Hierarchical anatase TiO(2) porous nanopillars with high crystallinity and stability were fabricated by the following four steps: (i) synthesis of a titanium glycolate nanopillar precursor; (ii) transformation into stable nanopillars consisting of amorphous TiO(2) primary nanoparticles at low temperature; (iii) treatment with ethylenediamine aqueous solution to protect the nanopillar structure, restrain nanoparticle growth and retard phase transformation; (iv) calcination at temperatures as high as 700 degrees C to form hierarchical anatase TiO(2) porous nanopillars. The results of SEM, TEM and XRD reveal that these TiO(2) nanopillars have a porous structure, and that their length can be easily controlled by the volume ratio of ethylene glycol to tetrabutyl titanate. In addition, dye-sensitized solar-cells (DSSCs) were assembled with sandwich-structure photoanodes, which are composed of a layer of TiO(2) nanopillars sandwiched between two layers of TiO(2) nanoparticles. The photoelectrical measurement results show that the power conversion efficiency of DSSCs enhances with the increase of nanopillar length and crystallinity. This is attributed to the effective transfer of photogenerated electrons in TiO(2) nanopillars and their porous microstructures in favor of dye adsorption, as demonstrated by surface photovoltage spectroscopy (SPS) and electrochemical impedance spectroscopy (EIS).
Novel hierarchical bow-like Cu2O crystals were successfully synthesized via a facile room temperature solution reaction using PVP as a structure-directing agent in the presence of NaBH4. The morphology evolution of the hierarchical bow-like Cu2O crystals were observed to be tunable as a function of reaction parameters, such as the reaction time, the quality of PVP and the reaction temperature. The possible growth mechanism of hierarchical bow-like Cu2O crystals was investigated. It involves the formation process of the intermediate octahedra Cu2O crystals and subsequent oxidation–erosion process from octahedra to hierarchical bow-like Cu2O crystals. It was found that the octahedra Cu2O crystals are a necessary intermediate for the formation of the bow-like Cu2O crystals. The prepared hierarchical bow-like Cu2O crystals exhibited a higher photocatalytic activity for photodegradation of rhodamine B aqueous solution under visible light illumination than the other prepared Cu2O crystal samples with different morphologies (nanoparticles and octahedra) because of its large surface area and specific hierarchical bow-like structure.
Ag–Y2O3:Eu3+ composite nanotubes were synthesized by growing Ag nanoparticles on the surface of Y2O3:Eu3+ nanotubes. The effects of the Ag content on the photoluminescence properties of the Ag–Y2O3:Eu3+ composite nanotubes were investigated in detail. In addition to the charge transfer from the 2p orbital of O2− to the 4f orbital of Eu3+, several sharp lines corresponding to the f–f transitions of Eu3+ were also observed in the excitation spectra of the Y2O3:Eu3+ nanotubes monitored at different emission wavelengths. However, only one excitation band centered at 535 nm was observed in the excitation spectrum of Ag–Y2O3:Eu3+ monitored at 590 nm, which is different from that monitored at 614 nm. We suggest that the change in the excitation spectra between Y2O3:Eu3+ and Ag–Y2O3:Eu3+ is attributed to the interaction between Ag and Ag–Y2O3:Eu3+. In particular, the inhomogeneous linewidth of the 5D0 → 7F1 transition from Ag–Y2O3:Eu3+ was observed to broaden when the excitation wavelength was set at 535 nm. Decay dynamics were performed to study the photoluminescence of the Ag–Y2O3:Eu3+ composite nanotubes, and the decay curve can be well fitted with a second order exponential decay function. Moreover, the surface-enhanced Raman scattering effect of the Ag aggregates was evaluated by using 4-aminothiophenol as a Raman probe molecule. It was demonstrated that a high SERS signal can be observed by increasing the Ag : Ln3+ ratios in the Ag–Y2O3:Eu3+ composite nanotubes.
Photocatalytic selective oxidation of benzyl alcohol into benzaldehyde at normal temperature and pressure is one of important topics in the catalysis field. Here, lead-free double perovskite Cs2AgBiBr6 nanocrystal/mesoporous black TiO2 composite was prepared by a vacuum-assisted method, and then they were applied for photocatalytic selective oxidation. The photocatalytic oxidation of benzyl alcohol to benzaldehyde was found to be up to 75% conversion and 99% selection with Cs2AgBiBr6nanocrystal/black TiO2 composite, which was better than that of single Cs2AgBiBr6 nanocrystals and black TiO2, respectively. This was due to the formation of Z-type heterogeneous structure between Cs2AgBiBr6 nanocrystals and black TiO2, which effectively promoted the separation and transfer of electrons and holes, ultimately leading to excellent photocatalytic activity. During the whole catalytic process, the carbon-centered radicals were the key intermediates for the dehydrogenation of benzyl alcohol. This work may provide some practical suggestions for the fabrication of benzyl alcohol selective oxidation photocatalyst.
High entropy alloy/carbon composite is a new type of electromagnetic (EM) absorbing material. Compared with traditional alloys, high entropy alloys have high hardness, high strength, excellent magnetic properties, corrosion resistance, temperature stability and other excellent properties. There are many excellent characteristics of carbon materials, including good stability, a wide range of dielectric properties, and diversity in morphology and microstructure. In this paper, high entropy Pt18Ni26Fe15Co14Cu27 nanoparticles were prepared by a simple high temperature oil phase synthesis method. Then high entropy Pt18Ni26Fe15Co14Cu27 nanoparticles were grown uniformly on the surface of reduced graphene oxide (rGO) to form Pt18Ni26Fe15Co14Cu27/rGO nanocomposites. A series of characterization and performance experiments have been carried out. Compared to pure high entropy Pt18Ni26Fe15Co14Cu27 nanoparticles, the composite exhibits a significantly improved EM absorption performance. In 2~18 GHz band, it exhibits strong reflection loss, which can largely attenuate the EM wave incident to the internal loss. The effective electromagnetic absorption bandwidth is up to 2.5 GHz when the thickness is 2 mm, and the reflection loss is up to -41.8 dB when the thickness is 4 mm. This novel high entropy alloy and graphene composite material is expected to be a potential candidate material with excellent electromagnetic wave absorption properties.
Stable porous TiO2 photocatalysts, with higher photocatalytic activity than Degussa P25, were synthesized via a hydrothermal process using cetyltrimethylammonium bromide as the template, followed by a posttreatment in the presence of ethylenediamine. The photocatalysts were characterized by X-ray diffraction, Raman spectroscopy, N2 adsorption−desorption, transmission electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, and UV−vis diffuse reflectance spectra. The posttreatment considerably increases the thermal stability of the porous framework and inhibits the undesirable grain growth and phase transformation during calcination. The prepared TiO2 photocatalysts have large surface areas of about 205 and 117 m2/g even after calcination at 700 and 800 °C, respectively. The formation mechanism of the stable porous titania was proposed. The high crystallinity, large specific surface area, and heterojunction microstructure between anatase and brookite may be responsible for the high photocatalytic activity in terms of the degradation of organic pollutants such as phenol and rhodamine B under UV irradiation.
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