X-ray and Synchrotron FTIR Studies of Partially Decomposed Magnesium Borohydride

Magnesium borohydride (Mg(BH4)(2)) is an attractive compound for solid-state hydrogen storage due to its lucratively high hydrogen densities and theoretically low operational temperature. Hydrogen release from Mg(BH4)(2) occurs through several steps. The reaction intermediates formed at these steps have been extensively studied for a decade. In this work, we apply spectroscopic methods that have rarely been used in such studies to provide alternative insights into the nature of the reaction intermediates. The commercially obtained sample was decomposed in argon flow during thermogravimetric analysis combined with differential scanning calorimetry (TGA-DSC) to differentiate between the H-2-desorption reaction steps. The reaction products were analyzed by powder X-ray diffraction (PXRD), near edge soft X-ray absorption spectroscopy at boron K-edge (NEXAFS), and synchrotron infrared (IR) spectroscopy in mid- and far-IR ranges (SR-FTIR). Up to 12 wt% of H-2 desorption was observed in the gravimetric measurements. PXRD showed no crystalline decomposition products when heated at 260-280 degrees C, the formation of MgH2 above 300 degrees C, and Mg above 320 degrees C. The qualitative analysis of the NEXAFS data showed the presence of boron in lower oxidation states than in (BH4)(-). The NEXAFS data also indicated the presence of amorphous boron at and above 340 degrees C. This study provides additional insights into the decomposition reaction of Mg(BH4)(2)

The role of carbon capture, utilization, and storage for economic pathways that limit global warming to below 1.5°C

The 2021 Intergovernmental Panel on Climate Change (IPCC) report, for the first time, stated that CO2 removal will be necessary to meet our climate goals. However, there is a cost to accomplish CO2 removal or mitigation that varies by source. Accordingly, a sensible strategy to prevent climate change begins by mitigating emission sources requiring the least energy and capital investment per ton of CO2, such as new emitters and long-term stationary sources. The production of CO2-derived products should also start by favoring processes that bring to market high-value products with sufficient margin to tolerate a higher cost of goods

Toward molecular wires confined in zeolite channels for an effective transport of electronic excitation energy.

Sunlight is the fundamental energy source sustaining life on Earth. Green plants are provided of very sophisticated and highly efficient tools to exploit light, they are able to harvest sunlight and to transport electronic excitation energy by means of a particular “antenna system” to reaction centres (natural photosynthesis). The antenna consists of regular arrangements of chlorophyll molecules held at fixed positions by means of proteins. Light absorbed by any of these molecules is transported - by radiationless energy transfer (FRET) - to reaction centres, providing the energy necessary for the chemical processes to be initiated. A green leaf consists of millions of such well-organized antenna devices. A long-standing challenge has been the development of an artificial system able to mimic the photosynthetic system. Artificial antenna systems can be realized once several organized chromophores are able to absorb the incident light and to channel the excitation energy to a common acceptor component1-3. Artificial antenna can be built by incorporating dyes into the one-dimensional channels of zeolite L (ZL). ZL crystals feature strictly parallel nano sized channels arranged in hexagonal symmetry. These channels can be filled with high concentration of suitable guests. The geometric constraints imposed by the host structure allow achieving supramolecular organization of photoactive guests1. It has been shown2,that the properties of the dye-ZL systems depend on the molecular packing inside the channels, controlling the intermolecular and the dyes/framework interactions In this work we presents a study on the optical properties of a two –dyes antenna system in which fluorenone molecules (donor molecule) and thionine(acceptor molecule) are organized in Zeolite L porosities. To interpret the optical properties of the hybrids a detailed structural study at atomistic level was mandatory. Due to the impossibility of studying from the structural point of view a two –dyes systems, two “one-dye” hybrids (ZL/fluorenone and ZL/thionine) were firstly synthesized and characterized to investigate the intermolecular and the dyes/framework interactions4. The results of thermogravimetric, IR, and X-ray structural refinements carried out for the one-dye system ZL/FL established that 1.5 molecules per unit cell is the maximum FL loading , in contrast with the data reported previously in literature5 and that the FL carbonyl group strong interact with a K+ of the ZL. The FL distribution at maximum loading can be consider as a self-assembly of planar dye molecules into a noncovalent nanoladder. FL molecules organized in such a single, continuous nanostructure of dye molecules did not exhibit significant electronic interactions. Indeed, both absorption (recorded in the diffuse reflectance mode) and photoemission electronic spectra of ZL/FL systems with different FL loading scaled almost linearly in intensity with the amount dye hosted in the unit cell (ranging from 0.5 to 1.5), without significant changes of the spectral profiles. Noticeably, the combination and steady state and time resolved photoluminescence data indicated that even at the maximum loading ca. 90% of FL molecules are photoluminescent, with significant increase in the average quantum yield with respect to FL molecules in solution. Such a finding clearly indicates that excited states coupling (Davydov splitting) is not contributing to the optical properties of the material. The structural study of the ZL/TH system revealed that the maximum possible loading of TH is equal to 0.3 molecules per unit cell in agreement with the TGA and literature data6. Short distances between the carbon, sulfur and nitrogen atoms and two water molecule sites , in turn at bond distance from the oxygen atoms of the main channel, suggested a water-mediated Th-ZL interactions7. Moreover, IR spectroscopy provided evidence of the interaction of the aromatic rings with the environment. This likely resulted in an increase of the rate of non-radiative decay of Th molecules in the electronic excited state, because only ca. 5% of Th molecules hosted in the ZL channel appeared photoluminescent. The occurrence of energy transfer from excited FL molecules forming the noncovalent nanoladder in the ZL channels and Th, in the ground state, deposited on the external surface of ZL particles are currently under investigation. In conclusion, we have here presented a study on the physico-chemical properties of dense molecular wires encapsulated in the one-dimensional pores arrays of Zeolite L. Concerning the optical properties of our composites, no evidence of Davydov splitting emerged from our study, indicating that one of the main competitors of the FRET mechanism is not operative notwithstanding the close packed arrangement of FL. We believe that this feature is of overwhelming relevance in view of application of such a system in artificial antenna systems

Molecular wires confined in zeolite L channels for an effective transport of electronic excitation energy: a synchrotron structural study.

Sunlight is the fundamental energy source sustaining life on Earth. Green plants are provided of very sophisticated and highly efficient tools to exploit light, they are able to harvest sunlight and to transport electronic excitation energy by means of a particular \u201cantenna system\u201d to reaction centers (natural photosynthesis).The development of an artificial system able to mimic the natural phenomenon has been a long-standing challenge. Artificial antenna systems can be realized once several organized chromophores are able to absorb the incident light and to channel the excitation energy to a common acceptor component [1-3]. The optical properties of the systems depend on the molecular packing inside the channels. Artificial antenna can be built by incorporating suitable guests into the one-dimensional channels of zeolite L (ZL). In this work we present a detailed structural study of two hybrid systems in which dyes (fluorenone and thionine) are encapsulated in zeolite L channels. These two molecules were chosen since it has been demonstrated that a \u201ctwo \u2013dyes antenna system\u201d - in which fluorenone (FL) (donor molecule) and thionine (Th) (acceptor molecule) are organized in Zeolite L porosities - shows remarkable optical properties. Due to the impossibility of studying, from the structural point of view a \u201ctwo \u2013dyes systems\u201d, two \u201cone-dye\u201d hybrids (ZL/fluorenone and ZL/thionine) were firstly synthesized and characterized [4]. The results of thermogravimetric, IR, and X-ray structural refinements carried out for the one-dye ZL/FL and ZL/Th systems established that 1.5 molecules of FL and 0.3 molecules of Th per unit cell is the maximum loading, respectively. The FL carbonyl group strong interacts with a K+ of the ZL. On the other hand, short distances between the carbon, sulfur and nitrogen atoms of Th and two water molecule sites, in turn at bond distance from the oxygen atoms of the main channel, suggested a water-mediated Th-ZL interactions. The energy transfer from excited FL molecules, forming the non-covalent nano-ladder in the ZL channel, and Th, deposited on the external surface of ZL particles, is currently under investigation. In conclusion concerning the optical properties of our composites, no evidence of Davydov splitting emerged from our study, indicating that one of the main competitors of the FRET mechanism is not operative notwithstanding the close packed arrangement of FL. We believe that this feature is of overwhelming relevance in view of application of such a system in artificial antenna devices. The authors acknowledge the Italian Ministry of Education, MIUR-Project: \u201cFuturo in Ricerca 2012 - ImPACT- RBFR12CLQD\u201d

Dye Loading influence on performances of Fluorenone/zeoliteL Light Harvester

Zeolite L (LTL), is an appealing and excellent host for the supramolecular organization of different kinds of molecules and complexes. However, relatively few experimental structural information is available about the orientation and alignment of the dye molecules in the zeolite pores. Hence, a detailed structural characterization is of great importance for understanding the functionality of these host-guest systems. Between all the possible guests, neutral dye fluorenone (C13H8O) (FL) has received a considerable attention [1,2] because of its ability to form a host-guest complex with LTL, stable if exposed at the atmosphere. Moreover, the fluorescent nature of fluorenone makes this complex interesting as a component of the energy relay system in artificial antennas. Although a detailed structural characterization is still lacking, theoretical studies have shown as the orientation of fluorenone is especially interesting as it is directly related to the light harvesting properties of fluorenone [3]. Moreover, it has shown as the presence of water can influence on the electronic spectra of this host-guest complex and then affect its performances as light harvester [3]. In this study, three different FL/K-LTL materials characterized by an increasing loading of FL have been synthesized by mixing in inert atmosphere the dehydrated K-LTL and FL powder in ratio of 0.5, 1.0, 1.5 and 2.0 molecules/unit cell, and then heating the samples at 120°C in air for 24 h. The vials were maintained under continuous rotation during the heating in order to optimize the contact between the zeolite and the dye. The samples so obtained were characterized by means of X-ray powder diffraction, thermo-gravimetric analysis, IR and UV-vis spectroscopies, fluorescence and nitrogen adsorption. The incorporation of FL into the K-LTL channels was confirmed by a significant change of the unit cell parameters and by drastic decrease in the K-LTL surface area also at low FL loading. The strong interaction between FL carbonyl group and the extraframework potassium cation predicted by theoretical modelling [1] was confirmed by the short bond distances (2.77 Å), evidenced in the Rietveld refined structure, and by the shift of the C=O stretching frequency evidenced in the IR spectra. Such an interaction explains why FL is not displaced by water molecules when FL/K-LTL hybrid is re-exposed to the air [1]. Interestingly, although the UV-vis absorption spectrum was almost unaffected by the FL loading, the corresponding emission spectrum evidenced a strong influence: the optimum FL/K-LTL ratio was then determined in order to optimize the performances of the device as light harvester. The structural information obtained theoretically and from XRD allowed also to explain the loading dependence of the optical properties of the material and to correlate it with the relative orientation of the fluorenone molecules in the zeolite channels

Visible-Light-Driven Photocatalytic Coupling of Benzylamine over Titanium-Based MIL-125-NH2 Metal-Organic Framework: A Mechanistic Study

This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.jpcc.0c06950.[EN] Imines are important building blocks in organic chemistry. Titanium-based metal-organic framework (MOF) MIL-125-NH2(Ti) can photocatalyze, under visible light and at room temperature, the selective aerobic oxidation of benzylamine to N-benzylidenebenzylamine. We investigated the reaction mechanism using catalytic tests, ex situ infrared spectroscopy, and density functional calculations. In the dark, the presence of MIL-125-NH2(Ti) alone does not improve the reaction yield with respect to a blank experiment. This poor catalytic performance in the dark is associated with the absence of polarizing species on the MOF surface, as confirmed by acetonitrile adsorption. Excitation with different spectral regions evidenced the determinant role of the 450 < lambda < 385 nm range for catalyst photoactivation. The calculations show that the last step of the reaction would have an energy barrier of 206 kJ mol(-1) in anhydrous conditions, while it decreases to 88 kJ mol(-1) only if the mechanism is mediated by two water molecules.Financial support by the Spanish Government is acknowledged through projects MAT2017-82288-C2-1-P and the Severo Ochoa program (SEV-2016-0683). We further thank Bartolomeo Civalleri for the kind help with the calculations and Diego Pellerej for experimental assistance.Vitillo, JG.; Presti, D.; Luz, I.; Llabrés I Xamena, FX.; Bordiga, S. (2020). Visible-Light-Driven Photocatalytic Coupling of Benzylamine over Titanium-Based MIL-125-NH2 Metal-Organic Framework: A Mechanistic Study. The Journal of Physical Chemistry C. 124(43):23707-23715. https://doi.org/10.1021/acs.jpcc.0c06950S23707237151244

Internal alignment and position resolution of the silicon tracker of DAMPE determined with orbit data

The DArk Matter Particle Explorer (DAMPE) is a space-borne particle detector designed to probe electrons and gamma-rays in the few GeV to 10 TeV energy range, as well as cosmic-ray proton and nuclei components between 10 GeV and 100 TeV. The silicon-tungsten tracker-converter is a crucial component of DAMPE. It allows the direction of incoming photons converting into electron-positron pairs to be estimated, and the trajectory and charge (Z) of cosmic-ray particles to be identified. It consists of 768 silicon micro-strip sensors assembled in 6 double layers with a total active area of 6.6 m$^2$. Silicon planes are interleaved with three layers of tungsten plates, resulting in about one radiation length of material in the tracker. Internal alignment parameters of the tracker have been determined on orbit, with non-showering protons and helium nuclei. We describe the alignment procedure and present the position resolution and alignment stability measurements

The DArk Matter Particle Explorer mission

The DArk Matter Particle Explorer (DAMPE), one of the four scientific space science missions within the framework of the Strategic Pioneer Program on Space Science of the Chinese Academy of Sciences, is a general purpose high energy cosmic-ray and gamma-ray observatory, which was successfully launched on December 17th, 2015 from the Jiuquan Satellite Launch Center. The DAMPE scientific objectives include the study of galactic cosmic rays up to $\sim 10$ TeV and hundreds of TeV for electrons/gammas and nuclei respectively, and the search for dark matter signatures in their spectra. In this paper we illustrate the layout of the DAMPE instrument, and discuss the results of beam tests and calibrations performed on ground. Finally we present the expected performance in space and give an overview of the mission key scientific goals.Comment: 45 pages, including 29 figures and 6 tables. Published in Astropart. Phy

Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of electrons and positrons

High energy cosmic ray electrons plus positrons (CREs), which lose energy quickly during their propagation, provide an ideal probe of Galactic high-energy processes and may enable the observation of phenomena such as dark-matter particle annihilation or decay. The CRE spectrum has been directly measured up to $\sim 2$ TeV in previous balloon- or space-borne experiments, and indirectly up to $\sim 5$ TeV by ground-based Cherenkov $\gamma$-ray telescope arrays. Evidence for a spectral break in the TeV energy range has been provided by indirect measurements of H.E.S.S., although the results were qualified by sizeable systematic uncertainties. Here we report a direct measurement of CREs in the energy range $25~{\rm GeV}-4.6~{\rm TeV}$ by the DArk Matter Particle Explorer (DAMPE) with unprecedentedly high energy resolution and low background. The majority of the spectrum can be properly fitted by a smoothly broken power-law model rather than a single power-law model. The direct detection of a spectral break at $E \sim0.9$ TeV confirms the evidence found by H.E.S.S., clarifies the behavior of the CRE spectrum at energies above 1 TeV and sheds light on the physical origin of the sub-TeV CREs.Comment: 18 pages, 6 figures, Nature in press, doi:10.1038/nature2447