Porous Alumina Membranes Research Articles

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.

Slip Casting of Alumina for Membrane Application

Porous alumina membranes were prepared from alumina matrix, polyvinyl alcohol binder (1–5%) and calcium carbonate additive (0–3%). The disc–shaped alumina samples were fabricated by slip casting process. The alumina paste was sintered at different temperatures of 1100, 1200, 1300 and 1400°C. The results showed that the porosity of the porous membrane reached 45%–46% at 1300°C sintering for the mixtures of alumina matrix with 3% PVA and alumina matrix with 2% CaCO3 plus 3% PVA. The water permeability was 150 L/m2.h at 20 kPa and the hydraulic conductivity coefficient was 1.06 × 10–9 – 2.43 × 10–9 ms–1Pa–1. The density, linear shrinkage water absorption and mechanical strength were ca. 3.92 g/cm3, 1.61–1.71% and 20.45–21.92%, 17.26–21 MPa, respectively. The SEM micrographs of alumina membrane using PVA binder showed a dense surface layers. An increase of the PVA binder resulted in a higher pure water fluxes and bigger pore sizes. An increase of CaCO3 in a 3% PVA binder mixtures resulted in a little decrease of porosity but increase in linear shrinkage from 1.57 to 2.04% at 1300°C sintering.

α-Alumina membrane having a hierarchical structure of straight macropores and mesopores inside the pore wall

We prepared a through-hole α-alumina membrane with a hierarchical porous structure from an anodic porous alumina membrane prepared using phosphoric acid electrolyte as the starting material. By heating the anodic porous alumina membrane to 1400°C, aluminum phosphate nanoparticles were segregated in the α-alumina matrix at the anion-incorporated outer layer and the high-purity alumina layer forming a cell boundary band sintered as a high-density α-alumina layer at the central core of the pore wall. When the heat-treated membrane was immersed in concentrated hydrochloric acid, a unique hierarchical porous α-alumina membrane structure was formed with straight macropores and mesopores inside the pore wall due to the dissolution of aluminum phosphate nanoparticles. The developed α-alumina membrane can be ultimately used as a multifunctional filter because of its unique hierarchical porous structure and extremely high chemical and thermal durability.

Variation of crystallinity of Cu and Cu2O nanowires arrays grown in various pores of porous alumina membrane

Various pore sizes of a porous alumina membrane were fabricated using H2SO4 and H2C2O4 electrolyte under different ionization voltages. Cu nanowire arrays with high aspect ratios, uniform pore size, and ordered pore arrangement were synthesized using the above porous alumina membrane (PAM). Moreover, Cu2O nanowire arrays were prepared through the oxidization of Cu metal nanowire arrays. From the microstructure and compositional analysis, it was observed that pores of different sizes, i.e. 20~30, 70~90 and 90~100 nm could be obtained by controlling various electrolytes and anodization voltage. The Cu nanowire synthesized with various pore sizes were found to be single crystal (20~90 nm) and polycrystalline (90~100nm) respectively. The single crystal Cu with (111) direction was occurred due to homogeneous current density distribution and relationship between current density (J) and nucleus radius (ro). After oxidation of Cu, the Cu2O nanowires with the pore sizes of 20~100 nm was found to be single crystal. The rearranged of Cu and O2 lattice sites promotes the enhancement of crystalline property.

Investigation of helium charged beams passing through the porous alumina membranes

Membranes of nanoporous aluminum oxide (alumina) have been obtained using the electrochemical etching technique by varying technological regimes. They were investigated by the Rutherford backscattering technique. The obtained spectra revealed distribution of elements over the entire thickness of the layer. It has been shown that almost all ions, which fly in the beam, fall into the channel - por Al2O3. This leads to a focusing of the charged particles beam.

Developing an Inositol-Phosphate-Actuated Nanochannel System by Mimicking Biological Calcium Ion Channels.

In eukaryotic cells, ion channels, which ubiquitously present as polypeptides or proteins, usually regulate the ion transport across biological membranes by conformational switching of the channel proteins in response to the binding of diverse signaling molecules (e.g., inositol phosphate, abbreviated to InsP). To mimic the gating behaviors of natural Ca2+ channels manipulated by InsPs, a smart poly[(N-isopropylacrylamide-co-4-(3-acryloylthioureido) benzoic acid)0.2] (denoted as PNI-co-ATBA0.2) was integrated onto a porous anodic alumina (PAA) membrane, building an InsP-actuated nanochannel system. Driven by the intensive hydrogen bonding complexation of ATBA monomer with InsP, the copolymer chains displayed a remarkable and reversible conformational transition from a contracted state to a swollen one, accompanied with significant changes in surface morphology, wettability, and viscoelasticity. Benefiting from these features, dynamic gating behaviors of the nanochannels located on the copolymer-modified PAA membrane could be precisely manipulated by InsPs, reflected as a satisfactory linear relationship between real-time variation in transmembrane ionic current and the InsP concentration over a wide range from 1 nmol L-1 to 10 μmol L-1, as well as a clear discrimination among InsP2, InsP3, and InsP6. This study indicates the great potential of biomolecule-responsive polymers in the fabrication of biomimetic ion nanochannels and other nanoscale biodevices.

Alumina membranes as a mask for the structures used in hydrogen energy

The paper deals with the advantages of porous alumina membranes as templates for technological structures used in hydrogen economy and describes the features of membrane technology as well as characterization methods of their geometrical parameters. In order to determine surface porosity, two methods (such as theoretical calculations and digital image processing) have been used. It has been shown that the results are in good agreement with each other.

Thickness Control of Porous Alumina Membranes and Observation of Their Optical Transmittance

Thickness Control of Porous Alumina Membranes and Observation of Their Optical Transmittance

Preparation of ideally ordered through-hole anodic porous alumina membranes by two-layer anodization

Ideally ordered anodic porous alumina through-hole membranes were prepared by a combination of the pretexturing of Al and subsequent two-layer anodization. In the two-layer-anodized sample, the selective dissolution of a layer formed in concentrated H2SO4 generated an ideally ordered through-hole membrane. The repetition of two-layer anodization and the detachment of the membrane allowed the high-throughput preparation of an ideally ordered anodic porous alumina membrane from a single pretextured Al substrate. The obtained ideally ordered through-hole membranes are expected to be used in various application fields that require ideally ordered through-hole membranes.

Determination of the alumina membrane geometrical parameters using its optical spectra

The transmission spectra for the porous alumina membranes prepared by electrochemical etching were investigated in a broad wavelength range from 0.2 to 12 μm. It is shown that the spectrum of the membrane maybe divided into regions enabling characterisation of average pore size and size distribution, the membrane thickness, and the presence of residual etching agent anions.

Enhanced Hall effect in Co/Pd multilayered nanodomes with perpendicular anisotropy

In this work, multilayers of Co/Pd with out of plane anisotropy have been deposited on the bottom of porous alumina membranes, forming nanodomes films with 100 and 200 nm diameter. The magnetization reversal of the multilayers is investigated by magnetization curves, extraordinary Hall effect and magnetic force microscopy (MFM) experiments. The results show that as the pore diameter increase, a larger hall resistivity is obtained, compared with the continuous film.

Domain wall propagation tuning in magnetic nanowires through geometric modulation

The magnetic behavior of nickel modulated nanowires embedded in porous alumina membranes is investigated. Their diameters exhibit a sharp transition between below (35nm) and above (52nm) the theoretical limit for transverse and vortex domain walls. Magnetic hysteresis loops and first-order reversal curves (FORCs) were measured on several ordered nanowire arrays with different wide-narrow segment lengths ratio and compared with those from homogenous nanowires. The experimental magnetic response evidences a rather complex susceptibility behavior for nanowires with modulated diameter. Micromagnetic simulations on isolated and first-neighbors arrays of nanowires show that the domain wall structure, which depends on the segment diameter, suffers a transformation while crossing the diameter modulation, but without any pinning. The experimental array magnetic behavior can be ascribed to a heterogeneous stray field induced by the diameter modulation, yielding a stronger interaction field at the wide extremity than at the narrow one. The results evidence the possibility to control the domain wall propagation and morphology by modulating the lateral aspect of the magnetic entity.

Fabrication of PMMA Membranes with Nano-Pillars Array Using Template/Spin-Coating Method

Template/spin-coating method was presented for fabricating single-layer nano-pillar array polymethylmethacrylate (SL-PMMA) and double-layer nano-pillar array polymethylmethacrylate (DL-PMMA) membranes. The different mass ratio of PMMA/DiMethyl Formamide (DMF) solution was dripped on single-layer porous anodic alumina (SL-PAA) or double-layer porous anodic alumina (DL-PAA) membrane and spun at 4000rpm speed for 30 seconds. The SL-PAA and DL-PAA membranes had been put into vacuum oven at 150°C for 2 hours, before SL-PMMA and DL-PMMA were removed. Experimental results show that the regularity degree of PAA fabricated in OAS/PAS is higher than that of PAA fabricated in PAS by two-step anodization method. The ordered pores and clear double-layer outline can be observed from the surface and cross-section FESEM images of DL-PAA membranes. When the content of PMMA in mixture solution is 20 wt%, the top shape of nano-pillars is convex, because the solution was completely filled in the pore of SL-PAA, and the length of nano-pillars is equal to the height of pore of PAA. However, the top pore amount on nano-pillars at ascending speed 20°C per minute is more than that of at ascending speed 10°C per minute. The PMMA membranes with ordered mid-hollow and porous nano-pillars will have wide application prospect in biosensors, chemical sensors, microcapsules fabrication fields due to many advantages such as simple operation, low cost, high specific surface area, etc.

Exceptional high selectivity of hydrogen/methane separation on a phosphonate-based MOF membrane with exclusion of methane molecules.

A phosphonate-based metal-organic framework membrane was constructed on a porous anodic alumina membrane (PAAM) substrate for H2/CH4 separation for the first time. Owing to the ultra-micro pore windows, this membrane exhibited effective size exclusion for CH4 molecules but suitable permeance for H2 molecules, giving rise to an exceptional high H2/CH4 separation selectivity.

A New Method for Highly Efficient Fabrication of Through-Hole Porous Anodic Alumina Membranes

Two-step anodization in 0.3 M oxalic acid electrolyte is used to grow highly ordered porous anodic alumina on both sides of Al sheet. The obtained sample is annealed and subsequently the annealed sample is re-anodized, producing two-layer PAAs on the Al. Since the re-anodized PAA has much higher etching rate than the annealed, it can be taken as a sacrificial layer to be selectively dissolved. As a result, through-hole PAAs are detached and highly ordered concaves maintain on the Al surfaces. So the Al sheet can be repeatedly used for highly efficient fabrication of through-hole PAAs. This method is also suitable for producing through-hole PAAs in other electrolytes, such as sulfuric acid and phosphoric acid.

Confining a bi-enzyme inside the nanochannels of a porous aluminum oxide membrane for accelerating the enzymatic reactions.

An artificial metabolon with high conversion efficiency was constructed by confining a bi-enzyme into porous aluminum oxide nanochannels, which accelerated enzymatic reactions by minimizing the diffusion loss of intermediate species.

Method for nanomodulation of metallic thin films following the replica-antireplica process based on porous alumina membranes

In this paper we have introduced a method for modulation of metallic thin films by sputtering of metals on anodized aluminum templates. Using a high deposition rate during deposition of the non-magnetic metal on the Al pattern, we have separated the two metallic surfaces and, thus, imprinted a pattern of nanohills on a non-magnetic metallic film, such as Au, Ag or Cu. The morphology of the nanostructured metallic films was determined by scanning electron microscopy. Thus, we have confirmed that the ordering degree of the Al template remained after the replication process. Additionally, and as an example of use of these films, we have prepared Supermalloy thin films deposited by sputtering onto these nanostructured non-magnetic metals. The room temperature magnetic behavior of these thin films is also studied. Interestingly, we have found that when the external magnetic field is applied out of plane of the substrate, the coercivity increases linearly as we increase the radius of the nanohills. These soft magnetic films can open new opportunities for magnetic field sensor applications.

(Invited) Preparation of Ordered Anodic Porous Alumina Through-Hole Membrane and Its Applications

The preparation of highly ordered anodic porous alumina through-hole membranes by two-layer anodization using concentrated sulfuric acid solution is described in detail. After the formation of a porous alumina layer in an oxalic acid solution, a highly soluble alumina layer was formed at the lower part of the first alumina layer by second anodization in a concentrated sulfuric acid solution. A porous alumina through-hole membrane was then obtained by selective dissolution of the second alumina layer in an appropriate etchant. The residual Al could be reused for the preparation of the ordered anodic porous alumina because an ordered concave array corresponding to the hole arrangement of the detached porous alumina membrane was maintained at the surface of the residual Al even after the etching treatment. The present process allows the high-throughput preparation of ordered anodic porous alumina through-hole membranes.

Stimulated Emission Depletion Microscopy Resolves Nanoparticle Assembly on a Porous Membrane Surface

Stimulated emission depletion microscopy—depending on the nature of fluorophore and sample, depletion laser power, and other experimental conditions—provides diffraction unlimited lateral resolution in the range of 20- 100 nm. In this paper, a detailed description of such a microscope along with one of the possible imaging schemes is provided. Application of such a microscope in resolving self assembly of polymeric nanoparticles on porous alumina membrane in wet condition is demonstrated. STED microscopy resolves formation of loose linear to quasi polygonal self-assembly patterns on the membrane surface. Possible reasons for the formation of such self assembly patterns are provided.

Nanofibrous alumina structures fabricated using high-yield alternating current electrospinning

Nanofibrous alumina (Al2O3) structures were fabricated from the precursor aluminum nitrate/polyvinylpyrrolidone (PVP) nanofibers prepared using a free-surface alternating current (AC) electrospinning method. Precursor nanofibers were generated at rates up to 6.4g/h and collected as 100–300µm thick sheets suitable for direct conversion into the nanofibrous alumina structures. The effects of process conditions and annealing temperature on the nanofiber diameter, morphology, shrinking behavior and crystalline phase formation were investigated by Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). Textural properties of Al2O3 fibrous sheets composed of micro-/meso-porous nanocrystalline γ-alumina nanofibers with 260±90nm diameters after the calcination at temperatures in the range from 700°C to 1000°C were determined from N2 adsorption/desorption isotherms. Preliminary air permeability and apparent air flow resistance studies of single sheet and multilayer nanofibrous alumina membranes were performed and compared with other porous alumina membrane structures for the evaluation of their possible usage in gas filtration, separation, and other applications.