Kazumi Kato

Formation and Photocatalytic Application of ZnO Nanotubes Using Aqueous Solution

Vertically aligned ZnO nanotubes were prepared by etching ZnO rod arrays in aqueous solution, which were previously developed by chemical bath deposition method. The morphological, structural, photoluminescence, as well as photocatalytic properties of the ZnO nanotubes were examined with respect to the pH values of chemical bath solution. The morphology of the products was found to be sensitive to the pH values and chemical bath temperatures. The nanotubes synthesized at a low pH value (5.82) exhibited a strong UV emission and a weak defect-related visible emission. The highest photocatalytic efficiency was also observed at pH = 5.82. The possible mechanism for the difference of photocatalytic efficiency was discussed.

In situ growth BaTiO3 nanocubes and their superlattice from an aqueous process

Ordered aggregated BaTiO(3) nanocubes with a narrow size distribution were obtained in an aqueous process by using bis(ammonium lactate) titanium dihydroxide (TALH) as Ti source in the presence of oleic acid and tert-butylamine. Kinetics of the formation of BaTiO(3) nanocubes indicated that an in situ growth mechanism was dominant and the superlattice of nanocubes formed in situ through the growth of BaTiO(3) nanoparticles in Ti-based hydrous gel. The size and morphology of nanocubes were controlled by tuning the concentration and molar ratio of surfactants. A novel growth model dependant on the structure of Ti precursor for the formation and morphology control of BaTiO(3) nanocubes and their superlattice was demonstrated.

Triblock copolymer templated semi-crystalline mesoporous titania films containing emulsion-induced macropores

Triblock copolymer templated synthesis of titania films in water (without ethanol) was demonstrated, which led to the formation of emulsions in the aqueous precursor solutions by adding hydrophobic 1,3,5-triisopropylbenzene (TIPBz). A cubic Im-3m mesoporous anatase film containing emulsion-induced macropores was prepared by spin-coating of an aqueous precursor solution of water-soluble triblock copolymer such as Pluronic F127 through the evaporation-induced self-assembly approach. The addition of TIPBz in the aqueous system also affords pinhole-like macrospaces in the mesostructured film. Expansion of the pinhole-like macrospaces during calcination would offset a tensile stress through shrinkage with the retention of the mesostructure, leading to complete crystallization of the titania framework that is important for effective adsorption of DNA molecules.

Rapid fabrication of mesoporous titania films with controlled macroporosity to improve photocatalytic property.

Hierarchically porous titania films were fabricated by dual templating using a triblock copolymer such as Pluronic F127 and polystyrene (PS) beads, affording mesoporous films with controlled macroporosity. The presence of the triblock copolymer in the precursor solutions suppressed a regular accumulation of spherical PS beads, and PS-derived macropores could be dispersed over the whole mesoporous titania film through rapid fabrication by spin-coating. Some of the macropores were clustered, but the presence of the large spaces was important for keeping the mesostructure after calcination. Photodegradation of methylene blue (MB) was investigated by using the photoactive anatase films. The photodegradation of MB over the porous anatase films was accelerated by effective diffusion of MB molecules in the PS-derived macropores, but it was important for improving photocatalytic performance to regulate the balance between the effectiveness of the diffusion in the macropores and the decrease of the surface area from the embedded macropores, as well as the reduction in the transparency of the porous films.

Ferro- and piezoelectric properties of polar-axis-oriented CaBi4Ti4O15 films

Polar-axis-oriented CaBi4Ti4O15 (CBTi144) films were fabricated on Pt foils using a complex metal alkoxide solution. The 500-nm-thick film showed the columnar structure and consisted of well-developed grains. The a/b-axis orientation of the ferroelectric films is considered to be associated with the preferred orientation of Pt foil. The film showed good ferro- and piezoelectric properties. The Pr and Ec were 25 μC/cm2 and 306 kV/cm, respectively, at an applied voltage of 115 V. The d33 was characterized as 30 pm/V by piezoresponse force microscopy. The values were twice as large as those of the CBTi144 thin film with random orientation. The polar-axis-oriented CBTi144 films would open up possibilities for devices as Pb-free piezoelectric materials.

Piezoresponse properties of orderly assemblies of BaTiO3 and SrTiO3 nanocube single crystals

Orderly assemblies of BaTiO3 (BT) nanocubes, SrTiO3 (ST) nanocubes and BT-ST mixture nanocubes were fabricated on Pt-coated Si substrate directly by solution self-assembly and heated at 850 °C. The dielectric nanocubes aligned face to face in a quite wide region of several tens of square-micrometers with a height of one micrometer, and even inside of the structures was ordered. The piezoresponse of BT-ST mixture assembly showed non-linear curve and stepwise behavior at high poling field, which differed from ferroelectric BT and paraelectric ST nanocube assemblies.

A new effect of ultrasonication on the formation of BaTiO3 nanoparticles

A new effect of ultrasonic irradiation on the formation of BaTiO(3) particles was identified. Ultrasonication caused the aggregation of the original 5-10nm BaTiO(3) particles in the same crystal axis and accelerated the formation of BaTiO(3) particles significantly. Furthermore, narrow size distribution was obtained for the aggregated particles under ultrasonic irradiation.

Micropatterning of ZnO nanoarrays by forced hydrolysis of anhydrous zinc acetate.

Micropatterns of ZnO nanoarrays were simply and successfully fabricated in an aqueous solution without any high-temperature treatment and/or expensive catalyst. In situ forced hydrolysis of patterned anhydrous zinc acetate, derived by ultraviolet irradiation with a photomask, resulted in heterogeneous nucleation and growth to form ZnO nanoarrays. Micropatterns of ZnO nanoarrays were characterized by FE-SEM and XRD. ZnO nanoarrays were well site-selectively deposited on anhydrous zinc acetate coated regions at 88 degrees C. HR-TEM clarified the formation mechanism in which anhydrous zinc acetate showed a tendency of forced hydrolyzation to ZnO nanocrystals at the initial stage in the reaction solution.

Microstructure Control and Dielectric/Piezoelectric Properties of Alkoxy-Derived Ba(Ti,Zr)O3 Thin Films

Lead-free ferroelectric Ba(Ti1-xZrx)O3 (BTZ, x=0.00–0.50) thin films were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates by the chemical solution deposition (CSD) process using complex alkoxide solutions. When the Zr content x was increased, the crystallinity of BTZ thin films was changed from the typical random orientation to the (111) preferred orientation. From the composition dependence of the dielectric constant er and piezoelectric constant d33, the pinching region at room temperature of BTZ thin films consisting of nano-crystals appeared around x=0.20. For the BTZ thin film (x=0.20) fabricated using an alkoxide solution with partial hydrolysis, the grain and crystallite size were increased, and the er and d33 were improved to 253 and 8.9 pm/V, respectively.

Growth of monodispersed SrTiO3 nanocubes by thermohydrolysis method

SrTiO3 nanocubes were synthesized in aqueous solution with Bis (ammonium lactate) titanium dihydroxide (TALH) as the Ti source under hydrazine-assisted hydrothermal condition. The SrTiO3 nanocubes grew from the Ti-based sol through a dissolution-precipitation process and large cubic particles formed through the oriented aggregation of nanocubes over a long time. The morphology, monodispersibility, and size of the nanocubes were controlled through the concentration and ratio of oleic acid and hydrazine.