Search

Recently, LiGa 5 O 8 was identified as a cubic spinel type ultra-wide-bandgap semiconductor with a gap of about 5.36 eV and reported to be unintentionally p -type. Here, we present first-principles calculations of native defects and their various complexes to try to explain the occurrence of p -type doping. Although we find Li vacancies (0.74 eV above VBM) to be shallower acceptors than in LiGaO 2 (1.63 eV above VBM), and becoming slightly shallower in complexes with donors such as V O (0.58 eV above VBM) and Ga Li antisites (0.65 eV above VBM), these V Li based defects are not sufficiently shallow to explain p -type doping. The dominant defects are donors and, in equilibrium, the Fermi level would be determined by compensation between donors and acceptors and pinned deep in the gap. [ABSTRACT FROM AUTHOR]

Recently, LiGa 5 O 8 was identified as a cubic spinel type ultra-wide-bandgap semiconductor with a gap of about 5.36 eV and reported to be unintentionally p -type. Here, we present first-principles calculations of native defects and their various complexes to try to explain the occurrence of p -type doping. Although we find Li vacancies (0.74 eV above VBM) to be shallower acceptors than in LiGaO 2 (1.63 eV above VBM), and becoming slightly shallower in complexes with donors such as V O (0.58 eV above VBM) and Ga Li antisites (0.65 eV above VBM), these V Li based defects are not sufficiently shallow to explain p -type doping. The dominant defects are donors and, in equilibrium, the Fermi level would be determined by compensation between donors and acceptors and pinned deep in the gap. [ABSTRACT FROM AUTHOR]

Block copolymers, known for their capacity to undergo microphase separation, spontaneously yield various periodic nanostructures. These precisely controlled nanostructures have attracted considerable interest due to their potential applications in microfabrication templates, conducting films, filter membranes, and other areas. However, it is crucial to acknowledge that microphase-separated structures typically exhibit random alignment, making alignment control a pivotal factor in functional material development. To address this challenge, researchers have explored the use of block copolymers containing liquid-crystalline (LC) polymers, which offer a promising technique for alignment control. The molecular structure and LC behavior of these polymers significantly impact the morphology and alignment of microphase-separated structures. In this study, we synthesized LC diblock copolymers with cyano-terminated phenyl benzoate moieties and evaluated the microphase-separated structures and molecular alignment behaviors. The LC diblock copolymers with a narrow molecular weight distribution were synthesized by atom transfer radical polymerization. Small angle X-ray scattering measurements revealed that the block copolymers exhibit smectic LC phases and form cylinder structures with a lattice period of about 18 nm by microphase separation. The examination of block copolymer films using polarized optical microscopy and polarized UV-visible absorption spectroscopy corroborated that the LC moieties were uniaxially aligned along the alignment treatment direction. [ABSTRACT FROM AUTHOR]

In this work, we studied the reaction mechanisms for CO2 reduction reaction (CRR) on the iron‐doped graphene and its coordinating sulfur (S) and nitrogen (N) variants, FeNnS4‐n (n=1–4), using density functional theory calculations. Our results revealed that the electronic property and catalytic reactivity of the surfaces can be tuned by varying the N and S atoms ratio. The CRR activities of the mixed surfaces, FeN3S1, FeN2S2, and FeN1S3, were better than FeN4 and FeS4, where the absolute value of the limiting potential of the mixed surface decreased by 0.3 V. Considering the stability, we suggest FeN3S surface to be favorable for CRR. For the bare surfaces, we found a positive linear correlation between the magnetic moment and the charge of Fe metal. For these surfaces, the reduction of CO (*CO+(H++e−)→*CHO) was important in deciding the limiting potential. We found that the adsorption energy of CO displayed a volcano relationship with the magnetic moment of the Fe atom. The study showed that the change of local coordinating structure around the Fe atom could modify the electronic and magnetic properties of the active Fe center and improve the CRR activity performance. [ABSTRACT FROM AUTHOR]

Infrared spectra have been used in many chemical applications, and theoretical calculations have been useful for analyzing these experimental results. While quantum mechanics is used for calculating the spectra for small molecules, classical mechanics is used for larger systems. However, a systematic understanding of the similarities and differences between the two approaches is not clear. Previous studies focused on peak position and relative intensities of the spectra obtained by various quantum and classical methods, but here, we included "absolute" intensities in the evaluation. The infrared spectrum of a one‐dimensional (1D) harmonic oscillator (HO) and Morse oscillator were examined using four treatments: quantum, Wigner, truncated Wigner, and classical microcanonical treatments. For a 1D HO with a linear dipole moment function (DMF), the quantum and Wigner treatments give nearly the same spectra. On the other hand, the truncated Wigner underestimates the fundamental transition's intensity by half. In the case of cubic DMF, the truncated Wigner and classical methods fail to reproduce the relative intensity between the fundamental and second overtone transitions. Unfortunately, all the Wigner and classical methods fail to agree with the quantum results for a Morse oscillator with just 1% anharmonicity. [ABSTRACT FROM AUTHOR]

Developing electrocatalysts with high catalytic performance and selectivity is crucial for electrochemical CO2 reduction reaction (CRR). There are many catalyst studies of transition metal (TM) atom doping to sp2 carbon material, such as graphene or carbon nanotubes. On the other hand, graphdiyne (GDY) has both sp and sp2 hybridization and stable pores, so we can tune its interaction with TM. Following the successful experimental synthesis of Ni atom doping to GDY monolayer, the CRR activity of double–atom catalysts was evaluated, including homo and hetero metal‐Ni doped on the GDY monolayer (MNi@GDY where M is Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) using the density functional theory calculations. The valence‐electron number of the catalytic center shows a strong positive correlation to the limiting potentials in the volcano plot. NiNi@GDY is the most promising candidate for converting CO2 to produce CH4 with a remarkable low limiting potential of −0.28 V, which is better than Ni@GDY and Ni3@GDY counterparts. NiNi@GDY shows excellent thermal stability and ability to suppress the competing hydrogen evolution reaction, showing its high selectivity to CH4. [ABSTRACT FROM AUTHOR]

Associations between urinary pentosidine, one of the advanced glycation end products in collagen, and the risk of fracture in patients with severe osteoporosis are unknown. In this study, we investigated whether the urinary pentosidine level is associated with the incidence of morphometric vertebral fracture and nonvertebral fracture using data of a randomized, controlled trial, JOINT‐05. JOINT‐05 enrolled Japanese women aged 75 years or older with primary osteoporosis. Patients were randomly assigned (1:1) to receive sequential therapy (teriparatide followed by alendronate) or monotherapy with alendronate for 120 weeks. Incidences of vertebral and nonvertebral fractures were assessed morphologically. During treatment, urinary levels of pentosidine and serum levels of bone turnover markers (osteocalcin, procollagen type I amino‐terminal propeptide, and tartrate‐resistant acid phosphatase 5b) were measured. A total of 967 patients with baseline pentosidine levels were included in the study. Of these, 137 had vertebral fractures, and 42 had nonvertebral fractures. The rate ratios for vertebral fracture for the second (30–39 pmol/mL), third (40–49 pmol/mL), and fourth quartile (≥50 pmol/mL) groups divided by pentosidine level compared with the first quartile (<30 pmol/mL) group were 1.65 (95% confidence interval [CI] 0.99–2.75, p = 0.06), 1.51 (95% CI 0.87–2.61, p = 0.14), and 1.69 (95% CI 1.01–2.83, p = 0.05), respectively. The corresponding rate ratios for nonvertebral fracture were 3.07 (95% CI 0.88–10.70, p = 0.08), 2.34 (95% CI 0.61–8.95, p = 0.22), and 3.95 (95% CI 1.14–13.67, p = 0.03), respectively. The association of the urinary pentosidine level with the incidence of nonvertebral fracture was the strongest among the biomarkers assessed in the study. In conclusion, the urinary pentosidine level was associated with the risk of fracture in patients with severe osteoporosis receiving teriparatide or alendronate. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research. [ABSTRACT FROM AUTHOR]

Acetic acid, CH3C(O)OH, plays an important role in the acidity of the troposphere. The reactions of Criegee intermediates with CH3C(O)OH have been proposed to be a potential source of secondary organic aerosol in the atmosphere. We investigated the detailed mechanism and kinetics of the reaction of the Criegee intermediate CH2OO with CH3C(O)OH. The time-resolved infrared absorption spectra of transient species produced upon irradiation at 308 nm of a flowing mixture of CH2I2/O2/CH3C(O)OH at 298 K were recorded using a step-scan Fourier-transform infrared spectrometer. The decrease in the intensity of the bands of CH2OO was accompanied by the appearance of bands near 886, 971, 1021, 1078, 1160, 1225, 1377, 1402, 1434, and 1777 cm−1, assigned to the absorption of hydroperoxymethyl acetate [CH3C(O)OCH2OOH, HPMA], the hydrogen-transferred adduct of CH2OO and CH3C(O)OH. Two types of conformers of HPMA, an open form and an intramolecularly hydrogen-bonded form, were identified. At a later reaction period, bands of the open-form HPMA became diminished, and new bands appeared at 930, 1045, 1200, 1378, 1792, and 1810 cm−1, assigned to formic acetic anhydride [CH3C(O)OC(O)H, FAA], a dehydrated product of HPMA. The intramolecularly hydrogen-bonded HPMA is more stable. From the temporal profiles of HPMA and FAA, we derived a rate coefficient k = (1.3 ± 0.3) × 10−10 cm3 molecule−1 s−1 for the reaction CH2OO + CH3C(O)OH to form HPMA and a rate coefficient k = 980 ± 40 s−1 for the dehydration of the open-form HPMA to form FAA. Theoretical calculations were performed to elucidate the CH2OO + CH3C(O)OH reaction pathway and to understand the distinct reactivity of these two forms of HPMA. [ABSTRACT FROM AUTHOR]

Single-atom catalysts (SACs) obtained by doping transition metal (TM) atoms into stable monolayers are a promising way to improve the CO2 reduction reaction (CRR) performance. In this work, we theoretically investigated the effect of ligand atoms around the doped TM (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) in ZnO and ZnS for promoting the CRR performance. We found that the ligand atoms around the TM can influence its oxidation state and the electronic properties of the SACs, thus affecting their CRR activity. Due to the smaller charge transfer between the TM and substrate for TM–ZnS compared to TM–ZnO, the TM binding is weaker for the former. In addition, the more negatively charged oxygen ligand atoms in TM–ZnO interact with reaction intermediates, resulting in CRR products with less electron transfer. Pristine ZnS and ZnO monolayers can produce HCOOH but require a high limiting potential (UL) of about −1.2 V. Doping with TMs can reduce UL compared to the pristine surface. At the same time, the ligand can alter the preferred CRR pathway and product selectivity. We found that Mn–ZnS is selective to the CH4 product with a UL of only −0.29 V, which is a nearly 1 V improvement in the UL compared to ZnS. [ABSTRACT FROM AUTHOR]