Showing papers on "Absorption spectroscopy published in 2013"
TL;DR: The photocatalytic degradation of organic dyes such as methylene blue and methyl orange in the presence of various percentages of composite catalyst under visible light irradiation was carried out by new thermal decomposition method, which is simple and cost effective.
911 citations
TL;DR: The ZnO layer used to improve the light-harvesting increases the charge collection efficiency, serves as a blocking layer for holes, and reduces the recombination rate and the combined optical and electrical improvements raise the power conversion efficiency to 8.9%, comparable to that of polymer counterparts.
Abstract: We demonstrate that the power conversion efficiency can be significantly improved in solution-processed small-molecule solar cells by tuning the thickness of the active layer and inserting an optical spacer (ZnO) between the active layer and the Al electrode. The enhancement in light absorption in the cell was measured with UV–vis absorption spectroscopy and by measurements of the photoinduced carriers generation rate. The ZnO layer used to improve the light-harvesting increases the charge collection efficiency, serves as a blocking layer for holes, and reduces the recombination rate. The combined optical and electrical improvements raise the power conversion efficiency of solution-processed small-molecule solar cells to 8.9%, that is, comparable to that of polymer counterparts.
551 citations
TL;DR: In situ XAS measurements on a bifunctional manganese oxide catalyst with high electrochemical activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) demonstrate that the OER activity scales with film thickness, which suggests that the films have porous structure, which does not restrict electrocatalysis to the top geometric layer of the film.
Abstract: In situ X-ray absorption spectroscopy (XAS) is a powerful technique that can be applied to electrochemical systems, with the ability to elucidate the chemical nature of electrocatalysts under reaction conditions. In this study, we perform in situ XAS measurements on a bifunctional manganese oxide (MnOx) catalyst with high electrochemical activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), we find that exposure to an ORR-relevant potential of 0.7 V vs RHE produces a disordered Mn3II,III,IIIO4 phase with negligible contributions from other phases. After the potential is increased to a highly anodic value of 1.8 V vs RHE, relevant to the OER, we observe an oxidation of approximately 80% of the catalytic thin film to form a mixed MnIII,IV oxide, while the remaining 20% of the film consists of a less oxidized phase, likely corresponding to unchanged Mn3II,III,IIIO4. XAS...
467 citations
TL;DR: In this paper, the interaction between NiO nanoparticles and glucose has been studied using UV-vis absorption and fluorescence spectroscopy, and the zeta-potential of NiO nano-articles was used to gain insight about the interaction mode.
458 citations
TL;DR: A universal temporal-phase formalism is introduced, mapping the Fano asymmetry parameter q to a phase ϕ of the time-dependent dipole response function, which uses quantum-phase control to amplify extreme-ultraviolet light resonantly interacting with He atoms.
Abstract: Symmetric Lorentzian and asymmetric Fano line shapes are fundamental spectroscopic signatures that quantify the structural and dynamical properties of nuclei, atoms, molecules, and solids. This study introduces a universal temporal-phase formalism, mapping the Fano asymmetry parameter q to a phase φ of the time-dependent dipole response function. The formalism is confirmed experimentally by laser-transforming Fano absorption lines of autoionizing helium into Lorentzian lines after attosecond-pulsed excitation. We also demonstrate the inverse, the transformation of a naturally Lorentzian line into a Fano profile. A further application of this formalism uses quantum-phase control to amplify extreme-ultraviolet light resonantly interacting with He atoms. The quantum phase of excited states and its response to interactions can thus be extracted from line-shape analysis, with applications in many branches of spectroscopy.
405 citations
TL;DR: In this paper, the authors theoretically study the optical absorption property of twisted bilayer graphenes with various stacking geometries and demonstrate that the spectroscopic characteristics serve as a fingerprint to identify the rotation angle between two layers.
Abstract: We theoretically study the optical absorption property of twisted bilayer graphenes with various stacking geometries and demonstrate that the spectroscopic characteristics serve as a fingerprint to identify the rotation angle between two layers. We find that the absorption spectrum almost continuously evolves in changing the rotation angle, regardless of the lattice commensurability. The spectrum is characterized by series of peaks associated with the van Hove singularity, and the peak energies systematically shift with the rotation angle. We calculate the optical absorption in two frameworks: the tight-binding model and the effective continuum model based on the Dirac equation. For small rotation angles, less than ${10}^{\ensuremath{\circ}}$, the effective model well reproduces the low-energy band structure and the optical conductivity of the tight-binding model and, also, explains the optical selection rule analytically in terms of the symmetry of the effective Hamiltonian.
384 citations
TL;DR: In this article, a converged ab initio calculation of the optical absorption spectra of single-layer, double-layer and bulk MoS was presented, where the authors explicitly include spin-orbit coupling, using the full spinorial Kohn-Sham wave functions as input.
Abstract: We present converged ab initio calculations of the optical absorption spectra of single-layer, double-layer, and bulk MoS${}_{2}$. Both the quasiparticle-energy calculations (on the level of the GW approximation ) and the calculation of the absorption spectra (on the level of the Bethe-Salpeter equation) explicitly include spin-orbit coupling, using the full spinorial Kohn-Sham wave functions as input. Without excitonic effects, the absorption spectra would have the form of a step function, corresponding to the joint density of states of a parabolic band dispersion in two dimensions. This profile is deformed by a pronounced bound excitonic peak below the continuum onset. The peak is split by spin-orbit interaction in the case of single-layer and (mostly) by interlayer interaction in the case of double-layer and bulk MoS${}_{2}$. The resulting absorption spectra are thus very similar in the three cases, but the interpretation of the spectra is different. Differences in the spectra can be seen in the shape of the absorption spectra at 3 eV where the spectra of the single and double layers are dominated by a strongly bound exciton.
364 citations
TL;DR: In this article, the absorption spectrum fitting method was applied to estimate the optical band gap and width of the band tail of the CdSe nanostructural films that requires only the measurement of the absorbance spectrum, and no additional information such as the film thickness or reflectance spectra is needed.
Abstract: In this article, using the Tauc model, the absorption spectrum fitting method was applied to estimate the optical band gap and width of the band tail of the CdSe nanostructural films that requires only the measurement of the absorbance spectrum, and no additional information such as the film thickness or reflectance spectra is needed. Samples are prepared by chemical bath deposition method. Fabricated nanostructural thin films are thick but are composed from nanoparticles.
304 citations
TL;DR: The atmospheric O4 distribution is for all practical means and purposes independent of temperature, and can be predicted with an accuracy of better than 10(-3) from knowledge of the oxygen concentration profile.
Abstract: The collisions between two oxygen molecules give rise to O4 absorption in the Earth atmosphere. O4 absorption is relevant to atmospheric transmission and Earth's radiation budget. O4 is further used as a reference gas in Differential Optical Absorption Spectroscopy (DOAS) applications to infer properties of clouds and aerosols. The O4 absorption cross section spectrum of bands centered at 343, 360, 380, 446, 477, 532, 577 and 630 nm is investigated in dry air and oxygen as a function of temperature (203–295 K), and at 820 mbar pressure. We characterize the temperature dependent O4 line shape and provide high precision O4 absorption cross section reference spectra that are suitable for atmospheric O4 measurements. The peak absorption cross-section is found to increase at lower temperatures due to a corresponding narrowing of the spectral band width, while the integrated cross-section remains constant (within <3%, the uncertainty of our measurements). The enthalpy of formation is determined to be ΔH250 = −0.12 ± 0.12 kJ mol−1, which is essentially zero, and supports previous assignments of O4 as collision induced absorption (CIA). At 203 K, van der Waals complexes (O2-dimer) contribute less than 0.14% to the O4 absorption in air. We conclude that O2-dimer is not observable in the Earth atmosphere, and as a consequence the atmospheric O4 distribution is for all practical means and purposes independent of temperature, and can be predicted with an accuracy of better than 10−3 from knowledge of the oxygen concentration profile.
297 citations
TL;DR: In this article, Al-doped ZnO (AZO) photocatalysts with different Al concentrations (0.5e6.0 mol%) were prepared through a facile combustion method and followed by calcination at 500 � C for 3 h.
TL;DR: In this paper, an in situ technique that combines time-resolved synchrotron X-ray diffraction and mass spectroscopy was used to provide direct correlation between structural changes and the evolution of gas that occurs during the thermal decomposition of (over)charged cathode materials used in lithium-ion batteries.
Abstract: In this work, we present results from the application of a new in situ technique that combines time-resolved synchrotron X-ray diffraction and mass spectroscopy. We exploit this approach to provide direct correlation between structural changes and the evolution of gas that occurs during the thermal decomposition of (over)charged cathode materials used in lithium-ion batteries. Results from charged LixNi0.8Co0.15Al0.05O2 cathode materials indicate that the evolution of both O2 and CO2 gases are strongly related to phase transitions that occur during thermal decomposition, specifically from the layered structure (space group R3m) to the disordered spinel structure (Fd3m), and finally to the rock-salt structure (Fm3m). The state of charge also significantly affects both the structural changes and the evolution of oxygen as the temperature increases: the more extensive the charge, the lower the temperature of the phase transitions and the larger the oxygen release. Ex situ X-ray absorption spectroscopy (XA...
TL;DR: It is shown herein how sites associated with a metal–ceria interface can dramatically change the reaction mechanism of the water–gas shift reaction (WGSR; CO + H2O!H2 + CO2).
Abstract: The traditional approach to the optimization of metal/oxide catalysts has focused on the properties of the metal and the selection of the proper oxide for its dispersion. The importance of metal–oxide interfaces has long been recognized, [1] but the molecular determination of their properties and role is only now emerging. [2] Atoms with properties ranging from metallic to ionic are available at the interface and create unique reaction sites. We show herein how sites associated with a metal–ceria interface can dramatically change the reaction mechanism of the water–gas shift reaction (WGSR; CO + H2O!H2 + CO2). The WGSR is critical in the production of hydrogen. Multiple reaction mechanisms have been proposed. [3] In the redox mechanism, CO reacts with oxygen derived from the dissociation of H2O. In the associative process, the formation of a carbonaceous COxHy intermediate must precede the production of H2 and CO2. In situ studies are essential for the detection of surface species and active phases only present under the reaction conditions. [4] We present a combination of near-ambient-pressure X-ray photoelectron spectroscopy (NAP XPS), infrared reflection absorption spectroscopy (IRRAS), and density functional theory (DFT) calculations used to study the WGSR on CeOx nanoparticles deposited on Cu(111) and Au(111). Under WGSR conditions, adsorbed bent carboxylate (CO2 d� ) species were identified over both CeOx/Cu(111) and CeOx/ Au(111), with the ceria in a highly reduced state. By combining in situ experimental results with calculations, we
TL;DR: It is shown that a clean and stoichiometric surface of CuO requires special environmental conditions to prevent loss of oxygen and contamination by background water.
Abstract: The electronic structure of Cu(2)O and CuO thin films grown on Cu(110) was characterized by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The various oxidation states, Cu(0), Cu(+), and Cu(2+), were unambiguously identified and characterized from their XPS and XAS spectra. We show that a clean and stoichiometric surface of CuO requires special environmental conditions to prevent loss of oxygen and contamination by background water. First-principles density functional theory XAS simulations of the oxygen K edge provide understanding of the core to valence transitions in Cu(+) and Cu(2+). A novel method to reference x-ray absorption energies based on the energies of isolated atoms is presented.
TL;DR: A broadband enhancement of the light absorption in graphene over the whole visible spectrum is experimentally demonstrated by using an Attenuated Total Reflectance (ATR) configuration and it is explained in terms of coherent absorption arising from interference and dissipation.
Abstract: We experimentally demonstrate a broadband enhancement of the light absorption in graphene over the whole visible spectrum. This enhanced absorption is obtained in a multilayer structure by using an Attenuated Total Reflectance (ATR) configuration and it is explained in terms of coherent absorption arising from interference and dissipation. The interference mechanism leading to the phenomenon of coherent absorption allows for its precise control by varying the refractive index and/or thickness of the medium surrounding the graphene.
TL;DR: A novel restricted-open-shell configuration interaction with singles (ROCIS) approach for the calculation of transition metal L-edge X-ray absorption spectra is introduced and it is advantageous to employ Kohn-Sham rather than Hartree-Fock orbitals thus defining the density functional theory∕R OCIS method.
Abstract: A novel restricted-open-shell configuration interaction with singles (ROCIS) approach for the calculation of transition metal L-edge X-ray absorption spectra is introduced. In this method, one first calculates the ground state and a number of excited states of the non-relativistic Hamiltonian. By construction, the total spin is a good quantum number in each of these states. For a ground state with total spin S excited states with spin S′ = S, S − 1, and S + 1 are constructed. Using Wigner-Eckart algebra, all magnetic sublevels with MS = S, …, −S for each multiplet of spin S are obtained. The spin-orbit operator is represented by a mean-field approximation to the full Breit-Pauli spin-orbit operator and is diagonalized over this N-particle basis. This is equivalent to a quasi-degenerate treatment of the spin-orbit interaction to all orders. Importantly, the excitation space spans all of the molecular multiplets that arise from the atomic Russell-Saunders terms. Hence, the method represents a rigorous first-principles approach to the complicated low-symmetry molecular multiplet problem met in L-edge X-ray absorption spectroscopy. In order to gain computational efficiency, as well as additional accuracy, the excitation space is restricted to single excitations and the configuration interaction matrix is slightly parameterized in order to account for dynamic correlation effects in an average way. To this end, it is advantageous to employ Kohn-Sham rather than Hartree-Fock orbitals thus defining the density functional theory/ROCIS method. However, the method can also be used in an entirely non-empirical fashion. Only three global empirical parameters are introduced and have been determined here for future application of the method to any system containing any transition metal. The three parameters were carefully calibrated using the L-edge X-ray absorption spectroscopy spectra of a test set of coordination complexes containing first row transition metals. These parameters are universal and transferable. Hence, there are no adjustable parameters that are used to fit experimental X-ray absorption spectra. Thus, the new approach classifies as a predictive first-principles method rather than an analysis tool. A series of calculations on transition metal compounds containing Cu, Ti, Fe, and Ni in various oxidation and spin states is investigated and a detailed comparison to experimental data is reported. In most cases, the approach yields good to excellent agreement with experiment. In addition, the origin of the observed spectral features is discussed in terms of the electronic structure of the investigated compounds.
TL;DR: Gold and silver nanoparticles were biosynthesised by a simple method using different algae as reducing agent and the application of dead algae in an eco-friendly procedure is explored.
Abstract: The increasing demand and limited natural resources of noble metals make its recovery from dilute industrial wastes attractive, especially when using environmentally friendly methods. Nowadays, the high impact that nanotechnology is having in both science and society offers new research possibilities. Gold and silver nanoparticles were biosynthesised by a simple method using different algae as reducing agent. The authors explored the application of dead algae in an eco-friendly procedure. The nanoparticle formation was followed by UV-vis absorption spectroscopy and transmission electron microscopy. The functional groups involved in the bioreduction were studied by Fourier transform infrared spectroscopy.
TL;DR: In this paper, the Er 3+ -doped boro-tellurite glasses with compositions 30B 2 O 3 +10ZnO+(60− x )TeO 2 + x Er 2 O3 (where x = 0, 0.5, 1, 1.5 and 2.5) were prepared by melt quenching method.
TL;DR: BF2bdks exhibit comparable fluorescence properties in both solutions and polymers when the diketonate group is functionalized with smaller aromatic ring systems such as benzene, but emission from a strong intramolecular charge-transfer state was also noted in both solution and in PLA.
Abstract: Aromatic difluoroboron β-diketonate complexes (BF2bdks) are classic fluorescent molecules that have been explored as photochemical reagents, two-photon dyes, and oxygen sensors. To gain a better understanding of their emissive properties in both solution and polymer matrices, BF2bdks with varying aromatic groups were synthesized and their photophysical properties were investigated in both methylene chloride and poly(lactic acid) (PLA). Absorption spectra showed systematic variations that are well correlated with structural features, including the size of the aryl substituent and the presence of a para electron-donating methoxy substituent. Computational modeling of the absorption spectra with the TD-B3LYP/6-311+G(d)//B3LYP/6-31G(d) formulation of density functional theory and a polarizable continuum model of dichloromethane solvent shows that all systems show intense π–π* one-electron excitations, usually from one of the highest occupied molecular orbitals (HOMO – k, k = 0, 1, 2) to the lowest unoccupied ...
TL;DR: In this paper, a generic and fully automatic method aimed at detecting absorption lines in the spectra of astronomical objects is presented, which estimates the source continuum flux using a dimensionality reduction technique and nonnegative matrix factorization, and then detects and identifies metal absorption lines.
Abstract: We present a generic and fully automatic method aimed at detecting absorption lines in the spectra of astronomical objects. The algorithm estimates the source continuum flux using a dimensionality reduction technique and nonnegative matrix factorization, and then detects and identifies metal absorption lines. We apply it to a sample of ~105 quasar spectra from the Sloan Digital Sky Survey and compile a sample of ~40,000 Mg II- and Fe II-absorber systems, spanning the redshift range 0.4 < z < 2.3. The corresponding catalog is publicly available. We study the statistical properties of these absorber systems and find that the rest equivalent width distribution of strong Mg II absorbers follows an exponential distribution at all redshifts, confirming previous studies. Combining our results with recent near-infrared observations of Mg II absorbers, we introduce a new parameterization that fully describes the incidence rate of these systems up to z ~ 5. We find the redshift evolution of strong Mg II absorbers to be remarkably similar to the cosmic star formation history over 0.4 < z < 5.5 (the entire redshift range covered by observations), suggesting a physical link between these two quantities.
TL;DR: In this paper, a systematic study of soft X-ray absorption spectroscopy in various manganese oxides and fluorides was performed and compared with each other, showing that the Mn-L spectra fingerprint the Mn valence and spin states through spectral lineshape and energy position consistently and evidently.
TL;DR: In this article, the authors reported synthesis of zinc oxide (ZnO) nanoparticles via wet chemical method using molar solutions of zinc nitrate hexahydrate [Zn(NO3)2·6H2O] and ammonium hydroxide (NH4OH) with polyvinylpyrollidone (PVP) as capping agent.
TL;DR: The results clearly demonstrate that temperature- and light-induced spin crossover is possible for isolated molecules on surfaces but that interactions with the surface may play a key role in determining when this can occur.
Abstract: Using X-ray absorption techniques, we show that temperature- and light-induced spin crossover properties are conserved for a submonolayer of the [Fe(H2B(pz)2)2(2,2′-bipy)] complex evaporated onto a Au(111) surface. For a significant fraction of the molecules, we see changes in the absorption at the L2,3 edges that are consistent with those observed in bulk and thick film references. Assignment of these changes to spin crossover is further supported by multiplet calculations to simulate the X-ray absorption spectra. As others have observed in experiments on monolayer coverages, we find that many molecules in our submonolayer system remain pinned in one of the two spin states. Our results clearly demonstrate that temperature- and light-induced spin crossover is possible for isolated molecules on surfaces but that interactions with the surface may play a key role in determining when this can occur.
TL;DR: In this paper, a new series of donor-acceptor (D-A) conjugated random terpolymers (PBDTT-DPP-TPD) were synthesized from electron-rich thienyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDTT), in conjugation with two electron-deficient units, pyrrolo[3,4-c]pyrrole-1, 4-dione (DPP) and thieno[
Abstract: A new series of donor–acceptor (D–A) conjugated random terpolymers (PBDTT–DPP–TPD) were synthesized from electron-rich thienyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDTT), in conjugation with two electron-deficient units, pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) and thieno[3,4-c]pyrrole-4,6-dione (TPD), of different electron-withdrawing strengths. The optical properties of these random terpolymers can be easily controlled by tuning the ratio between DPP and TPD; an increase in TPD induced increased absorption between 400 and 650 nm and a lower highest occupied molecular orbital energy level, while higher DPP contents resulted in stronger absorption between 600 and 900 nm. The best power conversion efficiency (PCE) of 6.33% was obtained from PBDTT–DPP75–TPD25 with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) due to the improved light absorption and thus a short-circuit current density (JSC) higher than 16 mA/cm2. Interestingly, the trend observed in the PCE values differed from that of optical be...
TL;DR: This work presents the time-resolved UV absorption spectrum of the B̃ ((1)A') ← X̃(A)') electronic transition of formaldehyde oxide,CH2OO, produced by the reaction of CH2I radicals with O2, and establishes the identity of the absorbing species as CH2OO.
Abstract: We present the time-resolved UV absorption spectrum of the B ((1)A') ← X ((1)A') electronic transition of formaldehyde oxide, CH2OO, produced by the reaction of CH2I radicals with O2. In contrast to its UV photodissociation action spectrum, the absorption spectrum of formaldehyde oxide extends to longer wavelengths and exhibits resolved vibrational structure on its low-energy side. Chemical kinetics measurements of its reactivity establish the identity of the absorbing species as CH2OO. Separate measurements of the initial CH2I radical concentration allow a determination of the absolute absorption cross section of CH2OO, with the value at the peak of the absorption band, 355 nm, of σabs = (3.6 ± 0.9) × 10(-17) cm(2). The difference between the absorption and action spectra likely arises from excitation to long-lived B ((1)A') vibrational states that relax to lower electronic states by fluorescence or nonradiative processes, rather than by photodissociation.
TL;DR: This work demonstrates a facile approach for the fabrication of visible-light responsive NiTi-LDH/RGO composite photocatalysts, which can be used as a promising candidate in solar energy conversion and environmental science.
Abstract: A visible-light responsive photocatalyst was fabricated by anchoring NiTi-layered double hydroxide (NiTi-LDH) nanosheets to the surface of reduced graphene oxide sheets (RGO) via an in situ growth method; the resulting NiTi-LDH/RGO composite displays excellent photocatalytic activity toward water splitting into oxygen with a rate of 1.968 mmol g–1 h–1 and a quantum efficiency as high as 61.2% at 500 nm, which is among the most effective visible-light photocatalysts. XRD patterns and SEM images indicate that the NiTi-LDH nanosheets (diameter: 100–200 nm) are highly dispersed on the surface of RGO. UV–vis absorption spectroscopy exhibits that the introduction of RGO enhances the visible-light absorption range of photocatalysts, which is further verified by the largely decreased band gap (∼1.78 eV) studied by cyclic voltammetry measurements. Moreover, photoluminescence (PL) measurements indicate a more efficient separation of electron–hole pairs; electron spin resonance (ESR) and Raman scattering spectroscop...
TL;DR: The results of Magellan/MMIRS and Keck/NIRSPEC spectroscopy for five Lyemitters (LAEs) at z ≃ 2.2 were presented in this paper.
Abstract: We present the results of Magellan/MMIRS and Keck/NIRSPEC spectroscopy for five Lyemitters (LAEs) at z ≃ 2.2 for which high-resolution FUV spectra from Magellan/MagE are available. We detect nebular emission lines including Hon the individual basis and low-ionization interstellar (LIS) absorption lines in a stacked FUV spectrum, and measure average offset velocities of the Lyline, �vLy�, and LIS absorption lines, �vabs, with respect to the systemic velocity defined by the nebular lines. For a sample of eight z ∼ 2−3 LAEs without AGN from our study and the literature, we obtain �vLy� = 175±35 km s −1 , which is significantly smaller than that of Lyman-break Galaxies (LBGs), �vLy� ≃ 400 km s −1 . The stacked FUV spectrum givesvabs = −179 ± 73 km s −1 , comparable to that of LBGs. These positivevLyand negativevabs suggest that LAEs also have outflows. In contrast to LBGs, however, the LAEs' �vLyis as small as |�vabs|, suggesting low neutral hydrogen column densities. Such a low column density with a small number of resonant scattering may cause the observed strong Lyemission of LAEs. We find an anti-correlation between Lyequivalent width (EW) andvLyin a compilation of LAE and LBG samples. Although its physical origin is not clear, this anti-correlation result appears to challenge the hypothesis that a strong outflow, by means of a reduced number of resonant scattering, produces a large EW. If LAEs at z > 6 have similarly small �vLyvalues, constraints on the reionization history derived from the Lytransmissivity may need to be revised. Subject headings: cosmology: observations — galaxies: formation — galaxies: evolution — galaxies: high-redshift —
TL;DR: A procedure to prepare Au(67)(SR)(35) nanomolecule, which is the smallest to adopt the complete truncated-decahedral motif for its core with a surface structure bearing greater similarity to the larger nanoparticles, allowing high-yield isolation of the title compound.
Abstract: The preparation of gold nanomolecules with sizes other than Au25(SR)18 ,A u 38(SR)24 ,A u 102(SR)44, and Au144(SR)60 has been hampered by stability issues and low yields. Here we report a procedure to prepare Au67(SR)35, for either R = −SCH2CH2Ph or -SC6H13, allowing high-yield isolation (34%, ∼10-mg quantities) of the title compound. Product high purity is assessed at each synthesis stage by rapid MALDI−TOF mass-spectrometry (MS), and high-resolution electrospray-ionization MS confirms the Au67(SR)35 composition. Electronic properties were explored using optical absorption spectroscopy (UV− visible−NIR regions) and electrochemistry (0.74 V spacing in differential-pulsed-voltammetry), modes of ligand binding were studied by NMR spectroscopy ( 13 C and 1 H), and structural characteristics of the metal atom core were determined by powder X- ray measurements. Models featuring a Au17 truncated-decahedral inner core encapsulated by the 30 anchoring atoms of 15 staple- motif units have been investigated with first-principles electronic structure calculations. This resulted in identification of a structure consistent with the experiments, particularly, the opening of a large gap (∼0.75 eV) in the (2−) charge-state of the nanomolecule. The electronic structure is analyzed within the framework of a superatom shell model. Structurally, the Au67(SR)35 nanomolecule is the smallest to adopt the complete truncated-decahedral motif for its core with a surface structure bearing greater similarity to the larger nanoparticles. Its electronic HOMO−LUMO gap (∼0.75 eV) is nearly double that of the larger Au102 compound and it is much smaller than that of the Au38 one. The intermediary status of the Au67(SR)35 nanomolecule is also reflected in both its optical and electrochemical characteristics.
TL;DR: A hybrid algorithm is developed to solve the 3D TC problem and the effects of the view orientations are investigated, suggesting that for an unknown flame, it is better to use projections measured from random orientations than restricted orientations.
Abstract: Three-dimensional (3D) measurements are highly desirable both for fundamental combustion research and practical monitoring and control of combustion systems. This work discusses a 3D diagnostic based on tomographic chemiluminescence (TC) to address this measurement need. The major contributions of this work are threefold. First, a hybrid algorithm is developed to solve the 3D TC problem. The algorithm was demonstrated in extensive tests, both numerical and experimental, to yield 3D reconstruction with high fidelity. Second, an experimental approach was designed to enable quantifiable metrics for examining key aspects of the 3D TC technique, including its spatial resolution and reconstruction accuracy. Third, based on the reconstruction algorithm and experimental results, we investigated the effects of the view orientations. The results suggested that for an unknown flame, it is better to use projections measured from random orientations than restricted orientations (e.g., coplanar orientations). These findings are expected to provide insights to the fundamental capabilities of the TC technique, and also to facilitate its practical application.
TL;DR: In this article, a new heterojunction Ag3PO4/Cr-SrTiO3 was designed to eliminate the gaseous pollutants under visible light irradiation.
Abstract: A new heterojunction Ag3PO4/Cr-SrTiO3 was designed to eliminate the gaseous pollutants under visible light irradiation. The phase compositions, optical properties, and morphologies of the heterojunction photocatalysts were systematically investigated via powder X-ray diffraction, UV–Visible absorption spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The photodegradation of Isopropyl alcohol (IPA) was carried out to test the photocatalytic activity of the heterojunction. The results revealed that the heterojunction exhibited considerably improved efficiency in IPA photodegradation (CO2, 13.2 ppm h−1) in comparison with pure Ag3PO4 (CO2, 0.4 ppm h−1) and Cr-SrTiO3 (CO2, 1.9 ppm h−1) under visible light irradiation. In addition, the effects of mixing ratio and calcination temperature of the heterojunction were studied. The highest activity was observed in the Ag3PO4/Cr-SrTiO3 heterojunction with the mass ratio of 1:4 (Ag3PO4:Cr-SrTiO3) sintered at 500 °C. An investigation of energy-band structure via valence-band X-ray photoelectron spectrum indicates that the conduction band (CB) and valence band (VB) of Ag3PO4 are both more positive than that of Cr-SrTiO3, which facilitates the separation and transfer of photogenerated electrons and holes between the two photocatalysts.