草酸中纳米孔阵列阳极氧化铝膜的一步法制备及其形貌表征

报道了用一步阳极氧化法在经过预处理的高纯铝片上制备具有纳米孔阵列结构的阳极氧化铝膜(AAM)的技术,并用扫描电子显微镜(SEM)和原子力显微镜(AFM)对样品形貌进行了表征。结果表明,高纯铝片在0~20℃、0.1~0.5 mol/L的草酸溶液中用30~60 V的直流电一步阳极氧化,再经过去铝和除阻挡层的过程,可制得纳米孔阵列阳极氧化铝膜。制得的阳极氧化铝膜中的孔,尺寸都在纳米级别,且大小均匀,相互平行排列成规整阵列,可用作制备纳米线阵列的模板。     

Through-hole membranes of nanoporous alumina formed by anodizing in oxalic acid and their applications in fabrication of nanowire arrays

The nanopore arrays were fabricated by two-step self-organized anodization of aluminum carried out in 0.3 M oxalic acid at the temperature of 20 °C. This relatively high temperature shortens significantly the anodizing time and allows to fabricate quickly thick through-hole membranes without the additional operating cost of a cooling circuit. The structural features of anodic porous alumina such as pore diameter, interpore distance, porosity, pore density and pore circularity were investigated at various durations of pore opening/widening process carried out in 5% H₃PO₄. An excellent agreement of AAO structural features measured in FE-SEM images of the studied samples with results from software calculations was observed. The pore shape can be monitored qualitatively by fast Fourier transforms (FFTs) and quantitatively by calculation the percentage of pore circularity. Additionally, the regularity of the hexagonal arrangement of nanopores in through-hole AAO membranes was compared for various opening/widening time ranging from 40 to 100 min. It was shown that three-dimensional (3D) representations of FE-SEM images and their surface-height distribution diagrams provide interesting information about the surface roughness evolution during the pore opening/widening process. A template-assisted fabrication of Ag and Sn nanowire arrays by electrochemical deposition into the pores of the prepared AAO templates was also successfully demonstrated.     

Self-ordering of anodic porous alumina formed in organic acid electrolytes

New self-ordering porous alumina films were fabricated in organic acid electrolytes. Highly ordered cell arrangements of porous alumina films were realized in malonic acid at 120 V and tartaric acid at 195 V having 300 nm and 500 nm pore intervals, respectively. Self-organization was achieved at the maximum voltage required to induce high-current-density anodization while preventing burning, i.e., an extremely high-current flow concentrated at local points. The cells of the film grown at a high field must be pressed against each other, so that the self-ordering proceeds with the porous layer growth. When the self-ordering of cell arrangement proceeds, the cells became smaller. To improve the regularity of the cell configuration, a low electrolyte temperature and a relatively high electrolyte concentration were effective for maintaining a high-current-density to prevent burning. Surface flatness was an essential factor for self-ordering, however, the surface oxide film produced by electropolishing an aluminum substrate prevented quick pore growth in the organic acids having a low dissociation constant. It is confirmed that electropolishing followed by alkaline treatment was most appropriate as the pre-treatment in preparing flat surfaces.     

Anion impurities in porous alumina membranes: Existence and functionality

We have carried out a detailed investigation on anion impurities in self-organized porous alumina membranes (PAMs) prepared by a two-step electrochemical anodization process in oxalic acid solutions. The employment of the energy dispersive spectroscopy, high resolution transmission electron microscope and infrared absorption spectra has demonstrated the existence and nonuniform distribution of the anions in the PAM sidewalls. The variation of the COO⁻ stretching vibration and CO₂ absorption bands indicates that annealing can lead to the decrease of the concentration in the PAMs due to the decomposition of impurity groups related to . We have further presented clear functionality that the anions have played key roles in the refractive index and absorption coefficient of the PAMs, and the surface morphology and crystallization of the deposited ZnO nanopore arrays.     

电泳沉积法γ-Al2O3微孔膜的制备与表征

采用电泳沉积法制备γ－Al2O3微孔膜，考察了干燥及烧成制度对膜形成的影响，并用IR，XRD，SEM，N2吸附－脱附等测试手段对γ－Al2O3微孔膜进行了表征。结果表明：采用电泳沉积法可成功地制备均匀的γ－Al2O3保护膜；实验中采用室温慢速干燥法，制得了完整的凝胶膜，经过焙烧可获得与基片结合良好的γ－Al2O3多孔膜，在焙烧过程中，γ－AlOOH发生如下的晶型转变：γ－AlOOH→345℃γ－Al2O3，并且随着焙烧温度的升高，γ－Al2O3膜的结晶性得到改善。此外，γ－Al2O3膜的断面结构较疏松，膜厚度大面均匀：一次成膜厚度达十几μm，γ－Al2O3微孔膜的孔径尺寸为纳米级。     

聚丙烯微孔膜的研究进展

介绍了由熔融纺丝-冷却拉伸法和热致相分离法制备聚丙烯微孔膜的原理和过程。对当前膜研究领域的热点即膜的亲水化改性研究进行了重点评述,包括暂时性改性和永久性改性。阐述了各种改性方法的特点,着重讨论了亲水化改性对膜性能如膜的微孔孔径、孔隙率、透水量等的影响,强调膜表面亲水性的提高可改善膜的耐生物污染性。指出聚丙烯微孔膜的应用领域和发展前景。     

Study on the activity and stability of urease immobilized onto nanoporous alumina membranes

Nanoporous alumina membranes were employed as substrate materials for urease immobilization. Anodic porous alumina was prepared by the two-step anodization of high purity aluminum. By controlling anodization conditions, the nanoporous structure with desired dimension was obtained. Urease immobilization onto nanoporous alumina membranes was performed by four different protocols. Effect of pore diameter, pore length and immobilization methods on the activity and stability of immobilized enzyme was discussed in detail. The results show that the enzymes immobilized onto porous alumina with big pore diameter possess high activity and poor stability as compared to small pore diameter. The effect of pore length is complicated, the activity of enzyme increases with the increasing pore length for big pore size; while for correspondingly small pore size, enzymatic activity slightly depends on pore length. The immobilization methods have a slight effect on enzymatic activity, whereas enzyme immobilization by chitosan coating and reticulation with glutaraldehyde exhibits a good long-term stability as compared to that only via physical adsorption.     

Embedded space charge in porous alumina films formed in phosphoric acid

The embedded charge in the barrier layers of porous alumina, formed potentiostatically in phosphoric acid was studied as a function of anodizing voltage (30-57 V) and bath temperature (18 and 21 °C). For that, the polarization measurements of as-grown and annealed alumina/Al samples were conducted in the same anodizing bath by anodic potential sweep at a scan rate of 2.6 V/min. The plane capacitor model was used for the assessment of the charge density in the barrier layers of as-grown porous alumina. For the barrier layers of films formed at 18 °C this value equals to 0.747 μC cm⁻² and does not depend on the anodizing voltage. Increase in electrolyte temperature rises the embedded charge density. Polarization measurements carried out in this paper clearly present that the barriers of phosphoric acid films grown at the anodizing voltages lower than 39 V contain a layer of virtual cathode while at higher voltages this layer disappers. The obtained results allow speaking about promising opportunities of potentiodynamic polarization measurements of alumina films in the same anodizing solution before and after annealing for the studies of charges embedded within the alumina barriers and for the regularities of ion transport.     

sol-gel法制备微孔SiO2分离膜的研究进展

微孔SiO2分离膜在气体分离、催化、膜反应器等领域有着巨大的应用潜力。本文首先简要介绍了获得微孔的两种途径，然后重点对sol—gel法制备微孔SiO2分离膜的研究进展进行综述。     

Production and characterization of durable self-cleaning and engineering porous Al2O3/CaAl12O19 ceramic membranes

The rapid development of engineering filtering process suggests that it is imperative to produce membrane substrates with a fine pore size, high gas permeation, and antifouling properties for efficient and long-term application. This study reports on a novel fabrication method of a porous Al₂O₃/CaAl₁₂O₁₉ ceramic membrane substrate by a direct foaming method combined with cement solidification and tape-casting technology. The microstructure of the produced ceramic membrane consisted of pores with a size of 50-150 μm, which were interconnected with each other with a large number of small filtering functional pores of <10 μm. By increasing the amount of the foaming agent, the porosity of the porous Al₂O₃/CaAl₁₂O₁₉ ceramic membranes was tailored from 64.8% to 80.5%, and the bending strength decreased from 32.1 ± 1.0 to 9.6 ± 0.9 MPa, respectively. The sintered hydrophilic ceramic substrate was successfully modified to a hydrophobic one (with water contact angles of 143°) by pyrolysis of dimethyldichlorosilane and dichloromethylsilane. The resultant membrane displayed high chemical stability and self-cleaning features. The membrane with a porosity of 64.8% had a N₂ permeation of 3.0 (±0.5) × 10⁷ L m⁻² h⁻¹ at 0.5 bar and a water flux which could be totally suppressed at a liquid entry pressure of 0.45 bar.     

面向气体分离膜应用的多孔陶瓷基体研究

在众多基体材料中,多孔陶瓷由于化学和热稳定性较好而成为气体分离膜基体材料的首选,但一般陶瓷基体表面粗糙并存在裂纹、针孔等缺陷,增加了气体分离膜的制备难度,并对分离膜的性能产生不利的影响。笔者采用溶胶—凝胶法对多孔陶瓷基体表面进行修饰,有效地降低了表面粗糙度,同时把基体渗透率调整到适宜值,以得到面向气体分离膜应用的多孔陶瓷基体。     

Micropatterning of alumina tubular membranes via laser carving for enhanced direct air capture

An approach for preparing and applying micropatterned alumina tubular membranes was developed for improved gas-liquid contact at low air pressure drop in direct air capture application. The paper demonstrated that the laser carving of micropatterns on the outer surface of the alumina tubular membranes could greatly increase their outer surface area and enhance gas-liquid turbulence for a reduced diffusion mass transfer resistance. Six kinds of micropattern configurations were fabricated and studied, including random and regular micropatterns. By introducing a 500-µm solid grid micropattern, the outer surface area doubles and enhances carbon dioxide capture efficiency from 61% to 97% after the membrane was hydrophobically modified with fluoroalkylsilane. The air pressure drop through the tube lumen remained low even when the packing density increased from 382 to 906 m²/m³. The liquid entry pressure of this micropatterned membrane was the same after testing for 220 h running with the help of periodic drying.     

Structural features of self-organized nanopore arrays formed by anodization of aluminum in oxalic acid at relatively high temperatures

Anodic aluminum oxide (AAO) membranes with a highly ordered nanopore arrangement typically serve as ideal templates for the formation of various nanostructured materials. A typical procedure of the template preparation is based on a two-step self-organized anodization of aluminum carried out at the temperature of about 1-3 °C. In the current study, AAO templates were fabricated in 0.3 M oxalic acid under the anodizing potential range of 30-65 V at a relatively high electrolyte temperature ranging from 20 to 30 °C. Due to a high rate of porous oxide growth, about 5-10-fold higher than in low-temperature anodizing, the process of the template fabrication can be shorten significantly. Similarly to the low-temperature anodization, the best hexagonal pore arrangement is observed for samples anodized at 40 V. With a prolonged duration of the first anodizing step the order degree of triangular nanoporous lattice, observed after the second anodization, improves considerably. The effects of the anodizing potential and the process duration on the structural features of porous anodic alumina such as: pore diameter (D_p), interpore distance (D_c), porosity (P), pore density (n) and anodizing ratio (B_U) were investigated in details at various temperatures. The obtained results were compared with theoretical predictions and data reported in the literature.     

Preparation and gas separation performance of silicone-coated polysulfone membranes

Composite membranes (CM) were prepared by coating the dense surface of different asymmetric polysulfone flat membranes (AM) with a solution of silicone rubber polymer. The surface porosity (ε) of the dense skin AM samples varied between 4 × 10^?5 and 1·5 × 10^?8, with an average mean pore size between 0·10 and 0·07 μm. Scanning electron microscopy (SEM), gas permeation experiments (H₂, N₂, CH₄, CO₂) and a simple resistance model were used for the determination of structure-permeability relationships. This study indicates that the CM prepared with polysulfone AM having ε < 3 × 10^?7, coated with a concentration of 6% silicone solution and a contact time of 1 min, has the best gas separation performance, with selectivities very close to the intrinsic polysulfone selectivities.     

Nanostructured materials prepared by use of ordered porous alumina membranes

We report on three different methods to prepare nanostructured materials using highly ordered porous alumina membranes as templates: (1) firstly, a new and simple method, termed as the paired cell method, was developed for the preparation of inorganic nanowires. Several kinds of inorganic nanowires were synthesized using this method. The structure and composition of these nanowires were determined by field emission scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. (2) Secondly, highly ordered platinum nanowire arrays were prepared by electrochemical method with the help of porous alumina membrane templates. The structure and composition of these nanowire arrays were also characterized by various experimental techniques. The electrochemically active surface area of the nanowire arrays was determined by cyclic voltammetry based on hydrogen adsorption. Results showed that the platinum nanowire arrays exhibited a large surface area. (3) Finally, we also present a simple and reliable procedure for the preparation of highly ordered metal nanohole and nanopillar arrays, based on the anodic oxidation of aluminum and vacuum evaporation technology. The field emission scanning electron microscopic images revealed that these metal nanostructure arrays were highly ordered over a large area. The nanoimprinting of aluminum surfaces using the as-prepared chromium nanopillar arrays was demonstrated, resulting in periodic indentation on the aluminum surface.     

动态水热法制备Silicalite-1分子筛膜包覆多孔缺陷Al2O3微球

采用晶种涂覆-预晶化-晶化成膜的动态水热法成功在具有多孔缺陷的氧化铝微球上合成Silicalite-1分子筛膜。以乙醇作为润湿试剂在氧化铝表面涂覆一层晶种,将涂覆过晶种的载体加入到分子筛合成液中预晶化,一层分子筛完全覆盖载体并与载体结合牢固。预晶化后的载体在动态水热条件下处理3天,得到致密分子筛膜包覆的Al₂O₃微球。运用X射线衍射（XRD）和扫描电镜（SEM）对所得材料进行表征。结果表明,包覆的分子筛膜具有典型的MFI结构,晶粒交互生长,厚度约为3μm。考察了TPAOH用量和水量对分子筛膜微观结构的影响,结果发现TPAOH用量主要影响Silicalite-1分子筛膜的形貌,当TPAOH用量为0.17时,合成的Silicalite-1分子筛膜连续致密,而水量对分子筛膜微观结构的影响较小。这种晶种涂覆-预晶化-晶化成膜的方法有助于在多孔缺陷的Al₂O₃微球上制备高质量的分子筛膜。     

Ultrafiltration of Fe(III) solutions in the presence of poly(vinyl alcohol) using modified poly(methyl methacrylate-co-methacrylic acid) membranes

Poly(methyl methacrylate-methacrylic acid) P(MMA-MA) copolymer membranes were used in the filtration process to concentrate Fe(III) solutions. Suitable gelation period and thickness were determined, and transport properties of the membranes were modified using poly(ethylene glycol) (PEG) in the casting solution. The effects of pH and a complexable polymer [poly(vinyl alcohol) (PVA)] on the rejection of iron were investigated. Maximum recovery of 74% was obtained when the filtration was carried out in the presence of PVA at pH 3.1. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1115–1121, 1997     

Preparation and characterization of photocatalytic titania–alumina composite membranes by sol–gel methods

Titania–alumina composite membranes containing 10 and 20 mol% alumina were prepared by two different sol–gel methods; co-hydrolysis and separately peptized. The samples were characterized by different techniques. XRD results showed that for the composite membranes the anatase to rutile transformation temperature was increased by 200 and 300 °C. According to specific surface area results, alumina effectively increased the specific surface area of composite membranes compared to pure titania membranes. Microstructure of composite supported membranes was considered by scanning electron microscopy and showed a crack-free layer with 1 μm thickness. The photocatalytic activity of composite samples showed that alumina addition up to an optimum amount can slightly affect the photocatalytic activity of titania.     

Highly water-selective mordenite membranes prepared via hydrothermal post-treatment in a dilute hydrochloric acid solution

The effect of hydrothermal post-treatment in the hydrochloric acid solution was investigated on the pervaporation performance of mordenite membranes, with an emphasis on the influence of the acid concentration. The mordenite membrane with the water/ethanol separation factor of higher than 10,000 was successfully prepared via hydrothermal post-treatment in the hydrochloric acid solution of 0.2 mol dm⁻³. The change in the pervaporation performance of mordenite membranes upon hydrothermal post-treatment was discussed.     

Porous WO3 formed by anodization in oxalic acid

This work reports the investigation of the anodic growth of porous tungsten oxide (WO₃) in oxalic acid. It was found that pore diameter increases from approximately 50 to 90 nm while the layer thickness of porous structures increases from approximately 100 to 400 nm as the voltage varies from 40 to 100 V. Extended anodization duration improves the homogeneity of the porous structure at 40 V but it has no effect on the pore layer thickness. During the pore formation process, nucleation of small pores in the existing pore is observed while several layers of pores with voids underneath the surface layer are formed especially at high anodization voltage. A possible growth mechanism of the pores is proposed.