Preparation of Fe-doped TiO2 nanotube arrays and their photocatalytic activities under visible light

Fe-doped TiO₂ nanotube arrays have been prepared by the template-based liquid phase deposition method. Their morphologies, structures and optical properties were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and UV-vis absorption spectroscopy. Their photocatalytic activities were evaluated by the degradation of methylene blue under visible light. The UV-vis absorption spectra of the Fe-doped TiO₂ nanotube arrays showed a red shift and an enhancement of the absorption in the visible region compared to the undoped sample. The Fe-doped TiO₂ nanotube arrays exhibited good photocatalytic activities under visible light irradiation, and the optimum dopant amount was found to be 5.9 at% in our experiments.     

Hydrothermal synthesis and characterization of TiO2 nanorod arrays on glass substrates

Large-scale, well-aligned single crystalline TiO₂ nanorod arrays were prepared on the pre-treated glass substrate by a hydrothermal approach. The as-prepared TiO₂ nanorod arrays were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. X-ray diffraction results show that the main phase of TiO₂ is rutile. Scanning electron microscopy and transmission electron microscopy results demonstrate that the large-scale TiO₂ nanorod arrays grown on the pre-treated glass substrate are well-aligned single crystal and grow along [0 0 1] direction. The average diameter and length of the nanorods are approximately 21 and 400 nm, respectively. The photocatalytic activity of TiO₂ nanorod arrays was investigated by measuring the photodegradation rate of methyl blue aqueous solution under UV irradiation (254 nm). And the results indicate that TiO₂ nanorod arrays exhibit relatively higher photocatalytic activity.     

CdS-sensitized ZnO nanorod arrays coated with TiO2 layer for visible light photoelectrocatalysis

A novel ZnO/CdS/TiO₂ nanorod array composite structure was fabricated by depositing CdS-sensitized layer onto ZnO nanorod arrays via chemical bathing deposition and subsequently coated by TiO₂ protection layer via a vacuum dip-coating process. The films were characterized by x-ray diffraction, field emission scanning electron microscopy, energy dispersive spectrum, and UV–Vis diffuse reflectance spectroscopy. For the films severed as the photoanodes, linear sweep voltammetry and transient photocurrent (i _ph) were investigated in a three-electrode system. The photoelectrocatalytic activity was evaluated by the degradation of methylene blue (MB) under visible light irradiation. The results show that the oriented ZnO nanorods are adhered by relatively uniform CdS-sensitized layer and coated with TiO₂ layer. Both the coated and uncoated CdS-sensitized ZnO nanorod arrays exhibit the visible light response and the photoelectrocatalytic activity on the degradation of MB under visible light irradiation. The ZnO/CdS/TiO₂ nanorod array film possesses stable and superior photoelectrocatalytic performance owing to the TiO₂ thin layer protecting the CdS from photocorrosion.     

Studies on nitrogen modified TiO2 photocatalyst prepared in different conditions

Nitrogen modified titania photocatalysts (TiO₂/N) were characterized using high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), Raman spectroscopy and BET surface area method. The presence of nitrogen in modified photocatalysts has been studied using FT-IR and XPS analyses. The influence of the calcination temperature in the range of 100-350 °C on nanocrystallite as well as particle size of the samples and their photocatalytic activity was investigated. The calcination of TiO₂/N samples caused a growth of the particle size and an increase of their crystallinity. TEM studies present changes of the diameter and shape of TiO₂ particles and nanocrystallites. The XRD and the Raman response of the samples confirmed an increase of the crystallinity of the samples when annealed at higher temperatures.The photocatalytic activity of the modified photocatalysts was determined using the reaction of phenol decomposition. It was shown that phenol decomposition rate was greatly influenced by pH of the solution. The highest phenol degradation using all the modified samples was observed for pH 7.1 which is close to the PZC point established for pristine TiO₂ at pH 6.8.     

Controllable synthesis of self-assembled Cu2S nanostructures through a template-free polyol process for the degradation of organic pollutant under visible light

Cu₂S nanostructures were fabricated by polyol method and then characterized by X-ray diffractometer, scanning electron microscopy, transmission electron microscopy (TEM) and high resolution TEM. The morphologically different Cu₂S nanostructures such as vertically nanorod arrays, nanoflowers assembled by nanorod arrays, nanoparticles and nanowires, can be successfully synthesized under different experimental conditions. The growth mechanism for the different nanostructures is proposed. The photocatalytic activity of the prepared samples was evaluated based on the degradation of organic pollutant, active brilliant red X-3B (X-3B), under visible light. Among the Cu₂S nanostructures, self-assembled nanoflowers have the highest photocatalytic activity. In addition, the prepared Cu₂S nanostructures are found to be able to decolorize X-3B with iron ions for the formation of Fenton reagent. This study provides a more choice to prepare self-assembled nanostructures for the application of environmental pollution control.     

Fabrication of solar light induced Fe-TiO2 immobilized on glass-fiber and application for phenol photocatalytic degradation

Iron-doped anatase titanium dioxide catalysts coated on glass-fiber were successfully synthesized by a dip-coating sol–gel method. The prepared catalysts were characterized by scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy to understand the synthesis mechanism, and their photocatalytic activities were evaluated by photodegradation of phenol under simulated solar irradiation. EDX analysis confirmed the existence of iron in the immobilized catalysts. XRD suggested that the phase transition of the catalysts from anatase to rutile were restrained, and almost pure anatase TiO₂ could retain even the calcination temperature reached 800 °C. The UV-Vis diffuse reflectance spectroscopy of the catalysts showed a red shift and increased photoabsorbance in the visible range for all the doped samples. Iron loading and calcination temperature have obvious influences on photocatalytic activity. In this study, the optimal doping dose and calcination temperature were around 0.005 wt% and 600 °C, respectively.     

Synthesis and characterization of solar photoactive TiO2 nanoparticles with enhanced structural and optical properties

The structural, morphological, and optical properties of the sol–gel derived TiO₂ nanoparticles at different pH and calcination temperature were investigated in the present study. X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM), UV–Visible(Vis) spectroscopy, energy dispersive studies (EDS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoluminescence (PL) spectroscopy, BET surface area analysis, and Barrett-Joyner-Halenda (BJH) pore size distribution and pore volume analysis were used to characterize the prepared TiO₂ photocatalyst. The range of crystallite size and band gap of the synthesized TiO₂ samples were in the range of 20–80?nm and 2.5–3.2?eV respectively. The photocatalytic performance of prepared TiO₂ photocatalysts was evaluated by photodegradation of Methylene Blue (MB) solution under simulated solar irradiation. Results illustrate that the synthesized TiO₂ exhibits visible light activity at higher calcination temperature. Crystallinity and surface area plays a vital role in the overall performance of the prepared TiO₂ photocatalyst.     

Fabrication and characterization of nano TiO2 thin films at low temperature

Anatase TiO₂ thin films were successfully prepared on glass slide substrates via a sol–gel method from refluxed sol (RS) containing anatase TiO₂ crystals at low temperature of 100 °C. The influences of various refluxing time on crystallinity, morphology and size of the RS sol and dried TiO₂ films particles were discussed. These samples were characterized by infrared absorption spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission-scanning electron microscopy (FE-SEM) and UV–vis absorption spectroscopy (UV–vis). The photocatalytic activities of the TiO₂ thin films were assessed by the degradation of methyl orange in aqueous solution. The results indicated that titania films thus obtained were transparent and their maximal light transmittance exceeded 80% under visible light region. The TiO₂ thin films prepared from RS-6 sol showed the highest photocatalytic activity, when the calcination temperature is higher than 300 °C. The degradation of methyl orange of RS-6 thin films reached 99% after irradiated for 120 min, the results suggested that the TiO₂ thin films prepared from RS sol exhibited high photoactivities.     

Fabrication and photocatalytic property of ZnO nanorod arrays on Cu2O thin film

ZnO nanorod arrays were fabricated on Cu₂O thin film by a simple low-temperature liquid-phase-deposition method. The samples were characterized by X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM). The UV-Vis spectroscopy showed that the obtained sample was able to absorb a large part of visible light (up to 650 nm). Their photocatalytic activities were investigated by degradation of dye methylene blue (MB) under UV-Vis and visible light irradiation. It was found that the photocatalytic activity of the ZnO/Cu₂O NRs was higher than the ZnO/ZnO NRs under UV-Vis light. In a word, Cu₂O played an important role in enhancing the photocatalytic activity of the ZnO/Cu₂O NRs.     

Nonaqueous sol-gel synthesis and growth mechanism of single crystalline TiO2 nanorods with high photocatalytic activity

In this paper, we report on a nonaqueous synthesis of single crystalline anatase TiO₂ nanorods by reaction between TiCl₄ and benzyl alcohol at a low temperature of 80 °C. The resulting samples were characterized with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, nitrogen adsorption, X-ray photoelectron spectrometry and UV-vis diffuse reflectance spectroscopy. We proposed that the TiO₂ nanorods were formed through an oriented attachment mechanism. More importantly, these single crystalline anatase TiO₂ nanorods exhibited significantly higher photocatalytic activities than commercial photocatalyst P25. This study provides an environmentally friendly and economic approach to produce highly active TiO₂ photocatalyst.     

Photocatalytic degradation of RhB over MgFe2O4/TiO2 composite materials

MgFe₂O₄/TiO₂ (MFO/TiO₂) composite photocatalysts were successfully synthesized using a mixing-annealing method. The synthesized composites exhibited significantly higher photocatalytic activity than a naked semiconductor in the photodegradation of Rhodamine B. Under UV and visible light irradiation, the optimal percentages of doped MgFe₂O₄ (MFO) were 2 wt.% and 3 wt.%, respectively. The effects of calcination temperature on photocatalytic activity were also investigated. The origin of the high level of activity was discussed based on the results of X-ray diffraction, UV-vis diffuse reflection spectroscopy, scanning electron microscopy, transmission electron microscopy, and nitrogen physical adsorption. The enhanced activity of the catalysts was mainly attributed to the synergetic effect between the two semiconductors, the band potential of which matched suitably.     

TiO<Subscript>2</Subscript> nanotube arrays: hydrothermal fabrication and photocatalytic activities

Titanium dioxide nanotube arrays (TiO₂ NTAs) with rutile phase have been fabricated successfully via a two-step hydrothermal method. TiO₂ nanorod arrays (TiO₂ NRAs) are first hydrothermally grown on FTO substrate. Then the TiO₂ NTAs can be obtained by controlling the HCl concentration of the hydrothermal etching process. The TiO₂ NTAs have been characterized by X-ray diffractometer, scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectroscopy, and ultraviolet–visible spectroscope. Evolution of TiO₂ nanoarrays are accompanied by enhanced of the surface area and optical properties. Compared with TiO₂ NRAs, the prepared TiO₂ NTAs is more efficient in the photodegradation of methyl orange. These results reveal that the hydrothermal chemical etching provide a flexible and straightforward route for design and preparation of TiO₂ NTAs, promising for new opportunities in photocatalysts and other fields.     

Ag<Subscript>2</Subscript>S/Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> co-sensitized TiO<Subscript>2</Subscript> nanorod arrays prepared on conductive glass as a photoanode for solar cells

TiO₂ nanorod arrays (TiO₂ NRAs) were synthesized through a hydrothermal method. Ag₂S and Bi₂S₃ were then grown on the surface of TiO₂ NRAs with successive ionic layer adsorption and reaction method. The pristine rutile TiO₂ NRAs, Ag₂S/TiO₂, Bi₂S₃/TiO₂, and Bi₂S₃/Ag₂S/TiO₂ electrodes were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet–visible absorption spectroscopy, and electrochemical analysis. According to photoelectrochemical (PEC) measurement, an enhanced short circuit current density was obtained for the co-sensitized TiO₂ NRAs under simulated sunlight illumination, which was 10.7 times higher than that of the TiO₂ NRAs. Appropriate potential positions of conduction band and valence band of Bi₂S₃ that match well those of rutile TiO₂ NARs and Ag₂S lead to the improved PEC performance. In addition, the PEC property of the co-sensitized TiO₂ NRAs under visible light irradiation was also investigated and showed a dramatically enhanced photocurrent response.     

Visible light photocatalytic degradation of paraoxon and parathion pesticides on carbon-doped TiO<Subscript>2</Subscript> nanorod thin films

In the present work the nanostructured carbon-doped TiO₂ thin films with nanorod morphology were deposited on glass substrate by a combination of ultrasonic and chemical vapor deposition methods, and for the first time were applied for the photocatalytic degradation of paraoxon and parathion organophosphorus pesticides under visible light irradiation. X-ray Diffraction, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, and scanning electron microscopy techniques were used for characterization of the prepared thin films. Obtained results show that presence of carbon element and also special nanorod morphology of the thin films remarkably improve the optical properties of TiO₂ in visible light region and results in the good visible light photocatalytic activity of the thin films for degradation of the pesticides. The photonic efficiencies of the prepared thin films were also examined based on the international ISO-10678:2010 standard protocol for photocatalytic degradation of methylene blue under UV light irradiation. The results show a maximum photonic efficiency of 0.0312% for the carbon-doped TiO₂ thin film with 570 nm thickness, which compared to a reference standard TiO₂ films indicates a 30% improvement in photonic efficiency.     

Synthesis and enhanced light absorption of alumina matrix nanocomposites containing multilayer oxide nanorods and silver nanoparticles

In this paper, multilayer oxide nanorods were deposited in the nanopores of anodic aluminum oxide (AAO) via solution infiltration followed by heat treatment. The nanorods have a core–shell structure. First, the shell (nanotube) with the thickness of about 40 nm was made of TiO₂ through the hydrolysis of (NH₄)₂TiF₆. Second, silver nanoparticles with the diameter of about 3 nm were added into the TiO₂ layer through thermal decomposition of AgNO₃ at elevated temperatures. Then, cylindrical cores (nanorods) of CoO and ZnO with 200 nm diameter were prepared, respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the structure and composition of the nanorods. UV–vis light absorption measurements in the wavelength range from 350 to 1000 nm were performed to study the effect of nanorod and nanoparticle addition on the light absorption property of the alumina nanocomposites. It is found that CoO nanorods increase the light absorption of the alumina matrix composite in the wavelength range from 500 nm to 800 nm, but the TiO₂ shell does not increase the light absorption much. The ZnO nanorods do not change the light absorption either. However, the addition of silver nanoparticles significantly enhances light absorption of both AAO/TiO₂/Ag/CoO and AAO/TiO₂/Ag/ZnO nanocomposites. This increase in the visible light absorption reveals that there exists surface plasmon around the fine silver nanoparticles in the nanorods.     

Phosphomolybdic acid-modified highly organized TiO2 nanotube arrays with rapid photochromic performance

TiO₂ nanotube arrays were prepared by means of an electrochemical anodization technique in an organic electrolyte solution doped with polyvinyl pyrrolidone (PVP) and were subsequently modified with phosphomolybdic acid (PMoA) to obtain PMoA/TiO₂ nanotube arrays. The microstructure and photochromic properties were investigated via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet–visible spectroscopy (UV–vis), and X-ray photoelectron spectroscopy (XPS). The results indicated that the Keggin structure of PMoA and the nanotube structure of TiO₂ were not destroyed, and there was a strong degree of interaction between PMoA and TiO₂ at the biphasic interface with lattice interlacing during the compositing process. The XPS results further indicated that there was a change in the chemical microenvironment during the formation process of the composite, and a new charge transfer bridge was formed through the Mo-O-Ti bond. Under visible light irradiation, the colorless PMoA/TiO₂ nanotube array quickly turned blue and exhibited a photochromic response together with reversible photochromism in the presence of H₂O₂. After visible light irradiation for 60 s, the appearance of Mo⁵⁺ species in the XPS spectra indicated a photoreduction process in accordance with a photoinduced electron transfer mechanism.     

Removal of fluoride from aqueous solution by polypyrrole/Fe3O4 magnetic nanocomposite

Highly efficient visible light TiO₂ photocatalyst was prepared by the sol-gel method at lower temperature (≤300 °C), and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and differential scanning calorimetry-thermogravimetric analysis (DSC-TGA). The effects of the heat treatment temperature and time of the as-prepared TiO₂ on its visible light photocatalytic activity were investigated by monitoring the degradation of methyl orange solution under visible light irradiation (wavelength ≥ 400 nm). Results show that the as-prepared TiO₂ nanoparticles possess an anatase phase and mesoporous structure with carbon self-doping and visible photosensitive organic groups. The visible light photocatalytic activity of the as-prepared TiO₂ is greatly higher than those of the commercial TiO₂ (P-25) and other visible photocatalysts reported in literature (such as PPy/TiO₂, P3HT/TiO₂, PANI/TiO₂, N-TiO₂ and Fe³⁺-TiO₂) and its photocatalytic stability is excellent. The reasons for improving the visible light photocatalytic activity of the as-prepared TiO₂ can be explained by carbon self-doping and a large amount of visible photosensitive groups existing in the as-prepared TiO₂. The apparent optical thickness (τ_app), local volumetric rate of photo absorption (LVRPA) and kinetic constant (k_T) of the photodegradation system were calculated.     

Preparation and properties of sliver and nitrogen co-doped TiO2 photocatalyst

TiO₂ photocatalysts co-doped with different content of Ag and N were prepared by sol–gel method combined with microwave chemical method. The samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), ultraviolet–visible diffuse reflectance spectrum (UV–vis) and photo-luminescence emission spectrum (PL). The photocatalytic activity was investigated by photocatalytic degradation of methylene blue (MB) under irradiation of fluorescent lamp. The results indicate that Ag and N co-doping can restrain the increase of grain size, broaden the absorption spectrum to visible light region, and inhibit the recombination of the photo-generated electron–hole pairs. Moreover, the photocatalytic activity of Ag–N–TiO₂ in MB degradation is remarkable improved. The degradation rate of the sample with Ag:TiO₂ = 0.05 at%, N:TiO₂ = 18.50 wt% in 5 h is 93.44%, which is much higher than that of Degussa P25 (39.40%).     

Nitrogen-doped TiO2 nanotubes with enhanced photocatalytic activity synthesized by a facile wet chemistry method

Nitrogen-doped TiO₂ nanotubes with enhanced photocatalytic activity were synthesized using titanate nanotubes as raw material by a facile wet chemistry method. The resulting nanotubes were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and UV-vis absorption spectroscopy, etc. The photocatalytic activity of nitrogen-doped TiO₂ nanotubes was evaluated by the decomposition of methylene blue under artificial solar light. And it was found that nitrogen-doped TiO₂ nanotubes exhibited much higher photocatalytic activity than undoped titanate nanotubes.     

Synthesis of potassium hexatitanate whiskers starting from metatitanic acid and potassium carbonate and sulfate by calcination method

Potassium hexatitanate whiskers were synthesized starting from metatitanic acid (H₂TiO₃), potassium carbonate and sulfate by calcination method. The effects of mole ratios of K₂CO₃ to metatitanic acid (H₂TiO₃), content of potassium sulfate, and calcination temperature on the crystallinity and morphology of the resultant potassium titanate whiskers were investigated by X-ray diffraction and scanning electron microscopy. Well crystallized potassium hexatitanate whiskers with an average length of 7.3 μm and an average diameter of 0.62 μm were synthesized when the molar ratio of K₂CO₃ to metatitanic acid was kept at 1:3.5 and the calcination temperature was up to 1150 °C. The presence of K₂SO₄ favored the formation of thin potassium hexatitanate whiskers as compared to the absence of K₂SO₄. The whiteness and brightness of the synthesized potassium hexatitanate whiskers were comparable to that of rutile TiO₂ pigment.