One-step Anodic Oxidation Research Articles

Atomic force microscopy in mechanical measurements of single nanowires

In this paper, we present the results of mechanical measurement of single nanowires (NWs) in a repeatable manner. Substrates with specifically designed mechanical features were used for NW placement and localization for measurements of properties such as Young's modulus or tensile strength of NW with an atomic force microscopy (AFM) system. Dense arrays of zinc oxide (ZnO) nanowires were obtained by one-step anodic oxidation of metallic Zn foil in a sodium bicarbonate electrolyte and thermal post-treatment. ZnO NWs with a hexagonal wurtzite structure were fixed to the substrates using focused electron beam-induced deposition (FEBID) and were annealed at different temperatures in situ. We show a 10-fold change in the properties of annealed materials as well as a difference in the properties of the NW materials from their bulk values with pre-annealed Young modulus at the level of 20 GPa and annealed reaching 200 GPa. We found the newly developed method to be much more versatile, allowing for in situ operations of NWs, including measurements with different methods of scanning probe microscopy.

Detailed Insight into Photocatalytic Inactivation of Pathogenic Bacteria in the Presence of Visible-Light-Active Multicomponent Photocatalysts.

The use of heterogeneous photocatalysis in biologically contaminated water purification processes still requires the development of materials active in visible light, preferably in the form of thin films. Herein, we report nanotube structures made of TiO2/Ag2O/Au0, TiO2/Ag2O/PtOx, TiO2/Cu2O/Au0, and TiO2/Cu2O/PtOx obtained via one-step anodic oxidation of the titanium-based alloys (Ti94Ag5Au1, Ti94Cu5Pt1, Ti94Cu5Au1, and Ti94Ag5Pt1) possessing high visible light activity in the inactivation process of methicillin-susceptible S. aureus and other pathogenic bacteria-E. coli, Clostridium sp., and K. oxytoca. In the samples made from Ti-based alloys, metal/metal oxide nanoparticles were formed, which were located on the surface and inside the walls of the NTs. The obtained results showed that oxygen species produced at the surface of irradiated photocatalysts and the presence of copper and silver species in the photoactive layers both contributed to the inactivation of bacteria. Photocatalytic inactivation of E. coli, S. aureus, and Clostridium sp. was confirmed via TEM imaging of bacterium cell destruction and the detection of CO2 as a result of bacteria cell mineralization for the most active sample. These results suggest that the membrane ruptures as a result of the attack of active oxygen species, and then, both the membrane and the contents are mineralized to CO2.

Controlled self-cleaning aluminum surfaces mediated by anodic aluminum oxide.

Special porous anodic aluminum oxide (AAO) membranes are created on Al in a phosphonic acid electrolyte solution through one-step anodic oxidation and modified with polydimethysiloxane using a vapor deposition technique. In this context, the anodic oxidation time is tuned during its process. As such, the Al surface's wettability, and self-cleaning property are controlled by the tunable anodic oxidation time, for the anodic oxidation, time can regulate the structure of the AAO and the proportion of the air-liquid interface.

Nanostructured films formed on Zn during anodic oxidation in different carbonate-based electrolytes

Electrochemical generation of nanowire arrays by one-step anodic oxidation of Zn in carbonate-based electrolytes of different pH values is described. Zn foil was anodized in a mixture containing 5 mM Na2CO3 and 5 mM NaHCO3, as well as in pure Na2CO3 and NaHCO3 (both 10 mM). The morphology of anodic films was verified by FE-SEM. A special emphasis was put on the analysis of the composition of as-received nanomaterials by various techniques including XRD, XPS, UV–Vis, and Raman spectroscopy. Contrary to previous reports, we confirmed that the unknown phase of zinc carbonate with a formula of ZnCO3·H2O or Zn(HCO3)(OH) is formed at the Zn surface during anodization. The formation of ZnO resulting in more evident electrode passivation was also observed in the electrolytes containing sodium carbonates. The changes occurring during the thermal treatment of as-received materials were described based on TG, XPS, XRD, Raman, and nitrogen adsorption-desorption measurements. It was verified that, except for a several-fold increase in the active surface area, no significant changes in the wire-like morphology of the anodically generated product occur during its thermal conversion to ZnO. Finally, no noticeable differences in the photoelectrochemical performance of ZnO nanostructures formed in different electrolytes were observed.

Preparation of TiO2 Nanotube Arrays with Controllable Morphology and their Superhydrophobic Modification for Photocatalytic Degradation of Water Pollution

TiO2, as a photoactive semiconductor material, where like photocatalysis technology is a hot topic of research in recent years, shows great potential for application in the direction of environmental pollution treatment and solar-chemical energy conversion. In this paper, we prepared titanium dioxide nanotube arrays (TNAs) by a simple one-step anodic oxidation method in an ethylene glycol electrolyte containing ammonium fluoride under optimized conditions. The effects of anodic oxidation voltage, anodic oxidation time and annealing temperature on the growth of TNAs were systematically investigated. It was shown that the sample parameters of TNAs prepared by anodic oxidation were influenced by the anodic oxidation conditions, and the tube diameter and anodic oxidation voltage were positively correlated in a certain range. The TNAs with the best characterization performance were selected for photocatalytic degradation, and methylene blue (MB) was used to simulate the organic pollutants. The results show that TNAs have better photocatalytic activity compared with conventional TiO2. On the basis of this, stearic acid (SA) and TNAs were compounded and modified. The TNAs were made to obtain superhydrophobic properties. The photocatalytic degradation experiments were carried out on them. The results show that the superhydrophobic modification does not affect their photocatalytic activity, so it is possible to achieve photocatalytic degradation of water pollution under the premise of superhydrophobicity, which has greater application prospects in water pollution treatment.

Preparation of CuO nanosheet array thin film with controlled morphology for SERS and photocatalysis

A CuO nanosheet array thin film was synthesized by one-step electrochemical anodic oxidation, exhibiting SERS and photocatalytic performance.

Heterostructures of Cut Carbon Nanotube-Filled Array of TiO2 Nanotubes for New Module of Photovoltaic Devices.

In this work, a new photovoltaic device was prepared. The device uses titanium (Ti) foil/TiO2 nanotubes as the photoanode and multi-walled carbon nanotubes (MWCNTs) as a photosensitizer. Titanium dioxide nanotube arrays (TiO2-NTs) were prepared by one-step anodic oxidation. Cut-MWCNTs with a length of less than 100 nm were obtained by the mixed-acid oxidation of MWCNTs. The two materials were combined to form a TiO2-NTs@cut-MWCNT heterostructure by electrophoresis. TiO2-NTs@cut-MWCNTs were characterized by field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD), which showed that the two materials were effectively combined. We fabricated the heterostructure into a photovoltaic device, showing an enhanced photocurrent response and an efficiency of 0.0138%, and explained this phenomenon by performing UV-vis absorption spectroscopy and electrochemical tests. It is hoped that this work can provide a reference value for the application of carbon nanotubes in photovoltaic devices.

A facile strategy to fabricate bionic superhydrophobic armor based on utilization of metallographic structure heredity and reconstruction of anodized oxide film on alloy

Focusing on alloy system, a facile strategy was proposed to fabricate a micro/nano-structured bionic superhydrophobic surface with enhanced anti-corrosion performance. It was implemented on iron carbon alloy substrate by combining one-step anodic oxidation with designed annealing to realize a protective armor. The study verified that the metallographic features in the alloy system and heredity during the anodic oxidation were crucial preconditions to construct bionic surface. The reconstruction of the anodized oxide films triggered by designed annealing changed the wetting mechanism as well as switching the hydrophilic/hydrophobic state by forming a smaller size point-to-point contact (Cassie-Baxter State) with the droplets. The synergistic effect of this unique bionic structures and low surface energy coating made the sample surface exhibit superhydrophobic state and excellent corrosion resistance. Such combination strategy lays the foundation for constructing functional surfaces of alloy systems. More importantly, it can be extended to multicomponent alloy systems, by selecting structure features even modulating feature components to simply realize a devisable protective armor, which provides more in-depth thinking for solving the longstanding corrosion problems of engineering materials.

Improving the photoelectrochemical performance of porous anodic SnO x films by adjusting electrosynthesis conditions

A comprehensive characterization of photoelectrochemical (PEC) properties of the nanoporous tin oxide (SnOx) films of different thicknesses and complex internal morphology is presented. Nanoporous SnOx layers were obtained by one-step anodic oxidation (anodization) of Sn foil in 1 M NaOH. Semiconducting films with a uniform diameter of ca. 50 nm were grown if the potential of 4 V was applied during anodization, and the layers with different thicknesses were synthesized by changing the duration of the process. Switching the potential between 2 and 4 V allows the formation of anodic films with segments of different channel diameters. The optimal anodizing duration for layers with uniform channels was found to be 50 minutes, which corresponds to the thickness of SnOx film of slightly above 6 μm. In the case of layers with segments of different channel diameters, the segment arrangement was found to be crucial for optimal PEC performance. Layers with the segment of narrower channels being in the contact with the current collector were found to exhibit enhanced photoelectrochemical performance compared to their counterparts with an opposite segment arrangement. This was mainly attributed to the favorable band arrangement facilitating the transfer of the photogenerated electrons to the external circuit as well as enhanced adhesion of the anodic SnOx layer to the current collector. Highlights Nanoporous SnOx films were synthesized electrochemically. Layers with various morphologies were studied as photoanodes. The optimal thickness of anodic SnOx was found to be 6 μm. Enhanced PEC performance was observed for multisegment anodic films. The segment arrangement is crucial for optimal PEC performance.

CdS-Decorated Porous Anodic SnOx Photoanodes with Enhanced Performance under Visible Light

Electrochemically generated nanoporous tin oxide films have already been studied as photoanodes in photoelectrochemical water splitting systems. However, up to now, the most significant drawback of such materials was their relatively wide band gap (ca. 3.0 eV), which limits their effective performance in the UV light range. Therefore, here, we present for the first time an effective strategy for sensitization of porous anodic SnOx films with another narrow band gap semiconductor. Nanoporous tin oxide layers were obtained by simple one-step anodic oxidation of metallic Sn in 1 M NaOH followed by further surface decoration with CdS by the successive ionic layer adsorption and reaction (SILAR) method. It was found that the nanoporous morphology of as-anodized SnOx is still preserved after CdS deposition. Such SnOx/CdS photoanodes exhibited enhanced photoelectrochemical activity in the visible range compared to unmodified SnOx. However, the thermal treatment at 200 °C before the SILAR process was found to be a key factor responsible for the optimal photoresponse of the material.

Preparation of multilayered C–Si–Al2O3 coatings on continuous carbon fibers and C–Si–Al2O3-coated carbon-fiber-reinforced hydroxyapatite composites

Multilayered C–Si–Al coatings with various morphologies were deposited on carbon fibers (CFs) using magnetron sputtering. The thickness of the coatings was increased from 0.5 to 1.5 μm by magnetron sputtering between 90 and 120 min. C–Si–Al coatings of suitable thickness were heat-treated at 600 °C and transformed into C–Si–Al2O3 coatings by one-step anodic oxidation (AO). The oxidation time for the one/two-step anodic oxidation and the ratio of oxidation time for the two-step anodic oxidation significantly influenced the morphologies of the C–Si–Al2O3(AO) coatings. Al2O3 coatings with satisfactory morphologies and structures were prepared by two-step anodic oxidation with a total time of 30 min and a ratio of 1:1 between the initial and secondary oxidation times. The multilayered C–Si–Al2O3(AO) coatings were modified to C–Si–Al2O3 coatings by secondary heat treatment at 1050 °C. Subsequently, hot-press sintering was used to prepare CFs with multilayered C–Si–Al2O3 coating-reinforced hydroxyapatite (CF/C–Si–Al2O3/HA) composites. The multilayered C–Si–Al2O3-coated CFs demonstrated good resistance to oxidation and thermal shock. This could effectively protect CFs from oxidative damage and maintain its strengthening effect during sintering. The multilayered C, Si, and Al2O3 coatings effectively reduced the difference between the coefficient of thermal expansion of the CFs and HA matrixes. The interfacial gaps between the multilayered coatings and HA were reduced. This could enhance the mechanical performance of the composites. The CF/C–Si–Al2O3/HA composites exhibited improved mechanical properties with a bending strength of 83.94 ± 12.29 MPa, and fracture toughness of 2.45 ± 0.08 MPa m1/2. This study can broaden the application of CF/C–Si–Al2O3/HA biocomposites as bone-repair materials and help obtain CF-reinforced composites with excellent mechanical properties that are fabricated or serviced at high temperatures.

Lithium and sodium storage performance of tin oxyphosphate anode materials

Two types of Sn-based nanostructured materials have been investigated as anodes in lithium-ion batteries (LIB) and sodium-ion batteries (SIB). Firstly, nanostructured Sn/SnOx powders were synthesized by one-step anodic oxidation of Sn foil in an alkaline electrolyte followed by mechanical separation of the anodic film from the remaining substrate. Secondly, as-anodized powders were converted for the first time to tin oxyphosphate (Sn/SnP2O7) hybrid via a simple phosphorization with red phosphorous at 500 °C. The XRD and HR-TEM analyses confirmed that the hybrid was comprised of Sn nanoparticles embedded in the SnP2O7 matrix. When used as anode materials, the Sn/SnP2O7 exhibits excellent storage performance for lithium and sodium ions compared to Sn/SnOx that can be attributed to the metal/matrix structure which is not only conducive to the electron transport but also can facilitate the accommodation of volume changes during intercalation/deintercalation processes. A stable reversible capacity with an excellent coulombic efficiency of nearly 100% at different current densities even up to 1000 cycles was achieved for the Sn/SnP2O7 anode in LIB.

Insights into the Intrinsic Creation of Heterojunction-Based Ordered TiO2 Nanotubes Obtained from the One-Step Anodic Oxidation of Titanium Alloys

To gain insights into how the presence of the second metal in Ti alloys affects the morphology, crystallinity, chemical structure, and photocatalytic/photoelectrochemical activity of mixed-oxide nanotubes (TiO2–MxOy), five systems were electrochemically synthesized in a fluoride-containing ethylene glycol-based electrolyte by using Ti alloys, with 10 wt % of the second metal, as precursors. The level of self-organization and -orientation in the obtained samples followed the order: Ag < Cu < Mn < V < Co, being the Ti90Ag10_40V sample, the only presenting single Ag nanoparticles embedded in the oxide layer. The highest photocatalytic and photoelectrochemical activities were reported for the Ti90Ag10_40V sample, which can be attained to the heterojunction between the oxides, the formation of single Ag nanoparticles, and the high level of self-organization. Apparently, the intrinsic heterojunction between the oxides depends on the still-needed-to-be-estimated stability of the oxides produced during the anodization of each system.

Formation of anodic TiO2 nanotube arrays with ultra-small pore size

TiO2 nanotubes prepared by anodization of titanium metal substrates are widely used as functional materials in various fields. Small pore size TiO2 nanotube arrays are demanded because of their excellent performance in applications. However, the minimum pore size of TiO2 nanotube arrays has been limited to ~15 nm (nm) despite of long time extensive studies. In the present work, we have fabricated TiO2 nanotube arrays with diameter down to an unprecedented low value of ~6 nm in ammonium fluoride-containing ethylene glycol electrolyte by a simple one-step anodic oxidation method under optimized condition. The influences of concentration of ammonium fluoride, viscosity of solution, amount of adding water and applied voltage on the anodic growth of small pore TiO2 nanotubes are studied systematically. Pore initiation and widening determined by the competition between chemical dissolution and field driven growth of anodic oxides under relative low formation field strength are investigated, where local concentration of fluoride anions and acidity near pore bottom are believed to play significant roles in the formation of nanoporous or nanotubular TiO2 with ultra-small pore diameter and cell size. By sealing the reaction cell to prevent the solution from absorbing ambient water, typical TiO2 nanotube arrays with a pore diameter of ~10.8 nm can grow up to ~1.1 μm in length, i.e. an aspect ratio up to 100, which is remarkable for TiO2 nanotubes with such small pore size.

Volcano-like hierarchical superhydrophobic surface synthesized via facile one-step secondary anodic oxidation

Superhydrophobic surface has been extensively applied in the field of self-cleaning and corrosion prevention, and the common preparation route of the superhydrophobic surface involves the construction of rough structure and modification with low-surface-energy regents in multistep process. Herein, a facile one-step method was proposed to fabricate the superhydrophobic surface with the simultaneous construction and modification of hierarchical microstructure and surface, the volcano-like anodic aluminium oxide (AAO) -based superhydrophobic surfaces with controllable roughness were synthesized via secondary anodic oxidation (SAO) process of AAO film in an organic–inorganic sol–gel system. During the SAO process, the perfluorooctyl triethoxysilane, which covalently bonded onto the surface, resulted in the inhomogeneous distribution of surface free energy and heterogeneous generation of volcano-like structure. The hydrophobic ability was enhanced by the rough hierarchical micro-/nanostructure with low surface energy, and the TiO2/PFOTS-AAO-15 exhibited the optimal water repellence with a WCA of ~154°, self-cleaning performance and anticorrosion property in corrosive medium. This convenient method is anticipated to unlock various superhydrophobic surfaces on different substrates in the practical fields of self-cleaning and anticorrosion.

The influence of water-induced crystallization on the photoelectrochemical properties of porous anodic tin oxide films

Nanoporous SnOx films with ultra-small channels (<20nm in diameter) were synthesized by one-step anodic oxidation of Sn foil in 1M sodium hydroxide. Then, as-prepared materials were immersed in distilled water for various durations (2–120h) to find out whether a simple soaking process can affect the photoelectrochemical performance of such kind of photoanodes. It was confirmed that during exposure to water, spontaneous crystallization of the amorphous SnOx matrix into rutile-type SnO2 occurs via a dissolution–redeposition process, which results in a gradual loss of the initial porous morphology and thinning of the anodic film. Moreover, due to the formation of less defective, more stoichiometric, and crystalline SnO2-x, gradual widening of the semiconductor band gap, the cathodic shift of the flat band and onset potentials, as well as decrease in the donor density are observed. All these factors are the reason for the significant deterioration of the photoelectrochemical performance of SnOx photoanodes during their exposure to water. Therefore, it was confirmed that even slight differences in the experimental procedure, especially sample washing, drying, and storage, can result in meaningful changes in the composition, and the photoelectrochemical properties of anodically generated tin oxide films.

Partially disordered nano-porous metallic oxide engineering: surface morphology controllability and multiple scattering properties

Random multiple light scattering in disordered photonics leads to interesting and unexpected physical phenomena. Here, we demonstrate two types of partially disordered nano-porous metallic oxide materials: disordered grating nano-pores and two-dimensional disordered nano-tubes, which are produced just with one-step anodic oxidation. The relations among the processing parameters, morphology properties and multiple scattering characteristics are investigated. The surface morphology controllability can be achieved by simply changing the processing direct voltages, leading to different scattering properties. The probabilistic model of partially disordered nano-porous metallic oxide is constructed according to the nano-structure characteristics of oxide, and the rigorous coupled wave analysis is utilized for optical field simulation to exhibit the theoretical multiple scattering properties. Futhermore, the experimental scattering fields are measured and are analysed by statistical method. The research focuses on the disorder caused by one-step oxidation, which is distinct from previous studies that introducing disorder into periodic materials, and would open up new prospects for sensing, bionics and structural color.

Synthesis and density functional theory study of free-standing Fe-doped TiO2 nanotube array film for H2S gas sensing properties at low temperature

Abstract To analyze the sensing performance of the TiO2 nanotube (TiNT) array film gas sensor to H2S at low working temperature, the free-standing Fe-doped TiNT array films were synthesized using the one-step anodic oxidation method followed by immersion and annealing processes. The results obtained from the field emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectra and ultraviolet–visible spectra methods indicate that the lattice of TiO2 was doped by iron ions. Subsequently, compared with undoped TiO2, the response intensity, response and recovery times of the gas sensor based on Fe-doped TiNT array film to 50 ppm H2S at 100 °C were improved. Furthermore, the improved selectivity and stability to H2S were also obtained with the Fe-doped TiNT gas sensor. Finally, based on the Density Functional Theory (DFT), the band structure of Fe-doped TiO2 and the electronic density of states of H2S and the compared gases are calculated and used for the systematical analysis of sensing and selectivity mechanisms of the Fe-doped TiNT gas sensor at low working temperature.

Substantially Improved Na-Ion Storage Capability by Nanostructured Organic-Inorganic Polyaniline-TiO2 Composite Electrodes.

Developing sodium (Na)-ion batteries is highly appealing because they offer the potential to be made from raw materials, which hold the promise to be less expensive, less toxic, and at the same time more abundant compared to state-of-the-art lithium (Li)-ion batteries. In this work, the Na-ion storage capability of nanostructured organic–inorganic polyaniline (PANI) titanium dioxide (TiO2) composite electrodes is studied. Self-organized, carbon-coated, and oxygen-deficient anatase TiO2–x-C nanotubes (NTs) are fabricated by a facile one-step anodic oxidation process followed by annealing at high temperatures in an argon–acetylene mixture. Subsequent electropolymerization of a thin film of PANI results in the fabrication of highly conductive and well-ordered, nanostructured organic–inorganic polyaniline-TiO2 composite electrodes. As a result, the PANI-coated TiO2–x-C NT composite electrodes exhibit higher Na storage capacities, significantly better capacity retention, advanced rate capability, and better Coulombic efficiencies compared to PANI-coated Ti metal and uncoated TiO2–x-C NTs for all current rates (C-rates) investigated.

Fast fabrication of nanostructured semiconducting oxides by anodic oxidation of brass

Nanostructured semiconducting oxide layers were synthesized on the surface of alpha brass (CuZn33) by its simple one-step anodic oxidation (anodization) in a strongly alkaline electrolyte (0.1 M NaOH) at various voltages (30–60 V) followed by thermal treatment in air at 200 °C. The morphology of anodic films was studied by FE-SEM, while its composition was confirmed by EDS, XRD, and Raman spectroscopy. All anodic films exhibited a cracked morphology and were composed of particles with a size of less than 100 nm. Although the presence of Zn in the oxide layer was confirmed, especially within the deeper parts of the film, the main component was monoclinic CuO. Band gaps (Eg) of all obtained materials were also estimated from reflectance spectra, and it was found that the higher the potential applied during anodic oxidation, the wider Eg is observed. Therefore, it can be stated that such a simple electrochemical approach can be an effective way for the fabrication of visible-light-driven photocatalysts.