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Abstract: A facile route was established to synthesize hierarchically structured high specific surface area (122 m2 g−1) TiO2 microspheres (diameter: 0.5–1 μm). In a heated Teflon‐coated stainless‐steel autoclave, titanium tetrabutoxide Ti(OBu)4, arginine, and absolute ethanol were reacted via the solvothermal reaction to generate the TiO2 precursor. The as‐formed precursor solid was further processed at 673 K under air to generate the TiO2 microspheres of nanosheets (thickness: 18 nm). The products were examined as potential anode materials for Li‐ion and Na‐ion batteries. After 100 cycles at 0.1 C (1C=335 mA h g−1), the assembled batteries showed respectable specific capacity 241 mA h g−1 and 145 mA h g−1 for Li‐ion and Na‐ion batteries, respectively. [ABSTRACT FROM AUTHOR]

The influence of heated surfaces and fluids on pool boiling heat transfer was investigated experimentally. As the test specimen, Plain Surface (PS) and Nano-Structured Surface (NSS) were used. As the test fluid, pure water, an aqueous Lithium Bromide (LiBr) solution, and an aqueous Sodium Dodecyl Sulfate (SDS) solution were tested. Under the saturated water and aqueous LiBr solution conditions, the NSS showed a lower Onset of Nucleate Boiling (ONB) and higher Nucleate Boiling Heat Transfer Coefficient (NBHTC) than the PS. On the other hand, under aqueous SDS boiling conditions, the NBHTC was increased on the PS, but decreased on the NSS, as compared with under pure water boiling conditions. It was found that the interaction and combination between the heated surface and fluid can be an important parameter affecting the boiling heat transfer performance, and both the surface tension and surface wettability (i.e., contact angle) should be taken into account. The change of water contact angle induced by the chemical reaction between the heated surface and fluid was examined and discussed. As the test surface, copper PS, titanium PS, and titanium dioxide NSS were prepared. Then, they were boiled under saturated water and butanol conditions for 8 h, and their water contact angles were compared with the fresh (i.e., pre-boiled) surfaces. The water-boiling process remarkably decreased the water contact angles for all surfaces, as compared with the butanol-boiling process. This implies that the chemical reaction between the heated surfaces and boiling fluids affects the surface wettability, which can strongly influence the pool boiling heat transfer performance. [ABSTRACT FROM AUTHOR]

Highly uniform hollow spheres were assembled from truncated rhomboid anatase TiO2 nanoparticles (HS), which were synthesized from the hydrothermal treatment of a NaF solution by using amorphous TiO2 spheres as a precursor and template. The submicron hollow spheres with highly photocatalytic active surfaces exhibited excellent photocatalytic behavior. In this investigation, the factors that enhanced the photocatalytic performance were examined in terms of light harvesting, photoefficiency, and reaction activity. The photocatalytic performance was increased by a factor of approximately 1.5 for the scattering structure of submicron hollow spheres than that of nanofragments of submicron hollow sphere powder. The rate constant of anatase TiO2 with specific photoactive surfaces at {0 0 1} and {1 0 1} was approximately six times higher than that of randomly exposed TiO2 particles. Furthermore, a heterogeneous mixture of the submicron hollow spheres and micro-sized anatase TiO2 (HS@micro-sized TiO2) prohibited electron-hole recombination in the catalyst during the degradation reaction. The rate constant for the heterojunction system was 3.4 times greater than that of the individual constituents. The rate constant for HS@micro-sized TiO2 ( k=0.175 min−1) was 1.8 times larger than that of commercial P25 ( k=0.099 min−1). HS@micro-sized TiO2 is a promising photocatalytic material. [ABSTRACT FROM AUTHOR]

Abstract: In the solution state, photocatalysis of micro- and nano-sized anatases can be optimized at flat band and in a high pH solution, respectively. Furthermore, a remarkable photocatalyst that can be adopted over a wide range of pH values was produced by mixing commercial micro- and nano-sized anatases. Mixing causes the electron transfer between the identical phase but different-sized TiO2 particles, subsequently separating the electrons and holes, as well as greatly facilitating photocatalysis. As is well known, the commercially available photocatalyst P25, a mixture of anatase and rutile, achieves a superior photocatalytic performance from pH 3 to 10, owing to the electron transfer between the various phases. This study elucidates these mixed photocatalysts, P25 and mixture of micro and nano-sized anatases. [Copyright &y& Elsevier]

Abstract: TiCl4 was employed to react with the reactive template Na@AAO, Na inside the channels of anodic aluminum oxide membranes, followed by O2 oxidation at 623K and annealed at 723 and 873K to form one-dimensional nanostructures of TiO2. Free standing polycrystals of anatase TiO2 (diameter=200–400nm, length=60μm) were obtained after the template was removed. [Copyright &y& Elsevier]

In the present experimental study, the pool boiling heat transfer performance was controlled and enhanced through the photo-induced wettability change of titania (TiO 2 ) nanotube arrayed surface (TNAS). The TNAS was analyzed using various spectroscopic techniques such as the scanning electron microscopy (SEM), energy dispersive spectrum (EDS), transmission electron microscopy (TEM), and water contact angle (WCA) measurements. The WCA of TNAS was tuned by the ultraviolet (UV) light irradiation time. The increase in UV light irradiation time to TNAS decreased the WCA. Enhanced wetting of TNAS had strong impact on the boiling heat transfer performance. As the WCA of TNAS decreased, the boiling curve was shifted to the right (i.e., higher wall superheat condition) accompanying critical heat flux (CHF) improvement. Measured CHF results of TNAS in the present study were different from those of plain TiO 2 surface without the special structures tested in some previous reports. This discrepancy could be caused by the nanotube arrayed structures of the present TiO 2 surface. The surface wettability was an important factor to determine the boiling heat transfer of TNAS. The present CHF measurement data were in good agreement with Liaw and Dhir (1989) correlation in the earlier CHF models tested in this work. Based on this study, it was found that the boiling heat transfer can be controlled and enhanced successfully by the photo-induced wettability change of TNAS through the UV light irradiation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Highly uniform hollow-spheres of TiO2 anatase with controllable diameter are synthesized through a self-sacrificing template method. [•] The roughness of hollow spheres could be controlled by NaF concentration. [•] Smaller hollow spheres have better photocatalytic than larger hollow spheres. [•] Each single hollow-sphere has absorption power equivalent to a solid sphere as the shell thickness parameter reaches a critical value, 0.3–0.6. [Copyright &y& Elsevier]

Abstract: TiO2 is one of the most promising photoanodes for solar-hydrogen conversion by water splitting. However, the solar-hydrogen efficiency of TiO2 remains limited because of a low photocurrent generation. A clear understanding of photoexcitations within photoanodes can predict the quantity of photocurrent and consequently determine the solar-hydrogen efficiency. In this work, hydrothermally synthesized rutile TiO2 nanorods were investigated for their photoelectrochemical (PEC) performance. A photogenerated hole concentration of TiO2 photoanode was derived as 8.40 × 1014 cm−3 under one sun illumination. In addition, Fermi level pinning associated with high density of surface states was also observed under PEC operation. Base on these results, a series of band diagrams of TiO2 photoanode were established to describe the photogeneration of holes and current at various bias potential. The main limitation of photocurrent generation is the distribution of surface-trapped states, which determines the hole concentration at the surface and consequently determines the open-circuit potential and the photocurrent density. [Copyright &y& Elsevier]

Highlights: [•] Nano/micro hierarchically structured TiO2 was synthesized by hydrothermal method. [•] Each particle constructed by nano sheets grew radially from the center of the matrix and the thickness gradually decreases. [•] Nano/micro hierarchically structured TiO2 shows superior photocatalytic activity. [•] The EPR spectra and the photo-reduction of AgNO3 demonstrate the excited electrons tend to migrate toward the center of particle. [•] The “cascade effect” is proposed to explain the superior photoactivity of nano/micro hierarchically structured materials. [ABSTRACT FROM AUTHOR]