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.     

Preparation N-F-codoped TiO2 nanorod array by liquid phase deposition as visible light photocatalyst

An efficient method for the preparation of N-F-codoped visible light active TiO₂ nanorod arrays is reported. In the process, simultaneous nitrogen and fluorine doped TiO₂ nanorod arrays on the glass substrates were achieved by liquid phase deposition method using ZnO nanorod arrays as templates with different calcination temperature. The as-prepared samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectra measurements. It was found that calcination temperature is an important factor influencing the microstructure and the amount of N and F in TiO₂ nanorod arrays samples. The visible light photocatalytic properties were investigated using methylene blue (MB) dye as a model system. The results showed that N-F-codoped TiO₂ nanorod arrays sample calcined at 450 °C demonstrated the best visible light activity in all samples, much higher than that of TiO₂ nanoparticles and P25 particles films.     

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.     

Preparation and antibacterial activity of Ag-TiO2 composite film by liquid phase deposition (LPD) method

A liquid phase deposition (LPD) method has been devised for the deposition of Ag-TiO₂ thin films on ceramic tiles with glazed surface at a low temperature. The Ag-TiO₂ thin films obtained were well-adhered, homogenous and coloured by interference of reflected light. The films were characterized by X-ray diffraction and scanning electron microscopy. From these analyses, it was found that silver ions were trapped in TiO₂ matrix and their reduction could be achieved at 600°C annealing temperature. The antibacterial activity against S. aureus and E. coli has been studied applying the so called antibacterial-drop test. The Ag-TiO₂ thin films exhibited a high antibacterial activity. AAS was used for the quantitave determination of silver ion concentration releasing from the Ag-TiO₂ thin film. The releasing rate of silver ions from the Ag-TiO₂ film was 0·118 μg/ml during 192 h. The antibacterial effect of Ag-TiO₂ thin film before and after aging in a weathering chamber for 48 h was compared and the results show that the antibacterial activity is not compromised after weathering.     

液相还原法制备纳米镍粉

为优化纳米镍粉的液相还原法制备工艺,本文以硫酸镍为主盐,水合肼为还原剂,水浴75 ℃条件下,选取产物纯度、产物粒径、反应速率等关键指标开展工艺优化试验,分别研究了NaOH加入量、溶剂种类、有无分散剂,反应物摩尔比,加料顺序五个变量对于镍粉制备的影响.采用XRD和TEM对产物镍粉进行了表征.结果表明,NaOH的加入量影响产物组成,溶剂种类影响产物粒径大小,分散剂对产物的团聚状态有影响,反应物摩尔比以及加料顺序影响体系的反应速率.最终获得如下的优化工艺：NaOH的加入量在0.015~0.02 mol,乙醇和乙二醇做反应溶剂,加入分散剂PVP,反应物摩尔比为4: 1以及采用氢氧化钠与水合肼混合后再向混合溶液中加入硫酸镍溶液的顺序可以获得较为纯净、粒径较小、分散性好的球形纳米镍粉,并且有较快的反应速率.     

Enlargement of diatom frustules pores by hydrofluoric acid etching at room temperature

Based on the fact that SiO₂ can dissolve in HF solution, three kinds of diatom frustules were treated with 1% HF solution at room temperature. Given the proper reaction times (0–2 h for the diatoms Coscinodiscus and Navicula, and 0–3 h for the diatom Melosira), the size of the pores on the frustules gradually increased and the structures of the frustules remained. While HF treatment does not affect the composition, chemical bonds, or photoluminescence signature of the diatom frustules, the treatment reduces their surface areas. This method may be beneficial to diatom studies, diatom nanotechnology, and diatom device applications that make use of diatom pores.     

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.     

Aroused problems in the deposition of diamond-like carbon films by using the liquid phase electrodeposition technique

Hydrogenated diamond-like carbon (DLC) films were prepared by using liquid phase electrodeposition technique. The effects of the applied potential and the carbon sources on the deposition process and film structures were studied. It has been found that the organic liquids with high dielectric constants, small viscosities and the methyl group bonding to the polar group are appropriate carbon sources. The increasing of potential improves the formation of sp³ carbon during the deposition process. In a high electric field, organic molecules are polarized and reacted on the surface of the electrode, turning out DLC and other products. It is believed that the reaction follows a polarization-reaction mechanism.     

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.     

Nanostructures in diatom frustules: functional morphology of valvocopulae in Cocconeidacean monoraphid taxa

Nanopositioning is one of the most intriguing challenges in nanoelectronics and photonics. As the optoelectronic circuit components become more and more complex, the importance of nanopositioning becomes critical. For example, in single-mode fiber telecommunications it is easy to show that an alignment deviation as small as a few tens of nanometers can yield to 50 percent of loss performance. Diatoms are unicellular plants occurring in almost every aquatic environment. Their main morphological character is the frustule, a silica cell wall that consists of two valves, encasing the protoplasm, joined together by a girdle. The girdle is composed of a series of silica bands (copulae) linked together along their margins. In several diatom species, the first girdle bands (valvocopulae), which associate the valves with the rest of the girdle, appear different in shape and bring specific nanostructures devoted to facilitate this linkage. The species of the diatom family Cocconeidaceae show elaborate linkage systems between the valves in which functionally complex valvocopulae are involved. Different levels of complexity and functional efficiency are recognizable in the valve-valvocopula and valvocopula-valvocopula linkages of different cocconeidacean taxa. This work briefly reviews the morphological characteristics and the functional role of the nanostructures involved in the linkages; in fact, we firmly believe that they are stimulating models for design and manufacturing engineers working in the technological nanoworld.     

Preparation of inorganic-organic hybrid films containing particles using electrophoretic deposition method

The composite films of methylsiloxane inorganic-organic hybrid and MoS₂ particles have successfully been fabricated by electrophoretic deposition of MoS₂ particles in a mixed solution of methyl ethyl ketone (MEK) and inorganic-organic hybrid sol. The addition of 20 vol% hybrid sol into a MEK suspension increased the amount of MoS₂ deposition twice as much as that of MoS₂ deposition in MEK alone. The fraction of particles deposited on a substrate in MEK-20 vol% sol was estimated to be much larger than that in MEK. The hydrolyzed methyltriethoxysilane in a hybrid sol modified MoS₂ particles, resulting in lower negative zeta potential, which reduces the repulsion force among particles and makes the incorporation of particles into a deposition film easier. The surface modification also enables the incorporation of particles into a deposit by the interaction of surface modifiers. These factors enhance the incorporation of MoS₂ particles in electrophoretic deposition in MEK-sol.     

Dopamine/TiO2 hybrid thin films prepared by the liquid phase deposition method

Liquid phase deposition method is applied to one-step production of a hybrid material composed by dopamine(DA) and TiO₂ anatase. An optimized amount of the enediol derivative is added to a fluoride titania precursor aqueous solution in order to entrap this modifier within the growing TiO₂, yielding a DA/TiO₂ nanocomposite material. Uniform, well-adhered and brown-colored thin films are deposited on indium tin oxide covered glass substrate. The DA/TiO₂ hybrid material has been characterized by infrared spectroscopy, electronic microscopy, X-ray diffraction and UV-vis spectroscopy. The formation of the hybrid material seems to be reasonably explained by linkage of different TiO₂ nanocrystallites taking advantage of both enediol and amine groups of DA.     

Preparation of titanium dioxide photocatalyst loaded onto activated carbon support using chemical vapor deposition: a review paper

Various methods to prepare and characterize TiO(2) photocatalyst loaded onto activated carbon (AC) support have been developed over the last decade. This photocatalyst has been used in a variety of investigations, i.e. from water decontamination to direct pollutant degradation in aqueous and gas phase systems using UV irradiation and lately with the assistance of ultrasonic sound waves. Chemical vapor deposition (CVD) method is one of the most promising and well-researched methods for deposition of catalysts onto supports. Given its advantage, from an engineering and fundamental aspect, CVD method also has commercial applications. A detailed search of published reports of these investigations was carried out and analyzed in this paper with focus on CVD techniques, activated carbon support and sonication.     

溶胶-凝胶法制备TiO_2-Al_2O_3复合光催化剂及其表征

以钛酸四正丁酯为钛源,异丙醇铝为铝源,采用溶胶-凝胶法制备了TiO2-Al2O3复合光催化剂,考察其对甲基橙的吸附性能和在紫外光照射下的光催化活性。采用X射线衍射(XRD)、X射线光电子能谱(XPS)、傅里叶变换红外光谱(FT-IR)、N2吸附-脱附等对催化剂的晶相结构、化学组成及BET比表面积和孔径分布等进行了表征。结果表明TiO2-Al2O3复合光催化剂由TiO2和Al2O3组成,其中TiO2为单一的锐钛矿晶相,Al2O3为非晶态,Al2O3的存在可抑制TiO2晶粒的生长。在n(Ti)/n(Al)=12,500℃煅烧3h制得的TiO2-Al2O3复合光催化剂比表面积达99.21m2/g,平均孔径为22.39nm,累计孔容积为0.4493cm3/g。在500℃煅烧制得的复合光催化剂具有最佳的光催化活性和吸附性能。与纯TiO2相比,相同条件下TiO2-Al2O3复合光催化剂的光催化活性和吸附性能都有较大提高。     

原位水解低温制备ZnO-TiO2复合半导体光催化剂

以乙二醇作反应物和溶剂，通过原位水解低温晶化法在较温和的条件下制备出纳米复合ZnO-TiO2光催化剂．通过TEM、XR-D、UV-Vis、BET、粒度分析等技术手段对光催化剂进行了表征，发现ZnO-TiO2是由纳米级的ZnO和TiO2粒子组成，该光催化剂分散性好，并且可以吸收部分可见光，扩大了光吸收范围。光催化降解甲基橙实验表明，ZnO-TiO2纳米复合氧化物的光催化活性明显高于自制的TiO2和ZnO单一氧化物和商业P25TiO2．     

CdS-石墨相氮化碳复合光催化剂的制备及其光催化性能

以硫脲和四水合硝酸镉为前驱体,设计了低比例、高比例两种不同石墨相氮化碳（g-C₃N₄）与CdS质量比,以简单的软化学法制备了CdS-g-C₃N₄复合光催化剂,采用SEM、XRD、紫外-可见漫反射光谱（UV-Vis DRS）、FTIR、物理吸附等对CdS-g-C₃N₄复合光催化剂的结构和性能进行表征,并通过NO光催化降解实验探究了CdS-g-C₃N₄复合光催化剂在可见光下的光催化活性。结果表明:低CdS质量比的CdS-g-C₃N₄复合光催化材料中,当CdS与g-C₃N₄质量比为7%时,CdS-g-C₃N₄复合光催化剂的降解效果最好,降解率达31%;低g-C₃N₄质量比的CdS-g-C₃N₄复合光催材料中,当g-C₃N₄与CdS的质量比为5%时,CdS-g-C₃N₄复合光催化剂的降解效果最佳,降解率为36%。CdS与g-C₃N₄质量比为大比例的CdS-g-C₃N₄复合光催化剂中,当CdS与g-C₃N₄的质量比为4:1时,CdS-g-C₃N₄复合光催化剂的降解效率最高,达33%。且g-C₃N₄与CdS质量比为5%的CdS-g-C₃N₄复合光催化剂具有良好的光稳定性,降解效果最佳。      

Preparation of BiFeO3 thin film by the liquid phase deposition (LPD) method on functionalized organic self-assembled monolayers (SAMs)

BiFeO₃ thin films were prepared for the first time on the functionalized self-assembled monolayers (SAMs) by the liquid phase deposition (LPD) method. The measurement of contact angle showed that after the substrate was immersed into octadecyl trichlorosilane (OTS) solution for 30 min, the surface of the substrate was covered with a layer of hydrophobe. The hydrophobe on the substrate was changed into hydrophile after UV irradiation. It was found that the octadecyl trichlorosilane self-assembled monolayers (OTS-SAMs) as chemical templates played an active role in controlling nucleation and growth of BiFeO₃ thin film. The study on the effect of different soaking times showed that the BiFeO₃ thin film was a layer growth model and the optimum deposition time was 12 h.     

电泳沉积法制备钛酸纳米管膜层

采用水热合成法制备钛酸钠纳米管,然后依次与HNO3,正四丁基氢氧化铵水溶液(TBAOH)离子交换后,经过高速离心,将所得沉淀物分散于无水乙醇溶液中,并应用电泳沉积的方法成功地在不锈钢或导电玻璃表面构筑了钛酸纳米管薄膜.采用TEM、XRD、SEM及EDS等对纳米管薄膜的表面形貌、结构和组成等进行表征.结果表明,电泳沉积法制备钛酸纳米管薄膜致密均匀、厚度可控并与基体结合力良好;经高温烧结后,形貌基本保持不变,可望成为一种新的功能材料.文中还对纳米管薄膜的形成机理进行了讨论.     

无电金属沉积法硅纳米线阵列的制备研究

采用无电金属沉积法在硅衬底上制备出了大面积规整的硅纳米线阵列,并对其形貌控制的影响因素和形成机理进行了研究。用扫描电子显微镜(SEM)、X射线衍射仪(XRD)对硅纳米线阵列和相应银枝晶的形貌和结构进行了表征。结果表明,硅纳米线阵列的形貌受水热体系中溶液配比、温度和时间的影响,在温度为50℃、HF和AgNO3浓度分别为4.6和0.02mol/L的条件下,容易得到大面积排列规整的硅纳米线阵列,并且硅纳米线的长度为30～50μm,直径为200nm左右。无电金属沉积法为硅纳米线及其阵列的制备提供了一种设备简单、条件温和的制备方法。