TiO2 NTAs Research Articles

Effect of ZnS layers on optical properties of prepared CdS/TiO2 nanotube arrays for photocatalyst

The TiO2 nanotube arrays (TiO2 NTAs) prepared by re-oxidation were chosen as basement. The NTAs prepared through re-oxidation show smoother surface and more uniform tube mouth on large scale compared with the first as-grown one. We use successive ionic layer adsorption and reaction method to deposit quantum dots (ZnS and CdS) onto the sample successively. The findings reveal that two kinds of quantum dots (∼10 nm) distribute regularly and the nanotube mouth is open. From the UV–Vis absorption spectrum of samples, the red shift occurs after the sedimentation of the two quantum dots, which proves that the double modification can expand the absorption to 650 nm. Among all specimens, the sample produced by co-deposition has the highest speed of catalytic efficiency of 90.7% compared with bare TiO2 NTAs (52.9%) and just CdS QDs sensitized sample (65.8%). In the test of photocatalysis durability, the decay percentages of CdS/TiO2 NTAs and ZnS/CdS/TiO2 NTAs were 35.8 and 48.4%, respectively, which means that the ZnS passivation layer plays a crucial role in enhancing photocatalytic activities.

Synergizing the multiple plasmon resonance coupling and quantum effects to obtain enhanced SERS and PEC performance simultaneously on a noble metal-semiconductor substrate.

Aiming to achieve the synergistic enhancement of the surface-enhanced Raman scattering (SERS) and photoelectrocatalytic (PEC) performance on a noble metal-semiconductor, such as Au nanoparticles (NPs)-TiO2 nanotube arrays (TiO2 NTAs@hybrid Au NPs), theoretical calculation and experiments are performed. Theoretical calculation indicates that both the SERS and PEC performance can be enhanced by coupling different sized Au NPs on TiO2 NTAs based on synergizing the multiple plasmon resonance coupling and quantum effects. To further verify this mechanism, TiO2 NTAs@hybrid Au NPs are assembled via synthesis of TiO2 NTAs through the anodic oxidation process, followed by the deposition of different sized Au NPs onto the TiO2 surface simultaneously using physical vapor deposition (PVD) in this work. Such substrates exhibit excellent detection sensitivity towards organic dyes including Rhodamine B (RhB), the organic herbicide dichlorophenoxyacetic acid (2,4-D) and the organophosphate pesticide methyl-parathion (MP) with high reproducibility, stability and reusability. Meanwhile the PEC performance based on this substrate remains efficient compared with the reported results in the literature. The efficient PEC performance mainly originates from both the quantum effect of Au nanoparticles and the formation of a metal-semiconductor heterojunction. It is proposed that other noble metal-semiconductor complex nanomaterials can also obtain both enhanced SERS and PEC performance based on the above mechanism.

Effect of Annealing Temperature on the Capacitive and Oxidant-generating Properties of an Electrochemically Reduced TiO2 Nanotube Array

Recently, the electrochemically reduced TiO2 nanotube array (r-TiO2 NTA) has been an attractive promising material for supercapacitors and anodes for water treatment because of its significantly enhanced capacitive and oxidant-generating electrocatalytic properties. However, most of the previous studies have focused on r-TiO2 NTA prepared at a specific annealing temperature (approximately 450°C). Accordingly, the effect of annealing temperature on the electrochemical properties of r-TiO2 NTA remained unclear. This study aimed to investigate the capacitive and electrocatalytic properties of r-TiO2 NTAs prepared at various annealing temperatures ranging from 350 to 750°C. The anatase-dominant r-TiO2 NTAs prepared at low annealing temperatures (350 and 450°C) exhibited significantly better capacitive and electrocatalytic properties than the rutile-dominant r-TiO2 NTAs prepared at high annealing temperatures (650 and 750°C). The areal capacitance (14.9mF/cm2) of r-TiO2 NTA (annealed at 350°C) was approximately 150 times higher than the areal capacitance of TiO2 NTAs (annealed at 750°C) (0.1mF/cm2). The significant production of hydroxyl radicals was found in r-TiO2 NTAs annealed at 350 and 450°C, whereas no production of hydroxyl radicals was found in r-TiO2 NTA annealed at a higher temperature. This result is attributed to the anatase-dominant phase of r-TiO2 NTAs developed at a low annealing temperature, which contributes to a high doping level, as well as its structural advantage for proton intercalation, yielding a large production of Ti3+.

Hydrothermal growth of nanorod arrays and in situ conversion to nanotube arrays for highly efficient Ag-sensitized photocatalyst

TiO2 nanorod arrays (NRAs) were hydrothermally grown on transparent fluorine-doped tin oxide (FTO) substrates, and were converted into nanotubes (NTAs) by hydrothermally in situ etching. Ag nanoparticles (NPLs) were sensitized on the NRAs and NTAs by a simple photodeposition approach (products were denoted as Ag-TiO2 NRAs and NTAs). The Ag-TiO2 NTAs samples possessed a large specific surface area (116 m2 g-1) with Ag NPLs homogeneously dispersed among the TiO2 NTAs. The Ag-TiO2 NTAs exhibited significantly enhanced photocatalytic activities (98.8%) in degradation of methyl orange (MO) compared to Ag-TiO2 NRAs (92.6%), TiO2 NTAs (86.2%), and NRAs (81.7%). The enhanced photocatalytic activities can be attributed to the large specific surface area of TiO2 NTAs and strong surface plasmon resonance (SPR) of Ag NPLs. In addition, Ag-TiO2 NTAs showed easy recovery feature in the recovery process and high durability in the recycling test, which was expected to be an efficient and practical photocatalyst used for waste water treatment.

All solid-state solar cells based on CH3NH3PbI3-sensitized TiO2 nanotube arrays

TiO2 nanotube arrays (TiO2 NTAs) were firstly used as photoanode in methylammonium lead iodide (CH3NH3PbI3) perovskite/TiO2 NTAs heterojunction solar cell, where CH3NH3PbI3 functions as both light absorber and hole conductor. The composition, structure and photoelectrochemical properties of the as-prepared samples were characterized by x-ray diffractometer (XRD), field-emission scanning electron microscope (FE-SEM), ultraviolet-visible (UV–vis) spectrophotometer and electrochemical workstation. The results indicate that the as-prepared CH3NH3PbI3 belongs to the cubic crystal system, and TiO2 NTAs sensitized by 0.3M CH3NH3I and PbI2 exhibit the best photoelectrochemical properties with an open-circuit voltage of 0.422V and a short-circuit current density of 173.4μAcm−2. The EIS result shows that the extremely large resistance at CH3NH3PbI3/FTO interface contributes to the low current density of the perovskite solar cell.

All‐Solid‐State Cable‐Type Supercapacitors with Ultrahigh Rate Capability

All‐Solid‐State Cable‐Type Supercapacitors with Ultrahigh Rate Capability

Visible‐light‐driven self‐cleaning SERS substrate of silver nanoparticles and graphene oxide decorated nitrogen‐doped titania nanotube array

Graphene oxide (GO) and silver nanoparticles (Ag NPs) sequentially decorated nitrogen‐doped titania nanotube array (N‐TiO2 NTA) had been designed as visible‐light‐driven self‐cleaning surface‐enhanced Raman scattering (SERS) substrate for a recyclable SERS detection application. N‐TiO2 NTA was fabricated by anodic oxidation and then doping nitrogen treatment in ammonia atmosphere, acting as a visible‐light‐driven photocatalyst and supporting substrate. Ag/GO/N‐TiO2 NTA was prepared by decorating GO monolayer through an impregnation process and then depositing Ag NPs through a polyol process on the surface of N‐TiO2 NTA, acting as the collection of organic molecule and Raman enhancement. The SERS activity of Ag/GO/N‐TiO2 NTA was evaluated using methyl blue as an organic probe molecule, revealing the analytical enhancement factor of 4.54 × 104. Ag/GO/N‐TiO2 NTA was applied as active SERS substrate to determine a low‐affinity organic pollutant of bisphenol A, revealing the detection limit of as low as 5 × 10−7 m. Ag/GO/N‐TiO2 NTA could also achieve self‐cleaning function for a recycling utilization through visible‐light‐driven photocatalytic degradation of the adsorbed organic molecules. Ag/GO/N‐TiO2 NTA has been successfully reused for five times without an obvious decay in accuracy and sensitivity for organic molecule detection. The unique properties of this SERS substrate enable it to have a promising application for the sensitive and recyclable SERS detection of low‐affinity organic molecules. Copyright © 2016 John Wiley & Sons, Ltd.

Electrochemical deposition of CdSe-sensitized TiO2 nanotube arrays with enhanced photoelectrochemical performance for solar cell application

Particular interest has been given to the self-organized titania nanotube TiO2 thin films prepared by using anodisation method followed by annealing in the air, while the CdSe layer was potentiostatically electrodeposited onto the TiO2 nanotube films at various pH. The resulting films were studied by using energy dispersive X-ray spectroscopy, X-ray diffraction, field emission scanning electron microscopy, UV–Vis spectroscopy and photoelectrochemical analysis to characterize their compositional, crystalline structure, surface morphological, optical, and photoconversion efficiency characteristics. The resulting CdSe/TiO2 nanotube exhibits significant enhancement in optical absorption, photocurrent density and photoconversion efficiency. CdSe/TiO2 nanotube prepared at pH 3 exhibited the highest photocurrent density of 2.13 mA cm−2 and photoconversion efficiency of 1.02 % which is 51 times higher than TiO2 nanotube array. This may due to the formation of CdSe nanocrystals which were well crystallized and bonded with TiO2 NTAs contributing to the enhanced photoresponse and photostability of the overall performance of CdSe/TiO2 NTAs heterostructures.

Ni3S2-Decorated TiO2 nanotube arrays as effective photoanodes for photoelectrochemical water splitting

Cocatalyst nickel sulfide (Ni3S2) was successfully loaded onto TiO2 nanotube array (TiO2 NTA) photoanodes for the first time by a simple two step hydrothermal process.

A titanium nitride nanotube array for potentiometric sensing of pH.

A titanium nitride nanotube array (TiN NTA) electrode was fabricated through anodic oxidation of titanium and reduction and nitridation of TiO2 NTA. The microstructure of TiN NTA was characterized to be uniform with inner diameters of about 120 nm, a wall thickness of 15-20 nm and an average length of 10 μm. Open-circuit potentials were measured to evaluate the TiN TNA electrode related to pH sensitivity, response time, stability, selectivity, hysteresis and reproducibility in the pH range of 2.0-11.0 at 20 ± 1 °C. The prepared TiN NTA electrode exhibits a near-Nernstian slope of 55.33 mV per pH with the correlation coefficient value of 0.995. It shows good selectivity for H(+) ions in the presence of cations and anions, especially in fluoride-containing media. It also has good stability and reproducibility with a response time of 4.4 s. These make it a promising candidate as a pH electrode sensor.

Photoelectrochemical performance of cadmium sulfide quantum dots modified titania nanotube arrays

The cadmium sulfide quantum dots modified titania nanotube arrays (CdS QDs/TiO2 NTAs) were prepared through a sequential sonication-assisted chemical bath deposition (CBD) process. The morphology and microstructure of CdS QDs/TiO2 NTAs were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectroscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy and UV–vis diffuse reflectance spectroscopy. The photoelectrochemical performance of CdS QDs/TiO2 NTAs was investigated under solar light illumination. The affecting parameters were studied including the nanotube length of TiO2 NTAs, CBD cycles of CdS QDs and the annealing treatment of CdS QDs/TiO2 NTAs. CdS QDs synthesized through 8 CBD cycles could uniformly cover on the tube walls of TiO2 NTAs to form unique CdS QDs/TiO2 NTAs with an open pore mouth. The appropriate annealing treatment at 400°C for 60min in N2 atmosphere could improve the crystallinity of CdS QDs, and accordingly enhance the photovoltaic properties of CdS QDs/TiO2 NTAs. Significantly, the nanotube length was the predominant factor affecting photoelectrochemical performance of CdS QDs/TiO2 NTAs. The unannealed CdS QDs/TiO2 NTAs with an optimal nanotube length of 12μm achieved a short-circuit photocurrent density of 4.37mAcm−2, an open circuit photovoltage of 1.10V and a top photoconversion efficiency of 3.56%. Comparatively, the annealed CdS QDs/TiO2 NTAs with an optimal nanotube length of 4μm achieved a short-circuit photocurrent density of 6.31mAcm−2, an open circuit photovoltage of 1.23V and a top photoconversion efficiency of 4.18%. The suitable modification of crystalline CdS QDs could well improve the photoelectrochemical performance of TiO2 NTAs photoanode.

Photogenerated charges transfer across the interface between NiO and TiO2 nanotube arrays for photocatalytic degradation: A surface photovoltage study

To better understand the behavior of photogenerated charges in the composite photocatalyst interface is beneficial to the designing of effective photocatalyst for photocatalytic reaction. In our work, the separation and transfer process of photogenerated charges in NiO/TiO2 nanotube arrays (NiO/TiO2 NTAs) has been studied by surface photovoltage (SPV) spectroscopy and transient photovoltage (TPV) measurement. Through the experimental results analysis, we find that an interfacial electric field is formed at NiO/TiO2 NTAs interface, which is attributed to the work function difference between NiO and TiO2 NTAs. The photogenerated holes in TiO2 can transfer to the NiO layer along the interface electric field under the ultraviolet irradiation. A large amount of photogenerated holes can be separated effectively and then prolonged the holes lifetime to participate in the photocatalytic oxidation reaction. The above results show that the favorable hole-collecting process of NiO in the surface of TiO2 NTAs is the main factor being responsible for the increase the photocatalytic efficiency.

Fabrication of quantum-sized CdS-coated TiO2 nanotube array with efficient photoelectrochemical performance using modified successive ionic layer absorption and reaction (SILAR) method

Quantum-sized CdS-coated TiO2 nanotube array (Q-CdS-TiO2 NTA) was fabricated by the modified successive ionic layer absorption and reaction method. Scanning electron microscope and transmission electron microscope images showed the regular structure of TiO2 NTA, where quantum-sized CdS (diameter <10nm) deposited on both the inside and outside of TiO2 nanotube wall. Fabrication conditions including immersing cycles, calcination temperature and drying process were well optimized, and the Q-CdS-TiO2 NTA and its photoelectrochemical (PEC) properties were characterized by X-ray fluorescence spectrometer, UV–Vis diffuse reflectance spectra and photovoltage. Distinct increases in visible light absorption and photocurrent were observed as the immersing cycle was increased from 5 to 20 times. The additional drying process accelerated the CdS crystal growth rate, and thus, the fabrication time could be shortened accordingly. Calcination temperature influenced the PEC property of Q-CdS-TiO2 NTA deeply, and the optimized calcination temperature was found as 500 °C. As the Q-CdS-TiO2 NTA was fabricated under such condition, the visible photocurrent density increased to 2.8mA/cm and the photovoltage between 350 and 480nm was enhanced by 2.33 times than that without calcination. This study is expected to optimize Q-CdS-TiO2 NTA fabrication conditions for the purpose of improving its PEC performance.

Enhanced photoelectrocatalytic hydrogen production activity of SrTiO3–TiO2 hetero-nanoparticle modified TiO2 nanotube arrays

SrTiO3–TiO2 hetero-nanoparticle modified TiO2 nanotube arrays (ST–TiO2 NTAs) were constructed by following these steps: firstly, highly ordered TiO2 nanotube arrays (TiO2 NTAs) were synthesized directly on Ti foils through electrochemical oxidation, then SrTiO3–TiO2 nanoparticles were deposited on the TiO2 NTAs using two-step hydrothermal treatment. SrTiO3–TiO2 nanotube arrays (S–TiO2 NTAs) were also prepared by directly hydrothermal treatment of TiO2 NTAs for comparison. The photoelectrocatalytic hydrogen production activities of all the samples were evaluated by using ethylene glycol as a sacrificial reagent in water under a 300 W xenon arc lamp. The photoelectrocatalytic hydrogen production rate of TiO2 NTAs can be significantly improved by modifying SrTiO3–TiO2 hetero-nanoparticles and achieved a greatly promoted value of 314.9 μmol cm−2 h−1 which was 2.1 times higher than that of the unmodified TiO2 NTAs. Compared to S–TiO2 NTAs, ST–TiO2 NTAs showed a 32.8% increase in hydrogen production rate. Furthermore, SrTiO3–TiO2 hetero-nanoparticle modified TiO2 nanotube arrays exhibited excellent stability and was facile to be safely reused. The improvement of photocatalytic hydrogen production efficiency is attributed to the difference of the conduction band potential between TiO2 and SrTiO3 in SrTiO3–TiO2 hetero-nanoparticles, thereby boosting the transfer and separation of the photogenerated electron–hole pairs.

Controlled deposition and enhanced visible light photocatalytic performance of Pt-modified TiO2 nanotube arrays

Highly ordered TiO2 nanotube arrays (TiO2 NTAs) have been fabricated by the potentiostatic anodization method with Ti foils. Pt nanoparticles have been successfully deposited onto TiO2 NTAs by UV light photoreduction method. In this work, X-ray diffraction, field emission scanning electron microscope, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy and energy dispersive X-ray spectrometer methods were adopted to characterize the samples. The influence of different concentration of H2PtCl6 precursor solution on the morphology and photocatalytic performances of samples was discussed. The SEM observations showed that Pt nanoparticles distributed on the wall of TiO2 nanotubes uniformly. UV–vis spectra analysis showed that the light absorption of Pt/TiO2 NTAs has been extended to the visible light range. When the concentration of H2PtCl6 was 3mM, the prepared sample showed the highest photodegradation rate. After irradiated under visible light for 2h, the degradation rate of methyl orange solution reached 84.27%. Under the same condition, no obvious photodegradation of methyl orange was found for TiO2 NTAs. Kinetic research showed that photodegradation process followed the first-order reaction, the apparent reaction rate constant of 3 Pt/TiO2 NTAs was 1.493×10−2min−1.

Preparation and characterization of CeO2 decorated TiO2 nanotube arrays photoelectrode and its enhanced photoelectrocatalytic efficiency for degradation of methyl orange

The highly oriented CeO2/TiO2 nanotube arrays (CeO2/TiO2 NTAs) were fabricated by the electrodeposition of CeO2 in 1.0 mol/L Na2SO4 aqueous solution on TiO2 NTAs. CeO2/TiO2 NTAs were characterized by SEM, TEM, XRD, XPS. Its ultraviolet–visible absorption and photoelectrochemical properties were investigated. The degradation of methyl orange was used to evaluate the photoelectrocatalytic activity of CeO2/TiO2 NTAs. The results showed that the CeO2 nanoparticles with a homogenous spherical size of about 15 nm were uniformly deposited onto the surface of TiO2 NTAs. The CeO2 composed with Ce4+ and Ce3+ ions could be observed. CeO2/TiO2 NTAs exhibited a stronger UV and visible light absorptions with 40 nm red-shift of the absorption edge compared with TiO2 NTAs. The separation efficiency of the photogenerated charge carriers of CeO2/TiO2 NTAs can significantly enhanced by the CeO2 deposited. The removal efficiencies (98.1 %) of methyl orange at the CeO2/TiO2 NTAs photoelectrodes was larger than that of the bare TiO2 nanotube arrays photoelectrode (78.1 %).

Enhanced supercapacitive performance on TiO2@C coaxial nano-rod array through a bio-inspired approach

A coaxial core–shell structured TiO2@carbon nano-rod arrays (TiO2@C NRAs) was constructed and tested as a supercapacitor electrode in this study. Dopamine was self-assembled into a polydopamine nano-rod arrays within the TiO2 nano-tube arrays (TiO2 NTAs) and was used as a precursor for the carbon nano-rod generation. Electrochemical measurements showed that the electrodes made with coaxial TiO2@C NRAs exhibited substantially higher electrochemical performances such as larger areal capacitance and faster charge/discharge capability than those of the pristine TiO2 NTA electrode and porous active carbon materials. Benefiting from the enhanced electrical conductivity and increased surface area of the coaxial nano-rod structure, the prepared coaxial TiO2@C NRAs electrode achieved a remarkable areal capacitance of 40.75mFcm−2 at a current density of 0.2mAcm−2, which was significantly higher than that of the pristine TiO2 NTAs (0.31mFcm−2).

Capacitive and Oxidant Generating Properties of Black-Colored TiO2 Nanotube Array Fabricated by Electrochemical Self-Doping

Recently, black-colored TiO2 NTA (denoted as black TiO2 NTA) fabricated by self-doping of TiO2 NTA with the amorphous phase led to significant success as a visible-light-active photocatalyst. This enhanced photocatalytic activity is largely attributed to a higher charge carrier density as an effect of electrochemical self-doping resulting in a higher optical absorbance and lower transport resistance. Nevertheless, the potential of black TiO2 NTA for other electrochemical applications, such as a supercapacitor and an oxidant-generating anode, has not been fully investigated. Here, we report the capacitive and oxidant generating properties of black TiO2 NTA. The black TiO2 NTA exhibited significantly a high value for areal capacitance with a good rate capability and novel electrocatalytic activity in generating (•)OHs and Cl2 compared to pristine TiO2 NTA with the anatase phase. This study suggests that the black TiO2 NTA be applied as a supercapacitor and an oxidant generating anode.

Fabrication of PANI/C‐TiO2 Composite Nanotube Arrays Electrode for Supercapacitor

Polyaniline/carbon doped TiO2 composite nanotube arrays (PANI/C‐TiO2 NTAs) have been prepared successfully by electrodepositing PANI in C‐TiO2 NTAs which were prepared by directly annealing the as‐anodized TiO2 NTAs under Ar atmosphere. The organic residual in the TiO2 NTAs during the process of anodization acts as carbon source and is carbonized in Ar atmosphere to manufacture the C‐TiO2 NTAs. The specific capacitance of the PANI/C‐TiO2 electrode is 120.8 mF cm−2 at a current density of 0.1 mA cm−2 and remains 104.3 mF cm−2 at a current density of 2 mA cm−2 with the calculated rate performance of 86.3%. After 5000 times of charge‐discharge cycling at a current density of 0.2 mA cm−2, the specific capacitance retains 88.7% compared to the first cycle. All these outstanding performances of the as‐prepared PANI/C‐TiO2 NTAs indicate it will be a promising electrode for supercapacitor.

TiO2 nanotube arrays loaded with reduced graphene oxide films: facile hybridization and promising photocatalytic application

A facile combination of electrodeposition and carbonation techniques was adopted to deposit reduced graphene oxide nanaosheets on TiO2 nanotube arrays. The RGO-TiO2 NTAs demonstrated significantly enhanced photocatalytic activity compared to pristine TiO2 NTAs and annealed TiO2 NTAs.