Porous Anodic Alumina Membranes Research Articles

Effects of pyrolysis temperature on structural, Raman, and infrared properties of perovskite PbTiO3 nanotubes

In this work, we investigated the effects of the pyrolysis temperature on the structural, Raman, and infrared properties of PbTiO3 nanotubes (PTO-NTs). The PTO-NTs were synthesized by spin coating a sol-gel solution on porous anodic alumina membranes, followed by the pyrolysis step at 400 − 600 ℃. Then, PTO-NTs were finally crystallized at 600 − 700 ℃ in an oxygen atmosphere to get the perovskite phase. The PTO-NTs had an outer diameter of about 420 nm and a wall thickness of about 10 nm. X-ray diffraction patterns showed that the tetragonality (c/a) increased from 1.019 to 1.028 as the pyrolysis temperature was increased from 400 to 600 ℃. Raman spectroscopy showed that the phonon modes of A 1(nTO) and E(nTO) increased with a redshift of the A 1(3TO) mode as the pyrolysis temperature was increased. In the Fourier-transform infrared spectra of PTO-NTs embedded in the porous anodic alumina membrane, the transmittance of the band at 499 cm−1 increased as the pyrolysis temperature was increased, which might be due to an increase in the tetragonality.

Hypersonic crystal band gaps in Ni/Cu superlattice nanowire arrays

Abstract The hexagonal and tetragonal ordered arrays were prepared by Ni/Cu superlattice nanowires on the porous anodic alumina membrane template, and their phonon band structures were calculated by using the plane wave expansion method. Numerical results show that the hypersonic band gaps can be acquired by adjusting the structural parameters. Along the different wave-vector directions, the width and position of band gap would vary. If the nanowires’filling fraction is increased continuously, the width of the first band gap firstly increases and then decreases within a certain range. The height of superlattice nanowire elementary unit can only affect the width of band gap within a quite narrow range. When the height of elementary unit remains unchanged, the decrease of the Cu-component ratio can contribute to the formation of a wider band gap. Additionally, the wide band gap is more easily formed in tetragonal structure than in hexagonal structure.

Fabrication and catalytic properties of three-dimensional ordered zeolite arrays with interconnected micro-meso-macroporous structure

The highly interconnected micro-meso-macroporous MFI zeolite nanorod arrays are synthesized using porous anodic alumina membranes as rigid scaffold.

A Highly Controllable Electrochemical Anodization Process to Fabricate Porous Anodic Aluminum Oxide Membranes.

Due to the broad applications of porous alumina nanostructures, research on fabrication of anodized aluminum oxide (AAO) with nanoporous structure has triggered enormous attention. While fabrication of highly ordered nanoporous AAO with tunable geometric features has been widely reported, it is known that its growth rate can be easily affected by the fluctuation of process conditions such as acid concentration and temperature during electrochemical anodization process. To fabricate AAO with various geometric parameters, particularly, to realize precise control over pore depth for scientific research and commercial applications, a controllable fabrication process is essential. In this work, we revealed a linear correlation between the integrated electric charge flow throughout the circuit in the stable anodization process and the growth thickness of AAO membranes. With this understanding, we developed a facile approach to precisely control the growth process of the membranes. It was found that this approach is applicable in a large voltage range, and it may be extended to anodization of other metal materials such as Ti as well.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-1202-y) contains supplementary material, which is available to authorized users.

Tailoring the porous nanostructure of porous anodic alumina membrane with the impurity control

Porous Anodic Alumina (PAA) membranes have been fabricated from pure and doped aluminum films (Pure Al, Al–0.5wt.%Cu and Al–1wt.%Si) by the one-step anodization method at room temperature. Formation of the PAA has been performed by three different electrolytes, namely: sulfuric (1 M), oxalic (0.3 M) and phosphoric (0.75 M) acids. For this purpose, potentiostatic anodization in a two-electrode cell configuration has been carried out. High quality alumina with straight pores have been obtained starting from pure aluminum metal films. It is found that, different types of branched structures are formed by aluminum films doped with impurities such as Si and Cu. The relationship between the electrochemical current response and the obtained pore architectures are discussed. Oxide formation rates, barrier layer thickness, vertical and horizontal inter-pore distances are investigated. The present synthesized templates have a large surface area make it one of the mostpopular nanomaterial with applications across a gamut of areas including, energy storage, sensors and biosensors.

A Bioinspired Multifunctional Heterogeneous Membrane with Ultrahigh Ionic Rectification and Highly Efficient Selective Ionic Gating.

A bioinspired multifunctional heterogeneous membrane composed of a block copolymer (PS-b-P4VP) membrane and a porous anodic alumina membrane is fabricated. The ionic rectification is so strong that the maximum ratio is ≈489, and the chemical actuation of the anion or cation gate from the "OFF" to the "ON" state promotes a 98.5% increase in the channel conductance.

Formation of silver nanorod arrays in an anodised aluminium oxide membrane

A highly ordered silver nanorod array (AgNRs) with a diameter of 90 nm has been prepared by chemical reduction from silver nitrate in a porous anodic aluminium oxide (AAO) membrane. The AAO membrane was fabricated electrochemically in an oxalic acid solution via a one-step anodisation process, followed by the growth of silver NR in the long-range ordered nanochannels of the AAO membrane via chemical reduction. The morphologies of AAO membrane and AgNRs with periodic rows of air-pockets encapsulated in the AAO membrane have been investigated using TEM. The crystalline structure and chemical composition have been confirmed by XRD, TEM and EDX techniques. The process, which has three stages, namely, (1) anodising of aluminium foil to form a mesoporous membrane, (2) adsorption of metal ions, then (3) chemical reduction of the adsorbed metal ions to form the nanorod array of AgNRs in the pores of AAO membrane, has not, to the authors’ knowledge, been reported to date.

Unifying the templating effects of porous anodic alumina on metallic nanoparticles for carbon nanotube synthesis

Carbon nanotubes (CNTs) are a promising material for many applications, due to their extraordinary properties. Some of these properties vary in relation to the diameter of the nanotubes; thus, precise control of CNT diameter can be critical. Porous anodic alumina (PAA) membranes have been successfully used to template electrodeposited catalyst. However, the catalysts used in CNT synthesis are frequently deposited with more precise techniques, such as electron beam deposition. We test the efficacy of PAA as a template for electron beam-deposited catalyst by studying the diameter distribution of CNTs grown catalyst of various thicknesses supported by PAA. These are then compared by ANOVA to the diameter distributions of CNTs grown on metal catalyst supported by a conventional alumina film. These results also allow a unified description of two templating effects, the more common particles-in-pores model, and the recently described particles-between-pores.

Propagation of concentration polarization affecting ions transport in branching nanochannel array.

A new ionic current rectification device responsive to a broad range of pH stimuli has been fabricated using porous anodic alumina membrane with tailor-made branching nanochannel array. The asymmetric geometry is achieved by changing oxidation voltage using a simple two-step anodization process. Due to the protonation/deprotonation of the intrinsic hydroxyl groups upon solution pH variation, the nanochannels array-based device is able to regulate ionic current rectification properties. The ion rectification ratio of the device is mainly determined by the branching size and surface charges, which is also confirmed by theoretical simulations. In addition, theoretical simulations show that the slight difference in ion rectification ratio for the nanochannel devices with different branching numbers is due to the propagation of concentration polarization. Three dimensional simulations clearly show the nonuniform concentration profiles in stem nanochannel near the junction interface due to the presence of branching nanochannels. The present ionic device is promising for biosensing, molecular transport and separation, and drug delivery in confined environments.

A Controllable and Widely Applicable Electrochemical Anodization Process to Fabricate Porous Anodic Aluminum Oxide Membrane

Inspired by the versatile applications of porous alumina nanostructures on solar cells, supercapacitors, biosensors, and so forth, research on fabrication of anodized aluminum oxide (AAO) with nanopore structure has achieved substantial advancements. Porous AAO membrane with nanostructures has become one of the most popular template materials for synthesis of a broad range of functional nanostructures such as nanowires, nanopillars, nanotubes, etc. While fabrication of highly ordered nanoporous AAO with tunable geometric features has been widely reported, its growth rate can be easily affected by the fluctuation of parameters such as acid concentration and temperature during the electrochemical anodization process. In order to meet the demand of fabricating AAO with various surface parameters and precise target pore depth control for scientific research and commercial applications, a controllable fabrication process is essential. Here, we developed a method which can implement precise pore depth control of AAO layer during the electrochemical anodization process, via monitoring the integrated charge. This method is applicable in a large voltage range and can be widely applied in fabrication of nanostructure with material such as TiO2and so on.

Nanoporous α-Alumina Membranes with Pore Diameters Tunable over Wide Range of 30-350 nm

Porous anodic oxide film, which is formed by anodizing of aluminum, is a typical self-ordered nanoporous material. Over the past several decades, studies have been carried out on the protection or design of aluminum surfaces for commercial applications. Recently, anodic alumina films have attracted considerable attention as a key material due to their potential technological applications in area such as filters, catalyst supports, biological applications, electronic, magnetic and optical devices. However, commercially available anodic porous alumina membranes have insufficient pore arrangement and low chemical resistance because the porous alumina films obtained by typical anodizing processes are amorphous. To expand the application of anodic porous alumina with ordered pore arrays, it is necessary to control the cell dimensions (e.g., pore interval, pore diameter, and pore depth) and to enhance the chemical resistance of alumina membranes in extreme environments such as high temperature, high vapor pressure, and high-concentration acid/base solutions. Several fundamental studies have been reported on the fabrication of crystalline anodic porous alumina aimed at improving the chemical properties of α-alumina membranes using a combination of anodizing and heat treatment processes. Since the 2000s, the crystallization of free-standing alumina membranes to the α-phase has also been attempted; however, curling and cracking as a result of thermal deformation caused by the change in density and decomposition and desorption of electrolyte anions from the outer anion-incorporated layer in the cell wall were unavoidable during the transition to crystalline alumina in addition to the desorption of bound water at lower temperatures. In this study, we investigated the optimum conditions for the fabrication of α-alumina membranes with pore diameters tunable over a wide range of approximately 30–350 nm by the anodizing of aluminum and subsequent heat treatment. The morphological and structural change of the porous alumina membrane during heat treatment was also evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), and thermogravimetry-mass spectrometry (TG-MS). Because the pore diameter could be adjusted by changing the anodizing conditions including the electrolyte species and formation voltage, anodizing of high-purity aluminum sheets was conducted in sulfuric acid, oxalic acid and phosphoric acid at each specific voltage. Here, we applied two-step anodizing process to improve the regularity of the pore arrangement of the anodic film. As a result, the deformation of alumina membrane such as warp and cracking during heat treatment for crystallization was effectively suppressed [1, 2]. By optimizing the conditions for anodizing, subsequent detachment, and heat treatment, nanoporous and single phase α-alumina membranes with pore diameters tunable over a wide range of approximately 30–350 nm were successfully fabricated. Even in the case of anodic porous film with short pore interval of approximately 60 nm, which was formed at 25 V in sulfuric acid, α-alumina membrane that maintained straight channels was obtained. The α-alumina membranes exhibited high chemical resistance in various concentrated acidic and alkaline solutions as well as when exposed to high temperature steam under pressure [2]. These results open a new route to technological and scientific applications.[1] T. Masuda, H. Asoh, S. Haraguchi, S. Ono, Electrochemistry, 82, 448-455 (2014)[2] T. Masuda, H. Asoh, S. Haraguchi, S. Ono, Materials, 8, 1350-1368 (2015)

Controlling of water wettability by structural and chemical modification of porous anodic alumina (PAA): Towards super-hydrophobic surfaces

Porous anodic alumina (PAA) membranes with increasing pore diameters (Dp) and various interpore distances (Dc) were fabricated and the water contact angles (WCAs) on the PAAs' surface were determined. No correlation was observed between the WCAs and Dp unless the Dc was taken into account. The WCAs were dependent on porosity (P); according to this dependence, there is a critical value of P beyond which the WCAs drop substantially. The critical P was ~50% and the maximal WCA obtained for this P value was 102°. No effect of pore arrangement on the water wettability was observed — the PAAs characterized by poor hexagonal pore ordering (the PAA NO) did not show any deviations from the observed trends. After modifying the PAAs surfaces by lauric acid and perfluorooctyltrichlorosilane (FOTS), the samples became more hydrophobic. For the FOTS-modified PAAs with the highest Dp (>230nm) and Dc (>260nm), the surfaces became superhydrophobic. The results obtained in this work can be used for controlling the PAAs' surface topography and chemistry to attain desired surface properties, ranging from hydrophilicity to ultrahydrophobicity.

Self- Agglomeration of Tin Nanoparticle Array on Porous Anodic Alumina Membranes: Fabrication and Characterization

In this paper, a facile method to fabricate two-dimensional (2D) Sn nanoparticles is demonstrated. Sn nanoparticles are deposited on porous anodic alumina membrane (PAA) by using thermal vapor deposition (TVD) technique. A set of PAA membranes fabricated under the same conditions was coated with Sn for different periods of time. SEM images showed the formation of hexagonal nanoarrays of Sn around each nanopore following a selective agglomeration growth mechanism on the active dots of the PAA surface. As the deposition time increased from 1 to 3 min, the agglomerated particles height increased from 20 to 75 nm. Moreover, Sn was thermally deposited for 2 min onto PAA substrates of different pore diameters. As the pore diameter increases, the formed Sn particles diameter decreases and their density distribution around each pore is improved, which may be attributed to the dimensions of the active area of the PAA surface. According to reflection spectra, it was found that the oscillation strength of the samples increased as the deposition time increased to 2 min. For the time greater than 2 min, the oscillation strength decreased due to the scattering of light, particularly in the short wavelength region, that caused by the increase of sample roughness. Keywords: Growth mechanism, nanoparticles, porous anodic alumina membrane, reflection spectra, thermal evaporation technique.

Synthesis and optical properties of single-crystalline indium zinc oxide (IZO) nanowires via co-deposition and oxidation methods

In this study, one-dimensional (1D) indium zinc oxide (IZO; Indium oxide with heavy zinc doping of 30 at %) nanowires was synthesized via electrodeposition and an oxidization method with porous anodic alumina membrane (AAM), which had an average diameter of about 60 nm. As FE-SEM results showed the synthesized IZO nanowires had an approximate length of 6–8 μm with a high aspect ratio of about 116. IZO nanowires with an Zn/(In + Zn) atomic ratio of 0.301 (∼0.3) were observed from EDS. XRD and SAED analyses show the synthesized nanowires were of single-crystal cubic structure. The UV/Visible/NIR absorption of the IZO nanowires showed an absorption peak of around 330 nm with a direct band gap energy (Eg) of 3.5 eV.

A novel DNA sensor using a sandwich format by electrochemical measurement of marker ion fluxes across nanoporous alumina membrane

A sandwich strategy for highly sensitive DNA analysis has been proposed by measuring the hindered diffusion flux of Fe(CN)63− caused by DNA hybridization in nanopores of a porous anodic alumina (PAA) membrane. The flux of Fe(CN)63− passing through the PAA nanopores is recorded using an electrochemical detector made with Au film sputtered on one face of PAA membrane. To achieve target DNA analysis, the PAA membranes are functionalized with capture DNA and followed by the hybridization event that gives rise to the pore blocking due to the synergetic effect of steric and electrostatic repulsion in the confined nanopores. Both of these two effects can be amplified by using 12-nm Au nanoparticle tags labeled with single strand DNA to perform a sandwich assay, which further amplified detection signals evidenced from the decreased flux of Fe(CN)63−. Based on this strategy, the proposed DNA biosensor gives a detection limit of 1pM. This thin piece of membrane sensor, coupled with the simple electrochemical system, fast response and high sensitivity, show potentials to be successfully used for bioanalysis.

Pervaporation separation of benzene/cyclohexane through AAOM-ionic liquids/polyurethane membranes

Supported ionic liquids/polyurethane (PU) membranes were prepared by immobilizing ionic liquids on a porous anodic aluminum oxide membrane (AAOM) support that was coated on one side with polyurethane (PU). The microstructure of all membranes was characterized using scanning electron microscopy (SEM). The pervaporation separation performance of the supported ionic liquids/polyurethane membranes was investigated for benzene/cyclohexane (Bz/Cy) mixtures. The SEM results demonstrated that the porous surface of the AAOM support was sealed by the dense polyurethane membrane and the pores of the AAOM support were impregnate with ionic liquids. The ionic liquids filling in the AAOM support enhanced the separation selectivity of Bz/Cy. The separation factor of Bz to Cy increased from 5 to 34.4 and the largest PSI of AAOM-[C4mim]PF6/PU membrane reached 452.54gm−2h−1 at 55°C for a 50wt.% Bz/Cy mixture. Because the polyurethane prevented the leakage of ionic liquids filled in the AAOM support, the supported ionic liquids/polyurethane membranes exhibited excellent stability.

Etching the Oxide Barrier of Micrometer-Scale Self-Organized Porous Anodic Alumina Membranes

We develop a quantitative model to calculate the optimal experimental conditions for the etching of the oxide barrier of porous anodic alumina (PAA) membranes. The method is applied to a membrane fabricated at 370 V in a solution of 2% citric acid. The process creates a network of small pores at the bottom of the larger pores, which accelerates the oxide barrier etching relatively to the pore walls of the PAA membranes, when etched in a solution of phosphoric acid. The oxide barrier etching is confirmed by observation of PAA membranes using scanning electron microscopy, revealing the formation of the small pores and the preferential etching of the bottom of the pores rather than the pore walls. The proposed method, which leads to a better control over the fabrication of nanoporous templates, can be adapted to oxide barriers of different PAA membranes formed at different voltages and in different acids.

Fabrication of ordered arrays of CNT/TiO2 nanotubes and their photocatalytic properties

In this work, fabrication and characterization of ordered arrays of CNT/TiO2 nanotubes imbedded in porous anodic aluminum oxide (AAO) membranes were reported.

Nanowire Fabrication in Porous Alumina Tempalets Produced by Employing Sulphuric, Oxalic and Phosphoric Acids

We report the growth of silver nanowires with varying diameters in porous anodic aluminum-oxide (AAO) membranes by using the electroless deposition approach. This objective is carried out in 2 phases. In Phase 1, AAO membranes on high purity aluminum foils are electrochemically grown by a double anodization procedure. Three different electrolytes, sulphuric acid (H2SO4), oxalic acid (H2C2O4) and phosphoric acid (H3PO4), are employed to produce membranes with varying pore diameters. Other parameters such as interpore distance, barrier layer thickness and membrane thickness are also explored. In addition, characterization to modify the pore diameter and open the barrier layer of free standing AAO templates has been carried out. In Phase 2, metallic silver nanowires are grown by electroless deposition inside pores with varying diameters in AAO membranes. AAO membranes immersed in aqueous silver nitrate solutions are thermally reduced, and the resulting silver nanowires are characterized by using a scanning electron microscope (SEM).

Structured Ni catalysts on porous anodic alumina membranes for methane dry reforming: NiAl2O4 formation and characterization.

This communication presents the successful design of a structured catalyst based on porous anodic alumina membranes for methane dry reforming. The catalyst with a strong Ni-NiAl2O4 interaction shows both excellent activity and stability.