatile organic compounds (VOCs) in indoor and test chamber air by sorbent-based active sampling, thermal desorption and gas chromatography coupled with mass spectrometry (GC/MS). It also gives directions to adapt this methodology to very volatile organic compounds (VVOCs). Indeed, toxicologically based guideline values are being implemented for these compounds and it becomes necessary to measure them. But a comprehensive and robust measurement method is lacking. This work highlights the points that still need to be explored towards the standardisation of a suitable procedure: investigations on sorbent combinations, the suitability of chromatography columns and the use of gaseous standards are required. The biggest challenge remains in the fact that strong sorbents adsorb water together with VVOCs. Water may impair the analysis and the optimal approach to eliminate it is still to be found and integrated into the sampling strategy.
Natural building materials for interior fitting and refurbishment - What about indoor emissions?
(2021)
Indoor air quality can be adversely affected by emissions from building materials, consequently having a negative impact on human health and well-being. In this study, more than 30 natural building materials (earth dry boards and plasters, bio-based insulation materials, and boards made of wood, flax, reed, straw, etc.) used for interior works were investigated as to their emissions of (semi-) volatile organic compounds ((S)VOC), formaldehyde, and radon. The study focused on the emissions from complete wall build-ups as they can be used for internal Partition walls and the internal insulation of external walls. Test chambers were designed, allowing the compounds to release only from the surface of the material facing indoors under testing Parameters that were chosen to simulate model room conditions. The emission test results were evaluated using the AgBB evaluation scheme, a procedure for the health-related evaluation of construction products and currently applied for the approval of specific groups of building materials in Germany.
Seventeen out of 19 sample build-ups tested in this study would have passed this scheme since they generally proved to be low-emitting and although the combined emissions of multiple materials were tested, 50% of the measurements could be terminated before half of the total testing time.
Formaldehyde is considered as carcinogenic and is emitted from particleboards and plywood used in toy manufacturing. Currently, the flask method is frequently used in Europe for market surveillance purposes to assess formaldehyde release from toys, but its concordance to Levels measured in emission test chambers is poor. Surveillance laboratories are unable to afford laborious and expensive emission chamber testing to comply with a new amendment of the European Toy Directive; they need an alternative method that can provide reliable results. Therefore, the application of miniaturised emission test chambers was tested. Comparisons between a 1 m3 emission test chamber and 44 mL microchambers with two particleboards over 28 days and between a 24 L desiccator chamber and the microchambers with three puzzle samples over 10 days resulted in a correlation coefficient r2 of 0.834 for formaldehyde at steady state. The correlation between the results obtained in microchambers vs. flask showed a high variability over 10 samples (r2: 0.145),
thereby demonstrating the error-proneness of the flask method in comparison to methods carried out under ambient parameters. An exposure assessment was also performed for three toy puzzles: indoor formaldehyde concentrations caused by puzzles were not negligible (up to 8 µg/m3), especially when more conservative exposure scenarios were considered.
Emission testing of volatile organic compounds (VOC) from materials and products is commonly based on emission test chamber measurements. To ensure the comparability of results from different testing laboratories, their measurement performance must be verified. For this purpose, Bundesanstalt für Materialforschung und -prüfung (BAM) organizes an international proficiency test (round robin test, RRT) every two years using well-characterized test materials (one sealant, one furniture board, and four times a lacquer) with defined VOC emissions. The materials fulfilled the requirements of homogeneity, reproducibility, and stability. Altogether, 36 VOCs were included of which 33 gave test chamber air concentrations between 13 and 83 µg/m3. This is the typical concentration range to be expected and to be quantified when performing chamber tests. Three compounds had higher concentrations between 326 and 1105 µg/m3. In this paper, the relative standard deviations (RSD) of BAM round robin tests since 2008 are compared and the improvement of the comparability of the emission chamber testing is shown by the decrease of the mean RSD down to 28 % in 2018. In contrast, the first large European interlaboratory comparison in 1999 showed a mean RSD of 51 %.
Bauprodukte und Einrichtungsgegenstände für Innenräume, wie Bodenbeläge und Wandpaneele, sollen das Wohlbefinden und die Gesundheit der Raumnutzerinnen und -nutzer nicht durch das Ausdünsten von Geruchsstoffen stören. Mit der Geruchsprüfung nach ISO 16000-28 „Innenraumluft - Bestimmung der Geruchsstoffemissionen aus Bauprodukten mit einer Emissionsprüfkammer“ wird der Produktgeruch zu einer messbaren Größe. So kann z. B. die empfundene Intensität, also die Stärke eines Geruchseindruckes, mit Hilfe eines Vergleichsmaßstabes von Probandinnen und Probanden ermittelt werden. Im hier vorgestellten Projekt werden Vorschläge zur Weiterentwicklung der Methode vorgestellt, um im Ergebnis die Reproduzierbarkeit der Messergebnisse weiter zu verbessern. Dabei werden vor allem das Probenpräsentationssystem und die Bewertungsmethodik für die empfundene Intensität bei der Bewertung von Bauprodukten gemäß AgBB-Schema betrachtet, da diese einen wesentlichen Einfluss haben.
Quantitative chemical analysis of airborne particulate matter (PM) is vital for the understanding of health effects in indoor and outdoor environments, as well as for enforcing EU air quality regulations. Typically, airborne particles are sampled over long time periods on filters, followed by lab-based analysis, e.g., with inductively coupled plasma mass spectrometry (ICP-MS). During the EURAMET EMPIR AEROMET project, cascade impactor aerosol sampling is combined for the first time with on-site total reflection X-ray fluorescence (TXRF) spectroscopy to develop a tool for quantifying particle element compositions within short time intervals and even on-site. This makes variations of aerosol chemistry observable with time resolution only a few hours and with good size resolution in the PM10 range. The study investigates the proof of principles of this methodological approach. Acrylic discs and silicon wafers are shown to be suitable impactor carriers with sufficiently smooth and clean surfaces, and a non-destructive elemental mass concentration measurement with a lower limit of detection around 10 pg/m3 could be achieved. We demonstrate the traceability of field TXRF measurements to a radiometrically calibrated TXRF reference, and the results from both analytical methods correspond satisfactorily.
A new facility has been developed which allows for a stable and reproducible production of ambient-like model aerosols (PALMA) in the laboratory. The set-up consists of multiple aerosol generators, a custom-made flow tube homogeniser, isokinetic sampling probes, and a system to control aerosol temperature and humidity. Model aerosols containing elemental carbon, secondary organic matter from the ozonolysis of α-pinene, inorganic salts such as ammonium sulfate and ammonium nitrate, mineral dust particles,and water were generated under different environmental conditions and at different number and mass concentrations. The aerosol physical and chemical properties were characterised with an array of experimental methods, including scanning mobility particle sizing, ion chromatography, total reflection X-ray fluorescence spectroscopy and thermo-optical analysis. The facility is very versatile and can find applications in the calibration and performance characterisation of aerosol instruments monitoring ambient air. In this study, we performed, as proof of concept, an intercomparison of three different commercial PM (particulate matter) monitors (TEOM1405, DustTrak DRX 8533 and Fidas Frog) with the gravimetric reference method under three simulated environmental scenarios. The results are presented and compared to previous field studies. We believe that the laboratory-based method for simulating ambient aerosols presented here could provide in the future a useful alternative to time-consuming and expensive field campaigns, which are often required for instrument certification and calibration.