Abstract: Mesoporous strontium hydroxyapatite (SrHAp) nanorods (NRs) have been successfully synthesized using a simple and efficient chemical route, i.e. the hydrothermal method. Structural and morphological characterization of the as-synthesized SrHAp NRs have been performed by transmission electron microscopy (TEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). TEM and HAADF-STEM measurements of the NRs reveal the coexistence of longer and shorter particles with the length ranging from 50 nm to 400 nm and a diameter of about 20-40 nm. Electron tomography measurements of the NRs allow us to better visualize the mesopores and their facets. Two model drugs, hydrophobic risperidone and hydrophilic pramipexole, were loaded into the SrHAp NRs. These nanorods were coated using a modified chitosan (CS) with poly(2-hydroxyethyl methacrylate) (PHEMA), in order to encapsulate the drug-loaded SrHAp nanoparticles and reduce the cytotoxicity of the loaded materials. The drug release from neat and encapsulated SrHAp NRs mainly depends on the drug hydrophilicity. Importantly, although neat SrHAp nanorods exhibit some cytotoxicity against Caco-2 cells, the Cs-g-PHEMA-SrHAp drug-loaded nanorods show an acceptable cytocompatibility.

Abstract: The use of fossil-based products induces a large environmental burden. To lighten this burden, green technologies are required that can replace their fossil-based counterparts. To enable the development of economically viable green technologies, an optimization towards both economic and environmental objectives is required. To perform this multi-objective optimization (MOO), the environmental techno-economic assessment (ETEA) methodology is extended towards a MOO-extended ETEA. The development of this MOO-extended ETEA is the main objective of this manuscript. As an example of a green technology, the concept of microalgae biorefineries is used as a case study to illustrate the MOO-extended ETEA. According to the results, all optimal value chains include open pond cultivation, a membrane for medium recycling and spray drying. The optimal economic value chain uses Nannochloropsis sp. in a one-stage cultivation to produce fish larvae feed, while the optimal environmental design uses Dunaliella salina or Haematococcus pluvialis to produce carotenoids and fertilizer or energy products, by means of anaerobic digestion or gasification. The crucial parameters for both environmental and economic feasibility are the content, price and reference impact of the main end product, the growth parameters and the biomass and carotenoid recovery efficiency alongside the different process steps. By identifying the economic and environmentally optimal algal-based value chain and the crucial drivers, the MOO-extended ETEA provides insights on how algae-based value chains can be developed in the most economic and environmentally-friendly way. For example, the inclusion of a medium recycling step to lower the water and salt consumption is required in all Pareto-optimal scenarios. Another major insight is the requirement of high-value products such as carotenoids or specialty food to obtain and economically and environmentally feasible algal-based value chain. Due to the modular nature of the MOO-extended ETEA, multiple processes can be included or excluded from the superstructure. Although this case study is limited to current microalgae biorefinery technologies, the MOO-extended ETEA can also be used to assess the economic and environmental effect of more innovative technologies. This way, the MOO-extended ETEA provides a methodology to assess the economic and environmental potential of innovative green technologies and shorten their time-to-market.

Abstract: Deactivation was investigated in Fe2O3-CeO2 oxygen storage materials during repeated H-2-reduction and CO2-reoxidation. In situ XRD, XAS, and TEM were used to identify phases, crystallite sizes, and morphological changes upon cycling operation. The effect of redox cycling was investigated both in Fe-rich (80 wt % Fe2O3-CeO2) and Ce-rich (10 wt %Fe2O3-CeO2) materials. The former consisted of 100 nm Fe2O3 particles decorated with 5-10 nm Ce1-xFexO2-x. The latter presented CeO2 with incorporated Fe, i.e. a solid solution of Ce1-xFexO2-x, as the main oxygen carrier. By modeling the EXAFS Ce-K signal for as-prepared 10 wt %Fe2O3-CeO2, the amount of Fe in CeO2 was determined as 21 mol %, corresponding to 86% of the total iron content. Sintering and solid solid transformations, the latter including both new phase formation and element segregation, were identified as deactivation pathways upon redox cycling. In Ce-rich material, perovskite (CeFeO3) was identified by XRD. This phase remained inert during reduction and reoxidation, resulting in an overall lower oxygen storage capacity. Further, Fe segregated from the solid solution, thereby decreasing its reducibility. In addition, an increase in crystallite size occurred for all phases. In Fe-rich material, sintering is the main deactivation pathway, although Fe segregation from the solid solution and perovskite formation cannot be excluded.

Abstract: Solar energy plays an important role in solving serious environmental
problems and meeting the high energy demand. However, the lack of suitable
materials hinders further progress of this technology. Here, we present the largest
inorganic solar cell material search till date using density functional theory (DFT) and
machine-learning approaches. We calculated the spectroscopic limited maximum
efficiency (SLME) using the Tran−Blaha-modified Becke−Johnson potential for 5097
nonmetallic materials and identified 1997 candidates with an SLME higher than 10%,
including 934 candidates with a suitable convex-hull stability and an effective carrier
mass. Screening for two-dimensional-layered cases, we found 58 potential materials
and performed G0W0 calculations on a subset to estimate the prediction uncertainty. As the above DFT methods are still computationally expensive, we developed a high accuracy machine-learning model to prescreen efficient materials and applied it to over a million materials. Our results provide a general framework and universal strategy for the design of high-efficiency solar
cell materials. The data and tools are publicly distributed at: https://www.ctcms.nist.gov/~knc6/JVASP.html, https://www.
ctcms.nist.gov/jarvisml/, https://jarvis.nist.gov/, and https://github.com/usnistgov/jarvis.

Abstract: Molecular dynamics (MD) simulations were performed to provide atomic scale insight in the initial interaction between hydroxyl radicals (OH) and peptide systems in solution. These OH radicals are representative reactive oxygen species produced by cold atmospheric plasmas. The use of plasma for biomedical applications is gaining increasing interest, but the fundamental mechanisms behind the plasma modifications still remain largely elusive. This study helps to gain more insight in the underlying mechanisms of plasma medicine but is also more generally applicable to peptide oxidation, of interest for other applications. Combining both reactive and nonreactive MD simulations, we are able to elucidate the reactivity of the amino acids inside the peptide systems and their effect on their structure up to 1 μs. Additionally, experiments were performed, treating the simulated peptides with a plasma jet. The computational results presented here correlate well with the obtained experimental data and highlight the importance of the chemical environment for the reactivity of the individual amino acids, so that specific amino acids are attacked in higher numbers than expected. Furthermore, the long time scale simulations suggest that a single oxidation has an effect on the 3D conformation due to an increase in hydrophilicity and intra- and intermolecular interactions.

Abstract: Novel compounds [Ge46−xPx]Tey (13.9≤x≤15.6, 5.92≤y≤7.75) with clathrate-like structures have been prepared and structurally characterized. They crystallize in the space group Fmequation image with the unit cell parameter changing from 20.544(2) to 20.698(2) Å (Z=8) on going from x=13.9 to x=15.6. Their crystal structure is composed of a covalently bonded Ge[BOND]P framework that hosts tellurium atoms in the guest positions and can be viewed as a peculiar variant of the type I clathrate superstructure. In contrast to the conventional type I clathrates, [Ge46−xPx]Tey contain tricoordinated (3b) atoms and no vacancies in the framework positions. As a consequence of the transformation of the framework, the majority of the guest tellurium atoms form a single covalent bond with the host framework and thus the title compounds are the first representative of semiclathrates with covalent bonding. A comparison is made with silicon clathrates and the evolution of the crystal structure upon changing the tellurium content is discussed.

Abstract: The phase transition processes induced by ultrashort, 100 fs pulsed laser irradiation of Au, Cu, and Ni are studied by means of a combined atomistic-continuum approach. A moderately low absorbed laser fluence range, from 200 to 600 J/m2 is considered to study phase transitions by means of a local and a nonlocal order parameter. At low laser fluences, the occurrence of layer-by-layer evaporation has been observed, which suggests a direct solid to vapor transition. The calculated amount of molten material remains very limited under the conditions studied, especially for Ni. Therefore, our results show that a kinetic equation that describes a direct solid to vapor transition might be the best approach to model laser-induced phase transitions by continuum models. Furthermore, the results provide more insight into the applicability of analytical superheating theories that were implemented in continuum models and help the understanding of nonequilibrium phase transitions.

Abstract: We illustrate the potential of advanced transmission electron microscopy for the characterization of a new class of soft porous materials: metal@Zn4O(bdc)3 (metal@MOF-5; bdc = 1,4-benzenedicarboxylate). By combining several electron microscopy techniques (transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and electron tomography) and by carefully reducing the electron dose to avoid beam damage, it is possible to simultaneously characterize the MOF-5 framework material and the loaded metal nanoparticles. We also demonstrate that electron tomography can be used to accurately determine the position and distribution of the particles within the MOF-5 framework. To demonstrate the implementation of these microscopy techniques and what kind of results can be expected, measurements on gas-phase-loaded metal−organic framework materials Ru@MOF-5 and Pd@MOF-5 are presented.

Abstract: This study aims at sensing in situ reactive oxygen and nitrogen species (RONS) and specifically superoxide anion (O-2(center dot-)) in aqueous buffer solutions exposed to cold atmospheric plasmas (CAPs). CAPs were generated by ionizing He gas shielded with variable N-2/O-2 mixtures. Thanks to ultramicroelectrodes protected against the high electric fields transported by the ionization waves of CAPs, the production of superoxide and several RONS was electrochemically directly detected in liquids during their plasma exposure. Complementarily, optical emissive spectroscopy (OES) was used to study the plasma phase composition and its correlation with the chemistry in the exposed liquid. The specific production of O-2(center dot-), a biologically reactive redox species, was analyzed by cyclic voltammetry (CV), in both alkaline (pH 11), where the species is fairly stable, and physiological (pH 7.4) conditions, where it is unstable. To understand its generation with respect to the plasma chemistry, we varied the shielding gas composition of CAPs to directly impact on the RONS composition at the plasma-liquid interface. We observed that the production and accumulation of RONS in liquids, including O(2)(center dot-)depends on the plasma composition, with N-2-based shieldings providing the highest superoxide concentrations (few 10s of micromolar at most) and of its derivatives (hundreds of micromolar). In situ spectroscopic and electrochemical analyses provide a high resolution kinetic and quantitative understanding of the interactions between CAPs and physiological solutions for biomedical applications.

Abstract: Analysis of the structural parameters of phases that adopt brownmillerite-type structures suggests the distribution of the different complex ordering schemes adopted within this structure type can be rationalized by considering both the size of the separation between the tetrahedral layers and the tetrahedral chain distortion angle. A systematic study using structural data obtained from La1−xAxMnO2,5 (A = Ba, Sr, Ca,) phases, prepared by the topotactic reduction of the analogous La1−xAxMnO3 perovskite phases, was performed to investigate this relationship. By manipulating the A-cation composition, both the tetrahedral layer separation and tetrahedral chain distortion angle in the La1−xAxMnO2,5 phases were controlled and from the data obtained a ¡°structure map¡± of the different brownmillerite variants was plotted as a function of these structural parameters. This map has been extended to include a wide range of reported brownmillerite phases showing the structural ideas presented are widely applicable. The complete structural characterization of La1−xAxMnO2,5 0.1 ¡Ü x ¡Ü 0.33, A = Ba; 0.15 ¡Ü x ¡Ü 0.5 A = Sr, and 0.22 ¡Ü x ¡Ü 0.5 A = Ca is described and includes compositions which exhibit complex intralayer ordered structures and Mn2+/Mn3+ charge ordering.

Abstract: Epitaxial thin films of GdBaCo2O5.5+δ (GBCO) grown by pulsed laser deposition have been studied as a function of deposition conditions. The variation in film structure, domain orientation, and microstructure upon deviations in the cation composition have been correlated with the charge transport properties of the films. The epitaxial GBCO films mainly consist of single- and double-perovskite regions that are oriented in different directions depending on the deposition temperature. Additionally, cobalt depletion induces the formation of a high density of stacking defects in the films, consisting of supplementary GdO planes along the c-axis of the material. The presence of such defects progressively reduces the electrical conductivity. The films closer to the stoichiometric composition have shown p-type electronic conductivity at high pO2 with values as high as 800 S/cm at 330 °C in 1 atm O2, and with a pO2 power dependence with an exponent as low as 1/25, consistent with the behavior reported for bulk GBCO. These values place GBCO thin films as a very promising material to be applied as cathodes in intermediate temperature solid oxide fuel cells.

Abstract: Pb cations in PbS quantum rods made from CdS quantum rods by successive complete cationic exchange reactions are partially re-exchanged for Cd cations. Using STEM-HAADF, we show that this leads to the formation of unique multiple dot-in-rod PbS/CdS heteronanostructures, with a photoluminescence quantum yield of 4555%. We argue that the formation of multiple dot-in-rods is related to the initial polycrystallinity of the PbS quantum rods, where each PbS crystallite transforms in a separate PbS/CdS dot-in-dot. Effective mass modeling indicates that electronic coupling between the different PbS conduction band states is feasible for the multiple dot-in-rod geometries obtained, while the hole states remain largely uncoupled.

Abstract: We evaluate the importance of quantum effects on the sticking of H2 on Al(110) for conditions that are close to those of molecular beam experiments that have been done on this system. Calculations with the quasi-classical trajectory (QCT) method and with quantum dynamics (QD) are performed using a model in which only motion in the six molecular degrees of freedom is allowed. The potential energy surface used has a minimum barrier height close to the value recently obtained with the quantum Monte Carlo method. Monte Carlo averaging over the initial rovibrational states allowed the QD calculations to be done with an order of magnitude smaller computational expense. The sticking probability curve computed with QD is shifted to lower energies relative to the QCT curve by 0.21 to 0.05 kcal/mol, with the highest shift obtained for the lowest incidence energy. Quantum effects are therefore expected to play a small role in calculations that would evaluate the accuracy of electronic structure methods for determining the minimum barrier height to dissociative chemisorption for H2 + Al(110) on the basis of the standard procedure for comparing results of theory with molecular beam experiments.

Abstract: Iron is a widely used catalyst for the growth of carbon nanotubes (CNTs) or carbon nanofibers (CNFs) by catalytic chemical vapor deposition. However, both Fe and FeC compounds (generally, Fe3C) have been found to catalyze the growth of CNTs/CNFs, and a comparison study of their respective catalytic activities is still missing. Furthermore, the control of the crystal structure of iron-based catalysts, that is α-Fe or Fe3C, is still a challenge, which not only obscures our understanding of the growth mechanisms of CNTs/CNFs, but also complicates subsequent procedures, such as the removal of catalysts for better industrial applications. Here, we show a partial control of the phase of iron catalysts (α-Fe or Fe3C), obtained by varying the growth temperatures during the synthesis of carbon-based nanofibers/nanotubes in a plasma-enhanced chemical vapor deposition reactor. We also show that the structure of CNFs originating from Fe3C is bamboo-type, while that of CNFs originating from Fe is not. Moreover, we directly compare the growth rates of carbon-based nanofibers/nanotubes during the same experiments and find that CNFs/CNTs grown by α-Fe nanoparticles are longer than CNFs grown from Fe3C nanoparticles. The influence of the type of catalyst on the growth of CNFs is analyzed and the corresponding possible growth mechanisms, based on the different phases of the catalysts, are discussed.