H 2 evolution through photocatalysis possesses has the advantage for achieving the carbon neutral, that relies on the highly efficient catalysts. Non-noble metals have lower prices than noble metals, which is beneficial for their large-scale applications in industry. In this paper, functionalized CuNi alloy and BaTi 4 O 9 (BTO) composite (Cu x Ni y /BTO(Z)) photocatalyst were synthesized successfully through hydrothermal calcination method. The acetates were selected the raw material to avoid the use of hazardous chemicals and pollution of photocatalysts by other elements, while also providing C=O for the photocatalyst to further enhance its photocatalytic activity. Under visible light irradiation, the photocatalytic hydrogen (H 2 ) evolution rate of Cu 3 Ni/BTO is 184.14 μmol·g −1 ·h −1 , which is 101.18 times that of pure BTO (1.82 μmol·g −1 ·h −1 ) under the same conditions. Combining density functional theory (DFT) calculations and experimental studies, it is concluded that electronic structural characteristics of BaTi 4 O 9 and the addition of CuNi alloy could provide more electrons and improve the photocatalytic H 2 evolution activity.
In recent years, photocatalytic H2 evolution technology has been one of the hot topics to solve the energy crisis. The Cu3Ni/BaTi4O9 composite through hydrothermal and calcination treatment could provide photoelectrons under light irradiation, intriguing the hydrogen (H2) from water molecules. While pursuing a narrow band gap of such materials cannot rely on a simple composite, a chemical bonding contribution is expected to improve the photoexcited electrons by doping the heteroatoms. In this work, boron (B) doping was used to regulate the electronic structure of BaTi4O9 (BTO) and reduce its band gap. Simultaneously, the influence of calcination temperature on the structure and performance of catalysts was explored according to physical characterizations. Due to this, the B(3)-Cu3Ni/BTO photocatalyst possessed macropores with 1–2 μm diameter and abundant mesopores. Under visible light irradiation, the photocatalytic H2 evolution rate reached 318.06 μmol g–1 h–1 at a B doping level of 3%, as determined by gas chromatography analysis. It is 1.73 times that of the undoped B composite catalyst (184.14 μmol g–1 h–1) under the same conditions. Combining density functional theory calculations and experimental studies, it is confirmed that the B-doped form mainly exists in the form of Ti–O–B in BaTi4O9, reducing its band gap value and improving photocatalytic hydrogen evolution activity.
Jie Zhang,Zhenxing Yue,Yu Luo,Xiaohua Zhang,Longtu Li
Relaxation phenomena in dielectrics are well known to be closely related to their defect chemistry. However, the relaxation behavior of microwave dielectrics has seldom been considered, despite these materials being an important member of the electroceramic family. Here, the relaxation behavior of the typical microwave dielectric ceramic barium tetratitanate (BaTi 4 O 9 ) was investigated. Significant thermally stimulated relaxation was observed in both dielectric spectroscopy and thermally stimulated depolarization current (TSDC) measurements, and the correlation between relaxation and defect behavior was addressed. TSDC characterization revealed that defect dipoles [(Ti Ti ' )−(V O •• )] with activation energies ( E a ) of 0.32–0.36 eV appeared at low temperature, while in-grain and across-grain boundary oxygen vacancies (V O •• ) appeared at higher temperature, yielding E a of 0.30–0.48 eV and 0.65–1.01 eV, respectively. It was further believed that these two types of defects, (Ti Ti ' )−(V O •• ) and V O •• , were correspondingly responsible for the dielectric relaxation observed at low and high temperature. The relaxation behavior of several typical Ti-containing microwave dielectrics, such as BaTi 4 O 9 , TiO 2 , MgTiO 3 and Ca 0.8 Sr 0.2 TiO 3 , was compared, which suggests that microwave dielectric performance and defect behavior are closely related to the connections of TiO 6 octahedra in the materials.
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