Porous Anodic Aluminum Oxide Template Research Articles

Anion exchange membrane with well-ordered arrays of ionic channels based on a porous anodic aluminium oxide template

A novel nanofibrous asymmetric framework based on a porous anodic aluminium oxide template has been proposed for the construction of ionic channels in a quaternized polysulfone anion exchange membrane (A-QAPSF AEM). The nanofibrous array layer (60 µm in length and ~ 400 nm in fibre diameter) provides good water sorption and through-plane pathways for effective hydroxide ion transport, whereas the dense layer (50 µm) suppresses fuel penetration and acts as a mechanical support for the nanofibres. The vertically aligned nanofibres in nanofibrous array layers contact with each other closely to form well-ordered arrays of ionic channels, leading to a remarkable twofold enhancement of the through-plane conductivity over that of a traditional homogeneous membrane (QAPSF) (7.11 vs. 2.19 mS cm− 1) at 25 °C and comparable in-plane conductivity. The micro-scale voids among the nanofibrous arrays in the A-QAPSF could function as reservoirs for water storage and cushion the dimensional change, simultaneously achieving a higher water uptake (46.0%) and lower swelling ratio (5.5%). This nanofibrous asymmetric framework represents a promising method to build up the aligned ionic channels along the thickness direction of AEMs.

Three-Dimensional Bi₂Te₃ Networks of Interconnected Nanowires: Synthesis and Optimization.

Self-standing Bi2Te3 networks of interconnected nanowires were fabricated in three-dimensional porous anodic alumina templates (3D–AAO) with a porous structure spreading in all three spatial dimensions. Pulsed electrodeposition parameters were optimized to grow highly oriented Bi2Te3 interconnected nanowires with stoichiometric composition inside those 3D–AAO templates. The nanowire networks were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and Raman spectroscopy. The results are compared to those obtained in films and 1D nanowires grown under similar conditions. The crystalline structure and composition of the 3D Bi–Te nanowire network are finely tuned by controlling the applied voltage and the relaxation time off at zero current density during the deposition. With this fabrication method, and controlling the electrodeposition parameters, stoichiometric Bi2Te3 networks of interconnected nanowires have been obtained, with a preferential orientation along [1 1 0], which makes them optimal candidates for out-of-plane thermoelectric applications. Moreover, the templates in which they are grown can be dissolved and the network of interconnected nanowires is self-standing without affecting its composition and orientation properties.

The effect of barrier layer conditions on the electrodeposition efficiency and magnetic properties of Fe nanowire arrays

Fabrication of different nanostructures based on template-assisted methods has become conventional, due to their numerous potential applications. In this paper, Fe nanowire arrays (NWAs) were fabricated using a pulsed electrodeposition in porous anodic alumina (PAA) templates. The effect of alumina barrier layer conditions such as barrier layer temperature (BLT) and Cu pre-plating at the dendritic sections of pores on the electrodeposition efficiency (EE) and magnetic properties of Fe NWAs in two pH regimes (2.6 and 4.0) has been investigated. At pH 4.0, BLT was changed from ~ 4 to ~ 32 °C, leading to an EE of approximately 60% for BLT ~ 24 °C. Moreover, to overcome the problem of low EE ~ 2% at the pH of 2.6, Cu pre-plating was performed with deposition current densities of 25 and 35 mA/cm2. This procedure increased the EE up to about 40%, providing a promising approach to enhance the EE in the fabrication of Fe NWAs. Furthermore, a nearly constant trend of magnetic properties was observed for highly crystalline Fe NWs.

(Invited) Fabrication of Ordered Semiconductor Nanostructures for Energy Conversion Based on Anodization Processes

High throughput fabrication of ordered nanostructures of semiconductors is an important subject for the preparation of the photo-energy devices with high conversion efficiencies1. Anodization process of metal is a promising candidate for the efficient fabrication of nanostructured semiconductors with controlled geometrical structures2. Anodic porous alumina, which is formed by anodization of Al in acidic solution, is a typical self-ordered material. The use of the anodic porous alumina as a starting structure allows the efficient preparation of the semiconductors with controlled geometrical structures, such as nanorods or nanodots arrays3. The anodization processes of appropriate metals can also generates the semiconductors with controlled geometrical structures. For example, the anodization of Ti in the electrolyte containing F- generates the porous TiO2 with controlled nanostructures4. In the present report, recent results concerning the fabrication processes for the semiconductors with ordered geometrical nanostructures for the photo-energy conversion will be described. The processes include the preparation of semiconductor nanorod arrays from anodic porous alumina templates and its application to organic photovoltaic solar cells. In addition, anodization process using pretextured Ti for the TiO2 with ideally ordered hole arrangement will be shown5. This process can be also applied to the fabrication of porous TiO2 with modified hole shapes6. The results of the efficient fabrication of ordered TiO2 will be also described. The obtained semiconductor nanostructures will be applied to various types of photo-energy conversion devices with high efficiency originated from precisely controlled geometrical structures. W. U. Huynh, J. J. Dittmer, A. P. Alivisatos, Science, 295, 2425 (2002). Masuda and K. Fukuda, Science, 268, 1466 (1995).Masuda, T. Kondo, T. Yanagishita, 231st ECS Meeting, 834 (2017). Roy, S. Berger, P. Scmuki, Angew. Chem. Int. Ed. 50, 2904 (2011).Kondo, S. Nagao, T. Yanagishita, N. T. Nguyen, K. Lee, P. Schmuki, H. Masuda, Electrochem. Commun., 50, 73 (2015).Kondo, S. Nagao, T. Yanagishita, H. Masuda, J. Electrochem. Soc., 163, E206 (2016).

Structural and magnetic properties of nickel nanowires grown in porous anodic aluminium oxide template by electrochemical deposition technique

We study the formation of nickel nanowires (Ni NWs) grown in porous anodic aluminium oxide (AAO) template by the electrochemical deposition technique. Here, the initial AAO template was grown by anodization of aluminium substrate in sulphuric acid solution. The cross-section, crystal structure, and magnetic properties of Ni NWs system were characterized by field-emission SEM, XRD, and SQUID. As a result, the highly-ordered Ni NWs are observed with the uniform diameter of 27 nm and the length from 31 to 163 nm. Based on XRD spectra analysis, Ni NWs have the face-centered cubic structure with the lattice parameter of 0.35 nm and average crystallite size of 17.19 nm. From SQUID measurement at room temperature, by maintaining the magnetic field perpendicular to Ni NWs axis, the magnetic hysteresis of Ni NWs system show the strong ferromagnetism with the coercivity and remanence ratio of ∼148 Oe and ∼0.23, respectively. The magnetic properties are also calculated by means of generalized gradient approximation methods. From the calculation result, we show that the ferromagnetism behavior comes from Ni NWs without any contribution from AAO template or the substrate. This study opens the potential application of Ni NWs system for novel functional magnetic devices.

Photocatalytic reduction of CO2 using CdS nanorods on porous anodic alumina support

Solar reduction of CO2 to valuable chemicals has captured attention of several researchers due to its cumulative effect on reduction of global warming and also as an alternative to fossil fuels. Hexagonally ordered porous anodic alumina (PAA), prepared from commercial aluminium foil, was used as a support for CdS photocatalyst due to its unique honeycomb structure. The CdS nanorods were vertically grown on the PAA template by successive ion layer adsorption reaction (SILAR) method. The photocatalytic reduction of CO2 by CdS to CH3OH was investigated using a flat sheet reactor under 10 W LED lamp. A peak CH3OH formation at 144.5 μmol/g/h with 45.4% of photocatalytic efficiency and 1.97% of CO2 conversion efficiency in a single pass were obtained.

Large-area and cost-effective fabrication of Ag-coated polymeric nanopillar array for surface-enhanced Raman spectroscopy

The throughput and cost of surface-enhanced Raman scattering (SERS) substrates are considered the main obstacles for widespread commercialization of this spectroscopy technology. Here, we demonstrate a facile, large-area, and cost-effective method for fabricating SERS substrates based on Ag-coated polyurethane acrylate (PUA) nanopillar arrays. Using a multistep anodization-widening and replication process we could cost-effectively produce the shape-controlled nanopillars and observed a unique beer-bottle morphology arranged in large-area of ca. 150 mm × 95 mm. Due to the softness and flexibility of PUA, the porous anodic aluminum oxide (AAO) template was repeatedly reused without requiring etching of the template to improve the reproducibility of nanopillar arrays. When the beer-bottle-shaped nanopillar array was uniformly coated with Ag nanoparticles and then thermally aged at 50 °C, the resulting SERS substrate exhibited a high enhancement factor of 2.8 × 106 with a low relative standard deviation of 9.0%. The linear sensitivity of our SERS substrate was also demonstrated, indicating that such a method is promising for developing Ag-coated nanopillar arrays suitable for quantitative chemical sensing.

The dramatic enhancement of ferromagnetism and band gap in Fe-doped In2O3 nanodot arrays

Ordered Fe-doped In2O3 nanodot arrays with diameters between 35 nm and 80 nm are fabricated using pulsed laser deposition with the aid of ultrathin porous anodized aluminumoxide templates. The 5 at.% Fe doped In2O3 nanodot arrays are shown to consist of the cubic bixbyite structure of In2O3. The nanodot arrays are demonstrated to be doped by Fe ions with mixed valences of +2 and +3, ruling out the presence of cluster and secondary phase related to Fe. The nanodot arrays exhibit the ferromagnetism at room temperature, where the magnetic moment increases as the dot size is reduced, rising to a maximum of about 230 emu/cm3 (equivalent to an average moment on the Fe ions of 15.30 µB/Fe). This indicates an effect due to the surface of the nanodot arrays. The optical band width is also increased to 4.55 eV for the smallest dot array, thus indicating that the surface states are responsible for the magnetism and also enhance the band gap due to Burstein-Moss effect. Our results will be benefit for understanding the physical properties of oxide semiconductor nanostructures in the application of nano-spintronics devices.

Fine-Tuning the Pore Diameter of Anodic Alumina Using Response Surface Methodology

We used oxalic and sulfuric acid electrolytes in conjunction with a home-made anodization cell (employing a two-step procedure) to fabricate porous anodic alumina (PAA) templates of various pore sizes. We chose applied voltage, electrolyte concentration, and anodization time as our explanatory variables at constant temperature. We carried out a central composite design and utilized response surface methodology to evaluate the significance of our explanatory parameters and deduce a model for generating the desired PAA pore diameter. We examined our PAA templates with a field-emission scanning electron microscope and we used a current density curve to optimize conditions that yield the desired pore diameter. Our work is directly pertinent to rigorously controlling and understanding the anodizing process of aluminum foil.

Three-dimensional layered double hydroxide membranes: fabrication technique, growth mechanism, and enhanced photocatalytic activity.

Novel three-dimensional ZnAl-LDH/AAO and NiAl-LDH/AAO membranes using porous anodic aluminum oxide (AAO) templates as a substrate and an Al3+ source were successfully fabricated via a simple precipitant-free in situ growth technique. These membranes with uniform layered double hydroxide (LDH) plates on the outer and inner surfaces exhibit enhanced activities in photocatalysis.

Growth Orientation Control of Co Nanowires Fabricated by Electrochemical Deposition Using Porous Alumina Templates

This paper reports an experimental and theoretical analysis of preferential orientation growth of metallic nanowires during electrochemical deposition using nanochanneled templates. In this work pure Co nanowire arrays were synthesized by electrochemical deposition using porous anodized aluminum oxide templates. The nanowire arrays are found to exhibit near complete preferential single axial orientation. The preferential orientation changed with increasing the applied voltage from [0002]hcp, [1010]hcp, [1210]hcp to [110]fcc. The observation is explained in terms of nucleation thermodynamics and crystal growth kinetics. The analysis demonstrates that at low applied voltages, when the wire growth is slow, the wire orientation is dictated by the criterion of minimum total surface energy, with the close-packed surfaces forming the external facets of the crystals. At high applied voltages, when the wire growth is fast, the crystal axial orientation is dictated by the growth kinetics, i.e., directions of the ...

Synthesis and photocatalytic properties of graphitic carbon nitride nanofibers using porous anodic alumina templates

In the present study, we describe an effective method for the synthesis of Graphitic carbon nitride (GCN) nanostructures using porous anodic alumina (AAO) membrane as template by simple thermal condensation of cyanamide. Synthesized nanostructure was fully analysed by various techniques to detect its crystalline nature, morphology, luminescent properties followed by the evaluation of its photocatalytic activity in the degradation of Methylene blue dye. Structural analysis of synthesized GCNNF was systematically carried out using x-ray powder diffraction (XRD) and scanning electron microscope (SEM), and. The results confirmed the growth of GCN inside the nanochannels of anodic alumina templates. Luminescent properties of GCNNF were studied using photoluminescence (PL) spectroscopy. PL analysis showed the presence of a strong emission peak in the wavelength range of 350–600 nm in blue region. GCNNF displays higher photocatalytic performance in the photodegradation of methylene blue compare to the bulk GCN.Highlights1. In the present paper, we report the synthesis of graphitic carbon nitride nanofibers (GCNNF) using porous anodic aluminium oxide membranes as templates through thermal condensation of cyanamide at 500 °C.2. The synthesis of Graphitic carbon nitride nanofibers using porous andic alumina template is the efficient approach for increasing crystallinity and surface area.3. The high surface area of graphitic carbon nitride nanofibers has a good impact on novel optical and photocatalytic properties of the bulkGCN.4. AAO templating of GCN is one of the versatile method to produce tailorable GCN nanostructures with higher surface area and less number of structural defects.5. Towards photocatalytic degradation of dyes, the tuning of physical properties is very essential thing hence we are succeeded in achieving better catalytic performance of GCN nanostructures by making use of AAO templates.

Annealing temperature dependence of structural, optical, and thermal properties of CdSe thin films grown on porous anodic alumina

In this study, cadmium selenide (CdSe) were synthesizd by a chemical route process using l-cysteine (l-cyst) as a ligand, cadmium acetate as a Cd source and Na2SeO3 as a Se precurseur. CdSe nanocrystals were embedded in porous anodic alumina (PAA) layer by the chemical bath deposition (CBD) method. The influence of annealing temperature in air-atmosphere from 150 to 350 °C on the microstructural, optical properties, and thermal conductivity of CdSe in PAA template has been studied by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, UV–Vis and photothermal deflection (PTD) techniques. The annealing temperature at 300 and 350 °C resulted in a considerable change in the surface morphology of CdSe film on the PAA layer, from a nonhomgeneous CdSe clusters into microrods array with a pyramidal ends. Raman spectroscopy measurements show an enhancement in the crystallinity of CdSe film on PAA layer and an increase of the average radius size of the nanocrystallites from 2.41 to 2.78 nm with the increase of air-annealing temperature. The optical reflectivity result of CdSe on PAA template showed that the crystal quality was significantly improved after the annealing step, bringing about an enhancement in optical absorption and a decrease in bandgap energy. The thermal conductivity Kth was studied via PTD technique, and the Kth increase was depicted with thermal treatement from 4.40 to 5.22 W M−1 K−1.

X-ray photoelectron spectroscopy studies of ZnS x Se1–x nanostructures produced in a porous aluminum-oxide matrix

Semiconductor nanostructures on the basis of ZnS x Se1–x (x = 0, 0.1, 0.3, 0.5, 0.7, and 1.0) compounds are synthesized by the template method based on the formation of semiconductor nanoparticles in porous anodic aluminum-oxide templates upon the vacuum thermal evaporation of a mixture of ZnS and ZnSe powders. The results of studies of the elemental composition of the nanostructures in relation to the composition of the initial mixture and to the parameters of the matrix substrate by means of X-ray photoelectron spectroscopy are reported. It is shown that the composition of the nanostructures is close to the composition of the initial powders and can be specified by the ZnS/ZnSe ratio in the initial mixture.

Electrodeposition of vertically standing Ag nanoplates and nanowires on transparent conductive electrode using porous anodic aluminum oxide template

We report fabricating vertically standing Ag nanoplates and nanowires on a transparent conductive substrate of indium tin oxides (ITO) with the assistance of a porous anodic aluminum oxide (AAO) template. Two-dimensional Ag nanoplates can be electrodeposited onto an AAO covered ITO surface without using an adhesion layer. Ag nanoplates obtained using AAO templates have 3 × {222} superlattice fringes, different from the 3 × {422} superlattice fringes reported in the previous study. Ag nanowires can be electrodeposited onto ITO which is initially covered with an AAO template through a conductive polymer poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The coverage, diameter, and thickness of Ag nanoplates are strongly dependent on the electrodeposition time. These Ag nanoplates and nanowires are used for surface enhanced Raman spectroscopy (SERS) and the influence of their shape, size, and coverage on SERS enhancement is studied.

Colloidal nanoparticle sorting and ordering on anodic alumina patterned surfaces using templated capillary force assembly

A new, robust technique of size-selective nanoparticle ordering on porous anodized aluminum oxide (PAAO) templates is presented. Simultaneous particle sorting and array formation is achieved for the first time using a polydisperse suspension of irregularly shaped diamond nanocrystals. The array parameters can be tuned through a balance of evaporation driven particle flux, capillary, electrostatic, and adhesion forces, which are influenced by the asperities of the surface during the capillary and convective assembly dip-coating process. The resulting structures are dense (lower limit approximately 50nm center separation), isolated (non-touching) nanoparticle arrays with a size distribution that matches the topology of the PAAO template surface. The method is demonstrated using nanodiamonds (ND) and Ag nanoparticle colloids of various sizes, on PAAO surfaces with different pore diameters as well as a patterned Al surface whose oxide layer had been removed. The transfer of the ND array to a polydimethylsiloxane (PDMS) matrix further illustrates the versatility of the method. The procedures presented here extend the range of templated nanoparticle array production to technologically important materials, which are difficult to handle using conventional evaporation, electrodeposition or imprint techniques, yet are available as polydisperse suspensions.

Comaprison of Iron Nanowires Fabricated via Porous Anodic Aluminium Oxide Template by a.c and d.c. Electrodeposition

Comaprison of Iron Nanowires Fabricated via Porous Anodic Aluminium Oxide Template by a.c and d.c. Electrodeposition

Thermoelectric battery based on bundles of Bi and Sb nanowires in anodic alumina matrices

A model of a microthermoelectric battery consisting of series connected thermoelectric cells of one-dimensional nanostructures formed into bundles by external contacts is proposed. The electrochemical processes of forming Bi and Sb nanowire arrays with the required dimensions and physicochemical properties in porous anodic alumina templates with large length-to-diameter ratios are studied and developed. The design and basis of the fabrication technology of microthermoelectric battery branches are developed, whose heat flow density will be controlled by the Seebeck coefficient measured at external contacts connecting the nanowire ends. It is shown that a set of parallel branches in the battery can be fabricated due to a high density of nanowire packing in a porous matrix, which will make it possible to achieve a fundamentally higher increase in the microheat meter efficiency.

Water repellency of large-scale imprinting-assisted polymer films

We report that the water repellency of polymeric film surfaces can be simply tuned by pressing softened polymer films into porous anodized aluminum oxide (AAO) templates. Highly-dense nano-pillars and nano-hairs on the polymer surfaces are reproduced via physically or chemically separating the AAO templates from the impressed polymer films. The resulting polymeric nano-textures show various aspect ratios (ARs) between height and cross-sectional diameter (from 2 to 130), depending on the viscoelastic response of the polymer chains during hot AAO pressing and the subsequent separation procedures. The water contact angle values on the nano-textured polymer films considerably changed from 91° to 160° with an increase in AR. Using hot pressing and physical detachment of a porous AAO-covered Al cylinder roller, we successfully demonstrated the potential for large-area fabrication of superhydrophobic polymer films with characteristics that are similar to lotus leaves.

Orthogonal Chemical Modification of Template-Synthesized Nanostructures with DNA.

Very few chemical strategies for the selective functionalization of nanostructures have been developed despite their potential for controlling high-order assembly processes. We report a novel approach for the selective chemical functionalization and localized assembly of one-dimensional nanostructures (rods), based upon the systematic activation (DNA functionalization) and passivation (self-assembled monolayers) of specific surface sites through the use of orthogonal chemical reactions on electrochemically grown metal nanorod arrays in porous anodic aluminum oxide templates. The ability to orthogonally functionalize the ends or the side of a nanorod, as well as the gaps between two rods, with different DNA strands allows one to synthesize nanostructure assemblies that would be difficult to realize any other way and that could ultimately be utilized for making a wide variety of device architectures.