Two-step Anodization Technique Research Articles

TiO2 Nanotubes Decorated with Mo2C for Enhanced Photoelectrochemical Water-Splitting Properties.

The presence of Ti3+ in the structure of TiO2 nanotube arrays (NTs) has been shown to enhance the photoelectrochemical (PEC) water-splitting performance of these NTs, leading to improved results compared to pristine anatase TiO2 NTs. To further improve the properties related to PEC performance, we successfully produced TiO2 NTs using a two-step electrochemical anodization technique, followed by annealing at a temperature of 450 °C. Subsequently, Mo2C was decorated onto the NTs by dip coating them with precursors at varying concentrations and times. The presence of anatase TiO2 and Ti3O5 phases within the TiO2 NTs was confirmed through X-ray diffraction (XRD) analysis. The TiO2 NTs that were decorated with Mo2C demonstrated a photocurrent density of approximately 1.4 mA cm-2, a value that is approximately five times greater than the photocurrent density exhibited by the bare TiO2 NTs, which was approximately 0.21 mA cm-2. The observed increase in photocurrent density can be ascribed to the incorporation of Mo2C as a cocatalyst, which significantly enhances the photocatalytic characteristics of the TiO2 NTs. The successful deposition of Mo2C onto the TiO2 NTs was further corroborated by the characterization techniques utilized. The utilization of field emission scanning electron microscopy (FESEM) allowed for the observation of Mo2C particles on the surface of TiO2 NTs. To validate the composition and optical characteristics of the decorated NTs, X-ray photoelectron spectroscopy (XPS) and UV absorbance analysis were performed. This study introduces a potentially effective method for developing efficient photoelectrodes based on TiO2 for environmentally sustainable hydrogen production through the use of photoelectrochemical water-splitting devices. The utilization of Mo2C as a cocatalyst on TiO2 NTs presents opportunities for the advancement of effective and environmentally friendly photoelectrochemical (PEC) systems.

Facile Preparation of Carbon Nanopillar Array

Carbon-based nanostructures have attracted extensive interest in obtaining advanced sensing electronic devices in environmental and biological monitoring applications as an alternative to conventional materials. Herein, the facile preparation, control of the growth, and artificial intelligence–based morphological information of the carbon nanopillar array in the Anodized Aluminum Oxide (AAO) template were investigated. A facile approach for controlling the growth of the nanostructure was proposed as a two-step anodization technique for AAO and Plasma Enhanced Chemical Vapor Deposition (PECVD) for carbon nanopillar array. It involved the competitive carbon deposition between the carbon nanopillars electrodeposited on the AAO template and at the bottom of the pores of AAO under vacuum conditions. The morphology and structure of the prepared carbon nanopillars were reported in detail. Hexagonally straight AAO nanotubes were approximately 65 nm in diameter and 360 nm in length, with 90 nm interpore distances. The AAO nanotube density is approximately 1.75x1014 cm-2. Carbon nanopillars with a width of ~60 nm were used to create a low-dimensional nanostructure. This controllable preparation leads to the facile and impressive preparation of a free-standing carbon nanopillar array, especially for various chemical sensor applications.

Fabrication of nanoporous free standing anodic alumina using two-step anodization for applicability in microhydraulic system as nano filter using surface acoustics

The current trend in nano/micro structured array fabrication for a variety of applications in microsystems development nanoporous anodic alumina (Al2O3) gained tremendous attention. In this research paper, Freestanding (FS) nanoporous anodic alumina were fabricated using a two-step anodization technique. Nanoporous honeycomb structure having an average 85 nm pore diameter and 135 nm distance between pores were achieved by electrochemical anodization at identical constant DC voltage 60 V. Nanoporous membrane thickness 0.25 µm were obtained with 36% porosity. Scanning electron microscopy (SEM) analysis investigation was done and it confirms honeycomb nanoporous structures were formed on the surface of FS AAO membrane. Additionally, Energy dispersive x-ray spectroscopy (EDS) microanalysis was conducted for the FS AAO membrane to analyze the chemical component after anodization. Finally, fabricated FS nanoporous AAO membrane response was presented under electrical excitation to enables its applicability as a nano filter in microhydraulic systems.

Growth of Zr–BiFeO3 nanostructures on two step anodized porous alumina for estimation of optical and dielectric response

Abstract Nanostructures decorated with perfectly ordered porous anodic aluminum oxide templates have attained recent research interest for the production of highly efficient energy storage devices. Anodic aluminum oxide porous templates were synthesized using a two-step anodization technique in this work. Pure BiFeO3 and Zr–BiFeO3 nanostructures were grown on these ordered templates by well-controlled fluoride ions assisted autoclave enclosed hydrothermal method. Crystallographic information discloses the presence of rhombohedral crystal structure with geometric space group R3c belongs to BiFeO3. The morphological analysis depicts the formation of an average pore size of approximately 75 nm in anodic aluminum oxide templates. BiFeO3 contains fibrous nanoflakes like morphology with minute content of the monoclinic zirconia phase in Zr–BiFeO3. Optical measurements demonstrate a considerable variation in absorption and bandgap of anodic aluminum oxide with the growth of nanostructures. A significant increase in dielectric permittivity from 17.17 for anodic aluminum oxide to 187.19 for Zr incorporated compositions with a relatively low tangent loss of 0.66.

Dielectric study of nanoporous alumina fabricated by two-step anodization technique

Nanoporous anodic alumina (NAA) samples of different porosities were synthesized by electrochemical anodization technique in two different electrolytes (C2H2O4 and H3PO4) via two-step anodization technique. The dielectric constant and dielectric loss of porous alumina was reported and decreasing trend of dielectric constant and dielectric loss of porous alumina was observed with both applied frequency as well as its porosity. This could be due to the reason that induced dipoles were unable to follow rapid fluctuations of the applied field at higher frequency. The observed dielectric constant of NAA samples prepared in C2H2O4 and H3PO4 solutions were 7.84 and 6.27 at 20 Hz, respectively. Owing to porous nature of the material, the resulting samples showed slightly less dielectric constant and exhibited enhanced conductivity as compared to barrier type alumina. Furthermore, a correlation between theoretical results and experimental results were established.

Enhanced photoelectrochemical properties of hierarchical black TiO2-x nanolaces for Cr (VI) photocatalytic reduction

In this work, hierarchical TiO2 nanolace (NL-TiO2) films have been synthesized by a two-step anodization technique. This was followed by a reduction in a hydrogen atmosphere to prepare the reduced black version of such hierarchical nanolaces (NL-TiO2-x). The FESEM images confirmed highly-ordered nanolace arrays structure for all the synthesized films. The Ti3+ ions/oxygen vacancies were confirmed using XPS spectra. The photoelectrochemical properties of NL-TiO2-x showed superior character in comparison with NL-TiO2 by the virtue of the promoted electron-hole separation efficiency, which induced by the Ti3+ ions/oxygen vacancies in NL-TiO2-x. The data showed that the NL-TiO2-x film annealed at 650 °C attained the maximum photoelectrochemical properties with a significant ABPE and IPCE of 0.58% and 52.51%, respectively. The applied photocatalytic reduction of Cr (VI) as an environmental contaminant to Cr (III) was effectively done using NL-TiO2-x and NL-TiO2 annealed at 650 °C with a photocatalytic reduction rate 48.15% and 27.5%, respectively.

Nanoporous anodic alumina (NAA) prepared in different electrolytes with different pore sizes for humidity sensing

The aim of present study is to design a simple and reliable capacitive humidity sensor based on the nanoporous alumina prepared by a two-step anodization technique. Owing to long-range-ordered structure of porous alumina, its electrical properties are sensitive to moisture; with the result, it finds potential applications as humidity sensor. Anodization parameters have been optimized to prepare a series of porous alumina samples in different acidic electrolytes, and the effect of pore size, porosity, and uniformity of pores on humidity sensing was investigated. The sensitivity of the sensor fabricated in oxalic acid at 40 V is 2–3 times higher than the sensors fabricated in sulphuric acid at 25 V and phosphoric acid at 98 V. Its enhanced sensitivity is justified by small porosity and uniformity in pore distribution of porous alumina. The sensitivity of the sensor fabricated in oxalic acid solution with pore diameter 34 ± 1 nm and porosity 10 ± 0.5% reaches up to 0.21 (pF/RH%).

Optical Losses in Hybrid Microcavity Based in Porous Semiconductors and its Application as Optic Chemical Sensor

In this study the experimental and theoretical optical analysis of a hybrid microcavity (HM) based in porous silicon (PS) and nanoporous anodic alumina (NAA) are presented. The microcavity was centered in the visible region at 760 nm. Distributed Bragg reflector (DBR) was obtained using galvanostatic anodizing method and while NAA by the two-step anodization technique. From SEM micrographs the HM different regions are observed. HM optical characterization in the visible region was done, considering two different light sources, point and non-point respectively. These results reveal a decrease in the quality factor (Q) from 350 to 190 when the source is exchanged; this behavior has been mainly attributed to the light scattering at NAA. Furthermore, it was possible to study Q change, through transmittance simulation using the transfer matrix and Landau-Lifshitz-Looyenga theoretical methods. When a point light source is used, there are no optical losses making possible to sense 1% of analyte resulting in a 0.29 nm redshift of the resonant peak. According with these results we propose to apply the HM as chemical optic sensor.

The effect of magnetic nickel nanowires structural parameterson the electrodeposition efficiency

In this work, magnetic Ni nanowire arrays were ac-pulse electrodeposited into the anodic aluminum oxide (AAO) template fabricated by the common two-step anodization technique. The barrier layers at the bottom of the pores were exponentially thinned in a non-equilibrium anodization process to 8, 12, 16 and 20 V. These were fabricated using the constant of 15 mA deposition current, 48 mS off-time between pulses, 10, 20 substrate temperatures, and 30°C electrolyte temperature. The effects of thinning voltage and substrate temperature on the electrodeposition efficiency and the magnetic quality of the Ni nanowires were investigated by a Vibrating sample magnetometer (VSM) and a scanning electron microscope (SEM). In this paper, we realized that the bed temperature of 10°C, by increasing the thickness of the barrier layer, reduced deposition efficiency and the temperature was 20 degrees backfired.

Fabrication of Al2O3 nanopores/SnO2 and its application in photocatalytic degradation under UV irradiation

In the present work, the photocatalytic degradation methyl orange (MO) by Al2O3-NP/SnO2 was investigated under UV light irradiation. For this purpose, the Al2O3-NP electrode was synthesized under the suitable conditions by two-step anodization technique and Al2O3-NP/SnO2 electrodes were prepared by sol-gel technique. The structure and morphology of the electrode were characterized by field-emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The FE-SEM results indicate that pore diameter and thickness of Al2O3-NP/SnO2 are 65.92 nm and 23.75 μm, respectively. EDX analysis shows that Al2O3-NP/SnO2 electrode contains 12.56 (wt.) % Sn and 44.43% O. The effect of some parameters, such as initial MO concentration, initial pH, temperature, irradiation area and reusability were determined. Kinetic analyses indicate that the photodegradation process of MO obeys the pseudo-first-order kinetic model. Additionally, thermodynamic parameters such as Ea, ΔH, ΔS and ΔG were calculated. The activation energy was determined to be 21.77 kJ/mol. This photocatalyst with good photocatalytic activity and a large surface area exhibits an effective potential in the treatment of wastewater.

The nanoporous anodic alumina oxide formed by two-step anodization

The nanoporous anodic aluminum oxide (AAO) was fabricated by two-step anodization technique. The effects of anodization electrolyte and time on the pore diameter and structural properties of the AAO were investigated. The Field Emission-Scanning Electron Microscopy was used for the analysis of the surface morphology of AAO structure. The nanoporous structures with the pore size in the range of 31–113 nm and oxide layer thickness 3.4–33 μm were obtained. Wetting properties of these surfaces were characterized by measurements of the water contact angle. It was seen that the surface of the AAO became hydrophilic with the increase in the anodization time. Furthermore, we explored the mechanical properties and thermal stabilities of the AAO by microhardness and thermo-gravimetric analysis measurements. It was found that the AAO structures synthesized in the electrolyte containing ethylene glycol solution have the highest hardness and display well thermal stability among the other structures. The surface area and crystal structure of AAO were determined by surface area analysis and X-ray diffraction patterns measurements. Experimental results showed that the AAO structures have amorphous phase and the highest surface area is 2.59 m2/g.

Fabricating Al2O3-nanopores array by an ultrahigh voltage two-step anodization technique: Investigating the effect of voltage rate and Al foil thickness on geometry and ordering of the array

A densely-packed hexagonal Al2O3 nanopores array was fabricated by using a relatively simple ultrahigh voltage two-step anodization method. The developed method was technologically simple and suitable for controlling the morphology and geometry of the nanopores array as a nanodevice which has specific applications in constructing biosensors. The anodization was carried out at different applied voltage rates and Al foil thicknesses. By increasing voltage, the current density showed a peak shape profile so that its maximum was directly depended on the rate of the applied voltage. The simulation curves evidenced direct dependency of the ordering of the nanopores to the anodization voltage rate. The most ordered array was achieved at an applied voltage rate of 0.600 Vs−1 when a 1.0-mm thick Al foil was used. Spontaneous oscillation patterns (self -oscillations) were appeared at the voltage rates of 0.300, 0.400 and 0.500 Vs−1 when a 0.25-mm thick Al foil was utilized. The cross-sectional SEM images revealed that a three-dimensional periodic modulation, along the interior surfaces of the nanopores has been developed.

TiO2-NT electrodes modified with Ag and diamond like carbon (DLC) for hydrogen production by alkaline water electrolysis

In present work, the two-step anodization technique was applied for synthesis of TiO2 nanotube (NT). Silver and diamond like carbon (DLC) were coated on the surface of as prepared TiO2-NT using chemical reduction method and MW ECR plasma system. The morphology, composition and structure of the electrodes were examined by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The results showed that Ag nanoparticles, having size in the range of 48–115nm, are evenly distributed on the top, inside and outside surface of TiO2-NT and when DLC was coated on the surface of TiO2-NT and TiO2-NT-Ag, the top of nanotubes were partially open and the pore diameter of hexagonal structure decreased from 165nm to of 38–80nm. On the other hand, the microhardness test and contact angle measurements revealed that additions of Ag and diamond like carbon have a positive effect on the mechanical properties of TiO2-NT film. The electrocatalytic properties of the electrodes towards the hydrogen evolution reaction (HER) were investigated by the electrochemical measurements recorded in 1M KOH solution. In addition, long-term durability of electrodes towards HER and the energy consumption of alkaline electrolysis were investigated. The energy requirement showed that while the deposition of silver provides approximately 14.95% savings of the energy consumption, the DLC coating causes increase in energy consumption.

Uniformity and homogeneity of FeXNi100−X nanowires electrodeposited in nanoporous alumina

Nanoporous alumina templates produced by two-step anodization technique with high purity aluminum (Al) sheets and oxalic acid electrolyte were used to synthesize FeXNi100−X nanowires via potentiostatic and galvanostatic electrodeposition methods (continuous or pulsed). Scanning and transmission electron microscopy and energy dispersive spectroscopy techniques were used to investigate pore filling, length and atomic composition of the nanowires. The main results showed that uniformity and homogeneity along the length of the nanowires depend on the applied electrodeposition methods, and only the galvanostatic ones enable uniform length along the whole nanoporous alumina template with atomic composition close to permalloy.

Effect of different nano-structured Ag doped TiO2-NTs fabricated by electrodeposition on the electrocatalytic hydrogen production

In this study, TiO2-NTs electrode was successfully fabricated by two-step anodization technique. Then, different Nano-structured Ag was loaded on the surface of as prepared TiO2-NTs using electrodeposition method at various deposition times. The morphology, composition and structure of Ag doped TiO2-NTs were determined by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The results showed that nanoparticle and nanodentrict Ag were formed on the TiO2-NTs depending on the deposition time and the particle size of anatase TiO2 increased with increasing Ag doping concentration. To evaluate the electrocatalytic properties of Ag doped TiO2-NTs towards the hydrogen evolution reaction (HER), the cyclic voltammetry, cathodic polarization curves and impedance measurements were recorded in 1 M KOH. The electrochemical data indicated that nanodentrict Ag doped TiO2, having the highest charge carrier density (9.02.1029 cm−3) as revealed by Mott–Schottky analysis, exhibits the most effective electrocatalytic activity towards the HER. In addition, long term stability of TiO2-NTs and Ag–TiO2-NTs electrodes and the energy requirement for the electrolytic hydrogen evolution were examined.

Pb(Zr0.52Ti0.48)O3 nanotubes synthesis and infrared absorption properties

Herein a useful methodology to synthesize the lead zirconate titanate (PZT) nanotubes via a dip-coating deposition process with anodic aluminum oxide (AAO) template is proposed. The nano-porous AAO templates were produced using a controlled two-step electrochemical anodization technique. The PZT/AAO composite was formed using the dip-coating wetting technique. The prepared PZT precursor solution was driven into the nanopore channels of AAO template under the driving force of capillary action, subsequently the sintering process of the as-filled templates was carefully tuned to obtain Pb(Zr0.52Ti0.48)O3 nanotubes of crystalline tetragonal phase with uniform pore size and ordered arrange. Fourier transform infrared spectroscopy (FTIR) results show that in the 1200–1900cm−1 band, the composite structure of PZT/AAO has obvious absorption peaks at 1471.56cm−1 and 1556.09cm−1, the absorption intensity of the composite structure is about six times of pure AAO template. The unusual optical properties found in PZT/AAO composite will stimulate further theoretical and experimental interests in ferroelectric nanostructures.

Fabrication of TiO2-NTs and TiO2-NTs covered honeycomb lattice and investigation of carrier densities in I−/I3− electrolyte by electrochemical impedance spectroscopy

The TiO2 nanotubes (NTs) were produced by one-step (1S) and two-step (2S) anodization technique. Effects of various anodization potential and times on the growth of TiO2-NTs were investigated by using Field Emission-Scanning Electron Microscopy (FE-SEM). The crystal structure of the electrodes was determined with X-ray powder diffractometry (XRD). The most suitable potential and time for TiO2-NTs obtained by both of anodization methods were found to be 21V and 4h. XRD results indicated that 2S anodization technique provided better crystallinity. The electrochemical behaviors of the electrodes in acetonitrile electrolyte contained I−/I3− were examined by utilizing electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques. Electrochemical results showed that 2S anodization technique increases the carrier densities (ND) value of TiO2-NTs, and flat band potential is shifted by 50mV to more negative values.

Investigations of Magnetic Properties Through Electrodeposition Current and Controlled Cu Content in Pulse Electrodeposited CoFeCu Nanowires

CoFeCu nanowires were deposited by pulsed electrodeposition technique into the porous alumina templates by a two-step mild anodization technique, using the single-bath method. The electrodeposition was performed in a constant electrolyte while Cu constant was controlled by electrodeposition current. The electrodeposition current was 3.5, 4.25, 5 and 6 mA. The effect of electrodeposition current and annealing on the magnetic behavior of the nanowires was investigated. Nanowires were fabricated with 30nm diameter and 100nm inter-pore distance with both bcc-CoFe and fcc- Cu phases. With increasing the electrodeposition current the Cu content decrease and the coercivity and magnetization increase up to its optimum value, then decrease. Annealing improved the coercivity, maximum coercivity was obtained for sample fabricated at 5 mA current. After annealing the magnetization decrease for all sampls. The X-ray diffraction pattern of the sample at electrodeposition current 3.5 mA after annealed indicates that Cu and CoFe phases separately was formed and separate peak related to CoFeCu alloy structure is not seen.

Enhancement in hydrogen generation using bamboo like TiO2 nanotubes fabricated by a modified two-step anodization technique

Bamboo like TiO2 nanotubes were successfully fabricated by a modified two-step anodization technique under different voltage and time. X-ray diffraction patterns and Raman spectra confirmed the anatase crystal phase of TiO2 nanotubes. Optical studies reveal that the band gaps of TiO2 nanotubes shrinked to 2.517(7) eV by varying the anodization parameters. The decrease in band gap was due to the improved crystallinity and the defect states formed in the forbidden gap. The photoluminescence spectra clearly revealed the formation of intermediate defect states, oxygen vacancies and color center defects. Bamboo like nanotubes exhibited higher photocurrent density than stack layered nanotubes due to the increase in crystallinity with higher surface area, enhanced light penetration depth and better scattering within the tubular structure. The photocatalytic activity of TiO2 nanotubes for methyl orange degradation followed pseudo first order kinetics.

Arrays of rhodium nanowires based on anodic alumina: Preparation and electrocatalytic activity for nitrate reduction

Rhodium nanowires with an average diameter of 55nm and a length of 1.5–11μm have been prepared by electrodeposition in the pores of anodic aluminium oxide (AAO) membranes which were fabricated by two-step anodization technique. Rh/AAO nanocomposites have been investigated by the combination of instrumental and electrochemical methods. The electrochemical surface area of Rh nanowires is about one order of magnitude higher than the geometrical one that is beneficial for catalytic applications. The efficiency of both isolated Rh nanowires and Rh/AAO nanocomposites towards nitrate electrochemical reduction in acidic medium has been demonstrated. The preliminary annealing of AAO templates allows us to obtain nanocomposites that are suitable for long-term catalytic applications in aggressive medium.