Nagahiro Saito

Correlation of Cell Adhesive Behaviors on Superhydrophobic, Superhydrophilic, and Micropatterned Superhydrophobic/Superhydrophilic Surfaces to Their Surface Chemistry

A micropatterned superhydrophobic/superhydrophilic surface was successfully fabricated by plasma CVD and VUV irradiation. Physicochemical properties of the superhydrophobic, superhydrophilic, and superhydrophobic/superhydrophilic surfaces were investigated. The roughness structures on the superhydrophilic surface remained intact compared to those of the superhydrophobic surface. The micropatterned superhydrophobic/superhydrophilic surface was used as a scaffold of cell culture. On the micropatterned surface, the cells attached to the superhydrophilic regions in a highly selective manner, forming circular microarrays of the cells corresponding to the pattern. On the micropatterned surface with pattern distances of 200 microm between superhydrophilic regions, the cells adhered on the superhydrophilic regions and partly extended to the neighboring cells. In contrast, when the pattern distances between the superhydrophilic regions were more than 400 microm, the cells did not extend to the neighboring cells. Cell adhesion behaviors on superhydrophobic and superhydrophilic surfaces were also examined. The cells adhered and proliferated on both superhydrophobic and superhydrophilic surfaces. However, on the superhydrophobic surface, constant contact to facilitate cell division and proliferation was required. On the other hand, the cells easily adhered and proliferated on the superhydrophilic surface immediately after seeding. These differences in cell adhesion behavior induced site-selective cell adhesion on the superhydrophilic regions. Furthermore, protein adsorption behavior that plays an important role in cell adhesion on flat hydrophobic and hydrophilic surface was also examined. The amounts of the protein adsorption on the flat hydrophilic surface were much greater than those on the flat hydrophobic surface.

Exotic shapes of gold nanoparticles synthesized using plasma in aqueous solution

Gold nanoparticles with exotic shapes, such as triangle, pentagon, and hexagon, have been synthesized by glow discharge in aqueous solutions. A pulsed power supply was used to generate discharges in the aqueous solutions. Pulse width and frequency were 2 μs and 15 kHz, respectively. Discharges were generated at applied voltages of 1600 and 3200 V. The shapes of the gold nanoparticles and electron diffraction patterns were observed by transmission electron microscopy. The nanoparticles obtained were about 20 nm in diameter. In particular, at the higher voltage of 3200 V, nanoparticles with anisotropic shapes were synthesized. In the initial stages of synthesis, diameter decreased with discharge time as the nanoparticles redissolved in the solution. After discharge for 25 min, nanoparticles with anisotropic shapes appeared. This discharge led to the generation of H2O2 and a decrease in pH as a result of the consumption of OH radicals during the generation of H2O2 and electron donation of H radicals to the s...

Simple one-step synthesis of fluorine-doped carbon nanoparticles as potential alternative metal-free electrocatalysts for oxygen reduction reaction

Fluorine-doped carbon nanoparticles (FCNPs) were synthesized via a simple one-step solution plasma process for the first time. This synthesis strategy can be achieved at relatively low temperature and atmospheric pressure without the involvement of a metal catalyst. A mixture of toluene (C6H5CH3) and trifluorotoluene (C6H5CF3) was used as a precursor for the synthesis. The fluorine doping content can be varied from 0.95 to 4.52 at%, depending on the precursor mixing ratio. The structural analyses reveal that FCNPs mainly exhibit a disordered amorphous structure. The incorporation of fluorine atoms results in the creation of more defect sites and disordered structure in the carbon particles. The electrocatalytic activity toward the oxygen reduction reaction (ORR) of FCNPs in an alkaline solution shows a significant improvement with increasing fluorine doping content, as reflected in an increased limiting current density and a positively shifted onset potential. In association with X-ray photoelectron spectroscopy (XPS) analysis, an improved ORR activity is possibly attributed to the intercalation of ionic C–F and semi-ionic C–F bonds in the carbon structure. In addition, FCNPs possess excellent long-term operation durability and strong tolerance to methanol oxidation compared to those of a commercial Pt-based catalyst. Our results from this study not only confirm the applicability of the solution plasma process to the synthesis of FCNPs with a controllable fluorine doping level but also provide detailed information of FCNPs as potential alternative ORR catalysts for the electrocatalysis research.

Behavior of Various Organosilicon Molecules in PECVD Processes for Hydrocarbon-Doped Silicon Oxide Films

Plasma diagnosis was performed by means of optical emission spectroscopy in the plasma-enhanced chemical vapor deposition process for preparation of hydrocarbon-doped silicon oxide films. The chemical bonding states were characterized by a fourier-transform infrared spectrometer. Based on the results of the diagnosis in organosilane plasma and the chemical bonding states, a reaction model for the formation process of hydrocarbon-doped silicon oxide films was discussed. From the results of optical emission spectroscopy, we found that the oxygen atoms of methoxy groups in TMMOS molecules can be dissociated easily in the plasma and behave as a kind of oxidizing agent. Siloxane bondings in HMDSO, on the other hand, hardly expel oxygen atoms.

In situ solution plasma synthesis of nitrogen-doped carbon nanoparticles as metal-free electrocatalysts for the oxygen reduction reaction

We report the in situ synthesis of nitrogen-doped carbon nanoparticles (NCNPs) by a solution plasma process without the addition of metal catalysts. Organic liquid mixtures of benzene and pyrazine were used as the precursors for the synthesis. The nitrogen-doping content can be easily controlled by changing the amount of pyrazine in the precursor. The NCNPs synthesized from the solution plasma process exhibit a turbostratic structure with highly uniform nanoscale particles. The nitrogen atoms can be homogeneously incorporated into the entire carbon structure due to the in situ doping during the growth and formation of the carbon particles. The electrochemical activity toward the oxygen reduction reaction (ORR) of the NCNPs in an alkaline medium reveals the improvement in terms of both the onset potential and current density as the nitrogen-doping content increases. The enhanced ORR activity of the NCNPS is mainly attributed to the presence of pyridinic-N and graphitic-N bonding configurations. They also possess long-term durability and excellent tolerance to methanol crossover effects. The results obtained in this study have demonstrated that the solution plasma process has great potential for the synthesis of metal-free nitrogen-doped carbon electrocatalysts for the ORR. We expect that this approach can be extended to the synthesis of other heteroatom-doped carbonaceous materials for a broad range of research applications in energy conversion and storage.

Prediction for thermodynamic function of dioxins for gas phase using semi-empirical molecular orbital method with PM3 Hamiltonian

In this investigation, respective thermodynamic parameters of heats of formation, standard entropy and specific heat capacity at constant pressure for PCDDs, PCDFs, Co-PCB and PCBs as well as polychlorinated-benzenes and polychlorinated-phenols have been evaluated by quantum chemical calculation using a semi-empirical molecular orbital method with the PM3 Hamiltonian and statistical thermodynamic correlation.

Nitrogen-Doped Carbon Nanoparticle–Carbon Nanofiber Composite as an Efficient Metal-Free Cathode Catalyst for Oxygen Reduction Reaction

Metal-free nitrogen-doped carbon materials are currently considered at the forefront of potential alternative cathode catalysts for the oxygen reduction reaction (ORR) in fuel cell technology. Despite numerous efforts in this area over the past decade, rational design and development of a new catalyst system based on nitrogen-doped carbon materials via an innovative approach still present intriguing challenges in ORR catalysis research. Herein, a new kind of nitrogen-doped carbon nanoparticle-carbon nanofiber (NCNP-CNF) composite with highly efficient and stable ORR catalytic activity has been developed via a new approach assisted by a solution plasma process. The integration of NCNPs and CNFs by the solution plasma process can lead to a unique morphological feature and modify physicochemical properties. The NCNP-CNF composite exhibits a significantly enhanced ORR activity through a dominant four-electron pathway in an alkaline solution. The enhancement in ORR activity of NCNP-CNF composite can be attributed to the synergistic effects of good electron transport from highly graphitized CNFs as well as abundance of exposed catalytic sites and meso/macroporosity from NCNPs. More importantly, NCNP-CNF composite reveals excellent long-term durability and high tolerance to methanol crossover compared with those of a commercial 20 wt % supported on Vulcan XC-72. We expect that NCNP-CNF composite prepared by this synthetic approach can be a promising metal-free cathode catalyst candidate for ORR in fuel cells and metal-air batteries.

Fabrication and characterization of ultra-water-repellent alumina-silica composite films

Ultra-water-repellent (UWR) films were prepared by microwave plasma-enhanced chemical vapour deposition using trimethylmethoxysilane and aluminium (III) diisopropoxide ethylacetoacetate (ADE) as raw materials. The film was mainly composed of silica and alumina and was apparently transparent. The film thickness was approximately 500 nm. The sample surface was treated with an organosilane in order to introduce hydrophobic groups. The hydrophobic modification led to a water contact angle of more than 150°, whose value corresponds to the UWR surface. The hardness of film with an optimized Al content was significantly improved compared with that without Al. The maximum hardness was 1.71 GPa. In consequence, we successfully prepared an UWR film in the silica–alumina system.

Fabrication of vertically aligned diamond whiskers from highly boron-doped diamond by oxygen plasma etching.

Conductive diamond whiskers were fabricated by maskless oxygen plasma etching on highly boron-doped diamond substrates. The effects of the etching conditions and the boron concentration in diamond on the whisker morphology and overall substrate coverage were investigated. High boron-doping levels (greater than 8.4 × 10(20) cm(-3)) are crucial for the formation of the nanosized, densely packed whiskers with diameter of ca. 20 nm, length of ca. 200 nm, and density of ca. 3.8 × 10(10) cm(-2) under optimal oxygen plasma etching conditions (10 min at a chamber pressure of 20 Pa). Confocal Raman mapping and scanning electron microscopy illustrate that the boron distribution in the diamond surface region is consistent with the distribution of whisker sites. The boron dopant atoms in the diamond appear to lead to the initial fine column formation. This simple method could provide a facile, cost-effective means for the preparation of conductive nanostructured diamond materials for electrochemical applications as well as electron emission devices.

Origin of N 1s spectrum in amorphous carbon nitride obtained by X-ray photoelectron spectroscopy

This paper focuses on determining a reasonable peak assignment for the N 1s spectrum of amorphous carbon nitride (a-CN) measured by X-ray photoelectron spectroscopy (XPS). Unfortunately, several peaks of a-CN have not been identified, that is, there has yet to be any shared understanding of their chemical bonding states. We investigated this by monitoring changes in spectra before and after vacuum ultraviolet (VUV) irradiation, thus obtaining information about the changes of chemical bonds. The observed changes were discussed based on the chemical shifts of components of a-CN determined from ab-initio molecular orbital (MO) calculations. We have proposed the following peak assignment for N 1s. The peaks located at approximately (1) 397.6, (2) 398.2, (3) 399.0, (4) 400.0, (5) 400.9 and (6) 401.9 eV were assigned to the chemical bonding states of (1) β-C3N4, (2) pyridine, (3) formonitril, (4) methylmethyleneamine, (5) pyrido[2,1,6-de]quinolizine, and (6) a nitroso group. This assignment did not agree with oft-quoted ones. However, only this peak assignment provides a reasonable interpretation for the changes we observed in a-CN introduced by VUV irradiation, and allows us to understand the chemical bonding states of a-CN film.