Show Abstract ▼

Abstract: That the boundaries of analysis using XRF spectrometry performed at SR sources continues to be pushed back is evidenced by the nanoscale spatial resolution with near single-atom sensitivity for the most efficiently detected elements in nanobeam applications and high speed 2D/3D imaging capabilities. The 4th generation SR facilities currently under development, such as the ESRF Extremely Brilliant Source (EBS), will be at the forefront of these advances. A clear trend is that SR-XRF spectrometry is increasingly applied with complementary X-ray spectroscopic/imaging techniques to combine spatially resolved elemental information with speciation and structural/morphological imaging. The wide range of applications of scanning (sub)microXRF spectrometry for elemental imaging published in the period covered by this review included biomedical, environmental, materials science and cultural heritage studies. Most applications involved XAS and XRD methods at hard X-ray micro- and nano-probe facilities. Full field microXRF spectrometry has made very promising advances with respect to the optics used. Coded apertures have potential for overcoming the low count rates that often restrict the full potential of laboratory-based full-field setups. The availability of commercial full-field detectors will increase the user community and thereby foster advancement in full field microXRF spectrometry. The TXRF spectrometry of ambient air is becoming more and more sophisticated and the advantages of this micro analytical tool over ICP-MS in terms of short sampling times with high particle size resolution are becoming ever more apparent. For example, the optimal sampling time for aerosols for TXRF analysis was well below 12 hours, whereas that for ICP-MS analysis was about 24 hours. High-quality grazing incidence XRF analysis in the laboratory has become more feasible with the development of prototype TXRF instrumentation and the availability of commercial XRD setups with energy dispersive detectors. Portable XRF spectrometry has undergone significant technological improvements in recent years and is now applied in a wide range of applications. This is reflected in a significant number of valuable review papers dealing with different aspects of the portable XRF technique. The growth in the use of macroXRF scanning systems in cultural heritage investigations has required development of new software and methodologies for efficient handling of the huge data files generated. In several contributions the possibilities of a new scanning station equipped with real time macroXRF spectrometry was demonstrated.

Show Abstract ▼

Abstract: Ashless dialkyldithiophosphate (DDP) antiwear additives are good candidates to replace the widely used metallic DDPs such as zinc dialkyldithiophosphate (ZDDP), which are less environmentally friendly. A newly designed in-situ tribological rig was utilised to perform in-situ synchrotron X-ray absorption spectroscopy (XAS) in order to examine the decomposition reactions of two types of DDPs; acidic and neutral. The tribological experiments showed that the two DDP additives decomposed to form protective tribofilms on the steel surface, which provided better antiwear protection than ZDDP regardless of the tribofilm thickness. The neutral DDP formed a thinner tribofilm (about 33 nm) than ZDDP (about 41 nm), whereas the tribofilm of the acidic DDP had a much lower thickness (<7 nm) but more superior antiwear protection. The two DDPs also provided lower friction coefficient (<0.1) than the 0.12 provided by ZDDP. The XAS experiments suggest that the DDPs decompose to form initially iron sulphate, which is quickly reduced to sulphide before forming the phosphate layers of the protective tribofilm. These layers consisted initially of iron phosphate of short chains but as rubbing continued organic phosphate with long chains started to form.

Show Abstract ▼

Abstract: Platinum nanoparticles exhibit unique catalytic properties and have a number of important applications: as an industrial catalyst for fuel cells, in the synthesis of nitric acid, as well as in the reduction of exhaust gases from vehicles. While there have been many studies demonstrating size and morphology control of platinum nanoparticles, a molecular level understanding of the nucleation and growth mechanisms underlying nanoparticle formation, which is crucial for efficient optimization of size controlled synthesis, is lacking in the literature. Structurally incisive experimental in situ probes with enough spatial and temporal resolution are needed to monitor nucleation and growth processes. Here we use operando X-ray Absorption Spectroscopy (XAS) coupled with continuous flow microfluidics to study the mechanisms of platinum nanoparticle formation by reduction of H2PtCl6 using ethylene glycol as a reducing agent. In contrast to a batch synthesis, a continuous flow device allows for rapid and efficient mixing of precursors and fine control over the synthesis parameters such as concentration, flow rate and temperature. The XAS results capture the intermediate stages of nanoparticle formation through to complete reduction to Pt nanoparticles. The setup described here can, in principle, be used to study nanoparticle nucleation and growth mechanisms of a wide range of nanoparticles that occur at fast (microsecond) timescales.

Show Abstract ▼

Abstract: Coal fly ash is an industrially useful by-product of coal combustion, with millions of tonnes held in repositories globally. This fine and cheaply-available waste material, is proven to sometimes be enriched in valuable elements/compounds, such as rare earth element (REE) minerals and actinides, alongside heavy toxic elements such as Cr, Pb, As and Cd, making coal fly ash both a potential unconventional source of valuable minerals and a hazardous material depending on the elemental trace chemistry of the parent coal body. The importance of REE and actinides for use in advanced electronics technologies and the nuclear industry, alongside concerns over geopolitics and instability in the global supply market, means there is now a renewed incentive for countries to secure native sources of economically-sustainable rare earth elements through research and development efforts. Unconventional sources of REE, such as coal fly ash, represent a potentially interesting value proposition, especially for developing countries. The work presented in this thesis provides a study of rare earth elements and actinides in Nigerian simulant coal fly ash from the perspective of resource recovery and environmental protection. A suite of advanced analytical laboratory techniques and novel synchrotron radiation techniques, alongside micromanipulation methods, were used in this study to understand the amounts and mineralogical association of REE and actinides in 3 different Nigerian coal deposits. Bulk and micro mineralogical analyses were first performed on the simulant coal fly ash using x-ray diffraction and scanning electron microscopy / with energy dispersive x-ray fluorescence and spectroscopy used for elemental analysis. It was observed that the Nigerian simulant coal fly ash samples were less complex in mineralogy than conventional rare earth ores (with quartz, mullite, haematite and cristobalite as the major mineral phases), composed of discrete micron-scale particles of rare earth mineral monazite ([Ce,La,Nd,Th]PO4), xenotime (YPO4) and zircon (ZrSiO4), alongside uraninite (UO2) and thorite (ThSiO4). Subsequent bulk elemental analysis performed using inductively-coupled plasma mass spectrometry, showed the simulant coal fly ash to be enriched in the rare earth elements, being more enriched in the higher-valued critical rare earth elements Nd, Eu, Tb, Dy, Y and Er, compared to conventional rare earth ores. Sequential extraction analysis of the simulant fly ash materials showed significant recoverability of rare earth elements in the acid-soluble fraction using cheap and environmentally-friendly ethanoic acid; the toxic heavy metals Cd and As were also significantly recovered in the acid-soluble fraction. Synchrotron radiation analysis of individual micro-particles of monazite and uraninite using micro-x-ray fluorescence mapping, micro-x-ray fluorescence tomography, micro-x-ray absorption near edge spectroscopy and micro-x-ray diffraction showed a zonation pattern in the monazite particles, with the rims rich in the rare earth elements, and the core rich in U and Th but depleted in the rare earth elements. In the uraninite particles, U was homogeneously-distributed, existing in the chemically reduced IV oxidation state. Gamma-ray spectrometry analysis of the bulk coal and simulant coal fly ash was also performed using a high-purity Ge gamma-ray detector. Compared to World mean levels, the radioactivity and associated hazard associated with the parent coal samples were insignificantly-low. However, the equivalent activity concentration and radiological hazard levels associated with the simulant coal fly ashes were significantly-high, above United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) World mean and recommended levels.

Show Abstract ▼

Abstract: Containing the global severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has been an unprecedented challenge due to high horizontal transmissivity and asymptomatic carriage rates. Lateral flow device (LFD) immunoassays were introduced in late 2020 to detect SARS-CoV-2 infection in asymptomatic or presymptomatic individuals rapidly. While LFD technologies have been used for over 60 years, their widespread use as a public health tool during a pandemic is unprecedented. By the end of 2020, data from studies into the efficacy of the LFDs emerged and showed these point-of-care devices to have very high specificity (ability to identify true negatives) but inadequate sensitivity with high false-negative rates. The low sensitivity (<50%) shown in several studies is a critical public health concern, as asymptomatic or presymptomatic carriers may wrongly be assumed to be noninfectious, posing a significant risk of further spread in the community. Here, we show that the direct visual readout of SARS-CoV-2 LFDs is an inadequate approach to discriminate a potentially infective viral concentration in a biosample. We quantified significant immobilized antigen–antibody-labeled conjugate complexes within the LFDs visually scored as negative using high-sensitivity synchrotron X-ray fluorescence imaging. Correlating quantitative X-ray fluorescence measurements and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) determined numbers of viral copies, we identified that negatively scored samples could contain up to 100 PFU (equivalent here to ∼10 000 RNA copies/test). The study demonstrates where the shortcomings arise in many of the current direct-readout SARS-CoV-2 LFDs, namely, being a deficiency in the readout as opposed to the potential level of detection of the test, which is orders of magnitude higher. The present findings are of importance both to public health monitoring during the Coronavirus Disease 2019 (COVID-19) pandemic and to the rapid refinement of these tools for immediate and future applications.