Nitrogen Doped TiO2 Nanotubes Research Articles

Fabrication of Ag3PO4/N-doped TiO2 nanotubes heterojunction photocatalysts for visible-light-driven photocatalysis

As an environmentally friendly and energy-efficient technology, photocatalysis holds considerable potential for eliminating organic pollutants. In this study, novel visible-light-driven Ag3PO4-decorated nitrogen-doped TiO2 nanotubes (Ag3PO4/N-TNTs) photocatalysts with advanced properties of heterostructures were successfully synthesized and used to degrade methylene blue (MB) dye. The fabrication of Ag3PO4/N-TNTs photocatalysts involved a two-step electrochemical anodization to obtain TiO2 nanotubes (TNTs) and the wet impregnation of the amorphous tubular structure in NH3 solution, followed by calcination in air to obtain crystallized nitrogen-doped TiO2 nanotubes (N-TNTs). Finally, the decoration of the N-TNTs with Ag3PO4 nanoparticles was conducted to enhance visible-light reactivity. Various heterojunction photocatalysts were obtained by changing the concentration of NH3 (0.5–2.5 M) and the dosage of Ag3PO4 (0.25–1.5 wt%) in the composites. Results of ultraviolet–visible (UV–Vis) absorption, photocurrent transient, and electrochemical impedance spectroscopy measurement revealed that Ag3PO4/N-TNTs possessed a significant response in the visible-light range and good photoelectronic properties. The superior photocatalytic activity of the Ag3PO4/N-TNTs catalyst was achieved under the optimal conditions of N-doping using 2-M NH3 and Ag3PO4 deposition at a dosage of 0.75 wt%. Based on the degradation efficiency (DE) of MB, the optimal Ag3PO4/N-TNTs exhibited rate constants of 4.5 and 2 times higher than those of the pristine TNTs and N-TNTs, respectively. The high stability of Ag3PO4/N-TNTs was confirmed through four cycles of reutilization, with a small decay of only 5.3% in the DE of MB dye for each run of photocatalysis. The scavenger tests of generated reactive oxygen species revealed that ·OH and ·O2− were the primary contributors to photocatalytic performance. The synthesized Ag3PO4/N-TNTs heterostructure photocatalysts were proven to possess efficient separation of photogenerated charge carriers, high reactivity, and stability in the visible-light region.

N-doped TiO2 nanotubes catalyzed solvent-free domino strategy for the synthesis of α-keto triazoles

The present work describes the catalytic activity of nitrogen-doped TiO2 nanotubes (NTNTs) for solvent-free domino synthesis of a series of α-ketotriazoles from methyl ketones, N,N-dimethylformamide dimethyl acetal (DMF-DMA) and tosyl azide. The reaction proceeds through the in situ enaminone formation from methyl ketones and DMF-DMA followed by reaction with tosyl azide via a 1,3-dipolar cycloaddition. To our delight, NTNTs exhibited high catalytic activity towards the solvent-free synthesis of α-ketotriazoles from methyl ketones, DMF-DMA and tosyl azide as compared to both commercially available TiO2 and TNTs. The present domino strategy has several advantages which include its large substrate scope, low NTNT-2 loading, shorter reaction times and high yields. Further, the obtained α-ketotriazoles does not require column purification and NTNT-2 is used again for 7 cycles without significant loss of activity.

Nitrogen-doped TiO2 nanotube anode enabling improvement of electronic conductivity for fast and long-term sodium storage

Titanium oxide has recently drawn much attention as anode material for sodium ion batteries. Nevertheless, its application is highly restricted by poor electronic conductivity and sluggish Na+ reaction kinetics. Herein, we report nitrogen(N)-doped-TiO2 nanotubes (N-TiO2-NTs) through a facile and cost-effective anodization process and annealing at NH3/Ar flow. XPS analysis investigates that the ratio of doped N element is 2.1 at% mainly in interstitial sites, which can effectively improve intrinsic electronic conductivity and enhance Na+ diffusivity of the TiO2 bulk. Due to the hetero-N doping and high specific area of nanotube structure, the kinetic activity of N-TiO2-NTs is observably enhanced. Therefore, the anode delivers high capacitive-controlled behaviors up to 80.3% and 86% of whole capacities at scanning rates of 0.6 and 1 mV s−1. The N-TiO2-NTs anode exhibits good and stable capacity (216.1 mA h g−1 at 0.2 C after 300 cycles) and high rate performance (114 mA h g−1 at 20 C). Moreover, the long-term cycling test after 5000 cycles obtains nearly 100% capacity retention at an ultrahigh current density of 10 C. Thus, we offer a facile strategy to develop N-TiO2-NTs as a hopeful product for the anode materials in sodium ion batteries.

A novel photoelectrochemical system to disrupt microalgae for maximizing lipid-extraction efficiency

Microalgae biodiesel is a candidate to provide renewable, C-neutral energy. However, microalgal cells possess strong cell walls and cell membranes with high selective permeability, both of which hinder the extraction of lipids from the microalgae. Optimizing lipid extraction involves disrupting the microalgae’s cell wall and membrane. The hydroxyl free radical (•OH) can attack the cell wall and cell membrane in the microalgae, making the microalgae more susceptible to lipid extraction. Introduced here is a PhotoElectroChemical (PEC) with TiO2-based photoanode utilized UV–Vis light to produce •OH at a phosphate-palladium cathode. Until now, PEC has not been utilized to disrupt microalgal cells to improve the extraction of microalgae lipids. Here, a novel PEC system -- comprised of two nitrogen-doped TiO2 nanotube photoanodes, a bipolar membrane, and a phosphorus-palladium cathode -- was demonstrated to disrupt microalgal biomass to improve lipid extraction. PEC utilizes ultraviolet and visible light as the only input energy for the effective disruption of the microalgal cell. Pretreatment of Chlorella using the PEC system resulted in 96% oil-extraction efficiency which was approximately 10 times higher than that achieved without the pretreatment and an increases in desirable C16:0. Also explored were the mechanisms underlying •OH generation and microalgae disruption. PEC promises to be an eco-friendly and low-energy technology that can promote the development of microalgae industries.

Experimental and computational study of visible light-induced photocatalytic ability of nitrogen ions-implanted TiO2 nanotubes**Project supported by the National Natural Science Foundation for Joint Fund Key Project of China (Grant No. U1865206), the National Science and Technology Major Project of China (Grant No. 2017-VII-0012-0107), the National Defense Science and Technology Key Laboratory Fund of China (Grant No. 614220207011802), and the Key

Nitrogen-doped TiO2 nanotubes (TNTs) were prepared by ion implantation and anodic oxidation. The prepared samples were applied in photocatalytic (PC) oxidation of methyl blue, rhodamine B, and bisphenol A under light irradiation. To explore the influence of doped ions on the band and electronic structure of TiO2, computer simulations were performed using the VASP code implementing spin-polarized density functional theory (DFT). Both substitutional and interstitial nitrogen atoms were considered. The experimental and computational results propose that the electronic structure of TiO2 was modified because of the emergence of impurity states in the band gap by introducing nitrogen into the lattice, leading to the absorption of visible light. The synergy effects of tubular structures and doped nitrogen ions were responsible for highly efficient and stable PC activities induced by visible and ultraviolet (UV) light.

Preparation of nitrogen-doped TiO2 nanotube deposited with gold nanoparticles for photocatalytic phenol degradation under visible light

One of the many functions of TiO2 photocatalysts is degrading organic compounds. TiO2 photocatalysts have a band gap of 3.2 eV, which is equivalent to the energy of ultraviolet (UV) photons with a wavelength of 388 nm and allows them to be effectively activated only by UV light. However, they are less effective under visible (Vis) light. Researchers have developed many ways to use the photocatalytic properties of TiO2 under visible light via nitrogen doping. Further, the photocatalytic activity of N-doped TiO2 can be improved via surface plasmon resonance. In this study, N-doped TiO2 nanotubes (N-TiO2 NTs) are prepared and deposited with Au nanoparticles (Au/N–TiO2 NTs) via electrodeposition. The TiO2 NTs and Au/N-TiO2 NTs are characterized using UV-VIS spectrometry, Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), field emission scanning electron microscopy, energy dispersive spectroscopy (EDS), and linear sweep voltammetry (LSV). The photocatalytic test under tungsten lamp illumination of a 20-ppm phenol solution in a batch reactor shows a phenol degradation of 60 %, whereas a 20-ppm bisphenol A (BPA) solution is degraded by 40 %.

Electrochemical Performance of Nitrogen-Doped TiO2 Nanotubes as Electrode Material for Supercapacitor and Li-Ion Battery.

Electrochemical anodized titanium dioxide (TiO2) nanotubes are of immense significance as electrochemical energy storage devices owing to their fast electron transfer by reducing the diffusion path and paving way to fabricating binder-free and carbon-free electrodes. Besides these advantages, when nitrogen is doped into its lattice, doubles its electrochemical activity due to enhanced charge transfer induced by oxygen vacancy. Herein, we synthesized nitrogen-doped TiO2 (N-TiO2) and studied its electrochemical performances in supercapacitor and as anode for a lithium-ion battery (LIB). Nitrogen doping into TiO2 was confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques. The electrochemical performance of N-TiO2 nanotubes was outstanding with a specific capacitance of 835 µF cm−2 at 100 mV s−1 scan rate as a supercapacitor electrode, and it delivered an areal discharge capacity of 975 µA h cm−2 as an anode material for LIB which is far superior to bare TiO2 nanotubes (505 µF cm−2 and 86 µA h cm−2, respectively). This tailor-made nitrogen-doped nanostructured electrode offers great promise as next-generation energy storage electrode material.

Enhanced Photocatalytic Performance of Nitrogen-Doped TiO2 Nanotube Arrays Using a Simple Annealing Process

Nitrogen-doped TiO2 nanotube arrays (N-TNAs) were successfully fabricated by a simple thermal annealing process in ambient N2 gas at 450 °C for 3 h. TNAs with modified morphologies were prepared by a two-step anodization using an aqueous NH4F/ethylene glycol solution. The N-doping concentration (0–9.47 at %) can be varied by controlling N2 gas flow rates between 0 and 500 cc/min during the annealing process. Photocatalytic performance of as-prepared TNAs and N-TNAs was studied by monitoring the methylene blue degradation under visible light (λ ≥ 400 nm) illumination at 120 mW·cm−2. N-TNAs exhibited appreciably enhanced photocatalytic activity as compared to TNAs. The reaction rate constant for N-TNAs (9.47 at % N) reached 0.26 h−1, which was a 125% improvement over that of TNAs (0.115 h−1). The significant enhanced photocatalytic activity of N-TNAs over TNAs is attributed to the synergistic effects of (1) a reduced band gap associated with the introduction of N-doping states to serve as carrier reservoir, and (2) a reduced electron‒hole recombination rate.

Fabrication, characterization and photocatalytic properties of CdS nanoparticles modified by N-doped TiO2 NTs

Abstract Highly ordered TiO2 nanotube arrays (TiO2 NTs) were prepared by anodic oxidizing method on a surface of Ti substrate. Fabrication of nitrogen-doped TiO2 nanotube arrays (N-TiO2 NTs) was carried out by immersion in ammonia solution. CdS nanoparticles loaded N-doped TiO2 nanotube arrays (CdS/N-TiO2 NTs) were obtained by successive ionic layer adsorption and reaction (SILAR) technique. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), photoluminescence (PL) emission spectra and ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy (DRS). The results indicate that the TiO2 nanotube diameter and wall thickness are 100 nm to 120 nm and 20 nm to 30 nm, respectively. Moreover, the morphology and structure of the highly ordered TiO2 NTs are not affected by N-doping. Furthermore, CdS nanoparticles are evenly distributed on the surface of TiO2 NTs. Finally, the photocatalytic activity of CdS/N-TiO2 NTs was evaluated by degradation of MO under visible-light irradiation. Compared with TiO2 NTs, N-TiO2 NTs, CdS/N-TiO2 NTs exhibited enhanced photocatalytic properties, and the highest degradation rate of CdS/N-TiO2NTs could reach 97.6 % after 90 min of irradiation.

Anodic growth of Nitrogen-doped Titanium dioxide nanotubes by anodization process of elemental Titanium in ethylene glycol based electrolyte solution with different water contents

Anatase Nitrogen-doped Titanium Dioxide (Nitrogen-doped TiO2) nanotubes were grown via an anodization process in an ethylene-glycol based electrolyte solution containing ammonium fluoride (NH4F) and different water contents (2–4 vol%). These electrolyte solutions act as the dopants sources of Nitrogen in anodic TiO2 nanotubes. The influence of different water content of electrolyte solution on physical properties of the Nitrogen-doped TiO2 nanotubes was studied. It was observed that the diameter of the Nitrogen-doped TiO2 nanotubes was increased by the water content increasing of the electrolyte solution. Also, the Nitrogen-doped TiO2 nanotubes which grown in the electrolyte solution with 3 vol% water content had maximum length. An energy dispersive X-Ray analysis (EDX) revealed that the TiO2 nanotubes were heavily doped with Nitrogen. UV–Vis diffuse reflectance spectroscopy (DRS) and Photoluminescence (PL) measurements showed that the Nitrogen-doped TiO2 nanotubes had narrow band gap energy (lower than 3 eV).

Enhanced Photocatalytic Properties of Ag-Loaded N-Doped Tio2 Nanotube Arrays

Abstract Highly ordered TiO2 nanotube (TiO2 NT) arrays were prepared by anodic oxidizing method on the surface of the Ti substrate. Nitrogen-doped TiO2 nanotube (N-TiO2 NT) arrays were carried out by ammonia solution immersion, and Ag nanoparticles loaded N-doped TiO2 nanotube (Ag/N-TiO2 NT) arrays were obtained by successive ionic layer adsorption and reaction (SILAR) technique. The samples were characterized by the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) emission spectra, ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS). The result indicated that the diameter and wall thickness of the TiO2 NT are 100–120 and 20–30 nm, respectively. Moreover, the morphology and structure of the highly ordered TiO2 NTs were not affected by N-doping. Furthermore, Ag nanoparticles were evenly deposited on the surface of TiO2 NTs in the form of elemental silver. Finally, the photocatalytic activity of Ag/N-TiO2 NTs was evaluated by degradation of methyl orange (MO) under visible-light irradiation. The Ag/N-TiO2 NTs exhibited enhanced photocatalytic properties, which could reach 95% after 90-min irradiation.

Electrochemical Enhancement of Photocatalytic Disinfection on Aligned TiO₂ and Nitrogen Doped TiO₂ Nanotubes.

TiO2 photocatalysis is considered as an alternative to conventional disinfection processes for the inactivation of waterborne microorganisms. The efficiency of photocatalysis is limited by charge carrier recombination rates. When the photocatalyst is immobilized on an electrically conducting support, one may assist charge separation by the application of an external electrical bias. The aim of this work was to study electrochemically assisted photocatalysis with nitrogen doped titania photoanodes under visible and UV-visible irradiation for the inactivation of Escherichia coli. Aligned TiO2 nanotubes were synthesized (TiO2-NT) by anodizing Ti foil. Nanoparticulate titania films were made on Ti foil by electrophoretic coating (P25 TiO2). N-doped titania nanotubes and N,F co-doped titania films were also prepared with the aim of extending the active spectrum into the visible. Electrochemically assisted photocatalysis gave higher disinfection efficiency in comparison to photocatalysis (electrode at open circuit) for all materials tested. It is proposed that electrostatic attraction of negatively charged bacteria to the positively biased photoanodes leads to the enhancement observed. The N-doped TiO2 nanotube electrode gave the most efficient electrochemically assisted photocatalytic inactivation of bacteria under UV-Vis irradiation but no inactivation of bacteria was observed under visible only irradiation. The visible light photocurrent was only a fraction (2%) of the UV response.

Photo-electro-catalytic performance of highly ordered nitrogen doped TiO2 nanotubes array photoanode

Highly ordered nitrogen doped TiO2 nanotube arrays (N-TNTAs) were synthesized via a one step anodization method at 40 V for 1 hour, in the electrolyte containing ammonium fluoride (NH4F), water and triethylamine solution, followed calcination under N2 atmosphere at 450oC for 3 h. The obtained samples were characterized by means of FE-SEM image showed that the N-TNTs are in a highly ordered array, having inner diameters, wall thickness, tube length of 65 nm, 30 nm and 900 nm, respectively. The X-ray diffraction (XRD) patterns of N-TNTAs and undoped TiO2 nanotubes arrays (TNTAs) are identical consists of anatase phase, which suggests that the doping of N does not affect the crystalline structure. X-ray photoelectron spectroscopy (XPS), revealed that N atom was incorporated into the lattice of a TiO2 nanotube array film. The infrared spectra, showed a new peak at 1240 cm-1 may indicate the incorporation of N into the lattice of TiO2 through substituting O atoms, in the form of ∼N-Ti-O∼. A red shift of the absorption edge toward the visible region of N-TNTAs are observed by diffuse reflectance spectroscopy (DRS), which is corresponding to a band gap of 2.8 eV. The photo-electro-catalytic (PEC) degradation efficiency toward methylene blue solution under visible light illumination of the N-TNTAs electrode was 89%, in which the rate constant of N-TNTAs electrode was 8 times better compared to that the undoped TNTAs photo-electrode.

Application of nitrogen-doped TiO2 nano-tubes in dye-sensitized solar cells

Our research aimed to improve the overall energy conversion efficiency of DSCs by applying nitrogen-doped TiO2 nano-tubes (N-TNT) for the preparation of DSCs photo-anodes. The none-doped TiO2 nano-tubes (TNTs) were synthesized by alkaline hydrothermal treatment of Degussa P25 TiO2 particles in 10M NaOH. The nano-tubes were N-doped by reflux in various concentrations of NH4NO3. The effects of nitrogen doping on the structure, morphology, and crystallography of N-TNT were analyzed by transmission electron microscopy (TEM), infrared spectroscopy (IR), Raman spectroscopy, and X-ray photoelectron spectra (XPS). DSCs fabricated with doped N-TNT and TNT was characterized by J-V measurements. Results showed that nitrogen doping significantly enhanced the efficiency of N-TNT cells, reaching the optimum value (η=7.36%) with 2M nitrogen dopant, compared to η=4.75% of TNT cells. The high efficiency of the N-TNT cells was attributed to increased current density due to the reduction of dark current in the DSCs.

Photocatalytic activity of nitrogen doped TiO2 nanotubes prepared by anodic oxidation: The effect of applied voltage, anodization time and amount of nitrogen dopant

Nitrogen doped TiO2 nanotube arrays were prepared by anodizing Ti foils in an organic electrolyte containing specified amounts of urea as nitrogen precursor. The photocatalytic activity of the samples was evaluated by analyzing the degradation kinetics of phenol in water. The influence of tubes’ length, tubes’ surface morphology and amount of nitrogen in the TiO2 lattice on hydroxyl radical formation efficiency, photocatalytic activity and stability in four cycles was investigated. It was found that the photocatalytic activity as well as the charge carrier recombination rate depends on nitrogen concentration and the process parameters. 3.5μm-long nanotubes containing 0.34at.% of nitrogen seems to be favorable in phenol degradation and OH radicals generation under visible light. Comparison of XPS and photocatalytic activity test results shows decrease in phenol degradation efficiency with increasing amount of carbon contaminants on photocatalysts’ surface.

Effect of graphene and Au@SiO2 core–shell nano-composite on photoelectrochemical performance of dye-sensitized solar cells based on N-doped titania nanotubes

We have investigated the role of graphene and Au@SiO2 core–shell nano-composite (NC), on the performance of dye-sensitized solar cells (DSSC) based on nitrogen doped TiO2 nanotubes (N-TNTs) as photoanodes.

Visible-light photocatalytic activity of NH4NO3 ion-exchanged nitrogen-doped titanate and TiO2 nanotubes

Titanium dioxide and titanate nanotubes (TiNTs) have attracted much attention because of their unique properties, which allow their application in energy conversion and storage devices, magnetic materials, electrocatalysis, and photocatalysis. However, these materials can only absorb UV radiation, which is approximately 5% of the incident solar radiation on Earth. The doping of TiNTs with metals or nonmetals, such as nitrogen, is one strategy that is used to make these materials sensitive to visible light. Here, we obtained TiNTs by hydrothermally treating anatase powder in a NaOH aqueous solution. The TiNTs were subsequently doped with nitrogen via an ion exchange process using different concentrations of NH4NO3 (1.0, 1.5, 2.0, 2.5, or 3.0molL−1) as the nitrogen source. After the ion-exchange process, the samples were calcined at 200 and 400°C, which produced nitrogen-doped titanate nanotubes (NTiNTs) and nitrogen-doped TiO2 nanotubes (NTiO2NTs), respectively. All of the samples were characterized by X-ray diffraction, electron microscopy, and various spectroscopic techniques. Electron paramagnetic resonance (EPR) was used to identify and quantify the defects created in the nanotube structures from doping and the calcination process. Our analysis revealed that the number of defects in the NTiO2NTs depended on the nominal NH4NO3 concentration, which formed paramagnetic NO species and single electron-trapped oxygen vacancies (SETOVs). As proof of this concept, the nanotubes were used as photocatalysts with visible light for the degradation of methylene blue (MB). The degradation rate significantly improved depending on the NH4NO3 concentration when the NTiO2NTs were used as the photocatalyst.

Photoelectrical properties of nitrogen doped TiO2 nanotubes by anodic oxidation of N+ implanted Ti foils

Ti foils were implanted by N+ with accelerating voltage of 60kV. The dose of implantation was chosen as 1×1016, 1×1017 and 5×1017ions/cm2 respectively. N-doped TiO2 nanotubes (TNTs) were produced by anodic oxidation method. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to study the structural and chemical properties of TNTs. The photocurrent of TNTs under both UV and visible light irradiation was measured and recorded in situ using an electrochemical station. The results showed that N-doped TNTs displayed strong absorption remarkably in both UV and visible range. Not only the separation efficiency of photo-generated electron–hole pairs of N-doped TNTs was improved, but the absorption edge of the samples was shifted to longer wavelength for the implantation. The best implanted dose with premier photocurrent was 1×1017ions/cm2 under both UV and visible light irradiation.

Nitrogen doped TiO2 nanotube arrays with high photoelectrochemical activity for photocatalytic applications

Nitrogen doped TiO2 nanotube arrays (N-TNAs) were prepared by immersing TNAs in 1M NH3·H2O solution and then annealing in different temperatures. The morphology, structure and composition of the N-TNAs were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–vis spectroscopy, respectively. Effects of annealing temperatures on structure, photocatalytic properties, and the crystal structure transformation process of the N-TNAs were discussed. Photocatalytic properties of the N-TNAs were evaluated in term of the degradation of methyl orange (MO) under UV light and visible light, and the photocurrent of N-TNAs were tested by electrochemical workstation. The XPS results showed that the N-TNAs were achieved by interstitial doping and substitutional doping, and the FESEM results showed the morphology was not changed after doping process. Compared with the pure TNAs, the N-TNAs annealed at 500̊C for 2h with a mixed phase of anatase and rutile exhibited higher photocatalytic degradation activity to MO. Furthermore, the photocatalytic mechanism of organic pollutants degradation (MO) was discussed based on our experiments.

Preparation and Characterization of the Highly Regular Nitrogen Doped Anatase TiO<sub>2 </sub>Nanotube

Nitrogen-doped TiO2 nanotubes (N-TNTs) were fabricated on the titanium foil by anodic oxidation and followed by annealing at NH3 environment. Highly ordered nanotubes, roughly 150 nm in the diameter and 20 μm in the length, were synthesized on the titanium foil. By controlling oxidation voltage, the thick TiO2 nanotubes were peeled off from the titanium substrate. In one step annealing at NH3 environment, nitrogen replaced oxygen and doped into TiO2, but anatase phase was formed.