Preparation of photocatalyst using diatom frustules by liquid phase deposition method

We prepared a photocatalyst using diatom frustules by the liquid phase deposition (LPD) method. Purified native frustules were reacted with boric acid (H3BO3) and ammonium hexafluorotitanate ((NH4)2TiF6) in order to cover the frustule surface with a TiO2 film. Scanning electron microscopy (SEM) observation revealed that the nanoporous structures of the frustules and grown TiO2 layers were co-existent after the LPD treatment when the incubation period was 6 and 12 h. Furthermore, photocatalytic activity of the functionalized frustules was clearly proved by the decomposition of methylene blue (MB) molecules. When the incubation periods were 12 and 24 h, reasonable photocatalytic activity was obtained. The results suggested that higher photocatalytic activity was achieved without losing nanoporous structures when the frustules were treated for 12 h by the LPD method.     

Photoluminescence of silica nanostructures from bioreactor culture of marine diatom Nitzschia frustulum

The marine diatom Nitzschia frustulum is a single-celled photosynthetic organism that uses soluble silicon as the substrate to fabricate intricately patterned silica shells called frustules consisting of 200 nm diameter pores in a rectangular array. Controlled photobioreactor cultivation of the N. frustulum cell suspension to silicon starvation induced changes in the nanostructure of the diatom frustule, which in turn imparted blue photoluminescence (PL) to the frustule biosilica. The photoluminescent properties were imbedded within a patterned substrate precisely ordered at the nano, submicron and microscales. The peak PL intensity increased by a factor of 18 from the mid-exponential to late stationary phase of the cultivation cycle, and the peak PL wavelength increased from 440 to 500 nm. TEM analysis revealed that the emergence of blue photoluminescence was associated with the appearance of fine structures on the frustule surface, including 5 nm nanopore arrays lining the base of the frustule pores, which were only observed at the late stationary phase when both silicon consumption and cell division were complete for two photoperiods. Photoluminescence was quenched by thermal annealing of diatom biosilica in air at 800 degrees C for 1.0 hr, commensurate with the loss of silanol (triple bond Si-OH) groups on the diatom biosilica, as confirmed by FT-IR. Consequently, the likely origin of blue photoluminescence in the diatom biosilica was from surface silanol groups and their distribution on the frustule fine structures.     

Controlled nanoporous structures of a marine diatom

We demonstrated chemical etching of a marine diatom shell with 1 N NaOH for controlling the pore size of nanoporous structures of the shell under various conditions. Scanning electron microscopy (SEM) images clearly revealed that the pore size of the diatom shells was regulated in the case of etching at 25 degrees C. In contrast, fluctuations in the etched structures was relatively high even during short periods degradation at 40, 60, and 90 degrees C; therefore, controlled nanoporous structures could not be fabricated. This is the first example of artificial modification of natural diatom shells at the nanoscale although diatom shells have been widely used in industry. In addition, a backbone-like structure was observed during the etching process. The structure was similar to the intermediate structure observed during the primitive stage of the diatom cell growth. Probably, this information is valuable for studying the mechanism of nanoporous structures of diatoms.     

Tin oxide-carbon nanotube composite for NOx sensing

Tin oxide-single wall carbon nanotube (SWCNT) nano composites are synthesized for gas sensor application. The fabrication includes deposition of porous SWCNTs on thermally oxidized SiO2 substrates followed by rheotaxial growth of Sn and thermal oxidation at 300, 400, 500, and 600 degrees C in air. The effects of oxidation temperature on morphology, microstructure, and gas sensing properties are investigated for process optimization. The tin monoxide oxidized at 400 degrees C showed the highest response at the operating temperature of 200 degrees C. Under the optimized test condition, the composite structure showed better response than both structures of SWCNTs and thin film SnO.     

Analysis of nanoindentation response of diatom frustules

Diatom frustules have been suggested for numerous nanotechnological applications. Experimental studies using nanoindenter have shown that the hardness and the stiffness of the frustules vary with location of indentation. To gain further insight, a computational framework has been developed where the Berkovich nanoindentation experiments were simulated by a rigid-deformable contact process. Three different approaches that provide progressively increasing level of understanding of the deformation behavior of frustules were adopted. The differences in the mechanical responses of the frustule due to variation of indentation location, size of pores, and distribution of pores were analyzed. It has been found that the effective stiffness of the frustule is linearly related to the porosity level and does not depend on the frustule size or its pore architecture. It has been shown that a 3D porous shell computational model is more appropriate to simulate the experimentally obtained mechanical response of diatom frustules.     

Electron microscopy of hexagonal boron nitride powder

The morphology and crystalline state of h-BN powder after one-stage or two-stage baking process were investigated extensively. The particles are scale-shaped and the flat surfaces have a (001) habit plane of hexagonal close-packed structure. The side shape of particles after one-stage baking is round, while that after two-stage baking is dodecan, a twelve-faced prism, with the side habit of (100), (110) or their variants. Lattice image observation shows that the side surface of a one-stage baked particle is wavy and thin, while that of a two-stage baked particle is straight and thick. Many particles after one-stage baking are composed of overlapped grains contacting with each other at (001) flat surfaces forming a twist boundary. These grains have relative rotation angles ranging from 5 ° to 26 ° around the common [001] axis and have a coincidence lattice relation with respect to (001) flat planes. X-ray photoelectron spectroscopy analysis shows that both C and O segregate onto the surface of one-stage baked particles, while only C segregates onto the surface of two-stage baked particles. Formation of coincidence lattice grain boundary and impurity segregation both restrict the growth of diameter and thickness in scale-shaped particles. It is concluded that two-stage baked particles, having side surface habits, are stable against various environments.     

Study of surface morphology control and investigation of hexagonal indium nitride nanorods grown on GaN/sapphire substrate

Heteroepitaxial growth of metal-catalyst-free indium nitride (InN) nanorods on GaN/sapphire substrates by radio-frequency metal-organic molecular beam epitaxy (RF-MOMBE) system was investigated. We found that different N/In flow ratios together with the growth temperatures greatly influenced the surface morphology of InN nanorods and their structural properties. The InN nanorods have been characterized in detail using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM). Optical property was evaluated by photoluminescence (PL) measurements. At lower growth temperatures, InN nanorods were successfully grown. A pronounced two-dimensional growth mode was observed at higher growth temperature of 500 degrees C, and these films showed preferred orientation along the c-axis. XRD patterns and SEM images reveal that InN nanorods has high quality wurtzite structure with FWHM approaching 900 arcsec, and they have uniform diameters of about 150 nm and length of about 800 nm. Meanwhile, no metallic droplet was observed at the end of the nanostructured InN, and this is strong evidence that the nanorods are grown via the self-catalyst process. The PL peak at 0.8 eV is attributed to the quantum confinement and Moss-Burstein effects. These observations provide some valuable insights into the physical-chemical process for manufacturing InN nanorods devices.     

Investigation of mechanical properties of diatom frustules using nanoindentation

Diatom frustules have been identified as potential candidate materials for nanotechnology applications. However, for successful engineering applications, their mechanical properties must be fully determined. Toward this end, indentation hardness and elastic properties frustules of the centric diatom Coscinodiscus concinnus were evaluated using nanoindentation. A series of nanoindentation tests were performed on the outer surfaces of frustules at various locations. Analysis of the indentations revealed that the Young's modulus and hardness values appear to be strongly dependent on the location of the indentation. The modulus varied from 0.591 to 2.768 GPa in the center and 0.347 to 2.446 GPa at locations away from the center. Similarly, frustule hardness varied between 0.033 and 0.116 GPa in the center and between 0.076 and 0.12 GPa away from the center. Another series of nanoindentation tests were performed on the frustules (positioned in both concave and convex orientations) at various locations to analyze the failure mode. It was found that the failure modes in each of the orientations were also drastically different. In convex orientation, cracks initiated along the sharp edges of the indentation were followed by circular ring cracks, whereas in concave orientation only cracks along the sharp edges (corresponding to the three edges of the indenter) were revealed. The porosity and the nonplanar nature of the frustules make it difficult to extract the mechanical properties accurately at each location.     

Effects of thermal annealing in oxygen plasma for buffer layers on properties of ZnO thin films

ZnO thin films with ZnO buffer layers were grown by plasma-assisted molecular beam epitaxy (PA-MBE) on p-type Si(100) substrates. Before the growth of the ZnO thin films, the ZnO buffer layers were deposited on the Si substrates for 20 minutes and then annealed at the different substrate temperature ranging from 600 to 800 degrees C in oxygen plasma. The structural and optical properties of the ZnO thin films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and room-temperature (RT) photoluminescence (PL). A narrower full width at half maximum (FWHM) of the XRD spectra for ZnO(002) and a larger grain are observed in the samples with the thermal annealed buffer layers in oxygen plasma, compared to those of the as-grown sample. The surface morphology of the samples is changed from rugged to flat surface. In the PL spectra, near-band edge emission (NBEE) at 3.2 eV (380 nm) and deep-level emission (DLE) around 1.77 to 2.75 eV (700 to 450 nm) are observed. By increasing the annealing temperatures up to 800 degrees C, the PL intensity of the NBEE peak is higher than that of the as-grown sample. These results imply that the structural and optical properties of ZnO thin films are improved by the annealing process.     

Pore architecture of diatom frustules: potential nanostructured membranes for molecular and particle separations

Diatoms produce diverse three-dimensional regular silica structures with nanometer to micrometer dimensions and hold considerable promise for biological and biomimetic fabrication of nanostructured materials and devices. In the present work, we describe the ultrastructural characterization of porous structures in diatom biosilica and discuss their potential as membrane filters for diffusion based separations. The frustules of two centric diatom species, Coscinodiscus sp. and Thalassiosira eccentrica, were investigated using scanning electron microscopy and atomic force microscopy. Their morphological features, including pore size, shape, porosity, and pore organization, are described. We observed that although pore organization in frustules of Thalassiosira eccentrica and Coscinodiscus sp. is in reverse order, a striking commonality is the size range of the smallest pores in both species (around 40 nm). The consensus lower pore size suggests that frustule valves have a common function at this size of excluding viruses or other deleterious particles, and the pore size and organization is optimized for this purpose. We suggest and implement an experimental approach to study the potential of diatom frustules for diffusive separation of molecular or nanoparticular components in microfluidic or lab-on-a-chip environments.     

Key factors influencing the optical detection of biomolecules by their evaporative assembly on diatom frustules

Diatoms have silica frustules with transparent and delicate micro/nano scale structures, multilevel pore arrays, and large specific surface areas. We explored the potential of diatom frustules as biomolecule support for use in optical detection, for example, in protein or DNA biochips and “lab-on-a-chip” sensors. After the solution was evaporated, most particles in the solution assembled on the frustules. Experiments indicated that this phenomenon occurs because of the large specific surface of the frustules; consequently, we studied the capacity of frustules to increase the density of antibodies. The frustules of diatoms Coscinodiscus sp., Navicula sp., and Nitzschia palea were used in this study. The colored particles for optical detection included standard protein, soybean lecithin, bovine serum albumin, and human immunoglobulin G labeled with fluorescein and carbonic black ink. The results showed that the fluorescein isothiocyanate protein was densely assembled on the frustules and exhibited a fluorescence signal that is 2.5 times stronger than that of glass. Compared with the traditional glass substrate, the frustules significantly improved the antibody density and detection signals. The evaporating assembly method was used for measuring the load capacity of frustules for different antibodies; this method can be used to quantitatively bind two or more antibodies to the frustule, which may be valuable in lab-on-a-chip sensors. The design scheme of high-throughput diatom-based biochips was discussed. Through analysis, we hypothesized that diatom frustules with a large specific surface area, high transparency and pore permeability, small sizes and heights, and flat surfaces are particularly suitable for optical detection of biomolecules.     

Structure and photoconductive properties of dip-deposited SnS and SnS2 thin films and their conversion to tin dioxide by annealing in air

SnS and SnS₂ thin films have been prepared by the dip technique. In this technique, a substrate was dipped into an alcoholic solution of the corresponding chloride and thiourea and then withdrawn vertically at a controlled speed, and finally baked in a high temperature furnace at atmospheric condition. XRD and SEM data suggest that good quality SnS and SnS₂ films are obtained at a baking temperature of 300 and 360°C, respectively. Values of band gap for SnS and SnS₂ obtained from spectral response of photoconductivity are 1.4 and 2.4 eV, respectively. The indirect allowed band gap values for SnS₂ film obtained from optical absorption measurements are 1.95 and 2.05 eV. Open-air annealing of both SnS and SnS₂ films at 400°C converts them to transparent conducting SnO₂.     

Corrosion behaviour of copper-reinforced carbon electrodes in dilute hydrochloric acid solutions

The corrosion behaviour of experimentally prepared copper-reinforced carbon electrodes in dilute hydrochloric acid is investigated. The electrodes are not only directly attacked by the acid, but they are also subjected to galvanic corrosion. The baking temperature and time are the most crucial processing variables. A minimum in the corrosion rate is always achieved when the electrodes are baked at 400 °C for 1.5 h, the level depending on the copper content. The corrosion resistance increases progressively with the baking temperature as long as the baking time is less than 1.5 h. Baking for more than 1.5 h results in increasing corrosion rate. The presence of copper increases the corrosion resistance of the prepared electrodes.     

The shape control of ZnO based nanostructures

Tetrapod-shape ZnO nanostructures are formed on Si substrates by vapor phase transportation method. The effects of two important growth parameters, growth temperature and VI/II ratio, are investigated. The growth temperature is varied in the range from 600 degrees C to 900 degrees C to control the vapor pressure of group II-element and the formation process of nanostructures. VI/II ratio was changed by adjusting the flux of carrier gas which affects indirectly the supplying rate of group VI-element. From the scanning electron microscopy (SEM), systematic variation of shape including cluster, rod, wire and tetrapod was observed. ZnO tetrapods, formed at 800 degrees C under the carrier gas flux of 0.5 cc/mm2 min, show considerably uniform shape with 100 nm thick and 1-1.5 microm long legs. Also stoichiometric composition (O/Zn - 1) was observed without any second phase structures. While, the decrease of growth temperature and the increase of carrier gas flux, results in the irregular shaped nanostructures with non-stoichiometric composition. The excellent luminescence properties, strong excitonic UV emission at 3.25 eV without deep level emission, indicate that the high crystalline quality tetrapod structures can be formed at the optimized growth conditions.     

Quasi-Carbon Fibers and the Composites

1. IntroductionDue to their high specific strength and stiffness,polymer matrix composites reinforced with carbonfibers (CF) have been applied in many areas, whereCF plays a great part. The performance and costof CF are greatly relative to the manufacturing processes, in which HTT is a key factor[1'2]. Some applications may require the development of lower-costfibers and composites that have reasonable mechanical integrity yet unique physical or chemical properties. Partially carbonized fi…     

The evolution of advanced mechanical defenses and potential technological applications of diatom shells

Diatoms are unicellular algae with silicified cell walls, which exhibit a high degree of symmetry and complexity. Their diversity is extraordinarily high; estimates suggest that about 10(5) marine and limnic species may exist. Recently, it was shown that diatom frustules are mechanically resilient, statically sophisticated structures made of a tough glass-like composite. Consequently, to break the frustules, predators have to generate large forces and invest large amounts of energy. In addition, they need feeding tools (e.g., mandibles or gastric mills) which are hard, tough, and resilient enough to resist high stress and wear, which are bound to occur when they feed on biomineralized objects such as diatoms or other biomineralized protists. Indeed, many copepods feeding on diatoms possess, in analogy to the enamelcoated teeth of mammals, amazingly complex, silica-laced mandibles. The highly developed adaptations both to protect and to break diatoms indicate that selection pressure is high to optimize material properties and the geometry of the shells to achieve mechanical strength of the overall structure. This paper discusses the mechanical challenges which force the development of mechanical defenses, and the structural components of the diatom frustules which indicate that evolutionary optimization has led to mechanically sophisticated structures. Understanding the diatom frustule from the nanometer scale up to the whole shell will provide new insights to advanced combinations of nanostructured composite ceramic materials and lightweight architecture for technological applications.     

A novel decomposition technique of friable asbestos by CHClF2-decomposed acidic gas

Asbestos was widely used in numerous materials and building products due to their desirable properties. It is, however, well known that asbestos inhalation causes health damage and its inexpensive decomposition technique is necessary to be developed for pollution prevention. We report here an innovative decomposition technique of friable asbestos by acidic gas (HF and HCl) generated from the decomposition of CHClF(2) by the reaction with superheated steam at 800 degrees C. Chrysotile-asbestos fibers were completely decomposed to sellaite and magnesium silicofluoride hexahydrate by the reaction with CHClF(2)-decomposed acidic gas at 150 degrees C for 30 min. At high temperatures beyond 400 degrees C, sellaite and hematite were detected in the decomposed product. In addition, crocidolite containing wastes and amosite containing wastes were decomposed at 500 degrees C and 600 degrees C for 30 min, respectively, by CHClF(2)-decomposed acidic gas. The observation of the reaction products by phase-contrast microscopy (PCM) and scanning electron microscopy (SEM) confirmed that the resulting products did not contain any asbestos.     

Thermal process effect on microstructure and magnetic properties of epitaxial FePd(001) multilayer films

Thermal process effect on the microstructure and magnetic characterizations of epitaxial FePd multilayer films grown on MgO(001) substrates via electron-beam deposition have been investigated. For the FePd films directly grown at 400 degrees C, the isolated island-like morphology was observed and displayed a perpendicular magnetic anisotropy with a large coercivity of 8000 Oe. On the other hand, the FePd films grown at 100 degrees C and then post-annealed at 400 degrees C showed continuous film morphology and with a lower remanence corresponded to the alternate up and down orientations of the magnetization. The significant distinction in magnetic exhibition of the FePd films was due to the remarkable change in surface and magnetic domain structures caused by varied interfacial energy during different thermal processes.     

热处理有机聚合物螺旋纤维制备螺旋炭纤维及其表征

在400～800℃、氩气气氛下对有机聚合物螺旋纤维进行热处理制备螺旋炭纤维,采用SEM、XRD、FT-IR和热分析等手段对其微观形貌和结构组成进行了研究。结果表明,在上述条件下热处理有机聚合物螺旋纤维,其螺旋形貌基本保持不变,而化学成分却发生了变化;随着热处理温度升高,有机螺旋纤维逐渐转变为以石墨结构为主的螺旋炭纤维。     

Superductile,Wavy Silica Nanostructures Inspired by Diatom Algae

Biology implements intriguing structural design principles that allow for attractive mechanical properties—such as high strength, toughness, and extensibility despite being made of weak and brittle constituents, as observed in biomineralized structures. For example, diatom algae contain nanoporous hierarchical silicified shells, called frustules, which provide mechanical protection from predators and virus penetration. These frustules generally have a morphology resembling honeycombs within honeycombs, meshes, or wavy shapes, and are surprisingly tough when compared to bulk silica, which is one of the most brittle materials known. However, the reason for its extreme extensibility has not been explained from a molecular level upwards. By carrying out a series of molecular dynamics simulations with the first principles‐based reactive force field ReaxFF, the mechanical response of the structures is elucidated and correlated with underlying deformation mechanisms. Specifically, it is shown that for wavy silica, unfolding mechanisms are achieved for increasing amplitude and allow for greater ductility of up to 270% strain. This mechanism is reminiscent to the uncoiling of hidden length from proteins that allows for enhanced energy dissipation capacity and, as a result, toughness. We report the development of an analytical continuum model that captures the results from atomistic simulations and can be used in multiscale models to bridge to larger scales. Our results demonstrate that tuning the geometric parameters of amplitude and width in wavy silica nanostructures are beneficial in improving the mechanical properties, including enhanced deformability, effectively overcoming the intrinsic shortcomings of the base material that features extreme brittleness.