Comparison of rhodamine B degradation under UV irradiation by two phases of titania nano-photocatalyst

Titania (TiO₂) nano-photocatalysts, with different phases, prepared using a modified sol?Cgel process were employed in the degradation of rhodamine at 10?mg?L^?1 concentration. The degradation efficiency of these nano-photocatalysts was compared to that of commercial Degussa P25 titania. It was found that the nanocatalysts calcined at 450?°C and the Degussa P25 titania had similar photoreactivity profiles. The commercial Degussa P25 nanocatalysts had an overall high apparent rate constant of (K _app) of 0.023?min^?1. The other nanocatalyst had the following rate constants: 0.017, 0.0089, 0.003 and 0.0024?min^?1 for 450, 500, 550 and 600?°C calcined catalysts, respectively. This could be attributed to the phase of the titania as the anatase phase is highly photoactive than the other phases. Furthermore, characterisation by differential scanning calorimetry showed the transformation of titania from amorphous to anatase and finally to rutile phase. SEM and TEM characterisations were used to study the surface morphology and internal structure of the nanoparticles. BET results show that as the temperature of calcinations was raised, the surface area reduced marginally. X-ray diffraction was used to confirm the different phases of titania. This study has led to a conclusion that the anatase phase of the titania is the most photoactive nanocatalyst. It also had the highest apparent rate constant of 0.017?min^?1, which is similar to that of the commercial titania.     

水热法合成掺杂铁离子的小管径TiO2纳米管

碳纳米管这种一维结构的新材料的发现为物理、化学、材料科学和纳米科学开辟了全新的研究领域.近年来,非碳无机类富勒烯(Inorganic Fullerenelike,简称IF)纳米管也受到人们的广泛关注.     

Titania nanotubes (TNTs) prepared through the complex compound of gallic acid with titanium; examining photocatalytic degradation of the obtained TNTs

It was for the first time that the complex compound of gallic acid with titanium (IV) salt was used as a precursor to synthesize titania nanotubes. The study was separated into four main sections; (I) synthesizing the complex of titanium with gallic acid, (II) synthesizing anatase and rutile phases through thermal decomposing of the complex, (III) investigating the possibility to synthesize titania nanotubes from the rutile and anatase phases, and (IV) photocatalytic ability of all the nanoparticles.Different methods were applied to analysis, including X-ray diffraction, 1H NMR, FT-IR spectroscopy, elemental analysis, quantum-chemical modeling, Raman spectroscopy, thermal analysis, photoluminescence, BET analysis (to investigate the specific surface activity, total pore volume), EDX, electron microscopy (SEM), acceleration voltages, electrical conductivity, BJH method (to determine average pore diameter), and UV-Vis spectroscopy.We illustrated the possibility of the synthesis of the titania nanotubes from the anatase phase, while rutile phase was not turned to a tube shape.The photocatalytic ability of the obtained nanoparticles was tested by degrading bromophenol blue, as an organic pollutant, under weak light. TiO₂ in the form of nanotubes could reduce the concentration of bromophenol blue to 82%, as well as the rutile phase - to 70%, and finally anatase as nan-spheres to 36%.     

Photocatalytic Activity in the 2,4-Dinitroaniline Decomposition Over TiO2 Sol-Gel Derived Catalysts

Titania was prepared by the sol-gel method from titanium alkoxide. Depending on the pH of the gelling solution, specific surface areas between 88 and 10 m²/g were obtained. The band gap (E _g) of the samples was found between 3.05 and 3.32 eV. In samples gelled at pH5 and 9 and calcined at 400°C only anatase phase is observed, while for pH3 and pH7 brookite, anatase and rutile or anatase-rutile phases coexist. It was found that the photoactivity in the 2,4-dinitroanailine decomposition depends on the E _g and on the crystalline phases. The highest activity corresponds to the catalysts having the lowest E _g and more than one crystalline phases co-existing.     

The sorption of Eu(III) on calcareous soil: effects of pH,ionic strength,temperature, foreign ions and humic acid

The sorption of Eu(III) on calcareous soil as a function of pH, humic acid (HA), temperature and foreign ions was investigated under ambient conditions. Eu(III) sorption on soil was strongly pH dependent in the observed pH range. The effect of ionic strength was significant at pH < 7, and not obvious at pH > 8. The type of salt cation used had no visible influence on Eu(III) uptake on soil, however at low pH values, the influence of anions was following the order: Cl⁻ ≈ NO₃ ⁻ > ClO₄ ⁻. In the presence of HA, the sorption edge obviously shifted about two pH units to the lower pH, whilst in range of pH 6–7, the sorption of Eu(III) decreased with increasing pH because a considerable amount of Eu(III) was present as humate complexes in aqueous phase, then increased again at pH > 11. The results indicated that the sorption of Eu(III) on soil mainly formed outer-sphere complexes and/or ion exchange below pH ~7; whereas inner-sphere complexes and precipitation of Eu(OH)₃(s) may play main role above pH ~8.     

The influence of cobalt doping on photocatalytic nano-titania: Crystal chemistry and amorphicity

Photocatalysts of nominal composition (Ti_1−xCo_x)O_2−δ with 0.001?x?0.05 were prepared via a sol-gel technique followed by air firing (200-1000 °C). The incorporation of cobalt inhibited crystal growth and slightly raised the anatase to rutile transformation temperature (∼700 °C). An amorphous component was invariably significant with the maximum content (41-53 wt%) appearing simultaneously with the removal of anatase, suggesting that rutile crystallizes via an aperiodic structure. While the introduction of cobalt shifted the apparent band gap to visible light energies this did not enhance performance as there was limited miscibility of cobalt in titania, non-catalytic secondary phases were present, and active Ti³⁺ sites were displaced by cobalt.     

Crystallization kinetics study of In-doped and (In-Cr) co-doped TiO2 nanopowders using in-situ high-temperature synchrotron radiation diffraction

The influence of TiO₂ nanopowder doping with 4 wt% indium and 2 wt% each of indium and chromium on phase transformation was studied. Samples were heated from ambient temperature to 950 °C in sealed quartz capillaries, and in-situ synchrotron radiation diffraction measurements were obtained. Capillary sealing yielded an increase in capillary gas pressure to 0.42 MPa at 950 °C in proportion to absolute temperature by Gay-Lussac’s Law. The initial synthesized samples were amorphous, and crystalline anatase appeared at 200 °C. Crystalline rutile appeared at 850 °C for the nanomaterials that were doped with In and In and Cr. A change in sealed-capillary oxygen partial pressure yielded a decrease and an increase in crystallization temperature, respectively, for the amorphous-to-anatase and anatase-to-rutile transformations. Crystalline titania (anatase and rutile) formed from the amorphous titania by 800 °C and 900 °C, for materials doped with In and In-Cr, respectively. The anatase concentration that was dominant in the In-doped materials up to 950 °C and the higher rutile concentration for the In-Cr doped materials from 900 to 950 °C results from the defect structure that was induced by doping. Cr-ions in the Ti sub-lattice retarded the transformation of anatase to rutile when compared with the retarding effect of mixed In/Cr ions. The transformation results because of the relatively smaller radius of Cr-ions when compared with the In-ions. The differences in phase-transformation kinetics for In, In-Cr and for undoped nanopowders in the literature agree with the calculated transformation activation energies.     

Effect of pH, ionic strength, foreign ions and temperatures on the sorption of Eu(III) on attapulgite-iron oxide magnetic composites

In this paper, the attapulgite-iron oxide magnetic composites were synthesized by coprecipitation method and were characterized by SEM, XRD and FTIR in detail. The characterization results indicated that the iron oxide was successfully formed on the surface of attapulgite. The prepared attapulgite-iron oxide magnetic composites were applied as adsorbents to remove Eu(III) from aqueous solutions by using batch sorption experiments under different experimental conditions. The sorption properties of Eu(III) on bare attapulgite were also performed as comparison. The results indicated that the sorption of Eu(III) on attapulgite-iron oxide magnetic composites was strongly dependent on pH and temperature. The attapulgite-iron oxide magnetic composites can be separated from aqueous solutions using magnetic separation method in large scale. At low pH values, the sorption of Eu(III) was influenced by ionic strength and pH obviously, while the sorption of Eu(III) was not affected by ionic strength at high pH values. The sorption of Eu(III) was dominated by ion exchange or outer-sphere surface complexation at low pH values, and mainly by inner-sphere surface complexation at high pH values. The thermodynamic parameters (i.e., ?G ^°, ?S ^°, ?H ^°) calculated from the temperature dependent sorption isotherms indicated that the sorption of Eu(III) on attapulgite-iron oxide magnetic composites was an endothermic and spontaneous process. Although the sorption capacities of Eu(III) on attapulgite-iron oxide magnetic composites were a little lower than those of Eu(III) on bare attapulgite, the magnetic separation in large scale is suitable for the application of the magnetic composites in the preconcentration of Eu(III) from large volumes of aqueous solutions in possible real applications.     

A Novel Route to the Synthesis of Mesoporous Titania with Full Anatase Nanocrystalline Domains

A porous, high surface area TiO₂ with anatase or rutile crystalline domains is advantageous for high efficiency photonic devices. Here, we report a new route to the synthesis of mesoporous titania with full anatase crystalline domains. This route involves the preparation of anatase nanocrystalline seed suspensions as the titania precursor and a block copolymer surfactant, Pluronic P123 as the template for the hydrothermal self-assembly process. A large pore (7–8 nm) mesoporous titania with a high surface area of 106–150 m²/g after calcination at 400°C for 4 h in air is achieved. Increasing the hydrothermal temperature decreases the surface area and creates larger pores. Characteristics of the seed precursors as well as the resultant mesoporous titania powder were studied using XRD analysis, N₂-adsorption/desorption analysis, and TEM. We believe these materials will be especially useful for photoelectrochemical solar cell and photocatalysis applications.     

水热法合成掺杂铁离子的小管径TiO_2纳米管

碳纳米管这种一维结构的新材料的发现为物理、化学、材料科学和纳米科学开辟了全新的研究领域。近年来,非碳无机类富勒烯(InorganicFullerene-like,简称IF)纳米管也受到人们的广泛关注。迄今为止报道的无机类富勒烯纳米管主要有:过渡金属硫化物(MS2,M=W,Mo,Nb)犤1～3犦、V2O5犤4犦、Al2O3犤5犦纳米管等。其中金属氧化物纳米管在催化、吸附、单电子晶体管等方面有着潜在的应用前景。TiO2纳米粉体和纳米膜材料在太阳能的存储与利用、光电转换、光致变色及光催化降解大气和水中的污染物等方面具有广泛的应用。为了提高其光催化活性和对…     

Preparation and Characterization of Peroxo Titanic Acid Solution Using TiCl3

The peroxo titanic acid solution was successfully prepared using titanium trichloride as a precursor. The basic properties of the TiO₂ film prepared by the solution were investigated in view of phase change, bandgap energy, crystalline size etc. The film displayed amorphous TiO₂ at room temperature, anatase above 281°C and a mixture of anatase and rutile at 990°C. The crystalline size increases with annealing temperatures, while the bandgap energies decrease due to the quantum size effect and the formation of rutile phase which has low bandgap energy. As a result of TG-DTA, it was found that annealing treatment at 990°C for 2 h formed a mixture of anatase and rutile through three steps: (1) the removal of physically adsorbed water (2) the decomposition of peroxo group (3) amorphous-anatase or anatase-rutile phase transformation.     

A Blinking Mesoporous TiO2−x Composed of Nanosized Anatase with Unusually Long‐Lived Trapped Charge Carriers

A mesoporous TiO_2?x material comprised of small, crystalline, vacancy‐rich anatase nanoparticles (NPs) shows unique optical, thermal, and electronic properties. It is synthesized using polymer‐derived mesoporous carbon (PDMC) as a template. The PDMC pores serve as physical barriers during the condensation and pyrolysis of a titania precursor, preventing the titania NPs from growing beyond 10 nm in size. Unlike most titania nanomaterials, during pyrolysis the NPs undergo no transition from the anatase to rutile phase and they become catalytically active reduced TiO_2?x. When exposed to a slow electron beam, the NPs exhibit a charge/discharge behavior, lighting up and fading away for an average period of 15 s for an extended period of time. The NPs also show a 50 nm red‐shift in their UV/Vis absorption and long‐lived charge carriers (electrons and holes) at room temperature in the dark, even long after UV irradiation. The NPs as photocatalysts show a good activity for CO₂ reduction.     

Aerosol-assisted synthesis of mesoporous titania nanoparticles with high surface area and controllable phase composition

Mesoporous titania nanoparticles (denoted as MTN) with high surface area (e.g., 252 m² g⁻¹) were prepared using tetrapropyl orthotitanate (TPOT) as a titania precursor and 10–20 nm or 20–30 nm silica colloids as templates. Co-assembly of TPOT and silica colloids in an aerosol-assisted process and immediate calcination at 450 °C resulted in anatase/silica composite nanoparticles. Subsequent removal of the silica colloids from the composite by NaOH solution created mesopores in the TiO₂ nanoparticles with pore size corresponding to that of silica colloids. Effects of silica colloids’ contents on MTN porosity and crystallites’ growth at a higher calcination temperature (e.g., 1000 °C) were investigated. Silica colloids suppressed the growth of TiO₂ crystallites during calcination at a higher calcination temperature and controllable contents of the silica colloids in precursor solution resulted in various atomic ratios of anatase to rutile in the calcinated materials. The mesostructure and crystalline structure of these titania materials were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD), differential thermal analysis (DTA)-thermo-gravimetric analysis (TGA), and N₂ sorption.     

Synthesis and characterization of nano titania powder with high photoactivity for gas-phase photo-oxidation of benzene from TiOCl(2) aqueous solution at low temperatures

Nano rutile, anatase, and bicrystalline (anatase + brookite) titania powders with an average crystal size of below 10 nm are prepared from aqueous TiOCl(2) solution at low temperatures by adjusting pH values of the starting solution and adding different additives. Adding a small amount of octyl phenol poly(ethylene oxide) into aqueous TiOCl(2) solution leads to the change of particle morphologies of obtained nano titania from needlelike to nano spherical rutile crystals. Amorphous-anatase transformation of titania could proceed in liquid-solid reaction at low temperatures, even at room temperature. A formation mechanism of rutile, anatase, and brookite titania was proposed. It is found that H(+) or H(3)O(+) plays a catalytic role in the phase transformation from amorphous to anatase titania and that the presence of a small amount of SO(4)(2)(-) ion is unfavorable to the formation of both rutile and brookite. By carefully adjusting preparation conditions, nano pure anatase with higher surface area, good crystallinity, and a lower recombination rate of photoexcited electrons and holes was obtained. This nano pure anatase showed a very good photocatalytic activity for gas-phase photo-oxidation of benzene.     

Synthesis of silica–titania composite oxide via “green” aqueous peroxo-route

The preparation procedure of silica–titania composite oxide using novel solution/sol single precursor containing titanium peroxocomplex and silicic acid has been described. Pechini-type sol–gel process has been used to prepare oxides from the aqueous precursor. Some structural, morphological and textural characteristics of the prepared material have been presented. Composite SiO₂/TiO₂ has high surface area (c.a. 300 m²/g), and it is composed of anatase nanoparticles with the mean diameter of 5 nm embedded in amorphous silica, then TiO₂ prepared via similar method is presented as a mixture of anatase and rutile phases. The proposed synthetic procedure meets the requirements of “green chemistry”.     

Factors affecting the sorption of Eu(III) on modified silica gel</p> </p>

Summary 8-Hydroxyquinoline in benzene, xylene, chloroform and toluene diluents was used to modify silica gel as a solid phase extractant (SPE) for the sorption of Eu(III) in batch extraction techniques. Influences of solid/liquid ratio, pH, metal ion concentration, particle size and temperature were studied. The optimum initial pH is 4.2, while the maximum sorption capacities for the prepared impregnated resins in benzene, xylene, chloroform and toluene diluents are 18.52, 14.98, 14.79 and 5.94 mg ^. g^-1, respectively. The sorption process is found to be affected by both metal ion concentration and particle size of the impregnated resin. Thermodynamic parameters for the sorption of Eu(III) were determined and the reaction is found to be exothermic and spontaneous with enthalpy-14.23 and-23.71 kJ ^. mol^-1 for benzene and xylene as diluents. Release of the element from the loaded solid particles into 0.01M HNO₃ is@85% and@53% from 8-HQ/benzene/silica gel and 8-HQ/xylene/silica gel.</p> </p>     

Precise Size Control over Ultrafine Rutile Titania Nanocrystallites in Hierarchical Nanotubular Silica/Titania Hybrids with Efficient Photocatalytic Activity

Hierarchical‐structured nanotubular silica/titania hybrids incorporated with particle‐size‐controllable ultrafine rutile titania nanocrystallites were realized by deposition of ultrathin titania sandwiched silica gel films onto each nanofiber of natural cellulose substances (e.g., common commercial filter paper) and subsequent flame burning in air. The rapid flame burning transforms the initially amorphous titania into rutile phase titania, and the silica gel films suppress the crystallite growth of rutile titania, thereby achieving nano‐precise size regulation of ultrafine rutile titania nanocrystallites densely embedded in the silica films of the nanotubes. The average diameters of these nanocrystallites are adjustable in a range of approximately 3.3–16.0 nm by a crystallite size increment rate of about 2.4 nm per titania deposition cycle. The silica films transfer the electrons activated by crystalline titania and generate catalytic reactive species at the outer surface. The size‐tuned ultrafine rutile titania nanocrystallites distributed in the unique hierarchical networks significantly improve the photocatalytic performance of the rutile phase titania, thereby enabling a highly efficient photocatalytic degradation of the methylene blue dye under ultraviolet light irradiation, which is even superior to the pure anatase‐titania‐based materials. The facile stepwise size control of the rutile titania crystallites described here opens an effective pathway for the design and preparation of fine‐nanostructured rutile phase titania materials to explore potential applications.     

Insights into sorption species of Eu(III) on γ-Al2O3 and bentonite under different pH: Studies at macro- and micro-scales

The sorption species of Eu(III) on γ-Al₂O₃ and bentonite was investigated by batch, surface complexation model (SCM), and X-ray absorption spectroscopy (XAS). The results showed that sorption edges of Eu(III) on γ-Al₂O₃ and bentonite were as expected shifted forward high pH with the increasing in Eu(III) concentration, and sorption of Eu(III) was strongly dependent on pH. In γ-Al₂O₃ system, sorption of Eu(III) was decreased above pH 8.5 at low concentration of Eu(III) because of water soluble carbonate species of Eu(III), however the decline did not appear at high concentration of Eu(III) possibly due to a offset effect of surface precipitation. Actually, the sorption species of Eu(III) on bentonite mainly referred to at least four kinds of species including ion exchange (>X₃Eu⁰) at low pH, inner-sphere complexes (>AlOEu²⁺ and >SiOEu²⁺) at neutral condition, and hydrolysis species (>SiOEu(OH) ₂ ⁰ ) at alkaline condition. Linear combination fitting (LCF) in k space testified that hydrolysis of Eu(OH)₃(s) and oxide of Eu₂O₃ species were major for Eu(III) sorption on γ-Al₂O₃, whereas Eu³⁺(aq) and hydrolysis species comprised sorption species on bentonite. Extended X-ray absorption fine structure (EXAFS) analysis further confirmed the prediction from SCM and LCF. In addition, the typical shells of Eu–Al in R range of 3.0–3.4 Å and Eu–Si at ~4.0 Å were found in radial structure functions, which was possibly identified to edge-shared bidentate of Eu(III) on Al₂O₃ and bentonite.     

Characterization of Fumed Alumina/Silica/Titania in the Gas Phase and in Aqueous Suspension

Fumed oxide alumina/silica/titania was studied in comparison with fumed alumina, silica, titania, alumina/silica, and titania/silica by means of XRD, ¹H NMR, IR, optical, dielectric relaxation, and photon correlation spectroscopies, electrophoresis, and quantum chemical methods. The explored Al₂O₃/SiO₂/TiO₂ consists of amorphous alumina (22 wt%), amorphous silica (28 wt%), and crystalline titania (50 wt%, with a blend of anatase (88%) and rutile (12%)) and has a wide assortment of Brønsted and Lewis acid sites, which provide a greater acidity than that of individual fumed alumina, silica, or titania and an acidity close to that of fumed alumina/silica or titania/silica. The changes in the Gibbs free energy (ΔG) of interfacial water in an aqueous suspension of Al₂O₃/SiO₂/TiO₂ are close to the ΔG values of the dispersions of pure rutile but markedly lower than those of alumina, anatase, or rutile covered by alumina and silica. The zeta potential of Al₂O₃/SiO₂/TiO₂ (pH of the isoelectric point (IEP) equals ≈3.3) is akin to that of fumed titania (pH(IEP_TiO2) ≈ 6) at pH > 6, but it significantly differs from the ζ of fumed alumina (pH(IEP_Al2O3) ≈ 9.8) at any pH value as well as those of fumed silica, titania/silica, and alumina/silica at pH < 6. The particle size distribution in the diluted aqueous suspensions of Al₂O₃/SiO₂/TiO₂ studied by means of photon correlation spectroscopy depends relatively slightly on pH in contrast to the titania/silica or alumina/silica dispersions. Theoretical calculations of oxide cluster interaction with water show a high probability of hydrolysis of Al–O–Ti and Si–O–Ti bonds strained at the interface of alumina/titania or silica/titania due to structural differences in the lattices of the corresponding individual oxides. Ab initio calculated chemical shift δ_H values of H atoms in different hydroxyl groups at the oxide clusters and in bound water molecules are in agreement with the ¹H NMR data and show a significant impact of charged particles (H₃O⁺ or OH⁻) on the average δ_H values of water droplets with (H₂O)_n at n between 2 and 48.     

Aerosol-assisted fabrication of mesoporous titania spheres with crystallized anatase structures and investigation of their photocatalitic properties

We demonstrate practical aerosol-assisted approach to synthesize spherical mesoporous titania particles with high surface areas. Scanning electron microscopy observation of the spray-dried products clearly shows spherical morphology. To remove surfactants and enhance crystallinity, the spray-dried products are calcined under various temperatures. The crystalline structures inside the particles are carefully detected by wide-angle XRD measurements. With increase of the calcination temperatures, anatase crystal growth proceeds and transformation from anatase to rutile is occurred. The effect of various calcination temperatures on the mesostructures is also studied by using N₂ adsorption desorption isotherms. The mesoporous titania particles calcined at 350, 400, and 500 °C exhibit type IV isotherms with a capillary condensation step and shows a hysteresis loop, which is a characteristic of mesoporous materials. The reduction in the surface areas and the pore volumes is confirmed by increasing the calcination temperatures, while the average pore diameters are increased gradually. This is attributed to the distortion of the mesostructures due to the grain growth of the anatase phase and the transformation to the rutile phase during the calcination process. As a preliminary experimental photocatalytic activity, oxidative decomposition of acetaldehyde under UV irradiation is examined. The mesoporous titania calcined at 400 °C shows the highest photocatalytic activity, due to both high surface area and well-developed anatase crystalline phase.