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

Designing porous photonic crystals for MIR spectral region-a deeper insight into the anodic alumina layer thickness versus charge density relation

The mid-infrared region (MIR) is crucial for many applications in security and industry, in chemical and biomolecular sensing, since it contains strong characteristic vibrational transitions of many important molecules and gases (e.g. CO₂, CH₄, CO). Despite its great potential, the optical systems operating in this spectral domain are still under development. The situation is caused mainly by the lack of inexpensive and adequate optical materials which show no absorption in the MIR. In this work, we present an easy and affordable way to develop 1D photonic crystals (PCs) based on porous anodic alumina for MIR region. The porous PCs were produced by the pulse anodization of aluminum using charge-controlled mode. The first order photonic stopbands (λ₁) were located within ca. 3.5-6.5μm. Annealing of the material at 1100 °C for an hour has allowed to recover the wavelength range from around 5.8 to 7.5μm owing to the decomposition of the absorption centers (oxalate anions) present in the anodic oxide framework while maintaining the PC structural stability. The spectral position and the shape of the resonances were regulated by the charge passing under high (U_H) and low (U_L) voltage pulses, porosity of the correspondingd_Handd_Lsegments, and dura tion of the process (t_tot). The thickness of thed_Handd_Llayers was proportional to the charge passing under respective pulses, with the proportionality coefficient increasing with the applied voltage. Despite the constant charge (2500 mC cm^-2) applied during the anodization, the thickness of anodic alumina (d) increased with applied voltage (10-60 V) and anodizing temperature (5 °C-30 °C). This behavior was ascribed to the different kinetics of the anodic alumina formation prompted by the variable electrochemical conditions. The photonic material can be used in portable nondispersive gas sensors as an enhancement layer operating up to around 9μm.

Surface Functionalized MXenes for Wastewater Treatment-A Comprehensive Review

Over 80% of wastewater worldwide is released into the environment without proper treatment. Whilst environmental pollution continues to intensify due to the increase in the number of polluting industries, conventional techniques employed to clean the environment are poorly effective and are expensive. MXenes are a new class of 2D materials that have received a lot of attention for an extensive range of applications due to their tuneable interlayer spacing and tailorable surface chemistry. Several MXene-based nanomaterials with remarkable properties have been proposed, synthesized, and used in environmental remediation applications. In this work, a comprehensive review of the state-of-the-art research progress on the promising potential of surface functionalized MXenes as photocatalysts, adsorbents, and membranes for wastewater treatment is presented. The sources, composition, and effects of wastewater on human health and the environment are displayed. Furthermore, the synthesis, surface functionalization, and characterization techniques of merit used in the study of MXenes are discussed, detailing the effects of a range of factors (e.g., PH, temperature, precursor, etc.) on the synthesis, surface functionalization, and performance of the resulting MXenes. Finally, the limits of MXenes and MXene-based materials as well as their potential future research directions, especially for wastewater treatment applications are highlighted.

One-Dimensional Photonic Crystals with Nonbranched Pores Prepared via Phosphorous Acid Anodizing of Aluminium

One-dimensional photonic crystals (1D PhCs) obtained by aluminium anodizing under oscillating conditions are promising materials with structure-dependent optical properties. Electrolytes based on sulphuric, oxalic, and selenic acids have been utilized for the preparation of anodic aluminium oxide (AAO) 1D PhCs with sub-100-nm pore diameter. AAO films with larger pores can be obtained by anodizing in phosphorous acid at high voltages. Here, for the first time, anodizing in phosphorous acid is applied for the preparation of AAO 1D PhCs with nonbranched macropores. The sine wave profile of anodizing voltage in the 135–165 V range produces straight pores, whose diameter is above 100 nm and alternates periodically in size. The pore diameter modulation period linearly increases with the charge density by a factor of 599 ± 15 nm·cm²·C⁻¹. The position of the photonic band gap is controlled precisely in the 0.63–1.96 µm range, and the effective refractive index of AAO 1D PhCs is 1.58 ± 0.05.

Direct MYD88L265P gene detection for diffuse large B-cell lymphoma (DLBCL) via a miniaturised CRISPR/dCas9-based sensing chip

Traditional methods for single-nucleotide variants based on amplification and fluorescence signals require expensive reagents and cumbersome instruments, and they are time-consuming for each trial. Here, a porous anodised aluminium (PAA)-based sensing chip modified with deactivated Cas9 (dCas9) proteins and synthetic guide RNA (sgRNA) as the biorecognition receptor is developed, which can be used for the label-free sensing of the diffuse large B-cell lymphoma (DLBCL) MYD88^L265P gene by integrating with electrochemical ionic current rectification (ICR) measurement. The sgRNA that can specifically identify and capture the MYD88^L265P gene was screened, which has been proved to be workable to activate dCas9 for the target MYD88^L265P. In the sensing process, the dCas9 proteins can capture the genome sequence, thus bringing negative charges over the PAA chip and correspondingly resulting in a variation in the ICR value due to the uneven transport of potassium anions through the ion channels of the PAA chip. The whole sensing can be finished within 40 min, and there is no need for gene amplification. The CRISPR/dCas9-based sensor demonstrates ultrasensitive detection performance in the concentration range of 50 to 200 ng μL^-1 and it has been proved to be feasible for the genome sequence of patient tissues. This sensor shows the potential of targeting other mutations by designing the corresponding sgRNAs and expands the applications of CRISPR/dCas9 technology to the on-chip electrical detection of nucleic acids, which will be very valuable for rapid diagnosis of clinically mutated genes. This makes the hybrid CRISPR-PAA chip an ideal candidate for next-generation nucleic acid biosensors.

Impedance-Based Nanoporous Anodized Alumina/ITO Platforms for Label-Free Biosensors

We report an experimental and computational approach for the fabrication and characterization of a highly sensitive and responsive label-free biosensor that does not require the presence of redox couples in electrolytes for sensitive electrochemical detection. The sensor is based on an aptamer-functionalized transparent electrode composed of nanoporous anodized alumina (NAA) grown on indium tin oxide (ITO)-covered glass. Electrochemical impedance changes in a thrombin binding aptamer (TBA)-functionalized NAA/ITO/glass electrode due to specific binding of α-thrombin are monitored for protein detection. The aptamer-functionalized electrode enables sensitive and specific thrombin protein detection with a detection limit of ∼10 pM and a high signal-to-noise ratio. The transient impedance of the alumina film-covered surface is computed using a computational electrochemical impedance spectroscopy (EIS) approach and compared to experimental observations to identify the dominant mechanisms underlying the sensor response. The computational and experimental results indicate that the sensing response is due to the modified ionic transport under the combined influence of steric hindrance and surface charge modification due to ligand/receptor binding between α-thrombin and the aptamer-covered alumina film. These results suggest that alumina film-covered electrodes utilize both steric and charge modulation for sensing, leading to tremendous improvement in the sensitivity and signal-to-noise ratio. The film configuration is amenable for miniaturization and can be readily incorporated into existing portable sensing systems.

ZnO nanostructures: synthesis by anodization and applications in photoelectrocatalysis

Solar energy is a clean and abundant energy source. In a photoelectrochemical cell, energy from sunlight is captured and converted into electric power, chemical fuels such as hydrogen is employed to degrade organic pollutants. ZnO is a promising material for photoelectrocatalysis due to its remarkable properties. The aim of this review is to perform an exhaustive revision of nanostructured ZnO synthesis by electrochemical anodization in order to control surface characteristics of this material through anodization parameters such as electrolyte type and concentration, potential, time, temperature, stirring, and post treatment. Finally, application of ZnO nanostructures is overviewed to observe how surface characteristics affected the ZnO photoelectrocatalytic performance.

A Self-Ordered Nanostructured Transparent Electrode of High Structural Quality and Corresponding Functional Performance

The preparation of a highly ordered nanostructured transparent electrode based on a combination of nanosphere lithography and anodization is presented. The size of perfectly ordered pore domains is improved by an order of magnitude with respect to the state of the art. The concomitantly reduced density of defect pores increases the fraction of pores that are in good electrical contact with the underlying transparent conductive substrate. This improvement in structural quality translates directly and linearly into an improved performance of energy conversion devices built from such electrodes in a linear manner.

Recent Advances in Nanoporous Anodic Alumina: Principles, Engineering, and Applications

The development of aluminum anodization technology features many stages. With the story stretching for almost a century, rather straightforward-from current perspective-technology, raised into an iconic nanofabrication technique. The intrinsic properties of alumina porous structures constitute the vast utility in distinct fields. Nanoporous anodic alumina can be a starting point for: Templates, photonic structures, membranes, drug delivery platforms or nanoparticles, and more. Current state of the art would not be possible without decades of consecutive findings, during which, step by step, the technique was more understood. This review aims at providing an update regarding recent discoveries-improvements in the fabrication technology, a deeper understanding of the process, and a practical application of the material-providing a narrative supported with a proper background.

Optimization of the Anodization Processing for Aluminum Oxide Gate Dielectrics in ZnO Thin Film Transistors by Multivariate Analysis

The present study reports a two-level multivariate analysis to optimize the production of anodized aluminum oxide (Al₂O₃) dielectric films for zinc oxide thin-film transistors (TFTs). Fourteen performance parameters were measured and analysis of variance (ANOVA) of the combined responses has been applied to identify how the Al₂O₃ dielectric fabrication process influences the electrical properties of the TFTs. Using this approach, the levels for the manufacturing factors to achieve optimal overall device performance have been identified and ranked. The cross-checked analysis of the TFT performance parameters demonstrated that the appropriate control of the anodization process can have a higher impact on TFT performance than the use of traditional methods of surface treatment of the dielectric layer. Flexible electronics applications are expected to grow substantially over the next 10 years. Given the complexity and challenges of new flexible electronics components, this "multivariate" approach could be adopted more widely by the industry to improve the reliability and performance of such devices.

Titania Photonic Crystals with Precise Photonic Band Gap Position via Anodizing with Voltage versus Optical Path Length Modulation

Photonic crystals based on titanium oxide are promising for optoelectronic applications, for example as components of solar cells and photodetectors. These materials attract great research attention because of the high refractive index of TiO₂. One of the promising routes to prepare photonic crystals based on titanium oxide is titanium anodizing at periodically changing voltage or current. However, precise control of the photonic band gap position in anodic titania films is a challenge. To solve this problem, systematic data on the effective refractive index of the porous anodic titanium oxide are required. In this research, we determine quantitatively the dependence of the effective refractive index of porous anodic titanium oxide on the anodizing regime and develop a model which allows one to predict and, therefore, control photonic band gap position in the visible spectrum range with an accuracy better than 98.5%. The prospects of anodic titania photonic crystals implementation as refractive index sensors are demonstrated.

Accelerating ion diffusion with unique three-dimensionally interconnected nanopores for self-membrane high-performance pseudocapacitors

Herein, a unique three-dimensionally interconnected nanoporous structure (3-D INPOS) pseudocapacitor electrode, which possesses a large surface area, an efficient electron and ion transport, together with a remarkable structural stability, has been constructed via soft anodization of an aluminum alloy, cost-effective ultrasonic spray pyrolysis (USP)-assisted deposition of fluorine-doped tin oxide (FTO), and controllable electrochemical deposition of nanostructured manganese dioxide (MnO₂). Taking the advantage of large surface area, the as-built 3-D INPOS pseudocapacitor electrode exhibits the highest areal capacitance of 540 mF cm^-2 and a volumetric capacitance of 135 F cm^-3, which is 53% higher than that achieved from the conventional 3-D nanopore pseudocapacitor electrode and 17.6 times higher than that of the planar electrode. More interestingly, the unique 3-D interconnected structure offers an unrestricted space for the diffusion of electrolyte ions. Thus, the 3-D INPOS electrode achieves a higher rate capability than the 3-D nanopore electrode. As a proof of concept, a symmetric self-membrane pseudocapacitor device was constructed by simply stacking two pieces of the 3-D INPOS electrodes. Without an added separator, the device possesses a largely reduced dead volume and achieves the highest volumetric capacitance of 28.9 F cm^-3 and a specific energy of 2.36 mW h cm^-3. The largely enhanced capacitance, rate capability, and specific energy certainly make the 3-D INPOS an ideal architecture for the fabrication of high-performance pseudocapacitors.

Scalable Indium Phosphide Thin-Film Nanophotonics Platform for Photovoltaic and Photoelectrochemical Devices

Recent developments in nanophotonics have provided a clear roadmap for improving the efficiency of photonic devices through control over absorption and emission of devices. These advances could prove transformative for a wide variety of devices, such as photovoltaics, photoelectrochemical devices, photodetectors, and light-emitting diodes. However, it is often challenging to physically create the nanophotonic designs required to engineer the optical properties of devices. Here, we present a platform based on crystalline indium phosphide that enables thin-film nanophotonic structures with physical morphologies that are impossible to achieve through conventional state-of-the-art material growth techniques. Here, nanostructured InP thin films have been demonstrated on non-epitaxial alumina inverted nanocone (i-cone) substrates via a low-cost and scalable thin-film vapor-liquid-solid growth technique. In this process, indium films are first evaporated onto the i-cone structures in the desired morphology, followed by a high-temperature step that causes a phase transformation of the indium into indium phosphide, preserving the original morphology of the deposited indium. Through this approach, a wide variety of nanostructured film morphologies are accessible using only control over evaporation process variables. Critically, the as-grown nanotextured InP thin films demonstrate excellent optoelectronic properties, suggesting this platform is promising for future high-performance nanophotonic devices.

Sustained, Controlled and Stimuli-Responsive Drug Release Systems Based on Nanoporous Anodic Alumina with Layer-by-Layer Polyelectrolyte

Controlled drug delivery systems are an encouraging solution to some drug disadvantages such as reduced solubility, deprived biodistribution, tissue damage, fast breakdown of the drug, cytotoxicity, or side effects. Self-ordered nanoporous anodic alumina is an auspicious material for drug delivery due to its biocompatibility, stability, and controllable pore geometry. Its use in drug delivery applications has been explored in several fields, including therapeutic devices for bone and dental tissue engineering, coronary stent implants, and carriers for transplanted cells. In this work, we have created and analyzed a stimuli-responsive drug delivery system based on layer-by-layer pH-responsive polyelectrolyte and nanoporous anodic alumina. The results demonstrate that it is possible to control the drug release using a polyelectrolyte multilayer coating that will act as a gate.

Three-dimensional nanotube electrode arrays for hierarchical tubular structured high-performance pseudocapacitors

Ordered three-dimensional (3-D) tubular arrays are highly attractive candidates for high performance pseudocapacitor electrodes. Here, we report 3-D fluorine doped tin oxide (FTO) tubular arrays fabricated by a cost-effective ultrasonic spray pyrolysis (USP) method in anodic aluminum oxide (AAO) channels with high uniformity. The large surface area of such a structure leads to remarkable surface area enhancement up to 51.8 times compared to a planar structure. Combining with electrochemically deposited manganese dioxide (MnO2) nanoflakes on the inner side wall of the FTO nanotubes, the unique hierarchical tubular structured pseudocapacitor electrode demonstrated the highest areal capacitance of 193.8 mF cm(-2) at the scan rate of 5 mV s(-1) and 184 mF cm(-2) at the discharge current density of 0.6 mA cm(-2), which is 18.5 times that of a planar electrode. And it also showed a volumetric capacitance of 112.6 F cm(-3) at the scan rate of 5 mV s(-1) and 108.8 F cm(-3) at the discharge current density of 0.6 mA cm(-2). In addition, the cyclic stability test also indicated that a nanostructured pseudocapacitive electrode has a much larger capacitance retention after 3000 cycles of the charge-discharge process compared with a planar electrode, primarily due to the mechanical stability of the nanostructure. Moreover, pseudocapacitor device fabrication based on such electrodes shows the volumetric capacitance of 17.5 F cm(-3), and the highest specific energy of 1.56 × 10(-3) Wh cm(-3). With the merit of facile fabrication procedures and largely enhanced electrochemical performance, such a 3-D structure has high potency for energy storage systems for a wide range of practical applications.