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“Erratum: Spontaneous magnetization and electron momentum density in three-dimensional quantum dots [Phys. Rev. B 68, 165326 (2003)]”. Saniz R, Barbiellini B, Denison AB, Bansil A, Physical review : B : condensed matter and materials physics 84, 119907 (2011). http://doi.org/10.1103/PhysRevB.84.119907
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
DOI: 10.1103/PhysRevB.84.119907
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Swerling G, Travaglini B, Van Grieken R, Spolnik Z, Bencs L, [et al.], European Project Freindly-Heating (2006) Il riscaldamento nelle chiese e la conservazione dei beni culturali = Church heating and the preservation of the cultural heritage. 240 p
Keywords: ME2 Book as editor or co-editor; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
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“High-Throughput Morphological Chirality Quantification of Twisted and Wrinkled Gold Nanorods”. Vlasov E, Heyvaert W, Ni B, Van Gordon K, Girod R, Verbeeck J, Liz-Marzán LM, Bals S, ACS Nano (2024). http://doi.org/10.1021/acsnano.4c02757
Abstract: Chirality in gold nanostructures offers an exciting opportunity to tune their differential optical response to left- and right-handed circularly polarized light, as well as their interactions with biomolecules and living matter. However, tuning and understanding such interactions demands quantification of the structural features that are responsible for the chiral behavior. Electron tomography (ET) enables structural characterization at the single-particle level and has been used to quantify the helicity of complex chiral nanorods. However, the technique is time-consuming and consequently lacks statistical value. To address this issue, we introduce herein a high-throughput methodology that combines images acquired by secondary electron-based electron beam-induced current (SEEBIC) with quantitative image analysis. As a result, the geometric chirality of hundreds of nanoparticles can be quantified in less than 1 h. When combining the drastic gain in data collection efficiency of SEEBIC with a limited number of ET data sets, a better understanding of how the chiral structure of individual chiral nanoparticles translates into the ensemble chiroptical response can be reached.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 17.1
DOI: 10.1021/acsnano.4c02757
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“Single Crystal and Pentatwinned Gold Nanorods Result in Chiral Nanocrystals with Reverse Handedness”. Van Gordon K, Ni B, Girod R, Mychinko M, Bevilacqua F, Bals S, Liz‐Marzán LM, Angewandte Chemie International Edition (2024). http://doi.org/10.1002/anie.202403116
Abstract: Handedness is an essential attribute of chiral nanocrystals, having a major influence on their properties. During chemical growth, the handedness of nanocrystals is usually tuned by selecting the corresponding enantiomer of chiral molecules involved in asymmetric growth, often known as chiral inducers. We report that, even using the same chiral inducer enantiomer, the handedness of chiral gold nanocrystals can be reversed by using Au nanorod seeds with either single crystalline or pentatwinned structure. This effect holds for chiral growth induced both by amino acids and by chiral micelles. Although it was challenging to discern the morphological handedness for<italic>L</italic>‐cystine‐directed particles, even using electron tomography, both cases showed circular dichroism bands of opposite sign, with nearly mirrored chiroptical signatures for chiral micelle‐directed growth, along with quasi‐helical wrinkles of inverted handedness. These results expand the chiral growth toolbox with an effect that might be exploited to yield a host of interesting morphologies with tunable optical properties.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 16.6
DOI: 10.1002/anie.202403116
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“Chiral Seeded Growth of Gold Nanorods Into 4‐Fold Twisted Nanoparticles with Plasmonic Optical Activity”. Ni B, Mychinko M, Gómez‐Graña S, Morales‐Vidal J, Obelleiro‐Liz M, Heyvaert W, Vila‐Liarte D, Zhuo X, Albrecht W, Zheng G, González‐Rubio G, Taboada JM, Obelleiro F, López N, Pérez‐Juste J, Pastoriza‐Santos I, Cölfen H, Bals S, Liz‐Marzán LM, Advanced materials , 2208299 (2022). http://doi.org/10.1002/adma.202208299
Abstract: A robust and reproducible methodology to prepare stable inorganic nanoparticles with chiral morphology might hold the key to the practical utilization of these materials. We describe herein an optimized chiral growth method to prepare 4-fold twisted gold nanorods, where the amino acid cysteine is used as a dissymmetry inducer. Four tilted ridges were found to develop on the surface of single-crystal nanorods upon repeated reduction of HAuCl4, in the presence of cysteine as the chiral inducer and ascorbic acid as a reducing agent. From detailed electron microscopy analysis of the crystallographic structures, we propose that dissymmetry results from the development of chiral facets in the form of protrusions (tilted ridges) on the initial nanorods, eventually leading to a twisted shape. The role of cysteine is attributed to assisting enantioselective facet evolution, which is supported by density functional theory simulations of the surface energies, modified upon adsorption of the chiral molecule. The development of R-type and S-type chiral structures (small facets, terraces, or kinks) would thus be non-equal, removing the mirror symmetry of the Au NR and in turn resulting in a markedly chiral morphology with high plasmonic optical activity.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 29.4
Times cited: 35
DOI: 10.1002/adma.202208299
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“Identification of a Robust and Durable FeN4CxCatalyst for ORR in PEM Fuel Cells and the Role of the Fifth Ligand”. Nematollahi P, Barbiellini B, Bansil A, Lamoen D, Qingying J, Mukerjee S, Neyts EC, ACS catalysis , 7541 (2022). http://doi.org/10.1021/acscatal.2c01294
Abstract: Although recent studies have advanced the understanding of pyrolyzed
Fe−N−C materials as oxygen reduction reaction (ORR) catalysts, the atomic and
electronic structures of the active sites and their detailed reaction mechanisms still remain unknown. Here, based on first-principles density functional theory (DFT) computations, we discuss the electronic structures of three FeN4 catalytic centers with different local topologies of the surrounding C atoms with a focus on unraveling the mechanism of their ORR activity in acidic electrolytes. Our study brings back a forgotten, synthesized pyridinic Fe−N coordinate to the community’s attention, demonstrating that this catalyst can exhibit excellent activity for promoting direct four-electron ORR through the addition of a fifth ligand such as −NH2, −OH, and −SO4. We also identify sites with good stability properties through the combined use of our DFT calculations and Mössbauer spectroscopy data.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 12.9
DOI: 10.1021/acscatal.2c01294
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“Study of rechargeable batteries using advanced spectroscopic and computational techniques”. Barbiellini B, Kuriplach J, Saniz R, Condensed Matter 6, 26 (2021). http://doi.org/10.3390/CONDMAT6030026
Abstract: Improving the efficiency and longevity of energy storage systems based on Li- and Na-ion rechargeable batteries presents a major challenge. The main problems are essentially capacity loss and limited cyclability. These effects are due to a hierarchy of factors spanning various length and time scales, interconnected in a complex manner. As a consequence, and in spite of several decades of research, a proper understanding of the ageing process has remained somewhat elusive. In recent years, however, combinations of advanced spectroscopy techniques and first-principles simulations have been applied with success to tackle this problem. In this Special Issue, we are pleased to present a selection of articles that, by precisely applying these methods, unravel key aspects of the reduction-oxidation reaction and intercalation processes. Furthermore, the approaches presented provide improvements to standard diagnostic and characterisation techniques, enabling the detection of possible Li-ion flow bottlenecks causing the degradation of capacity and cyclability.
Keywords: Editorial; Electron microscopy for materials research (EMAT)
DOI: 10.3390/CONDMAT6030026
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“Nature of the Positron State in CdSe Quantum Dots”. Shi W, Callewaert V, Barbiellini B, Saniz R, Butterling M, Egger W, Dickmann M, Hugenschmidt C, Shakeri B, Meulenberg R W, Brück E, Partoens B, Bansil A, Eijt SW H, Physical review letters 121, 057401 (2018). http://doi.org/10.1103/PhysRevLett.121.057401
Abstract: Previous studies have shown that positron-annihilation spectroscopy is a highly sensitive probe of the electronic structure and surface composition of ligand-capped semiconductor quantum dots (QDs) embedded in thin films. The nature of the associated positron state, however, whether the positron is confined inside the QDs or localized at their surfaces, has so far remained unresolved. Our positron-annihilation lifetime spectroscopy studies of CdSe QDs reveal the presence of a strong lifetime component in the narrow range of 358–371 ps, indicating abundant trapping and annihilation of positrons at the surfaces of the QDs. Furthermore, our ab initio calculations of the positron wave function and lifetime employing a recent formulation of the weighted density approximation demonstrate the presence of a positron surface state and predict positron lifetimes close to experimental values. Our study thus resolves the long-standing question regarding the nature of the positron state in semiconductor QDs and opens the way to extract quantitative information on surface composition and ligand-surface interactions of colloidal semiconductor QDs through highly sensitive positron-annihilation techniques.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 8.462
Times cited: 6
DOI: 10.1103/PhysRevLett.121.057401
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“Modeling electron competition among nitrogen oxides reduction and N2Oaccumulation in hydrogenotrophic denitrification”. Liu Y, Ngo HH, Guo W, Peng L, Chen X, Wang D, Pan Y, Ni B-J, Biotechnology and bioengineering 115, 978 (2018). http://doi.org/10.1002/BIT.26512
Abstract: Hydrogenotrophic denitrification is a novel and sustainable process for nitrogen removal, which utilizes hydrogen as electron donor, and carbon dioxide as carbon source. Recent studies have shown that nitrous oxide (N2O), a highly undesirable intermediate and potent greenhouse gas, can accumulate during this process. In this work, a new mathematical model is developed to describe nitrogen oxides dynamics, especially N2O, during hydrogenotrophic denitrification for the first time. The model describes electron competition among the four steps of hydrogenotrophic denitrification through decoupling hydrogen oxidation and nitrogen reduction processes using electron carriers, in contrast to the existing models that couple these two processes and also do not consider N2O accumulation. The developed model satisfactorily describes experimental data on nitrogen oxides dynamics obtained from two independent hydrogenotrophic denitrifying cultures under various hydrogen and nitrogen oxides supplying conditions, suggesting the validity and applicability of the model. The results indicated that N2O accumulation would not be intensified under hydrogen limiting conditions, due to the higher electron competition capacity of N2O reduction in comparison to nitrate and nitrite reduction during hydrogenotrophic denitrification. The model is expected to enhance our understanding of the process during hydrogenotrophic denitrification and the ability to predict N2O accumulation.
Keywords: A1 Journal article; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL)
DOI: 10.1002/BIT.26512
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“Model-based assessment of estrogen removal by nitrifying activated sludge”. Peng L, Dai X, Liu Y, Sun J, Song S, Ni B-J, Chemosphere 197, 430 (2018). http://doi.org/10.1016/J.CHEMOSPHERE.2018.01.035
Abstract: Complete removal of estrogens such as estrone (E1), estradiol (E2), estriol (E3) and ethinylestradiol (EE2) in wastewater treatment is essential since their release and accumulation in natural water bodies are giving rise to environment and health issues. To improve our understanding towards the estrogen bioremediation process, a mathematical model was proposed for describing estrogen removal by nitrifying activated sludge. Four pathways were involved in the developed model: i) biosorption by activated sludge flocs; ii) cometabolic biodegradation linked to ammonia oxidizing bacteria (AOB) growth; iii) non growth biodegradation by AOB; and iv) biodegradation by heterotrophic bacteria (HB). The degradation kinetics was implemented into activated sludge model (ASM) framework with consideration of interactions between substrate update and microorganism growth as well as endogenous respiration. The model was calibrated and validated by fitting model predictions against two sets of batch experimental data under different conditions. The model could satisfactorily capture all the dynamics of nitrogen, organic matters (COD), and estrogens. Modeling results suggest that for El, E2 and EE2, AOB-linked biodegradation is dominant over biodegradation by HB at all investigated COD dosing levels. However, for E3, the increase of COD dosage triggers a shift of dominant pathway from AOB biodegradation to HB biodegradation. Adsorption becomes the main contributor to estrogen removal at high biomass concentrations. (C) 2018 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Sustainable Energy, Air and Water Technology (DuEL)
DOI: 10.1016/J.CHEMOSPHERE.2018.01.035
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“Enhancing immobilization of arsenic in groundwater: A model-based evaluation”. Peng L, Liu Y, Sun J, Wang D, Dai X, Ni B-J, Journal of cleaner production 166, 449 (2017). http://doi.org/10.1016/J.JCLEPRO.2017.08.051
Abstract: The mobilization of arsenic (As) in aquatic environment (groundwater) can cause severe environmental and healthy issues. To develop remediation strategies, we proposed a comprehensive mathematical model to describe the As removal in a arsenite (As (III)) oxidizing and ferrous iron (Fe (II)) oxidizing denitrifying granular biofilm system. In the model framework, the growth-linked microbial oxidation of As (III) and Fe (II) was coupled to chemolithotrophic denitrification of one-step reduction of nitrate to nitrogen gas. Meanwhile, the precipitation of ferric iron (Fe (III)) and adsorption of arsenate (As (V)) onto the biogenic Fe (III) (hydr)oxides were also considered. The model was calibrated by comparing the model predictions against experimental data from batch experiments. The validity of the model was further demonstrated through testing against long-term experimental results from five independent bioreactors with different reactor configurations and operational conditions. Modeling results revealed that the granule size would exert a limited impact on arsenic and iron removal. Nevertheless, their removal efficiencies increased rapidly with the increase of hydraulic retention time (HRT) from 1 h to 12 h, but became independent of HRT as it further increased. The established model framework enables interpretation of a range of experimental observations on As and Fe removal and helps to identify the optimal conditions for enhanced arsenic remediation. (C) 2017 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL)
DOI: 10.1016/J.JCLEPRO.2017.08.051
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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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“Modelling cometabolic biotransformation of sulfamethoxazole by an enriched ammonia oxidizing bacteria culture”. Peng L, Kassotaki E, Liu Y, Sun J, Dai X, Pijuan M, Rodriguez-Roda I, Buttiglieri G, Ni B-J, Chemical engineering science 173, 465 (2017). http://doi.org/10.1016/J.CES.2017.08.015
Abstract: Antibiotics such as sulfamethoxazole (SFX) are environmentally hazardous after being released into the aquatic environment and challenges remain in the development of engineered prevention strategies. In this work, a mathematical model was developed to describe and evaluate cometabolic biotransformation of SFX and its transformation products (TPs) in an enriched ammonia oxidizing bacteria (AOB) culture. The growth-linked cometabolic biodegradation by AOB, non-growth transformation by AOB and nongrowth transformation by heterotrophs were considered in the model framework. The production of major TPs comprising 4-Nitro-SFX, Desamino-SFX and N-4-Acetyl-SFX was also specifically modelled. The validity of the model was demonstrated through testing against literature reported data from extensive batch tests, as well as from long-term experiments in a partial nitritation sequencing batch reactor (SBR) and in a combined SBR + membrane aerated biofilm reactor performing nitrification/denitrification. Modelling results revealed that the removal efficiency of SFX increased with the increase of influent ammonium concentration, whereas the influent organic matter, hydraulic retention time and solid retention time exerted a limited effect on SFX biodegradation with the removal efficiencies varying in a narrow range. The variation of influent SFX concentration had no impact on SFX removal efficiency. The established model framework enables interpretation of a range of experimental observations on SFX biodegradation and helps to identify the optimal conditions for efficient removal. (C) 2017 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Sustainable Energy, Air and Water Technology (DuEL)
DOI: 10.1016/J.CES.2017.08.015
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“Application of the weighted-density approximation to the accurate description of electron-positron correlation effects in materials”. Callewaert V, Saniz R, Barbiellini B, Bansil A, Partoens B, Physical review B 96, 085135 (2017). http://doi.org/10.1103/PhysRevB.96.085135
Abstract: We discuss positron-annihilation lifetimes for a set of illustrative bulk materials within the framework of the weighted-density approximation (WDA). The WDA can correctly describe electron-positron correlations in strongly inhomogeneous systems, such as surfaces, where the applicability of (semi-)local approximations is limited. We analyze the WDA in detail and show that the electrons which cannot screen external charges efficiently, such as the core electrons, cannot be treated accurately via the pair correlation of the homogeneous electron gas. We discuss how this problem can be addressed by reducing the screening in the homogeneous electron gas by adding terms depending on the gradient of the electron density. Further improvements are obtained when core electrons are treated within the LDA and the valence electron using the WDA. Finally, we discuss a semiempirical WDA-based approach in which a sum rule is imposed to reproduce the experimental lifetimes.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 6
DOI: 10.1103/PhysRevB.96.085135
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“Visualizing redox orbitals and their potentials in advanced lithium-ion battery materials using high-resolution x-ray Compton scattering”. Hafiz H, Suzuki K, Barbiellini B, Orikasa Y, Callewaert V, Kaprzyk S, Itou M, Yamamoto K, Yamada R, Uchimoto Y, Sakurai Y, Sakurai H, Bansil A, Science Advances 3, e1700971 (2017). http://doi.org/10.1126/sciadv.1700971
Abstract: Reduction-oxidation (redox) reactions are the key processes that underlie the batteries powering smartphones, laptops, and electric cars. A redox process involves transfer of electrons between two species. For example, in a lithium-ion battery, current is generated when conduction electrons from the lithium anode are transferred to the redox orbitals of the cathode material. The ability to visualize or image the redox orbitals and how these orbitals evolve under lithiation and delithiation processes is thus of great fundamental and practical interest for understanding the workings of battery materials. We show that inelastic scattering spectroscopy using high-energy x-ray photons (Compton scattering) can yield faithful momentum space images of the redox orbitals by considering lithium iron phosphate (LiFePO4 or LFP) as an exemplar cathode battery material. Our analysis reveals a new link between voltage and the localization of transition metal 3d orbitals and provides insight into the puzzling mechanism of potential shift and how it is connected to the modification of the bond between the transition metal and oxygen atoms. Our study thus opens a novel spectroscopic pathway for improving the performance of battery materials.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Times cited: 9
DOI: 10.1126/sciadv.1700971
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“Auger electron emission initiated by the creation of valence-band holes in graphene by positron annihilation”. Chirayath VA, Callewaert V, Fairchild AJ, Chrysler MD, Gladen RW, Mcdonald AD, Imam SK, Shastry K, Koymen AR, Saniz R, Barbiellini B, Rajeshwar K, Partoens B, Weiss AH, Nature communications 8, 16116 (2017). http://doi.org/10.1038/ncomms16116
Abstract: Auger processes involving the filling of holes in the valence band are thought to make important contributions to the low-energy photoelectron and secondary electron spectrum from many solids. However, measurements of the energy spectrum and the efficiency with which electrons are emitted in this process remain elusive due to a large unrelated background resulting from primary beam-induced secondary electrons. Here, we report the direct measurement of the energy spectra of electrons emitted from single layer graphene as a result of the decay of deep holes in the valence band. These measurements were made possible by eliminating competing backgrounds by employing low-energy positrons (<1.25 eV) to create valence-band holes by annihilation. Our experimental results, supported by theoretical calculations, indicate that between 80 and 100% of the deep valence-band holes in graphene are filled via an Auger transition.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 12.124
Times cited: 20
DOI: 10.1038/ncomms16116
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“Approach of describing dynamic production of volatile fatty acids from sludge alkaline fermentation”. Wang D, Liu Y, Ngo HH, Zhang C, Yang Q, Peng L, He D, Zeng G, Li X, Ni B-J, Bioresource technology 238, 343 (2017). http://doi.org/10.1016/J.BIORTECH.2017.04.054
Abstract: In this work, a mathematical model was developed to describe the dynamics of fermentation products in sludge alkaline fermentation systems for the first time. In this model, the impacts of alkaline fermentation on sludge disintegration, hydrolysis, acidogenesis, acetogenesis, and methanogenesis processes are specifically considered for describing the high-level formation of fermentation products. The model proposed successfully reproduced the experimental data obtained from five independent sludge alkaline fermentation studies. The modeling results showed that alkaline fermentation largely facilitated the disintegration, acidogenesis, and acetogenesis processes and severely inhibited methanogenesis process. With the pH increase from 7.0 to 10.0, the disintegration, acidogenesis, and acetogenesis processes respectively increased by 53%, 1030%, and 30% while methane production decreased by 3800%.However, no substantial effect on hydrolysis process was found. The model also indicated that the pathway of acetoclastic methanogenesis was more severely inhibited by alkaline condition than that of hydrogentrophic methanogenesis. (C) 2017 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL)
DOI: 10.1016/J.BIORTECH.2017.04.054
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“Nitrous oxide production in a granule-based partial nitritation reactor : a model-based evaluation”. Peng L, Sun J, Liu Y, Dai X, Ni B-J, Scientific reports 7, 45609 (2017). http://doi.org/10.1038/SREP45609
Abstract: Sustainable wastewater treatment has been attracting increasing attentions over the past decades. However, the production of nitrous oxide (N2O), a potent GHG, from the energy-efficient granule-based autotrophic nitrogen removal is largely unknown. This study applied a previously established N2O model, which incorporated two N2O production pathways by ammonia-oxidizing bacteria (AOB) (AOB denitrification and the hydroxylamine (NH2OH) oxidation). The two-pathway model was used to describe N2O production from a granule-based partial nitritation (PN) reactor and provide insights into the N2O distribution inside granules. The model was evaluated by comparing simulation results with N2O monitoring profiles as well as isotopic measurement data from the PN reactor. The model demonstrated its good predictive ability against N2O dynamics and provided useful information about the shift of N2O production pathways inside granules for the first time. The simulation results indicated that the increase of oxygen concentration and granule size would significantly enhance N2O production. The results further revealed a linear relationship between N2O production and ammonia oxidation rate (AOR) (R-2 = 0.99) under the conditions of varying oxygen levels and granule diameters, suggesting that bulk oxygen and granule size may exert an indirect effect on N2O production by causing a change in AOR.
Keywords: A1 Journal article; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL)
DOI: 10.1038/SREP45609
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“New insights into the nanostructure of innovative thin film solar cells gained by positron annihilation spectroscopy”. Eijt SWH, Shi W, Mannheim A, Butterling M, Schut H, Egger W, Dickmann M, Hugenschmidt C, Shakeri B, Meulenberg RW, Callewaert V, Saniz R, Partoens B, Barbiellini B, Bansil A, Melskens J, Zeman M, Smets AHM, Kulbak M, Hodes G, Cahen D, Brück E, Journal of physics : conference series 791, 012021 (2017). http://doi.org/10.1088/1742-6596/791/1/012021
Abstract: Recent studies showed that positron annihilation methods can provide key insights into the nanostructure and electronic structure of thin film solar cells. In this study, positron annihilation lifetime spectroscopy (PALS) is applied to investigate CdSe quantum dot (QD) light absorbing layers, providing evidence of positron trapping at the surfaces of the QDs. This enables one to monitor their surface composition and electronic structure. Further, 2D-Angular Correlation of Annihilation Radiation (2D-ACAR) is used to investigate the nanostructure of divacancies in photovoltaic-high-quality a-Si:H films. The collected momentum distributions were converted by Fourier transformation to the direct space representation of the electron-positron autocorrelation function. The evolution of the size of the divacancies as a function of hydrogen dilution during deposition of a-Si:H thin films was examined. Finally, we present a first positron Doppler Broadening of Annihilation Radiation (DBAR) study of the emerging class of highly efficient thin film solar cells based on perovskites.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Times cited: 1
DOI: 10.1088/1742-6596/791/1/012021
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“Surface states and positron annihilation spectroscopy: results and prospects from a first-principles approach”. Callewaert V, Saniz R, Barbiellini B, Partoens B, Journal of physics : conference series 791, 012036 (2017). http://doi.org/10.1088/1742-6596/791/1/012036
Abstract: The trapping of positrons at the surface of a material can be exploited to study quite selectively the surface properties of the latter by means of positron annihilation spectroscopy techniques. To support these, it is desirable to be able to theoretically predict the existence of such positronic surface states and to describe their annihilation characteristics with core or valence surface electrons in a reliable way. Here, we build on the well-developed first-principles techniques for the study of positrons in bulk solids as well as on previous models for surfaces, and investigate two schemes that can improve the theoretical description of the interaction of positrons with surfaces. One is based on supplementing the local-density correlation potential with the corrugated image potential at the surface, and the other is based on the weighted-density approximation to correlation. We discuss our results for topological insulators, graphene layers, and quantum dots, with emphasis on the information that can be directly related to experiment. We also discuss some open theoretical problems that should be addressed by future research.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Times cited: 1
DOI: 10.1088/1742-6596/791/1/012036
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“Positron surface state as a spectroscopic probe for characterizing surfaces of topological insulator materials”. Callewaert V, Shastry K, Saniz R, Makkonen I, Barbiellini B, Assaf BA, Heiman D, Moodera JS, Partoens B, Bansil A, Weiss AH;, Physical review B 94, 115411 (2016). http://doi.org/10.1103/PHYSREVB.94.115411
Abstract: Topological insulators are attracting considerable interest due to their potential for technological applications and as platforms for exploring wide-ranging fundamental science questions. In order to exploit, fine-tune, control, and manipulate the topological surface states, spectroscopic tools which can effectively probe their properties are of key importance. Here, we demonstrate that positrons provide a sensitive probe for topological states and that the associated annihilation spectrum provides a technique for characterizing these states. Firm experimental evidence for the existence of a positron surface state near Bi2Te2Se with a binding energy of E-b = 2.7 +/- 0.2 eV is presented and is confirmed by first-principles calculations. Additionally, the simulations predict a significant signal originating from annihilation with the topological surface states and show the feasibility to detect their spin texture through the use of spin-polarized positron beams.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 15
DOI: 10.1103/PHYSREVB.94.115411
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“Accurate description of the van der Waals interaction of an electron-positron pair with the surface of a topological insulator”. Saniz R, Vercauteren S, Lamoen D, Partoens B, Barbiellini B, Journal of physics : conference series 505, 012002 (2014). http://doi.org/10.1088/1742-6596/505/1/012002
Abstract: Positrons can be trapped in localized states at the surface of a material, and thus quite selectively interact with core or valence surface electrons. Hence, advanced surface positron spectroscopy techniques can present the ideal tools to study a topological insulator, where surface states play a fundamental role. We analyze the problem of a positron at a TI surface, assuming that it is a weakly physisorbed positronium (Ps) atom. To determine if the surface of interest in a material can sustain such a physisorption, an accurate description of the underlying van der Waals (vdW) interaction is essential. We have developed a first-principles parameterfree method, based on the density functional theory, to extract key parameters determining the vdW interaction potential between a Ps atom and the surface of a given material. The method has been successfully applied to quartz and preliminary results on Bi2Te2Se indicate the existence of a positron surface state. We discuss the robustness of our predictions versus the most relevant approximations involved in our approach.
Keywords: P1 Proceeding; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Times cited: 2
DOI: 10.1088/1742-6596/505/1/012002
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