Titania deposited on soft magnetic activated carbon as a magnetically separable photocatalyst with enhanced activity

Magnetically separable composite photocatalysts, TiO₂ deposited on soft magnetic ferrite activated carbon (TFAC), were prepared by sol-gel and dip-coating technique. The prepared composites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectra (FTIR), optical absorption spectroscopy, vibrating sample magnetometer (VSM) and nitrogen adsorption. These photocatalysts exhibited enhanced photocatalytic activity compared to Degussa P25 for the degradation of methyl orange (MO) in aqueous solution. The kinetics of MO degradation was well fitted to the Langmuir-Hinshelwood model. The samples showed good magnetic response and could be completely recovered by an external magnet. Furthermore, the photocatalysts could maintain high photocatalytic activity after five cycles, and the degradation rate of MO was still close to 90%.     

Preparation of titania hollow spheres by catalyst-free hydrothermal method and their high thermal stabilities

TiO₂ hollow spheres have been prepared by hydrothermal method using carbon spheres as hard templates based on template-directed deposition and calcination in order to remove templates. The morphology and structure of samples were systematically characterized by using various techniques, including XRD, zeta analyzer, SEM, TEM, DRS and FTIR. In this approach, the anatase phase was retained for temperatures up to 900 °C. Moreover, negative charged titania is deposited onto the negative charged surface of carbon spheres, which is proved by nanoparticle size analyzer. Therefore, a possible formation mechanism of TiO₂ hollow spheres was proposed. TiO₂ hollow spheres calcined at 550 °C exhibited the superior photocatalytic activity for the degradation of Rhodamine B, 2.9 times greater than that of Degussa P25. Furthermore, thermal stability of TiO₂ hollow spheres was examined. Fortunately, we found that hollow structures could still be visible distinctly after calcining at 900 °C.     

Photocatalytic behavior of heavy La-doped TiO2 films deposited by pulsed laser deposition using non-sintered target

We have investigated the control of photocatalytic behavior under deposited conditions of non-sintered target of different molar ratios with TiO₂ and La₂O₃ from 1:0 to 1:2 for heavily La doping, and post-annealing temperature from 600 °C to 1000 °C for crystallizing by pulsed laser deposition. We have successfully crystallized heavily La-doped TiO₂ films with post-annealing temperature over 800 °C and with molar ratio of TiO₂:La₂O₃ over 1:1 on a quartz substrate. Heavily La-doped TiO₂ films are observed the decomposition of methylene blue and a water-splitting reaction in photocatalytic behavior under Xe light irradiation. When stoichiometric La-doped TiO₂ (TiO₂:La₂O₃ = 1: 1) is synthesized with heat-treatment at 900 °C, the best results are obtained under photocatalytic behavior and pure La₂Ti₂O₇ crystalline were obtained.     

Gallium- and iodine-co-doped titanium dioxide for photocatalytic degradation of 2-chlorophenol in aqueous solution: Role of gallium

Visible-light-driven TiO₂-based catalysts for the degradation of pollutants have become the focus of attention. In the present work, iodine-doped titania photocatalysts (I-TiO₂) were improved by doping with gallium (Ga,I-TiO₂) and the resulting physicochemical properties and photocatalytic activity were investigated. The structural properties of the catalysts were determined by X-ray diffraction, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller analysis and transmission electron microscopy. We found that Ga probably enters the TiO₂ framework for doping levels <0.5 mol%. A further increase in Ga content probably leads to dispersal of excess Ga on the TiO₂ surface. The photocatalytic activity of Ga,I-TiO₂ catalysts was evaluated using 2-chlorophenol (2-CP) as a model compound under visible and UV-vis light irradiation. The results indicate that 0.5 mol% Ga loading and calcination at 400 °C represent optimal conditions in the calcining temperature range 400-600 °C and with doping levels from 0.1% to 1 mol%. The effective enhancement of 2-CP degradation might be attributed to the formation of oxygen vacancies by Ga doping, which could decrease the recombination of electron-hole pairs.     

TiO2 thick films supported on reticulated macroporous Al2O3 foams and their photoactivity in phenol mineralization

TiO₂ thick films deposited on macroporous reticulated Al₂O₃ foams with pore size of 10 ppi and 15 ppi were prepared using dip coating from slurries of Aeroxide^® P25 nanopowder and precipitated titania. All prepared films have sufficiently good adhesion to the surface of the substrate also in case of strongly cracked films. No measurable release of deposited TiO₂ after repeated photocatalytic cycles was observed. The photocatalytic activity was characterized as the rate of mineralization of aqueous phenol solution under irradiation of UVA light by TOC technique. The best activity was obtained with Aeroxide^® P25 coated Al₂O₃ foam with the pore size of 10 ppi, annealed at 600 °C. The optimal annealing temperature for preparation of films from precipitated titania could be determined at 700 °C. Films prepared by sol-gel deposition technique were considerably thinner compared to coatings made of suspensions and their photocatalytic activity was significantly smaller.     

Effect of heat treatment on morphology, crystalline structure and photocatalysis properties of TiO2 nanotubes on Ti substrate and freestanding membrane

Highly ordered titanium oxide (TiO₂) nanotubes were prepared by electrolytic anodization of titanium electrodes. Morphological evolution and phase transformations of TiO₂ nanotubes on a Ti substrate and that of freestanding TiO₂ membranes during the calcinations process were studied by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction microscopy. The detailed results and mechanisms on the morphology and crystalline structure were presented. Our results show that a compact layer exists between the tubular layer and Ti substrate at 600 °C, and the length of the nanotubes shortens dramatically at 750 °C. The freestanding membranes have many particles on their tubes during calcinations from 450 to 900 °C. The TiO₂ nanotubes on the Ti substrate transform to rutile crystals at 600 °C, while the freestanding TiO₂ membranes retain an anatase crystal with increasing temperature to 800 °C. The photocatalytic activity of TiO₂ nanotubes on a Ti substrate annealed at different temperatures was investigated by the degradation of methyl orange in aqueous solution under UV light irradiation. Due to the anatase crystals in the tubular layer and rutile crystals in the compact layer, TiO₂ nanotubes annealed at 450 °C with pure anatase crystals have a better photocatalytic activity than those annealed at 600 °C or 750 °C.     

Preparation and characterization of iodine-doped mesoporous TiO2 by hydrothermal method

Iodine-doped mesoporous TiO₂ (I/TiO₂) was prepared by hydrothermal method, using tetrabutyl titanate as precursor, potassium iodate as iodine sources. The as-prepared I/TiO₂ catalysts were characterized by UV-vis, XRD, TEM, BET, TG/DTA, XPS and photoluminescence (PL) spectroscopy. Production of OH radicals on the I/TiO₂ surface was detected by the PL technique using terephthalic acid as a probe molecule. The effects of hydrothermal reaction temperature, calcination temperature and iodine doping content on the structure and properties of the catalysts were investigated. The results showed that iodine-doped TiO₂ calcinated at 300 °C have good anatase crystal. The optimal hydrothermal conditions have been determined to be that reaction temperature 120 °C, calcinated temperature 300 °C and added 1.16 mmol iodine dopants. The average particle size of I/TiO₂ synthesized under optimal condition (I-3 sample) is about 3.9 nm. The I-3 photocatalyst contains 100% anatase crystalline phase of TiO₂. BET specific surface area of I-3 sample is184.8 m² g⁻¹ and is 3.67 times that of pure TiO₂ (50.37 m² g⁻¹). Iodine in I/TiO₂ catalyst mainly exists in the form of I₂, and photoactivity of I/TiO₂ catalyst in visible light comes from photosensitize of I₂. I/TiO₂ catalysis shows very high efficiency for the degradation of phenol under visible light.     

Optical properties of ITO/TiO2 single and double layer thin films deposited by RPLAD

Indium tin oxide (ITO) and titanium dioxide (TiO₂) single layer and double layer ITO/TiO₂ films were prepared using reactive pulsed laser ablation deposition (RPLAD) with an ArF excimer laser for applications in dye-sensitized solar cells (DSSCs). The films were deposited on SiO₂ substrates either at room temperatures (RT) or heated to 200-400 °C. Under optimized conditions, transmission of ITO films in the visible (vis) range was above 89% for films produced at RT and 93% for the ones deposited at higher temperatures. Increasing the substrate temperature from RT to 400 °C enhances the transmission of TiO₂ films in the vis-NIR from about 70% to 92%. High transmission (≈90%) was observed for the double layer ITO/TiO₂ with a transmission cut-off above 900 nm. From the transmission data, the energies gaps (E_g), as well as the refractive indexes (n) for the films were estimated. n ≈ 2.03 and 2.04, respectively for ITO films and TiO₂ film deposited at 400 °C in the visible region. Post-annealing of the TiO₂ films for 3 h at 300 and 500 °C was performed to enhance n. The refractive index of the TiO₂ films increases with the post-annealing temperature. The direct band gap is 3.6, 3.74 and 3.82 eV for ITO films deposited at RT, 200, and 400 °C, respectively. The TiO₂ films present a direct band gap of 3.51 and 3.37 eV for as deposited TiO₂ films and when annealed at 400 °C, respectively. There is a shift of about 0.1 eV between ITO and ITO/TiO₂ films deposited at 200 °C. The shift decreases by half when the TiO₂ film was deposited at 400 °C. Post-annealing was also performed on double layer ITO/TiO₂.     

Preparation and characterization of Fe-doped TiO2 on fly ash cenospheres for photocatalytic application

Fe³⁺-doped TiO₂ film deposited on fly ash cenosphere (Fe-TiO₂/FAC) was successfully synthesized by the sol-gel method. These fresh photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analyses (TGA). The XRD results showed that Fe element can maintain metastable anatase phase of TiO₂, and effect of temperature showed rutile phase appears in 650 °C for 0.01% Fe-TiO₂/FAC. The SEM analysis revealed the Fe-TiO₂ films on the surface of a fly ash cenosphere with a thickness of 2 μm. The absorption threshold of Fe-TiO₂/FACs shifted to a longer wavelength compared to the photocatalyst without Fe³⁺-doping in the UV-vis absorption spectra. The photocatalytic activity and kinetics of Fe-TiO₂/FAC with varying the iron content and the calcination temperatures were investigated by measuring the photodegradation of methyl blue (MB) during visible light irradiation. Compared with TiO₂/FAC and Fe³⁺-doped TiO₂ powder (Fe-TiO₂), the degradation ratio using Fe-TiO₂/FAC increased by 33% and 30%, respectively, and the best calcined temperature was 450 °C and the optimum doping of Fe/Ti molar ratio was 0.01%. The Fe-TiO₂/FAC particles can float in water due to the low density of FAC in favor of phase separation to recover these photocatalyst after the reaction, and the recovery test shows that calcination contributes to regaining photocatalytic activity of Fe-TiO₂/FAC photocatalyst.     

Highly ordered anodic TiO2 nanotube arrays and their stabilities as photo(electro)catalysts

Highly ordered TiO₂ nanotube arrays with an average diameter of 230 nm, a wall thickness of 30 nm and a length of 1.8 μm were fabricated within a large domain by electrochemically anodizing of a titanium foil in a mixed solution of glycerol and NH₄F aqueous electrolyte. The TiO₂ nanotubes exhibit an anatase structure after annealing at 450 °C in air for 3 h. The direct photolysis (DP), photocatalytic (PC), electrocatalytic (EC) and photoelectrocatalytic (PEC) activities of the TiO₂ nanotube arrays were investigated using methyl orange (MO) as the model pollutant. The degradation of MO in PC process is faster than that in DP process, which confirms the photocatalysis of TiO₂ nanotube arrays. The degradation rate in PEC process is much higher than those in EC and PC processes, which demonstrates the synergetic effect between PC and EC processes. The synergetic factor is 4.1, which suggests that the synergetic effect is strong. Moreover, the stabilities of morphology, structure and photo(electro)catalytic degradation performance of the TiO₂ nanotube arrays were studied in order to evaluate their applicability as photo(electro)catalysts. The photo(electro)catalytic experiments bring neither morphological nor structural modifications to the nanotube arrays. The photo(electro)catalytic degradation rates of the TiO₂ nanotube arrays maintain stable in 10 cycles, which indicates that the TiO₂ nanotube arrays are appropriate to be applied as photo(electro)catalysts.     

Effect of post heat treatment on microstructure and photocatalytic activities of TiO2 nanoribbons

Low-dimensional TiO₂ nanoribbons were synthesized by a simple one-step hydrothermal method. The TiO₂ nanoribbons were calcined over the temperature range 200-800 °C in order to enhance their photocatalytic properties by altering their crystal phase and increasing crystallization. Effects of hydrothermal temperature, calcinated temperature and calcination time on the formation of nanostructures have been observed and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The (BET) specific surface area of the samples which with different post treatments were determined by N₂ absorption-desorption experiment. In addition, photocatalytic activities of the nanoribbons were evaluated by photodegradation of organic dyes methyl orange under the radiation of UV light. The results reveal that the post-treatments have great effects on the microstructures and the photocatalytic activities of TiO₂ nanoribbons.     

Sputter deposition of high transparent TiO2−xNx/TiO2/ZnO layers on glass for development of photocatalytic self-cleaning application

In this study, TiO_2−xN_x/TiO₂ double layers thin film was deposited on ZnO (80 nm thickness)/soda-lime glass substrate by a dc reactive magnetron sputtering. The TiO₂ film was deposited under different total gas pressures of 1 Pa, 2 Pa, and 4 Pa with constant oxygen flow rate of 0.8 sccm. Then, the deposition was continued with various nitrogen flow rates of 0.4, 0.8, and 1.2 sccm in constant total gas pressure of 4 Pa. Post annealing was performed on as-deposited films at various annealing temperatures of 400, 500, and 600 °C in air atmosphere to achieve films crystallinity. The structure and morphology of deposited films were evaluated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). The chemical composition of top layer doped by nitrogen was evaluated by X-ray photoelectron spectroscopy (XPS). Photocatalytic activity of samples was measured by degradation of Methylene Blue (MB) dye. The optical transmittance of the multilayer film was also measured using ultraviolet-visible light (UV-vis) spectrophotometer. The results showed that by nitrogen doping of a fraction (∼1/5) of TiO₂ film thickness, the optical transmittance of TiO_2−xN_x/TiO₂ film was compared with TiO₂ thin film. Deposited films showed also good photocatalytic and hydrophilicity activity at visible light.     

Preparation, characterization and visible-light photocatalytic activity of AgI/AgCl/TiO2

In this paper, a novel composite photocatalyst AgI/AgCl/TiO₂ was prepared by ion exchange method and characterized by XRD, SEM and UV-Vis spectrometry. The as-prepared AgI/AgCl/TiO₂ composites show much higher photocatalytic activity than AgCl/TiO₂ and AgI/TiO₂ under visible-light irradiation (λ > 400 nm) in the process of methyl orange (MO) degradation. When the molar percentage of AgI to initial AgCl is 20% (sample SE-20%), the maximal degradation efficiency of MO has reached 85.8% after irradiation for 120 min. The enhancement of photocatalytic activity of the composite photocatalyst AgI/AgCl/TiO₂ will be attributed to its good absorption in the visible-light region, especially low recombination rate of the electron-hole pairs based on the photoluminescence (PL) spectra investigation of AgI/AgCl/TiO₂ and the matching band structures of AgI, AgCl and TiO₂. The detection of reactive species by radical scavengers displays that O₂⁻ and H₂O₂ are the main reactive species for the degradation of MO under visible-light irradiation. Moreover, PL analysis by using terephthalic acid (TA) as a probe molecule further reveals that OH can be negligible for the degradation of MO.     

Surface effect of natural zeolite (clinoptilolite) on the photocatalytic activity of TiO2

The surface interaction between TiO₂ and natural zeolite, clinoptilolite, has been investigated by means of transmission electron microscope (TEM), atom force microscope (AFM), X-ray diffractometer (XRD), diffuse reflectance infrared Fourier transform (DRIFT) and far Fourier transform infrared ray (FTIR) spectroscopy. And the photocatalytic degradation (PCD) rate of methyl orange (MO), a model of recalcitrant azo dye, in aqueous system has been measured to compare the photocatalytic activities of different photocatalysts. A model has been carried out to explain the incorporation between TiO₂ particles and natural zeolite. The results show that the TiO₂ particles loaded on zeolite are 50 nm or so, smaller than the pure one, and combine with zeolite via chemical force. Since the reserved adsorption ability and the existence of electron trapper, the TiO₂-zeolite performed more efficient at low initial concentration and in the later period of PCD process, as compared with pure TiO₂ nanopowders.     

Preparation and performance of photocatalytic TiO2 immobilized on palladium-doped carbon fibers

Pd-modified carbon fibers (CFs) are obtained by a facile oxidation-reduction method and then dip-coated in a sol-gel of titanium dioxide (TiO₂) to form supported TiO₂/Pd-CF photocatalysts. The morphology of the Pd-modified CFs and the amount Pd deposited are characterized by field emission scanning electron microscopy and atomic absorption spectrometry, respectively. X-ray diffraction is used to investigate the crystal structures of the TiO₂ photocatalyst. Acid orange II is used as a model contaminant to evaluate the photocatalytic properties of the photocatalyst under UV irradiation. TiO₂/Pd-CF exhibits higher catalytic activity than TiO₂/CF towards the degradation of acid orange II. Optimum photocatalytic performance and support properties are achieved when the Pd particle loading is about 10.8 mg/g.     

Sonodegradation and photodegradation of methyl orange by InVO4/TiO2 nanojunction composites under ultrasonic and visible light irradiation

The InVO₄/TiO₂ nanojunction composites with different weight ratio of 1:10, 1:25, 1:50 and 1:100 were successfully constructed using an ion impregnate method, followed by calcining temperature 400 °C for 2 h in Ar. The sono- and photo-catalytic activities of the InVO₄/TiO₂ nanojunction composites were evaluated through the degradation of methyl orange (MO) in aqueous solution under ultrasonic and visible light irradiation, respectively. The experimental results determined that the (1:50) InVO₄/TiO₂ nanojunction composite has exhibited the highest sonocatalytic activity. It can be ascribed to vectorial charge transfer at the co-excited InVO₄/TiO₂ interface under ultrasonic irradiation, results in the complete separation of electrons and holes. Interestingly, the (1:25) InVO₄/TiO₂ nanojunction composite displayed superior photocatalytic activity for MO degradation under visible light, indicating that InVO₄ as a narrow band gap sensitizer can expand photocatalytic activity of TiO₂ to visible region, and the charge transfer can be formed from high energy level of InVO₄ conduction band to the low energy level of TiO₂ conduction band in a present of excited InVO₄ alone under visible light irradiation. The sono- and photo-catalytic activities of the InVO₄/TiO₂ nanojunction composites were found to be dependent significantly on different InVO₄ contents, which can be explained by the influence of charge transfer on the basis of the work functions of different catalysis mechanism.     

Photocatalytic activity of multielement doped TiO2 in the degradation of congo red

TiO₂ although considered a promising photocatalyst for the degradation of aqueous pollutants, it suffers from poor absorption in the visible region and hence requires ultraviolet (UV) light for activation. To make TiO₂ a visible active photocatalyst, multielement (C, N, B, and F) doping has been done. The synthesised CNBF/TiO₂ catalysts were calcined at different temperatures and characterized by XRD, BET surface area, UV DRS, XPS, HRSEM-EDAX, and TEM techniques. These catalysts found to show less band gap values when compared to bare TiO₂. These catalysts were tested for their catalytic activity towards the degradation of a textile dye - congo red (CR) under different reaction conditions. It was found that the photocatalytic activity was dependent on both doping of multielement and the calcination temperature of CNBF/TiO₂. The co-doped catalysts which were calcined at 400 °C and 600 °C (100% intensity in anatase phase) were found to be the best catalysts (100% decolourisation of CR in 21/2 h and 2 h respectively). TOC analysis carried out for the samples at the reaction time of 5 h showed very high percentage (83%) degradation of CR over CNBF/TiO₂ catalysts calcined at 600 °C when compared to the other catalysts calcined at different temperatures. CNBF/TiO₂ (1000 °C) showed very less photocatalytic activity due to the formation of rutile phase.     

Characterization and activity of visible-light-driven TiO2 photocatalyst codoped with lanthanum and iodine

The novel visible-light-activated La/I/TiO₂ nanocomposition photocatalyst was successfully synthesized using precipitation-dipping method, and characterized by X-ray powder diffraction (XRD), the Brunauer-Emmett-Teller (BET) method, transmission electron microscopy (TEM), thermogravimetry-differential scanning calorimetry (TG-DSC) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The photocatalytic activity of La/I/TiO₂ was evaluated by studying photodegradation of reactive blue 19 as a probe reaction under simulated sunlight irradiation. Photocatalytic experiment results showed that the maximum specific photocatalytic activity of the La/I/TiO₂ photocatalyst appeared when the molar ratio of La/Ti was 2.0 at%, calcined at 350 °C for 2 h, due to the sample with good crystallization, high BET surface area and small crystal size. Under simulated sunlight irradiation, the degradation of reactive blue 19 aqueous solution reached 98.6% in 80 min, which showed La/I/TiO₂ photocatalyst to be much higher photocatalytic activity compared to standard Degussa P25 photocatalyst. The higher visible light activity is due to the codoping of lanthanum and iodine.     

Synthesis of efficient TiO2-based photocatalysts by phosphate surface modification and the activity-enhanced mechanisms

A simple strategy to greatly increase the thermal stability of nanocrystalline anatase has been put forward to fabricate efficient TiO₂-based photocatalysts under ultraviolet irradiation, via the surface modification with phosphate anions. The results show that the increased anatase thermal stability is attributed to the roles of the phosphate modification effectively inhibiting the contacts among anatase nanocrystals. Compared to un-modified TiO₂, the modified TiO₂ calcined at high temperature (over 700 °C) exhibits much high photocatalytic activity for degrading Rhodamine B (or phenol) solution, even superior to the commercial P25 TiO₂. The activity enhancement is mainly attributed to the increased separation rate of photogenerated charge carriers on the basis of the measurements of steady state- and transient state-surface photovoltage spectroscopy. This work would provide a practical route to reasonably design and synthesize high-performance TiO₂-based nanostructured photocatalysts with high anatase thermal stability.     

The photocatalytic application and regeneration of anatase thin films with embedded commercial TiO2 particles deposited on glass microrods

Anatase thin films (<200 nm in thickness) embedding Degussa P25 TiO₂ were prepared by sol-gel method. TiO₂-anatase thin films were deposited on a fiberglass substrate and then ground to obtain glass microrods containing the composite films. The film structure was characterized using Raman spectroscopy, atomic absorption and UV-vis spectrophotometry, and atomic force microscopy. The photocatalytic activity of the composite films, calcined at 450 °C, and the regeneration of the activity under the same experimental conditions, were assessed using gas chromatography to study the photodegradation of phenol, an industrial pollutant, in water under 365 nm irradiation. The film with 15.0 wt.% of P25 TiO₂ was found to be more photoactive (54 ppm of degraded phenol at 6 h of illumination) than the other ones.