- About crystalline sodium hydroxogallates
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Two crystalline sodium hydroxogallates 4,5Na2O · Ga2O3 · 13,5 H2O (I) and 5 Na2O · Ga2O3 · 8 H2O (II), as well as a crystalline phase of the composition Na2O · Ga2O3 · 4 H2O · 2NaCl (III) are described. (I) crystallizes from sodium gallate solutions in a wide concentration field; from the X-ray single crystal diffraction analysis [1] results a three dimensional network structure, consisting of monomeric [Ga(OH)6]3- anions connected by NaO6 octahedra groups. Furthermore the structure contains water of crystallization and further hydroxide ions. (I) has to be formulated as nonasodium bis(hexahydroxogallate) trihydroxide hexahydrate Na9[Ga(OH)6]2(OH)3 · 6H2O; it is isotypic with the corresponding sodium hydroxoaluminate [2, 3]. 5 Na2O · Ga2O3 · 8 H2O (II) was obtained from (I) in presence of sodium hydroxide by dehydration over P4O10 in an inert atmosphere (N2) at room temperature. (II) crystallizes tetragonally and is isotypic with Na10[Al(OH)6]2(OH)4 [4]. Accordingly it could be described as a decasodium bis(hexahydroxogallate) tetrahydroxide, Na10[Ga(OH)6]2(OH)4. Na2O · Ga2O3 · 4H2O · 2NaCl (III) was obtained by addition of sodium chloride to sodium gallate solutions. (III) crystallizes also tetragonally and is isotypic with (Na2[Al(OH)4]Cl [5]. Correspondingly, it has to be formulated as disodium tetrahydroxogallate chloride Na2[Ga(OH)4]Cl. The results of 71Ga and 23Na MAS NMR investigations of the compounds (I) to (III) and their thermal behaviour are discussed.
- Loeper,Ge?ner,Müller,Schneider
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- Synthesis of NiGa2O4 octahedron nanocrystal with exposed {111} facets and enhanced efficiency of photocatalytic water splitting
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For the first time, octahedral NiGa2O4 nanocrystals having reactive pH-dependent {111} facets are synthesized through a facile hydrothermal route without using any template or organic surfactant. The {111} facets of octahedral NiGa2O4 display clearly enhanced photocatalytic generation of hydrogen and oxygen from water splitting and good photocatalytic stability. Density functional calculations suggest that mixed statistically occupied Ga/Ni (fourfold- and sixfold-coordinated Ga/Ni) are most likely to be exposed at the (111) surface of NiGa2O4, which is very favorable for enhancing the photocatalytic activities, and the photoelectrochemical properties show that the NiGa2O4 octahedron displays a better photocurrent than NiGa2O4 nanorods with the [100] growth direction. The transient photocurrent decay scan results demonstrate that the NiGa2O4 octahedron exposed {111} facet electrode exhibits a transient decay time of 4 s, whereas this time is only 2 s for NiGa2O4 nanorod electrodes with the [100] growth direction. This longer transient decay time indicates that the charge-carrier recombination rate is lower in the NiGa2O4 octahedron electrode, which will contribute to the enhancement of the photocatalytic activity. The present study also demonstrates that designing nanostructures with the appropriate morphology and surface structures is a feasible approach for enhancing the photoexcited charge-transfer lifetime and developing highly active semiconductor photocatalysts.
- Zhou, Shi-Xiong,Lv, Xiao-Jun,Zhang, Chen,Huang, Xing,Kang, Lei,Lin, Zhe-Shuai,Chen, Yong,Fu, Wen-Fu
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- Energetics of the charge-coupled substitution Si4+ → Na+ + T3+ in the glasses NaTO2-SiO2 (T = Al, Fe, Ga, B)
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Heats of solution in molten 2PbO·B2O3 at 973 K are reported for glasses xNaT3+O2-(1 - x)SiO2 for T = Fe, Ga. These measurements, combined with previous data for T = Al, B, give a relative measure of the enthalpy of the charge-coupled substitution Si4+ → Na+ + T3+. The heats of solution become more endothermic with increasing x for x ≤ 0.5 and exhibit a maximum near x = 0.5. This indicates an exothermic enthalpy for the substitution and an overall stabilization of the glasses.
- De Yoreo,Navrotsky,Dingwell
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- Structural and thermal properties of ternary narrow-gap oxide semiconductor; Wurtzite-derived β-CuGaO2
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The crystal structure of the wurtzite-derived β-CuGaO2 was refined by Rietveld analysis of high-resolution powder diffraction data obtained from synchrotron X-ray radiation. Its structural characteristics are discussed in comparison with the other I-III-VI2 and II-VI oxide semiconductors. The cation and oxygen tetrahedral distortions of the β-CuGaO2 from an ideal wurtzite structure are small. The direct band-gap nature of the β-CuGaO2, unlike β-Ag(Ga,Al)O2, was explained by small cation and oxygen tetrahedral distortions. In terms of the thermal stability, the β-CuGaO2 irreversibly transforms into delafossite α-CuGaO2 at >460 °C in an Ar atmosphere. The transformation enthalpy was approximately -32 kJ mol-1, from differential scanning calorimetry. This value is close to the transformation enthalpy of CoO from the metastable zincblende form to the stable rock-salt form. The monovalent copper in β-CuGaO2 was oxidized to divalent copper in an oxygen atmosphere and transformed into a mixture of CuGa2O4 spinel and CuO at temperatures >350°C. These thermal properties indicate that β-CuGaO2 is stable at ≤300°C in both reducing and oxidizing atmospheres while in its metastable form. Consequently, this material could be of use in optoelectronic devices that do not exceed 300°C.
- Nagatani, Hiraku,Suzuki, Issei,Kita, Masao,Tanaka, Masahiko,Katsuya, Yoshio,Sakata, Osami,Miyoshi, Shogo,Yamaguchi, Shu,Omata, Takahisa
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- New double formates Na3M(HCOO)6 (M = Ga, In) with diamond-like metal framework: Synthesis, structure and coordination modes
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Two new double formates, Na3M(HCOO)6 (M = Ga, In), have been synthesized by using quasi-solvothermal method. Both compounds are isostructural, crystallizing in orthorhombic space group Pccn, with lattice parameters a = 14.6279(5) ?,
- Su, Jie,Wang, Yingxia,Li, Weihong,Yang, Sihai,Li, Guobao,Liao, Fuhui,Lin, Jianhua
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- P -type electrical conduction in α-AgGaO2 delafossite thin films
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Thin films of delafossites of α-AgGa O2 were prepared on α- Al2 O3 (0001) and on Si (100) single crystal substrates by pulsed laser deposition. The films have a band gap of 4.12 eV and a transparency of more than 50% in the visible region. The electrical conductivity at 300 K was 3.2× 10-4 S cm-1. The positive sign of Seebeck coefficient (+70 μV K-1) demonstrated the p -type conduction in the films. Transparent p-n heterojunctions on a glass substrate having a structure glass/ ITOn-ZnOp-AgGa O2 were fabricated. The ratio of forward to reverse current was more than 100 in the range of -2 to +2 V.
- Vanaja,Ajimsha,Asha,Jayaraj
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- γ-Sodium gallate: A rietveld refinement using X-ray powder diffraction
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The synthesis and the structural characterization of γ-sodium gallate was presented. The crystal structure was found to belong to the orthorhombic system and was characterized by a Rietveld refinement of the x-ray powder diffraction pattern. The structure of this compound was similar to the structures exhibited by the γ phases of many tetrahedral oxides.
- Villafuerte-Castrejon, Maria-Elena,Bucio, Lauro,Sanchez-Arjona, Angel,Duque, Julio,Pomes, Ramon
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- Highly selective electrochemical CO2 reduction to CO using a redox-active couple on low-crystallinity mesoporous ZnGa2O4 catalyst
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The substantial overpotential of CO2 activation, the complex CO2 reduction pathway, and the competitive H2 evolution reaction (HER) limit the practical applications of CO2-based electrochemical energy conversion and storage technologies due to their low energy efficiency and product selectivity. Here, we proposed a strategy that combines mesopores and redox-active couple to effectively capture CO2 and selectively generate CO product. As an example, we construct a redox-active couple, Zn2+/Zn+, on the low-crystallinity mesoporous ZnGa2O4 electrocatalyst. The mesopores not only help to capture CO2 effectively but also inhibit the H2 evolution. The weak lattice constraint of low crystallinity benefits the formation of a Zn2+/Zn+ redox couple to strongly interact with CO2 molecule for subsequent activation and catalytic conversion, thus effectively decreasing the activation energy of CO2 to the active species CO2- and accelerating the proton transfer to form the crucial COOH? intermediate. Consequently, this catalyst exhibited a high faradaic efficiency of 96% among Zn-based electrodes for CO generation at the relatively low applied potential of -1.4 V vs. Ag/AgCl (-0.8 V vs. RHE), and excellent stability during 10 h operation in a 0.1 M KHCO3 solution.
- Zhao, Meiming,Gu, Yaliu,Chen, Ping,Xin, Zhenyu,Zhu, Heng,Wang, Bing,Zhu, Kai,Yan, Shicheng,Zou, Zhigang
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- Shape-controlled synthesis and facet-dependent performance of single-crystal Bi25GaO39 photocatalysts
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Single-crystal Bi25GaO39 cubes with exposed {100} facets and Bi25GaO39 tetrahedra with exposed {111} and {112} facets were successfully synthesized through a facile hydrothermal route without using any template or organic surfactant for the first time. The formation process studies indicate that the amounts of NaOH and NaGaO2 play an important role in the nucleation and growth rate of Bi25GaO39 crystals. PL spectra and photoelectrochemical measurements indicate that the separation efficiency of photogenerated electron-hole pairs in Bi25GaO39 tetrahedra is higher than that in Bi25GaO39 cubes. Moreover, Bi25GaO39 tetrahedra exhibited superior photocatalytic activity in comparison with Bi25GaO39 cubes for the degradation of AR1 and 4-NP pollutants, which may be primarily ascribed to the differences in exposed facets.
- Liu, Jin,Lu, Wei,Tian, Boshi,Hu, Bin,Jin, Lin,Shi, Yurong,Li, Lili,Wang, Zhenling
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- Visible light sensitive photocatalyst, delafossite structured α-AgGaO2
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Delafossite structured α-AgGaO2 powder was successfully synthesized through a cation exchange reaction. α-AgGaO2 has a band gap of 2.4 eV, absorbs visible light up to 520 nm, and effectively decomposes 2-propanol to CO2 via acetone by irradiating with either UV light (300-400 nm) or visible light (420-530 nm). The values of the quantum efficiency are similar (ca. 0.6%) under light irradiations with wavelengths of 365, 390, 430, 470, and 510 ± 10 nm, but steeply decrease with wavelengths longer than 530 ± 10 nm, which support a 2.4 eV band gap. In contrast, the other polymorph, β-AgGaO2 powder, which has a band gap of 2.1 eV, shows a negligible activity when irradiating with either UV light or visible light. The higher oxidation activity of α-AgGaO 2 is probably due to its larger band gap, which is formed at the top of its valence band in a lower energy region as compared to β-AgGaO 2. Moreover, the first-principle calculations of α-AgGaO 2 and β-AgGaO2 clearly indicate that α-AgGaO2 has a remarkably larger dispersed valence band as compared to β-AgGaO2, which is advantageous to the photocatalytic activity due to the efficient hole conduction.
- Maruyama, Yoshihiko,Irie, Hiroshi,Hashimoto, Kazuhito
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- GaN crystals prepared through solid-state metathesis reaction from NaGaO2 and BN under high pressure and high temperature
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GaN crystals are successfully obtained through solid-state metathesis (SSM) reaction between sodium gallium oxide (NaGaO2) and boron nitride (BN) under high pressure and high temperature. X-ray diffraction (XRD) pattern indicates that the attained GaN crystals possess a hexagonal wurtzite-type structure. Scanning electron microscopy (SEM) is used to estimate the size and morphology of GaN crystals, and results show that GaN grains with the size over 100 μm can be prepared at 5 GPa and 1600 °C. Moreover, pressure-temperature (P-T) formation region of GaN has been discussed. Our results suggest a promising novel route for synthesizing GaN crystals from SSM reactions under high pressure.
- Ma, Huan,He, Duanwei,Lei, Li,Wang, Shanmin,Chen, Ying,Wang, Haikuo
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- A room-temperature reactive-template route to mesoporous znga 2o4 with improved photocatalytic activity in reduction of co2
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Multimetal mesoporous materials MGa2O4 (M=Zn, Ni, Co) can be synthesized by ionexchange reactions of colloidal mesoporous NaGaO2 (see scheme with TEM images), which acts as both template and precursor, so that a template-removal process can be dispensed with. Copyright
- Yan, Shi Cheng,Ouyang, Shu Xin,Gao, Jun,Yang, Ming,Feng, Jian Yong,Fan, Xiao Xing,Wan, Li Juan,Li, Zhao Sheng,Ye, Jin Hua,Zhou, Yong,Zou, Zhi Gang
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- A porous ZnGaNO photoanode for efficient water oxidation modified by a Co-based electrocatalyst
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Porous ZnGaNO microrods were synthesized by a single crystal internal decomposition route, and exhibited high performance in photoelectrochemical water splitting due to the high specific area and short charge transfer distance of the microstructure. This journal is
- Yan,Zou
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supporting information
p. 3856 - 3861
(2015/03/04)
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- Catalytic reduction of NOx by CO over a Ni-Ga based oxide catalyst
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The removal of nitrogen oxides (NOx) originating from human activities continues to be a challenge for environmental protection due to the lack of an efficient method to capture and convert nitrogen oxides. Here, as a typical example of a bifunctional catalyst, a new low-cost Ni-Ga based oxide catalyst with an inverse spinel structure was developed for NO removal. It exhibits the synergetic catalysis properties of Ni and Ga: strong NO capture properties from the Ni species and applicable NO catalytic conversion from both the Ni and Ga species. The NO removal by the Ni-Ga based catalyst is strongly dependent on the Ga ligand environment. The largely inverse spinel structure with an inversion parameter of 92% and the tetrahedral preference of Ga3+ greatly contribute to the high performance for NO conversion due to the electron transfer occurring easily in the low coordination environment of the Ga ions. The electron transfer process in the Ni-Ga based catalyst can be further activated by Zn doping, increasing the catalytic ability for NO conversion. Our results open up a new route for designing efficient catalysts, combining the strong gas capture properties of a specific element with high catalytic NO conversion properties, by constructing an appropriate element ligand environment.
- Yan, Shicheng,Wu, Zhaochun,Xu, Qian,Wang, Jia Jia,Hong, Jinhua,Li, Jixue,Wang, Peng,Zou, Zhigang
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p. 15133 - 15140
(2016/01/08)
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- Phase transition of NaGaO2 at high pressure and high temperature
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This work presents a comprehensive study on phase transition in NaGaO 2 under high pressure and temperature (PT) conditions. X-ray diffraction (XRD) was used to identify the phase composition of the recovered samples. Our results revealed that NaGaO2 could undergo astructural phase transition from orthorhombic β- NaGaO2 to hexagonal α- NaGaO2 under high pressure and tempera ture. The pressuretemperature phase boundaries of NaGaO2 weredetermined up to 5 GPa and 2073 K. The hexagonal α- NaGaO2 sample recovered from higher pressure and temperature exhibited a highly (003) preferred orientation. Besides, a reversible transition fromα- to β- NaGaO2 was observed above 473 K under no rmal-pressure condition. The high-pressure melting curve of NaGaO2, for the first time, was measured by using in-situ thermal measurement.
- Wang, Kaixue,Kou, Zili,Ma, Huan,Wang, Yanfei,Wang, Shanmin,et al.
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p. 540 - 544
(2012/05/04)
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