Hidenori Saito

Mesoporous TiO2 Core–Shell Spheres Composed of Nanocrystals with Exposed High-Energy Facets: Facile Synthesis and Formation Mechanism

A facile new method that combines electrospray and hydrothermal treatment is used to prepare mesoporous core-shell TiO(2) spheres with high specific surface areas and high pore volumes. Interestingly, the resulting TiO(2) spheres are composed of anatase TiO(2) nanocrystals with exposed step-like {001} and smooth {010} facets. The percentage of exposed {001} facets can be adjusted by changing the experimental parameters used in the electrospray and hydrothermal treatment processes, such as the contents of poly(N-vinyl-2-pyrrolidone) and acetic acid. The combination of high specific surface area (>100 m(2) g(-1)), high pore volume (>0.30 cm(3) g(-1)), useful pore size (10-15 nm), spherical core-shell structure, and exposed high energy facets makes these TiO(2) spheres an important candidate for use in many photoelectrochemical applications. The formation mechanism of the mesoporous TiO(2) spheres is also studied. The great advantage of this method is that interesting and complicated mesoporous superstructures can be prepared using electrospray technology.

Hierarchical TiO2 spherical nanostructures with tunable pore size, pore volume, and specific surface area: facile preparation and high-photocatalytic performance

Anatase TiO2 hierarchical nanostructural microspheres with tunable pore size, pore volume, and specific surface area were prepared by a facile two-step method of electrospray and hydrothermal treatment. Compared to the calcination, the hydrothermal treatment can transfer the electrosprayed TiO2 microspheres to porous hierarchical nanostructures. Adding ammonia in the hydrothermal process has a great effect on the pore structure of TiO2 microspheres. The hydrothermal-treated samples with >2.0 ml ammonia being added are composed of both big and small nanocrystals. Some of the large nanocrystals grow in the [001] direction and contain step-like {101} surfaces. The large nanoparticles are formed through the combination of small particles by dehydration, which finally leads to the change of TiO2 microspheres from mesoporous to large-porous structure. The effects of the specific surface area, the pore volume, and the pore size on the photocatalytic activity are studied. It is considered that the pores on the surface layer of TiO2 microspheres are like a door that can control the diffusion of reactants between the outside and the inside. If the size of pores on the surface is big enough to allow the fast diffusion of reactants, the photocatalytic activity will increase with the increase of specific surface area and pore volume. In addition, further calcination on the TiO2 spheres after hydrothermal treatment can increase the photocatalytic activity, which is better than the commercial P25.

Performance Evaluation Method of Organic Photovoltaics under Indoor Light Condition

Organic photovoltaics are expected to be suitable for indoor use because they have a relatively high conversion efficiency even at a low irradiance when compared to crystalline silicon photovoltaics. However, the performance measurement procedures of such photovoltaics under indoor light have not been established. In this paper, the illuminance fluctuation of a commercially-available light device originating from an AC power source has been precisely investigated, and the methods to decrease the influence of this fluctuation on the J-V measurements of the photovoltaics were proposed. Furthermore, an LED light irradiation apparatus was developed for more reliable and reproducible J-V measurements of the photovoltaics. This apparatus was found to provide an excellent time stability of illuminance and in-plane uniformity, both of which satisfy the Class A solar simulator permitted by IEC 60904-9. J-V characteristics of the photovoltaics determined by using this apparatus was coincident with that determined by using a commercially-available LED light driven by an AC power source. Finally, it was confirmed that the conversion efficiency of a DSC is greater than that of a Si photovoltaic under the indoor light condition, the illuminance of which is several tens to hundreds lx.