Ordered Metal Nanohole Arrays Made by a Two-Step Replication of Honeycomb Structures of Anodic Alumina

V-Shaped Heterostructure Nanocavities Array with CM and EM Coupled Enhancement for Ultra-Sensitive SERS Substrate

The field of semiconductor surface-enhanced Raman scattering (SERS) substrates has experienced significant advancements, leading to a wide range of applications in several fields. However, the quest for new ultra-sensitive semiconductor SERS materials is still of utmost importance. In this regard, an efficient and novel substrate, F4TCNQ/MoS2 heterostructure is introduced, assisted by V-shaped aluminum anodic oxide (AAO) nanocavities with different depths. Utilizing the efficient charge transfer of organic/inorganic semiconducting heterostructure and the photoconfinement capability of the nanocavity structure of the AAO nanotemplate, excellent stability, fast sensing, enhanced Raman, and photodegradation activities are achieved. Due to its unique 3D structure, the optimized F4TCNQ/MoS2/AAO with 1500 nm depth achieves ultra-high sensitivity detection of 9.0×10-16 M for conventional probe molecules. Furthermore, precise detection of water contaminants is observed for the first time with a V-shaped heterostructure due to combined organic/inorganic features that differ significantly from conventional MoS2 structures or other metal/inorganic or inorganic/inorganic semiconductors. This research presents a novel and versatile strategy for SERS and demonstrates its diverse potential performance in practical applications.

2D Materials for Potable Water Application: Basic Nanoarchitectonics and Recent Progresses

Water polluted by toxic chemicals due to waste from chemical/pharmaceuticals and harmful microbes such as E. Coli bacteria causes several fatal diseases; and therefore, water filtration is crucial for accessing clean and safe water necessary for good health. Conventional water filtration technologies include activated carbon filters, reverse osmosis, and ultrafiltration. However, they face several challenges, including high energy consumption, fouling, limited selectivity, inefficiencies in removing certain contaminants, dimensional control of pores, and structural/chemical changes at higher thermal conditions and upon prolonged usage of water filter. Recently, the advent of 2D materials such as graphene, BN, MoS2, MXenes, and so on opens new avenues for advanced water filtration systems. This review delves into the nanoarchitectonics of 2D materials for water filtration applications. The current state of water filtration technologies is explored, the inherent challenges they face are outlines, and the unique properties and advantages of 2D materials are highlighted. Furthermore, the scope of this review is discussed, which encompasses the synthesis, characterization, and application of various 2D materials in water filtration, providing insights into future research directions and potential industrial applications.

Magnetism of metastable γ-Fe85Pd15 nanowire arrays across an unusually broad temperature range (5 K to 800 K)

Arrays of 50 nm diameter Fe85Pd15 cylindrical nanowires were electrochemically grown, crystallizing in a metastable γ-Fe(Pd) fcc A1 disordered solid solution. After performing a heating-cooling thermal cycle between 300 K and 1000 K, the γ-Fe(Pd) fcc metastable phase still predominates (97%), coexisting with a not-fully-identified minority phase. The thermal cycling induces a moderate increase in the crystallite size and a reduction of the lattice parameter although leading to a significant heating-cooling magnetic hysteresis. No further changes in temperature-dependent magnetization, M(T), are observed during subsequent cycling. The full-range (5 K to 800 K) saturation magnetization Ms(T) curve is quite accurately described by a phenomenological expression, which provides a Bloch-type contribution as T → 0 and undergoes the critical behavior near the Curie temperature TC. An upturn in Ms(T) is observed below 100 K which is described by a spin-glass-like second contribution, with freezing temperature Tf = (80 ± 2) K, and kBTf comparable to the exchange interactions in Fe-Pd systems. A Curie temperature of TC = 830 K, and a critical exponent value β = 0.42 ± 0.05 are estimated. These regimes (below and above 100 K) are also observed in the magnetization process. The temperature dependence of coercivity between 100 K and 800 K is consistent with a nucleation/propagation remagnetization mechanism, with activation energy of (320 ± 20) kJ mol-1 and critical field for magnetization reversal of (65 ± 1) mT, at 0 K. The analysis of the effective magnetic anisotropy as a function of temperature allows us to conclude that it essentially arises from the balance between different magnetostatic contributions.

Recent advances of small molecule detection in nanopore sensing

Due to its advantages of label-free and highly sensitive, the resistive pulse sensing with a nanopore has recently become even more potent for the discrimination of analytes in single molecule level. Generally, a transient interruption of ion current originated from the captured molecule passing through a nanopore will provide the rich information on the structure, charge and translocation dynamics of the analytes. Therefore, nanopore sensors have been widely used in the fields of DNA sequencing, protein recognition, and the portable detection of varied macromolecules and particles. However, the conventional nanopore devices are still lack of sufficient selectivity and sensitivity to distinguish more metabolic molecules involving ATP, glucose, amino acids and small molecular drugs because it is hard to receive a large number of identifiable signals with the fabricated pores comparable in size to small molecules for nanopore sensing. For all this, a series of innovative strategies developed in the past decades have been summarized in this review, including host-guest recognition, engineering alteration of protein channel, the introduction of nucleic acid aptamers and various delivery carriers integrating signal amplification sections based on the biological and solid nanopore platforms, to achieve the high resolution for the small molecules sensing in micro-nano environment. These works have greatly enhanced the powerful sensing capabilities and extended the potential application of nanopore sensors.

Controlled electrodeposition of cobalt nanowires usingiRcompensation and their electron transport properties

Superconducting hybrid structures based on single nanowires are a new type of nanoscale devices with peculiar transport characteristics. Control over the nanowire structure is essential for understanding hybrid electronic phenomena arising in such complex systems. In this work, we report a technique for the fabrication of cobalt nanowires by template-assisted electrodeposition usingiRcompensation, which allows revealing the fundamental dependence of the preferred direction of nanowire growth on the deposition potential. Long coarse-grained cobalt nanowires with a diameter of 70 nm have been implemented into Nb/Co/Nb hybrid structures. We demonstrate that using electrode fabrication techniques that do not contaminate the surface of the nanowire leads to a high quality of devices with low-resistance interfaces. Low-temperature resistivity of 4.94 ± 0.83µΩ cm and other transport characteristics of Co nanowires are reported. The absence of long-range superconducting proximity effect for Nb/Co/Nb systems with different nanowire length is discussed.

Quantifying and Modeling the Crystallinity of Polymers Confined in Nanopores

We propose a methodology to characterize the crystalline content of interfacial polymer layers in systems confined at the nanoscale level in a 2D geometry. Based on the crystallinity data of a set of polymers, we introduce a simple model to describe the gradient in crystallinity introduced by confining polymer chains in nanopores. Our model underscores the pivotal role that interfaces play in crystallization and unequivocally contradicts the existence of interfacial "dead" layers where crystallization cannot take place. Further, we verified that the organization of crystals near the pore walls resembles the macromolecular architecture of adsorbed layers, hinting at a strong interplay between crystallization and adsorption.

Facile Fabrication of Hierarchical Structured Anodic Aluminum Oxide Molds for Large-Scale Production of Superhydrophobic Polymer Films

Anodized aluminum oxide (AAO) molds were used for the production of large-area and inexpensive superhydrophobic polymer films. A controlled anodization methodology was developed for the fabrication of hierarchical micro-nanoporous (HMN) AAO imprint molds (HMN-AAO), where phosphoric acid was used as both an electrolyte and a widening agent. Heat generated upon repetitive high-voltage (195 V) anodization steps is effectively dissipated by establishing a cooling channel. On the HMN-AAO, within the hemispherical micropores, arrays of hexagonal nanopores are formed. The diameter and depth of the micro- and nanopores are 18/8 and 0.3/1.25 µm, respectively. The gradual removal of micropatterns during etching in both the vertical and horizontal directions is crucial for fabricating HMN-AAO with a high aspect ratio. HMN-AAO rendered polycarbonate (PC) and polymethyl methacrylate (PMMA) films with respective water contact angles (WCAs) of 153° and 151°, respectively. The increase in the WCA is 80% for PC (85°) and 89% for PMMA (80°). On the PC and PMMA films, mechanically robust arrays of nanopillars are observed within the hemispherical micropillars. The micro-nanopillars on these polymer films are mechanically robust and durable. Regular nanoporous AAO molds resulted in only a hydrophobic polymer film (WCA = 113-118°). Collectively, the phosphoric acid-based controlled anodization strategy can be effectively utilized for the manufacturing of HMN-AAO molds and roll-to-roll production of durable superhydrophobic surfaces.

Preparation and Characterization of Oxide Nanotubes on Titanium Surface for Use in Controlled Drug Release Systems

Preventing or treating infections at implantation sites where the risk of bacterial contamination is high requires the development of intelligent drug delivery systems. The objective of this work was to develop a production method and characterization of fourth-generation oxide nanotubes on titanium grade 4 surface as a potential drug carrier. This study focused on the anodizing process; physico-chemical characterization using FE-SEM, EDS, and FTIR; in vitro corrosion resistance in an artificial saliva solution; and determining the drug release kinetics of gentamicin sulfate using UV-VIS. The anodizing process was optimized to produce fourth-generation oxide nanotubes in a fluoride-free electrolyte, ensuring rapid growth and lack of order. Results showed that the length of the oxide nanotubes was inversely proportional to the anodizing voltage, with longer nanotubes formed at lower voltages. The nanotubes were shown to have a honeycomb structure with silver particles co-deposited on the surface for antibacterial properties and were capable of carrying and releasing the antibiotic gentamicin sulfate in a controlled manner, following Fick's first law of diffusion. The corrosion resistance study demonstrates that the oxide nanotubes enhance the corrosion resistance of the titanium surface. The oxide nanotubes show promise in enhancing osseointegration and reducing post-implantation complications.

Self-Assembled TiN-Metal Nanocomposites Integrated on Flexible Mica Substrates towards Flexible Devices

The integration of nanocomposite thin films with combined multifunctionalities on flexible substrates is desired for flexible device design and applications. For example, combined plasmonic and magnetic properties could lead to unique optical switchable magnetic devices and sensors. In this work, a multiphase TiN-Au-Ni nanocomposite system with core-shell-like Au-Ni nanopillars embedded in a TiN matrix has been demonstrated on flexible mica substrates. The three-phase nanocomposite film has been compared with its single metal nanocomposite counterparts, i.e., TiN-Au and TiN-Ni. Magnetic measurement results suggest that both TiN-Au-Ni/mica and TiN-Ni/mica present room-temperature ferromagnetic property. Tunable plasmonic property has been achieved by varying the metallic component of the nanocomposite films. The cyclic bending test was performed to verify the property reliability of the flexible nanocomposite thin films upon bending. This work opens a new path for integrating complex nitride-based nanocomposite designs on mica towards multifunctional flexible nanodevice applications.

Fabrication of nanoparticle array membranes by integrating semi-crystalline polymer self-assembly with NIPS for water treatment

The integration of polymer self-assembly with non-solvent induced phase separation (SNIPS) represents a recent advancement in membrane fabrication. This breakthrough allows for the fabrication of membranes with uniformly sized pores, enabling precise and fast separation through a phase inversion process commonly used in industrial fabrication. Currently, block copolymers are used in implementing the SNIPS strategy. In order to facilitate an easier and more flexible fabrication procedure, we employed the widely used semi-crystalline polymer polyvinylidene fluoride (PVDF) as the base material for achieving SNIPS through self-seeding. This process involves filtering the PVDF casting solution to induce microphase separation and generate crystal seeds. Subsequently, NIPS is applied to enable the growth of crystal seeds into uniformly distributed nanoparticles with consistent size and shape, ultimately resulting in a membrane with a uniform pore size. The fabricated membrane exhibited improved flux (2924.67 ± 28.02 L m-2 h-1 at 0.5 bar) and rejection (91% for 500 nm polystyrene particles). Notably, the microphase separation in the casting solution is a distinguishing feature of the SNIPS compared to NIPS. In this study, we found that the microphase separation of semi-crystalline polymers is also crucial for achieving membranes with uniform pore sizes. This finding may extend the potential application of the SNIPS strategy to include semi-crystalline polymers.

Nature of instability in flow-driven porous anodic oxide

Self-organized porous anodic oxide films are formed by the electrochemical oxidation of reactive metal aluminum in acidic solutions in which the oxide is soluble. Recently, viscous flow models have shown using linear stability analysis that the instability results from a trade-off between the destabilizing effect of viscous flow of oxide and the stabilizing effect of oxide formation, which provides the wavelength selection mechanism for pattern formation. Anion adsorption on surface growth sites causes nonuniform compressive stress at the oxide-solution interface, which drives the flow. This anodic instability is analogous to the classical Marangoni instability induced by surface tension gradients. In this work, nature of the instability beyond the stability threshold is determined using a weakly nonlinear analysis. For the growth of well-developed pores beyond the threshold, a subcritical nature of the instability is essential. However, our weakly nonlinear analysis shows that the solutions emerging from neutral stability are supercritical in nature at all wavenumbers for the practical range of anodizing control parameters investigated. We also determine the region where the model is Hadamard stable, a necessary condition for well-posedness.

Incorporation of Anions into Anodic Alumina-A New Track in Cr(VI) Anodizing Substitution?

Aluminum technical alloys are well known for their outstanding mechanical properties, especially after heat treatment. However, quenching and aging, which improve the mechanical properties, by the formation of Cu-rich zones and phases that are coherent with the matrix and block the dislocation motion, cause uneven distribution of the elements in the alloy and consequently make it prone to corrosion. One method providing satisfactory corrosion protection of aluminum alloys is anodizing. On an industrial scale, it is usually carried out in electrolytes containing chromates that were found to be cancerogenic and toxic. Therefore, much effort has been undertaken to find substitutions. Currently, there are many Cr(VI)-free substitutes like tartaric-sulfuric acid anodizing or citric-sulfuric acid anodizing. Despite using such approaches even on the industrial scale, Cr(VI)-based anodizing still seems to be superior; therefore, there is an urge to find more complex but more effective approaches in anodizing. The incorporation of anions into anodic alumina from the electrolytes is a commonly known effect. Researchers used this phenomenon to entrap various other anions and organic compounds into anodic alumina to change their properties. In this review paper, the impact of the incorporation of various corrosion inhibitors into anodic alumina on the corrosion performance of the alloys is discussed. It is shown that Mo compounds are promising, especially when combined with organic acids.

Optical Modification of a Nanoporous Alumina Structure Associated with Surface Coverage by the Ionic Liquid AliquatCl

This manuscript analyses changes in the optical parameters of a commercial alumina nanoporous structure (AnodiscTM or AND support) due to surface coverage by the ionic liquid (IL) AliquatCl (AlqCl). XPS measurements were performed for chemical characterization of the composite AND/AlqCl and the AND support, but XPS resolved angle analysis (from 15° to 75°) was carried out for the homogeneity estimation of the top surface of the ANDAlqCl sample. Optical characterization of both the composite AND/AlqCl and the AND support was performed by three non-destructive and non-invasive techniques: ellipsometry spectroscopy (SE), light transmittance/reflection, and photoluminescence. SE measurements (wavelength ranging from 250 nm to 1250 nm) allow for the determination of the refraction index of the AND/AlqCl sample, which hardly differs from that corresponding to the IL, confirming the XPS results. The presence of the IL significantly increases the light transmission of the alumina support in the visible region and reduces reflection, affecting also the maximum position of this latter curve, as well as the photoluminescence spectra. Due to these results, illuminated I-V curves for both the composite AND/AlqCl film and the AND support were also measured to estimate its possible application as a solar cell. The optical behaviour exhibited by the AND/AlqCl thin film in the visible region could be of interest for different applications.

An investigation using DFT into the impact of hydrogen on oxygen migration processes during aluminum anodization

First-principles computations were utilized to examine the impact of H atoms on the surface behavior of O atoms on the (111) surface of Al and their infiltration behavior into the Al crystal, with the aim of elucidating the behavior of ions in the anodic process during aluminum oxidation. According to the findings, the "abstract" action of H atoms significantly lowers the energy barrier preventing O from entering the Al crystal. The addition of a H atom influences the diffusion of O atoms in the Al crystal as well, and this can lower the activation energy of O atom migration between the tetrahedral interstitial locations from 1.23 eV to 0.35 eV. We can benefit from knowing how ions are transported and anodic oxidation occurs.

Control of Water Droplet Transport Using Anodic Porous Alumina with a Wettability Gradient

Water droplets can spontaneously move on surfaces with a wettability gradient, and such surfaces can be used in various functional devices. In this study, surfaces with a wettability gradient were prepared from anodic porous alumina with different pore arrangement regularities. The evaluation of the water droplet transport distance on the surfaces of the prepared samples showed that the pore arrangement regularity of the anodic porous alumina had no effect on the droplet transport distance. It was also shown that the droplet transport distance was affected by the droplet size and the width of the wettability gradient structure. When two water droplets were formed at both ends of the anodic porous alumina with an increasing gradient of pore diameter from the center to both ends, they moved from the ends toward the center and merged. The method reported in this paper shows that by controlling the pore size of anodic porous alumina, one can fabricate a substrate on which droplets can move in any direction. The anodic porous alumina with a wettability gradient as obtained in this study has potential use for various applications such as microfluidic devices and analytical chips.

Surface Modification of Nanopores in an Anodic Aluminum Oxide Membrane through Dopamine-Assisted Codeposition with a Zwitterionic Polymer

Surface modification through dopamine-assisted codeposition with functional zwitterionic polymers can provide a simple and one-step functionalization under ambient conditions with robust and stable dopamine-surface interactions to improve the hydrophilicity of nanoporous membranes, thereby expanding their applicability to nanofiltration, ion transport, and blood purification. However, a significant knowledge gap remains in our comprehension of the mechanisms underlying the formation and deposition of dopamine/polymer aggregated coatings within nanoscale confinement. This study explores a feasible method for membrane modification through the codeposition of dopamine hydrochloride (DA) and poly(sulfobetaine methacrylate) (PSBMA) on nanopores of anodic aluminum oxide (AAO) membranes. Our findings demonstrate that the aggregated coatings of DA and PSBMA nanocomposites can effectively deposit on the surfaces within cylindrical AAO nanopores, significantly enhancing the hydrophilicity of the nanoporous membranes. The morphology and homogeneity of the nanocomposite coatings within the nanopores are further investigated by varying PSBMA molecular weights and AAO pore sizes, revealing that higher molecular weights result in more uniform deposition. This work sheds light on understanding the codeposition of DA and zwitterionic polymers in nanoscale environments, highlighting a straightforward and stable surface modification process of nanoporous membranes involving functional polymers.

Wave absorbing properties of Ni Nanoparticle/CNT composite film fabricated by AAO/CNTs electrode

An effective wave absorbing Nano-Ni/carbon nanotubes (CNTs) composite film was developed by electrodeposition using an anodic aluminum oxide (AAO)/CNTs electrode. Scanning electron microscopy images confirmed the uniform dispersion of Ni nano-particles within the CNTs, and the particle diameter increasing from 20 nm to 100 nm as the deposition time increased. XRD test results revealed that the crystal phase of the Ni nano-particles remained unchanged during different deposition time, exhibiting a Face Center Cubic (fcc) structure. The microwave electromagnetic properties of the film were evaluated using a vector network analyzer, and the return loss curve demonstrated that the Ni nano-particles/CNTs composite exhibited exceptional wave absorption capabilities. The composite film showed an effective absorption width of 13 GHz (4-17 GHz) and achieved a minimum reflection loss (RL) of -17 dB at 14 GHz.

2D-Like Catalyst with a Micro-nanolinked Functional Surface for Water Purification

In water purification, the performance of heterogeneous advanced oxidation processes significantly relies upon the utilization of the catalyst's specific surface area (SSA). However, the presence of the structural "dead volume" and pore-size-induced diffusion-reaction trade-off limitation restricts the functioning of the SSA. Here, we reported an effective approach to make the best SSA by changing the traditional 3D spherule catalyst into a 2D-like form and creating an in situ micro-nanolinked structure. Thus, a 2D-like catalyst was obtained which was characterized by a mini "paddy field" surface, and it exhibited a sharply decreased dead volume, a highly available SSA and oriented flexibility. Given its paddy-field-like mass-transfer routine, the organic capture capability was 7.5-fold higher than that of the catalyst with mesopores only. Moreover, such a catalyst exhibited a record-high O3-to-·OH transition rate of 2.86 × 10-8 compared with reported millimetric catalysts (metal base), which contributed to a 6.12-fold higher total organic removal per catalyst mass than traditional 3D catalysts. The facile scale preparation, performance stability, and significant material savings with the 2D-like catalyst were also beneficial for practical applications. Our findings provide a unique and general approach for designing potential catalysts with excellent performance in water purification.

In situ optical sub-wavelength thickness control of porous anodic aluminum oxide

Porous anodic aluminum oxide (PAAO), sometimes referred to as nanoporous anodic alumina, serves as a cost-effective template for nanofabrication in many fields of science and engineering. However, production of ultrathin PAAO membranes with precise thickness in the optical sub-wavelength range remains challenging because of difficulties regarding process control at the initial stage of anodic oxidation. In this study, we demonstrate a technique for consistently manufacturing PAAO with the targeted thickness. An electrochemical cell with an optical window was designed for reflectance spectroscopy of PAAO during anodization. Real-time fitting of spectra to a transfer-matrix model enabled continuous monitoring of the thickness growth of the PAAO layer. Automation software was designed to terminate the anodization process at preset PAAO thickness values. While the concept was illustrated using the widely used method of anodization in a 0.3 M oxalic acid electrolyte with a 40 V potential, it can be readily customized for other protocols. PAAO layers with effective thickness below 300 nm could be produced with a few nanometers accuracy using single-crystal aluminum substrates. The results were confirmed using spectroscopic ellipsometry. The method for controlling the thickness during anodization eliminates the necessity of sample sectioning for electron microscopy and is particularly valuable for the small-scale production of PAAO-based functional optical coatings.

Recent Advances in Nanowire-Based Wearable Physical Sensors

Wearable electronics is a technology that closely integrates electronic devices with the human body or clothing, which can realize human-computer interaction, health monitoring, smart medical, and other functions. Wearable physical sensors are an important part of wearable electronics. They can sense various physical signals from the human body or the surrounding environment and convert them into electrical signals for processing and analysis. Nanowires (NW) have unique properties such as a high surface-to-volume ratio, high flexibility, high carrier mobility, a tunable bandgap, a large piezoresistive coefficient, and a strong light-matter interaction. They are one of the ideal candidates for the fabrication of wearable physical sensors with high sensitivity, fast response, and low power consumption. In this review, we summarize recent advances in various types of NW-based wearable physical sensors, specifically including mechanical, photoelectric, temperature, and multifunctional sensors. The discussion revolves around the structural design, sensing mechanisms, manufacture, and practical applications of these sensors, highlighting the positive role that NWs play in the sensing process. Finally, we present the conclusions with perspectives on current challenges and future opportunities in this field.

Asymmetric Nanoporous Alumina Membranes for Nanofluidic Osmotic Energy Conversion

The potential of harnessing osmotic energy from the interaction between seawater and river water has been recognized as a promising, eco-friendly, renewable, and sustainable source of power. The reverse electrodialysis (RED) technology has gained significant interest for its ability to generate electricity by combining concentrated and diluted streams with different levels of salinity. Nanofluidic membranes with tailored ion transport dynamics enable efficient harvesting of renewable osmotic energy. In this regard, anodic aluminum oxide (AAO) membranes with abundant nanochannels provide a cost-effective nanofluidic platform to obtain structures with a high density of ordered pores. AAO can be utilized in constructing asymmetric composite membranes with enhanced ion flux and selectivity to improve output power generation. In this review, we first present the fundamental structure and properties of AAO, followed by summarizing the fabrication techniques for asymmetric membranes using AAO and other nanostructured materials. Subsequently, we discuss the materials employed in constructing asymmetric structures incorporating AAO while emphasizing how material selection and design can resist and promote efficient energy conversion. Finally, we provide an outlook on future applications and address the challenges that need to be overcome for successful osmotic energy conversion.

Flat and roll-type translucent anodic porous alumina molds anodized in oxalic acid for UV nanoimprint lithography

There is much interest in UV nanoimprinting as a fabrication method for various functional devices because of its suitability for efficient fine patterning. To form patterns on opaque substrates by UV nanoimprinting, it is essential to use molds through which UV light can pass. In this study, translucent anodic porous alumina (APA) molds for UV nanoimprinting were fabricated by the anodization of an Al substrate. To fabricate a translucent APA mold, an ordered APA film used as a mold for UV nanoimprinting was formed on the surface side of the Al substrate, and then anodization was continued from the back surface of the Al substrate to increase its transparency in the UV spectral range. A gradient change of Al thickness is necessary for the production of a large-area translucent mold, since it lowers the thickness of opaque defects remaining in the mold. The resulting translucent mold was effective for UV nanoimprinting to prepare ordered polymer nanopillar arrays on the surfaces of opaque substrates because the transmittance of the resulting translucent APA mold was 40% at a wavelength of 365 nm, which was confirmed to be sufficiently translucent to polymerize the photocurable monomer used in this study. In addition, it was possible to fabricate roll-type translucent APA molds by using Al pipes as a starting material. A seamless ordered nanopillar array can be effectively formed on a substrate by continuous UV nanoimprinting using the resulting roll-type translucent APA molds. Ordered nanopillar arrays formed on opaque substrates by UV nanoimprinting using translucent APA molds have various potential applications, such as those for forming antireflective and water-repellent surfaces.

Recent Progress of Self-Supported Metal Oxide Nano-Porous Arrays in Energy Storage Applications

The demand for high-performance and cost-effective energy storage solutions for mobile electronic devices and electric vehicles has been a driving force for technological advancements. Among the various options available, transitional metal oxides (TMOs) have emerged as a promising candidates due to their exceptional energy storage capabilities and affordability. In particular, TMO nanoporous arrays fabricated by electrochemical anodization technique demonstrate unrivaled advantages including large specific surface area, short ion transport paths, hollow structures that reduce bulk expansion of materials, and so on, which have garnered significant research attention in recent decades. However, there is a lack of comprehensive reviews that discuss the progress of anodized TMO nanoporous arrays and their applications in energy storage. Therefore, this review aims to provide a systematic detailed overview of recent advancements in understanding the ion storage mechanisms and behavior of self-organized anodic TMO nanoporous arrays in various energy storage devices, including alkali metal ion batteries, Mg/Al-ion batteries, Li/Na metal batteries, and supercapacitors. This review also explores modification strategies, redox mechanisms, and outlines future prospects for TMO nanoporous arrays in energy storage.

Water Activation in Solar-Powered Vapor Generation

Solar-powered vapor evaporation (SVG), based on the liquid-gas phase conversion concept using solar energy, has been given close attention as a promising technology to address the global water shortage. At molecular level, water molecules escaping from liquid water should overcome the attraction of the molecules on the liquid surface layer to evaporate. For this reason, it is better to reduce the energy required for evaporation by breaking a smaller number of hydrogen bonds or forming weak hydrogen bonds to ensure efficient and convenient vapor production. Many novel evaporator materials and effective water activation strategies have been proposed to stimulate rapid steam production and surpass the theoretical thermal limit. However, an in-depth understanding of the phase/enthalpy change process of water evaporation is unclear. In this review, a summary of theoretical analyses of vaporization enthalpy, general calculations, and characterization methods is provided. Various water activation mechanisms are also outlined to reduce evaporation enthalpy in evaporators. Moreover, unsolved issues associated with water activation are critically discussed to provide a direction for future research. Meanwhile, significant pioneering developments made in SVG are highlighted, hoping to provide a relatively entire chain for more scholars who are just stepping into this field.

High-Performance 3D Nanostructured Silver Electrode for Micro-Supercapacitor Application

In the current energy crisis scenario, the development of renewable energy forms such as energy storage systems among the supercapacitors is an urgent need as a tool for environmental protection against increasing pollution. In this work, we have designed a novel 3D nanostructured silver electrode through an antireplica/replica template-assisted procedure. The chemical surface and electrochemical properties of this novel 3D electrode have been studied in a 5 M KOH electrolyte. Microstructural characterization and compositional analysis were studied by SEM, energy-dispersive X-ray spectroscopy, XRD technique, and Kripton adsorption at -198 °C, together with cyclic voltammetry and galvanostatic charge-discharge cycling measurements, Coulombic efficiency, cycle stability, and their leakage current drops, in addition to the self-discharge and electrochromoactive behavior, were performed to fully characterize the 3D nanostructured electrode. Large areal capacitance value of 0.5 F/cm2 and Coulombic efficiency of 97.5% are obtained at a current density of 6.4 mA/cm2 for a voltage window of 1.2 V (between -0.5 and 0.8 V). The 3D nanostructured silver electrode exhibits excellent capacitance retention (95%) during more than 2600 cycles, indicating a good cyclic stability. Additionally, the electrode delivers a high energy density of around 385.87 μWh/cm2 and a power density value of 3.82 μW/cm2 and also displays an electrochromoactive behavior. These experimental results strongly support that this versatile combined fabrication procedure is a suitable strategy for improving the electrochemical performances of 3D nanostructured silver electrodes for applications as micro-supercapacitors or in electrochemical devices.

Advances in the Fabrication of Nanoporous Anodic Aluminum Oxide and Its Applications to Sensors: A Review

Nanoporous anodic aluminum oxide (AAO) is an important template for 1D nanomaterial synthesis. It is used as an etching template for nanopattern transfer in a variety of contexts, including nanostructured material synthesis, electrical sensors, optical sensors, photonic and electronic devices, photocatalysis, and hardness and anticorrosion improvement. In this review, we focus on various fabrication methods, pore geometry modification, and recent advances of AAO, as well as sensor applications linked to our environment, daily life, and safety. Pore geometry is concerned with the material composition, applied voltage mold, electrolyte type, temperature, and anodizing time during the fabrication of AAOs and for adjusting their pore size and profile. The applied voltage can be divided into four types: direct current anodization (DCA), reverse pulse anodization, pulse anodization (PA), and hybrid pulse anodization (HPA). Conventional AAOs are fabricated using DCA and mild anodization (MA) at a relatively low temperature (-5~15 °C) to reduce the Joule heating effect. Moreover, the issues of costly high-purity aluminum and a long processing time can be improved using HPA to diminish the Joule heating effect at relatively high temperatures of 20-30 °C with cheap low-purity (≤99%) aluminum. The AAO-based sensors discussed here are primarily divided into electrical sensors and optical sensors; the performance of both sensors is affected by the sensing material and pore geometry. The electrical sensor is usually used for humidity or gas measurement applications and has a thin metal film on the surface as an electrode. On the contrary, the AAO optical sensor is a well-known sensor for detecting various substances with four kinds of mechanisms: interference, photoluminescence, surface plasma resonance, and surface-enhanced Raman scattering (SERS). Especially for SERS mechanisms, AAO can be used either as a solid support for coating metal nanoparticles or a template for depositing the metal content through the nanopores to form the nanodots or nanowires for detecting substances. High-performance sensors will play a crucial role in our living environments and promote our quality of life in the future.

Electrical surface properties of nanoporous alumina membranes: influence of nanochannels' curvature, roughness and composition studied via electrokinetic experiments

Among classical nanoporous oxide membranes, anodic aluminum oxide (AAO) membranes, made of non-connected, parallel and ordered nanochannels, are very interesting nanoporous model systems widely used for multiple applications. Since most of these applications involve local phenomena at the nanochannel surface, the fine description of the electrical surface behavior in aqueous solution is thus of primordial interest. Here, we use an original experimental approach combining several electrokinetic techniques (tangential and transverse streaming potential as well as electrophoretic mobility experiments) to measure the ζ-potential and determine the surface isoelectric points (IEPs) of several AAOs having different characteristic sizes and compositions. Using such an approach, all the different surfaces available in AAOs can be probed: outer surfaces (top and bottom planes), pore wall surfaces (i.e., inner surfaces) and surfaces created by the grinding of the AAOs. We find clear IEP differences between the outer, pore wall and ground surfaces and discuss these in terms of nanochannel and surface morphology (curvature and roughness) and of modifications of the chemical environment of the surface hydroxyl groups. These results highlight the heterogeneities between the different surfaces of these AAO membranes and emphasize the necessity to combine complementary electrokinetic techniques to properly understand the material, an approach which can be extended to many nanoporous systems.

Hydride formation and dynamic phase changes during template-assisted Pd electrodeposition

We investigated the structural evolution of electrochemically fabricated Pd nanowiresin situby means of grazing-incidence transmission small- and wide-angle x-ray scattering (GTSAXS and GTWAXS), x-ray fluorescence (XRF) and two-dimensional surface optical reflectance (2D-SOR). This shows how electrodeposition and the hydrogen evolution reaction (HER) compete and interact during Pd electrodepositon. During the bottom-up growth of the nanowires, we show thatβ-phase Pd hydride is formed. Suspending the electrodeposition then leads to a phase transition fromβ-phase Pd hydride toα-phase Pd. Additionally, we find that grain coalescence later hinders the incorporation of hydrogen in the Pd unit cell. GTSAXS and 2D-SOR provide complementary information on the volume fraction of the pores occupied by Pd, while XRF was used to monitor the amount of Pd electrodeposited.

Understanding the Intrinsic Rectification Properties of Nanoporous Anodic Alumina by Selective Chemical Etching

The distribution of oxygen and aluminum vacancies across the hemispherical barrier oxide layer (BOL) of nanoporous anodic alumina (NAA) relies intrinsically on the electric field-driven flow of electrolytic species and the incorporation of electrolyte impurities during the growth of anodic oxide through anodization. This phenomenon provides new opportunities to engineer BOL's inherited ionic current rectification (ICR) fingerprints. NAA's characteristic ICR signals are associated with the space charge density gradient across BOL and electric field-induced ion migration through hopping from vacancy to vacancy. In this study, we engineer the intrinsic space charge density gradient of the BOL of NAA under a range of anodizing potentials in hard and mild anodization regimes. Real-time characterization of the ICR fingerprints of NAA during selective etching of the BOL makes it possible to unravel the distribution pattern of vacancies through rectification signals as a function of etching direction and time. Our analysis demonstrates that the space charge density gradient varies across the BOL of NAA, where the magnitude and distribution of the space charge density gradient are revealed to be critically determined by anodizing the electrolyte, regime, and potential. This study provides a comprehensive understanding of the engineering of ion transport behavior across blind-hole NAA membranes by tuning the distribution of defects across BOL through anodization conditions. This method has the potential to be harnessed for developing nanofluidic devices with tailored ionic rectification properties for energy generation and storage and sensing applications.

Taming Multiscale Structural Complexity in Porous Skeletons: From Open Framework Materials to Micro/Nanoscaffold Architectures

Recent developments in the design and synthesis of more and more sophisticated organic building blocks with controlled structures and physical properties, combined with the emergence of novel assembly modes and nanofabrication methods, make it possible to tailor unprecedented structurally complex porous systems with precise multiscale control over their architectures and functions. By tuning their porosity from the nanoscale to microscale, a wide range of functional materials can be assembled, including open frameworks and micro/nanoscaffold architectures. During the last two decades, significant progress is made on the generation and optimization of advanced porous systems, resulting in high-performance multifunctional scaffold materials and novel device configurations. In this perspective, a critical analysis is provided of the most effective methods for imparting controlled physical and chemical properties to multifunctional porous skeletons. The future research directions that underscore the role of skeleton structures with varying physical dimensions, from molecular-level open frameworks (<10 nm) to supramolecular scaffolds (10-100 nm) and micro/nano scaffolds (>100 nm), are discussed. The limitations, challenges, and opportunities for potential applications of these multifunctional and multidimensional material systems are also evaluated in particular by addressing the greatest challenges that the society has to face.

Tsuchime-like Aluminum Film to Enhance Absorption in Ultra-Thin Photovoltaic Cells

Ultra-thin solar cells enable materials to be saved, reduce deposition time, and promote carrier collection from materials with short diffusion lengths. However, light absorption efficiency in ultra-thin solar panels remains a limiting factor. Most methods to increase light absorption in ultra-thin solar cells are either technically challenging or costly, given the thinness of the functional layers involved. We propose a cost-efficient and lithography-free solution to enhance light absorption in ultra-thin solar cells-a Tsuchime-like self-forming nanocrater (T-NC) aluminum (Al) film. T-NC Al film can be produced by the electrochemical anodization of Al, followed by etching the nanoporous alumina. Theoretical studies show that T-NC film can increase the average absorbance by 80.3%, depending on the active layer's thickness. The wavelength range of increased absorption varies with the active layer thickness, with the peak of absolute absorbance increase moving from 620 nm to 950 nm as the active layer thickness increases from 500 nm to 10 µm. We have also shown that the absorbance increase is retained regardless of the active layer material. Therefore, T-NC Al film significantly boosts absorbance in ultra-thin solar cells without requiring expensive lithography, and regardless of the active layer material.

Effect of Al Polishing Conditions on the Growth and Morphology of Porous Anodic Alumina Films

The conditions applied during the electrochemical polishing of aluminum were found to be important parameters for the successive formation of nanoporous alumina films. First, a high-purity Al foil was electrochemically polished in an aqueous solution containing C2H5OH and HClO4 at various sets of conditions, such as applied potential (5-35 V), temperature (0-20 °C), and process duration (10-180 s). Extensive studies of the topography of Al after polishing by scanning electron microscopy and atomic force microscopy allow verification of the correlations between conditions applied during the substrate pretreatment and dimensions of the nanopatterns generated on the metal surface. Next, Al polished samples at two different sets of conditions were used as starting materials for anodization. Unpolished Al samples were also anodized for reference. It was confirmed that electropolishing conditions do not significantly affect the oxide growth rate during anodization and the efficiency of anodic film formation. On the contrary, it was proved that the dimensions of the surface texture formed during Al polishing significantly affect the morphology and pore order within the anodic film. Therefore, it can be stated that it is possible to tune to some extent the arrangement of nanochannels within anodic aluminum oxide films by simply changing conditions during the electropolishing procedure..

Essence of the Giant Reduction of Power Density in Osmotic Energy Conversion in Porous Membranes: Importance of Testing Area

Harvesting osmotic energy through nanofluidic devices with diverse materials has received considerable attention in recent years. Often, a small testing area on a membrane was chosen to assess its power performance by calculating power density as output power per effective area. Since the choice of this testing area is arbitrary, and it is usually quite small, the result obtained can be too optimistic. There is a need to come up with a common standard so that the performance of a device/membrane can be assessed reasonably. In this study, we systematically investigate the power density as a function of testing area in nanoporous anodic-aluminum-oxide membranes. Through changing the aperture size of substrates, we clearly show that the obtained power density decreases drastically with increasing testing area. For instance, the power density acquired from the testing area of μm2-scale can be five orders of magnitude larger than that from the pristine membrane of cm2-scale. We also advance simulations by building a 3D model to simulate osmotic-driven ion transport in the multichannel system. The result of modeling agrees with our experimental observation that the power density decreases with increasing number of channels, and the ionic concentration profile reveals that the concentration polarization becomes serious as the number of channels increases. Our result highlights the importance of effective area on testing the power performance in nanofluidic devices.

Electrochemical Characterization of Charged Membranes from Different Materials and Structures via Membrane Potential Analysis

Electrochemical characterization of positively and negatively charged membranes is performed by analyzing membrane potential values on the basis of the Teorell-Meyer-Sievers (TMS) model. This analysis allows the separate estimation of Donnan (interfacial effects) and diffusion (differences in ions transport through the membrane) contributions, and it permits the evaluation of the membrane's effective fixed charge concentration and the transport number of the ions in the membrane. Typical ion-exchange commercial membranes (AMX, Ionics or Nafion) are analyzed, though other experimental and commercial membranes, which are derived from different materials and have diverse structures (dense, swollen or nanoporous structures), are also considered. Moreover, for some membranes, changes associated with different modifications and other effects (concentration gradient or level, solution stirring, etc.) are also analyzed.

Conductivity of Ionic Liquids In the Bulk and during Infiltration in Nanopores

The conductivity of ionic liquids (ILs) in nanopores is essential when considering their application as materials for energy. However, no consensus has been reached about the influence of confinement on the mobility of the ions. A series of ILs bearing the same cation, 1-butyl-3-methylimidazolium ([BMIM]+), and six different anions ([Cl]-, [Br]-, [I]-, [BF4]-, [PF6]-, and [TFSI]-) with radii from 0.168 to 0.326 nm were investigated with respect to their self-assembly, the thermodynamics, and the ionic conductivity in the bulk, during flow and under confinement in cylindrical nanopores with sizes in the range from 400 to 25 nm. In the bulk, the [BMIM]+[X]- exhibits weak ordering as a result of cation-anion correlations (charge alteration peak), and nanophase separation of polar/apolar groups. Liquid-to-glass temperatures were found to differ by ∼50 K, their viscosities by a factor of ∼270, and their conductivities by a factor of 24 (all at a temperature of 303 K). Electrostatic interactions were largely responsible for variations in the glass temperature, the viscosity, and the conductivity. Confined ILs behave differently from the bulk. The majority of ILs in the bulk were prone to crystallization during heating but were unable to crystallize in the smaller pores. Changes in dc-conductivity were used as markers of the phase state. This allowed the construction of the effective phase diagrams under confinement. The ILs penetrate the pores with an effective viscosity of the order of their viscosity in their bulk state. However, within the pores the dc-conductivity was reduced relative to bulk, indicating the immobilization of ions at the pore walls. Hydrophobization of the pore walls by hexamethyldisilazane could partially restore the conductivity. ILs are model systems where the phase state and ion mobility can be controlled by confinement.

Structure and Optical Anisotropy of Spider Scales and Silk: The Use of Chromaticity and Azimuth Colors to Optically Characterize Complex Biological Structures

Herein, we give an overview of several less explored structural and optical characterization techniques useful for biomaterials. New insights into the structure of natural fibers such as spider silk can be gained with minimal sample preparation. Electromagnetic radiation (EMR) over a broad range of wavelengths (from X-ray to THz) provides information of the structure of the material at correspondingly different length scales (nm-to-mm). When the sample features, such as the alignment of certain fibers, cannot be characterized optically, polarization analysis of the optical images can provide further information on feature alignment. The 3D complexity of biological samples necessitates that there be feature measurements and characterization over a large range of length scales. We discuss the issue of characterizing complex shapes by analysis of the link between the color and structure of spider scales and silk. For example, it is shown that the green-blue color of a spider scale is dominated by the chitin slab's Fabry-Pérot-type reflectivity rather than the surface nanostructure. The use of a chromaticity plot simplifies complex spectra and enables quantification of the apparent colors. All the experimental data presented herein are used to support the discussion on the structure-color link in the characterization of materials.

Preparation of Polymer Nanopillar Arrays with Controlled Tip Shapes and Their Application to Hydrophobic and Oleophobic Surfaces

Ordered arrays of nanopillars with controlled tip shapes were fabricated by a template formation process using anodic porous alumina with controlled pore shapes. Although various studies have been reported on the preparation of nanopillar arrays using anodic porous alumina as a template, there have been no reports on the formation of nanopillar arrays with precisely controlled tip shapes. Re-anodization of anodized samples in a neutral electrolyte can flatten the bottom of pores. The use of the resulting anodic porous alumina as a template enabled the fabrication of ordered nanopillar arrays with a flattened tip. The formation of overhanging nanopillar arrays was also possible by using anodic porous alumina with a controlled pore shape as a template, which was fabricated by a combination of anodization, TiO₂ coating by atomic layer deposition, and pore-widening treatment. The contact angles of water and oil droplets were measured using the obtained polymer nanopillar arrays with controlled tip shapes. The contact angle of water droplets did not change regardless of the tip shape of the nanopillars, whereas the contact angle of oil droplets changed depending on the tip shape of the nanopillars. This indicates that liquids with high surface tension are not affected by the nanopillar tip shape, whereas liquids with low surface tension are greatly affected by the nanopillar tip shape. Among the nanopillar arrays fabricated in this study, it was confirmed that the overhanging nanopillar array with many edge structures that have the pinning effect of suppressing the wetting spread of the solution exhibited the highest oil repellency. The method reported here can be used to fabricate nanopillar arrays with a precisely controlled tip geometry, and it is expected that optimization of the geometry will further improve the water- and oil-repellent properties.

Preparation of size-controlled LiCoPO4 particles by membrane emulsification using anodic porous alumina and their application as cathode active materials for Li-ion secondary batteries

Membrane emulsification using anodic porous alumina is an effective method for preparing monodisperse droplets with controlled sizes. In this study, membrane emulsification using anodic porous alumina was applied to the preparation of size-controlled particles composed of composite metal oxides. To obtain size-controlled composite metal oxide particles, membrane emulsification was performed using an aqueous solution containing a water-soluble monomer and metal salts as a dispersed phase. After the membrane emulsification, composite metal oxide particles were obtained by solidifying the droplets in a continuous phase and subsequent heat treatment. Here, as a demonstration of this process, the fabrication of size-controlled LiCoPO4 particles, which are considered high-potential cathode active materials for Li-ion secondary batteries (LIBs), was investigated. The application of the obtained LiCoPO4 particles as cathode active materials for LIBs was also investigated. The results of this study showed that LiCoPO4 particles with controlled sizes could be fabricated on the basis of this process and that their cathode properties could be improved by optimizing the heat treatment conditions and particle sizes. According to this process, size-controlled particles composed of various metal oxides can be fabricated by changing the metal salt in the dispersed phase, and the resulting size-controlled particles are expected to be applied not only as cathode active materials for LIBs but also as components of various functional devices.

Electrochemistry of Thin Films and Nanostructured Materials

In the last few decades, the development and use of thin films and nanostructured materials to enhance physical and chemical properties of materials has been common practice in the field of materials science and engineering. The progress which has recently been made in tailoring the unique properties of thin films and nanostructured materials, such as a high surface area to volume ratio, surface charge, structure, anisotropic nature, and tunable functionalities, allow expanding the range of their possible applications from mechanical, structural, and protective coatings to electronics, energy storage systems, sensing, optoelectronics, catalysis, and biomedicine. Recent advances have also focused on the importance of electrochemistry in the fabrication and characterization of functional thin films and nanostructured materials, as well as various systems and devices based on these materials. Both cathodic and anodic processes are being extensively developed in order to elaborate new procedures and possibilities for the synthesis and characterization of thin films and nanostructured materials.

When crystals flow

Semicrystalline polymers are solids that are supposed to flow only above their melting temperature. By using confinement within nanoscopic cylindrical pores, we show that a semicrystalline polymer can flow at temperatures below the melting point with a viscosity intermediate to the melt and crystal states. During this process, the capillary force is strong and drags the polymer chains in the pores without melting the crystal. The unexpected enhancement in flow, while preserving the polymer crystallites, is of importance in the design of polymer processing conditions applicable at low temperatures, e.g., cold drawn polymers such as polytetrafluoroethylene, self-healing, and in nanoconfined donor/acceptor polymers used in organic electronics.

Optical Characterization of ALD-Coated Nanoporous Alumina Structures: Effect of Sample Geometry or Coated Layer Material

Optical characterization of nanoporous alumina-based structures (NPA-bSs), obtained by ALD deposition of a thin conformal SiO₂ layer on two alumina nanosupports with different geometrical parameters (pore size and interpore distance), was performed by two noninvasive and nondestructive techniques such as spectroscopic ellipsometry (SE) and photoluminescence (Ph) spectra. SE measurements allow us to estimate the refraction index and extinction coefficient for the studied samples and their dependence with wavelength for the 250-1700 nm interval, showing the effect of sample geometry and cover-layer material (SiO₂, TiO₂, or Fe₂O₃), which significantly affect the oscillatory character of both parameters, as well as changes associated with the light incidence angle, which are attributed to surface impurities and inhomogeneity. Photoluminescence curves exhibit a similar shape independently of sample pore-size/porosity, but they seem to affect intensity values. This analysis shows the potential application of these NPA-bSs platforms to nanophotonics, optical sensing, or biosensing.

Physical Aging of Polystyrene Confined in Anodic Aluminum Oxide Nanopores

We investigated the glassy dynamics of polystyrene (PS) confined in anodic aluminum oxide (AAO) nanopores by differential scanning calorimetry. Based on the outcome of our experiments, we show that the cooling rate applied to process the 2D confined PS melt has a significant impact on both the glass transition and the structural relaxation in the glassy state. A single glass transition temperature (T_g) is observed in quenched samples, while slow-cooled PS chains show two T_gs corresponding to a core-shell structure. The former phenomenon resembles what is observed in freestanding structures, while the latter is imputed to the adsorption of PS onto AAO walls. A more complex picture was drawn for physical aging. In the case of quenched samples, we observed a non-monotonic trend of the apparent aging rate that in 400 nm pores, reaches a value almost twice as larger than what is measured in bulk and decreases upon further confinement in smaller nanopores. For slow-cooled samples, by adequately varying the aging conditions, we were able to control the equilibration kinetics and either separate the two aging processes or induce an intermediate aging regime. We propose a possible explanation of these findings in terms of distribution in free volume and the presence of different aging mechanisms.

Solid-State Nanopore Array: Manufacturing and Applications

Nanopore brings extraordinary properties for a variety of potential applications in various industrial sectors. Since manufacturing of solid-state nanopore is first reported in 2001, solid-state nanopore has become a hot topic in the recent years. An increasing number of manufacturing methods have been reported, with continuously decreased sizes from hundreds of nanometers at the beginning to ≈1 nm until recently. To enable more robust, sensitive, and reliable devices required by the industry, researchers have started to explore the possible methods to manufacture nanopore array which presents unprecedented challenges on the fabrication efficiency, accuracy and repeatability, applicable materials, and cost. As a result, the exploration of fabrication of nanopore array is still in the fledging period with various bottlenecks. In this article, a wide range of methods of manufacturing nanopores are summarized along with their achievable morphologies, sizes, inner structures for characterizing the main features, based on which the manufacturing of nanopore array is further addressed. To give a more specific idea on the potential applications of nanopore array, some representative practices are introduced such as DNA/RNA sequencing, energy conversion and storage, water desalination, nanosensors, nanoreactors, and dialysis.

Polymerization within Nanoporous Anodized Alumina Oxide Templates (AAO): A Critical Survey

In the last few years, the polymerization of monomers within the nanocavities of porous materials has been thoroughly studied and developed, allowing for the synthesis of polymers with tailored morphologies, chemical architectures and functionalities. This is thus a subject of paramount scientific and technological relevance, which, however, has not previously been analyzed from a general perspective. The present overview reports the state of the art on polymerization reactions in spatial confinement within porous materials, focusing on the use of anodized aluminum oxide (AAO) templates. It includes the description of the AAO templates used as nanoreactors. The polymerization reactions are categorized based on the polymerization mechanism. Amongst others, this includes electrochemical polymerization, free radical polymerization, step polymerization and atom transfer radical polymerization (ATRP). For each polymerization mechanism, a further subdivision is made based on the nature of the monomer used. Other aspects of "in situ" polymerization reactions in restricted AAO geometries include: conversion monitoring, kinetic studies, modeling and polymer characterization. In addition to the description of the polymerization process itself, the use of polymer materials derived from polymerization in AAO templates in nanotechnology applications, is also highlighted. Finally, the review is concluded with a general discussion outlining the challenges that remain in the field.

Bi2O3 modified TiO2 nanotube arrays and their application towards unsymmetrical dimethylhydrazine degradation in wastewater by electroassisted photocatalysis

In the present research, the preparation process parameters of TiO₂ nanotube arrays (TNAs) prepared by anodic oxidation were systematically studied by the orthogonal experimental method for the first time. Herein, the parameters of nine factors were optimized; the optimal parameters were: the electrolyte was a 0.2 mol L^-1 NaF solution with 3% vol H₂O at pH 7, the anodic oxidation voltage was 40 V, the electrode spacing was 4 cm and the reaction was carried out for 60 minutes. The physicochemical properties of the materials were characterized by SEM, XRD, EDS, UV-vis, and PL spectroscopy. By electrodeposition of Bi₂O₃ modified TNAs, the degradation rate of unsymmetrical dimethylhydrazine (UDMH) wastewater on the TNAs-10 was 89.14% within 10 h, which was 2.69 times that on pure TNAs. A bias potential of +0.3 V (vs. open circuit potential) was applied to the modified TNAs-10. The degradation rate of UDMH was significantly enhanced on the TNAs-10 (bias) process as compared to the TNAs-10 process. The degradation rate of UDMH wastewater on TNAs-10 (bias) exhibited an exponential distribution. UDMH and its toxic by-products FDMH, NDMA were completely degraded after 8 h.

Control of the Nanopore Architecture of Anodic Alumina via Stepwise Anodization with Voltage Modulation and Pore Widening

Control of the morphology and hierarchy of the nanopore structures of anodic alumina is investigated by employing stepwise anodizing processes, alternating the two different anodizing modes, including mild anodization (MA) and hard anodization (HA), which are further mediated by a pore-widening (PW) step in between. For the experiment, the MA and HA are applied at the anodizing voltages of 40 and 100 V, respectively, in 0.3 M oxalic acid, at 1 °C, for fixed durations (30 min for MA and 0.5 min for HA), while the intermediate PW is applied in 0.1 M phosphoric acid at 30 °C for different durations. In particular, to examine the effects of the anodizing sequence and the PW time on the morphology and hierarchy of the nanopore structures formed, the stepwise anodization is conducted in two different ways: one with no PW step, such as MA→HA and HA→MA, and the other with the timed PW in between, such as MA→PW→MA, MA→PW→HA, HA→PW→HA, and HA→PW→MA. The results show that both the sequence of the voltage-modulated anodizing modes and the application of the intermediate PW step led to unique three-dimensional morphology and hierarchy of the nanopore structures of the anodic alumina beyond the conventional two-dimensional cylindrical pore geometry. It suggests that the stepwise anodizing process regulated by the sequence of the anodizing modes and the intermediate PW step can allow the design and fabrication of various types of nanopore structures, which can broaden the applications of the nanoporous anodic alumina with greater efficacy and versatility.

Overview of Engineering Carbon Nanomaterials Such As Carbon Nanotubes (CNTs), Carbon Nanofibers (CNFs), Graphene and Nanodiamonds and Other Carbon Allotropes inside Porous Anodic Alumina (PAA) Templates

The fabrication and design of carbon-based hierarchical structures with tailored nano-architectures have attracted the enormous attention of the materials science community due to their exceptional chemical and physical properties. The collective control of nano-objects, in terms of their dimensionality, orientation and size, is of paramount importance to expand the implementation of carbon nanomaterials across a large variety of applications. In this context, porous anodic alumina (PAA) has become an attractive template where the pore morphologies can be straightforwardly modulated. The synthesis of diverse carbon nanomaterials can be performed using PAA templates, such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and nanodiamonds, or can act as support for other carbon allotropes such as graphene and other carbon nanoforms. However, the successful growth of carbon nanomaterials within ordered PAA templates typically requires a series of stages involving the template fabrication, nanostructure growth and finally an etching or electrode metallization steps, which all encounter different challenges towards a nanodevice fabrication. The present review article describes the advantages and challenges associated with the fabrication of carbon materials in PAA based materials and aims to give a renewed momentum to this topic within the materials science community by providing an exhaustive overview of the current synthesis approaches and the most relevant applications based on PAA/Carbon nanostructures materials. Finally, the perspective and opportunities in the field are presented.