Photocatalytic Activity Of TiO2 Nanotubes Research Articles

Phenomenal Insight into Electrochemically Induced Photocatalytic Degradation of Nitrobenzene on Variant Au-Modified TiO2 Nanotubes

TiO2 nanotubes are a prominent type of TiO2-based nanostructure compared to nanorod arrays. A promising way to improve photocatalytic performance is modifying TiO2 nanotubes with metals, either on the surface or inside the tubes. There is a substantial demand for enhancing the conductivity and charge separation of TiO2 nanotubes, with a major focus on gold (Au) modification. Gold (Au) coatings have significantly improved the photocatalytic activity of TiO2 nanotubes, particularly in pollutant oxidation. However, the mechanism underlying the action of Au-modified TiO2 nanotubes in photocatalytic nitrobenzene oxidation under electrochemical induction remains unclear. Therefore, we conducted related experiments to explore the optimal Au concentration under various conditions. Under electric field induction, the maximum removal rate achieved was 54.9%. Lastly, we analyzed the relevant photocatalytic mechanism to elucidate the responses of electrons and holes to a simulated contaminant under a photo-electrochemical field.

Copper oxide modified biphasic titania for enhanced hydrogen production through photocatalytic water splitting

Recently, TiO2(B) has been extensively used in catalytic and energy fields owing to its exceptional crystal structure. But being a metastable state, TiO2(B) is transformed easily into other stable crystalline forms like anatase or rutile phase, and the low crystallinity limits the application of the material in catalysis. A combination of TiO2(B) with anatase, which is benefitted by a homojunction, is proven to be blessed with high activity. Herein, hydrogen production via photocatalytic water-splitting is presented using Cu modified biphasic titania nanotubes achieved by a facile hydrothermal procedure. The systems are well characterized using SEM, TEM, XRD analysis, N2 adsorption study, FTIR, DR-UV, Raman, Photoluminescence, and X-ray photoelectron spectral analysis. The homo-junction developed in titania due to anatase –TiO2 (B), as well as the heterojunction created by the co-catalyst, tune the photocatalytic activity of TiO2 nanotubes positively, as evident from the enhanced hydrogen production over the system.

Effect of the Deposition of Vanadium-Oxide on the Photocatalytic Activity of TiO2 Nanotubes and Its Photodiode Performance Interfaced with CH3NH3PbI3 Single Crystal

In this study, we report the influence of vanadium oxide (VO), as a photosensitive component, on the photoactivity of TiO2 nanotubes (TNTs). A series of TNTs of varying tube diameter were synthesized by the anodization of titanium foils at different voltages, while vanadium oxide was deposited on TNTs by wet chemical deposition. An improvement in the optical properties of nanotubes was observed after the deposition of vanadium oxide. An improvement in the optical properties (redshift in UV-Vis spectra) of TNTs and TNT/VO was noted. The photocatalytic activity was improved with increasing tube diameter, while it was weakened after the deposition of VO. Furthermore, photoactivity was investigated in photodiodes based on TNTs or TNT/VO and single crystals of CH3NH3PbI3. The photoelectric measurement revealed that different TNT diameters did not influence the I-V characteristic of the photodiodes, while the deposition of VO improved the photocurrent for smaller TNTs.

Effect of Au position on the photoelectrochemical and photocatalytic activity of TiO2 nanotubes under UV irradiation

Heterostructures have excellent physicochemical properties, which have attracted much attention in photoelectrochemical and photocatalytic fields. Au-TiO2NTs and Au@TiO2NTs were fabricated by the impregnation method and a vacuum-assisted-impregnation route, respectively. The effects of Au position on the structural and photoelectrochemical properties and photocatalytic activity of TiO2 have been characterized and studied. The Au@TiO2NTs photoelectrode showed a significant photocurrent (∼17 μA/cm2), which was approximately 8.5 and approximately 2.3 times greater than that of TiO2NTs and Au-TiO2NTs. Meanwhile, Au@TiO2NTs also exhibited the best photocatalytic activity and stability for tetracyclines degradation. The characterization and experimental results revealed that the better performance of Au@TiO2NTs may be attributed to the smaller Au nanoparticles inside the nanotube space, the reduced interfacial charge transfer resistance, and the stronger electronic interaction between Au nanoparticles and TiO2NTs.

Enhanced photocatalytic activity of TiO2 nanotubes decorated with Ag nanoparticles by simultaneous electrochemical deposition and reduction processes

The photocatalytic activity of the modified TiO2 nanotubes (TNTs) for water purification was studied. Three modification methods including Ag nanoparticles (NPs) decoration (TNT-Ag), electrochemical reduction of the TNTs (TNT-H), and a simultaneous combination of these two methods in one cell (TNT-Ag-H) were investigated. The TEM results showed that the defects formed during the electrochemical reduction, when two methods are combined, act as preferred sites for Ag nucleation, resulting in finer Ag NPs with better distribution. The average size of homogeneous distributed Ag NPs was measured in the range of 3–5 nm. Accordingly, XPS analysis showed an increased amount of Ag NPs on the surface of the modified TNTs in TNT-Ag-H sample. It was also observed that electrochemical reduction was not stable and thus had minor effects on the optical properties of the TNTs. Moreover, the TNT-Ag-H sample showed enhanced SPR and increased absorption in the whole visible light region in DRS analysis. This sample also showed a higher photocatalytic performance in the degradation of two different organic pollutants. The kinetic rate constant after 300 min reached up to 9.12 × 10-3 and 1.39 × 10-3 min−1 for MB degradation under UV and visible irradiation, respectively, which are two times higher than unmodified TNT samples.

Fast monitoring of organic dye degradation coupled with a colorimetric approach in a Ag-modified TiO2 nanotube photocatalytic system

Monitoring the contents of organic dyes in real-time is crucial for the valuation of photocatalyst performance. To achieve this, a method of detecting organic dyes was designed based on color variations by using Ag nanoparticle modified TiO2 nanotubes (Ag/TiO2) as photocatalysts. The obtained Ag/TiO2 photocatalyst possesses strong visible-light absorption, and 1.0% Ag/TiO2 exhibited the best performance under UV and simulated sunlight. The investigation indicates that the photocatalytic activity of TiO2 nanotubes is greatly improved by the modification with silver. Moreover, the photodegradation intermediates and pathways are demonstrated by trapping experiments and density functional theory calculations. To quantitatively determine the concentration of methyl orange, a partial least squares model was built using RGB values and the concentration of a methyl orange solution. This finding provides a new idea to fabricate a sensor for point-of-care test of organic dyes in the field of environmental applications.

Fabrication of Mo-doped TiO2 nanotube arrays photocatalysts: The effect of Mo dopant addition time to an aqueous electrolyte on the structure and photocatalytic activity

Molybdenum-doped TiO2 nanotubes (TNTs) samples were synthesized in two routes by a single-step anodization method for a sustainable photocatalytic process. This study aimed to evaluate the effectiveness of dopant adding time on the photocatalytic activity of TiO2 nanotubes. In the first route, molybdenum dopant with three initial concentrations of 0.02, 0.06, and 0.1 M was added to the electrolyte at the beginning of the anodizing process, while in the second route, molybdenum precursors were added to the electrolyte after 30 min from the beginning of anodization (after the formation of nanotubes). The structural characteristics of Mo-doped TNTs in both routes were compared with non-doped nanotubes using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. The optical properties and efficiency of electron-hole pairs separation and charge transfer kinetics were evaluated by diffuse reflectance spectroscopy (DRS) and electrochemical impedance spectroscopy (EIS) methods. Moreover, methylene blue (MB) degradation under visible light was performed to investigate the photocatalytic activity. The results indicate that the second route of synthesis causes the formation of well-aligned TNTs while increasing the Mo concentration will destroy the tube structure in some places on the surface and cause the loss of structural order, in the first path. By Mo doping into TiO2 nanotubes, the optical properties are improved and the absorption edge of TiO2 nanotubes was extended to the visible region. The Mo-doped samples in the second route with concentrations of 0.1 M exhibited the highest visible light absorption and charge transfer rate among all the Mo-doped samples. Also, Mo-doped samples had better photocatalytic activity than non-doped samples in MB degradation and the highest photocatalytic efficiency was related to the Mo-doped sample synthesized in the second route with a Mo concentration of 0.1 M.

Investigation of photocatalytic activity of TiO2 nanotubes synthesized by hydrothermal method

TiO2 nanotubes were synthesized by hydrothermal reaction using commercially available TiO2 powder at 150 °C for 24 h. The transmission electron microscopy, X-ray diffraction, nitrogen adsorption-desorption isotherms and Fourier Transform-Infrared spectroscopy were used to characterize the nanotubes. Anatase phase was not transformed into rutile phase in the range of calcination temperature studied. Increase in calcination temperature result in enhancement of crystallinity and reduction in BET surface area. Photocatalytic removal of Reactive Red 239 (RR239) was investigated using prepared TiO2 nanotubes. Effects of pH, TiO2 nanotube dosage, initial RR239 concentration and calcination temperature were studied. 99%, 97% and 55% of removal efficiency values were attained at pH = 3, 5 and 7, respectively within 60 min or reaction time. With an increase in dosage of TiO2 nanotube in the range of 0.25–0.75 g dm−3, removal rate increased by a steeper slope. Complete removal of RR239 was observed at 20 mg dm−3 RR239 concentrations within 30 min but longer time was required for complete removal at higher concentrations. Langmuir-Hinshelwood kinetic expression was proposed based on nonlinear regression analysis. The removal efficiency of nanotubes calcined at 300 − 450 °C significantly increased but further increase in calcination temperature caused to decrease the efficiency.100% and 85% removal efficiency values were observed using actual solar light within 120 min of reaction time in July and January, respectively. Experiments conducted with scavengers showed that holes and adsorbed hydroxyl radicals were the major species involved in removal of RR239. A pathway for degradation of RR239 was suggested according to detected intermediate compounds.

Enhanced photoelectrochemical characteristic of TiO2 nanotubes via surface plasma treatment

Photoelectrochemical (PEC) water splitting is one of promising green method to generated renewable energy such as hydrogen. To realize PEC for hydrogen production, it is indispensable to develop a high-performance photocatalyst. In this study, a facile surface engineering using plasma treatment is developed for TiO2 nanotubes where the surface becomes porous and partially amorphized resulting in the enhanced photocatalytic activity. Moreover, electronic configuration of TiO2 nanotubes were effectively modulated via ion plasma treatment, which improves charge transport and light-absorption in TiO2 nanotubes. Electronic modulations in combination with the intriguing nanoporous structure after ion plasma treatment leads to significantly enhanced photocatalytic activity of TiO2 nanotubes, which can be applied for designing next high-performance photocatalysts.

Enhanced photocatalytic activity of graphene/TiO2 nanotubes composites prepared by wet transfer method

To enhanced photocatalytic activity of TiO2 nanotubes, graphene was transferred on the surface of TiO2 nanotubes by wet transfer method. The results showed that the introduction of graphene reduced the band gap of composites and inhibited the recombination of photoinduced electrons and holes. Therefore, the degradation rate of the graphene/TiO2 nanotubes composites is about 44% higher than that of the TiO2 nanotubes. It was proved that the photoinduced holes play an important role in the degradation process of methylene blue by trapping experiments. This work provides a new pathway for preparing semiconducting TiO2 based catalysts with enhanced photocatalytic activity. Highlights The graphene/TiO2 nanotubes composites were prepared by simple anodic oxidation and wet transfer method, which is convenient for large-scale production. The introduction of graphene can effectively reduce the band gap and inhibit the recombination of photoinduced electrons and holes. The photocatalytic performance of graphene/TiO2 nanotubes composites is obviously higher than that of TiO2 nanotubes. The results of trapping experiments showed that the photoinduced holes play an important role in the degradation of methylene blue.

Enhanced photocatalytic activity of TiO2 nanotubes decorated with erbium and reduced graphene oxide

Highly ordered TiO2 nanotubes (TNTs) decorated with erbium and reduced graphene oxide (rGO) were prepared through anodization, electrochemical deposition, and/or drop-casting. The characteristics of the as-prepared photocatalysts were identified, and the photoelectrochemical and photocatalytic properties were investigated through water splitting and organic degradation. All samples (pure TNTs, Er-TNTs, rGO-TNTs, and rGO-Er-TNTs) were prepared in the anatase phase without any changes in the crystalline phase or impurities. The ternary rGO-Er-TNT photocatalyst exhibited the best performance, with an increased hydrogen evolution rate of 115.37 μmol cm-2h−1, methylene blue degradation of 91.58%, and photoconversion efficiency of 2.3% (0 V vs. reversible hydrogen electrode). The increased photocatalytic efficiency can be attributed to the combination of enhanced optoelectronic properties and the path for the separation of charge carriers by erbium and rGO. In this study, high-potential solar-active photocatalysts were achieved through the synergistic effect owing to the combination of Er and rGO with TiO2 nanotubes.

Photoelectrochemical, photocatalytic and electrochemical hydrogen peroxide production using Fe/S-codoped TiO2 nanotubes as new visible-light-absorbing photocatalysts

Codoping of TiO2 nanotube with iron and sulfur considerably improved the photocatalytic and photoelectrocatalytic preparation of hydrogen peroxide using TiO2 in the absence of organics scavengers. One-step anodization of titanium was used to synthesize Fe-doped, S-doped and Fe/S-codoped TiO2 nanotubes. FE-SEM, TEM, XRD, EDX and EDX-Mapping analyses were used to characterize the structure of the nanomaterials prepared. The photoelectrochemical characteristics of the doped and codoped titanium dioxide electrodes were studied under xenon lamp illumination in 0.1 M aqueous solution of potassium hydrogen phthalate. A maximum photocurrent density of 130 µA/cm2 was shown by Fe/S-codoped TiO2 nanotube electrode (sample Fe3S-TNT), which is 13 times greater than that of undoped TiO2 nanotube. H2O2 production remarkably increased by the simultaneous application of the bias potential and light irradiation compared with photocatalytic and electrocatalytic H2O2 preparation. According to the results, more photogenerated electrons are produced with the help of bias potential and the recombination of photogenerated electron–hole pairs is reduced in photoelectrocatalytic (PEC) production of hydrogen peroxide. Therefore, more electrons are available to reduce oxygen and thus more hydrogen peroxide is produced. In this work, a novel method has been developed to improve the photocatalytic activity of TiO2 nanotubes by codoping of iron and sulfur, and new insights into the development of a photoelectrocatalytic system for H2O2 synthesis are provided.

Preparation and photocatalytic activity of TiO2 nanotube arrays prepared on transparent spinel substrate

TiO2 nanotubes (TNTs) were prepared on transparent spinel (MgAl2O4) ceramic material by anodic oxidation of magnetron sputtered Ti layer. The properties of TNTs were compared with nanotubes produced on other three different substrates, Si wafer, polymeric Kapton film, and Ti foil. The photocatalytic activity of TNTs was tested by the removal of two model pollutants rhodamine B (RhB) and bisphenol A (BPA). Depending on the used substrate, the efficiency of TNTs in the degradation of both pollutants increases in the order of Kapton < spinel < Si < Ti. Nanotubes grown on Ti foil exhibited the best photocatalytic activity reaching 88% for the removal of RhB and 36% for the removal of BPA. The degradation rates of RhB could be well described by the pseudo-first order reaction, while the degradation of BPA could be better fitted with fractional first-order kinetic model. The calculations of residual stresses and deformations in the prepared materials with TNT surface layer showed that the composite with spinel substrate is the most stable structure with minimal warping of the laminate.

Recent Progress in Anodic Oxidation of TiO2 Nanotubes and Enhanced Photocatalytic Performance: A Short Review

By adjusting the oxidation voltage, electrolyte, anodizing time and other parameters, TiO2 nanotubes with high aspect ratio can be prepared by oxidation in organic system because anodic oxidation method has the advantage of simple preparation process, low material cost and controllable morphology. This review focusses on the influence of anodizing parameters on the morphology of TiO2 nanotube arrays prepared by anodizing. In order to improve the photocatalytic activity of TiO2 nanotubes under visible light and to prolong the life of photo-generated carriers, the research status of improving the photocatalytic activity of TiO2 nanotubes in recent years is reviewed. This review focusses on the preparation and modification of TiO2 nanotubes by anodic oxidation, which is helpful to understand the best structure of TiO2 nanotubes and the appropriate modification methods, thus guiding the application of TiO2 nanotubes in practical photocatalysis. Finally, the development of TiO2 nanotubes is prospected.

FABRICATION AND PHOTOCATALYTIC ACTIVITY OF TiO2 NANOTUBES BY HYDROTHERMAL TREATMENT

TiO2 nanotubes were prepared by hydrothermal method using P25 as raw material. The effect of hydrothermal duration and calcination temperature on the crystal structure and morphology of intermediate product and TiO2 was investigated by XRD, SEM and TEM. The photocatalytic activity of TiO2 was evaluated by the degradation of methylene blue. The result revealed the formation process of nanotube and indicated that the photocatalytic activity of TiO2 nanotubes strongly depended on the calcination temperature. The crystallinity of nano-TiO2 was gradually improved with the increasing calcination temperature up to 750 oC resulting in the increase of degradation rate of methylene blue. With further increase in calcination temperature, anatase TiO2 began to transform into rutile phase and the nanotubes completely transformed to particles, leading to the decrease of photocatalytic activity. It was found that TiO2 annealed at 750 oC showed the highest degradation rate, resulting from the excellent crystallinity of anatase phase and nanorod structure.

Fabrication and photocatalytic performance of C, Pt‐comodified TiO 2 nanotubes

Compared with common TiO2 powder, TiO2 nanotubes can exhibit better catalytic performance for their high specific surface area. By using hydrogen TiO2 nanotubes synthesised via the hydrothermal process as carriers, carbon and platinum co-modified TiO2 nanotubes (C-Pt/TiO2NTs) were prepared via impregnation–photoreduction method in this study. X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and infrared spectrum were used to characterise the structure and composition of the prepared samples. Their catalytic activities for degrading methyl orange under ultraviolet (UV) illumination and simulated sunlight were evaluated. The influences and mechanism of dopants and their contents on the catalysts’ activity were investigated. Obtained results indicated that the modification can improve the photocatalytic activity of TiO2 nanotubes under both UV light and simulated sunlight. Among them, C-Pt/TiO2NTs with 0.5 wt% Pt exhibited the best performance.

Synthesis of N and S Co-doped TiO2 Nanotubes for Advanced Photocatalytic Degradation of Volatile Organic Compounds (VOCs) in Gas Phase

In this study, sol–gel combining with hydrothermal methods were successfully used to synthesize N and S co-doped TiO2 nanotubes (N@S-TiO2 NTT) for efficient photocatalytic degradation of volatile organic compounds (VOCs). The obtained characterization results indicated that the synthesized N@S co-doped TiO2 existed as nanotubes. Specific surface areas of these synthesized nanotubes was greatly that of these nanoparticles. The largest surface area recorded at N@S-TiO2 nanotubes was 105.3 m3/g. FTIR spectrum results showed that the presence of N–H and S–O bond, which confirmed that nitrogen and sulfur were successfully doped into TiO2 lattice. We also investigated that N@S dopants significantly improved the photocatalytic activity of TiO2 nanotubes for efficient degradation of gaseous VOCs. Therefore, photocatalytic activity for VOCs degradation by the N@S-TiO2 nanotubes was greater than that by the undoped TiO2 nanotube. Optimized humidity for degradation of VOCs was medium condition (55–70%). Under dry conditions, lack of water for hydroxyl radical production led to decrease in photocatalytic activity. Under humidity conditions, the excess water molecules competed with VOCs for adsorbing on material surface leading to decrease in photocatalytic degradation efficiency. Under the optimized humidity, the highest photocatalytic efficiency of the synthesized N@S-TiO2 nanotubes for degradation of gaseous VOCs for 3 h was approximately 94%. The VOCs degradation capacity by the synthesized N@S-TiO2 nanotubes was approximately 90 (ppm/g h).

Construction of g-C3N4/TiO2 nanotube arrays Z-scheme heterojunction to improve visible light catalytic activity

A simple anodic oxidation method was used to prepare TiO2 nanotubes (TNTs), and calcined at 500 °C with urea to prepare g-C3N4/TNTs (CN/TNTs) composites. The photocatalytic activity of TNTs was improved by constructing a Z-scheme transfer mechanism. The results show that 2 g CN/TNTs greatly improves the separation efficiency of electron-hole pairs and reduces its recombination efficiency, and the visible light absorption also undergoes a significant redshift. The degradation of rhodamine B can reach 96.3 %, and the degradation rate is 0.0195min−1. The sample has good stability and can be used repeatedly without losing activity. In the CN/TNTs system, h+, O2- and OH are active species.

Visible/solar-light driving photocatalytic activity of TiO2 nanotubes upon coating with phosphotungstate hybrid

ABSTRACT This study introduces coloured titanium dioxide nanotubes by phosphotungstate hybrid as an activated photocatalyst for the degradation of organic pollutants under visible and solar light irradiation. The prepared coloured TiO2 nanotubes are characterised by Fourier transform infrared spectroscopy, powder X-ray diffraction, diffuse reflectance spectrometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy and N2 adsorption–desorption isotherms. Then, performance of this catalyst is evaluated using decolourisation of model dyes methylene blue (MB), methyl orange (MO) and mixtures of MB and MO solutions. It is confirmed that the presence of coloured hybrid in the context of white TiO2 enables photocatalytic activity in the visible and solar light. Also, its noticeable efficiency is verified in the photodegradation of organic dyes and its reusability without any significant loss of activity. Removal is via combination of adsorption and then photocatalytic degradation through oxidation by •OH radicals or reduction by reduced polyoxometalate. While the visible light is not able to degrade alone MO solution in the presence of composite, it degrades the MO mixed with MB solution.

Effect of Temperature and Anodizing Potential on the Photocatalytic Activity of TiO₂ Nanotubes.

In this research, the effect of temperature and anodizing voltage on the morphology and photocatalytic activity of TiO₂ nanotubes which were fabricated in the organic electrolyte containing sodium carbonate as an additive was investigated. The FESEM results indicate that by increasing temperature, the growth rate, wall thickness of nanotubes decreased and disordered nanotube was fabricated. Besides, the photocatalytic activity of nanotubes was decreased as well. Furthermore, enhancing the anodizing voltage from 30 to 50 V leads to improvement of morphology and photocatalytic activity of TiO₂ nanotubes.