Fabrication of mesoporous titania membrane of dual-pore system and its photocatalytic activity and dye-sensitized solar cell performance

We report the fabrication of a novel titania membrane of the dual-pore system that is strategically designed and prepared by a two-step replication process and sol-gel reaction. The primary nanoporous channel structure is fabricated by the cage-like PMMA template (CPT) obtained from the nanoporous alumina membrane and the secondary mesoporous structure is formed by the sol-gel reaction of the lyotropic precursor solution within the CPT. Furthermore the mesoporous titania membrane (MTM) frame consists of the titania nanoparticles of 10-12?nm in diameter. Morphology and structural properties of the MTM are investigated by field emission scanning electron microscopy, high resolution transmission electron microscopy, x-ray diffraction and Brunauer-Emmett-Teller surface area. The photocatalytic activity and the solar energy properties of the MTM are characterized by UV-vis spectrophotometer, spectrofluorometer and photoinduced I-V measurement. The photocatalytic test indicates that the MTM has higher efficiency than the commercial P25 with a good recyclability due to its large-scale membrane style and the preliminary result on the solar cell application shows a solar energy conversion efficiency of 3.35% for the dye-sensitized solar cell utilizing the MTM.     

Properties and catalytic activity of NOx reduction of alumina-titania catalysts prepared by sol-gel method

The alumina-titania catalysts were prepared from various alumina and titania sources by sol-gel method, which were metal alkoxide and metal alkoxide modified with organic groups. Specific surface area, pore size distribution, solid acidity and catalytic activity of NO reduction for the alumina-titania catalysts depended on the alumina and titania sources. The alumina-titania catalyst prepared from metal alkoxide for alumina source and metal alkoxide modified with organic groups for titania source exhibited higher activity of NO reduction than the other alumina-titania catalysts. Catalytic activity of NO reduction for the alumina-titania catalysts depended on specific surface area and solid acidity. It was suggested that solid acidity of the alumina-titania catalysts depended on the coordination structure of Al atoms and the homogeneity of alumina and titania components.     

纳米介孔氧化铝的制备工艺及性能

分别采用碳黑和十六烷基三乙基溴化铵作为模板剂,硝酸铝为前驱体,用溶胶-凝胶法合成介孔氧化铝.通过N2吸附一脱附、TG-DSC等测试手段对样品进行了对比分析表征.考察了两种不同模板剂对其晶体结构、比表面及孔径大小的影响.实验结果表明,相对于十六烷基三甲基溴化铵或碳黑做模板剂,采用十六烷基三甲基溴化铵和碳黑组成的复合模板剂可以合成较大的比表面积、孔径和孔容(分别为370m2/g、6.5nm和1.54cm3/g)的介孔氧化铝,而且具有较窄的孔径分布.     

Estimation of Pore Charge on Zirconia Membrane Prepared by Sol-gel Route Using Zeta Potential Measurement

Zirconia membrane was prepared in the sol-gel process by filtering viscous colloidal zirconia sol through microporous alumina support and gelling followed by sintering at 743 K. The scanning electron micrograph show that mean pore size was 543 nm and pore density was 1.47×107/cm2.The filtration characteristics during membrane layer formation showed that the membrane layer formation started after 40 min. The membrane layer thickness and the porosity of the membrane were determined gravimetrically by finding out the amount of water present in the pores. The membrane layer thickness was found to be 3 micron and the porosity was found out to be 0.38. The pore charge density was estimated from the particle charge density, pore density, pore diameter and the thickness of the membrane layer.     

硼掺杂的γ-A12O3催化膜的制备及其热稳定性的研究

在勃姆石AlOOH溶胶中引入一定量的H2BO3溶液,经不同温度的热处理,制成不同硼掺杂含量的无支撑的γ-A12O3催化膜。用XRD、BET分别对膜的晶相和膜的微孔结构,包括比表面积、孔径和孔容进行了研究,结果发现：随着硼含量的增加,在低温下,膜的比表面积和孔容都不断增加,而对孔径的影响不大;经1200℃处理后,未掺杂硼的膜的比表面积,孔径和孔容分别为5.4m2/g,49nm和0.063cm3/g,而经掺杂16％摩尔硼的膜的比表面积,孔径和孔容分别为35m2/g,13nm和0.225cm3/g,这说明硼的掺杂对γ-A12O3膜的热稳定性有很好的改善作用。     

Mesoporous titania films with adjustable pore size coated on stainless steel substrates

Mesoporous layers of titania were prepared on stainless steel substrates of defined roughness by dip coating. Ordered arrays of micelles formed from amphiphilic block copolymers served as pore templates during film drying. Coating of the precursors solution on freshly grinded steel resulted in extensively fractured films with severely distorted templated porosity. In contrast, films produced on precalcined steel showed good integrity, high substrate coverage and narrow pore size distribution with pores interconnected and ordered in a short range. This difference in film quality and morphology was ascribed to the reaction between template polymers and metal ions leached from the steel of grinded substrate surfaces. Films were ca. 700 nm thick and composed of nanocrystalline titania. The pore size of titania coatings was varied between 5 and 16 nm employing polymer templates of different structure and molecular weight.     

Vertically Oriented Titania Nanotubes Prepared by Anodic Oxidation on Si Substrates

Vertically oriented titania nanotube arrays were fabricated by anodization of titanium film deposited on silicon substrates under different processing conditions. The anodic formation of nanoporous titania on silicon substrate was investigated in aqueous solutions mixed with highly corrosive Na₂SO₄/NaF/citric acid. In the result of the anodization of titanium film deposited at room temperature, a very thin layer of ~70 nm having a worm-like structure was grown on the top of the porous layer. But, in the case of titanium film deposited at 500deg, vertically oriented TiO₂ nanotube arrays were formed. The average tube outer diameter of the nanotube was 74 nm to 100 nm. The longest nanotube of 681 mum was obtained at 15 V and 30 min. The current density transient curve recorded during anodization under a constant voltage showed a typical behavior for self-organized pore formation.     

纳米多孔SiO2/PI杂化薄膜的制备与性能研究

采用碱催化正硅酸乙酯(TEOS)的溶胶-凝胶法与分子模板法相结合,通过旋转涂覆在硅衬底上制备了掺杂聚酰亚胺(PI)的纳米多孔SiO2薄膜,并利用差热分析(DSC-TGA)、红外吸收光谱(FTIR)、原子力显微镜(AFM)、X射线衍射(XRD)、台阶仪(Atom-ic-Profiler)等对薄膜的性能进行了分析表征.结果表明,所制备的SiO2/PI杂化多孔薄膜为多孔的无定型结构,具有较好的热稳定性及力学性能,一层膜和两层膜的平均孔径分别为68和72nm,厚度分别为917和1288nm.     

Role of alumina nanoporosity in acute cell response

This work studied the effect of nanoporous alumina in acute cellular response in an in vivo model. Nanoporous alumina membranes, with pore size diameters of 20 and 200 nm, were fabricated by anodic oxidation of aluminium. The membranes were thereafter characterized in terms of pore size distribution and chemical composition. To evaluate acute inflammatory response, the membranes were implanted in the peritoneal cavity of mice. Cell recruitment to the implant site was determined by fluorescence activated cell sorting (FACS) analysis. Cell adhesion to material surfaces was studied in terms of cell number, type, and morphology using scanning electron microscopy (SEM) and immunocytochemical staining followed by fluorescence microscopy. The fabricated nanoporous alumina membranes were found to have narrow pore size distribution. The in vivo study showed that 200 nm alumina membranes induced stronger inflammatory response than 20 nm membranes. This was reflected by the number of implant-associated phagocytes and the number of cells recruited to the implantation site. Since both pore-size membranes possess similar chemical composition, we believe that the observed difference in cell recruitment and adhesion is an effect of the material nanotopography. Our results suggest that nanotopography can be used to subtly control the recruitment and adherence of phagocytic cells during the acute inflammatory response to alumina membranes.     

Gas-tight alumina films on nanoporous substrates through oxidation of sputtered metal films

The fabrication of ultrathin oxide films without gas leakage was investigated for the application to low-temperature solid oxide fuel cells (SOFCs). Aluminum thin films were deposited onto two types of anodic nanoporous alumina substrates with pore diameter of 20 and 200 nm, respectively, using dc-magnetron sputter at room temperature. By subsequent oxidation at temperatures over 500 °C, the metal films were successfully transformed into oxide films with thickness of about 35 and 410 nm. Volume expansion induced from oxidation of metal resulted in dense thin films that are free from hydrogen permeation.     

Modifications in the microstructure of alumina porous materials by hydrothermal treatment

Thin films of microporous γ-alumina were prepared by hydrothermal treatment of boehmite which was obtained by a sol-gel process. Films of boehmite hydrothermally treated at different temperatures and times were studied by X-ray diffraction, Nitrogen Adsorption, DTA/TG Thermal Analysis and Scanning Electron Microscopy. The results showed that a well-crystallized boehmite with an anisotropic particle growth mainly in the (002) plane was obtained. The modifications introduced into the boehmite affected the microstructure, such as surface area, pore morphology, pore volume, pore size distribution and thermal stability of the corresponding alumina. Received: 30 March 2000     

TEM characterization of iron-oxide-coated ceramic membranes

Commercially available porous alumina–zirconia–titania ceramic (AZTC) membranes having a titania surface coating were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and the Brunauer–Emmett–Teller (BET) method. TEM photomicrographs showed the as-received AZTC membrane to be a multi-layered structure consisting of a porous alumina–zirconia–titania core having ultrafine pore sizes, coated by an additional layer of nanoporous titania. Electron diffraction studies revealed an amorphous surface titania layer while the underlying AZTC membrane was crystalline. The AZTC membranes were coated 20, 30, 40, 45, or 60 times with iron oxide (Fe₂O₃) nanoparticles, after which the membranes were sintered in air at 900 °C for 30 min. TEM revealed a relatively uniform nanoporous Fe₂O₃ coating on the sintered, coated membranes, where the Fe₂O₃ coating thickness increased with increasing number of layers. Electron diffraction patterns showed the Fe₂O₃ coating to be crystalline in nature. This was confirmed by the XRD results showing the structure to be α-Fe₂O₃, while the AZTC membrane was a mixture of the anatase and rutile phase of TiO₂ as well as ZrO₂ and corundum, Al₂O₃. The average pore size of the underlying AZTC membrane increased after the Fe₂O₃-coated membrane was sintered. The nanoporosity in the sintered Fe₂O₃ coating increased until 40 layers, beyond which no significant increases in the average pore size were observed. The iron-oxide-coated membrane improved catalytic properties when used in combination with ozone to treat water. The optimal benefit, in terms of water treatment efficacy, was found at 40 layers of Fe₂O₃.     

Alternating nanopore diameters in anodic alumina grown within aluminium tubes

In a two-step anodization process within sulphuric acid, aluminium tubes were anodized from inside to outside. The formed nanoporous alumina layers appear stacked since the pore diameters alternate between (15 ± 7) nm and (30 ± 10) nm. During the anodization process the current was measured and it was found that it oscillates. The oscillation rate (approximately 1 per hour) corresponds to the alternating rate of the pore diameter. During the alumina growth within the tubular substrate, the area of the alumina/aluminium interface increases continuously. Therefore, it can be supposed that the switching between two pore diameters allows the system to reduce the internal stress, which would otherwise continuously increase. Other or additional reasons for the alternating nanopore sizes could be fluctuations of concentration gradients in the electrolyte within the tubes or the formation of oxygen bubbles.     

Concentration and temperature effect on controlling pore size and surface area of mesoporous titania by using template of F-68 and F-127 co-polymer in the sol-gel process

Mesoporous titania with crystalline pore walls and controlled pore sizes was fabricated through triblock copolymer (pluronic series) templated sol-gel process by changing the copolymer concentration and by adjusting their calcination temperature. Compared with mesoprous silicate, the synthetic condition of mesoporous titania would be sensitive to calcination temperature. Their pore arrangement and pore size depend strongly on the concentration of copolymer used as a template. Their arrangement of pores and specific surface area increases with the increase of calcination temperature up to critical limit, 320 degrees C. Beyond the critical temperature, the orderness of pores and specific surface area decreases due to the collapse of the pore walls. The specific surface area, pore size and pore orderness can be controlled by optimizing calcination temperature as well as polymer concentration. We demonstrate the mechanism of pore formation and their collapse in the sol-gel synthesis of mesoporous titania.     

Bioactive nanocrystalline sol-gel hydroxyapatite coatings

Sol-gel technology offers an alternative technique for producing bioactive surfaces for improved bone attachment. Previous work indicated that monophasic hydroxyapatite coatings were difficult to produce. In the present work hydroxyapatite was synthesized using the sol-gel technique with alkoxide precursors and the solution was allowed to age up to seven days prior to coating. It was found that, similar to the wet-chemical method of hydroxyapatite powder synthesis, an aging time is required to produce a pure hydroxyapatite phase. A methodology that has been successfully used to produce nanocrystalline hydroxyapatite thin film coatings via the sol-gel route on various substrates including alumina, Vycor glass, partially stabilized zirconia, Ti–6Al–4V alloy and single crystal MgO is described. Coatings produced on MgO substrates were characterized by X-ray diffraction and atomic force microscopy, while the analogous gels were examined with thermogravimetric and differential thermal analyses. The coatings were crack free and the surface was covered with small grains, of approximately 200 nm in size for samples fired to 1000 °C. Coating thickness varied between 70 and 1000 nm depending on the number of applied layers.     

Novel, nanoporous silica and titania layers fabricated by magnetron sputtering

Composite asymmetric membranes are fabricated through the deposition of submicrometer thick (100 nm) silica (SiO(2)) and titania (TiO(2)) films onto flat nanoporous silica and zirconia substrates by magnetron sputtering. The deposition conditions for both coating types were systematically altered to determine their influence on the deposited coating morphology and thickness. Ideal He/N(2) gas selectivity was measured for all of the membranes. The TiO(2) coatings, when deposited onto a ZrO(2) support layer with a pore size of 3 nm, formed a long columnar grain structure with average column diameter of 38 nm. A similar columnar structure was observed for TiO(2) coatings deposited onto a SiO(2) support layer with a pore size of 1 nm. Under the same conditions, SiO(2) coatings, deposited onto the same SiO(2) supports, formed a closely packed spherical grain structure whereas, when deposited onto ZrO(2) supports, the SiO(2) coatings formed an open grain structure. The average SiO(2) grain diameter was 36 nm in both cases. This preliminary investigation was aimed at studying the effect of sputtering parameters on the density and morphology of the deposited coatings. For the depositions carried out, the coating material was found to be very dense. However, the presence of grain boundaries resulted in poor ideal He/N(2) separation efficiencies.     

Investigation of transmission of 1.7-MeV He+ beams through porous alumina membranes

The process of charged particles transmission through nanoporous alumina membranes with a pore diameter of about 20 nm was studied. A guiding effect was observed for particles passing through dielectric nanocapillaries, which is also typical of glass microcapillaries. The maximum transmission factor measured was 0.625. It was shown in an experiment that Rutherford backscattering is capable of analyzing the quality of the structure of nanoporous membranes.     

A novel method for enzyme immobilization: direct encapsulation of acid phosphatase in nanoporous silica host materials

Immobilization of acid phosphatase (ACP) in mesoporous or, more generally, nanoporous silica has been accomplished via the sol-gel reactions of tetramethyl orthosilicate in the presence of ACP and of D-glucose (DG) as a nonsurfactant template, which is subsequently removed by water extraction after the formation of nanocomposite gels. Characterization of the silica host after the removal of DG shows that the pore size and volume generally increase with the DG content. At high DG contents, the silica hosts are nanoporous with interconnected nanoscaled pores/channels of regular diameter (e.g., 3.4 nm). Catalytic activity of ACP encapsulated in nanoporous hosts is significantly improved over that in microporous host prepared in the absence of DG. The apparent enzymatic activity at various pH values and substrate concentrations correlates well with the nanostructures of the host matrices. As the DG content is increased in the synthesis, the activity tends to increase. At a DG content of 42-60 wt%, the samples exhibit activities about triple that of the template-free control. These and other results from enzymatic kinetic studies suggest that the increase in the pore size and volume facilitates the transport of the substrate and product molecules in the host matrices, leading to the observed increase in activity. The thermal stability of ACP is remarkably improved upon immobilization. There is no detectable leakage of ACP from the host matrices and the biogels are reuseable. This study provides a useful protocol for the development of nanotechnology for various biocatalysts and biosensors.     

多级孔材料研究进展

多孔材料具有孔隙率高、比表面积大、导热系数低、体积密度小及化学性质稳定等优点,在吸附与分离、催化剂载体、隔热材料、能量储存、传感器等领域拥有广阔的应用前景。基于孔直径的大小可将多孔材料分为三类:孔径大于50nm的大孔材料(Macroporous materials),孔径介于2～50nm的介孔材料(Mesoporous materials)和孔径小于2nm的微孔材料(Microporous materials)。但是,由于孔径的限制,这三类材料的应用均存在一定的局限性。多级孔材料兼具通透性好、孔隙结构发达、体积密度小、比表面积和孔体积大等优点,打破了传统单级孔材料孔结构单一的局限,因此越来越受到研究人员的关注。然而,多级孔材料在制备中仍存在较多问题。例如,其合成过程通常会涉及到两种及两种以上的方法,制备工艺复杂;现有的多级孔材料的制备成本高,孔结构难以控制。因此,研究者们主要从优化多级孔材料的制备工艺以及降低生产成本等方面入手,制备出孔径均一且可控的多级孔材料。多级孔材料主要有大孔-介孔材料(Macro-mesoporous materials)、微孔-介孔材料(Micro-mesoporous materials)以及含有两种或多种不同孔径的介孔-介孔材料(Meso-mesoporous materials)。大孔-介孔材料常见的制备方法有模板法、发泡法、溶胶-凝胶法及熔盐法等;微孔-介孔材料的主要制备方法有化学活化法、模板法和水热法等;介孔-介孔材料的制备方法主要有水热法、模板法、溶胶-凝胶法及自组装法等。本文综述了近年来多级孔材料的最新研究进展,分别对大孔-介孔、微孔-介孔及介孔-介孔材料的制备方法进行了介绍,并简要分析了未来本领域研究的发展趋势。     

Thermal stability and its improvement of the alumina membrane top-layers prepared by sol-gel methods

The thermal stability of unsupported alumina membrane top-layers was studied by determining the pore structure (mainly pore size) change of alumina gels, prepared by sol-gel methods, after sintering at different temperatures ranging from 450 to 1200 °C. The average pore size of the pure alumina membranes and PVA-added membranes increased sharply after sintering at temperatures higher than 1000 °C. Addition of 3% lanthanum, either by mixing lanthanum nitrate in the alumina sol or impregnating lanthanum nitrate into calcined alumina gel, followed by a second heat treatment, can considerably stabilize the pore structure of the alumina membrane top-layers. The pore diameter for the lanthanum-doped membranes was stabilized within 25 nm after sintering at 1200 °C for 30 h, about one-sixth of that for the pure alumina membranes after sintering at 1200 °C for 30 h. The substantial increase in the pore size for the pure alumina membranes at the sintering temperature of 1000 to 1200 °C was accompanied by the phase transformation from -to -alumina. The addition of lanthanum can raise this phase transformation temperature by about 200 °C.