Efficient decomposition of organic compounds with FeTiO3/TiO2 heterojunction under visible light irradiation

FeTiO₃/TiO₂, a new heterojunction-type photocatalyst working at visible light, was prepared by a simple sol–gel method. Not only did FeTiO₃/TiO₂ exhibit greatly enhanced photocatalytic activity in decomposing 2-propanol in gas phase and 4-chlorophenol in aqueous solution, but also it induced efficient mineralization of 2-propanol under visible light irradiation (λ ≥ 420 nm). Furthermore, it showed a good photochemical stability in repeated photocatalytic applications. FeTiO₃ showed a profound absorption over the entire visible range, and its valence band (VB) position is close to that of TiO₂. The unusually high photocatalytic efficiency of the FeTiO₃/TiO₂ composite was therefore deduced to be caused by hole transfer between the VB of FeTiO₃ and TiO₂.     

Photocatalytic activities of AgSbO3 under visible light irradiation

A novel visible light sensitive photocatalyst, AgSbO₃ was prepared by a conventional solid-state reaction method. This oxide belonging to a cubic-pyrochlore structure can absorb visible light with wavelength up to about 480 nm. From the band structure calculation, we found that the top of the valence band consists of the hybridized Ag 4d and O 2p orbitals and the bottom of the conduction band mainly consists of the Ag 5s and the Sb 5s orbitals. Photocatalytic activities were evaluated using O₂ evolution from an aqueous silver nitrate solution and decomposition of gaseous 2-propanol under visible light irradiation. We found that AgSbO₃ shows a higher O₂ evolution activity than WO₃ and 2-propanol can be mineralized by the AgSbO₃ photocatalysis under visible light irradiation.     

Photocatalytic activation of TiO2 under visible light using Acid Red 44

The activation of TiO₂ photocatalyst for photocatalysis under the visible light using Acid Red 44 (C₁₀H₇N=NC₁₀H₃(SO₃Na)₂OH) is described. Adjustment of the pH enhanced the photocatalytic activation of TiO₂ in the presence of visible light. This confirms that the adsorption of a dye on TiO₂ surface is an important factor in dye-photosensitization. The differences in the photocatalytic activation mechanism under visible irradiated conditions with that of UV irradiated condition are proposed. The dye-sensitized photocatalysis under visible light was applied to the decomposition of phenol, is a toxic chemical used in industry and frequently discharged into water.     

Photocatalytic activity of AgBr/TiO2 in water under simulated sunlight irradiation

In this paper, the synthesis of AgBr/TiO₂ catalyst and the photocatalytic activity in water under simulated sunlight irradiation were studied. The influence of AgBr content in catalyst and the incident light intensity on the degradation of methyl orange (MO) was investigated. It was found that the initial reaction rate constant was dependent on the relative levels of AgBr content and incident light intensity, ranging between 0.008 min⁻¹ and 0.023 min⁻¹. At higher levels of AgBr content (>9 wt%), MO degradation was exclusively dependent on the incident light intensity, which implied that the excessive AgBr in catalyst had negligible effect on catalyst activity. However, at lower AgBr contents, the reaction rate increased with the increase of incident light intensity, and eventually reached a plateau level, indicating that the degradation of MO was limited by AgBr content. The results from powder X-ray diffraction (XRD) analysis showed that more than 80% of AgBr remained intact after 14 h of irradiation, although metallic silver was also detected.     

Enhanced visible light photocurrent generation at surface-modified TiO2 nanotubes

Photoelectrodes consisting of TiO₂ nanotube layers with different thicknesses (0.5 μm, 1.7 μm, 3 μm, 6 μm, 9 μm, and 18 μm) were prepared by anodization of titanium substrates and subsequent surface modification by a heat treatment at 400 °C in the presence of urea pyrolysis products. In contrast to unmodified TiO₂ nanotubes, the modified photoelectrodes exhibit photocurrents under visible light irradiation down to 750 nm. Photocurrent transients indicate enhanced recombination unless a suitable hole-scavenger, like iodide, is present since the photogenerated holes do not oxidize water efficiently. In the visible light the photoconversion efficiency increases significantly with nanotube length. The maximum incident photon-to-current efficiency (IPCE) was observed for tubes with the length of 6-9 μm (IPCE ∼4.5% and 1.4% at 450 nm and 550 nm, respectively) and the photocurrent enhancement with increasing tube length is found to be stronger at longer irradiations wavelengths.     

Degradation of atrazine using metalloporphyrins supported on TiO2 under visible light irradiation

A combined solar photo-Fenton and biological treatment is proposed for the decontamination of a mixture of five commercial pesticides commonly used in intensive agriculture Vydate (10% Oxamyl), Metomur (20% Methomyl), Couraze (20% Imidacloprid), Ditimur-40 (40% Dimethoate) and Scala (40% Pyrimethanil). Photo-Fenton experiments were conducted in a solar pilot reactor consisting of four compound parabolic collectors in which the pesticide mixture was treated at an original dissolved organic carbon (DOC) concentration of 200 mg/L in the presence of Fe²⁺ or Fe³⁺ concentration of 5, 20 and 55 mg/L. Ferrous ions were marginally more active than ferric in terms of active ingredient degradation, which followed zero order kinetics, more so in the early reaction stages. Photo-Fenton was also far more effective (by at least two orders of magnitude) than the respective dark reaction under identical experimental conditions.Irradiation for 50–100 min (normalized at 30 W/m² light intensity) at 20 mg/L Fe²⁺ was able to completely eliminate the active ingredients, and reduce DOC by about 15–50% and COD by 40–70%, respectively. At these conditions, ecotoxicity to the marine bacteria V. fischeri was substantially lessened, while aerobic biodegradability in tests with activated sludge was enhanced.     

Photo-induced charging effect and electron transfer to the redox species on nitrogen-doped TiO2 under visible light irradiation

Energy levels for sub-band structures of the nitrogen-doped TiO₂ (N-TiO₂) and photo-excitation mechanism for the visible light response were investigated by photo-electrochemical and spectroscopic measurements. It was demonstrated that the photo-excitation from the N-doping level of N-TiO₂ causes the accumulation of electrons into the sub-band level at the potential energy of ca. +0.35 V vs. NHE (pH 2.5) under visible light irradiation. Subsequently, electron transfer does not take place from the photo-charged N-TiO₂ under visible light irradiation into such redox species as methyl viologen (MV²⁺), H⁺, Cu²⁺ ions, but into O₂ molecules, Pt⁴⁺, Ag⁺ and Au³⁺ ions by way of the sub-band level. These findings shed light on a mechanism for the photocatalytic reactions on the N-TiO₂ under visible light irradiation.     

Photocatalytic inactivation of bacteria by photocatalyst Bi2WO6 under visible light

The photocatalytic inactivation of Escherichia coli under visible light irradiation (λ > 420 nm) was performed with Bi₂WO₆ to investigate the photocatalytic bactericidal capability. Our work shows that the single phase oxide photocatalyst Bi₂WO₆ is effective in photocatalytic inactivation on E. coli. And the results revealed that the photocatalytic inactivation rate of E. coli with Bi₂WO₆ followed pseudo-first-order kinetics. The bactericidal action was directly observed by TEM and further proved by the measurement of K⁺ leakage from the inactive E. coli through the ICP-OES analysis. The results demonstrated that the photocatalysis could cause drastic damage in E. coli cells.     

Properties of sol-gel SnO2/TiO2 electrodes and their photoelectrocatalytic activities under UV and visible light illumination

A visible light active binary SnO₂-TiO₂ composite was successfully prepared by a sol-gel method and deposited on Ti sheet as a photoanode to degrade orange II dye. Titanium and SnO₂ can promote the development of rutile phase of TiO₂ and inhibit the formation of anatase phase of TiO₂. Formation of SnO₂ crystalline is insignificant even when the calcination temperature increases to 700 °C. Heterogenized interface between SnO₂ and TiO₂ inhibits growth of TiO₂ linkage and leads to the particle-filled surface morphology of SnO₂-containing films. The carbonaceous, Ti-O-C bonds and Ti³⁺ species are likely to account for the photoabsorption and photoelectrocatalytic (PEC) activity under visible light illumination. The electrode with 30% SnO₂ exhibits higher photocurrent when compared with those in the region of 0-50%. The 600 °C-calcined SnO₂-TiO₂ electrode indicates higher activity when compared with those at 400, 500, 700 and 800 °C. PEC degradation of orange II follows the Langmuir-Hinshelwood model and takes place much effectively in a solution of pH 3.0 than those in pH 7.0 and pH 11.0.     

Preparation and characterisation of visible light responsive iodine doped TiO2 electrodes

Characteristics are presented of new iodine doped TiO₂ (I-TiO₂) prepared via the hydrothermal method, where titania (IV) complexes with a ligand containing an iodine atom have been used as a precursor. The structure of samples has been examined by XPS, XRD, UV-vis and FT-IR-ATR techniques. These studies confirm that the obtained powder exhibits a decrease in the bandgap energy value (E_g = 2.8 eV). The report presents electrochemical studies of I-TiO₂ films on a Pt electrode, which allow determination of the flatband potential E_fb = −0.437 V vs. SCE (in 0.5 M Na₂SO₄). Cyclic voltammetry measurements show anodic and cathodic activities under Vis and UV-vis radiation. The photocurrent enhancement due to visible light radiation reached 30% of the whole photoacitivity exhibited under UV-vis illumination.     

Sulfanilic acid-modified P25 TiO2 nanoparticles with improved photocatalytic degradation on Congo red under visible light

Visible-light-induced titania/sulfanilic acid nano-composite photocatalysts were prepared and characterized by FTIR, XPS, UV-vis, XRD, and SEM. The results indicate that the formation of Ti-O-S bonds after the modification of P25 TiO₂ nanoparticles with sulfanilic acid ligands extends the photoresponse of the photocatalyst from the UV to the visible range. The photocatalytic activity of the nano-composite photocatalyst was examined by degrading Congo red under visible light, in which its effecting factors such as irradiation time, catalyst dosage, solution pH and the addition of H₂O₂, were investigated in detail. The possible mechanism of photocatalytic degradation under visible irradiation has been also presented.     

Photocatalytic effect of carbon-modified n-TiO2 nanoparticles under visible light illumination

The present research focused on wet process synthesis of visible light active carbon-modified (CM)-n-TiO₂ nanoparticles and their photocatalytic activity. The CM-n-TiO₂ was synthesized by hydrolysis of TiCl₄ in the presence of tetrabutylammonium hydroxide and also in the presence of glucose and sodium hydroxide. UV–vis spectra, X-ray diffraction (XRD), and FT-IR were used to characterize these photocatalysts. It was found that the CM-n-TiO₂ nanoparticles synthesized by hydrolysis with tetrabutylammonium hydroxide or with sodium hydroxide and glucose when subjected to extended aging and subsequent calcinations absorb well into the visible to near infrared region up to 800 nm and exhibit enhanced visible light photocatalytic activity on degradation of 4-chlorophenol. CM-n-TiO₂ synthesized using glucose as the carbon source generated 13-fold increase in the initial rate of photodegradation of 4-chlorophenol compared to those by regular n-TiO₂, whereas, it increased only eight-fold when tetrabutylammonium hydroxide was used as the carbon source.     

Enhancement of the visible light photocatalytic performance of C-doped TiO2 by loading with V2O5

V₂O₅ was loaded on the surface of C-doped TiO₂ (C-TiO₂) by incipient wetness impregnation in order to enhance the visible light photocatalytic performance. The physicochemical properties of the C-TiO₂/V₂O₅ composite were characterized by XRD, Raman, TEM, XPS, UV–vis diffuse reflectance spectra, and PL in detail. The result indicated that a heterojunction between C-TiO₂ and V₂O₅ was formed and the separation of excited electron–hole pairs on C-TiO₂/V₂O₅ is greatly promoted. Thus, this composite photocatalyst exhibited enhanced visible light photocatalytic activity in degradation of gas-phase toluene compared with the pristine C-TiO₂.     

Photocatalytic degradation of organic compounds diluted in water using visible light-responsive metal ion-implanted TiO2 catalysts: Fe ion-implanted TiO2

The application of metal ion-implantation method has been made to improve the electronic properties of the TiO₂ photocatalyst to realize the utilization of visible light. The photocatalytic properties of these unique TiO₂ photocatalysts for the purification of water have been investigated. By the metal ion-implantation method, metal ions (Fe⁺, Mn⁺, V⁺, etc.) are accelerated enough to have the high kinetic energy (150 keV) and can be implanted into the bulk of TiO₂. TiO₂ photocatalysts which can absorb visible light and work as a photocatalyst efficiently under visible light irradiation were successfully prepared using this advanced technique. The UV-Vis absorption spectra of these metal ion-implanted TiO₂ photocatalysts were found to shift toward visible light regions depending on the amount and the kind of metal ions implanted. They were found to exhibit an effective photocatalytic reactivity for the liquid-phase degradation of 2-propanol diluted in water at 295 K under visible light (λ>450 nm) irradiation. The investigation using XAFS analysis suggested that the substitution of Ti ions in TiO₂ lattice with implanted metal ions is important to modify TiO₂ to be able to adsorb visible light.     

Simple fabrication and photocatalytic activity of S-doped TiO2 under low power LED visible light irradiation

A series of S-doped TiO₂ with visible-light photocatalytic activity were prepared by a simple hydrolysis method using titanium tetrachloride (TiCl₄) and sodium sulfate (Na₂SO₄) as precursors. The photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectrophotometer (UV–Vis DRS), and X-ray photoelectron spectroscopy (XPS). With the doping of S, photocatalysts with small crystal size, high content of anatase phase were obtained. The result showed that S-doped TiO₂ demonstrate considerably high photoactivity under low power visible LED light irradiation, while undoped TiO₂ and the Degussa P25 have nearly no activity at all. The possible mechanism of S-doped for the visible-light activity was discussed.     

Efficient photocatalytic activity of MnO2-loaded ZrO2/carbon cluster nanocomposite materials under visible light irradiation

Nano-sized ZrO₂/carbon cluster nanocomposite material was successfully prepared by the calcination of Zr(acac)₄/epoxy resin complex in air. The composite material obtained by calcining at 200 °C was treated with hydrogen hexachloroplatinate hexahydrate (H₂PtCl₆) to obtain Pt-loaded materials denoted as Ic₂₀₀Pt'sH's. The Pt-loaded material modified with MnO₂ particles efficiently decompose water into H₂ and O₂ with a [H₂]/[O₂] ratio of 2 under the irradiation of visible light (λ > 460 nm) through the electron transfer process of MnO₂ → carbon clusters → ZrO₂ → Pt.     

A unique Cu2O/TiO2 nanocomposite with enhanced photocatalytic performance under visible light irradiation

A unique Cu₂O/TiO₂ nanocomposite with high photocatalytic activity was synthesized via a two-step chemical solution method and used for the photocatalytic degradation of organic dye. The structure, morphology, composition, optical and photocatalytic properties of the as-prepared samples were investigated in detail. The results suggested that the Cu₂O/TiO₂ nanocomposite is composed of hierarchical TiO₂ hollow microstructure coated by a great many Cu₂O nanoparticles. The photocatalytic performance of Cu₂O/TiO₂ nanocomposite was evaluated by the photodegradation of methylene blue (MB) under visible light, and compared with those of the pure TiO₂ and Cu₂O photocatalysts synthesized by the identical synthetic route. Within 120 min of reaction time, nearly 100% decolorization efficiency of MB was achieved by Cu₂O/TiO₂ photocatalyst, which is much higher than that of pure TiO₂ (26%) or Cu₂O (32%). The outstanding photocatalytic efficiency was mainly ascribed to the unique architecture, the extended photoresponse range and efficient separation of the electron-hole pairs in the Cu₂O/TiO₂ heterojunction. In addition, the Cu₂O/TiO₂ nanocomposite also retains good cycling stability in the photodegradation of MB.     

TiO2 nano-flakes with high activity obtained from phosphorus doped TiO2 nanoparticles by hydrothermal method

TiO₂ nano-wires (Ti-NWs) and nano-flakes (Ti-NFs) were obtained from phosphorus doped TiO₂ nanoparticles (Ti-P) by hydrothermal method and by subsequent heat treatment respectively. FE-SEM micrograph of the as prepared sample depicts well formed, entangled and randomly oriented nano-wires morphology, which changes to nano-flakes morphology after heat treatment. Structural characterization of the samples by X-ray diffraction shows anatase phase for both the samples. Absorption edge of the Ti-NWs sample shows blueshift where as the Ti-NFs sample exhibit redshift compared to precursor sample as evidenced by UV–Visible absorption spectra, which is due to change in morphology and crystallinity of the samples. XPS studies indicate the presence of titanium and oxygen species only. From the EPR measurements with in-situ visible light irradiation, the number of photogenerated charge carriers is found to be very high for nano-flakes sample. Methyleneblue degradation profiles depict very high activity of Ti-NFs sample compared to Ti-NWs and the precursor samples, which is due to the observed redshift in the absorption edge, change in morphology and high crystallinity of the sample which in turn increases the optical response and separation of photogenerated charge carriers as evidenced by the optical and EPR measurements respectively.