Through-hole Membranes Research Articles

Fabrication of Tubular Alumina through-Hole Membranes by Anodization of Al Wires

Membrane filters with uniformly sized pores have attracted considerable attention because they are useful for filtering a variety of particulates. Among them, anodic porous alumina, obtained by the anodization of Al in an electrolyte, has been studied as a membrane filter for microfiltration because it can form a nanohole array structure with regularly arranged pores of uniform size. We previously reported that a two-layer anodization method using concentrated sulfuric acid can form highly ordered alumina through-hole membranes with high throughput [1]. Using this method, it was possible to form not only flat membrane filters but also tubular membrane filters [2]. Tubular alumina membrane filters have potential applications in filter modules for space savings and efficient microfiltration. To achieve efficient filtration in filter modules consisting of tubular membrane filters, it is necessary to increase the density of the filter packed in the module, which requires the fabrication of tubular filters with small diameters. However, it is difficult to form tubular alumina membrane filters thinner than 1 cm in diameter using a previously reported method. In this report, we describe the results of a new method based on a two-layer anodization process using concentrated sulfuric acid to form tubular membrane filters with millimeter diameters. Electropolished Al wire was anodized in 0.3 M oxalic acid at 40 V to form anodic porous alumina. The sample was then re-anodized in 12M sulfuric acid at 40V to form a highly soluble alumina layer at the bottom of the previously formed anodic porous alumina. After anodization, the sample was immersed in a mixed solution of chromic acid and phosphoric acid to selectively dissolve the alumina layer formed in concentrated sulfuric acid, thereby exposing the Al substrate at the bottom of the pores. Tubular alumina membrane filters were obtained by selectively dissolving the Al substrate through nanopores in an iodine-methanol solution. In this study, Al wires with diameters ranging from 2 to 5 mm were used as the starting materials, and in all cases, it was possible to form tubular alumina membrane filters without cracks. SEM observations of the obtained samples showed that the tubular alumina membrane filter was uniformly sized through the holes. The tubular alumina membrane filter obtained in this study is expected to be useful in a variety of applications.

Effects of Heat Treatment on Anodic Porous Alumina Membranes for Mass Spectrometry

Abstract Desorption ionization using through-hole alumina membrane (DIUTHAME) method is a mass spectrometry imaging (MSI) method that uses an anodic porous alumina membrane (APAM) with an array of submicron-sized through-holes as a surface-assisted laser desorption/ionization (SALDI) substrate. The DIUTHAME method is particularly promising for MSI because it does not generate interfering peaks in the low-molecular-weight region. However, the SALDI effect cannot be obtained if the nanostructures of the substrate are destroyed owing to laser irradiation before sample vaporization. APAMs that maintain their structures after irradiation with a high-intensity laser must be fabricated to realize highly sensitive measurements. In this study, we investigated the role of heat treatment suppressing the laser irradiation induced fracture of APAMs. We found that heat treatment at higher temperatures more effectively suppressed APAM fracture associated with laser irradiation. This result was attributed to the reduction of anion-derived impurities in APAMs upon heat treatment. The resulting heat-treated APAM is expected to serve as a substrate for highly sensitive and robust MSI.

A flexible strategy to fabricate trumpet-shaped porous PDMS membranes for organ-on-chip application.

Porous polydimethylsiloxane (PDMS) membrane is a crucial element in organs-on-chips fabrication, supplying a unique substrate that can be used for the generation of tissue-tissue interfaces, separate co-culture, biomimetic stretch application, etc. However, the existing methods of through-hole PDMS membrane production are largely limited by labor-consuming processes and/or expensive equipment. Here, we propose an accessible and low-cost strategy to fabricate through-hole PDMS membranes with good controllability, which is performed via combining wet-etching and spin-coating processes. The porous membrane is obtained by spin-coating OS-20 diluted PDMS on an etched glass template with a columnar array structure. The pore size and thickness of the PDMS membrane can be adjusted flexibly via optimizing the template structure and spinning speed. In particular, compared to the traditional vertical through-hole structure of porous membranes, the membranes prepared by this method feature a trumpet-shaped structure, which allows for the generation of some unique bionic structures on organs-on-chips. When the trumpet-shape faces upward, the endothelium spreads at the bottom of the porous membrane, and intestinal cells form a villous structure, achieving the same effect as traditional methods. Conversely, when the trumpet-shape faces downward, intestinal cells spontaneously form a crypt-like structure, which is challenging to achieve with other methods. The proposed approach is simple, flexible with good reproducibility, and low-cost, which provides a new way to facilitate the building of multifunctional organ-on-chip systems and accelerate their translational applications.

A Rapid, Efficient Method for Anodic Aluminum Oxide Membrane Room-Temperature Multi-Detachment from Commercial 1050 Aluminum Alloy.

For commercial processes, through-hole AAO membranes are fabricated from high-purity aluminum by chemical etching. However, this method has the disadvantages of using heavy-metal solutions, creating large amounts of material waste, and leading to an irregular pore structure. Through-hole porous alumina membrane fabrication has been widely investigated due to applications in filters, nanomaterial synthesis, and surface-enhanced Raman scattering. There are several means to obtain freestanding through-hole AAO membranes, but a fast, low-cost, and repetitive process to create complete, high-quality membranes has not yet been established. Here, we propose a rapid and efficient method for the multi-detachment of an AAO membrane at room temperature by integrating the one-time potentiostatic (OTP) method and two-step electrochemical polishing. Economical commercial AA1050 was used instead of traditional high-cost high-purity aluminum for AAO membrane fabrication at 25 °C. The OTP method, which is a single-step process, was applied to achieve a high-quality membrane with unimodal pore distribution and diameters between 35 and 40 nm, maintaining a high consistency over five repetitions. To repeatedly detach the AAO membrane, two-step electrochemical polishing was developed to minimize damage on the AA1050 substrate caused by membrane separation. The mechanism for creating AAO membranes using the OTP method can be divided into three major components, including the Joule heating effect, the dissolution of the barrier layer, and stress effects. The stress is attributed to two factors: bubble formation and the difference in the coefficient of thermal expansion between the AAO membrane and the Al substrate. This highly efficient AAO membrane detachment method will facilitate the rapid production and applications of AAO films.

Fabrication and Optimisation of Alumina Nanoporous Membranes for Drug Delivery Applications: A Comparative Study.

Neurodegenerative disorders cause most physical and mental disabilities, and therefore require effective treatment. The blood-brain barrier (BBB) prevents drug molecules from crossing from the blood to the brain, making brain drug delivery difficult. Implantable devices could provide sustained and regulated medication to solve this problem. Two electrolytes (0.3 M oxalic acid and 0.3 M sulphuric acid) were used to anodise Al2O3 nanoporous membranes, followed by a third anodisation in concentrated H2SO4 to separate the through-hole membranes from the aluminium substrate. FTIR, AFM, and SEM/EDX were used to characterise the membranes' structure and morphology. The effects of the anodisation time and electrolyte type on the AAO layer pore density, diameter, interpore distance, and thickness were examined. As a model drug for neurodegenerative disorders, donepezil hydrochloride (DHC) was loaded onto thin alumina nanoporous membranes. The DHC release profiles were characterised at two concentrations using a UV-Vis spectrophotometer. Oxalic acid membranes demonstrated an average pore diameter of 39.6-32.5 nm, which was two times larger than sulphuric acid membranes (22.6-19.7 nm). After increasing the anodisation time from 3 to 5 h, all of the membranes showed a reduction in pore diameter that was stable regardless of the electrolyte type or period. Drug release from oxalic acid-fabricated membranes was controlled and sustained for over 2 weeks. Thus, nanoporous membranes as implantable drug delivery systems could improve neurodegenerative disease treatment.

Straightforward Cell Patterning with Ultra-Low Background Using Polydimethylsiloxane Through-Hole Membranes.

Micropatterning is becoming an increasingly popular tool to realize microscale cell positioning and decipher cell activities and functions under specific microenvironments. However, a facile methodology for building a highly precise cell pattern still remains challenging. In this study, A simple and straightforward method for stable and efficient cell patterning with ultra-low background using polydimethylsiloxane through-hole membranes is developed. The patterning process is conveniently on the basis of membrane peeling and routine pipetting. Cell patterning in high quality involving over 97% patterning coincidence and zero residue on the background is achieved. The high repeatability and stability of the established method for multiple types of cell arrangements with different spatial profiles is demonstrated. The customizable cell patterning with ultra-low background and high diversity is confirmed to be quite feasible and reliable. Furthermore, the applicability of the patterning method for investigating the fundamental cell activities is also verified experimentally. The authors believe this microengineering advancement has valuable applications in many microscale cell manipulation-associated research fields including cell biology, cell engineering, cell imaging, and cell sensing.

Electrochemical Separation of Porous Anodic Aluminum Oxide with Thick Barrier Layers

We investigated an electrochemical separation method for anodic aluminum oxide (AAO) films possessing thicker barrier layers by electrolysis in sodium chloride (NaCl) and ethylene glycol (EG) solution and subsequent fabrication of through-hole AAO membranes by immersion in phosphoric acid (H3PO4) solution. The AAO films with different barrier layer thicknesses were formed on the aluminum surface by anodizing in sulfuric, oxalic, and H3PO4 solutions at up to 130 V. The AAO-covered aluminum specimens were immersed in NaCl/EG solution, and then constant voltage electrolysis at 10 V higher than the anodizing voltage was performed for the separation of AAO from the aluminum surface. Many nanoscale paths were formed throughout the barrier alumina layer in the initial stage of electrolysis, and then the aluminum substrate electrochemically dissolved through these narrow paths during electrolysis. Although the AAO film formed by anodizing at 130 V was partially fractured by electrolysis, the AAO films formed at up to 80 V were uniformly separated from the aluminum surface. As the separated AAO membrane was immersed in H3PO4 aqueous solution after electrolysis, the barrier layer with narrow paths preferentially dissolved into the solution, and a through-hole AAO membrane could be successfully obtained.

Through-hole composite membrane with an ultrathin oxide shell for highly robust and transparent air filters

Exploring pore structures that are optically transparent and have high filtration efficiency for ultrafine dust is very important for realizing passive window filters for indoor air purification. Herein, a polyester track-etched (PETE) membrane with vertically perforated micropores is investigated as a cost-effective candidate for transparent window filters. The pore size, which governs transparency and filtration efficiency, can be precisely tuned by conformally depositing an ultrathin oxide layer on the PETE membrane via atomic layer deposition. The maximum visible light transmittance (∼81.2 %) was achieved with an alumina layer of approximately 55 nm, and the resulting composite membrane exhibited competitive filtration efficiency compared to commercial products. The chemically inert alumina layer also increased resistance to various external stimuli and enabled simple cleaning of the contaminated membrane surface with a solvent. The membrane installed on an insect screen effectively maintained its filtration performance (∼85 % for PM2.5) even after 10 reuse cycles under extremely harsh conditions (PM2.5 concentration: ∼5000 μg cm−3). The proposed through-hole composite membrane can expand the choice of aesthetic window filters to situations that require high outside visibility and daylighting.

Facile Fabrication of Flexible Polymeric Membranes with Micro and Nano Apertures over Large Areas.

Freestanding, flexible and open through-hole polymeric micro- and nanostructured membranes were successfully fabricated over large areas (>16 cm2) via solvent removal of sacrificial scaffolds filled with polymer resin by spontaneous capillary flow. Most of the polymeric membranes were obtained through a rapid UV curing processes via cationic or free radical UV polymerisation. Free standing microstructured membranes were fabricated across a range of curable polymer materials, including: EBECRYL3708 (radical UV polymerisation), CUVR1534 (cationic UV polymerisation) UV lacquer, fluorinated perfluoropolyether urethane methacrylate UV resin (MD700), optical adhesive UV resin with high refractive index (NOA84) and medical adhesive UV resin (1161-M). The present method was also extended to make a thermal set polydimethylsiloxane (PDMS) membranes. The pore sizes for the as-fabricated membranes ranged from 100 µm down to 200 nm and membrane thickness could be varied from 100 µm down to 10 µm. Aspect ratios as high as 16.7 were achieved for the 100 µm thick membranes for pore diameters of approximately 6 µm. Wide-area and uniform, open through-hole 30 µm thick membranes with 15 µm pore size were fabricated over 44 × 44 mm2 areas. As an application example, arrays of Au nanodots and Pd nanodots, as small as 130 nm, were deposited on Si substrates using a nanoaperture polymer through-hole membrane as a stencil.

Achieving high response of poly (3-hexylthiophene-2,5-diyl) molecules to gaseous ammonia using anodic aluminum oxide nanoporous substrate operated under 1 V

ppb level sensing of gaseous ammonia is of utmost importance in several sectors including health and industrial zones. Among various ammonia gas sensors based on different transducing principles (optical, electrical, electrochemical), conductometric sensors are highly promising due to simplicity in device fabrication and measurements but suffer from relatively low sensitivity and limit of detection. In this work, we have fabricated highly efficient conductometric ammonia gas sensors with custom-made interdigitated electrodes by laser-patterning 200 nm thick silver layer on anodic aluminum oxide (AAO) and on glass substrates for comparison. Poly (3-hexylthiophene-2,5-diyl) molecules (P3HT molecules) is used as the indicator molecules in the proposed ammonia gas sensor. The proposed sensor fabricated on AAO substrate exhibits an extraordinarily high response (ratio of difference in currents in presence and absence of gas molecules to the current in absence of gas molecules) of 0.56 at 100 ppb ammonia environment under 0.5 V, which is the highest response hitherto achieved in ammonia gas sensor based on P3HT molecules. The results suggest that a simple custom-made laser patterned silver electrode could replace the electrode designed by photolithographic or rigorous nano-engineering methods to achieve highly efficient devices. Interestingly, the unique application of AAO through-hole membrane as a substrate allows gas molecules to enter through the bottom of the substrate to interact with the indicator molecules on top, suggesting complete accessibility of the top substrate for the fabrication of devices without hindering the gas sensing phenomenon.

Dependence of size distribution of nanoparticles on hole size uniformity in membrane emulsification

Metal oxide nanoparticles were fabricated by membrane emulsification using alumina through-hole membranes with different hole size uniformity. Hole size of alumina through-hole membrane used for membrane emulsification and the size of obtained nanoparticles were evaluated by SEM observation, and the relationship between the uniformity of hole size and the size distribution of the obtained nanoparticles was investigated. As a result, nanoparticles with higher size uniformity were obtained when the RSD (relative standard deviation) of hole size was 3.8%. This indicates that the hole size uniformity of the emulsification membrane is important for the fabrication of droplets and nanoparticles of uniform size by membrane emulsification.

Rapid electrochemical separation of anodic porous alumina films from aluminum surfaces using a highly safe sodium chloride–ethylene glycol solution

A rapid electrochemical separation of an anodic porous alumina (APA) film formed by anodizing an aluminum substrate was achieved using a highly safe sodium chloride (NaCl)/ethylene glycol (EG) mixture. A thick APA film (thickness: 20–80 µm) with an ordered pore structure was formed on the aluminum surface by anodizing the substrate in a 0.3 M sulfuric acid solution at 25 V, and the specimens were subsequently polarized anodically in a 1.0 M NaCl/EG solution. A large current density was measured when a voltage higher than the anodizing voltage of 25 V was applied, and the APA film was completely separated from the aluminum substrate. This may be due to the formation of extremely small through-holes at the bottom barrier oxide layer of the APA film and the subsequent dissolution of aluminum from the substrate. The separation time of the APA film decreased with increasing applied voltage in the NaCl/EG solution, and rapid separation within 0.5 s was successfully achieved via anodic polarization at 36 V. We demonstrate that large-area and thick APA films can also be isolated from the aluminum surface by anodic polarization in the benign NaCl/EG solution. Moreover, an APA through-hole membrane can be successfully fabricated by subsequent immersion in a 0.52 M H3PO4 solution.

Oleophilic to oleophobic wettability switching of isoporous through-hole membranes by surface structure control for low-voltage electrowetting-based oil-water separation

Wettability control is a critical element in oil-water mixture separation, which is usually implemented by complicated chemical treatment steps such as grafting, coating or chemical deposition. The chemically treated surfaces may degrade both chemically and physically upon repeated use and exposure to harsh conditions. Therefore, facile control of wettability of separation membrane, without applying any chemical treatment steps, is highly demanding. In this work, we have demonstrated wettability switching, from oleophilic to oleophobic, of soft-lithographically fabricated isoporous through-hole membranes by structure control only, while maintaining their intrinsic hydrophobicity. Applied voltage converts the water wettability from hydrophobic to hydrophilic by electrowetting phenomenon, without affecting oleophobicity; this hydrophilic/oleophobic combination has enabled successful oil-water separation. Soft lithographic fabrication of isoprous membranes has enabled easy variation of pore size, ranging from tens of microns down to sub-micron scale in diameter, so that those membranes can be applied for both stratified and emulsified oil-water mixture separation. Based on these properties, stratified and emulsified (both oil-in-water and water-in-oil) oil-water mixtures could be separated in high efficiency (or selectivity) (>99%) and relatively high flux (200–1500 Lm -2 h -1 for stratified and 250–1000 Lm -2 h -1 for emulsified mixtures, respectively). Furthermore, the membranes showed excellent durability by maintaining its hydrophobic/oleophobic wettability even after exposure to chemicals and high temperature, thanks to the thermoset nature of polyurethane acrylate (PUA) membrane material. Wettability switching by structure control only, without complicated chemical processing steps, may find widespread applications in various fields. • Isoporous through-hole membranes having various pore sizes by soft lithography. • Oil wettability switching from oleophilic to oleophobic by structure control only. • Water wettability switching by low-voltage electrowetting phenomenon. • High flux and efficiency separation of both layered and emulsified mixtures. • Robust membranes to harsh conditions such as high T and acidic/basic chemicals.

Selective Extraction of Trace Arsenite Ions Using a Highly Porous Aluminum Oxide Membrane with Ordered Nanopores.

Metal ion extraction and determination at trace level concentration are challenging due to sample complexity or spectral interferences. Herein, we prepared a through-hole aluminum oxide membrane (AOM) by electrochemical anodization of aluminum substrates. The prepared AOM was characterized by scanning electron microscopy, surface area analysis, porosity measurements, and X-ray photoelectron spectroscopy. The AOM with ordered nanopores was highly porous and possess inherent binding sites for selective arsenite sorption. The AOM was used as a novel sorbent for solid-phase microextraction and preconcentration of arsenite ions in water samples. The AOM’s sub-micrometer thickness allows water molecules to flow freely across the pores. Before instrumental determination, the suggested microextraction approach removes spectral interferents and improves the analyte ion concentration, with a detection limit of 0.02 μg L–1. Analyzing a standard reference material was used to validate the procedure. Student’s t-test value was less than critical Student’s t-value of 4.303 at a 95% confidence level. With coefficients of variation of 3.25%, good precision was achieved.

Efficient fabrication of ordered alumina through-hole membranes using a TiO2 protective layer prepared by atomic layer deposition.

Ordered alumina through-hole membranes were obtained by a combination of the anodization of Al, formation of a TiO2 protective layer, and subsequent etching. Two-layered anodic porous alumina materials composed of TiO2-coated and noncoated alumina were prepared by the combination of the anodization of Al and the formation of a TiO2 protective layer by atomic layer deposition (ALD). The obtained two layers of anodic porous alumina have different solubilities because the TiO2 thin layer formed by ALD acts as a protective layer that prevents the dissolution of the alumina layer during wet etching of the sample in an etchant. After the selective dissolution of the bottom layer of porous alumina without the TiO2 layer, an ordered alumina through-hole membrane could be detached from the Al substrate. This process allows the repeated preparation of ordered alumina through-hole membranes from a single Al substrate. By this process, ordered alumina through-hole membranes with large interhole distances could also be obtained. The obtained alumina through-hole membrane can be used in various applications.

Recyclable, Antibacterial, Isoporous Through-Hole Membrane Air Filters with Hydrothermally Grown ZnO Nanorods.

Reusable, antibacterial, and photocatalytic isoporous through-hole air filtration membranes have been demonstrated based on hydrothermally grown ZnO nanorods (NRs). High-temperature (300~375 °C) stability of thermoset-based isoporous through-hole membranes has enabled concurrent control of porosity and seed formation via high-temperature annealing of the membranes. The following hydrothermal growth has led to densely populated ZnO NRs on both the membrane surface and pore sidewall. Thanks to the nanofibrous shape of the grown ZnO NRs on the pore sidewall, the membrane filters have shown a high (>97%) filtration efficiency for PM2.5 with a rather low-pressure (~80 Pa) drop. The membrane filters could easily be cleaned and reused many times by simple spray cleaning with a water/ethanol mixture solution. Further, the grown ZnO NRs have also endowed excellent bactericidal performance for both Gram-positive S. aureus and Gram-negative S. enteritidis bacteria. Owing to the wide bandgap semiconductor nature of ZnO NRs, organic decomposition by photocatalytic activity under UV illumination has been successfully demonstrated. The reusable, multifunctional membrane filters can find wide applications in air filtration and purification.

A Microfluidic Flip-Chip Combining Hydrodynamic Trapping and Gravitational Sedimentation for Cell Pairing and Fusion.

Cancer cell–immune cell hybrids and cancer immunotherapy have attracted much attention in recent years. The design of efficient cell pairing and fusion chips for hybridoma generation has been, subsequently, a subject of great interest. Here, we report a three-layered integrated Microfluidic Flip-Chip (MFC) consisting of a thin through-hole membrane sandwiched between a mirrored array of microfluidic channels and saw-tooth shaped titanium electrodes on the glass. We discuss the design and operation of MFC and show its applicability for cell fusion. The proposed device combines passive hydrodynamic phenomenon and gravitational sedimentation, which allows the transportation and trapping of homotypic and heterotypic cells in large numbers with pairing efficiencies of 75~78% and fusion efficiencies of 73%. Additionally, we also report properties of fused cells from cell biology perspectives, including combined fluorescence-labeled intracellular materials from THP1 and A549, mixed cell morphology, and cell viability. The MFC can be tuned for pairing and fusion of cells with a similar protocol for different cell types. The MFC can be easily disconnected from the test setup for further analysis.

Desorption ionization using through-hole alumina membrane offers higher reproducibility than 2,5-dihydroxybenzoic acid, a widely used matrix in Fourier transform ion cyclotron resonance mass spectrometry imaging analysis.

DIUTHAME (desorption ionization using through-hole alumina membrane), a recently developed matrix-free ionization-assisting substrate, was examined for reproducibility in terms of mass accuracy and intensity using standard lipid and mouse brain sections. The impregnation property of DIUTHAME significantly improved the reproducibility of mass accuracy and intensity compared with 2,5-dihydroxybenzoic acid (DHB). Frozen tissue sections were mounted on indium tin oxide-coated glass slides. DIUTHAME and DHB were applied to individual sections. Subsequently, a solution of a phosphatidylcholine standard, PC(18:2/18:2), was poured onto the DIUTHAME and matrix. Finally, the samples were subjected to laser desorption ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry. The reproducibility was tested by calculating the mean ± standard deviation values of mass errors and intensities of individual ion species. Analysis of the PC(18:2/18:2) standard showed significantly (p < 0.01) lower mass error for DIUTHAME-MS than for MALDI-MS. Endogenous PC(36:4) analysis in mouse brain section also showed significantly (p < 0.05) lower mass errors for DIUTHAME-MS. Furthermore, we investigated the mass error of some abundant lipid ions in brain sections and observed similar results. DIUTHAME-MS displayed lower signal intensity in standard PC analysis. Interestingly, it offered higher signal intensities for all the endogenous lipid ions. Lower fluctuations of both mass accuracies and signal intensities were observed in DIUTHAME-MS. Our results demonstrated that DIUTHAME-MS offers higher reproducibility for mass accuracies and intensities than MALDI-MS in both standard lipid and mouse brain tissue analyses. It can potentially be used instead of conventional MALDI-MS and mass spectrometry imaging analyses to achieve highly reproducible data for mass accuracy and intensity.

Ultra-thin graphene oxide membrane deposited on highly porous anodized aluminum oxide surface for heavy metal ions preconcentration

Analyte extraction using graphene oxide (GO) can be challenging owing to the stochastic behavior of the permeation of water molecules and heavy metal ions, imperfect pore structures, and irregular distribution of multi-layer sheets. We prepared a free standing, through-hole graphene oxide membrane deposited on porous anodic aluminum oxide (AAO) substrate. The hydrophilicity of the GO membrane was improved via oxygen plasma treatment. The resulting AAO–GO membrane was used as novel adsorbent for the heavy metal ions preconcentration prior to their determination using inductively coupled plasma optical emission spectroscopy. This sub-micrometer-thick membrane allowed unimpeded permeation of water molecules via two-dimensional capillaries formed across the pores and in between the closely spaced GO sheets. The proposed method shows good detection limit of 1.2 ng L−1, and the co-existing ions did not affect the extraction efficiency of the adsorbent. The accuracy of the method was assessed by analyzing standard reference materials, where the Student’s t-test values were less than the critical Student’s t-value of 4.303 (95% confidence level). Good precision was achieved, as coefficients of variation ranged between 4% and 5%. The developed SPE adsorbent is a promising alternative for bulk adsorbents owing to the wide variety of available 2D materials and deposition methods.

SnO2 nanofibers prepared by wet spinning using an ordered porous alumina spinneret

SnO2 nanofibers with uniform diameters were obtained by wet spinning using ordered anodic porous alumina as a spinneret, followed by heat treatment. Ordered alumina through-hole membrane is a suitable spinneret material for nanofiber spinning owing to its nanohole array structure with uniform-sizes holes. A polymer solution containing a Sn salt was used as a precursor solution for the wet spinning. Polymer nanofibers containing the Sn salt were continuously formed as the precursor passed through the alumina holes into a coagulating solution. Monodisperse nanofiber structures were successfully maintained, even after heat treatment at 600 °C. This process enabled the preparation of monodisperse SnO2 nanofibers with diameters below 100 nm, as well as the precise control of fiber diameter by changing the hole size of the porous alumina spinneret. The obtained SnO2 nanofibers will be useful in various functional devices.