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“State-of-the-art X-ray fluorescence instrumentation for chemical analysis”. Margui E, Van Grieken R, Petro Industry News , 16 (2013)
Abstract: Nowadays, X-ray fluorescence spectrometry (XRF) is a well-established analytical technique for qualitative and quantitative elemental analysis (sometimes from Be to U) of a wide variety of samples. In particular, the truly multi-element character, acceptable speed and economy, ease of automation and the possibility to directly analyse solid samples are the most important features among the many that have made it a very mature analytical tool for routine quality controls in many industries, as well as for analytical support for the research laboratory.e recent technological advances, including the design of low-power micro-focus tubes and the novel X-ray optics and detectors have made it possible to extend XRF to the determination of low-Z elements and to obtain 2D or 3D information on a micrometre-scale. Furthermore, the recent development and commercialisation of benchtop and portable instrumentation, that offer extreme simplicity of operation in a low-cost design, have promoted even more the approach of XRF for many analytical problems.is article highlights this state-of-the art technique with regards to currently available XRF instrumentation on the market as well as recent applications in environmental and industrial fields.
Keywords: A3 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Additional Links: UA library record
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De Luca F, Abate S, Bogaerts A, Centi G (2024) Electrified CO2 conversion : integrating experimental, computational, and process simulation methods for sustainable chemical synthesis. xv, 152 p
Abstract: Nowadays, the burning of fossil fuels, particularly petroleum, natural gas, and coal, meets the rising need for power and fuels for automobiles and industries. This has given rise to ecological and climate challenges. This thesis explores these issues from three distinct perspectives: (i) experimental, (ii) computational, and (iii) process simulation, with a focus on studying CO2 as an alternative and economically viable raw material. Firstly, the experimental study is focused on the synthesis, characterization, and testing of novel catalysts for electroreduction of CO2 and oxalic acid, an intermediate product of CO2. Electrocatalysts based on Cu supported by citrus (orange and lemon) peel biomass are prepared. These catalysts exhibit activity in the electrochemical reduction of CO2, emphasizing the effectiveness of biomasses, particularly orange peels, as environmentally friendly precursors for sustainable and efficient electrocatalysts. In addition, graphitic carbon nitrides/TiO2 nanotubes (g-C3N4/TiNT) composites are prepared for the electrocatalytic reduction of oxalic acid to glycolic acid, revealing superior electrocatalytic properties compared to pristine TiNT. Characterization by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electronic microscopy were performed for all the prepared electrocatalysts. Delving into the reduction of CO2 on Cu catalysts, a computational study about the synthesis of methanol on Cu(111) surface is performed by using the Vienna Ab initio Simulation Package. A systematic study is carried out to define the activation energies of the elementary reactions by using mGGA DF. Consequently, it is shown that the rate-controlling step is CH3O* hydrogenation and the formate pathway on Cu(111) proceeds through the HCOOH* intermediate. Finally, the process simulation, performed by using the software Aspen Plus 11 from AspenTech Inc., is based on the comparison of a catalytic (oxidation of ethylene glycol) and an electrocatalytic process (CO2 electroreduction chain) to synthesize glycolic acid. An economic analysis of the operational and investment costs reveals that the catalytic process is more cost-effective due to the current instability of electrocatalysts and proton exchange membranes, resulting in increased maintenance costs and, consequently, higher prices for the product.
Keywords: Doctoral thesis; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Additional Links: UA library record
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“Hyperfine electric parameters calculation in Si samples implanted with 57Mn\rightarrow57Fe”. Abreu Y, Cruz CM, Pinera I, Leyva A, Cabal AE, van Espen P, Van Remortel N, Physica: B : condensed matter 445, 1 (2014). http://doi.org/10.1016/J.PHYSB.2014.03.028
Abstract: Nowadays the electronic structure calculations allow the study of complex systems determining the hyperfine parameters measured at a probe atom, including the presence of crystalline defects. The hyperfine electric parameters have been measured by Mossbauer spectroscopy in silicon materials implanted with Mn-57 ->,Fe-57 ions, observing four main contributions to the spectra. Nevertheless, some ambiguities still remain in the Fe-57 Mossbauer spectra interpretation in this case, regarding the damage configurations and its evolution with annealing. In the present work several implantation environments are evaluated and the Fe-57 hyperfine parameters are calculated. The observed correlation among the studied local environments and the experimental observations is presented, and a tentative microscopic description of the behavior and thermal evolution of the characteristic defects local environments of the probe atoms concerning the location of vacancies and interstitial Si in the neighborhood of Fe-57 ions in substitutional and interstitial sites is proposed. (C) 2014 Elsevier B.V. All rights reserved
Keywords: A1 Journal article; Particle Physics Group; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
DOI: 10.1016/J.PHYSB.2014.03.028
Additional Links: UA library record; WoS full record; WoS citing articles
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“Rebound effects following technological advancement? The case of a global shock in ferrochrome supply”. Buyle M, Audenaert A, Brusselaers J, Van Passel S, Journal of cleaner production 391, 136264 (2023). http://doi.org/10.1016/J.JCLEPRO.2023.136264
Abstract: Novel recycling technologies aim at increasing material efficiency by turning former waste products into valuable reclaimed resources. A key question is whether such technologies really reduce primary resource consumption or instead stimulate aggregated market demand. In this study the consequences of a positive shock in ferrochrome supply to the global stainless steel value chain is assessed quantitatively. This new source might be unlocked by technology under development for the recovery of chromium from carbon and stainless steel slags. The aim of this study is to quantitatively assess the income and substitution effects of reclaimed ferrochrome along a part of the stainless steel value chain. The impact of the supply shock is analysed by means of a vector autoregression (VAR), a dynamic model where lagged values of all included variables estimate current state of the system. Additionally, the VAR model is extended to a structural vector autoregression (SVAR) to account for contemporary effects as well. Both the VAR and SVAR model indicate that additional ferrochrome supply leads to an increase in aggregated supply of stainless steel, in combination with a substitution effect between ferrochrome and nickel. The extended SVAR model additionally highlights that contemporaneous effects do play an important role as well to capture the direct rebound effect in the ferrochrome market when working with quarterly data. In other words, an additional supply of reclaimed ferrochrome triggers a complex combination of interactions and consequences, yet it does not necessarily lead to a lower overall material consumption. The main contributions of this paper are the assessment of direct rebound effects of supplying reclaimed metals along the value chain and the demonstration that quantifying the effects of circular strategies is feasible.
Keywords: A1 Journal article; Economics; Engineering sciences. Technology; Energy and Materials in Infrastructure and Buildings; Engineering Management (ENM)
Impact Factor: 11.1
DOI: 10.1016/J.JCLEPRO.2023.136264
Additional Links: UA library record; WoS full record
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Sabzalipour A (2021) Charge transport in magnetic topological insulators. xiv, 185 p
Abstract: Novel quantum phases of matter and developing practical control over their characteristics is one of the primary aims of current condensed matter physics. It offers the potential for a new generation of energy, electronic and photonic technologies. Among all the newly found phases of matter, topological insulators are novel phases of quantum matter with fascinating bulk band topology and surface states protected by specific symmetries. For example, at the boundary of a strong topological insulator and a trivial insulator, metallic surface states appear that are protected by time-reversal symmetry. As a result, the bulk continues to be insulating, while the surface can support exotic high-mobility spin-polarized electronic states. Since there is no such thing as a clean system, impurities and other disorders are always present in materials. Even while impurities appear to be unfavorable to a system at first look, doping the host system with impurities allows us to engineer different electronic properties of systems, such as the Fermi level or electron density. Because of the symmetry protected metallic states in topological insulators, charge transport responds distinctively to magnetic and non-magnetic impurities. This doctoral dissertation explores how the longitudinal charge transport in magnetic topological thin films and the anomalous Hall effect on the surface of 3D magnetic topological insulators is influenced by point-like and randomly distributed dilute magnetic impurities. We are interested in how charge transport in these systems responds to the orientation of the magnetization orientation and how this response evolves based on the system's main characteristics, such as the magnitude of the Fermi level or gate voltage. Because topological insulators have a strong spin-orbit coupling, the interaction between conducting electrons and local magnetic impurities is very anisotropic. We will show that this anisotropy even enhances when magnetic topological thin films are exposed to a substrate or gate voltage. Therefore, to properly capture this anisotropy in charge transport calculations, we rely on a generalized Boltzmann formalism together with a modified relaxation time scheme. We show that magnetic impurities affect the charge transport in topological insulators by inducing a transition selection rule that governs scatterings of electrons between various electronic states. We see that this selection rule is highly sensitive to the spin direction of the magnetic impurities as well as the position of the Fermi level. According to this selection rule and depending on the position of the Fermi level, two different transport regimes are realized in magnetic topological thin films. In one of these regimes, our findings show that a dissipation less charge current can be generated. In other words, even if there are many magnetic impurities in the system, electrons do not notice them and, remarkably, conduct charge without dissipation. Outside this regime, the charge transport is always dissipative and its sensitivity to the spatial orientation of the magnetic impurities can be effectively modulated by a substrate or gate voltage. In this doctoral thesis, we also explore the anomalous Hall effect (AHE) on the surface of 3D magnetic topological insulators. The AHE is generated by three mechanisms: the intrinsic effect (owing to a nonzero Berry curvature), the side jump effect, and the skew scattering effect. They compete to dominate the AHE in distinct regimes. Analytically, we calculate the contributions of all three mechanisms to the scattering of massive Dirac fermions by magnetic impurities. Our results reveal three transport regimes based on the relative importance of the engaged mechanisms. The identification of these three distinctive transport regimes can assist experimentalists in achieving a regime in which each contribution is dominant over the others, allowing them to measure them separately. Typically, this is not feasible empirically since the total value of the experimentally observed AHE conceals the specific information of each of the three contributions. Based on our analytical calculations, we prove that the AHE can change sign by varying the orientation of the surface magnetization, the concentration of impurities, and the location of the Fermi level, which is consistent with previous experimental findings. In addition, we show that by suitably adjusting the given parameters, any contribution to the AHE, or even the entire AHE, can be turned off. For example, in a system with in-plane magnetization, one can turn off the AHE by pushing the system into the completely metallic regime. Furthermore, we demonstrate that any contribution to the AHE, or even the whole AHE, can be turned off by appropriately changing the provided parameters. For example, in a system with in-plane magnetization, the AHE can be turned off by pushing the system into the fully metallic regime.
Keywords: Doctoral thesis; Condensed Matter Theory (CMT)
Additional Links: UA library record
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Tschulkow M (2022) A techno-environmental economic assessment of a lignin-first biorefinery : a dynamic and prospective framework for emerging technologies. 175 p
Abstract: Novel emerging biorefinery technologies have gained interest and have the potential to tackle several sustainability challenges in our society. A lignin-first biorefinery process – reductive catalytic fractionation (RCF) – is currently under development with the aim to process wood into high-value end-products that replace highly polluting fossil oil-based products. However, such emerging technologies are not matured yet, holding a certain degree of technological, economic, and environmental uncertainty. Hence, an appropriate assessment method is required to assess techno-economic feasibility and environmental impacts of emerging uncertain technologies (e.g lignin-first RCF process). This dissertation aims to develop an integrated techno-environmental economic assessment framework to assess emerging technologies dynamically and prospectively from economic and environmental points of view. First, a techno-economic assessment (TEA) is performed to assess the economic feasibility and the most influential economic and technological parameters of the lignin-first RCF biorefinery taking the whole wood value chain into account. By making the relations across the wood value chain, the scale of the biorefinery, wood species, and output prices highly determine the economic feasibility. The economic feasibility can be reached by a sufficient capacity level which depends on wood species-specific conditions. Also, waste wood proves to be the most profitable feedstock in comparison to virgin wood. Second, an analytical real options analysis (ROA) is performed taking two correlated market uncertainties and the value of flexibility into account to identify the optimal investment decision in an RCF biorefinery. Two different investment options, separated and united investments in harvesting equipment and RCF biorefinery, are analyzed. In both scenarios, market uncertainty postpones the investment. When both investment decisions are united, the probability of investment increases in comparison to separated investments. The study reveals that RCF has the potential to stimulate investments within the wood value chain. Third, a consequential life cycle assessment (LCA) is performed to assess the carbon emissions and the environmental consequences of the lignin-first RCF process and its products. The study reveals that at the current stage RCF products have higher carbon emissions than their alternative counterparts. Several options to improve the environmental performance are discussed such as different RCF technology configurations, targeting different RCF products with the ability to replace higher polluting alternative counterparts on the markets. Other discussion points such as transportation type and the distance, (in-)direct land-use change, the use stage and disposal stages implications, and a more comprehensive environmental view of the RCF products, show the potential to improve the environmental performance of the RCF technology. Overall, the study shows that the RCF process can be environmentally desirable if the appropriate RCF configuration and products are chosen. Finally, the above-mentioned methods – techno-economic assessment, analytical real options analysis, and consequential life cycle assessment – are uniquely integrated within the newly developed integrated assessment framework. The framework has the aim to complement the shortcomings and combine the advantages of all three methods. The framework assesses emerging technologies to give predictive insights about the time-specific economic and environmental performance under the newly developed three threshold conditions: technological readiness, economic feasibility, and environmental desirability. The developed integrated assessment framework assesses dynamically and prospectively the RCF biorefinery implementation under Belgian conditions. It reveals that the economic feasibility increases and carbon emissions decrease over time. The RCF biorefinery fulfills all three threshold conditions – technological readiness, economic feasibility, and environmental desirability – consecutively. The newly developed integrated assessment framework offers decision support to several stakeholders of emerging technologies starting from low technology readiness level (TRL). Practitioners such as the technology developers, researchers, and policymakers can use the framework to evaluate emerging technologies that deal with high levels of technological, economic, and environmental uncertainties. The framework assesses emerging technologies on a detailed level to give decision-makers in-depth insights into the intertwined nature of the technological, economic, and environmental dimensions. It offers insights into the expected time-specific economic and environmental performances, potential, and challenges of the emerging technology to further improve the technology and direct R&Ds along the right path.
Keywords: Doctoral thesis; Engineering sciences. Technology; Engineering Management (ENM)
Additional Links: UA library record
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“Electrical stability and performance of a nitrogen-oxygen atmospheric pressure gliding arc plasma”. Manaigo F, Bahnamiri OS, Chatterjee A, Panepinto A, Krumpmann A, Michiels M, Bogaerts A, Snyders R, ACS Sustainable Chemistry and Engineering 12, 5211 (2024). http://doi.org/10.1021/ACSSUSCHEMENG.3C08257
Abstract: Nonthermal plasmas are currently being studied as a green alternative to the Haber-Bosch process, which is, today, the dominant industrial process allowing for the fixation of nitrogen and, as such, a fundamental component for the production of nitrogen-based industrial fertilizers. In this context, the gliding arc plasma (GAP) is considered a promising choice among nonthermal plasma options. However, its stability is still a key parameter to ensure industrial transfer of the technology. Nowadays, the conventional approach to stabilize this plasma process is to use external resistors. Although this indeed allows for an enhancement of the plasma stability, very little is reported about how it impacts the process efficiency, both in terms of NOx yield and energy cost. In this work, this question is specifically addressed by studying a DC-powered GAP utilized for nitrogen fixation into NOx at atmospheric pressure stabilized by variable external resistors. Both the performance and the stability of the plasma are reported as a function of the utilization of the resistors. The results confirm that while the use of a resistor indeed allows for a strong stabilization of the plasma without impacting the NOx yield, especially at high plasma current, it dramatically impacts the energy cost of the process, which increases from 2.82 to 7.9 MJ/mol. As an alternative approach, we demonstrate that the replacement of the resistor by an inductor is promising since it allows for decent stabilization of the plasma, while it does not affect either the energy cost of the process or the NOx yield.
Keywords: A1 Journal article; Engineering sciences. Technology; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 8.4
DOI: 10.1021/ACSSUSCHEMENG.3C08257
Additional Links: UA library record; WoS full record
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Clavel J (2024) Plant-mycorrhizal interactions and their role in plant invasions in mountains. 182 p
Abstract: Non-native species invasions are one of the most impactful drivers of biodiversity and ecosystem services loss worldwide. One aspect of plant species invasion, which is only recently starting to be recognized as a determinant of invasion success, is the symbiosis between plant and mycorrhizal fungi. Here, I focus on anthropogenic disturbance in mountain ecosystems and its impact on plant communities and mycorrhizal fungi to answer how these communities are impacted by disturbance and whether non-native plants can benefit to establish and spread. To this end I used a combination of different approaches: 1) repeated surveys of plants and arbuscular mycorrhizal fungi along disturbed roadsides in the mountains of Norway, 2) combining a global dataset of native and non-native plants along mountain roads with a database associating plants with their mycorrhizal types, and 3) an in-situ experiment measuring non-native plant success and changes in fungal community following different types of disturbances. Through these methods, I could assess the effects of anthropogenic disturbance on mycorrhizal symbiosis and non-native plant species at multiple scales and resolutions. We found that road disturbance has a globally consistent effect on mycorrhizal types in mountain systems, as plants associated with arbuscular mycorrhizal (AM) fungi were more abundant following disturbance. Conversely, vegetation associated with either ectomycorrhizal (EcM) or ericoid mycorrhizal (ErM) fungi was less abundant in disturbed sites. In the regional study, AM fungi were most abundant and diverse in the roots of plant communities affected by road disturbance. Non-native plants were also restricted to these disturbed sites. The experimental results showed that physical disturbance and nutrient addition have negative effects on EcM fungi and positive effects on fungal pathogens, and facilitate non-native plant success. Our results show that anthropogenic disturbance does have an effect on mycorrhizal fungi that in turn impacts the distribution of plant species in disturbed mountain systems. The resulting shift in mycorrhizal fungi benefiting AM fungi and AM plant species could have implications for non-native plant invasions. Indeed, we know that non-native plants predominantly form associations with AM fungi. Therefore, anthropogenic disturbance can facilitate non-native plant success through disruption of the native fungal communities, and especially so in high elevation and cold climate regions which are naturally less dominated by AM plants. I believe this highlights the importance of mycorrhizal symbiosis in understanding plant invasions and emphasizes the importance of monitoring sources of anthropogenic disturbance in mountains to prevent future establishment of non-native plants.
Keywords: Doctoral thesis; Plant and Ecosystems (PLECO) – Ecology in a time of change
Additional Links: UA library record
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“Low-pressure inductively coupled plasmas in hydrogen : impact of gas heating on the spatial distribution of atomic hydrogen and vibrationally excited states”. Smith GJ, Diomede P, Gibson AR, Doyle SJ, Guerra V, Kushner MJ, Gans T, Dedrick JP, Plasma sources science and technology 33, 025002 (2024). http://doi.org/10.1088/1361-6595/AD1ECE
Abstract: Non-equilibrium inductively coupled plasmas (ICPs) operating in hydrogen are of significant interest for applications including large-area materials processing. Increasing control of spatial gas heating, which drives the formation of neutral species density gradients and the rate of gas-temperature-dependent reactions, is critical. In this study, we use 2D fluid-kinetic simulations with the Hybrid Plasma Equipment Model to investigate the spatially resolved production of atomic hydrogen in a low-pressure planar ICP operating in pure hydrogen (10-20 Pa or 0.075-0.15 Torr, 300 W). The reaction set incorporates self-consistent calculation of the spatially resolved gas temperature and 14 vibrationally excited states. We find that the formation of neutral-gas density gradients, which result from spatially non-uniform electrical power deposition at constant pressure, can drive significant variations in the vibrational distribution function and density of atomic hydrogen when gas heating is spatially resolved. This highlights the significance of spatial gas heating on the production of reactive species in relatively high-power-density plasma processing sources.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.8
DOI: 10.1088/1361-6595/AD1ECE
Additional Links: UA library record; WoS full record
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“Finding the optimal fatty acid composition for biodiesel improving the emissions of a one-cylinder diesel generator”. Maes RR, Potters G, Fransen E, Cayetano FC, Van Schaeren R, Lenaerts S, Sustainability 13, 12089 (2021). http://doi.org/10.3390/SU132112089
Abstract: Nitrogen oxides (NOx) and particulate matter (PM) currently are the main pollutants emitted by diesel engines. While there is a start in using hybrid and electric cars, ships will still be fueled by mineral oil products. In the quest to achieve zero-pollution and carbon-free shipping, alternative forms of energy carriers must be found to replace the commonly used mineral oil products. One of the possible alternative fuels is biodiesel. This paper explores the optimization of the composition of biodiesel in order to reduce the concentration of particulate matter and NOx in exhaust gases of a one-cylinder diesel generator.
Keywords: A1 Journal article; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL)
Impact Factor: 1.789
DOI: 10.3390/SU132112089
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“Disproportionation of nitrogen induced by DC plasma-driven electrolysis in a nitrogen atmosphere”. Pattyn C, Maira N, Buddhadasa M, Vervloessem E, Iseni S, Roy NC, Remy A, Delplancke M-P, De Geyter N, Reniers F, Green Chemistry 24, 7100 (2022). http://doi.org/10.1039/D2GC01013E
Abstract: Nitrogen disproportionation i.e. its simultaneous conversion to compounds of higher (NOx) and lower (NH3) oxidation states in a N-2 DC plasma-driven electrolysis process with a plasma cathode is investigated. This type of plasma-liquid interaction exhibits a growing interest for many applications, in particular nitrogen fixation where it represents a green alternative to the Haber-Bosch process. Optical emission spectroscopy, FTIR and electrochemical sensing systems are used to characterize the gas phase physico-chemistry while the liquid phase is analyzed via ionic chromatography and colorimetric assays. Experiments suggest that lowering the discharge current enhances nitrogen reduction and facilitates the transfer of nitrogen compounds to the liquid phase. Large amounts of water vapor appear to impact the gas discharge physico-chemistry and to favor the vibrational excitation of N-2, a key parameter for an energy-efficient nitrogen fixation.
Keywords: A1 Journal article; Engineering sciences. Technology; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 9.8
DOI: 10.1039/D2GC01013E
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“Monitoring of NO2 in the ambient air with passive samplers before and after a road reconstruction event”. Stranger M, Krata A, Kontozova-Deutsch V, Bencs L, Deutsch F, Worobiec A, Naveau I, Roekens E, Van Grieken R, Microchemical journal 90, 93 (2008). http://doi.org/10.1016/J.MICROC.2008.04.001
Abstract: Nitrogen dioxide (NO2) concentrations were used to evaluate the air quality before and after the infrastructural change of an important traffic artery in Mortsel, Antwerp (Belgium). During the reconstruction works two pairs of traffic lanes were reduced to one in each direction. Two sampling campaigns were conducted: the first one before the works in 2003 and the second one in 2005, after the road works were finished. Sampling was performed on a weekly base with the use of passive diffusion tubes on the streets, and also indoors in nearby houses. The samples were analyzed by ion chromatography, from which data the NO2 concentrations in air could be calculated. These results were compared with NO2 values from the air monitoring station 42R801 of the Flemish Environment Agency in Borgerhout, Antwerp. On the base of different NO2 concentrations, correlated well with the traffic density, sampling locations were classified into three groups as follows: 1) heavily polluted (heavy traffic); 2) moderately polluted (medium traffic); or 3) less polluted (low traffic density). Sampling sites located further from the road works, enclosed to the group less polluted, showedthe lowestNO2 concentrations. The highestNO2 levelwas found for the locations close to reconstructionworks, which belonged to the group heavily polluted. The contribution of NO2 was at the samelevel before and after the roadworks. During the first campaign it ranged from30±7 µg/m3 to 71±11 µg/m3 and during the second sampling itwas between 36±17 µg/m3 and 73±17 µg/m3. These modernizationworks had no impact on preventing the traffic-related pollutant as NO2 and as a consequence no significant effect on the air quality in the studied region. It has been proven that the impact of traffic on the air quality is unmistakably high and simply reduction of the number of the traffic lanes, intended to discourage the traffic flow, had apparently no environmentally advantageous effect
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Laboratory Experimental Medicine and Pediatrics (LEMP)
DOI: 10.1016/J.MICROC.2008.04.001
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Vervloessem E (2023) The role of pulsing and humidity in plasma-based nitrogen fixation : a combined experimental and modeling study. 358 p
Abstract: Nitrogen (N) is an indispensable building block for all living organisms as well as for pharmaceutical and chemical industry. In a nutshell, N is needed for plants to grow and beings to live and nitrogen fixation (NF) is the process that makes N available for plants as food by converting N2 into a reactive form, such as ammonia (NH3) or nitrogen oxides (NOx), upon reacting with O2 and H2. The aim of this thesis is to elucidate (wet) plasma-based nitrogen fixation with a focus on (1) the role of pulsing in achieving low energy consumption, (2) the role of H2O as a hydrogen source in nitrogen fixation and (3) elucidation of nitrogen fixation pathways in humid air and humid N2 plasma in a combined experimental and computational study. Furthermore, this thesis aims to take into account the knowledge-gaps and challenges identified in the discussion of the state of the art. Specifically, (1) we put our focus on branching out to another way of introducing water into the plasma system, i.e. H2O vapor, (2) we de-couple the problem for pathway elucidation by starting with characterization of the chosen plasma, next a simpler gas mixture and building up from there, (3) we include modelling, though not under wet conditions and (4) we focus on also analyzing species and performance outside liquid H2O. Firstly, based on the reaction analysis of a validated quasi-1D model, we can conclude that pulsing is indeed the key factor for energy-efficient NOx- formation, due to the strong temperature drop it causes. Secondly, the thesis shows that added H2O vapor, and not liquid H2O, is the main source of H for NH3 generation. Related to this, we discuss how the selectivity of plasma-based NF in humid air and humid N2 can be controlled by changing the humidity in the feed gas. Interestingly, NH3 production can be achieved in both N2 and air plasmas using H2O as a H source. Lastly, we identified a significant loss mechanism for NH3 and HNO2 that occurs in systems where these species are synthesized simultaneously, i.e. downstream from the plasma, HNO2 reacts with NH3 to form NH4NO2, which decomposes into N2 and H2O. This reduces the effective NF when not properly addressed, and should therefore be considered in future works aimed at optimizing plasma-based NF. In conclusion, this thesis adds further to the current state of the art of plasma-based NF both in the presence of H2O and in dry systems.
Keywords: Doctoral thesis; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Additional Links: UA library record
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“Optimizing control strategies for urine nitrification : narrow pH control band enhances process stability and reduces nitrous oxide emissions”. Faust V, Boon N, Ganigué, R, Vlaeminck SE, Udert KM, Frontiers in environmental science 11, 1275152 (2023). http://doi.org/10.3389/FENVS.2023.1275152
Abstract: Nitrification is well-suited for urine stabilization. No base dosage is required if the pH is controlled within an appropriate operating range by urine feeding, producing an ammonium-nitrate fertilizer. However, the process is highly dependent on the selected pH set-points and is susceptible to process failures such as nitrite accumulation or the growth of acid-tolerant ammonia-oxidizing bacteria. To address the need for a robust and reliable process in decentralized applications, two different strategies were tested: operating a two-position pH controller (inflow on/off) with a narrow pH control band at 6.20/6.25 (∆pH = 0.05, narrow-pH) vs. a wider pH control band at 6.00/6.50 (∆pH = 0.50, wide-pH). These variations in pH also cause variations in the chemical speciation of ammonia and nitrite and, as shown, the microbial production of nitrite. It was hypothesized that the higher fluctuations would result in greater microbial diversity and, thus, a more robust process. The diversity of nitrifiers was higher in the wide-pH reactor, while the diversity of the entire microbiome was similar in both systems. However, the wide-pH reactor was more susceptible to tested process disturbances caused by increasing pH or temperature, decreasing dissolved oxygen, or an influent stop. In addition, with an emission factor of 0.47%, the nitrous oxide (N2O) emissions from the wide-pH reactor were twice as high as the N2O emissions from the narrow-pH reactor, most likely due to the nitrite fluctuations. Based on these results, a narrow control band is recommended for pH control in urine nitrification.
Keywords: A1 Journal article; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL)
DOI: 10.3389/FENVS.2023.1275152
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“Determining stoichiometry and kinetics of two thermophilic nitrifying communities as a crucial step in the development of thermophilic nitrogen removal”. Vanderkerckhove TGL, Kerckhof F-M, De Mulder C, Vlaeminck SE, Boon N, Water research 156, 34 (2019). http://doi.org/10.1016/J.WATRES.2019.03.008
Abstract: Nitrification and denitrification, the key biological processes for thermophilic nitrogen removal, have separately been established in bioreactors at 50 °C. A well-characterized set of kinetic parameters is essential to integrate these processes while safeguarding the autotrophs performing nitrification. Knowledge on thermophilic nitrifying kinetics is restricted to isolated or highly enriched batch cultures, which do not represent bioreactor conditions. This study characterized the stoichiometry and kinetics of two thermophilic (50 °C) nitrifying communities. The most abundant ammonia oxidizing archaea (AOA) were related to the Nitrososphaera genus, clustering relatively far from known species Nitrososphaera gargensis (95.5% 16S rRNA gene sequence identity). The most abundant nitrite oxidizing bacteria (NOB) were related to Nitrospira calida (97% 16S rRNA gene sequence identity). The nitrification biomass yield was 0.200.24 g VSS g−1 N, resulting mainly from a high AOA yield (0.160.20 g VSS g−1 N), which was reflected in a high AOA abundance in the community (5776%) compared to NOB (511%). Batch-wise determination of decay rates (AOA: 0.230.29 d−1; NOB: 0.320.43 d−1) rendered an overestimation compared to in situ estimations of overall decay rate (0.0260.078 d−1). Possibly, the inactivation rate rather than the actual decay rate was determined in batch experiments. Maximum growth rates of AOA and NOB were 0.120.15 d−1 and 0.130.33 d−1 respectively. NOB were susceptible to nitrite, opening up opportunities for shortcut nitrogen removal. However, NOB had a similar growth rate and oxygen affinity (0.150.55 mg O2 L−1) as AOA and were resilient towards free ammonia (IC50 > 16 mg NH3-N L−1). This might complicate NOB outselection using common practices to establish shortcut nitrogen removal (SRT control; aeration control; free ammonia shocks). Overall, the obtained insights can assist in integrating thermophilic conversions and facilitate single-sludge nitrification/denitrification.
Keywords: A1 Journal article; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL)
DOI: 10.1016/J.WATRES.2019.03.008
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“Optimizing sulfur-driven mixotrophic denitrification process : system performance and nitrous oxide emission”. Liu Y, Ngo HH, Guo W, Zhou J, Peng L, Wang D, Chen X, Sun J, Ni B-J, Chemical engineering science 172, 414 (2017). http://doi.org/10.1016/J.CES.2017.07.005
Abstract: Nitrate contamination of groundwater has been recognized as a significant environmental problem world widely. Sulfur-driven mixotrophic denitrification has been demonstrated as a promising groundwater treatment process, which though plays an important role in nitrous oxide (N2O) emissions, significantly contributing to the overall carbon footprint of the system. However, the current process optimizations only focus on nitrate removal and excess sulfate control, with the N2O emission being ignored. In this work, an integrated mathematical model was proposed to evaluate the N2O emission as well as the excess sulfate production and carbon source utilization in sulfur-driven mixotrophic denitrification process. In this model, autotrophic and heterotrophic denitrifiers use their corresponding electron donors (sulfur and organic matter, respectively) to reduce nitrate to nitrogen gas, with each modeled as three-step denitrification (NO3 to N-2 via NO2 and N2O) driven by sulfur or organic matter to describe all potential N2O accumulation steps. The developed model, employing model parameters previously reported in literature, was successfully validated using N2O and sulfate data from two mixotrophic denitrification systems with different initial conditions. Modeling results revealed substantial N2O accumulation due to the relatively low autotrophic N2O reduction activity as compared to heterotrophic N2O reduction activity, explaining the observation that higher carbon source addition resulted in lower N2O accumulation in sulfur-driven mixotrophic denitrifying system. Based on the validated model, optimizations of the overall system performance were carried out. Application of the model to simulate long-term operations of sulfur-driven mixotrophic denitrification process indicates that longer sludge retention time reduces N2O emission due to better retention of active biomass. High-level total nitrogen removal with significant N2O emission mitigation, appropriate excess sulfate control and maximized COD utilization can be achieved simultaneously through controlling the influent nitrate and COD concentrations. (C) 2017 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Sustainable Energy, Air and Water Technology (DuEL)
DOI: 10.1016/J.CES.2017.07.005
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“Analysis of lateritic material from Cerro impacto by instrumental neutron activation employing a low-energy photon semiconductor and a high-energy Ge(Li) detector”. LaBrecque JJ, Beusen JM, Van Grieken RE, Applied spectroscopy 40, 140 (1986). http://doi.org/10.1366/0003702864509600
Abstract: Nineteen elements were determined in four different grain size fractions of a bulk geological material from Cerro Impacto for a study of the physical (mechanical) concentration process of different elements based upon the hardness of the different minerals. The analysis was performed by excitation of the sample with a high, slow neutron flux followed by gamma-ray spectroscopy with both a conventional Ge(Li) high-energy detector and a low-energy photon detector (LEPD). The accuracy of this method was studied with the use of two standard reference materials, SY-2 and SY-3, which are similar to the real samples. The values determined were also compared with a secondary target x-ray fluorescence method for all the elements that were suitable to both methods. Actually, the x-ray fluorescence method was found to be more complementary than competitive.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
DOI: 10.1366/0003702864509600
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“Critical reflections on Cinema Belgica : the database for New Cinema History in Belgium”. Ducatteeuw V, Biltereyst D, Meers P, Verbruggen C, Moreels D, Noordegraaf J, Chambers S, De Potter P, Cachet T, Franck N, Deroo F, Journal of open humanities data 9, 1 (2023). http://doi.org/10.5334/JOHD.91
Abstract: New Cinema History broadened film studies by emphasising the complexity of cinema as a multifaceted phenomenon that includes the socio-economic context in which films were made, circulated, shown and received. As part of the digital turn, the discipline adopted computational methods and created quantitative research data to research this socio-economic context at scale. However, not all datasets created in this context adhere to FAIR principles, decreasing their reusability. By reconciling 14 cinema-related datasets, Cinema Belgica facilitates research into the history of Belgian cinema. This research paper documents and critically reflects on the choices made when selecting, modelling and reconciling information for the Cinema Belgica database.
Keywords: A1 Journal article; Mass communications; Art; History; Visual and Digital Cultures Research Center (ViDi)
DOI: 10.5334/JOHD.91
Additional Links: UA library record
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“Combined first-principles and experimental study on the microstructure and mechanical characteristics of the multicomponent additive-manufactured Ti-35Nb-7Zr-5Ta alloy”. Grubova IY, Surmenev RA, Neyts EC, Koptyug AV, Volkova AP, Surmeneva MA, ACS Omega 8, 27519 (2023). http://doi.org/10.1021/ACSOMEGA.3C03157
Abstract: New & beta;-stabilizedTi-based alloys are highly promising forbone implants, thanks in part to their low elasticity. The natureof this elasticity, however, is as yet unknown. We here present combinedfirst-principles DFT calculations and experiments on the microstructure,structural stability, mechanical characteristics, and electronic structureto elucidate this origin. Our results suggest that the studied & beta;Ti-35Nb-7Zr-5Ta wt % (TNZT) alloy manufacturedby the electron-beam powder bed fusion (E-PBF) method has homogeneousmechanical properties (H = 2.01 & PLUSMN; 0.22 GPa and E = 69.48 & PLUSMN; 0.03 GPa) along the building direction,which is dictated by the crystallographic texture and microstructuremorphologies. The analysis of the structural and electronic properties,as the main factors dominating the chemical bonding mechanism, indicatesthat TNZT has a mixture of strong metallic and weak covalent bonding.Our calculations demonstrate that the softening in the Cauchy pressure(C & PRIME; = 98.00 GPa) and elastic constant C ̅ ( 44 ) = 23.84 GPa is the originof the low elasticity of TNZT. Moreover, the nature of this softeningphenomenon can be related to the weakness of the second and thirdneighbor bonds in comparison with the first neighbor bonds in theTNZT. Thus, the obtained results indicate that a carefully designedTNZT alloy can be an excellent candidate for the manufacturing oforthopedic internal fixation devices. In addition, the current findingscan be used as guidance not only for predicting the mechanical propertiesbut also the nature of elastic characteristics of the newly developedalloys with yet unknown properties.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 4.1
DOI: 10.1021/ACSOMEGA.3C03157
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“Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)”. Van Grieken R, de Bruin M, Pure and applied chemistry 66, 2513 (1994). http://doi.org/10.1351/PAC199466122513
Abstract: Nearly 200 terms commonly used in radioanalytical chemistry are unambiguously defined. The list is partially based on an earlier IUPAC-glossary (Pure Appl. Chem. 54 (1982) 1533-1554), but some modifications have been made, terms related to nuclear physics and technology have not been reconsidered and numerous new entries from the realm of radiometric analysis, radioimmunoassay and related techniques have been included.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
DOI: 10.1351/PAC199466122513
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“Dynamic spectral cues do not affect human sound localization during small head movements”. McLachlan G, Majdak P, Reijniers J, Mihocic M, Peremans H, Frontiers in neuroscience 17, 1027827 (2023). http://doi.org/10.3389/FNINS.2023.1027827
Abstract: Natural listening involves a constant deployment of small head movement. Spatial listening is facilitated by head movements, especially when resolving front-back confusions, an otherwise common issue during sound localization under head-still conditions. The present study investigated which acoustic cues are utilized by human listeners to localize sounds using small head movements (below ±10° around the center). Seven normal-hearing subjects participated in a sound localization experiment in a virtual reality environment. Four acoustic cue stimulus conditions were presented (full spectrum, flattened spectrum, frozen spectrum, free-field) under three movement conditions (no movement, head rotations over the yaw axis and over the pitch axis). Localization performance was assessed using three metrics: lateral and polar precision error and front-back confusion rate. Analysis through mixed-effects models showed that even small yaw rotations provide a remarkable decrease in front-back confusion rate, whereas pitch rotations did not show much of an effect. Furthermore, MSS cues improved localization performance even in the presence of dITD cues. However, performance was similar between stimuli with and without dMSS cues. This indicates that human listeners utilize the MSS cues before the head moves, but do not rely on dMSS cues to localize sounds when utilizing small head movements.
Keywords: A1 Journal article; Psychology; Condensed Matter Theory (CMT); Engineering Management (ENM)
DOI: 10.3389/FNINS.2023.1027827
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Ková,cs A (2023) A structured methodology for natural deep eutectic solvent selection and formulation for enzymatic reactions. viii, 216 p
Abstract: Natural deep eutectic solvents (NADES) show great promise as media for enzymatic reactions in areas where (bio)compatibility with natural or medicinal products is a must. While in theory they can be tailored to the intended reaction to ensure optimized yields, the knowledge to date is predominantly empirical, with some mechanistic reports providing a fragmented view at best. Therefore, it is not easy to explain experimental observations, let alone make predictions. The aim of this study was to develop a structured, holistic understanding of the effects of NADES media on enzymatic reactions, distinguishing between effects on solubility, solvation, viscosity, inhibition and denaturation. Experimental and computational chemistry methods were combined to separately study the interactions between enzyme, substrate, and NADES as reaction media. The initial enzyme activity and the final conversion of vinyl laurate transesterification by immobilized Candida antarctica lipase were studied experimentally. The direct effect of NADES on the same enzyme was modeled by molecular dynamics simulation. The effect of solubility was studied by both experimental and computational methods. To predict the solubility and viscosity of NADES, data-driven models were developed by combining group contribution and machine learning methods, based on the accumulated experimental knowledge on NADES found in the literature. Finally, the composed relationships and prediction models were applied to the practical example of deacetylation of mannosylerythritol lipids (MELs). The experimental findings show that the chosen NADES system has a significant effect on both the apparent initial activity and the final conversion. However, in the simulations, the enzyme retains its original structure; moreover, NADES has an additional stabilizing effect on the enzyme. In addition, changes in the molar ratio of the compounds in NADES do not show a significant effect on the stability of the enzyme. These results indicate that the main effect of NADES on the reaction is mainly related to the substrate-solvent interactions (solvation energy) and the viscosity of the system. On the other hand, the experimental results only confirmed the significance of solvation, viscosity did not show a clear correlation with the studied reaction parameters. The machine learning models built for solubility and viscosity gave quantitative predictions of these properties. The accumulated knowledge was used to optimize the yield in the deacetylation reaction of MELs. The combination of these methods provides fundamental knowledge about the effect of NADES on biocatalysis, but the results are also applicable to other uses of NADES.
Keywords: Doctoral thesis; Engineering sciences. Technology; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT); Biochemical Wastewater Valorization & Engineering (BioWaVE); Intelligence in PRocesses, Advanced Catalysts and Solvents (iPRACS)
Additional Links: UA library record
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“Effect of natural deep eutectic solvents of non-eutectic compositions on enzyme stability”. Kovács A, Yusupov M, Cornet I, Billen P, Neyts EC, Journal Of Molecular Liquids 366, 120180 (2022). http://doi.org/10.1016/J.MOLLIQ.2022.120180
Abstract: Natural deep eutectic solvents (NADES) represent a green alternative to common organic solvents in the biochemical industry due to their benign behavior and tailorable properties, in particular as media for enzymatic reactions. However, to fully exploit their potential in enzymatic reactions, there is a need for a more fundamental understanding of how these neoteric solvents influence the course of these reac-tions. Thus, the aim of this study is to investigate the influence of NADES with various molar composi-tions on the stability and structure of enzymes, applying molecular dynamics simulations. This can help to better understand the effect of individual compounds of NADES, in addition to eutectic mixtures. More specifically, we simulate the behavior of Candida antarctica lipase B (CALB) enzyme in NADES com-posed of choline chloride with either urea, ethylene glycol or glycerol. Hereto, we monitor the NADES microstructure, the general stability of the enzyme and changes in the structure of its active sites and sur-face residues. Our simulations show that none of the studied NADES systems significantly disrupt the microstructure of the solvent or the stability of the CALB enzyme within the time scales of the simula-tions. The enzyme preserves its initial structure, size and intra-chain hydrogen bonds in all investigated compositions and, for the first time reported, also in NADES with increased hydrogen bond donating com-pound ratios. As the main novelty, our results indicate that, in addition to the composition, the molar ratio can be an additional variable to fine-tune the physicochemical properties of NADES without altering the enzyme characteristics. These findings could facilitate the development and application of task -tailored NADES media for biocatalytic processes. (c) 2022 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT); Biochemical Wastewater Valorization & Engineering (BioWaVE); Intelligence in PRocesses, Advanced Catalysts and Solvents (iPRACS)
Impact Factor: 6
DOI: 10.1016/J.MOLLIQ.2022.120180
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“Modeling the physicochemical properties of natural deep eutectic solvents : a review”. Kovács A, Billen P, Cornet I, Wijnants M, Neyts EC, Chemsuschem 13, 3789 (2020). http://doi.org/10.1002/CSSC.202000286
Abstract: Natural deep eutectic solvents (NADES) are mixtures of naturally derived compounds with a significantly decreased melting point due to the specific interactions among the constituents. NADES have benign properties (low volatility, flammability, toxicity, cost) and tailorable physicochemical properties (by altering the type and molar ratio of constituents), hence they are often considered as a green alternative to common organic solvents. Modeling the relation between their composition and properties is crucial though, both for understanding and predicting their behavior. Several efforts were done to this end, yet this review aims at structuring the present knowledge as an outline for future research. First, we reviewed the key properties of NADES and relate them to their structure based on the available experimental data. Second, we reviewed available modeling methods applicable to NADES. At the molecular level, density functional theory and molecular dynamics allow interpreting density differences and vibrational spectra, and computation of interaction energies. Additionally, properties at the level of the bulk media can be explained and predicted by semi-empirical methods based on ab initio methods (COSMO-RS) and equation of state models (PC-SAFT). Finally, methods based on large datasets are discussed; models based on group contribution methods and machine learning. A combination of bulk media and dataset modeling allows qualitative prediction and interpretation of phase equilibria properties on the one hand, and quantitative prediction of melting point, density, viscosity, surface tension and refractive indices on the other hand. In our view, multiscale modeling, combining the molecular and macroscale methods, will strongly enhance the predictability of NADES properties and their interaction with solutes, yielding truly tailorable solvents to accommodate (bio)chemical reactions.
Keywords: A1 Journal article; Engineering sciences. Technology; Intelligence in PRocesses, Advanced Catalysts and Solvents (iPRACS); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT); Biochemical Wastewater Valorization & Engineering (BioWaVE)
Impact Factor: 8.4
DOI: 10.1002/CSSC.202000286
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“Recent advances in electrochemical biosensors based on fullerene-C60 nano-structured platforms”. Pilehvar S, De Wael K, Biosensors 5, 712 (2015). http://doi.org/10.3390/BIOS5040712
Abstract: Nanotechnology is becoming increasingly important in the field of (bio)sensors. The performance and sensitivity of biosensors is greatly improved with the integration of nanomaterials into their construction. Since its first discovery, fullerene-C60 has been the object of extensive research. Its unique and favorable characteristics of easy chemical modification, conductivity, and electrochemical properties has led to its tremendous use in (bio)sensor applications. This paper provides a concise review of advances in fullerene-C60 research and its use as a nanomaterial for the development of biosensors. We examine the research work reported in the literature on the synthesis, functionalization, approaches to nanostructuring electrodes with fullerene, and outline some of the exciting applications in the field of (bio)sensing.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
DOI: 10.3390/BIOS5040712
Additional Links: UA library record
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Friedrich T (2023) Quantifying atomic structures using neural networks from 4D scanning transmission electron microscopy (STEM) datasets. 127 p
Abstract: Nanoscience and nanotechnologies are of immense importance across many fields of science and for numerous practical applications. In this context, scanning transmission electron microscopy (STEM) and 4D-STEM are among the most powerful characterization methods at the atomic scale. Annular dark-field (ADF)-STEM can be used to quantify atomic structures in 3D by counting atoms based on a single projection image. In 4D-STEM a full diffraction pattern is recorded at each scan step, which enables more dose efficient imaging and the utilization of various advanced imaging modalities, which can however be complex and slow. Both, STEM and 4D-STEM suffer from noise and distortions. In the first section of this work the most important of these distortions are discussed and it is shown how image restoration with a dedicated convolutional neural network (CNN) can be beneficial for atomic structure quantifications in ADF-STEM. In the second part, a new 4D-STEM imaging method real-time-integrated-centre-of-mass (riCOM) is introduced, which is a very dose-efficient and fast algorithm that enables unprecedented live-imaging capabilities for 4D-STEM. It is based on the integrated centre-of-mass approach, but is reformulated with variable integration ranges and optional filters, which allows for a tunable contrast transfer function. This enables the imaging of light and heavy elements simultaneously at very low doses. In the third part another new 4D-STEM method, coined AIRPI (AI-assisted rapid phase imaging) is introduced, which uses a CNN to retrieve a patch of the specimen's phase image for each scan position, based on the diffraction patterns in the probe's immediate surroundings. This allows also live imaging in principle and surpasses comparable state-of-the-art algorithms in terms of resolution also at low doses. Different atomic columns can be reliably distinguished over a wide range of atomic numbers, enabling a very good image interpretability. Further, AIRPI can recover low frequency image components, which preserves thickness information. This is a unique and important feature which could make quantitative 4D-STEM feasible.
Keywords: Doctoral thesis; Electron microscopy for materials research (EMAT)
Additional Links: UA library record
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Arslan Irmak E (2022) Modelling three-dimensional nanoparticle transformations based on quantitative transmission electron microscopy. 169 p
Abstract: Nanomaterials are materials that have at least one dimension in the nanometer length scale, which corresponds to a billionth of a meter. When three dimensions are confined to the nanometer scale, these materials are referred to as nanoparticles. These materials are of great interest since they exhibit unique physical and chemical properties that cannot be observed for bulk systems. Due to their unique and often superior properties, nanomaterials have become central in the field of electronics, catalysis, and medicine. Moreover, they are expected to be one of the most promising systems to tackle many challenges that our society is facing, such as reducing the emission of greenhouse gases and finding effective treatments for cancer. The unique properties of nanomaterials are linked to their size, shape, structure, and composition. If one is able to measure the positions of the atoms, their chemical nature, and the bonding between them, it becomes possible to predict the physicochemical properties of nanomaterials. In this manner, the development of novel nanostructures can be triggered. However, the morphology and structure of nanomaterials are highly sensitive to the conditions for relevant applications, such as elevated temperatures or intense light illumination. Furthermore, any small change in the local structure at higher temperatures or pressures may significantly modify their performance. Hence, three-dimensional (3D) characterization of nanomaterials under application-relevant conditions is important in designing them with desired functional properties for specific applications. Among different structural characterization approaches, transmission electron microscopy (TEM) is one of the most efficient and versatile tools to investigate the structure and composition of nanomaterials since it can provide atomically resolved images, which are sensitive to the local 3D structure of the investigated sample. However, TEM only provides two-dimensional (2D) images of the 3D nanoparticle, which may lead to an incomplete understanding of their structure-property relationship. The most known and powerful technique for the 3D characterization of nanomaterials is electron tomography, where the images of a nanostructured material taken from different directions are mathematically combined to retrieve its 3D structure. Although these experiments are already state-of-the-art, 3D characterization by TEM is typically performed under ultra-high vacuum conditions and at room temperature. Such conditions are unfortunately not sufficient to understand transformations during synthesis or applications of nanomaterials. This limitation can be overcome by in situ TEM where external stimuli, such as heat, gas, and liquids, can be controllably introduced inside the TEM using specialized holders. However, there are some technical limitations to successful perform 3D in situ electron tomography experiments. For example, the long acquisition time required to collect a tilt series limits this technique when one wants to observe 3D dynamic changes with atomic resolution. A solution for this problem is the estimation of the 3D structure of nanomaterials from 2D projection images acquired along a single viewing direction. For this purpose, annular dark field scanning TEM (ADF STEM) imaging mode provides a valuable tool for quantitative structural investigation of nanomaterials from single 2D images due to its thickness and mass sensitivity. For quantitative analysis, an ADF STEM image is considered as a 2D array of pixels where relative variation of pixel intensity values is proportional to the total number of atoms and the atomic number of the elements in the sample. By applying advanced statistical approaches to these images, structural information, such as the number or types of atoms, can be retrieved with high accuracy and precision. The outcome can then be used to build a 3D starting model for energy minimization by atomistic simulations, for example, molecular dynamics simulations or the Monte Carlo method. However, this methodology needs to be further evaluated for in situ experiments. This thesis is devoted to presenting robust approaches to accurately define the 3D atomic structure of nanoparticles under application-relevant conditions and understand the mechanism behind the atomic-scale dynamics in nanoparticles in response to environmental stimuli.
Keywords: Doctoral thesis; Electron microscopy for materials research (EMAT)
Additional Links: UA library record
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De wael A (2021) Model-based quantitative scanning transmission electron microscopy for measuring dynamic structural changes at the atomic scale. xiv, 146 p
Abstract: Nanomaterialen kunnen uiterst interessante eigenschappen vertonen voor een verscheidenheid aan veelbelovende toepassingen, gaande van zonnecrème tot batterijen voor elektrische auto’s. Een nanometer is een miljard keer kleiner dan een meter. Op deze schaal kunnen de materiaaleigenschappen volledig verschillen van bulkmaterialen op grotere schaal. Bovendien hangen de eigenschappen van nanomaterialen sterk af van hun exacte grootte en vorm. Kleine verschillen in de posities van de atomen, in de grootte-orde van een picometer (nog eens duizend maal kleiner dan een nanometer), kunnen de fysische eigenschappen al drastisch beïnvloeden. Daarom is een betrouwbare kwantificering van de atomaire structuur van kritisch belang om de evolutie naar materiaalontwerp mogelijk te maken en inzicht te verwerven in de relatie tussen de fysische eigenschappen en de structuur van nanomaterialen. Daarnaast kan de atomaire structuur van nanomaterialen ook veranderen in de loop van de tijd ten gevolge van verschillende fysische processen. Het onderzoek dat in deze thesis gepresenteerd wordt, maakt het mogelijk om de dynamische structuurveranderingen van nanomaterialen betrouwbaar te kwantificeren op atomaire schaal door gebruik te maken van raster transmissie elektronenmicroscopie (STEM). Ik heb dit gerealiseerd door methodes te ontwikkelen waarmee ik het aantal atomen “achter elkaar” kan tellen in elke atoomkolom van een nanomateriaal, en dit op basis van beelden opgenomen met een elektronenmicroscoop. Een belangrijk verschil met telmethodes voor de analyse van een enkel beeld is het schatten van de kans dat een atoomkolom atomen zal verliezen of bijkrijgen van het ene naar het andere beeld in de tijdreeks. Deze kwantitatieve methode kan het ontrafelen van de tijdsafhankelijke structuur-eigenschappen relatie van een nanomateriaal mogelijk maken, wat uiteindelijk kan leiden tot efficiënter design en productie van nanomaterialen voor innovatieve toepassingen.
Keywords: Doctoral thesis; Electron microscopy for materials research (EMAT)
Additional Links: UA library record
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“Sensitivity of nanocrystalline tungsten oxide to CO and ammonia gas determined by surface catalysts”. Marikutsa A, Yang L, Rumyantseva M, Batuk M, Hadermann J, Gaskov A, Sensors and actuators : B : chemical 277, 336 (2018). http://doi.org/10.1016/J.SNB.2018.09.004
Abstract: Nanocrystalline tungsten oxide with variable particle size and surface area was synthesized by aqueous deposition and heat treatment for use in resistive gas sensors. Surface modification with 1 wt.% Pd and Ru was performed by impregnation to improve the sensitivity to CO and ammonia. Acid and oxidation surface sites were evaluated by temperature-programmed techniques using probe molecules. The surface acidity dropped with increasing particle size, and was weakly affected by additives. Lower crystallinity of WO3 and the presence of Ru species favoured temperature-programmed reduction of the materials. Modifying WO3 increased its sensitivity, to CO at ambient condition for modification by Pd and to NH3 at elevated temperature for Ru modification. An in situ infrared study of the gas – solid interaction showed that the catalytic additives change the interaction route of tungsten oxide with the target gases and make the reception of detected molecules independent of the semiconductor oxide matrix.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
DOI: 10.1016/J.SNB.2018.09.004
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“Effects of Ag additive in low temperature CO detection with In2O3 based gas sensors”. Naberezhnyi D, Rumyantseva M, Filatova D, Batuk M, Hadermann J, Baranchikov A, Khmelevsky N, Aksenenko A, Konstantinova E, Gaskov A, Nanomaterials 8, 801 (2018). http://doi.org/10.3390/NANO8100801
Abstract: Nanocomposites In2O3/Ag obtained by ultraviolet (UV) photoreduction and impregnation methods were studied as materials for CO sensors operating in the temperature range 25-250 degrees C. Nanocrystalline In2O3 and In2O3/Ag nanocomposites were characterized by X-ray diffraction (XRD), single-point Brunauer-Emmet-Teller (BET) method, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with energy dispersive X-ray (EDX) mapping. The active surface sites were investigated using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy and thermo-programmed reduction with hydrogen (TPR-H-2) method. Sensor measurements in the presence of 15 ppm CO demonstrated that UV treatment leads to a complete loss of In2O3 sensor sensitivity, while In2O3/Ag-UV nanocomposite synthesized by UV photoreduction demonstrates an increased sensor signal to CO at T < 200 degrees C. The observed high sensor response of the In2O3/Ag-UV nanocomposite at room temperature may be due to the realization of an additional mechanism of CO oxidation with participation of surface hydroxyl groups associated via hydrogen bonds.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
DOI: 10.3390/NANO8100801
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