RESUMO
A new TeZnO3 phase was synthesized by high-pressure techniques. Different from the ambient-pressure orthorhombic phase composed of ZnO5 units, the current high-pressure one crystallizes to a monoclinic structure with space group P21/ n. Moreover, both ZnO4 tetrahedral and ZnO6 octahedral polyhedra are found to occur in this new phase, providing a unique Zn-based material system that simultaneously possesses two distinct coordinated units. Because the outermost orbitals are fully occupied for both Zn2+ and Te4+, the compound exhibits diamagnetism and strong insulating behavior with a wide bandgap as large as 6.0 eV. Dielectric constant and specific heat measurements show a broad anomaly around 240 K. Low-temperature synchrotron X-ray diffraction reveals an isostructural phase transition at this temperature.
RESUMO
In this work, by taking commercial P25 hydrophilic titanium dioxide (TiO2) as a photocatalyst, the magnetic field effect (MFE) on the photodegradation rate of methyl orange is studied. It is found that a relatively lower magnetic field B = 0.28 T can efficiently enhance the photodegradation efficiency of commercial TiO2 by 24%. However, the photodegradation efficiency of commercial TiO2 will be suppressed slightly by 7% under a magnetic field of 0.5 T. Moreover, such MFE on the photocatalyst is dependent on the settling state of the reaction solution. Additional experiments on the degradation of other pollutants (methylene blue) and with other photocatalysts (g-C3N4) indicate that the MFE is a ubiquitous phenomenon in the photocatalytic degradation process. These observations suggest that the magnetic field can be taken as an efficient strategy to regulate the catalytic process of commercial catalysts and improve the catalytic efficiency.
RESUMO
Rate and product control are crucial for a chemical process and are useful in a wide range of applications. Traditionally, thermodynamic parameters, such as temperature or pressure, have been used to control the chemical reactions. Here, by using the fabrication of a hollow MnxFeyO4 nanostructure as a model system, we report an experimental tuning of both chemical reaction rate and product by a high magnetic field. A 12 times magneto-acceleration of the galvanic replacement (GR) reaction was observed. Moreover, it is first demonstrated that a magnetic field can unravel and accelerate the hidden Kirkendall effect (KE) in addition to the pristine GR reaction. With coaction of magneto-tuned KE and GR, not only the rate but also the composition as well as magnetic property of the products could be modulated. These observations suggest that not only is a magnetic field a variable parameter that cannot be ignored, but also it can effectively control both rate and product in a chemical reaction, which provides a new route for chemical process controlling and shape/composition designing in material synthesis.