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.     

Three-dimensionally ordered macroporous Ti1−xTaxO2+x/2 (x = 0.025, 0.05, and 0.075) nanoparticles: Preparation and enhanced photocatalytic activity

Anatase phase, three-dimensionally ordered macroporous (3 DOM) Ti_1−xTa_xO_{2 + x / 2} (x = 0.025, 0.05, and 0.075) nanoparticles with macropore diameter 290 to 310 nm, wall thickness 50 to 80 nm, and particle size 10 to 12 nm were prepared by combination of the sol–gel chemistry and polystyrene (PS) templating procedure. The products exhibited relatively narrower band gaps and larger BET surface areas than those of the starting solitary 3 DOM metal oxides, and their photocatalytic activities for the degradation of an aqueous 4-nitrophenol remarkably enhanced compared with 3 DOM anatase TiO₂, Ta₂O₅, and Degussa P-25.     

Effects of ZrO2 addition on phase stability and photocatalytic activity of ZrO2/TiO2 nanoparticles

ZrO₂/TiO₂ nanoparticles with various Zr/Ti ratios (0–0.9) were prepared by a polymer complex solution method (PCSM). The prepared samples were characterized using transmission electron microscopy (TEM), the Brunauer, Emmett & Teller (BET) method, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The ZrO₂/TiO₂ photocatalyst showed a high specific area and small crystal size. The XRD pattern for the Zr/Ti = 0.1 sample indicated that the addition of ZrO₂ stabilized the anatase phase of TiO₂ up to 800 °C. The photocatalytic activity of Zr/Ti = 0.1 sample was higher than that of the TiO₂ sample and commercially available Degussa P25. The high photocatalytic activity can be attributed to stronger adsorption in the visible light region, higher specific area, smaller crystal size and increased surface OH groups.     

Photocatalytic behavior of TiO2 nanoparticles supported on porous aluminosilicate surface modified by cationic surfactant

In order to utilize the photocatalytic function of TiO₂ nanoparticles in materials manufactured from organic polymeric compounds, such as paper, resins, and textiles, TiO₂ nanoparticles supported on aluminosilicate, which contained 1, 5, and 10 wt% of TiO₂ were prepared by mixing commercial TiO₂ nanoparticles and porous aluminosilicate at pH 7 in a cationic surfactant aqueous solution. Most of the supported TiO₂ nanoparticles on the aluminosilicate surface were observed by TEM–EDS (energy depressive X-ray spectroscopy) analysis. TiO₂ nanoparticles supported on aluminosilicate reduced the formaldehyde concentration from 20 to 0 ppm after UV irradiation for 20 h; the reduction of formaldehyde concentration under UV irradiation was obviously different from that in the dark. Moreover, a paper mixed with 20 wt% of TiO₂ nanoparticles supported on aluminosilicate bleached the stains colored with cigarette tar after UV irradiation for 6 h. However, the paper maintained its initial tensile strength even after UV irradiation for 1 year; in contrast, the paper mixed with a simple dry mixture of TiO₂ powder and aluminosilicate lost approximately half of its initial tensile strength after a year. TiO₂ nanoparticles supported on aluminosilicate could exhibit photocatalytic activity without decomposing the organic polymeric compounds.     

Adsorption and photocatalysis of nanocrystalline TiO2 particles prepared by sol–gel method for methylene blue degradation

Titanium dioxide (TiO₂) powders were synthesized by using TiO₂ colloidal sol prepared from titanium-tetraisopropoxide (TTIP) and used as a starting material by applying the sol–gel method. The effect of aging times and temperatures on physical and chemical properties of TiO₂ sol particles was systematically investigated. The results showed that the crystallinity and average particle size of TiO₂ can be successfully controlled by adjusting the aging time and temperature. The samples after calcination of TiO₂ powders were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and nitrogen adsorption measurements. In addition, the photocatalytic activity of synthesized TiO₂ powders was evaluated by studying the degradation of 10 ppm aqueous methylene blue dye under 32 W high pressure mercury vapor lamp with 100 mg of TiO₂ powders. The highest photocatalytic activity was observed in TiO₂ powder synthesized at 90 °C for 0 h attributed to the presence of anatase and rutile phases in an 80:20 ratio.     

High pressure behaviors of nanoporous anatase TiO2

High pressure behaviors of nanoporous anatase TiO₂ were studied using in situ Raman spectroscopy up to 37 GPa. The nanoporous anatase phase starts to transform into the baddeleyite phase with poor crystallinity at ～15.2 GPa, and the baddeleyite phase coexists with anatase phase up to 18.4 GPa. The baddeleyite form transforms into an amorphous phase above 20.5 GPa. Upon decompression, the amorphous phase recovers to the baddeleyite phase and then transforms to the α-PbO₂ phase. The phase transition from the baddeleyite phase to the amorphous form is reversible. The poor crystalline baddeleyite phase acts as an intermediate state in the amorphization process. The phase transitions of the nanoporous anatase TiO₂ are obviously different from the pressure-induced amorphization in the anatase TiO₂ nanoparticles. These results indicate that the porous microstructure plays important roles in the high pressure phase transitions of the nanoporous anatase TiO₂.     

Effect of TiO2 nanoparticles aggregation in silicate thin coating films on photocatalytic behavior for antifouling materials

Two types of disperser namely, a high speed agitation bead mill and a colloidal mill, were used for the dispersion behavior control of TiO₂ nanoparticles (20 nm in average primary diameter) in an aqueous suspension. A composite thin film raging in thickness from 90 to 400 nm was prepared from the coating suspension following the addition of a commercial ethyl silicate oligomer binder into the prepared suspension by means of a spray coating method. The mean aggregate size of TiO₂ nanoparticles in the aqueous suspension was found to be 80 nm and 290 nm in diameter, respectively, when using the agitated bead and colloidal milling methods. Large aggregates on the order of several hundred nanometers were found to remain in the suspension after colloidal milling. Further, a fine dispersion of TiO₂ nanoparticles in the thin film produced using the agitation bead milling process promoted the photocatalytic activity and enhanced transparency of the film for visible light. The aggregate structure of TiO₂ nanoparticles in an aqueous suspension was well maintained in the film prepared by a spray coating process.     

Effect of SiO2 nanoparticles on the phase transformation of TiO2 in micron-sized porous TiO2–SiO2 mixed particles

Spherical and nanoporous TiO₂ and TiO₂–SiO₂ mixed micro-particles with four different compositions (20/80, 50/50, 80/20, 90/10 in weight ratio of TiO₂/SiO₂) were prepared by spray drying method from colloidal mixtures of amorphous silica and anatase titania nanoparticles. The as-prepared particles were heat-treated at 900 °C for 0.5–5 h. The TiO₂ and TiO₂–SiO₂ particles were spherical in shape and the average particle diameter was about 1 μm. The anatase mass fraction and the specific surface area of TiO₂–SiO₂ (50 wt.% SiO₂) mixed particles were kept to 61.5% and 30.6%, respectively, of their initial values after 5 h heat-treatment whereas these values of TiO₂ particles were rapidly decreased to 13.0% and 1.2% of their initial values, respectively, within 30 min after heat-treatment. And the anatase mass fraction and specific surface area increased as SiO₂ content in the TiO₂–SiO₂ mixed particles increased.     

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.     

Band gap tuning and nonlinear optical characterization of TiO2–SiO2 nanocomposites with respect to composition and phase

We report on the linear and nonlinear optical studies on TiO₂–SiO₂ nanocomposites with varying percentage ratio. It is found that optical band gap of the material varies with respect to the amount of the SiO₂ in the composite. Nonlinear optical characterization of these samples was studied by using open as well as closed aperture Z-scan technique using an Nd:YAG laser (532 nm, 7 ns, 10 Hz). The nanocomposites showed enhanced nonlinear optical properties than pure TiO₂ and this can be attributed to the surface states and weak dielectric confinement of TiO₂ nanoparticles by SiO₂ matrix. The nanocomposites were thermally treated and similar studies were performed. The anatase form of TiO₂ in the nanocomposites showed superior properties relative to the amorphous and rutile phase of the composite. The involved mechanism is explained by taking into account the dominant role played by the excitons in the TiO₂ nanoparticles.     

A facile decoration of anatase Fe3O4/TiO2 nanocomposite with graphene quantum dots: Synthesis,characterization, and photocatalytic activity

A combination of electron-rich graphene quantum dots (GQDs) with Fe₃O₄/TiO₂ nanocomposites may develop an efficient electron transfer for enhanced photocatalytic activity. In this report, a facile decoration of GQDs with maltose precursor was synthesized and loaded onto magnetic anatase TiO₂ nanocomposites under hydrothermal methods. The as-synthetized magnetic TiO₂/GQDs nanocomposite resulted in a specific surface area of 38.00 m²/g and a total pore volume of 0.186 cm³/g. The HRTEM images showed a lattice plane distance of 0.350 nm related to the interplanar spacing of the anatase TiO₂ (1 0 1) plane and that of 0.299 nm observed for the in-plane lattice part of GQDs. The effects of magnetic loading ratio and GQDs loading onto TiO₂, pH, photocatalyst dosage, and methylene blue (MB) concentration were thoroughly evaluated to find the optimum conditions of mineralization MB for getting the highest photocatalytic efficiency. The removal efficiency of around 86.08 ± 3.62% was obtained at pH11, photocatalytic dose 400 mg/100 mL, and MB concentration 10 mg/L. Moreover, the photogenerated electron transfers and MB degradation mechanism by the resulting Fe₃O₄/TiO₂/GQD_S under irradiation of UVA light are proposed. The as-synthesized material improved meaningfully greater photocatalytic efficiency for degrading MB under UVA light irradiation than merely pure anatase TiO₂. Also, the predominant mechanism of MB degradation was direct oxidative decomposition through the photogenerated holes. The photocatalytic destruction of MB complied with the apparent first-order models under UVA light irradiation.     

Synthesis and characterization of anatase photocatalyst powder from sodium titanate compounds

The synthesis of anatase photocatalyst powder from sodium titanate compounds prepared from rutile and sodium carbonate powder was studied. The sodium titanate compounds were derived from the solid-state reactions of three different (1:4, 1:1.58 and 1:0.73) (m/m) ratios of TiO₂:Na₂CO₃ at 850 °C. Then, the powder was dissolved in 5 M H₂SO₄ solution, filtered, washed, dried and calcined at 400, 500 or 600 °C for 2 h. The effects of processing parameters on the resultant phase structure, crystallite size, morphology and the surface area of the synthesized powders were investigated. It was found that the anatase powder with a crystallite size of about 102 nm and a specific surface area of 16.7 m²/g synthesized from sodium titanate compounds with a 1:1.58 (m/m) ratio of TiO₂:Na₂CO₃ and calcined at 600 °C showed the best photocatalytic activity to degrade of methylene blue in aqueous solution under UV irradiation.     

Visible-light absorption and photocatalytic activity of Cr-doped TiO2 nanocrystal films

Chromium doped titanium dioxide (TiO₂) nanocrystal films with various doping concentration have been successfully prepared by a sol–gel dip-coating process. These films have been characterized by XRD, XPS, AFM, and UV–vis absorption spectroscopy. It is found that Cr doping can effectively reduce the transition temperature of anatase to rutile phase as well as the grain size. The absorption edges of TiO₂ thin films shift towards longer wavelengths (i.e. red shifted) from 375 nm to about 800 nm with increasing Cr concentration, which greatly enhances TiO₂ nano-materials on the absorption of solar spectrum. The appearance of UV–vis absorption features in the visible region can be ascribed to the newly formed energy levels such as Cr 2p level and oxygen vacancy state between the valence and the conduction bands in the TiO₂ band structure. The enhancement of the photocatalytic properties is observed for Cr-doped TiO₂ thin film.     

Influence of TiO2 dimension and graphene oxide content on the self-cleaning activity of methylene blue-stained photocatalytic films

In the present study, TiO₂ and graphene oxide (GO)/TiO₂ composite films were simply fabricated by hot-plate spray coating technique. The influences of TiO₂ dimension and GO content on the self-cleaning activity of methylene blue (MB)-stained films were investigated. The matrix of anatase TiO₂ quasi-cubic and octahedral particles in diameter of 6–9 nm (ST film) degraded 80% stained dye, much higher than those either in bigger size (30–50 nm) or in flower morphology due to the nano effect. Moreover, the photocatalytic performance of such nanostructured film was strongly enhanced by the combination with GO sheets. Increasing GO content led to significant enhancement in film transmittance and MB adsorptivity. In the aspect of the self-cleaning activity for MB, the addition of GO up to 1 wt.% showed higher efficiency but excess content led to similar performance in comparison with pure TiO₂ film.     

Photocatalytic properties of SrTiO3 nanoparticles prepared by a polyacrylamide gel route

A polyacrylamide gel method has been used to prepare SrTiO₃ nanoparticles. It is found that the choice of chelating agent has a great influence on the SrTiO₃ synthesis. The use of citric acid as the chelating agent leads to the synthesis of pure SrTiO₃ at a calcination temperature of 550 °C. By using the chelating agent acetic acid, however, a much higher calcination temperature at 800 °C is required to produce a single sample. The citric acid- and acetic acid-resulted samples exhibit both sphere- particle morphology, and have an average particle size of ~ 55 nm and ~ 100 nm, respectively. The photocatalytic properties of the as-prepared SrTiO₃ nanoparticles have been investigated by the degradation of Congo Red, RhB, MO, and MB under ultraviolet irradiation. The citric acid-resulted sample is found to exhibit a photocatalytic activity higher than the acetic acid-resulted sample, expectedly due to its relatively smaller particle size. In addition, different degradation efficiencies are found between the dyes, and the highest degradation efficiency is observed for Congo Red.     

Enhanced photoactivity and anatase thermal stability of silica–alumina mixed oxide additives on sol–gel nanocrystalline titania

Nanocrystalline titania with silica and silica–alumina mixed oxide as additives has been prepared through a sequential approach sol–gel method starting from titanyl sulphate in aqueous medium. The mixed oxide added titania shows increased anatase phase stability and high surface area. The complete transformation of anatase to rutile in the mixed oxide added titania occurs only above 1100 °C. The silica and silica–alumina added titania precursor even after calcination at 800 °C show specific surface area of 53 m² g^− 1 and 63 m² g^− 1 respectively. Further, the mixed oxide added titania sample shows excellent photoactivity compared to the commercially available Hombikat UV 100 titania, with respect to degradation of methylene blue. The addition of mixed oxide has resulted in better properties with respect to specific surface area, increased anatase to rutile phase transformation and photocatalytic activity of titania.     

Structural phase analysis,band gap tuning and fluorescence properties of Co doped TiO2 nanoparticles

This paper reports on structural and optical properties of Co (0, 3, 5 & 7 mol%) doped TiO₂ (titania) nanoparticles (NPs) synthesized by employing acid modified sol–gel method. The crystalline phase of the pure and doped NPs was observed with X-ray diffraction (XRD) followed by Raman scattering technique. Field emission scanning electron microscope and transmission electron microscopy give the morphological details. Fourier transform infrared spectra indicate the bonding interactions of Co ions with the titania lattice framework. Optical studies were attained with UV–visible absorption and fluorescence emission spectroscopy. XRD analysis reveals that all prepared samples have pure anatase phase with tetragonal symmetry devoid of any other secondary phase. The average crystallite size of all samples was calculated using Scherrer’s formula and was found to vary from 8 to 10 nm with doping concentration of Co. The Raman spectroscopy further confirmed the formation of TiO₂ in anatase structure in both pure and Co doped TiO₂ NPs. The most intense Raman active E_g peak of TiO₂ NPs shifted to higher energy on doping. Both UV–visible and fluorescence spectra show a blue shift in their absorption and band edge emission subsequently on increasing with Co percentage in titania host matrix, wherever there is an indication of quantum confinement effect with widening of band gap on decreasing in NPs size. There is also a possibility of strong Coulomb interaction effect on the optical processes involving the Co ions. However, the intensities of different emission spectra are not the same but decrease profoundly for doping samples due to concentration quenching effect.     

Zr doped anatase supported reticulated ceramic foams for photocatalytic water purification

Titanium dioxide films were deposited on macroporous reticulated Al₂O₃ and alumina–mullite foams with pore sizes of 15 ppi (pores per inch). Coatings were prepared from suspensions of precursor powders of Aeroxide^® P25 nanopowder and precipitated TiO₂ by using a dip coating process. The TiO₂ forms films with a thickness of ～2–20 μm. The photocatalytic activity was characterized as the mineralization rate of an aqueous phenol solution under UVA irradiation by the TOC technique. Precipitated TiO₂ films have nearly the same photocatalytic activity as a titania suspension, in which powder aggregates have a size comparable with the thickness of the films. Samples made of Aeroxide^® P25 nanopowder, in which the size of aggregates is ～0.1 μm show higher efficiency of photodecomposition in suspensions with films. The doping of precipitated anatase with Zr(IV) in the atomic ratio Zr/Ti = 0.008 significantly improves the photocatalytic activity of the foam supported titania. Zr doped anatase films show better performance as the films prepared only from Aeroxide^® P25 nanopowder.     

Reactively sputtered N-doped titanium oxide films as visible-light photocatalyst

Nitrogen-doped titanium oxide (TiO_xN_y) films were prepared by reactive magnetron sputtering of a titanium metal target in gas mixtures of argon, oxygen and nitrogen. Two types of nitrogen species are formed in the films following the fraction of N₂ (F_N2) in the reactive atmosphere. One is substitutional nitrogen in anatase titania phase and the other is nitrogen in TiN phase. In a large range of F_N2 from 0 to 0.57, TiO_xN_y films in anatase structure with about 1.0–1.4 at.% substitutional nitrogen are produced and the films exhibit red shifts to ∼ 500 nm from the absorption edge of ∼ 380 nm of undoped TiO₂. The nitrogen is readily doped in the films by energetic nitrogen ions in the plasma and the films exhibited photocatalytic properties under visible light. When excess nitrogen is supplied as the F_N2 above 0.75, the resulting film contains 20.8 at.% of nitrogen with formation of TiN that makes the film opaque and destroys the photocatalytic activity largely.     

Enhanced photocatalytic property of nanoporous TiO2/SiO2 micro-particles prepared by aerosol assisted co-assembly of nanoparticles

Nanoporous TiO₂/SiO₂ composite micro-particles were prepared by an aerosol assisted co-assembly (AACA) and their characteristics were investigated for photocatalytic application. The average diameter of resulting co-assembled TiO₂/SiO₂ particles was ranged 4–10 μm, and increased as the precursor concentration increased. The TiO₂/SiO₂ particles were spherical in shape and pores ranged 1–100 nm in diameter. Photocatalytic activity of the as-prepared nanoporous TiO₂/SiO₂ particles was evaluated by measuring the photodegradation of methylene blue (MB) and NO_x. Furthermore, the photocatalytic activity of nanoporous TiO₂/SiO₂ particles was compared with those of commercial TiO₂ nanoparticles and nanoporous TiO₂ particles. The nanoporous TiO₂/SiO₂ particles exhibited the highest photodegradation of MB and NO_x among three samples, which was 80% after 3 h and 55% at 10 min, respectively.