Nanoporous Anodic Titanium Oxide Research Articles

Band gap engineering of nanotubular Fe2O3-TiO2 photoanodes by wet impregnation

Due to many limitations of titanium oxide, its direct use in photoelectrochemical water splitting under solar radiation is ineffective. Band gap engineering based on introduction of the Fe2O3 phase into TiO2 by wet impregnation has been proposed. In particular, nanoporous anodic titanium oxide layers were soaked in solutions with different concentrations of iron ion (5–100 mM) followed by their air annealing at 400 °C. As-prepared nanotubular Fe2O3-TiO2 materials were characterized by using field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, X-ray diffraction (XRD), reflectance measurements, Mott-Schottky analysis, and photoelectrochemical tests. It was found that increasing the iron content in anodic materials strongly affects their resulting semiconducting and photoelectrochemical properties. The maximum of generated photocurrent shifts towards visible light as the band gap energy decreases (from 3.36 to 2.89 eV) with the respect to increasing the iron content in the anodic materials.

Surface modification of nanoporous anodic titanium dioxide layers for drug delivery systems and enhanced SAOS-2 cell response.

Nowadays, titanium and its alloys are the most commonly used implantable materials. The surface topography and chemistry of titanium-based implants are responsible for osseointegration. One of the methods to improve biocompatibility of Ti implants is a modification with sodium hydroxide (NaOH) or 3-aminopropyltriethoxysilane (APTES). In the present study, anodic titanium dioxide (ATO) layers were electrochemically fabricated, and then immersed in a NaOH solution or in NaOH and APTES solutions. The functionalized samples were characterized by using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). All samples were examined as drug delivery systems and scaffolds for cell culturing. Based on the parameters of the fitted desorption-desorption-diffusion (DDD) model parameters, it was concluded that the modification with NaOH increased the amount of released ibuprofen and inhibited the release process. Osteoblast-like cell line (SAOS-2) was used to investigate the cell response on the non-modified and modified ATO samples. The MTS test and immunofluorescent staining were carried out to examine cell adhesion and proliferation. The data showed that the modification of nanoporous TiO2 layers with small molecules such as APTES enhanced metabolic activity of adhered cells compared with the non-modified and NaOH-modified TiO2 layers. In addition, the cells had a polygonal-like morphology with distinct projecting actin filaments and were well dispersed over the whole analyzed surface.

3D nanoporous titania formed by anodization as a promising photoelectrode material

Nanoscale control of the growth of inorganic metal oxides determines their structures and properties, and leads to development of novel nanostructured materials with fundamental and practical importance from a point of view their further applications. After anodic aluminum oxide, the next nanoporous material which has attracted tremendous interest of researchers around the world, is nanoporous anodic titanium oxide (ATO) formed by anodization. The main objective of this work was to investigate the ability of formation of anodic titanium oxide structures, particularly in the form of TiO2 nanopore arrays on 3D titanium substrates (Ti mesh) in viscous electrolyte containing fluoride ions. Three-dimensional (3D) TiO2 nanopore arrays grown on Ti mesh were prepared via two-step electrochemical anodization process, and the effect of anodizing potential and duration of the process on the formation of ATO layers on titanium mesh were investigated. The 3D TiO2 nanopore arrays on Ti mesh were characterized by using field emission scanning electron microscopy and X-ray diffraction (XRD) technique. The results showed that the optimized anodization conditions for preparation of titanium dioxide nanopore arrays are 40 and 50 V of the applied potential, and 10 min of time processing. The effect of annealing temperature of ATO layers on their morphology and phase composition was also investigated in detail. The amorphous ATO layers on titanium mesh transform to anatase phase at 400 °C and further to rutile phase at 600 °C. However, photoelectrochemical tests demonstrated that the best photoelectrochemical performance of fabricated 3D photoanodes was observed for the samples anodized at 40 V or 50 V for 10 min, and annealed at 400 °C. The photoelectrochemical properties of the mesh-based and typical plate TiO2/Ti electrodes were compared. It was found that the higher photoconversion efficiency was observed for the 3D TiO2/Ti mesh electrode than for a typical plate TiO2/Ti electrode. It is expected that anodizing of three dimensional (3D) Ti substrates will offer an opportunity to enhance various properties of anodic titanium oxide, especially its photoactivity.

Electroless Ni–P alloys on nanoporous ATO surface of Ti substrate

Followed by well-known AAO templates, anodic titanium oxide (ATO) surface with nanoporous structure has gained extensive attraction as implants due to its excellent surface properties. So, the objective of this work was to explore a novel approach for electroless Ni–P film on nanoporous ATO surface, with an aim to obtain a strong bonding interface between Ti substrate and its surface films. Impressively, with anodizing DC potential extending from 100 to 300 V, a two-step anodizing process was created to achieve nanoporous ATO surface with a suitable diameter size that acted as bonding pinholes for amorphous Ni–P growth. Structural design of electroless Ni–P film onto ATO surface was innovatively addressed for increasing interfacial bonding strength between Ti substrate and its surface film. Regarding the ATO surface with nondestructive characteristics, several pretreatments were processed with anodizing, sensitizing, activating, following by electroless Ni–P film. Among them, Pd-reducing crystal sites, which were capable of effectively adsorbing on ATO surface, were emerged as preferential locations for catalytic growth of Ni–P film to make pinning effects toward ATO nanopores. Results indicated that the well-organized ATO nanoporous arrays were successfully processed onto the surface of Ti substrate through the mixed sulfuric–phosphoric acids electrolyte at DC 210 V. When nanosized Ni–P grains were planted inside nanoporous arrays of ATO surface, it was expected as growing sites to refine the subsequent Ni–P growth and thus resulting in higher compactness of electroless Ni–P film on ATO surface. Further studies of the laser-assisted MAG welding on the as-received ATO surface within electroless Ni–P film were conducted, thereby achieving a superior metallurgical bonding for Ti/Ni–P interface. More important, this was the first attempt to design nanoporous arrays for Ni–P growth on ATO surface to increase its weldability of Ti alloys, also supporting a new guideline for multi-functional films on porous surface of the as-anodized Ti, Mg, and Al alloys.

Co-delivery of ibuprofen and gentamicin from nanoporous anodic titanium dioxide layers

Although single-drug therapy may prove insufficient in treating bacterial infections or inflammation after orthopaedic surgeries, complex therapy (using both an antibiotic and an anti-inflammatory drug) is thought to address the problem. Among drug delivery systems (DDSs) with prolonged drug release profiles, nanoporous anodic titanium dioxide (ATO) layers on Ti foil are very promising. In the discussed research, ATO samples were synthesized via a three-step anodization process in an ethylene glycol-based electrolyte with fluoride ions. The third step lasted 2, 5 and 10min in order to obtain different thicknesses of nanoporous layers. Annealing the as-prepared amorphous layers at the temperature of 400°C led to obtaining the anatase phase. In this study, water-insoluble ibuprofen and water-soluble gentamicin were used as model drugs. Three different drug loading procedures were applied. The desorption-desorption-diffusion (DDD) model of the drug release was fitted to the experimental data. The effects of crystalline structure, depth of TiO2 nanopores and loading procedure on the drug release profiles were examined. The duration of the drug release process can be easily altered by changing the drug loading sequence. Water-soluble gentamicin is released for a long period of time if gentamicin is loaded in ATO as the first drug. Additionally, deeper nanopores and anatase phase suppress the initial burst release of drugs. These results confirm that factors such as morphological and crystalline structure of ATO layers, and the procedure of drug loading inside nanopores, allow to alter the drug release performance of nanoporous ATO layers.

Fabrication of Anodic Titanium Oxide (ATO) for waste water treatment application

In this study, forming of Anodic Titanium Oxide (ATO) that has a nanoporous and nanotube morphology was studied for waste water treatment application. Nanoporous anodic titanium oxide was obtained by anodization, using ethylene glycol merging with ammonium fluoride at room temp as electrolyte. The variables of the process were anodization time (5, 10, 15 and 20 min) and anodization voltages (20, 40 and 60 V). Field emission scanning electron microscopy revealed that separated nanotubes became obvious when the voltage is high. The samples with different ATO conditions were investigated by the degradation of methylene blue under UV light irradiation. It was found that the activity of the photocatalysis of ATO was significantly enhancement of the degradation of methylene blue. These results suggest that ATO/UV photocatalysis as a method for treatment of diluted waste waters in textile industries.

Effects of anodizing potential and temperature on the growth of anodic TiO2 and its photoelectrochemical properties

Although nanoporous/nanotubular anodic TiO2 has been broadly investigated, there is still much to be learned about the fabrication, morphological characterization and applications of anodic TiO2 formed in the glycerol-based electrolyte. Nanoporous anodic titanium oxide (ATO) layers on Ti were prepared via a three-step anodization in a glycerol solution containing NH4F (0.38wt%) and H2O (1.79wt%). The effects of anodizing potential (30–70V) and temperature (10–40°C) on the growth and morphology of ATO layers were investigated in detail. The structural and morphological characterizations of received ATO layers were performed for the studied potentials and temperatures. Moreover, photoelectrochemical properties of formed TiO2 were studied as well. It has been shown, that the morphology of fabricated nanoporous ATO layers are strongly altered by anodizing temperature and potential. Particularly, an interesting finding is that the growth rate gradually increases up to 50V independently of anodizing temperature and then decreases when anodizing potential increases to 70V. Moreover, for all investigated anodizing temperatures, the structural features of ATO layers, such as the cell size, inner layer pore diameter, outer layer pore diameter, increase with increasing anodizing potential. The annealing of ATO samples synthesized at 20°C revealed that the anatase grain size increases with increasing anodizing potential. It is noteworthy to mention that the highest photoconversion efficiency values were observed for samples synthesized at the anodizing temperature of 20°C and 40V.

The influence of nanoporous anodic titanium oxide substrates on the growth of the crystalline hydroxyapatite coatings

In this study we investigate the effect of the nanoporous anodic titanium oxide substrate on the morphology and uniformity of hydrothermally precipitated hydroxyapatite coatings. Nanotubular TiO2 substrates were synthesized on a titanium plate by anodic oxidation and subsequently annealed at 500 °C or 600 °C to create the crystalline anatase and/or rutile forms of TiO2. The substrates were further used for HAp growth under hydrothermal conditions. The samples were then characterized with the XRD, Raman and SEM techniques. The results show that hydrothermal synthesis leads to formation of needle-like coating layer of HAp particles. The diameter and length of HAp crystals decrease with increasing annealing temperature of TiO2 nanotubular arrays. Furthermore, we demonstrate that nanostructured surface of titanium oxide has beneficial influence on the HAp nucleation and coverage.

Effects of nanoporous anodic titanium oxide on human adipose derived stem cells.

The aim of current bone biomaterials research is to design implants that induce controlled, guided, successful, and rapid healing. Titanium implants are widely used in dental, orthopedic, and reconstructive surgery. A series of studies has indicated that cells can respond not only to the chemical properties of the biomaterial, but also, in particular, to the changes in surface topography. Nanoporous materials remain in focus of scientific queries due to their exclusive properties and broad applications. One such material is nanostructured titanium oxide with highly ordered, mutually perpendicular nanopores. Nanoporous anodic titanium dioxide (TiO2) films were fabricated by a three-step anodization process in propan-1,2,3-triol-based electrolyte containing fluoride ions. Adipose-derived stem cells offer many interesting opportunities for regenerative medicine. The important goal of tissue engineering is to direct stem cell differentiation into a desired cell lineage. The influence of nanoporous TiO2 with pore diameters of 80 and 108 nm on cell response, growth, viability, and ability to differentiate into osteoblastic lineage of human adipose-derived progenitors was explored. Cells were harvested from the subcutaneous abdominal fat tissue by a simple, minimally invasive, and inexpensive method. Our results indicate that anodic nanostructured TiO2 is a safe and nontoxic biomaterial. In vitro studies demonstrated that the nanotopography induced and enhanced osteodifferentiation of human adipose-derived stem cells from the abdominal subcutaneous fat tissue.

Effect of Anodizing Voltage on Anodic Titanium Dioxide (ATO) Growth Based on an Ethylene Glycol Solution Containing NH<sub>4</sub>F

We reported on the influence of applied voltage on the surface morphology of anodic titanium dioxide (ATO) thin films. At first, titanium (Ti) thin films were prepared by DC-magnetron sputtering for use as a base material in the anodization process. The titanium dioxide (TiO2) nanoporous ATO was fabricated by the anodization process from the Ti thin film, with different applied voltages from 20 V to 60 V in an electrolyte based on an ethylene glycol containing NH4F. Pore size distribution of ATO thin films can be varied from 20-50 nm by increasing the applied voltage, while the thickness of the film also increases. In addition, to observe the effect of time, the optimal condition of anodizing voltage was studied by increasing the anodizing time. The results clearly showed the nanoporous ATO over the films and the thickness of the nanoporous ATO is approximately 260 nm.

An ordered array of hierarchical spheres for surface-enhanced Raman scattering detection of traces of pesticide

An ordered array of hierarchically-structured core-nanosphere@space-layer@shell-nanoparticles has been fabricated for surface-enhanced Raman scattering (SERS) detection. To fabricate this hierarchically-structured chip, a long-range ordered array of Au/Ag-nanospheres is first patterned in the nano-bowls on the planar surface of ordered nanoporous anodic titanium oxide template. A ultra-thin alumina middle space-layer is then conformally coated on the Au/Ag-nanospheres, and Ag-nanoparticles are finally deposited on the surface of the alumina space-layer to form an ordered array of Au/Ag-nanosphere@Al2O3-layer@Ag-nanoparticles. Finite-difference time-domain simulation shows that SERS hot spots are created between the neighboring Ag-nanoparticles. The ordered array of hierarchical nanostructures is used as the SERS-substrate for a trial detection of methyl parathion (a pesticide) in water and a limit of detection of 1 nM is reached, indicating its promising potential in rapid monitoring of organic pollutants in aquatic environment.

Nanoporous anodic titanium dioxide layers as potential drug delivery systems: Drug release kinetics and mechanism

Nanoporous anodic titanium dioxide (ATO) layers on Ti foil were prepared via a three step anodization process in an electrolyte based on an ethylene glycol solution with fluoride ions. Some of the ATO samples were heat-treated in order to achieve two different crystallographic structures – anatase (400°C) and a mixture of anatase and rutile (600°C). The structural and morphological characterizations of ATO layers were performed using a field emission scanning electron microscope (SEM). The hydrophilicity of ATO layers was determined with contact angle measurements using distilled water. Ibuprofen and gentamicin were loaded effectively inside the ATO nanopores. Afterwards, an in vitro drug release was conducted for 24h under a static and dynamic flow conditions in a phosphate buffer solution at 37°C. The drug concentrations were determined using UV–Vis spectrophotometry. The absorbance of ibuprofen was measured directly at 222nm, whether gentamicin was determined as a complex with silver nanoparticles (Ag NPs) at 394nm. Both compounds exhibited long term release profiles, despite the ATO structure. A new release model, based on the desorption of the drug from the ATO top surface followed by the desorption and diffusion of the drug from the nanopores, was derived. The proposed release model was fitted to the experimental drug release profiles, and kinetic parameters were calculated.

Effect of electrolyte agitation on anodic titanium dioxide (ATO) growth and its photoelectrochemical properties

Nanoporous anodic titanium dioxide (ATO) layers were synthesized at 20°C by a three-step anodization carried out at the constant voltage of 30V in the electrolyte based on an ethylene glycol containing fluoride ions. The effect of stirring speed on the growth of anodic TiO2 layers was investigated in the range of 0–500rpm. It was found that the thickness of grown oxide layer, and consequently, the rate of oxide formation depend directly on the stirring speed. The morphological characterizations – porosity, cell density, cell size, oxide thickness, percentage of defective cells and their arrangement in ATO layers were correlated with different electrolyte stirring speeds. The influence of ultrasound irradiation during ATO formation and extended time of third anodization on photoelectrochemical response of ATO electrodes was studied. Photoelectrochemical properties of received anodic oxide layers were measured in a 0.1M KNO3 aqueous solution under the applied potentials of 0–1000mV vs. SCE. The generated photocurrents were studied at the wavelength range of 300–400nm. The highest values of generated photocurrents were observed at 350nm. For all studied stirring speeds, photoconversion efficiencies, determined as incident photon-to-current efficiency (IPCE), were calculated.

Nanoporous anodic titania observed at the bottom side of the oxide layer

Abstract The morphology and pore arrangement of nanoporous anodic TiO 2 arrays, prepared in the electrochemical cells with different sample alignments by the three-step self-organized anodic oxidation of titanium, were investigated at the bottom side of oxide layers. The quantitative analyses of pore spacing (cell size), pore density and pore arrangement were performed on the basis of FE-SEM bottom view images. The results show that the type of sample alignment and anodizing potential influence the pore spacing, pore density and pore arrangement. On the contrary, the anodizing temperature has a little effect on nanoporous anodic titanium dioxide (ATO) layers. Quantitative information on the nanopore arrangement, based on Delaunay triangulations, is also provided. The cells, which are not six-fold coordinated by neighboring cells, were recognized as defects and the percentage of defects, defined as a ratio between the number of defective pores and number of all pores on the analyzed surface was calculated for all the samples. A quite poor hexagonal arrangement with a relatively high percentage of defective pores (above 30%) was found for all studied anodizing conditions. However, the least percentage of defective pores suggesting the best nanopore arrangement was obtained for the potential of 60 V and 50 V at 10 °C and 20 °C, respectively.

Effect of the previous usage of electrolyte on growth of anodic titanium dioxide (ATO) in a glycerol-based electrolyte

Nanoporous anodic titanium dioxide (ATO) layers were formed via a three-step anodization process in glycerol-based electrolyte containing 0.38wt.% NH4F and 1.79wt.% H2O. The effects of applied potential (10–70V), duration of the third step of anodization (15, 30 and 60min) and the previous usage of the electrolyte on formation of ATO layers were examined at the anodizing temperature of 40°C. It was found that at 10V in both the fresh and used electrolytes, the porous layers are observed for short anodizing times and the compact oxide layers were formed when the time was extended to 60min. On the other hand, the uneven oxide layers were obtained at 70V. The structure and surface morphology analyses showed that for the fresh electrolyte the pore diameter increases with increasing anodizing potential and time. However, for the used electrolyte the pore diameter increases with potential and decreases or remains constant with time. The latter one is attributed to the enhanced precipitation of hydrous titanium dioxide on the ATO surface. The precipitation of hydrous titanium dioxide is also confirmed by oxide thickness analyses performed for the fresh and used electrolytes. The current density-time plots showed that usage of the previously used electrolyte leads to retardation of the oxide formation as a result of partial depletion of the fluoride ions from the electrolyte. These results were confirmed by measurements of the electrolyte conductance. The calculated efficiency of the anodization process, based on the thickness of the oxide layers, are significantly higher for the fresh electrolyte than for the used one.

Anodic growth of TiO2 nanopore arrays at various temperatures

Nanoporous anodic titanium oxide (ATO) layers with different cell sizes, pore diameters and the thicknesses are successfully grown by three-step self-organized anodization in ethylene glycol containing 0.38wt% of NH4F and 1.79wt% of H2O at applied potential differences ranging from 30V to 70V at various electrolyte temperatures. A relatively high growth speed (about 40μmh−1) of nanopore arrays is achieved at 30°C under the potential difference of 70V. The morphology and the structure of ATO layers are directly affected by anodizing conditions, especially temperature and potential difference. It was found that the oxide thickness and the cell size are linearly dependent on anodizing potential difference. On the other hand, the anodizing temperature in the range of 10–30°C does not affect the cell size in ATO films. Analyses of the pore diameter, pore circularity and regularity of the pore arrangement suggests that nanoporous anodic titania with the best pore arrangement can be formed in a controlled manner by anodization performed at 50V and 20°C. Surprisingly, below and above this critical potential difference and temperature, pore diameters are smaller and obtained ATO structures are less regular. At higher anodizing temperatures, the regularity of pore arrangement observed at the surface and the pore diameter are considerably affected by the precipitated hydrous titanium dioxide.

Pore diameter control in anodic titanium and aluminium oxides

A nonlinear relation between the pore diameter and anodising voltage is established for nanoporous anodic titanium oxide (ATO) and anodic aluminium oxide (AAO). The pore diameters of both ATO and AAO have been found to increase with the anodising voltage and drop down when the voltage exceeds a critical value. The origin for the existence of this maximum value of pore diameter in AAO and ATO is discussed.