Titanate Nanotube Arrays Research Articles

Photoelectrochemical degradation of TMAH by green synthesized silver modified titanate nanotube arrays

In this study, titanate nanotube arrays (TNAs) were prepared by using electrochemical anodization, and the silver nanoparticles were deposited on a titanate dioxide nanotube array (Ag/TNAs) by green synthesis methods. The Ag/TNAs was further applied to degrade tetramethylammonium hydroxide (TMAH) in a photoelectrochemical (PEC) system. SEM results showed that the diameter and length were 121.7 nm and about 3.45 µm, respectively, for TNAs. The deposited silver nanoparticles showed spherical and flaky shapes depending on using tea and coffee as green reducing agents, respectively. XPS showed that the atomic percentage of silver in Ag/TNAs-CTC5 and Ag/TNAs-CGA2.5 was 6.60% and 1.76%, individually. Results of UV–vis analyses indicated that the absorbance edge of TNAs red-shifts to a more extended wavelength region after silver modification. The photocurrents of Ag/TNAs-CTC5 (5.03 mA/cm2) and Ag/TNAs-CGA2.5 (3.63 mA/cm2) were 51% and 32% higher than that of TNAs (2.45 mA/cm2), illustrating that the photocatalytic ability of TNAs was significantly enhanced after silver nanoparticles modifying. Electrochemical impedance analysis (EIS) results confirmed that the electron lifetime of Ag/TNA-CTC and Ag/TNAs-CGA was 6.6 and 1.82 times longer than that of the TNA in the PEC system. Mott-Schottky analyses indicated that TNAs, Ag/TNAs-CTC5, and Ag/TNAs-CGA2.5 are n-type semiconductors with a density of dopants of 3.16 × 1019, 1.42 × 1020, and 9.49 × 1019 cm−3. The results of TMAH degradation showed that Ag/TNAs-CTC5 performed the highest efficiency at pH= 3 in the PEC system. EPR analyses of TNAs and Ag/TNAs-CTC5 showed a peak intensity of 1:2:2:1 which represented the characteristic DMPO−OH, revealing the dominant oxidants of the PEC system.

Direct fabrication of graphitic carbon nitride-wrapped titanate nanotube arrays toward photoelectrochemical water oxidation in neutral medium

Direct fabrication of graphitic carbon nitride-wrapped titanate nanotube arrays toward photoelectrochemical water oxidation in neutral medium

Iron Modified Titanate Nanotube Arrays for Photoelectrochemical Removal of E. coli.

This study used iron modified titanate nanotube arrays (Fe/TNAs) to remove E. coli in a photoelectrochemical system. The Fe/TNAs was synthesized by the anodization method and followed by the square wave voltammetry electrochemical deposition (SWVE) method with ferric nitrate as the precursor. Fe/TNAs were characterized by SEM, XRD, XPS, and UV-vis DRS to investigate the surface properties and light absorption. As a result, the iron nanoparticles (NPs) were successfully deposited on the tubular structure of the TNAs, which showed the best light utilization. Moreover, the photoelectrochemical (PEC) properties of the Fe/TNAs were measured by current-light response and electrochemical impedance spectroscopy. The photocurrent of the Fe/TNAs-0.5 (3.5 mA/cm2) was higher than TNAs (2.0 mA/cm2) and electron lifetime of Fe/TNAs-0.5 (433.3 ms) were also longer than TNAs (290.3 ms). Compared to the photolytic (P), photocatalytic (PC), and electrochemical (EC) method, Fe/TNAs PEC showed the best removal efficiency for methyl orange degradation. Furthermore, the Fe/TNAs PEC system also performed better removal efficiency than that of photolysis method in E. coli degradation experiments.

LED-driven photocatalysis of toluene, trichloroethylene and formaldehyde by cuprous oxide modified titanate nanotube arrays

In this study, cuprous oxide modified titanate nanotube arrays photocatalyst (Cu2O/TNAs), a p-n type hetero-structure, was successfully synthesized by square wave voltammetry electrodeposition method (SWVE) with copper (II) acetate monohydrate as precursor. Cu2O/TNAs photocatalysts were characterized by SEM, XRD, XPS, and UV–vis DRS to investigate the physical and chemical properties such as surface structure, light absorption, and element composition. Results of characterization indicated that the Cu2O nanoparticles (Cu2O NPs) were firmly deposited on the surface of TNAs without significant morphological change. The enhanced photocatalytic (PC) performance of as-synthesized materials was exemplified by the test of photocurrent, which revealing that the average photocurrent density of Cu2O/TNAs (0.95 μA cm−2) was 1.38 times higher than TNAs (0.69 μA cm−2) under 24.2 mW cm−2 LED irradiation. Three VOCs (volatile organic compounds), namely, Toluene, Formaldehyde and Trichloroethylene can be completely removed in the Cu2O/TNAs PC process with rate constants (kobs) of 2.08 × 10−2, 3.11 × 10−2, and 6.58 × 10−2 min−1, respectively, with the effort of the synergism of the photo-generated holes and hydroxyl radicals. Detail mechanism of hetero-junction Cu2O/TNAs composite PC system was proposed to clarify the redox reaction.

Simultaneous hydrogen production and ibuprofen degradation by green synthesized Cu2O/TNTAs photoanode

This study aimed to produce a clean energy, hydrogen, and to remove pollutants simultaneously in water by photoelectrochemical (PEC) method. The photo-anode of cuprous oxide modified titanate nanotube arrays (Cu2O/TNTAs) was synthesized by using lactic acid, green tea, and coffee as reductants individually. The characterizations of Cu2O/TNTAs were performed by ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), field emission scanning electron microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) to investigate the physical and chemical properties such as structure, crystallization, element contents, and optical performance. The electrochemical analyses of Cu2O/TNTAs showed the photo-current of Cu2O/TNTAs-t (using green tea as reductant) was 2.4 times higher than pure TNTAs, illustrating the effective separation of electron-hole pairs after Cu2O modification. The photoelectrochemical performances of Cu2O/TNTAs-t and Cu2O/TNTAs-c (using coffee as the reductant) were better than Cu2O/TNTAs-L (using lactic acid as the reductant) in terms of photo-current density, Ibuprofen degradation, and hydrogen generation, implying that depositing Cu2O on TNTAs can significantly improve the electron mobility by reducing the recombination rate of electron-hole pairs, which is beneficial to simultaneously ibuprofen degradation and hydrogen production.

Green synthesis of nano-silver–titanium nanotube array (Ag/TNA) composite for concurrent ibuprofen degradation and hydrogen generation

Silver deposited titanate nanotube array composite (Ag/TNA-c) was successfully synthesized using tea leaves and ground coffee as reducing agent for the first time. The synthesis method was effective, eco-friendly, and reproducible in producing quality nano-composite. The Ag/TNA composite was characterized via XPS, SEM, UV–vis, XRD, and electrochemical analyses for chemical and physical properties. Additionally, chlorogenic acid, caffeine, and catechin were selected as reducing agents for purpose of comparison. Results indicated that catechin and chlorogenic acid were the main reducing agents responsible for Ag+ reduction in tea leaves and ground coffee, respectively. The synthesized Ag/TNA-c exhibited the best photocatalytic (PC) performance in terms of photo-current response, EIS, Ibuprofen degradation, and hydrogen generation in a PEC system. Pairing with a Pt cathode, the photoelectrochemical (PEC) system using the synthesized Ag/TNA composite photo-anode, was capable of concurrent anodic oxidation of Ibuprofen and cathodic generation of hydrogen. Deposition of nano-Ag particles on TNA enhanced the concurrent oxidation and reduction reaction in the PEC system. Results of ESR analysis confirmed the role of hydroxyl radical on Ibuprofen degradation over Ag/TNA-c in the PEC system. Mechanism of Ag/TNA PEC system was proposed to illustrate the oxidation and reduction reaction.

Piezoelectric energy conversion by lead-free perovskite BaTiO3 nanotube arrays fabricated using electrochemical anodization

Synthesis approaches for diverse morphologies of 1D piezoelectric ceramic nanomaterials are still challenging to investigate nanoscale properties and applications. In this work, we demonstrated a vertically grown barium titanate (BaTiO3; BT) nanotube (BT NT) arrays fabricated using optimized electrochemical anodization and hydrothermal reaction. The centimeter-scale synthesized BT NT arrays with a high aspect ratio of up to 300 showed the complete perovskite crystal structure and the notable piezoelectric coefficient of ~180 pm·V−1. A single BT NT-based piezoelectric device was fabricated on a flexible plastic substrate using a highly controlled focused ion beam-assisted method. The single BT NT device produced a piezoelectric voltage of ~150 mV and a current of ~3 nA when the NT was mechanically stimulated by bending and releasing, which are higher than previously reported values for 1D piezoelectric nanoscale materials. Finally, a flexible piezoelectric energy harvester (f-PEH) was achieved using vertically grown BT NT arrays with an elastomer as a vertically aligned nanocomposite; its generated maximum open-circuit voltage and short-circuit current were ~1.0 V and ~20 nA, respectively. The approach in this study can propose the vision for more advanced 1D piezoceramic nanomaterials and future piezoelectric nanodevices.

Water Splitting: Engineering Highly Ordered Iron Titanate Nanotube Array Photoanodes for Enhanced Solar Water Splitting Activity (Adv. Funct. Mater. 35/2017)

Water Splitting: Engineering Highly Ordered Iron Titanate Nanotube Array Photoanodes for Enhanced Solar Water Splitting Activity (Adv. Funct. Mater. 35/2017)

Engineering Highly Ordered Iron Titanate Nanotube Array Photoanodes for Enhanced Solar Water Splitting Activity

Highly ordered iron titanate (Fe2TiO5) nanotube array photoanode is synthesized on F:SnO2 glass with ultrathin anodized aluminum oxide as a hard template. Highly crystalline, yet the nanotube array morphology‐preserved Fe2TiO5 is fabricated by hybrid microwave annealing (HMA). The effects of the synthesis parameters on photoelectrochemical (PEC) water splitting activity under simulated sunlight are systematically studied including HMA time, pore size, wall thickness, and length of the nanotubes to optimize the nanotube array photoanode. In addition, triple modification strategies of TiO2 underlayer, hydrogen treatment, and FeNiOx cocatalyst loading effectively improve the PEC activity further. The systematically engineered nanotube array photoanode achieves a photocurrent density of 0.93 mA cm−2 at 1.23 VRHE under 1 sun (100 mW cm−2) irradiation, which corresponds to 2.6 times that of the previous best Fe2TiO5 photoanode. In addition, the photocurrent onset potential shifts cathodically by ≈280 mV relative to the pristine nanotube array electrode.

Electrochemical capacitance of titanium nitride modified lithium titanate nanotube array

Titanium nitride modified lithium titanate nanotube array (TiN-Li4Ti5O12 NTA) was designed as the electrode material of lithium-ion supercapacitor for electrochemical energy storage. Li4Ti5O12 NTA was prepared through lithiation treatment of anodic TiO2 NTA and then annealing treatment in argon. TiN-Li4Ti5O12 NTA was formed through coating TiO2 sol on the surface of Li4Ti5O12 NTA and then full nitridation treatment in ammonia. Partially nitridized Li4Ti5O12 (N-Li4Ti5O12) NTA was also prepared through a controlled nitridation treatment of Li4Ti5O12 NTA in ammonia. TiN-Li4Ti5O12 NTA with full TiN coating layer exhibited higher conductivity than N-Li4Ti5O12 NTA with partially incorporated TiN. The capacitance accordingly increased from 79.58 F g−1 for N-Li4Ti5O12 to 143.83 F g−1 for TiN-Li4Ti5O12 at 0.5 A g−1 in 0.5 M Li2SO4. The capacitance retention ratio also increased from 72.95% to 82.41% after 1000 cycles at 3.0 A g−1. The all-solid-state supercapacitor was constructed using TiN-Li4Ti5O12 NTA electrode and polyvinyl alcohol gel electrolyte containing Li2SO4, showing high capacitance of 40.45 F g−1, energy density of 32.36 Wh kg−1 and power density of 0.6 kW kg−1 at the high output voltage of 2.4 V and current density of 0.5 A g−1. Therefore, TiN-Li4Ti5O12 NTA could act as a feasible electrode material of lithium-ion supercapacitor.

Titanate nanotube array membranes filled with polyelectrolyte brushes for proton conduction

Development of effective ion conductors with high volumetric stability is essential for micro-electrochemical devices. Herein, we report the synthesis of orderly aligned proton conductors based on polyelectrolyte brushes grafted on the surface of free-standing and through-hole TiO2 nanotube array membranes. The proton conductivity observation of the formed membranes with partially and fully filled polymers indicates that the ionic segments close to the surface play major role on proton transportation through membranes. The formed membrane exhibits promising proton conductivity at elevated temperature (0.125Scm−1 at 140°C) and the proton conductivity remains stable within the test period of time (100h). The results provide a potential nanotechnology for preparation of orderly aligned ionic conductors not only for transportation of proton but also for other ions.

Superior Sodium Storage in Na2Ti3O7 Nanotube Arrays through Surface Engineering

Sodium‐ion batteries have attracted extraordinary attention owing to their low cost and raw materials in abundance. A major challenge of practical implementation is the lack of accessible and affordable anodes that can reversibly store a substantial amount of Na ions in a fast and stable manner. It is reported that surface engineered sodium titanate (Na2Ti3O7) nanotube arrays directly grown on Ti substrates can serve as efficient anodes to meet those stringent requirements. The fabrication of the nanotube arrays involves hydrothermal growing of Na2Ti3O7 nanotubes, surface deposition of a thin layer of TiO2, and subsequent sulfidation. The resulting nanoarrays exhibit a high electrochemical Na‐storage activity that outperforms other Na2Ti3O7 based materials. They deliver high reversible capacities of 221 mAh g−1 and exhibit a superior cycling efficiency and rate capability, retaining 78 mAh g−1 at 10 C (1770 mA g−1) over 10 000 continuous cycles. In addition, the full cell consisting of Na2Ti3O7 nanotube anode and Na2/3(Ni1/3Mn2/3)O2 cathode is capable of delivering a specific energy of ≈110 Wh kg−1 (based on the mass of both electrodes). The surface engineering can provide useful tools in the development of high performance anode materials with robust power and cyclability.

Cu2O loaded titanate nanotube arrays for simultaneously photoelectrochemical ibuprofen oxidation and hydrogen generation

A p–n junction Cu2O doped TiO2 nanotube arrays (Cu2O/TNAs) were synthesized by square wave voltammetry electrochemical (SWVE) deposition method and employed as the working anode. The crystalline, optical properties, surface morphology, and structure of the Cu2O/TNAs were characterized by XRD, UV–vis absorbance edges, SEM, and XPS. Results showed that the Cu2O/TNAs were dominated by anatase phase after sintering at 450 °C with significant visible light response. XPS finding confirmed XRD results that the copper element in Cu2O/TNAs was Cu (I) instead of Cu (II). SEM images illustrated the diameter and the length of supported TiO2 nanotubes was approximately 100 nm and 2.75–4.34 μm, respectively. After Cu2O doping, the nano-tubular structure of TiO2 nanotube kept its integrity with no significant morphological change, which was beneficial for PEC applications. The photocurrent of Cu2O/TNAs was 1.45 times larger than that of TNAs, implying that Cu2O doping significantly enhanced electron mobility by reducing the recombination of electron–hole pairs. In addition, electrochemical impedance spectroscopy (EIS) measurements revealed that the recombination of photogenerated electron–hole pairs was inhibited as the bias potential was applied. Results of Bode plot further demonstrated that the electron lifetime τel of Cu2O/TNAs-20 (30.79 ms), under 0.5 V bias potential, was about 2.23 times higher than that of pure TNAs (13.82 ms). Results of electron spin resonance (ESR) analyses demonstrate that the hydroxyl radicals (OH) are responsible for the PEC decomposition of Ibuprofen.

Additive-free sodium titanate nanotube array as advanced electrode for sodium ion batteries

Low cycling stability and poor rate performance are two of the distinctive drawbacks of most electrode materials for sodium (Na) ion batteries due to the large size of the Na ions. The TiO6 octahedrons interconnect with each other by edges or corners to form both layer- and tunnel-structured sodium titanates (NTO). Such open structures make NTO promising anode materials for sodium (Na) ion batteries. Herein, (conduction and binder) additive-free NTO nanotube array chemically engraved on a Ti foil is used as an electrode and exhibits outstanding rate performance and long-term cycling stability. When a current density of 3200mAg−1 (i.e., one complete cycle in one minute) is applied, the array delivers a reversible capacity of 42mAhg−1. Even after 5000 galvanostatic (400mAg−1) cycles, the electrode retains a capacity of 55mAhg−1. These excellent performances are attributed to the open structure and the nano-architecture of the NTO nanotube arrays.

Effects of Functionalization of TiO2 Nanotube Array Sensors with Pd Nanoparticles on Their Selectivity

This study compared the responses of Pd-functionalized and pristine titanate (TiO2) nanotube arrays to ethanol with those to acetone to determine the effects of functionalization of TiO2 nanotubes with Pd nanoparticles on the sensitivity and selectivity. The responses of pristine and Pd-functionalized TiO2 nanotube arrays to ethanol gas at 200 °C were ∼2877% and ∼21,253%, respectively. On the other hand, the responses of pristine and Pd-functionalized TiO2 nanotube arrays to acetone gas at 250 °C were ∼1636% and 8746% respectively. In the case of ethanol sensing, the response and recovery times of Pd-functionalized TiO2 nanotubes (10.2 and 7.1 s) were obviously shorter than those of pristine TiO2 nanotubes (14.3 and 8.8 s), respectively. In contrast, in the case of acetone sensing the response and recovery times of Pd-functionalized TiO2 nanotubes (42.5 and 19.7 s) were almost the same as those of pristine TiO2 nanotubes (47.2 and 17.9 s). TiO2 nanotube arrays showed the strongest response to ethanol and Pd functionalization was the most effective in improving the response of TiO2 nanotubes to ethanol among six different types of gases: ethanol, acetone, CO, H2, NH3 and NO2. The origin of the superior sensing properties of Pd-functionalized TiO2 nanotubes toward ethanol to acetone is also discussed.

Hydrothermal Synthesis of Tetragonal BaTiO<SUB>3</SUB> Nanotube Arrays with High Dielectric Performance

Tetragonal Barium titanate (BaTiO3) nanotube arrays have been prepared using the template-assisted hydrothermal method combined with an annealing process. The in-situ chemical conversion of TiO2 nanotube array templates ensured that BaTiO3 maintained the morphology of the nanotube architectures. Moreover, X-ray diffraction and Raman spectrum characterization were used to confirm that the BaTiO3 nanotube arrays had a tetragonal phase after the use of a simple annealing technique. Typical hysteresis loops showed their ferroelectricity, with the remanent polarization and coercive fields being 2.57 microC/cm2 and 2.52 kV/cm, respectively. The relative dielectric constant of the tetragonal BaTiO3 nanotube arrays reached up to 1000 and the dielectric loss was as low as 0.02 at 1 kHz at room temperature.

Development of sensitive determination method for fungicides from environmental water samples with Titanate nanotube array micro-solid phase extraction prior to high performance liquid chromatography

Fungicides have been widely used throughout the world, and the resulted pollution has absorbed great attention in recent years. Present study described an effective measurement technique for fungicides including thiram, metalaxyl, diethofencarb, myclobutanil and tebuconazole in environmental water samples. A micro-solid phase extraction (μSPE) was developed utilizing ordered TiO2 nanotube array for determination of target fungicides prior to a high performance liquid chromatography (HPLC). The experimental results indicated that TiO2 nanotube arrays demonstrated excellent merits on the preconcentration of fungicides, and excellent linear relationship between peak area and the concentration of fungicides was obtained in the range of 0.1–50μgL−1. The detection limits for the targeted fungicides were in the range of 0.016–0.086μgL−1 (S/N=3). Four real environmental water samples were used to validate the applicability of the proposed method, and good spiked recoveries in the range of 73.9–114% were achieved. A comparison of present method with conventional solid phase extraction was made and the results exhibited that proposed method resulted in better recoveries. The results demonstrated that this μ-SPE technique was a viable alternative for the analysis of fungicides in complex samples.

Self-Assembled-Monolayers (SAMs) Modified Template Synthesis and Characterization of SrTiO3 Nanotube Arrays

A self-assembled-monolayers (SAMs) modified anodic aluminum oxide (AAO) membranes were used to generate crystalline strontium titanate (SrTiO3) nanotube arrays, which have been characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM), coupled with electron diffraction analysis. The possible formation mechanism can be explained by the induced nucleation effect of the functional headgroups in the SAMs.

Development of micro-solid phase extraction with titanate nanotube array modified by cetyltrimethylammonium bromide for sensitive determination of polycyclic aromatic hydrocarbons from environmental water samples

This paper described a simple and novel analytical technique for the determination of polycyclic aromatic hydrocarbons (PAHs) in environmental water samples. A micro-solid phase extraction (μ-SPE) was developed utilizing cetyltrimethylammonium bromide modified ordered TiO 2 nanotube array. The experimental results indicated that modified TiO 2 nanotube arrays demonstrated an excellent merit on the preconcentration of PAHs, and there were excellent linear relationships between peak area and the concentration of PAHs in the range of 0.2–100 μg L −1 and 1.0–100 μg L −1, respectively. The detection limits of proposed method for the targeted PAHs were in the range of 0.026–0.82 μg L −1 (S/N = 3). The real-world environmental water samples were used to validate the applicability of the proposed method and good spiked recoveries were in the range of 75.0–114%. All these results demonstrated that this new μ-SPE technique was a viable alternative to conventional enrichment techniques for the extraction and analysis of PAHs in complex samples.

Quantum dot photoelectrochemical solar cells based on TiO2-SrTiO3 heterostructure nanotube array scaffolds

Titania-Strontium titanate (TiO2-SrTiO3) nanotube array with heterostructure has been demonstrated as an efficient scaffold applied to quantum dot photoelectrochemical solar cells. Quantum dot CdS serviced as solar light absorbent is chosen as an example to illustrate superior performance and deposited on scaffolds by successive ionic layer adsorption and reaction (SILAR) technique. The photoelectro-chemical performance of such solar cell is strongly dependent on the structure of heterostructured scaffolds. Only well-dispersed SrTiO3 nanocrystallites on TiO2 could improve the overall conversion efficiency. Transient absorption spectra and photoelectrochemical measurements show that the formation of SrTiO3 energy gradient between TiO2 and electrolyte slows down the rate of electronic injection from 19.3 × 108 to 6.30 × 108 s−1, while it greatly increases electronic collection efficiency via reduced charge recombination. Cadmium sulfide (CdS) quantum dots used to decorate TiO2-SrTiO3 (1 h hydrothermal treatment) electrode exhibits superior photoelectrochemical performance with nearly 70% increase in external quantum efficiency at 460 nm and also in overall cell conversion efficiency. The photostability and high efficiency properties of TiO2-SrTiO3 composites would enable its practical application in solar energy conversion devices.