Model Building of Metal Oxide Surfaces and Vibronic Coupling Density as a Reactivity Index: Regioselectivity of CO2_2 Adsorption on Ag-loaded Ga2_2O3_3

The step-by-step hydrogen-terminated (SSHT) model is proposed as a model for the surfaces of metal oxides. Using this model, it is found that the vibronic coupling density (VCD) can be employed as a reactivity index for surface reactions. As an example, the regioselectivity of CO$_2$ adsorption on the Ag-loaded Ga$_2$O$_3$ photocatalyst surface is investigated based on VCD analysis. The cluster model constructed by the SSHT approach reasonably reflects the electronic structures of the Ga$_2$O$_3$ surface. The geometry of CO$_2$ adsorbed on the Ag-loaded Ga$_2$O$_3$ cluster has a bent structure, which is favorable for its photocatalytic reduction to CO.Comment: 18 pages, 11 figure

Visible-light-assisted selective catalytic reduction of NO with NH[3] on porphyrin derivative-modified TiO[2] photocatalysts

Accepted 16 Sep 2014.Porphyrin-derivative-modified TiO[2] photocatalysts showed high photocatalytic activity for the selective catalytic reduction of NO with NH[3] in the presence of O[2] under visible-light irradiation. Tetra(p-carboxyphenyl)porphyrin (TCPP) was the most effective photosensitizer among the five porphyrin derivatives investigated. NO conversion and N[2] selectivity of 79.0% and 100%, respectively, were achieved at a gas hourly space velocity of 50 000 h[−1]. UV–Vis and photoluminescence spectroscopies revealed the presence of two species of TCPP on the TiO2surface; one was a TCPP monomer and the other was an H-aggregate of the TCPP molecules. It was concluded that the TCPP monomer is an active species for the photo-assisted selective catalytic reduction (photo-SCR). Moreover, an increase in the fraction of H-aggregates with increasing TCPP loading amount resulted in a decrease in the photocatalytic activity of the photo-SCR

Bifunctionality of Rh3+ Modifier on TiO2 and Working Mechanism of Rh3+/TiO2 Photocatalyst under Irradiation of Visible Light

A rhodium(III) ion (Rh3+)-modified TiO2 (Rh3+/TiO2) photocatalyst, prepared by a simple adsorption method and exhibiting high levels of photocatalytic activity in degradation of organic compounds, was investigated by using X-ray absorption fine structure (XAFS) measurements, (photo)electrochemical measurements, double-beam photoacoustic (DB-PA) spectroscopic measurements, and photoluminescence measurements. Based on the results, the features of the Rh3+ modifier and the working mechanism of the Rh3+/TiO2 photocatalyst are discussed. XAFS measurements revealed that the Rh3+ species were highly dispersed and almost atomically isolated on TiO2. The (photo)electrochemical measurements, DB-PA spectroscopic measurements, and photoluminescence showed a unique bifunction of the Rh3+ modifier as a promoter for O2 reductions and an electron injector to the conduction band of TiO2 for response to visible light. The reasons for the Rh3+/TiO2 photocatalyst exhibiting higher levels of photocatalytic activity than those of TiO2 photocatalysts modified with other metal ions are also discussed on the basis of obtained results

Disentangling Cooper-pair formation above Tc from the pseudogap state in the cuprates

The discovery of the pseudogap in the cuprates created significant excitement amongst physicists as it was believed to be a signature of pairing, in some cases well above the room temperature. In this "pre-formed pairs" scenario, the formation of pairs without quantum phase rigidity occurs below T*. These pairs condense and develop phase coherence only below Tc. In contrast, several recent experiments reported that the pseudogap and superconducting states are characterized by two different energy scales, pointing to a scenario, where the two compete. However a number of transport, magnetic, thermodynamic and tunneling spectroscopy experiments consistently detect a signature of phase-fluctuating superconductivity above leaving open the question of whether the pseudogap is caused by pair formation or not. Here we report the discovery of a spectroscopic signature of pair formation and demonstrate that in a region of the phase diagram commonly referred to as the "pseudogap", two distinct states coexist: one that persists to an intermediate temperature Tpair and a second that extends up to T*. The first state is characterized by a doping independent scaling behavior and is due to pairing above Tc, but significantly below T*. The second state is the "proper" pseudogap - characterized by a "checker board" pattern in STM images, the absence of pair formation, and is likely linked to Mott physics of pristine CuO2 planes. Tpair has a universal value around 130-150K even for materials with very different Tc, likely setting limit on highest, attainable Tc in cuprates. The observed universal scaling behavior with respect to Tpair indicates a breakdown of the classical picture of phase fluctuations in the cuprates.Comment: 9 pages, 4 figure

Mg-doped SrTiO₃ photocatalyst with Ag-Co cocatalyst for enhanced selective conversion of CO₂ to CO using H₂O as the electron donor

Photocatalytic conversion of CO₂ by H₂O is a promising method for solving energy and environmental problems. In this context, efficient photocatalysts that facilitate the selective conversion of CO₂ to the value-added chemical CO are essential. In this study, for the first time in the literature, we used an Mg-doped SrTiO₃ photocatalyst (Mg–SrTiO₃) for the photocatalytic conversion of CO₂ to CO using H₂O as the electron donor under monochromatic UV-light irradiation at 365 nm. Compared to pristine SrTiO₃, Mg–SrTiO₃, which was prepared via a flux method, exhibited dramatically enhanced conversion of CO₂ to CO in the presence of an Ag–Co cocatalyst. Moreover, the selectivity toward CO evolution was >99%, which indicates suppression of the unnecessary and competitive H₂ evolution. Scanning electron microscopy of Mg–SrTiO₃ revealed edge-shaved cubic particles, which were correlated to the anisotropic distribution of photogenerated electrons and holes and the consequent enhancement of photocatalytic activity. Furthermore, the Mg-doping temperature and amount used to prepare Mg–SrTiO₃ influenced the substitution of Ti⁴⁺ sites by Mg²⁺ in the bulk of SrTiO₃, thereby affecting the CO evolution. The apparent quantum efficiency of optimal Mg–SrTiO₃ in the photocatalytic conversion of CO₂ was determined to be 0.05%

Surface Modifications of Heterogeneous Photocatalysts for Photocatalytic Conversion of CO₂ by H₂O as the Electron Donor

The photocatalytic conversion of CO₂ using H₂O over heterogeneous photocatalysts has attracted worldwide attention because it enables direct solar-to-chemical energy conversion. However, further development of this technology requires solutions to overcome the low formation rates of CO₂ reduction products and their insufficient selectivity, mainly caused by the rapid charge recombination of photogenerated electron/hole pairs, competition for thermodynamically preferential H₂ evolution from H₂O, and the relatively low concentration of CO₂ on the surface of the photocatalysts. Surface modification of heterogeneous photocatalysts is crucial for improving their formation rates and selectivity. This review article introduces four strategies for designing photocatalyst surfaces for the photocatalytic conversion of CO₂ by H₂O: (I) loading of an Ag cocatalyst, (II) utilisation of cocatalysts for H₂O oxidation, (III) suppression of undesired H₂ evolution, and (IV) loading of basic materials for CO₂ adsorption. The strategies introduced in this review successfully enhanced the formation rates of the products and/or their selectivity in the heterogeneous photocatalytic conversion of CO₂ by H₂O

Persistent Synapse Loss Induced by Repetitive LTD in Developing Rat Hippocampal Neurons

Synaptic pruning is a physiological event that eliminates excessive or inappropriate synapses to form proper synaptic connections during development of neurons. Appropriate synaptic pruning is required for normal neural development. However, the mechanism of synaptic pruning is not fully understood. Strength of synaptic activity under competitive circumstances is thought to act as a selective force for synaptic pruning. Long-term depression (LTD) is a synaptic plasticity showing persistent decreased synaptic efficacy, which is accompanied by morphological changes of dendritic spines including transient retraction. Repetitive induction of LTD has been shown to cause persistent loss of synapses in mature neurons. Here, we show that multiple, but not single, induction of LTD caused a persistent reduction in the number of dendritic synapses in cultured rat developing hippocampal neurons. When LTD was induced in 14 days in vitro cultures by application of (RS)-3,5-dihydroxyphenylglycine (DHPG), a group I metabotropic glutamate receptor (mGluR) agonist, and repeated three times with a one day interval, there was a significant decrease in the number of dendritic synapses. This effect continued up to at least two weeks after the triple LTD induction. The persistent reduction in synapse number occurred in the proximal dendrites, but not the distal dendrites, and was prevented by simultaneous application of the group I/II mGluR antagonist (S)-a-methyl-4-carboxyphenylglycine (MCPG). In conclusion, we found that repetitive LTD induction in developing neurons elicits synaptic pruning and contributes to activity-dependent regulation of synapse number in rat hippocampal neurons

Sugar-Recognizing Ubiquitin Ligases: Action Mechanisms and Physiology

F-box proteins, the substrate recognition subunits of SKP1–CUL1–F-box protein (SCF) E3 ubiquitin ligase complexes, play crucial roles in various cellular events mediated by ubiquitination. Several sugar-recognizing F-box proteins exist in both mammalian and plant cells. Although glycoproteins generally reside outside of cells, or in organelles of the secretory pathway, these lectin-type F-box proteins reside in the nucleocytoplasmic compartment. Mammalian sugar-recognizing F-box proteins commonly bind to the innermost position of N-glycans through a unique small hydrophobic pocket in their loops. Two cytosolic F-box proteins, Fbs1 and Fbs2, recognize high-mannose glycans synthesized in the ER, and SCFFbs1 and SCFFbs2 ubiquitinate excess unassembled or misfolded glycoproteins in the ERAD pathway by recognizing the innermost glycans, which serve as signals for aberrant proteins. On the other hand, endomembrane-bound Fbs3 recognizes complex glycans as well as high-mannose glycans, and SCFFbs3 ubiquitinates exposed glycoproteins in damaged lysosomes fated for elimination by selective autophagy. Plants express stress-inducible lectin-type F-box proteins recognizing a wider range of N- and O-glycans, suggesting that the roles of mammalian and plant lectin-type F-box proteins have diverged over the course of evolution to recognize species-specific targets with distinct functions. These sugar-recognizing F-box proteins interpret glycans in the cytosol as markers of unwanted proteins and organelles, and degrade them via the proteasome or autophagy

Understanding the anomalous thermoelectric behaviour of Fe-V-W-Al based thin films

We have investigated the thermoelectric and thermal behaviour of Fe-V-W-Al based thin films prepared using radio frequency magnetron sputtering technique at different base pressures (0.1 ~ 1.0 X 10-2 Pa) and on different substrates (n, p and undoped Si). Interestingly, at lower base pressure, formation of bcc type of Heusler structure was observed in deposited samples, whereas at higher base pressure, we have noted the development of non-Heusler amorphous structure in these samples. Our findings indicates that the moderately oxidized Fe-V-W-Al amorphous thin film deposited on n-Si substrate, possesses large magnitude of absoulte S ~ 1098 microvolt per kelvin near room temperature, which is almost the double the previously reported value for thin films. Additionally, the power factor indicated enormously large values ~ 33.9 milliwatt per meter per kelvin sqaure near 320 K. The thermal conductivity of the amorphous thin film is also found to be 2.75 watt per meter per kelvin, which is quite lower compared to bulk alloys. As a result, the maximum figure of merit is estimated to be extremely high i.e. ~ 3.9 near 320 K, which is among one of the highest reported values so far. The anomalously large value of Seebeck coefficient and power factor has been ascribed to formation of amorphous structure and composite effect of thin film and substrate

Role of Catalyst Support and Regioselectivity of Molecular Adsorption on a Metal Oxide Surface: NO Reduction on Cu/{\gamma}-alumina

The role of catalyst support and regioselectivity of molecular adsorption on a metal oxide surface is investigated for the NO reduction on a Cu/{\gamma}-alumina heterogeneous catalyst. For the solid surface, computational models of the {\gamma}-alumina surface are constructed based on the Step-by-Step Hydrogen Termination (SSHT) approach. Dangling bonds, which appear by cutting the crystal structure of a model, are terminated stepwise with H atoms until the model has an appropriate energy gap. The obtained SSHT models exhibit the realistic infrared (IR) and ultraviolet-visible (UV/Vis) spectra. Vibronic coupling density (VCD), as a reactivity index, is employed to elucidate the regioselectivity of the Cu adsorption on the {\gamma}-alumina and that of the NO adsorption on the Cu/{\gamma}-alumina in place of the frontier orbital theory that could not provide clear results. We discovered that the highly dispersed Cu atoms are loaded on Lewis-basic O atoms, which is known as anchoring effect, located in the tetrahedral sites of the {\gamma}-alumina surface. The role of the {\gamma}-alumina support is to raise the frontier orbital of the Cu catalyst, which in turn gives rise to the electron back-donation from the Cu/{\gamma}-alumina to NO. In addition, the penetration of the VCD distribution of the Cu/{\gamma}-alumina into the {\gamma}-alumina support indicates that the excessive reaction energies dissipate into the support after the NO adsorption and reduction. In other words, the support plays the role of a heat bath. The NO reduction on the Cu/{\gamma}-alumina proceeds even in an oxidative atmosphere because the Cu-NO bond is strongly bounded compared to the Cu-O2 bond