Ichiro Tanabe

Fabrication of a highly sensitive surface-enhanced Raman scattering substrate for monitoring the catalytic degradation of organic pollutants

In this paper, we demonstrate a simple and reliable two-step strategy based on an electrospinning technique combined with in situ calcination for the fabrication of ZnO nanofibers deposited on a silver foil surface. These nanofibers are used as a novel sensitive surface-enhanced Raman scattering (SERS) substrate. The strong interactions between ZnO nanofibers and silver foil afford continuous delocalized surface plasmons, resulting in localization of the electric field at the gap between the ZnO nanofibers and silver foil; thus, the exciton–plasmon interactions between ZnO nanofibers and the silver foil surface contribute to the enhanced scattering, generating a large electromagnetic field enhancement. In addition, the ZnO nanofibers deposited on the silver foil surface exhibit enhanced photocatalytic activity toward the degradation of organic pollutants because of the charge separation effect and increase in the lifetime of the photogenerated excitons under ultraviolet light irradiation; thus, this new substrate can be used as a SERS substrate for determining the catalytic activity and reaction kinetics during the photodegradation of organic pollutants.

The effects of Au nanoparticle size (5–60 nm) and shape (sphere, rod, cube) over electronic states and photocatalytic activities of TiO2 studied by far- and deep-ultraviolet spectroscopy

Absorption spectra of anatase and rutile TiO2 modified with various sizes of Au nanospheres (5–60 nm) in the 150–300 nm region were measured by using attenuated total reflection spectroscopy. The smaller Au nanospheres induced larger spectral changes, which mean larger electronic state changes and higher charge-separation efficiency enhancements. In fact, TiO2 with the smaller Au nanospheres showed the higher photocatalytic activities. In contrast, although Au nanorods with various aspect ratios or Au nanocubes were deposited instead of Au nanospheres on TiO2, their spectra (i.e. electronic states) were not significantly changed. Therefore, it was revealed that while there was little shape dependence, the smaller Au nanoparticles induced the larger electronic state change. This may be due to the difference in the potential gradient generated in the interfacial region between TiO2 and the metal, and the smaller Au nanoparticle deposition leads to the higher photocatalytic activities.

Nanoporous silver microstructure for single particle surface-enhanced Raman scattering spectroscopy

The potential of a nanoporous Ag microstructure (np-AgMs) for use as a single particle for surface-enhanced Raman scattering spectroscopy (SERS), with the added advantages of being easy to manipulate and reusable, was successfully demonstrated. The np-AgMs with interconnected pore and controllable pore size were fabricated from symmetric hexapod AgCl via a galvanic replacement reaction in NaCl solution with zinc (Zn) as the sacrificed metal. The clean surface of np-AgMs enables rapid surface functionalization with easy handling and sample preparation as no particle aggregation occurs. The SERS acquisition spots on the np-AgMs can be visually selected using a normal Raman microscope. SERS spectra of p-aminothiophenol (PATP) with a concentration range of 10−8–10−3 M can be achieved. The position-dependent enhancement of np-AgMs was expendably evaluated. The signal-position correlation was confirmed by electric filed enhancement obtained from Finite-difference time-domain (FDTD) calculation. In addition, the highly stable substrate showed insignificant loss of the enhanced Raman signal after several cycles of chemical re-generation. Finally, the potential application of np-AgMs in label-free detection of biomolecules including hemoprotein, protein without chromophore and DNA strains at low concentration of 500 μg mL−1 was demonstrated.

Far- and Deep-UV Spectroscopy of Semiconductor Nanoparticles Measured Based on Attenuated Total Reflectance spectroscopy.

Far- and deep-ultraviolet spectra (150-300 nm) of semiconductor nanoparticles (zinc oxide and zinc sulfide) are successfully measured by using attenuated total reflectance (ATR) spectroscopy, and analyzed using finite-difference time-domain (FDTD) simulations. The obtained spectra show good consistency with earlier synchrotron-radiation spectra and with theoretical calculations. The FDTD simulation results show that the present system collected the correct spectra. In the present system, the obtained spectra are affected by the real part n of the complex refractive index more strongly than the imaginary part k. It is also revealed both experimentally and theoretically that spectral intensities of the semiconductor nanoparticles are approximately one tenth those of liquid samples. These results provide insights into the far- and deep-ultraviolet spectroscopy based on the ATR system, and show the general applicability of our original ATR spectroscopy to semiconductor nanoparticles. The system needs neither high vacuum nor much space, and enables rapid and systematic investigation of the electronic states of various materials.

Microspectroscopy – Promising Techniques to Characterize Phosphorus in Soil

ABSTRACT Phosphorus (P) is an essential element for all forms of life and is applied as fertilizer in agriculture. The P availability for plants may be highly dependent on the chemical state of P in fertilizers and soils; however, the nature of this dependence remains obscure due to the limitations of generally applied wet chemical and instrumental analytical approaches. This paper focuses on recently developed infrared, Raman, ultraviolet and X-ray microspectroscopic techniques for the characterization of P in soil. Microspectroscopic techniques have the advantage that discrete P phases can be distinguished and characterized even if their mass fractions are very low. However, only small volumes of soil can be analyzed by microspectroscopic methods hence a combination of macro- and microspectroscopic techniques is a promising concept.

Electronic Structure of TiO2 Studied by Far-Ultraviolet and Deep-Ultraviolet Spectroscopy

The electronic structure and photocatalytic activities of TiO2 and metal-nanoparticle-modified TiO2 were investigated by far-ultraviolet and deep-ultraviolet spectroscopy and photodegradation reaction of methylene blue. First, spectra of naked anatase TiO2 (Sect. 6.2) and metal (Au, Pd, Pt)-nanoparticle-modified TiO2 (Sect. 6.3) were measured. The naked TiO2 spectrum corresponded well with the previously reported reflection spectrum and theoretical calculations. Then, the deposition of metal nanoparticles substantially changed the spectral shape, which indicates changes in the electronic states of TiO2, and the degree of spectral changes strongly depends on the work function of the modified metal. In addition, consistent changes of photocatalytic activities were also observed. Next, two crystalline types of TiO2 (anatase and rutile) were compared (Sect. 6.4), and a larger enhancement of the photocatalytic activity of rutile TiO2 upon Pt nanoparticle deposition was revealed. Subsequently, size effects of modified Au nanoparticle on electronic structures and photocatalytic activities of TiO2 were discussed (Sect. 6.5), and it was made clear that the smaller Au nanoparticle induced the larger electronic-state changes and the higher photocatalytic-activity enhancements. These results demonstrated that the novel far-ultraviolet and deep-ultraviolet spectroscopy is a considerable promising method to investigate the electronic states of materials, leading to the development of high-efficiency optical materials such as photocatalysts and solar cells.

Imaging of Hydrophilicity and its Inhomogeneity on a Titanium Dioxide Film Exposed to Ultraviolet Irradiation Using a Newly Developed Near-Infrared Camera

This study has investigated hydrophilicity changes and their inhomogeneity of TiO2 films on Pyrex glasses by near-infrared (NIR) spectral imaging. Near-infrared spectra of TiO2 films in the 9000–4000 cm−1 region were measured using a newly developed NIR camera named Compovision. A band in the 5400–4800 cm−1 region, which is assigned to a combination (v2 + v3) mode of bending (v2) and antisymmetric stretching (v3) modes of the H2O molecule, was clearly identified and its intensity increased with time in the air. It is interesting that the increased rate rose with ultraviolet (UV) light irradiation (300–400 nm, 1 mW cm−2) compared to without UV light irradiation. This result suggested that the hydrophilicity of TiO2 was enhanced about twice upon the UV light irradiation. Moreover, the NIR images clarified spatial distributions of the hydrophilicity on the TiO2 surface with a significantly wide area (20 × 40 mm) and a high speed (within 5 s for one image). This rapid imaging system enabled us to detect the hydrophilicity change during only 1 min. The potential of this camera is quite superior, not only for basic research, but also for diverse industrial applications.