Jaturong Jitputti

Photocatalytic Activity for Hydrogen Evolution of Electrospun TiO2 Nanofibers

We report herein a simple procedure for the fabrication of TiO2 nanofibers by the combination of electrospinning and sol-gel techniques by using poly(vinylpyrrolidone) (PVP), titanium(IV) butoxide, and acetylacetone in methanol as a spinning solution. TiO2 nanofibers (260-355 nm in diameter), with a bundle of nanofibrils (20-25 nm in diameters) aligned in the fiber direction, or particle-linked structures were obtained from the calcination of as-spun TiO2/PVP composite fibers at temperatures ranging from 300 to 700 degrees C. These nanofibers were utilized as photocatalysts for hydrogen evolution. The nanofiber photocatalyst calcined at 450 degrees C showed the highest activity among the TiO2 nanofibers tested such as ones prepared by the hydrothermal method and anatase nanoparticles (Ishihara ST-01). These results indicate that one-dimensional electrospun nanofibers with highly aligned bundled nanofibrils are beneficial for enhancement of the crystallinity, large surface area, and higher photocatalytic activity.

Synthesis of TiO2 Nanotubes and Its Photocatalytic Activity for H2 Evolution

TiO2-derived nanotubes were prepared by hydrothermal treatment in 10 M NaOH(aq) by using commercially available TiO2 (Degussa P-25) as starting material. N2-adsorption/desorption analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) observations of the obtained product revealed the formation of titanate nanotube structure with its diameter of about 10–20 nm. The effect of post-heat-treatment on the phase structure, morphology, specific surface area and photocatalytic activity was investigated. The TiO2 (B) nanotubes could be observed at post-heat-treatment of 300 °C. As post-heat-treatment was increased to 400 °C, the nanotubes began to transform into nanoparticles of anatase phase, producing a bi-crystalline mixture of TiO2 (B) nanotubes and anatase nanoparticles. Moreover, the particles changed into rutile phase through the post-heat-treatment at higher temperatures over 700 °C. The photocatalytic activity of prepared samples was evaluated with photocatalytic H2 evolution. The results showed that the TiO2-derived nanotubes treated at appropriate temperature exhibited high H2 evolution.

Optical Properties of the Carbon-Modified TiO2 Prepared by Microwave Carbonization Process

The carbon-modified TiO2 were synthesized through microwave carbonization of ethanol by using a domestic microwave oven. This process enabled to form the carbonaceous compounds on the surface of TiO2 and created several new mid-gap bands into the original bandgap within few minutes operation. The sample showed a remarkable visible-light absorption even at the wavelength of around 800 nm. The promotion of photocatalytic activity under visible and ultraviolet (UV) light irradiation were also confirmed by the I3- formation in KI aqueous solution. The I3- formation rate of carbon-modified TiO2 per unit mass under visible light is almost 25 times higher than that of pure TiO2. The mid-gap optical absorption mechanisms were investigated through analysis of absorption edges. It is revealed that surface state change against microwave-treatment time results in different mid-gap optical absorption processes.

Fabrication of Size-controllable Flower-like TiO2 and its Photocatalytic Activity

Size-controllable flower-like titante superstructure was prepared by simple hydrothermal method from amorphous TiO2 sphere precursor without any template. By changing concentration of electrolyte (KCl), the size of amorphous TiO2 sphere precursor could be controlled. N2-sorption analysis, scanning electron microscopy (SEM), and X-ray diffraction (XRD) observation of as-prepared samples revealed the formation of titanate nanosheet structure with high surface area of 350.7 mg. Upon thermal treatment at 500 C, the titanate nanosheets were converted into anatase TiO2 with deformation of their structures. The as-prepared flower-like titanate showed high photocatalytic activity for H2 evolution from water splitting reaction. Moreover, the sample heat treated at 500 C exhibited higher photocatalytic activity than that of commercial TiO2 anatase powder (ST-01).

Photocatalytic Hydrogen Evolution over Tantalate Photocatalysts

Tantalate and titanate photocatalysts were prepared by solid-state reaction at 1273 K using various ratios of SrCO 3 , Ta 2 O 5 , and TiO 2 as starting materials. The prepared solid photocatalysts were characterized using XRD and SEM analysis. These prepared tantalate and titanate photocatalysts showed high photocatalytic H 2 evolution activity by water splitting without co-catalyst loading. The highest H 2 evolution rate of prepared photocatalysts was found to be 138 μmolh −1 with the starting materials ratio of 2/0.5/1.5 (Sr/Ta/Ti; mol). Furthermore, this photocatalyst showed photocatalytic activity for H 2 evolution from distilled water.