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Direct observation of alkaline and enzymatic poly(ethylene terephthalate) hydrolysis via neutron reflectivity: Kinetics and mechanistic insights
No full textOne of the challenges in achieving industrial enzymatic depolymerization of poly(ethylene terephthalate) (PET) is the rapid loss of catalytic activity leading to incomplete polymer hydrolysis. While there are several possible explanations for this phenomenon, there is a lack of methods that can measure polymer hydrolysis directly, which makes it challenging to reliably infer mechanistic details. Here, we introduce neutron reflectivity of polymer thin films as a method that allows for direct assessment of the hydrolysis rate of polymers like PET. Through matching and variation of the isotopic contrasts, one can directly observe the reaction kinetics, while simultaneously obtaining structural information on the polymer/enzyme/water system. We show that the Michaelis-Menten theory describes well the enzymatic chain scission kinetics, whereas the alkaline one follows a (pseudo)-first order kinetics. At the concentrations used in the experiments, the areal density of enzymes at the polymer surface is very low, ruling out surface passivation or overcrowding as inhibition mechanisms
Short-Range Structural Correlations and Property Anomalies in Non-MPB Compositions of the Pb-Free Piezoelectric NaBiTiO-KBiTiO
No full textAmong Pb-free piezoelectrics, Na0.5Bi0.5TiO3 (NBT)-based ferroelectric systems have a unique distinction of offering a complex interplay of ferroelectric and nonferroelectric (in-phase octahedral tilt) structural instabilities, influencing its ferroelectric, dielectric, and electromechanical behavior. The morphotropic phase boundary (MPB) system like (1 – x)Na0.5Bi0.5TiO3-xK0.5Bi0.5TiO3 (NBT-KBT) is where this complexity plays out in full measure. While consistent with the conventional view of the MPB with a consensus regarding the existence of composition driven rhombohedral–tetragonal ferroelectric–ferroelectric instability at x ≈ 0.20, this system presents a puzzle by exhibiting considerable structural disorder and property anomalies at x ≈ 0.40 within the tetragonal ferroelectric composition regime. Here, we exploit the mutual complementarity of X-ray diffraction, neutron powder diffraction, and electron diffraction and microscopy techniques to gain comprehensive structural insights at the global and local length scales. We found that the anomalous behavior is associated with a simultaneous onset of (i) a short-ranged rhombohedral ferroelectric correlations and (ii) a relatively long-ranged in-phase tilt distortion. The consequent spatial fluctuation in the local polar displacements, as imaged with the high-angle annular dark-field technique, provides the necessary structural insights regarding the unusual property anomalies
A low-cost and high-energy aqueous potassium-ion battery
No full texto address challenges related to the intermittency of renewable energy sources, aqueous potassium-ion batteries (AKIBs) are a promising and sustainable alternative to conventional systems for large-scale energy storage. To enable their practical application, maximizing energy density and longevity while minimizing production and material costs is a key goal. In this work, we propose an AKIB consisting only of abundant and cost-efficient materials, which delivers a high energy density of more than 70 Wh kg−1. We combine simple strategies to stabilize the Mn-rich Prussian blue analog cathode by Fe-doping, improving the crystallinity, and tuning the electrolyte composition without employing expensive water-in-salt electrolytes. Using a mixed 2.5 M Ca(NO3)2 + 1.5 M KNO3 electrolyte, we assemble a novel AKIB with a Fe-doped manganese hexacyanoferrate cathode and an organic poly(naphthalene-4-formyl-ethylenediamine) anode. Besides a high energy density, the full cell delivers a specific capacity of approximately 60 mA h g−1, a power density of 5000 W kg−1, and 80% capacity retention after 600 cycles
Large field-of-view event-mode camera for high-precision epithermal neutron resonance imaging
No full textA large-area event-mode camera system coupled with a LiF-ZnS:Ag scintillator is applied for neutron resonance imaging (NRI) on the energy-resolved neutron imaging (ERNI) flight path, also known as Flight Path 5 (FP5), at the Los Alamos Neutron Science Center (LANSCE). This novel neutron imaging system, featuring a 120120 mm field of view, efficiently captures resonance information across the entire image in a single acquisition, significantly reducing beam time requirements compared to conventional energy-resolved neutron imaging systems. High-quality neutron radiographs with enhanced spatial resolution are achieved through the reconstruction of neutron events based on observations of individual photons emitted from the scintillator. The system demonstrates reduced background through neutron/gamma discrimination capabilities while maintaining sharpness across a large fields of view. In the measurements presented here, a spatial resolution of approximately 340 m was achieved using center-of-gravity photon cluster centroiding. We demonstrate the system’s capability for quantitatively determining isotopic distributions in various thin samples, as well as automatically reconstructing complex scenes with overlapping resonances from diverse samples. These results are obtained using standard data analysis tools, despite the relatively slow LiF-ZnS:Ag scintillator, which may not be optimal for absorption resonance detection. The capabilities demonstrated here offer a valuable, versatile, and cost-effective solution for high spatial and temporal resolution, large field-of-view energy-resolved neutron imaging, with potential applications across various scientific and industrial domains
Permanent magnet array with reduced stray field designed for a neutron supermirror polarizer
No full textNuclear Analytical Facilities at the Heinz Maier-Leibnitz Centre (MLZ), Garching, Germany
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In hospite and ex hospite architecture of photosynthetic thylakoid membranes in Symbiodinium spp. using small-angle neutron scattering
No full textStructural and Magnetic Properties of Biocompatible Iron Oxide Nanoparticles for Medical Applications
No full textThis thesis presents a comprehensive investigation of the structural and magnetic properties of biocompatible iron oxide nanoparticles coated with three different ligand materials: sodium citrate, (3-aminopropyl)triethoxysilane (APTES), and dextran. The influence of the coating agents on the agglomeration of iron oxide nanoparticles and their oxidation stability over time was studied. Various experimental techniques were used to characterize the structural and magnetic properties of the coated nanoparticles, including cryogenic transmission electron microscopy (cryo-TEM), magnetometry, and small-angle X-ray and neutron scattering. The results show that the coatings successfully stabilize the particles leading to various aggregate structures and sizes. These samples exhibit large saturation magnetization levels close to those of bulk iron oxide and a small coercivity as evidenced by the magnetization hysteresis loop at room temperature. We find that the zero-fieldcooled (ZFC) and field-cooled (FC) magnetization behaviour is influenced by magnetic interactions among the nanoparticles inside clusters. The interaction leads to a shift of the blocking temperature to higher values and a flattening of the FC curves at lower temperatures. Notably, the blocking temperature of the citrate-coated samples were lower than would have been expected for the large clustered structure. Furthermore, for this sample magnetic small-angle neutron scattering (SANS) reveals a multidomain structure, with the magnetic size corresponding to half of the cluster size as observed by SAXS. In the aging study, M¨ossbauer spectroscopy was used to follow the changes in Fe2+ and Fe3+ composition over time, while magnetometry allowed the determination of the net magnetization. In all systems, rapid oxidation was observed after less than 0.1 days (the time between the end of synthesis and the sealing of the samples under N2 atmosphere). This led to a complete oxidation of the magnetite nanoparticles to maghemite with the dextran coating, while the nanoparticles with citrate and APTES coating showed slower oxidation with 10% - 20% of the magnetite fraction after one month. The variation inoxidation behaviour is linked to the variations in particle size, which in turn are influenced by the coating agent and the synthesis method. Micromagnetic simulations were performed with the Object Oriented Micromagnetic Framework (OOMMF) software for ensembles of randomly arranged and randomly connected nanoparticles. The ”Theta Evolver” within OOMMF was used to include thermal fluctuations of the magnetic superspin moments of the nanoparticles to model the ZFC and FC curves, in addition to the magnetization hysteresis loops. The simulation results help us to understand the effect of exchange and dipolar inter-particle interactions on the energy barriers for magnetization reversal and, thus, on the magnetization hysteresis curves. This knowledge of the altered magnetic behaviour is required in tuning the synthesis route to obtain the desired magnetic properties for future medical applications. Part of the results presented in this thesis was published in Ref. [1], and a secondmanuscript on micromagnetic simulations is in preparation