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

Enhanced CO evolution for photocatalytic conversion of CO2 by H2O over Ca modified Ga2O3

高効率で二酸化炭素を再資源化する光触媒の合成に成功 --CO2を「ひかり」と「みず」でリサイクル--. 京都大学プレスリリース. 2020-10-14.Artificial photosynthesis is a desirable critical technology for the conversion of CO2 and H2O, which are abundant raw materials, into fuels and chemical feedstocks. Similar to plant photosynthesis, artificial photosynthesis can produce CO, CH3OH, CH4, and preferably higher hydrocarbons from CO2 using H2O as an electron donor and solar light. At present, only insufficient amounts of CO2-reduction products such as CO, CH3OH, and CH4 have been obtained using such a photocatalytic and photoelectrochemical conversion process. Here, we demonstrate that photocatalytic CO2 conversion with a Ag@Cr-decorated mixture of CaGa4O7-loaded Ga2O3 and the CaO photocatalyst leads to a satisfactory CO formation rate (>835 µmol h−1) and excellent selectivity toward CO evolution (95%), with O2 as the stoichiometric oxidation product of H2O. Our photocatalytic system can convert CO2 gas into CO at >1% CO2 conversion (>11531 ppm CO) at ambient temperatures and pressures

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

Dual Ag/Co cocatalyst synergism for the highly effective photocatalytic conversion of CO2 by H2O over Al-SrTiO3

金属ナノ粒子で光触媒のモチベーションを上げることに成功 --人工光合成で二酸化炭素(CO2)の再資源化の新展開--. 京都大学プレスリリース. 2021-03-11.Loading Ag and Co dual cocatalysts on Al-doped SrTiO3 (AgCo/Al-SrTiO3) led to a significantly improved CO-formation rate and extremely high selectivity toward CO evolution (99.8%) using H2O as an electron donor when irradiated with light at wavelengths above 300 nm. Furthermore, the CO-formation rate over AgCo/Al-SrTiO3 (52.7 μmol h−1) was a dozen times higher than that over Ag/Al-SrTiO3 (4.7 μmol h−1). The apparent quantum efficiency for CO evolution over AgCo/Al-SrTiO3 was about 0.03% when photoirradiated at a wavelength at 365 nm, with a CO-evolution selectivity of 98.6% (7.4 μmol h−1). The Ag and Co cocatalysts were found to function as reduction and oxidation sites for promoting the generation of CO and O2, respectively, on the Al-SrTiO3 surface

Parotid salivary secretion induced by stimulation of periodontal regions with toothbrush in humans

The act of brushing teeth induces salivary secretion (1). However, there is no evidence to show which particular regions of the teeth and oral cavity in brushing induces the most effective salivary secretion. We investigated the effects of tooth brushing in different oral regions on parotid salivary secretion in humans. Saliva was collected using a modified Lashley cup. Brushing of the gingival margin was performed according to the Bass method, which may stimulate periodontal mechanoreceptors. The occulsal surface of the molars, gingiva, tongue, and palatal rugae were also brushed with a toothbrush. Compared to the flow rate of saliva from the unstimulated parotid gland, the salivary flow rates were enhanced when every oral region was brushed. The flow rate produced by brushing the palatal gingival margin of the ipsilateral maxillary molars was greater than that produced by brushing the occlusal surface of ipsilateral maxillary molars and palatal gingiva beside the molars. The flow was also significantly greater than that produced by brushing the palatal gingival margins of the contralateral maxillary molars, the maxillary/mandibular incisors, the dorsum of tongue and the palatal rugae. No significant difference was observed between brushing the gingival margins of the ipsilateral maxillary versus mandibular molars. These data indicate that brushing the gingival margin of molars is the most effective region to stimulate parotid saliva secretion. This likely activates periodontal mechanoreceptors, and this technique may be a simple way to improve salivary secretion in oral rehabilitation. The degree of salivary secretion caused by brushing the teeth is specific to particular oral regions. Brushing of the gingival margins is the most effective location to induce parotid salivary secretion

Effects of pilocarpine and cevimeline on Ca2+ mobilization in rat parotid acini and ducts

Previous reports suggested that there is no significant difference in the binding affinity of pilocarpine and cevimeline on muscarinic receptors (1). However, in vivo studies from our laboratory suggested that pilocarpine-induced salivation from the parotid gland is greater than that induced by cevimeline in rats (2, 3). Therefore, in the present study, sialogogue-induced intracellular Ca2+ mobilization was investigated in isolated parotid gland cells in vitro. Pilocarpine and cevimeline increased the intracellular Ca2+ concentration of parotid gland acinar and duct cells over 1 μM in a dose-dependent manner. Pilocarpine-induced responses were higher than cevimeline-induced responses. Ca2+ responses to both agents were completely blocked by 1 μM 4-DAMP, an M3 muscarinic receptor antagonist. In the absence of extracellular Ca2+, both sialogogues induced transient Ca2+ increase in parotid gland acinar cells. These results suggest that the sialogogues stimulate some common routes via the Ca2+ signaling in parotid gland acinar cells. We also report a significant difference of Ca2+ responses in concentration between pilocarpine and cevimeline in parotid gland acinar cells. The different Ca2+ responses between the sialogogues would explain the different saliva volumes from the parotid gland between them that we have observed in previous in vivo studies (2, 3)

Ca2+ mobilization by nicotine through synaptic activation in rat parotid acini

Nicotine has been reported to increase the intracellular Ca2+ concentration ([Ca2+]i) in sublingual acini due to neurotransmitter release from nerve terminals associated with the cell preparation (1). However, it is unclear whether or not the same reaction exists in parotid cells. Therefore, we investigated effect of nicotine on Ca2+ mobilization in digested parotid acini from rats. After removing the parotid gland from Wistar rats, the tissues were minced and digested with collagenase. Then, the intracellular Ca2+ indicator fura-2 was added to the preparation, and the change in [Ca2+]i was monitored using fluorescent microscope. In many but not all parotid acini, K+ stimulation induced transient increases in [Ca2+]i. The K+-induced Ca2+ response in parotid acini was completely blocked by Cd2+-containing solution. These results suggest that the parotid cell preparation has nerve terminals. In all high-K+-sensitive parotid acini, over 3μM of nicotine increased [Ca2+]i, and the response was blocked by a Cd2+-containing solution and nicotinic receptor antagonists. All high-K+-insensitive acinar cells were resistant to the effect of nicotine on Ca2+ mobilization. These results suggest that nicotine induces increases in [Ca2+]i in parotid acini due to neurotransmitter release from associated nerve terminals

Ca2+ mobilization by nicotine through synaptic activation in rat parotid acini

Nicotine has been reported to increase the intracellular Ca2+ concentration ([Ca2+]i) in sublingual acini due to neurotransmitter release from nerve terminals associated with the cell preparation (1). However, it is unclear whether or not the same reaction exists in parotid cells. Therefore, we investigated effect of nicotine on Ca2+ mobilization in digested parotid acini from rats. After removing the parotid gland from Wistar rats, the tissues were minced and digested with collagenase. Then, the intracellular Ca2+ indicator fura-2 was added to the preparation, and the change in [Ca2+]i was monitored using fluorescent microscope. In many but not all parotid acini, K+ stimulation induced transient increases in [Ca2+]i. The K+-induced Ca2+ response in parotid acini was completely blocked by Cd2+-containing solution. These results suggest that the parotid cell preparation has nerve terminals. In all high-K+-sensitive parotid acini, over 3μM of nicotine increased [Ca2+]i, and the response was blocked by a Cd2+-containing solution and nicotinic receptor antagonists. All high-K+-insensitive acinar cells were resistant to the effect of nicotine on Ca2+ mobilization. These results suggest that nicotine induces increases in [Ca2+]i in parotid acini due to neurotransmitter release from associated nerve terminals