Pristine TiO2 Nanotube Arrays Research Articles

Binary junctions enhance electron storage and potential difference for photo-assisted electrocatalytic CO2 reduction to HCOOH

Photo-assisted electrocatalytic (PAEC) CO2 conversion is a crucial approach for achieving sustainable carbon neutrality. Here, we have developed a binary-junctions photoanode by integrating SrTiO3 and anatase-rutile TiO2 nanotube arrays (STO/A-R TNTAs), which exhibits exceptional activity and selectivity in converting CO2 to HCOOH. The synergetic effects of the SrTiO3/TiO2 heterogeneous junction and the anatase-rutile TiO2 heterophase junction effectively facilitate photoelectron separation and storage, leading to a potential difference between anode and cathode. The establishment of the electron storage strategy, triggered by hetero- junction/phase interfaces, serves as remarkably efficient electron trapping regions with dam-like characteristics. As a result, the STO/A-R TNTAs achieves a generation rate of 68.24 μmol cm−2 h−1 with 92.25% selectivity and 90.70% Faradic efficiency. This performance is approximately 8 times higher compared to the pristine TiO2 nanotube arrays photoanode. The implementation of the electron storage mechanism presents a promising approach to improve CO2 reduction activity and selectivity.

In situ transformation of TiO2 hierarchical nanostructures toward efficient photoelectrochemical water splitting

TiO2 hierarchical nanomaterials have been intensively investigated as a very promising photoanode in photoelectrochemical water splitting due to its combined effects of large surface area and fast electron transfer. However, the TiO2 hierarchical nanostructures prepared by most prevailing synthesis methods currently are at distinct disadvantages such as complicated process, poor controllability, poor interfacial contact, excessive impurities and so on. Here we report a facile route to construct a well-defined TiO2 hierarchical nanostructure via in-situ transformation of TiO2 nanoparticles with highly exposed {001} facets in the tube wall of the pristine TiO2 nanotube arrays. The resulted TiO2 hierarchical nanostructures exhibit enhanced light harvesting, lowe recombination rate of photo-generated charger carrier. Upon these synergistic effects, the target hierarchical nanostructure shows significantly improved PEC performance and excellent photo-switching response with good reproducibility and stability. Corresponding photocurrent density and photon-to-current efficiency achieve 0.76 mA cm−2 and 0.50%, respectively, which show an enhancement of 1.70 and 1.32 times to those of the control one. This work provides a possible route for fabrication of TiO2 starting materials with decent efficiencies.

Anodic Oxidation of TC4 Substrate to Synthesize Ce-Doped TiO2 Nanotube Arrays with Enhanced Photocatalytic Performance

Starting from the urgent need for water pollution treatment, TiO2 nanotube arrays (TNAs) and Ce-doped TNAs have been prepared on TC4 titanium alloy substrate via anodic oxidation. Several properties of TNAs and Ce-doped TNAs were characterized utilizing field emission scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction and ultraviolet-visible spectrophotometer to analyze their morphology, phase structure, distribution of element and optical property respectively. The photocatalytic performance was evaluated by the photo-degradation of methylene blue (MB) under simulated visible light irradiation. The result indicated that the best photodegradation rate of the Ce-doped TNAs on MB reached to 90.4%, which was a huge improvement compared with pristine TNAs.

Vertically-aligned Pt-decorated MoS2 nanosheets coated on TiO2 nanotube arrays enable high-efficiency solar-light energy utilization for photocatalysis and self-cleaning SERS devices

The ability to reproducibly create a surface enhanced Raman scattering (SERS) substrate renders an effective means of detecting and degrading organic contaminants. Vertically aligned (VA) nanomaterials have been extensively explored as highly efficient catalysts due to their excellent electron transportability and high concentration of exposed active edge sites. Herein, we report on a ternary ultrafast-electron-transfer heterostructure composed of Pt nanoparticles in-situ grown on VA-MoS2 nanosheet edge sites decorated on TiO2 nanotube arrays (NTAs) (denoted Pt/VA-MoS2/NTAs). Compared with pristine TiO2 NTAs, the Pt/VA-MoS2/NTAs possess a strong resonant SERS effect for detecting rhodamine 6G and an outstanding UV-assisted self-cleaning effect, displaying an excellent photocatalytic performance under visible light irradiation. Such markedly improved performance of the ternary Pt/VA-MoS2/TiO2 NTAs nanocomposites can be attributed to the synergy of catalytic activity of Pt-deposited MoS2 edge sites, the ultrafast electron transfers of VA-MoS2 NS/TiO2 NTAs, and the appropriate band alignment among these three constituents. As such, it represents a robust mean of developing advanced energy utilization nanocomposites for high-performance catalysts and sensors.

Enhanced photoelectrochemical cathodic protection performance of MoS2/TiO2 nanocomposites for 304 stainless steel under visible light

In this work, TiO2 nanotube arrays (NTAs) sensitized with MoS2 microspheres (MoS2/TiO2 nanocomposites) were prepared on a flat Ti substrate via two-step anodization and hydrothermal method sequentially. TiO2 NTAs were composed of many orderly nanotubes, whose large specific surface area was favorable for light absorption and MoS2 microsphere adhesion. The MoS2 microsphere as a narrow band gap semiconductor extended the TiO2 NTAs’ absorption band edge to the visible region. The 2D structure of MoS2 microspheres and the construction of heterojunction electronic field at the interface of MoS2 microspheres and TiO2 NTAs promoted the separation of photoinduced carriers. The MoS2/TiO2 nanocomposites could provide higher photoelectrochemical cathodic protection for 304 stainless steel (304 SS) under visible light than pristine TiO2 NTAs.

In situ synthesis of MoO3/Ag/TiO2 nanotube arrays for enhancement of visible-light photoelectrochemical performance

A ternary composites of MoO3/Ag/TiO2 nanotube arrays were synthesized by in-situ annealing of TiO2 nanotube arrays impregnated with AgNO3 over MoO3 powders. During the annealing process, the crystallization of the TiO2 nanotubes, the thermo-decomposition of AgNO3 to Ag nanoparticles, and the sublimation of MoO3 occur jointly. The photoelectrochemical measurements of the resultants indicate that MoO3/Ag/TiO2 nanotube arrays present better photoelectrochemical properties compared with Ag/TiO2 nanotube arrays and pristine TiO2 nanotube arrays. Especially, the highest photocurrent and open circuit voltage are up to 21.29 μA/cm2 and 0.058 V under visible light irradiation, whereas 1.77 and 3.87 times larger than those of TiO2 nanotube arrays, respectively. Superior photoelectrochemical stability and larger photo-conversion efficiency of the ternary composites are also demonstrated. The improved photoelectrochemical properties are related to the close interfacial contact among MoO3, Ag, and TiO2 as well as the surface plasma resonance of Ag in the ternary composites, which broaden the range of light response and enhance the efficiency of charge separation. This study provides a skillful solution to construct TiO2-based composite materials and demonstrates it is an unique architecture to promote the visible light driven photocatalytic application of TiO2.

Fabrication of a self‐doped TiO2 nanotube array electrode for electrochemical degradation of methyl orange

Self‐doped TiO2 nanotube array (DTNA) electrodes were fabricated through anodic oxidation combined with cathodic reduction. The morphology and structural features of pristine TiO2 nanotube arrays and DTNA electrodes were studied through scanning electron microscopy, X‐ray diffractometry, and X‐ray photoelectron spectroscopy. An accelerated life test was used to test the electrode service lifetime and thus the electrode's stability. The service lifetime of the DTNA electrode prepared at constant 40 V for 6 hr was approximately 338.7 hr at constant 1 mA/cm2 in a 1 M NaClO4 solution. Methyl orange (MO) was employed as the degradation probe for measuring electrochemical oxidation performance. The color removal rate of 200 mg/L MO of the DTNA electrode (85.2% at 1 mA/cm2) was greater than that of the Ti/IrO2 electrode (31.1% at 1 mA/cm2). The larger the surface area of the DTNA electrode is, the more conductive the electrode is for the degradation of organic substances. Organic degradation on the DTNA electrode occurred primarily through an indirect pathway (producing [∙OH]).

Spatial dual-electric fields for highly enhanced the solar water splitting of TiO2 nanotube arrays

Efficient charge separation is essential for improving the photo-conversion efficiency in both photocatalytic and photoelectrochemical (PEC) water splitting. Herein, we have demonstrated the selective spatial-construction of Au nanolayer and SrTiO3 nanocubes on inner and outer surfaces of TiO2 nanotubes for enhancing the charge separation and PEC activity. More specifically, the outer SrTiO3 nanocubes with a spontaneous ferroelectric polarization could effectively engineer the electrical band bending of TiO2 nanotubes, facilitating hole transfer to the electrode/electrolyte interface for water oxidation. Meanwhile, the inner Au nanolayer with a favorable plasmonic electric-field induced by the visible light promote charge separation and rapid electron transfer to the counter electrode for hydrogen generation. Benefiting from the spatial dual-electric fields, this SrTiO3/TiO2/Au ternary-photoanode exhibits a significantly enhanced photocurrent density of 2.11 mA cm−2 at 1.23 V (vs. RHE), which is nearly 3.5 times higher than that of the pristine TiO2 nanotube arrays. Additionally, a low onset potential (~ 0.17 VRHE) for water oxidation as well as an excellent PEC stability has also been achieved. These demonstrations may provide a new strategy toward the rational construction of highly efficient PEC water splitting systems.

Synthesis of TiO2-based nanocomposites by anodizing and hydrogen annealing for efficient photoelectrochemical water oxidation

Black TiO2 based nanomaterials have shown considerable potential towards photoelectrochemical water oxidation due to their low cost, raw material availability and operational stability. In this work, thermal annealing of anatase TiO2 nanotube arrays under hydrogen-argon atmosphere at high temperatures (>600 °C) is employed to induce significant oxygen deficiency and phase transitions to substoichiometric structures (Magnéli phases), with the aim to limit interfacial recombination processes and increase the density of charge carriers. Particle-nanowire porous TiO2 sub-stoichiometries are formed at 800 °C, which is quantitatively investigated via X-ray diffraction and Rietveld refinement. The photocurrent of this Ti-O compounds is increased by 2.4-fold at 1.23VRHE and the photoconversion efficiency is enhanced by 2.8-fold at a reduced bias under simulated solar illumination in comparison with pristine TiO2 nanotube arrays. The improved performance is owed to slower interfacial recombination, resulting in the increase of water oxidation selectivity from 65% to 92%, and by the increase in charge carrier density up to two orders of magnitude, as evaluated via electrochemical impedance spectroscopy. Finally, this method is compared to electrochemical hydrogen doping, with the latter exhibiting a significantly lower energy conversion efficiency.

Rational Construction of LaFeO3 Perovskite Nanoparticle-Modified TiO2 Nanotube Arrays for Visible-Light Driven Photocatalytic Activity

LaFeO3 nanoparticle-modified TiO2 nanotube arrays were fabricated through facile hydrothermal growth. The absorption edge of LaFeO3 nanoparticle-modified TiO2 nanotube arrays displaying a red shift to ~540 nm was indicated by the results of diffuse reflectance spectroscopy (DRS) when compared to TiO2 nanotube arrays, which means that the sample of LaFeO3 nanoparticle-modified TiO2 nanotube arrays had enhanced visible light response. Photoluminescence (PL) spectra showed that the LaFeO3 nanoparticle-modified TiO2 nanotube arrays efficiently separated the photoinduced electron–hole pairs and effectively prolonged the endurance of photogenerated carriers. The results of methylene blue (MB) degeneration under simulated visible light illumination showed that the photocatalytic activity of LaFeO3 nanoparticle-modified TiO2 nanotube arrays is obviously increased. LaFeO3 nanoparticle-modified TiO2 nanotube arrays with 12 h hydrothermal reaction time showed the highest degradation rate with a 2-fold enhancement compared with that of pristine TiO2 nanotube arrays.

In situ construction of N/Ti3+ codoped triphasic TiO2 layer on TiO2 nanotube arrays to improve photoelectrochemical performance

Different numbers of N/Ti3+ codoped triphasic TiO2 layer are deposited on TiO2 nanotube arrays by hydrothermal reaction of TiN and TiO2 nanotube arrays. The crystal structure, morphology, and composition of the as-prepared samples and their photoelectrochemical properties are investigated and discussed. There are obviously red shift of the optical edge and enhanced visible light absorption for the resulting samples in the ultraviolet–visible diffuse reflectance spectroscopy. Besides, the photoelectrochemical tests indicate that the N/Ti3+ codoped triphasic TiO2-TiO2 nanotube array samples exhibit an enhanced photocurrent density and photovoltage under visible light irradiation. The maximum photoconversion efficiency of N/Ti3+ codoped triphasic TiO2-TiO2 nanotube array sample is 2.1 times higher than that of pristine TiO2 nanotube arrays. In addition, reduced impedance, higher carrier density, and excellent stability of photoelectrochemical performance of N/Ti3+ codoped triphasic TiO2-TiO2 nanotube array samples are also demonstrated. Finally, a plausible mechanism for the charge migration and separation on N/Ti3+ codoped triphasic TiO2-TiO2 nanotube array samples is proposed. This study provides a novel strategy to design and fabricate visible-light-driven TiO2 based composites and promote their applications in the field of solar energy utilization.

Fabrication of IrO2 decorated vertical aligned self-doped TiO2 nanotube arrays for oxygen evolution in water electrolysis

To fabricate effective and stable OER electrode in water electrolysis, self-doped TiO2 nanotube arrays which has a higher electrical conductivity than pristine TiO2 nanotube arrays was used as the support for loading IrO2. The self-doped TNTA was fabricated by a simple electrochemical reduction of TNTA in neutral electrolyte solution, and then IrO2 nano particles were deposited by pulse electro-deposition method. The cyclic voltammetric behavior, electrical conductivity and micro structure of self-doped TNTA prepared at different reduction potential were characterized to obtain an optimal performance, and self-doped TNTA prepared under −1.9 V (vs. Ag/AgCl) shows the best electrochemical performance. After depositing IrO2, the OER activity and stability of new electrodes were also determined. Due to the enhanced electrical conductivity of support, the mass activity of IrO2/self-doped TNTA are 50 times higher than IrO2/TNTA. The OER stability of new electrode was evaluated under constant current of 5 mA/cm2, IrO2/TNTA and IrO2/Ti were also tested for comparison. A higher stability of IrO2/self-doped TNTA electrode is observed than the other two electrodes, and XPS studies indicate a lower oxidation state of Ir in IrO2/self-doped TNTA, this shows a possible interactions between IrO2 and the new support.

Laser-Induced Surface Modification at Anatase TiO2 Nanotube Array Photoanodes for Photoelectrochemical Water Oxidation

Nanostructured titanium dioxide (TiO2) presents considerable potential as a photoanode in low cost, sustainable photoelectrochemical systems for solar water splitting. The wide band gap combined with the presence of trap states and reduced water oxidation kinetics limit, however, the photocurrent performance to only ∼1 mA cm–2. Increasing the disorder of the crystal structure at the surface, on the other hand, has been proven to increase light absorption via band gap narrowing, and conversion efficiency. In this work, anodized TiO2 nanotubes have been irradiated with a pulsed UV laser in deionized water environment to introduce lattice disorder. As a result, the photocurrent improved by 1.6-fold under simulated sunlight compared with pristine TiO2 nanotube arrays at 1.23 VRHE. For all samples the water oxidation reaction kinetics is determined to be the limiting step for the solar-to-current conversion at low bias (0.5–0.7 VRHE), while modified nanotube arrays display a 78% water oxidation selectivity at ...

Immobilization of Pt Nanoparticles via Rapid and Reusable Electropolymerization of Dopamine on TiO2 Nanotube Arrays for Reversible SERS Substrates and Nonenzymatic Glucose Sensors.

Inspired by mussel-adhesion phenomena in nature, polydopamine (PDA) coatings are a promising route to multifunctional platforms for decorating various materials. The typical self-polymerization process of dopamine is time-consuming and the coatings of PDA are not reusable. Herein, a reusable and time-saving strategy for the electrochemical polymerization of dopamine (EPD) is reported. The PDA layer is deposited on vertically aligned TiO2 nanotube arrays (NTAs). Owing to the abundant catechol and amine groups in the PDA layer, uniform Pt nanoparticles (NPs) are deposited onto the TiO2 NTAs and can effectively prevent the recombination of electron-hole pairs generated from photo-electrocatalysis and transfer the captured electrons to participate in the photo-electrocatalytic reaction process. Compared with pristine TiO2 NTAs, the as-prepared Pt@TiO2 NTA composites exhibit surface-enhanced Raman scattering sensitivity for detecting rhodamine 6G and display excellent UV-assisted self-cleaning ability, and also show promise as a nonenzymatic glucose biosensor. Furthermore, the mussel-inspired electropolymerization strategy and the fast EPD-reduced nanoparticle decorating process presented herein can be readily extended to various functional substrates, such as conductive glass, metallic oxides, and semiconductors. It is the adaptation of the established PDA system for a selective, robust, and generalizable sensing system that is the emphasis of this work.

Time-dependent formation of oxygen vacancies in black TiO2 nanotube arrays and the effect on photoelectrocatalytic and photoelectrochemical properties

Black TiO2 nanotube arrays were synthesized via a two-step anodization procedure by controlling the duration of anodization and annealing in an argon atmosphere. Oxygen vacancies were introduced in black TiO2 nanotube arrays during the anodization and annealing process due to an insufficient oxygen atomosphere, as confirmed by EPR, XRD, SEM, TEM, XPS, and Raman analysis. Black TiO2 nanotube arrays prepared in 6 h (denoted as Ar TNT-6h) exhibited excellent photoelectrocatalytic performance and stable photoelectrochemical performance due to a considerable amount of oxygen vacancies, which ensured charge separation efficiency and strong visible light absorption. The photoelectrocatalytic activities of the samples were monitored by the decomposition of Rhodamine B (RhB). Notably, the black TiO2 nanotube arrays exhibited lower charge-transfer resistance in electrochemical impendence spectroscopy (EIS). The photocurrent density of Ar TNT-6h (1.2 mA/cm2) was nearly twelve times higher than that of air-TNTs (pristine TiO2 nanotube arrays annealed in air, 0.1 mA/cm2). The formation of oxygen vacancies in black TiO2 nanotube arrays was influenced by the duration of anodization and the annealing atmosphere. A considerable amount of oxygen vacancies significantly improved the separation efficiency of photogenerated electrons and holes, thus enhancing the photoelectrocatalytic efficiency.

Enhanced field emission from titanium dioxide nanotube arrays decorated with graphene sheets and silver nanoparticles

The TiO2 nanotube arrays decorated with graphene sheets (GSs) and Ag nanoparticles were prepared on Ti foils and field emission performances were explored in detail. The conventional electrochemical anodization process was used to synthesize TiO2 nanotube arrays on Ti foils. The GSs and Ag nanoparticles were deposited on as-prepared TiO2 nanotube arrays by electrophoretic deposition process and chemical deposition. The field emission properties of samples were dramatically improved after depositing GSs and Ag nanoparticles on TiO2 nanotube arrays. Compared with pristine TiO2 nanotube arrays, the TiO2 nanotube arrays decorated with GSs and Ag nanoparticles composite film show good field emission stability and a higher field enhancement factor of 3450. The turn-on and threshold fields can be decreased from 6.63 to 2.68 V/μm and from 15.28 to 6.13 V/μm, respectively. Quantitative discussion about the hybrid hetero-nanostructure field emission improvement is presented. The good field emission properties of the decorated TiO2 make it a promising candidate for applying in high-performance emission device.

Reduction Mechanism and Capacitive Properties of Highly Electrochemically Reduced TiO2 Nanotube Arrays

Highly reduced and ordered TiO2 nanotube arrays have been fabricated using two-step anodization and three-electrode reduction. A proton-electron coupled reduction mechanism has been proposed based on the combined paradigms of a conventional energy-band model and chemical evolution of basic building blocks of TiO2. Under optimized reduction conditions, about 22% of Ti4+ ions in tube surface regions are converted into Ti3+ ions while the morphology of the highly reduced TiO2 nanotube arrays keeps unchanged. The reduced nanotube arrays show superior electrochemical properties such as high areal capacitance, good rate capability, and high cycling stability. The areal capacitance of the reduced electrode is 24.07mFcm−2 at a scan rate of 10mVs−1, much higher than that of the pristine TiO2 nanotube arrays (0.02mFcm−2). This kind of highly reduced one-dimensional oxide nanostructures can find a large array of applications in supercapacitors, photocatalysis, electrochromic display, and Li ion batteries.

Electrochemically Self-Doped TiO2 Nanotube Arrays for Efficient Visible Light Photoelectrocatalytic Degradation of Contaminants

In this study, a simple electrochemical reduction approach is reported to enhance the photoelectrochemical performance of TiO2 nanotube arrays towards degrading water contaminants such as Rhodamine B, phenol and E. coli K-12. The results obtained from X-ray diffraction and X-ray photoelectron spectroscopy demonstrate that oxygen vacancies i.e., Ti3+ self-doping, were formed in the lattices of TiO2 nanotube arrays during the electrochemical reduction process of pristine TiO2 nanotube arrays at different negative potentials ranging from −1.2 to −1.5V. Comparing the pristine TiO2 nanotube arrays, the treatment TiO2 nanotube arrays samples by electroreduction process were found to be showing enhanced photoelectrocatalytic activity in the UV and visible regions in the entire potential window tested. Further, the photocurrent density of self-doped TiO2 nanotube arrays sample prepared at −1.3V was 250% higher than that of the pristine TiO2 under visible-light illumination. Impedance analysis revealed that the electrical conductivity of the nanotubes significantly enhanced after self-doping. The photoelectrocatalytic activity of the self-doped TiO2 nanotube increased dramatically due to the enhanced electrical conductivity and absorption in the visible light region, as well as an accelerated charge transfer rate between the interface of solid and electrolyte.

Enhancing the capacitance of TiO2 nanotube arrays by a facile cathodic reduction process

TiO2 nanotube arrays are modified by a facile cathodic reduction process treatment and the results are discussed in terms of their electrochemical activity and conductivity. The instrumental characterizations such as X-ray photoelectron spectroscopy and Raman spectroscopy indicate that the formation of oxygen vacancies in the lattice and introduction of hydroxyl groups on the surface of TiO2 take place. The capacitance of the modified sample is found to be 13 times larger than the pristine TiO2 nanotube arrays. This work reveals a feasible and simple method to improve electrochemical activity and conductivity of TiO2 for supercapacitors application.

Enhanced field emission from hydrogenated TiO2 nanotube arrays

The field emission (FE) properties of TiO2 nanotube arrays (TNAs) synthesized by anodization are dramatically improved after hydrogenation at various temperatures in a range of 400–550 °C. Compared with pristine TNAs, the turn-on fields of hydrogenated TNAs (H:TNAs) are significantly decreased from 18.23 to 1.75 V μm−1, and closely related to hydrogenation temperature. Importantly, the optimized sample of H:TNAs prepared at 550 °C shows excellent FE performances involving both a low turn-on field of 1.75 V μm−1, a high current density of 4.0 mA cm−2 at 4.50V μm−1, and a remarkable FE stability over 480 min. The substantially enhanced FE properties can be attributed to the combination of a typical tubular morphology, a reduced work function and the improved conductivity of H:TNAs.