Investigation on solar photocatalytic activity of TiO2 loaded composite: TiO2/Eggshell, TiO2/Clamshell and TiO2/CaCO3

The TiO₂/Eggshell, TiO₂/Clamshell and TiO₂/CaCO₃ loaded composites were prepared by sol-gel method and characterized by XRD and SEM. Their photocatalytic activities were measured through the degradation of Acid Red B under solar light irradiation. The influences of TiO₂ loaded content, heat-treated temperature and time on the photocatalytic activities were reviewed. The effects of irradiation time and dye initial concentration on the photocatalytic degradation were also investigated. The results showed that the photocatalytic activity can be greatly enhanced by appropriate TiO₂ loaded content.     

Synthesis of nanostructure rutile TiO2 in a carboxyl-containing ionic liquid

Nanostructure rutile TiO₂ was prepared in a carboxyl-containing ionic liquid, 1-methylimidazolium-3-acetate chlorine ([AcMIm]Cl), by using TiOCl₂ solution as a precursor at low temperature. The obtained nanostructure TiO₂ was analyzed with fourier transform infrared (FTIR), X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The as-prepared TiO₂ present only rutile crystal phase and a novel flower-like morphology. The as-prepared rutile TiO₂ shows better photocatalytic performance in the degradation of methyl orange. The template-directing performance of ionic liquid is due to the bidentate chelating complexation between the carboxylic functional group of ionic liquid and titania.     

Visible light absorption ability and photocatalytic oxidation activity of various interstitial N-doped TiO2 prepared from different nitrogen dopants

Nitrogen-doped TiO₂ was developed to enable photocatalytic reactions using the visible range of the solar spectrum. This work reports on the synthesis, characterisation and kinetic study of interstitial N-doped TiO₂ prepared by the sol–gel method using three different types of nitrogen dopants: diethanolamine, triethylamine and urea. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV–visible spectroscopy were used to analyse the titania. Different interstitial N-doped TiO₂ properties, such as absorption ability in the UV–visible light region, redshift in adsorption edge, good crystallisation and composition ratio of titania structures (anatase and rutile) could be obtained from different nitrogen dopants. Amongst investigated nitrogen precursors, diethanolamine provided the highest visible light absorption ability of interstitial N-doped TiO₂ with the smallest energy bandgap and the smallest anatase crystal size, resulting in the highest efficiency in 2-chlorophenol degradation. The photocatalytic activity of all N-doped TiO₂ can be arranged in the following order: TiO₂/diethanolamine > TiO₂/triethylamine > TiO₂/urea > un-doped TiO₂. The initial rate of 2-chlorophenol degradation using the interstitial N-doped TiO₂ with diethanolamine was 0.59 mg/L-min and the kinetic constant was 2.34 × 10⁻² min⁻¹ with a half-life of 98 min. In all cases, hydroquinone was detected as a major intermediate in the degradation of 2-chlorophenol.     

Ag2S quantum dots-sensitized TiO2 nanotube array photoelectrodes

Ag₂S quantum dots (QDs) were deposited on ordered TiO₂ nanotube arrays (TNTAs) using a sequential chemical bath deposition (S-CBD) approach. AgNO₃ and thiourea were used as the precursor materials of Ag⁺ and S²⁻ ions, respectively. The decoration of Ag₂S QDs significantly shifted the absorption spectrum of the TNTAs to visible light region. As a result, Ag₂S QDs-sensitized TNTAs exhibited much higher photocurrent density than pure TNTAs under visible light irradiation.     

TiO2-SnO2 system for gas sensing—Photodegradation of organic contaminants

Catalytic photodegradation of organic contaminants by means of UV light has been demonstrated for gas sensors based on composites of TiO₂-SnO₂. Thin film resistive-type gas sensors of TiO₂-SnO₂ have been deposited at 350 °C by RF sputtering from a Ti-SnO₂ target with varying surface ratio of SnO₂/Ti. Photodegradation experiments of bromothymol blue by UV light have been performed by means of the optical spectrophotometry over the wavelength range extending from 300 nm to 600 nm. The influence of the UV illumination on the sensor response to 100-20,000 ppm of H₂ has been investigated in situ on motor oil contaminated sensors. It has been found that sequential exposures to UV light lead to a partial recovery of the sensor signal to hydrogen.     

Glycine assisted synthesis of flower-like TiO2 hierarchical spheres and its application in photocatalysis

Flower-like anatase TiO₂ hierarchical spheres assembled by nanosheets were synthesized by glycine assistant via a simple hydrothermal approach and after-annealing process. These flower-like spheres are about 2 μm in diameter with sheet thickness about 20 nm. Results showed reaction time, temperature, solution pH and glycine dosage all played an important role in control of shape and size of the as-synthesized TiO₂ nanocrystals. The photocatalytic activity of this nano-TiO₂ was evaluated by the photocatalytic oxidation decomposition of methyl orange under sunlight illumination in the presence of hydrogen peroxide (H₂O₂). The photocatalytic activity of the obtained TiO₂ was higher than that of commercial TiO₂.     

Photocatalytic Zn-doped TiO2 films prepared by DC reactive magnetron sputtering

Zn-doped TiO₂ films were prepared by means of pulsed DC reactive magnetron sputtering method using Ti and Zn mixed target. The deposition condition was optimized to produce uniform and transparent TiO₂ films. Titanium was in the Ti⁴⁺ oxidation state in all Zn-doped TiO₂ films. The zinc oxide deposited on the substrate was in the fully oxidized state of ZnO. Increase of zinc concentration inhibited the crystal growth in the TiO₂ films. The surface morphology gradually changed from crystalline to amorphous along with the increase of doped zinc concentration. The optical transmittances of these films decreased only slightly with increasing zinc concentration due to very similar band edges of ZnO and anatase TiO₂. The doped ZnO had weak influence on light absorption of the TiO₂ films. When zinc concentration was very low (<1 at%), the photocatalytic activities of the doped films had nearly no difference from that of pure TiO₂ film. Photocatalytic activities decreased obviously in the films containing high amount of zinc oxide.     

Photocatalytic performance of very thin TiO2/SnO2 stacked-film prepared by magnetron sputtering

TiO₂/SnO₂ stacked-layers are synthesized by reactive sputter deposition on the glass substrate. Very thin TiO₂/SnO₂ bilayer-photocatalysts exhibited a very high photocatalytic activity for a degradation of gaseous acetaldehyde. Both the control of an electronic structure of TiO₂ overlayer in the near-surface region and the interfacial separation of photogenerated electrons/holes in the TiO₂/SnO₂ stacked-layer are keys to improve the photocatalytic performance.     

Characterization of SiO2 and TiO2 films prepared using rf magnetron sputtering and their application to anti-reflection coating

Preparation of TiO₂ and SiO₂ films for optical applications was attempted using conventional rf magnetron sputtering in the sputtering ambient with various O₂/Ar+O₂ ratios and at substrate temperatures between room temperature and 400 °C. X-ray photoelectron spectroscopy (XPS) and optical spectroscopy investigations indicated that oxygen addition in the sputtering ambient was essential for growing TiO₂ films with stoichiometric compositions and good transmittance, while SiO₂ films had a stoichiometric composition of O/Si ratio=2.1-2.2 and were highly transparent in the visible wavelength region, independent of gas composition in the growing ambient. It was also identified from scanning electron microscope (SEM), atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FTIR) measurements that the structural characteristics of both TiO₂ and SiO₂ films were significantly improved with O₂ addition in the sputtering ambient, showing smoother surface morphologies and higher resistances to water absorption when compared with films grown without O₂ addition. Heating of the substrate between 200 and 400 °C considerably increased the refractive index of TiO₂ layers, resulting in dense structures along with an improvement of crystallinity. For optical applications, AR coatings composed of 2-4 multi-layers on glass were designed and manufactured by stacking in turn the SiO₂ and TiO₂ films at room temperature and O₂/Ar+O₂=10%, and the performance of the produced coatings was compared with simulation results.     

Structural investigations on TiO2 and Fe-doped TiO2 nanoparticles synthesized by laser pyrolysis

Undoped and Fe-doped TiO₂ nanopowders with Fe/Ti (atomic ratio) precursor concentration ranging from 7% up to 25% have been prepared by the IR laser pyrolysis technique. A sensitized mixture of TiCl₄ and Fe (CO)₅ was used as titanium and iron precursor, respectively. Reference undoped titania samples with a major concentration of anatase phase (about 90%) were obtained by the same technique by using very high flows of the oxidizing agent (air). The effects of the iron-dopant concentration on the essential structural properties of the resultant powders such as the phase formation, the crystallinity, the average particle size and distributions were systematically investigated by X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The decrease of the TiO₂-anatase crystalline phase, the simultaneous increase of the amorphous phase and the decrease in size of particle mean diameter appear as main effects induced by the Fe-dopant concentration.     

A facile approach to synthesize N and B co-doped TiO2 nanomaterials with superior visible-light response

N and B co-doped TiO₂ nanoparticles were prepared by a facile one-step combustion reaction where Ti(OC₄H₉)₄ and H₃BO₃ were used as the precursors and urea served as the fuel and the N source. The formation of TiO₂ nanoparticles and the co-doping of N and B into the TiO₂ matrix lattices were achieved simultaneously. Our experimental results have shown that the optical absorption edges of the N and B co-doped TiO₂ nanoparticles significantly shift toward long wavelength compared to that of non-doped TiO₂ photocatalysts. The estimated optical bandgap of the N&B co-doped TiO₂ nanoparticles is 2.13 eV, which is much smaller than that of pure anatase TiO₂ (3.18 eV). We further studied the photocatalytic activity of the synthesized N&B co-doped TiO₂ nanoparticles through the decomposition of acetic acid, showing that the N&B co-doped TiO₂ exhibits superb photocatalytic activity and visible light response compared to one of the best commercially available TiO₂ photocatalysts, P25.     

Fabrication of photocatalytic heat-mirror with TiO2/TiN/TiO2 stacked layers

The photocatalytic heat-mirror based on TiO₂/TiN/TiO₂ stacked layers is prepared by reactive magnetron sputtering on quartz substrates under substrate-heating condition. We find that the addition of a thin Ti interlayer between the TiN and the outer TiO₂ layers drastically improves the heat-insulating performance. This type of stacked layer also exhibits higher photocatalytic activity for decomposition of acetaldehyde gas, compared with a TiO₂ single layer. The optical property of the TiN in TiO₂/TiN/TiO₂ stacked layers is the key not only revealing excellent heat-insulating effect but also improving the photocatalytic performance of the outer TiO₂ layers in the stacked layers.     

Fabrication of TiO2 nanostructured films by spray deposition with high photocatalytic activity of methylene blue

TiO₂ films were successfully deposited onto hot quartz substrates by airbrush spraying using an aqueous dispersion. The films consisting of cubic or cauliflower-shaped structures expressed higher photodegradation efficiencies of methylene blue than those with prism-, flower- or fan-blade-shaped morphology due to the difference in the optical band gap energy. The photodegradation obeyed the pseudo-first-order Langmuir-Hinshelwood kinetic model with apparent rate constants ranging from 3.95 × 10^− 3 to 19.38 × 10^− 3 min^− 1 based on the film surface morphology.     

Photocatalytic degradation of 2,4-dichlorophenol wastewater using porphyrin/TiO2 complexes activated by visible light

The use of TiO₂ as photocatalyst to degrade the organic compounds is an effective method of oxidation process and has been widely studied in environmental engineering. However, TiO₂ absorbed the UV light which is only small part of sunlight reaching earth surface to activate photocatalytic procedure effectively is a major disadvantage. Therefore, studies on the development of new TiO₂ wherein its photocatalytic activity can be activated by visible light which is the major part of sunlight will be valuable for field application. In this study, we evaluate the photocatalytic degrading efficiency of porphyrins/TiO₂ complexes on the organic pollutants under irradiation with visible light (λ = 419 nm). The results showed that the photodecomposition efficiency of 2,4-dichlorophenol (2,4-DCP) wastewater by using porphyrin/TiO₂ irradiated under visible light for 4 h was up to 42-81% at pH 10. These evidences reveal that the system of porphyrin/TiO₂ complexes has also significantly efficiency of photocatalytic degradation for some hazardous or recalcitrant pollutants under visible light irradiation.     

Photo-fixation of SO2 in nanocrystalline TiO2 films prepared by reactive DC magnetron sputtering

We report on photo-fixation of SO₂ onto nanostructured TiO₂ thin films prepared by reactive DC magnetron sputtering. The films were exposed to 50 ppm SO₂ gas mixed in synthetic air and illuminated with UV light at 298 and 473 K. The evolution of the adsorbed SO_x species was monitored by in situ Fourier transform infrared specular reflection spectroscopy. Significant photo-fixation occurred only in the presence of UV illumination. The SO₂ uptake was dramatically enhanced at elevated temperatures and then produced strongly bonded surface-coordinated SO_x complexes. The total SO_x uptake is consistent with Langmuir adsorption kinetics. The sulfur doping at saturation was estimated from X-ray photoelectron spectroscopy to be ~ 2.2 at.% at 473 K. These films were pale yellowish and had an optical absorption coefficient being ~ 3 times higher than in undoped film. The S-doped films exhibit interesting oleophobic properties, exemplified by the poor adherence of stearic acid. Our results suggest a new method for sulfur doping of TiO₂ to achieve combined anti-grease and photocatalytic properties.     

Photocatalytic activity of TiO2 thin films deposited by RF magnetron sputtering

Nano-TiO₂ thin films were deposited on silicon and glass substrates by radio-frequency (RF) magnetron sputtering using TiO₂ ceramic target and characterized by X-ray diffractometer, X-ray photoelectron spectrometer, atomic force microscope, and ultraviolet-visible spectrophotometer. Photocatalytic activity was evaluated by light induced degradation of 5 ppm methyl orange solution using a high pressure mercury lamp as lamp-house. It was found that the film as deposited is polymorph, with energy gap of 3.02 eV, and can absorb visible light. The film was repeatedly used for six times in degradation of 5 ppm methyl orange, and the degradation rates of methyl orange solution are 36.566%, 33.112%, 32.824%, 32.248%, 30.521% and 28.794%, respectively. After ultrasonic treatment in de-ionized water for ten minutes, the degradation rate of methyl orange solution resumes to 33.975%.     

Characterization of sol-gel derived TiO2/ZrO2 films and powders by Raman spectroscopy

The effect of zirconium dioxide addition on crystal structure of sol-gel TiO₂ mesoporous films and powders has been investigated by means of Raman spectroscopy, X-Ray diffraction, and Atomic force microscopy. Zirconium incorporation (up to 30 mol%) into TiO₂ lattice resulted in the formation of Ti_1 − xZr_xO₂ solid solution with anatase structure for the binary powders has been proved. Appearance of tetragonal ZrO₂ phase was observed for the samples with high zirconium content.     

Photocatalytic degradation of phenol in aqueous solutions by Pr-doped TiO2 nanoparticles

Photocatalytic degradation of phenol in water was examined using Pr-doped TiO₂ nanoparticles. These photocatalysts were synthesized by an acid-peptized sol–gel method from titanium tetra-isopropoxide with different concentrations of Pr(III) dopant and calcination temperatures. Several tools such as XRD, BET surface area, SEM, and EDX, were used to evaluate particle structure, size distribution, and composition. The optical absorption properties of the prepared particles were also measured. Photocatalytic activity of the particles was studied in a batch reactor containing phenol solution with 400 W UV irradiation. Parameters affecting photocatalytic process such as the catalyst crystallinity, light absorption efficiency, the dosage of catalyst, dopant and phenol concentrations were investigated. The Pr-doped TiO₂ showed high activity for photocatalytic degradation of phenol. The presence of Pr ions in the TiO₂ particles would cause a significant absorption shift towards the visible region. The degradation process was optimized using 1 g/L Pr-doped TiO₂ with a Pr(III) concentration of 0.072 mol% after 2 h irradiation. It was shown that photodegradation followed a pseudo-first-order kinetics and the rate constant changed with phenol concentration.     

Photocatalytic properties of porous TiO2/Ag thin films

In this study, nanocrystalline TiO₂/Ag composite thin films were prepared by a sol-gel spin-coating technique. By introducing polystyrene (PS) spheres into the precursor solution, porous TiO₂/Ag thin films were prepared after calcination at a temperature of 500 °C for 4 h. Three different sizes (50, 200, and 400 nm) of PS spheres were used to prepare porous TiO₂ films. The as-prepared TiO₂ and TiO₂/Ag thin films were characterized by X-ray diffractometry (XRD) and by scanning electron microscopy to reveal structural and morphological differences. In addition, the photocatalytic properties of these films were investigated by degrading methylene blue under UV irradiation.When PS spheres of different sizes were introduced after calcination, the as-prepared TiO₂ films exhibited different porous structures. XRD results showed that all TiO₂/Ag films exhibited a major anatase phase. The photodegradation of porous TiO₂ thin films prepared with 200 nm PS spheres and doped with 1 mol% Ag exhibited the best photocatalytic efficiency where ∼ 100% methylene blue was decomposed within 8 h under UV exposure.     

One-pot synthesis of intestine-like SnO2/TiO2 hollow nanostructures

In the present study the intestine-like binary SnO₂/TiO₂ hollow nanostructures are one-pot synthesized in aqueous phase at room temperature via a colloid seeded deposition process in which the intestine-like hollow SnO₂ spheres and Ti(SO₄)₂ are used as colloid seeds and Ti-source, respectively. The novel core (SnO₂ hollow sphere)-shell (TiO₂) nanostructures possess a large surface area of 122 m²/g (calcined at 350 °C) and a high exposure of TiO₂ surface. The structural change of TiO₂ shell at different temperatures was investigated by means of X-ray diffraction and Raman spectroscopy. It was observed that the rutile TiO₂ could form even at room temperature due to the presence of SnO₂ core and the unique core-shell interaction.