Enhanced inactivation of E. coli bacteria using immobilized porous TiO2 photoelectrocatalysis

Immobilized TiO₂ nanotube electrodes with high surface areas were grown via electrochemical anodization in aqueous solution containing fluoride ions for photocatalysis applications. The photoelectrochemical properties of the grown immobilized TiO₂ film were studied by potentiodynamic measurements (linear sweep voltammetry), in addition to the calculation of the photocurrent response. The nanotube electrode properties were compared to mesoporous TiO₂ electrodes grown by anodization in sulfuric acid at high potentials (above the microsparking potential) and to 1 g/l P-25 TiO₂ powder. Photocatalyst films were evaluated by high resolution SEM and XRD for surface and crystallographic characterization. Finally, photoelectrocatalytic application of TiO₂ was studied via inactivation of E. coli. The use of the high surface area TiO₂ nanotubes resulted in a high photocurrent and an extremely rapid E. coli inactivation rate of ∼10⁶ CFU/ml bacteria within 10 min. The immobilized nanotube system is proven to be the most potent electrode for water purification.     

Cyclic voltammetry studies of TiO2 nanotube arrays electrode: Conductivity and reactivity in the presence of H and aqueous redox systems

In this paper, we use cyclic voltammetry to investigate the effect of protons on the conductivity and reactivity of TiO₂ nanotube array (NTA) electrodes in an aqueous redox system. The H⁺ ion can change the TiO₂ nanotube (anatase phase) surface states for electrons transfer. It can also act as an intermediate state for electron transfer to the acceptor species in the electrolyte surrounding the TiO₂. The higher the concentration of H⁺ ions in the aqueous electrolyte, the easier it is for the electrons transfer from the TiO₂ to the electrolyte oxidized species. The reduction is facile, with a similar reduction potential for various acceptor species, but re-oxidation is not possible. It is apparently an electrochemical reduction involving a single-proton transfer and single-electron transfer. Based on this conclusion, an electrode (PB/Au/TiO₂ NTAs) was fabricated by means of electrodeposition. The electrode used to detect hydrogen peroxide. The sensitivity of the detector is high, and its the detection limit can be as low as 100 nM.     

Light energy storage and photoelectrochemical behavior of the titanate nanotube array/Ni(OH)2 electrode

A new kind of TiO₂ nanotube array/Ni(OH)₂ (TiO₂/Ni(OH)₂) composite electrode with the storage ability of light energy was prepared by the deposition of Ni(OH)₂ on the TiO₂ nanotube array, which was synthesized by anodizing Ti foils in an HF aqueous solution. SEM and XRD results showed that Ni(OH)₂ particles were well distributed on high density, well-ordered and uniform TiO₂ nanotube arrays. The photoelectrochemical properties of the TiO₂/Ni(OH)₂ electrode were investigated in NaHCO₃/NaOH buffer solution (pH 10) by means of UV-vis absorption spectra, cyclic voltammogram (CV) and photocurrent measurements. It was found that the TiO₂/Ni(OH)₂ electrode was highly sensitive to light and exhibited excellent photoelectrochromic properties. Upon UV irradiation, the photogenerated holes by TiO₂ nanotube arrays can oxidize Ni(OH)₂ to NiOOH, and thus the TiO₂/Ni(OH)₂ electrode can be photo-charged by light.     

Structural and photoelectrochemical characterization of TiO2 nanowire/nanotube electrodes by electrochemical etching

TiO₂ nanowire/nanotube electrodes were synthesized by anodization of titanium foils in ethylene glycol solution containing 0.5 wt% NH₄F and 1 wt% water at 60 V for 6 h. The microstructure and morphology of the asprepared electrodes were investigated by XRD and SEM. A possible formation mechanism and oxidation parameters of nanocomposite structure were discussed. The relationship between structural characteristics of TiO₂ nanowire/nanotube electrodes and its photoelectrochemical characterization were evaluated by electrochemical analyzer and photocatalytic degradation of methylene blue (MB) solution. Furthermore, these TiO₂ nanowire/nanotube electrodes promoted the photoelectrochemical characterization due to the larger surface areas, enhanced light harvesting and electron transport rate. The results show that photocurrent density of 1.44mA/cm² and photocatalytic degradation of 95.51% was achieved for TiO₂ nanowire/nanotube electrodes, which were 0.55mA/cm² and 20.52% higher than the TiO₂ nanotube electrodes under a similar condition, respectively.     

Effect of TiO2 doped Ni electrodes on the dielectric properties and microstructures of (Ba0.96Ca0.04)(Ti0.85Zr0.15)O3 multilayer ceramic capacitors

The effects of TiO₂-doped Ni electrodes on the microstructures and dielectric properties of (Ba_0.96Ca_0.04)(Ti_0.85Zr_0.15)O₃ multilayer ceramic capacitors (MLCCs) have been investigated. Nickel paste with a TiO₂ dopant was used as internal electrodes in MLCCs based on (Ba_0.96Ca_0.04)(Ti_0.85Zr_0.15)O₃ (BCTZ) ceramic with copper end-termination. The microstructures and defects were analysed by microstructural techniques (SEM/HRTEM) and energy-dispersive spectroscopy (EDS). The continuity of the electrode of the MLCC was measured using a scanning electron microscope, which showed that the continuity of the electrode for the MLCC with a TiO₂-doped Ni electrode was approximately 90%. However, continuity of the electrode for a conventional MLCC was below 80%. The continuity of the TiO₂-doped Ni electrode showed significant improvement in the MLCC, which was due to no reaction between Ni and BCTZ.     

Immobilization of horseradish peroxidase in three-dimensional macroporous TiO2 matrices for biosensor applications

Three-dimensional macroporous TiO₂ was synthesized by a sol-gel procedure using polystyrene colloidal crystals as templates. SEM showed that a face-centered cubic (FCC) 3D macroporous structure was obtained. Horseradish peroxidase (HRP) was successfully immobilized on the surface of an optically transparent electrode (OTE). Photoelectrochemical properties were characterized using a three electrodes system and an ultraviolet lamp. The HRP/TiO₂/OTE displays a rapid photocurrent response, approximately 178.7 nA, under UV illumination (380 nm). The sensitivity of H₂O₂ detection was 70.04 μA/mM without UV illumination, and it increased to 102.97 μA/mM when illuminated by UV. The amperometric response was also enhanced. The high response was due to the good biocompatibility of TiO₂ and excellent photoelectrical property and the large effective surface of the three-dimensionally ordered macroporous structure.     

The photoelectrochemical properties of N3 sensitized CaTiO3 modified TiO2 nanocrystalline electrodes

The preparation of nanoporous TiO₂ electrodes modified with CaTiO₃ layers and their application in dye-sensitized solar cells (DSSCs) were reported. The as-prepared TiO₂/CaTiO₃ electrodes were characterized by XPS and XRD, indicating that a thin CaTiO₃ layer was formed on the surface of nanoporous TiO₂ electrodes. Compared with bare TiO₂ electrodes, CaTiO₃ modified TiO₂ electrodes presented more dye adsorption. Moreover spectroelectrochemical studies showed that the concentration of free electrons in the conduction band of TiO₂ was remarkably increased after surface modification. As a result, the photocurrent and photoelectric conversion efficiency of the modified electrodes were increased. The influence of the thickness of CaTiO₃ layer on the photoelectrochemical properties of the modified electrodes was investigated. Experiment results showed that proper thickness of the modification layer is crucial to the photoelectrochemical properties of modified electrodes. The highest conversion efficiency reaches 9.23% under irradiation of 100 mW cm⁻² white light, obtained with the electrode TiO₂/CaTiO₃(45 min), a 34% increase than that of bare TiO₂ electrodes.     

Electro-oxidation of coal on NiO and/or Co3O4 modified TiO2/Pt electrodes

A TiO₂/Pt based electrode exhibited better activity for the oxidation of coal in a basic system compared to Ti/Pt, TiO₂–Cu/Pt and pure metal electrodes. The surface morphologies and composition of the electrodes were studied by SEM and XRD, respectively. Linear sweep voltammetry was employed to investigate the catalytic effects of electrodes, and the product of coal oxidization was determined by a gas collection test. The TiO₂/Pt electrodes that were modified with NiO and/or Co₃O₄ exhibited higher average currents and a lower decrease in mass during electrolysis compared to the other electrodes; this finding indicated that NiO and Co₃O₄ play important roles as catalysts.     

Anatase TiO2 spheres with high surface area and mesoporous structure via a hydrothermal process for dye-sensitized solar cells

Spherical pure anatase TiO₂ spheres with a mesoporous structure and high surface area of up to 116.5 m² g⁻¹ were prepared by a simple urea-assisted hydrothermal process and investigated as dye-sensitized solar-cell electrodes. Although the particle diameters of the prepared TiO₂ spheres ranged from 0.4 to 1.3 μm, due to the high specific surface area, mesoporous TiO₂ sphere electrode was obtained with enhanced light harvesting and a larger amount of dye loading. An overall light conversion efficiency of 7.54% under illumination of simulated AM 1.5G solar light (100 mW cm⁻²) was achieved using the mesoporous TiO₂ spheres electrode, which was significantly higher than a commercial Degussa P25 TiO₂ nanocrystals electrode (5.69%).     

Efficient synthesis of titania nanotubes and enhanced photoresponse of Pt decorated TiO2 for water splitting

We investigated the effect of HMT (hexamethylenetetraamine) on the anodic growth of TiO₂ nanotube arrays. The tube length increases to 4.3 μm with HMT concentration increasing to 0.04 mol·L⁻¹. Adsorption of HMT on the TiO₂ surface is shown to markedly decrease the chemical dissolution rate of tube mouth, resulting in longer nanotube length. Furthermore, Pt nanoparticles were successfully deposited on the surface of TiO₂ nanotubes by ac electrodeposition method. The TiO₂/Pt composites were characterized by field emission scanning electron microscope (FESEM), X-ray photoelectron spectra (XPS), and photoelectrochemistry. An enhancement in photocurrent density has been achieved upon modification of TiO₂ nanotubes with Pt nanoparticles.     

Solvothermal fabrication of three-dimensionally sphere-stacking Sb–SnO2 electrode based on TiO2 nanotube arrays

TiO₂-NTs-based Sb–SnO₂ electrode with three-dimensionally sphere-stacking structure was successfully fabricated by the solvothermal method, followed by annealing at 500 °C for 1 h. The physico-chemical properties of electrodes were characterized through scanning electron spectroscopy (SEM), X-ray diffraction (XRD) and electrochemical measurements. SEM result showed that TiO₂-NTs/Sb–SnO₂ electrode has morphology of vertically sphere-stacking coralline. Compared with Ti/Sb–SnO₂, TiO₂-NTs/Sb–SnO₂ electrode has smaller grain size and greater specific surface area which can provide with more active sites. Compared with Ti/Sb–SnO₂ electrode, TiO₂-NTs/Sb–SnO₂ has a higher oxygen evolution potential and stronger phenol oxidation peak, indicating an improved catalytic activity for phenol degradation. The kinetic analysis of electrochemical phenol degradation showed that the first-order kinetics rate constant on TiO₂-NTs/Sb–SnO₂ electrode is 1.33 times as much as that on Ti/Sb–SnO₂, confirming that the sphere-stacking Sb–SnO₂ based on TiO₂ nanotube has a good electrocatalytic activity.     

Self-assembled CdS quantum dots-sensitized TiO2 nanospheroidal solar cells: Structural and charge transport analysis

A nanospheroidal TiO₂ mesoporous layer combined with cadmium sulfide (CdS) quantum dots (QDs) as a sensitizer was firstly utilized for solar cell applications, resulting in an efficiency of 1.2% at a 1 sun condition. CdS quantum dots (18 nm) were attached to the TiO₂ nanospheroidal electrode by using a chemical bath deposition technique. The influence of surface treatment using dimethyl formamide on the interconnectivity of the TiO₂ nanospheroidal electrodes was investigated. The charge transport of TiO₂/CdS QDs/electrolyte sandwich-type cells was characterized by electrochemical impedance spectroscopy and the device performance was compared with conventional nanospherical TiO₂ (Degauusa P25) electrodes. The electrodes with nanospheroidal morphology showed better device performance than the P25 nanoparticle electrodes primarily due to both better connectivity among nanospheroidal TiO₂ particles and larger mesopores, resulting in deeper penetration of the electrolyte in QD-sensitized solar cells.     

Fabrication of dye-sensitized solar cells using ordered and vertically oriented TiO2 nanotube arrays with open and closed ends

Highly ordered and vertically oriented TiO₂ nanotube arrays were prepared and applied to dye sensitized solar cell (DSSC) as working electrodes. The nanotube arrays were fabricated using atomic layer deposition and AAO template. The two types of nanotube's end, closed-end and open-end, were produced by reactive ion etching (RIE) process. The structure of nanotube arrays was characterized by FE-SEM, TEM, and XRD. DSSCs using the TiO₂ nanotube arrays as working electrodes were fabricated and characterized. The DSSCs prepared from the TiO₂ nanotubes with open end exhibited higher power conversion efficiency of 1.17% than that with closed end. This result is attributed to that the open-ended TiO₂ nanotubes provided larger surface area, leading to more amount of dye molecules to adsorb followed by the higher light absorption.     

Photoelectrocatalytic properties of Ag nanoparticles loaded TiO2 nanotube arrays prepared by pulse current deposition

A pulse current deposition technique was adopted to construct highly dispersed Ag nanoparticles on TiO₂ nanotube arrays which were prepared by the electrochemical anodization. The morphology, crystallinity, elemental composition, and UV-vis absorption of Ag/TiO₂ nanotube arrays were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and diffuse reflectance spectra (DRS). In particular, the photoelectrochemical properties and photoelectrocatalytic activity under UV light irradiation and the photocatalytic activity under visible light irradiation for newly synthesized Ag/TiO₂ nanotube arrays were investigated. The maximum incident photon to charge carrier efficiency (IPCE) value of Ag/TiO₂ nanotube arrays was 51%, much higher than that of pure TiO₂ nanotube arrays. Ag/TiO₂ nanotube arrays exhibited higher photocatalytic activities than the pure TiO₂ nanotube arrays under both UV and visible light irradiation. The photoelectrocatalytic activity of Ag/TiO₂ nanotube arrays under UV light irradiation was 1.6-fold enhancement compared with pure TiO₂ nanotube arrays. This approach can be used in synthesizing various metal-loaded nanotube arrays materials.     

TiO2 micro-flowers composed of nanotubes and their application to dye-sensitized solar cells

TiO₂ micro-flowers were made to bloom on Ti foil by the anodic oxidation of Ti-protruding dots with a cylindrical shape. Arrays of the Ti-protruding dots were prepared by photolithography, which consisted of coating the photoresists, attaching a patterned mask, illuminating with UV light, etching the Ti surface by reactive ion etching (RIE), and stripping the photoresist on the Ti foil. The procedure for the blooming of the TiO₂ micro-flowers was analyzed by field emission scanning electron microscopy (FESEM) as the anodizing time was increased. Photoelectrodes of dye-sensitized solar cells (DSCs) were fabricated using TiO₂ micro-flowers. Bare TiO₂ nanotube arrays were used for reference samples. The short-circuit current (J_sc) and the power conversion efficiency of the DSCs based on the TiO₂ micro-flowers were 4.340 mA/cm² and 1.517%, respectively. These values of DSCs based on TiO₂ micro-flowers were higher than those of bare samples. The TiO₂ micro-flowers had a larger surface area for dye adsorption compared to bare TiO₂ nanotube arrays, resulting in improved J_sc characteristics. The structure of the TiO₂ micro-flowers allowed it to adsorb dyes very effectively, also demonstrating the potential to achieve higher power conversion efficiency levels for DSCs compared to a bare TiO₂ nanotube array structure and the conventional TiO₂ nanoparticle structure.     

Synthesis and electrochemical properties of CeO2 nanoparticle modified TiO2 nanotube arrays

In this paper, a cerium dioxide (CeO₂) modified titanium dioxide (TiO₂) nanotube array film was fabricated by electrodeposition of CeO₂ nanoparticles onto an anodized TiO₂ nanotube array. The structural investigation by X-ray diffraction, scanning electron microscopy and transmission electron microscopy indicated that the CeO₂ nanoparticles grew uniformly on the walls of the TiO₂ nanotubes. The composite was composed of cubic-phase CeO₂ crystallites and anatase-phase TiO₂ after annealing at 450 °C. The cyclic voltammetry and chronoamperometric charge/discharge measurement results indicated that the CeO₂ modification obviously increased the charge storage capacity of the TiO₂ nanotubes. The charge transfer process at the surface, that is, the pseudocapacitance, was the dominate mechanism of the charge storage in CeO₂-modified TiO₂ nanotubes. The greater number of surface active sites resulting from uniform application of the CeO₂ nanoparticles to the well-aligned TiO₂ nanotubes contributed to the enhancement of the charge storage density.     

Diameter-sensitive biocompatibility of anodic TiO2 nanotubes treated with supercritical CO2 fluid

This work reports on the diameter-sensitive biocompatibility of anodic TiO₂ nanotubes with different nanotube diameters grown by a self-ordering process and subsequently treated with supercritical CO₂ (ScCO₂) fluid. We find that highly hydrophilic as-grown TiO₂ nanotubes become hydrophobic after the ScCO₂ treatment but can effectively recover their surface wettability under UV light irradiation as a result of photo-oxidation of C-H functional groups formed on the nanotube surface. It is demonstrated that human fibroblast cells show more obvious diameter-specific behavior on the ScCO₂-treated TiO₂ nanotubes than on the as-grown ones in the range of diameters of 15 to 100 nm. This result can be attributed to the removal of disordered Ti(OH)₄ precipitates from the nanotube surface by the ScCO₂ fluid, thus resulting in purer nanotube topography and stronger diameter dependence of cell activity. Furthermore, for the smallest diameter of 15 nm, ScCO₂-treated TiO₂ nanotubes reveal higher biocompatibility than the as-grown sample.     

Photoelectrocatalytic activity of mesoporous TiO<Subscript>2</Subscript> films prepared using the sol–gel method with tri-block copolymer as structure directing agent

Mesoporous TiO₂ films were synthesized using a sol–gel process with a tri-block copolymer (Pluronic F127) as a structure directing agent. The films were dip-coated onto conductive glass substrates followed by thermal treatment to remove the polymeric surfactant. The specific surface area, the pore size and morphology, and the crystallinity of the films were characterized. The analysis showed the structural properties of the films could be tailored by varying the surfactant concentration as well as the annealing temperature. The photocurrent responses of the prepared films were measured using a three-electrode photoelectrochemical cell in the presence of oxalic acid. When annealed at 450 °C, the dense electrode (control sample) had the strongest photoelectrocatalytic oxidation aptitude toward oxalic acid. The lower photocurrent response of the mesoporous electrodes compared to the dense electrode can be explained by poor inter-particle connectivity within the mesoporous TiO₂ network, leading to high electron transport resistance. The mesoporous electrode annealed at 550 °C, with improved connectivity, outperformed the dense electrode at a high oxalic concentration, as the lower surface area of the dense electrode restricted photoelectrocatalysis reactions on the surface. A further increase in annealing temperature to 650 °C resulted in a poor photocurrent response as the significant decrease in surface area outweighed the beneficial effect of improved connectivity.     

Effect of TiO2 nanotubes with TiCl4 treatment on the photoelectrode of dye-sensitized solar cells

In this study, we used the electrochemical anodization to prepare TiO₂ nanotube arrays and applied them on the photoelectrode of dye-sensitized solar cells. In the field emission scanning electron microscopy analysis, the lengths of TiO₂ nanotube arrays prepared by electrochemical anodization can be obtained with approximately 10 to 30 μm. After titanium tetrachloride (TiCl₄) treatment, the walls of TiO₂ nanotubes were coated with TiO₂ nanoparticles. XRD patterns showed that the oxygen-annealed TiO₂ nanotubes have a better anatase phase. The conversion efficiency with different lengths of TiO₂ nanotube photoelectrodes is 3.21%, 4.35%, and 4.34% with 10, 20, and 30 μm, respectively. After TiCl₄ treatment, the efficiency of TiO₂ nanotube photoelectrode for dye-sensitized solar cell can be improved up to 6.58%. In the analysis of electrochemical impedance spectroscopy, the value of R_k (charge transfer resistance related to recombination of electrons) decreases from 26.1 to 17.4 Ω when TiO₂ nanotubes were treated with TiCl₄. These results indicate that TiO₂ nanotubes treated with TiCl₄ can increase the surface area of TiO₂ nanotubes, resulting in the increase of dye adsorption and have great help for the increase of the conversion efficiency of DSSCs.     

TiO2/modified natural clay semiconductor as a potential electrode for natural dye-sensitized solar cell

TiO₂/modified natural bentonite clay semiconductor, as a potential electrode of dye-sensitized solar cell, having a Ti:Si molar ratio of 85:15 was, for the first time, compared with pure TiO₂ (commercial P25) electrode in terms of solar cell efficiency and characteristics. 4-Chloro-2,5-difluorobenzoic acid and 4-(chloromethyl)benzoyl chloride were added to the electrodes to increase light harvesting ability of natural dyes extracted from red cabbage, rosella, and blue pea. The results showed that the TiO₂/clay semiconductor provided a higher surface area but a slightly lower efficiency than the pure TiO₂. The best natural sensitizer was found to be the dye extracted from red cabbage. Besides, the 4-(chloromethyl)benzoyl chloride provided a higher short circuit current for the TiO₂/clay semiconductor.