Photoelectrochemical water splitting and simultaneous photoelectrocatalytic degradation of organic pollutant on highly smooth and ordered TiO2 nanotube arrays

The photoelectrochemical water splitting and simultaneous photoelectrocatalytic degradation of organic pollutant were achieved on TiO₂ nanotube electrodes with double purposes of environmental protection and renewable energy production under illumination of simulated solar light. The TiO₂ nanotube arrays (TiO₂ NTs) were fabricated by a two-step anodization method. The TiO₂ NTs prepared in two-step anodization process (2-step TiO₂ NTs) showed much better surface smoothness and tube orderliness than TiO₂ NTs prepared in one-step anodization process (1-step TiO₂ NTs). In the photoelectrochemical water splitting and simultaneous photoelectrocatalytic decomposition process, the 2-step TiO₂ NTs electrode showed both highest photo-conversion efficiency of 1.25% and effective photodecomposition efficiency with existing of methylene blue (MB) as sacrificial agent and as pollutant target. Those results implied that the highly ordered nanostructures provided direct pathway and uniform electric field distribution for effective charges transfer, as well as superior capabilities of light harvesting.     

A facile one-step preparation of hierarchically-structured TiO2 nanotube array photoanodes with enhanced photocatalytic activity

Hierarchically structured TiO₂ (HST) films composed of top porous nanoparticle layer and underneath nanotube array layer are obtained by an anodization method on fluorine doped tin oxide surfaces. Compared with the TiO₂ nanotube arrays photoanode on Ti substrate, the HST photoanode exhibits a higher photoelectrocatalytic activity towards the oxidation of water and organics (e.g., glucose).     

Pyrite (FeS2)-decorated 1D TiO2 nanotubes in a bilayer as a sustainable photoanode for photoelectrochemical water splitting activity

Herein, FeS₂@TiO₂ nanotubes photocatalyst was prepared by electrochemical anodization method followed by successive ionic layer adsorption and reaction method, and then finally annealed in a tube furnace for homogenous crystallization. The surface morphology, elemental composition, optical properties, and crystalline structure of the prepared FeS₂@TiO₂ nanocomposite were found out by performing scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, UV–Vis diffuse reflectance spectroscopy, and fluorescence spectroscopy, respectively, while bonds vibrations and various functional groups' presence were analyzed using Raman and Fourier transform infrared spectroscopy. A higher photocurrent density of 1.59 mA/cm² at 0.3 V versus reference electrode of Ag/AgCl (1.23 V versus reversible hydrogen electrode) using 100 mW/cm² intensive light source was shown by 15-FeS₂@TiO₂ nanotubes (uniformly loaded photoanode) while donor density (N_D) of 3.68 × 10⁻¹³ cm⁻³ as compared to pure TiO₂ NTs (0.09 mA/cm²), 05-FeS₂@TiO₂ NTs (0.19 mA/cm²), 10-FeS₂@TiO₂ NTs (0.53 mA/cm²) and 20-FeS₂@TiO₂ NTs (0.61 mA/cm²), respectively. The exceptional photoelectrochemical activity results were attributed to the homogenous integration of FeS₂ that not only increase the charge separation but also, intensively interacted with the substrate (TiO₂ nanotubes), which results in an excellent photoelectrochemical activity.     

Significant enhancement of the photoelectrochemical activity of TiO2 nanotubes

In the present work, we report on a facile and effective approach to significantly enhance the photocatalytic activity of TiO₂ nanotubes. The TiO₂ nanotubes prepared by the electrochemical oxidation of titanium in dimethyl sulfoxide (DMSO) with 2% HF were treated in a methanol solution under UV light irradiation. In comparison with the untreated TiO₂ nanotubes, the treatment resulted in a dramatic increase in the donor density of the TiO₂ nanotubes by approximately 3 orders of magnitude. The treated TiO₂ nanotubes exhibited a 15-fold enhancement in photocurrent and a 6.8-fold increase in the photoelectrochemical degradation of 4-nitrophenol, significant for hydrogen generation and wastewater treatment.     

A self-cleaning nonenzymatic glucose detection system based on titania nanotube arrays modified with platinum nanoparticles

In the present work, we show how TiO₂ nanotube layers that are decorated with a Pt-nanoparticle coating can be fabricated and operated as a reusable glucose sensing system. A critical amount of Pt coating is essential not only to provide an effective catalyst for glucose oxidation but also to establish a sufficient conductivity along TiO₂ nanotube walls to allow an efficient amperometric operation of the electrode. On such an electrode the self-cleaning photocatalytic features of TiO₂ can be maintained and used to re-establish poisoned activity of the Pt particles.     

Preparation and characterization of Zr doped TiO2 nanotube arrays on the titanium sheet and their enhanced photocatalytic activity

This paper described a new method for the preparation of Zr doped TiO₂ nanotube arrays by electrochemical method. TiO₂ nanotube arrays were prepared by anodization with titanium anode and platinum cathode. Afterwards, the formed TiO₂ nanotube arrays and Pt were used as cathode and anode, respectively, for preparation of Zr/TiO₂ nanotube arrays in the electrolyte of 0.1 M Zr(NO₃)₄ with different voltage and post-calcination process. The nanotube arrays were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and UV-Vis diffusion reflection spectra (DRS). The photocatalytic activities of these nanotubes were investigated with Rhodamine B as the model pollutant and the results demonstrated that the photocatalytic efficiency of Zr doped TiO₂ nanotubes was much better than that of TiO₂ nanotubes under UV irradiation. Zr/TiO₂ nanotube arrays doped at 7 V and calcined at 600 °C (denoted as TiO₂-7 V-600) achieved the best photocatalytic efficiency and the most optimal doping ratio was 0.047 (Zr/Ti). TiO₂-7 V-600 could be reused for more than 20 times and maintained good photocatalytic activities.     

TiO_2纳米管双室光电化学池光催化制氢的研究

以阳极氧化法在纯钛表面制备了高度有序的Ti O2纳米管阵列,并通过SEM观察其表面形貌。采用双室光电化学池制氢体系,利用太阳光照Ti O2产生的光电压与双室电解液p H差产生的化学偏压的协同效应,不施加外加电压,可直接在阴极室还原制取氢气。通过在碱性电解液中添加乙二醇为电子给体,将光解水制氢与有机物的降解耦合为一体,提高太阳能的利用率,同时考察了阳极室电解液中添加不同含量乙二醇对Ti O2纳米管光阳级的光电化学性能及产氢量的影响。实验结果表明,乙二醇的添加降低了光生电子-空穴对的复合几率,使Ti O2纳米管的光电流、光电压、产氢量得到显著提高。当添加乙二醇的浓度为10vol%时光电流达到13.7 m A·cm-2,无外加电压条件下,双室光电化学池中的产氢速率最高达到3.8μmol·min-1·cm-2。     

TiO2纳米管双室光电化学池光催化制氢的研究

以阳极氧化法在纯钛表面制备了高度有序的TiO₂纳米管阵列,并通过SEM观察其表面形貌。采用双室光电化学池制氢体系,利用太阳光照TiO₂产生的光电压与双室电解液pH差产生的化学偏压的协同效应,不施加外加电压,可直接在阴极室还原制取氢气。通过在碱性电解液中添加乙二醇为电子给体,将光解水制氢与有机物的降解耦合为一体,提高太阳能的利用率,同时考察了阳极室电解液中添加不同含量乙二醇对TiO₂纳米管光阳级的光电化学性能及产氢量的影响。实验结果表明,乙二醇的添加降低了光生电子-空穴对的复合几率,使TiO₂纳米管的光电流、光电压、产氢量得到显著提高。当添加乙二醇的浓度为10vol%时光电流达到13.7mA·cm^-2,无外加电压条件下,双室光电化学池中的产氢速率最高达到3.8μmol·min^-1·cm^-2。     

High activity of novel Pd/TiO2 nanotube catalysts for methanol electro-oxidation

Electro-oxidation of methanol in sulfuric acid solution was studied using palladium well-dispersed on titanium nanotubes, in relation to methanol oxidation processes in the direct oxidation methanol fuel cell. Pd dispersed on titania nanotubes, which leads to high surface area substrates, showed excellent catalytic activities compared to those of pure Pd and Pd-TiO₂ nanoparticles. TEM results show a narrow distribution of TiO₂ nanoparticles whose particle size is about 10 nm, and uniform nano-sized TiO₂ nanotubes with 10 nm in diameters are seen from HRTEM . A homogeneous structure in the composite nanomaterials is indicated by XRD analysis. The composite electrode activities were measured by cyclic voltammetry (CV) and at 25 °C it was found that 3 wt% Pd in titania nanotubes had the best activity for methanol oxidation.     

Liquid phase deposition of hemoglobin/SDS/TiO2 hybrid film preserving photoelectrochemical activity

This work demonstrates that liquid phase deposition (LPD) technique provides a novel approach to the immobilization of hemoglobin (Hb) in TiO(2) film for studying the direct electron transfer of Hb. Using the LPD process, a hybrid film composed of Hb, TiO(2) and sodium dodecylsulfonate (SDS) is successfully prepared on the electrode surface. The surface morphology of as-deposited Hb/SDS/TiO(2) film shows a flower-like structure. The cyclic voltammetric measurement indicates that the LPD hybrid film facilitates the electron transfer of Hb, which yields a pair of redox peaks prior to the characteristic voltammetric peaks of TiO(2). Due to the electrocatalytic activity of Hb towards H(2)O(2), the Hb/SDS/TiO(2) hybrid LPD film can be utilized as an H(2)O(2) sensor, showing a sensitive response linearly proportional to the concentration of H(2)O(2) in the range of 5.0×10(-7)-4.0×10(-5) mol/L. At the same time, the Hb/SDS/TiO(2) hybrid film preserves the photoelectrochemical activity of TiO(2). The photovoltaic effect on the electrochemical behavior of Hb/SDS/TiO(2) film is observed after long-time UV irradiation on the film, which could improve the calibration sensitivity for H(2)O(2).     

Fabrication and photocatalytic activity of high-efficiency visible-light-responsive photocatalyst ZnTe/TiO2 nanotube arrays

A new ZnTe modified TiO₂ nanotube (NT) array catalyst was prepared by pulse potential electrodeposition of ZnTe nanoparticles (NPs) onto TiO₂ NT arrays, and its application for photocatalytic degradation of anthracene-9-carboxylic acid (9-AnCOOH) was investigated. The even distribution of ZnTe NPs was well-proportionately grown on the top surface of the TiO₂ NT while without clogging the tube entrances. Compared with the unmodified TiO₂ NT, the ZnTe modified TiO₂ NT (ZnTe/TiO₂ NT) showed significantly enhanced photocatalytic activity towards 9-AnCOOH under simulated solar light. After 70 min of irradiation, 9-AnCOOH was degraded with the removal ratio of 45% on the bare TiO₂ NT, much lower than 80%, 90%, and 100% on the ZnTe/TiO₂ NT with the ZnTe NPs prepared under the pulsed “on” potentials of −0.8, −1.0, and −2.0 V, respectively. The increased photodegradation efficiency mainly results from the improved photocurrent density as results of enhanced visible-light absorption and decreased hole-electron recombination due to the presence of narrow-band-gap p-type semiconductor ZnTe.     

TiO2 nanorods branched on fast-synthesized large clearance TiO2 nanotube arrays for dye-sensitized solar cells

A large clearance TiO₂ nanotube arrays (LTAs) has been synthesized by a not more than 12 h anodization duration and based on this a branched TiO₂ nanotube arrays (BLTs) has been achieved through TiO₂ nanorods branch-like grown on the LTAs. Some key factors and probable mechanisms of the fabrication processes on two novel nanoarchitectures are discussed. Exhilaratingly, it is found that the obtained LTAs has demonstrated large pore diameter and void spaces (pore diameter ∼350 nm; void spaces ∼160 nm; and tube length ∼3.5 μm), and the synthesized hierarchical BLTs, compared with conventional TiO₂ nanotube arrays, has shown a much stronger dye absorption performance and an approximately double of the solar cell efficiency (in our case from 1.62% to 3.18% under simulated AM 1.5 conditions).     

Bi2S3/CdSe共修饰TiO2纳米管膜的构建及其光电化学阴极保护效应

为获得良好光电化学性能的TiO₂半导体复合膜,采用Bi₂S₃和CdSe对TiO₂纳米管膜进行共修饰。以阳极氧化法在Ti表面先制备TiO₂纳米管膜,再通过恒电流电沉积和连续离子层吸附反应在纳米管表面依次沉积CdSe和Bi₂S₃,构建了具有级联能带结构的Bi₂S₃/CdSe共修饰的TiO₂纳米管复合膜。结果表明,Bi₂S₃/CdSe/TiO₂纳米管复合膜对可见光吸收显著增强,光电化学性能大幅度提高。白光照射下,复合膜的光电流密度为670μA·cm^-2,达到了纯TiO₂纳米管膜的17.6倍。Bi₂S₃/CdSe/TiO₂复合膜作为光阳极可使0.5 mol·L^-1 NaCl溶液中的4...     

The Preparation and Characterization of La Doped TiO2 Nanotubes and Their Photocatalytic Activity

La-doped TiO₂ nanotubes (La/TiO₂ NTs) were prepared by the combination of sol-gel process with hydrothermal treatment. The prepared samples were characterized by using transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectra, and ultraviolet-visible spectra. The photocatalytic performance of La/TiO₂ NTs was studied by testing the degradation rate of methyl orange under ultraviolet (UV) irradiation. The results indicated La/TiO₂ NTs calcined at 300°C consisted of anatase as the unique phase. The absorption spectra of the La/TiO₂ NTs showed a stronger absorption in the UV range and a slight red shift in the band gap transition than that of pure TiO₂ nanotubes. The photocatalytic performance of TiO₂ NTs could be improved by the doping of lanthanum ions, which is ascribed to several beneficial effects the formation of Ti-O-La bond and charge imbalance, existing of oxygen defects and Ti³⁺ species, stronger absorption in the UV range and a slight red shift in the band gap transition, as well as higher equilibrium dark adsorption of methyl orange. 0.75 wt% La/TiO₂ NTs had the best catalytic activity.     

Thermal behaviour study of some sol-gel TiO2 based materials

Among the great number of sol-gel materials prepared, TiO₂ holds one of the most important places due to its photocatalytic properties, both in the case of powders and coatings. Impurity doping is one of the typical approaches to extend the spectral response of a wide band gap semiconductor to visible light. This work has studied some un-doped and Pd-doped sol-gel TiO₂ nanopowders, presenting various surface morphologies and structures. The obtained powders have been embedded in vitreous TiO₂ matrices and the corresponding coatings have been prepared by dipping procedure, on glass substrates. The relationship between the synthesis conditions and the properties of titania nanosized materials, such as thermal stability, phase composition, crystallinity, morphology and size of particles, and the influence of dopant was investigated. The influence of Pd on TiO₂ crystallization both for supported and unsupported materials was studied (lattice parameters, crystallite sizes, internal strains). The hydrophilic properties of the films were also connected with their structure, composition and surface morphology. The methods used for the characterization of the materials have been: simultaneous thermogravimetry and differential thermal analysis, powder X-ray diffraction, electron microscopy (TEM, SAED) and AFM.     

In vitro corrosion study of different TiO2 nanotube layers on titanium in solution with serum proteins

Titanium oxide nanotubes prepared by anodization have received considerable attention in the biomaterials domain. The objective of this study was to demonstrate the electrochemical behavior of different diameter TiO(2) nanotube layers on titanium in phosphate buffered saline (PBS) and Dulbecco's minimum essential medium+10% fetal calf serum (D-FCS) using open circuit potentials (OCP), electrical impedance spectroscopy (EIS), and a potentiodynamic polarization test. The results showed that the nanotubes had higher OCP, higher resistance of the inter barrier layer (R(b)), and lower I(pass) in the two test solutions compared to the smooth Ti, especially the 30 nm diameter nanotubes. The corrosion resistance of the nanotubes in D-FCS was higher than in PBS because of protein adsorption from the D-FCS solution as suggested by scanning electron microscope (SEM) images. In addition, protein aggregates of 30 nm diameter nanotubes caused the model of EIS spectra to transform from two-layer to three-layer. The corrosion behavior of the nanotubes for use as a dental implant material is discussed.     

DFT Study of Methylene Blue Adsorption on ZnTiO3 and TiO2 Surfaces (101)

The search for alternative materials with high dye adsorption capacity, such as methylene blue (MB), remains the focus of current studies. This computational study focuses on oxides ZnTiO₃ and TiO₂ (anatase phase) and on their adsorptive properties. Computational calculations based on DFT methods were performed using the Viena Ab initio Simulation Package (VASP) code to study the electronic properties of these oxides. The bandgap energy values calculated by the Hubbard U (GGA + U) method for ZnTiO₃ and TiO₂ were 3.17 and 3.21 eV, respectively, which are consistent with the experimental data. The most favorable orientation of the MB adsorbed on the surface (101) of both oxides is semi-perpendicular. Stronger adsorption was observed on the ZnTiO₃ surface (−282.05 kJ/mol) than on TiO₂ (–10.95 kJ/mol). Anchoring of the MB molecule on both surfaces was carried out by means of two protons in a bidentate chelating (BC) adsorption model. The high adsorption energy of the MB dye on the ZnTiO₃ surface shows the potential value of using this mixed oxide as a dye adsorbent for several technological and environmental applications.     

Electrochemical wettability control on conductive TiO2 nanotube surfaces modified with a ferrocene redox system

This work reports on an electrochemical system which allows the control of surface wettability properties by voltage induced changes in contact angle (Θ) of ΔΘ  50°. For this we used conductive TiO₂ nanotubular layers that were modified with ferrocene coupled to the TiO₂ surface via triethoxysilane. To enhance the hydrophobic character of the nanotubular TiO₂ surface, also mixed organic monolayers namely perfluorotriethoxysilane, were explored. Formation of the ferrocene and mixed organic monolayer was confirmed by X-ray-photoelectron-spectroscopy (XPS). Contact angle combined with electrochemical measurements show that ferrocene in these monolayers can successfully be switched from Fe²⁺ to Fe³⁺ and that this change in the redox state considerably alters the wetting properties. Using a conductive nanotube substrate allows us to amplify this change by a factor of more than 10, and thus this surface can be used to trigger significant wetting alterations.     

Graphene-modified TiO2 nanotube arrays as an adsorbent in micro-solid phase extraction for determination of carbamate pesticides in water samples

Graphene is a good adsorbent for organic pollutants, especially for compounds containing benzene rings. When used in TiO₂ nanotube arrays for micro-solid phase extraction (μ-SPE), the combination of graphene’s strong adsorptive properties with its good separation capabilities results in excellent sample preconcentration performance. In the present study, graphene-modified TiO₂ nanotube arrays were prepared by electrodeposition using a cyclic voltammetric reduction method. Four carbamate pesticides, including metolcarb, carbaryl, isoprocarb, and diethofencarb, were used as model analytes to validate the enrichment properties of the prepared adsorbent in μ-SPE. Factors affecting the enrichment efficiency of the μ-SPE procedure were optimized and included sample pH, elution solvents, salting-out effect, adsorption time and desorption time. Under optimal conditions, graphene-modified TiO₂ nanotube arrays exhibited excellent enrichment efficiency for carbamate pesticides. The detection limits of these carbamate pesticides ranged from 2.27 to 3.26 μg L⁻¹. The proposed method was validated using four environmental water samples, and yields of pesticides recovered from spiked test samples of the four analytes were in the range of 83.9–108.8%. These results indicate that graphene-modified TiO₂ nanotube arrays exhibit good adsorption to the target pollutants, and the method described in this work could be used as a faster and easier alternative procedure for routine analysis of carbamate pesticides in real water samples.