Impact of synthesis methods on nanosized silver modified titania photocatalysts

This work reports the synthesis and studies on photocatalytic activity of a material based on titanium oxide doped with silver. Two kinds of Ag-deposited TiO₂ were synthesized via soft chemical reduction (SCR) and photodeposition (PD) methods. The structure, composition and chemical properties of the obtained products were investigated by X-ray diffraction, UV-vis diffuse reflectance spectroscopy, photoluminescence spectra and Fourier transformation infrared spectroscopy techniques. The photocatalytic oxidation activity in a course of removal and destruction of organic compounds such as methyl orange dye using Ag/TiO₂ hybrid material was studied. The results suggest that SCR synthesized Ag/TiO₂ exhibited better photocatalytic performance that that obtained by PD method. The relationship between the synthesis method and photocatalytic activity of synthesized Ag/TiO₂ was analyzed with a focus on the plasmonic photocatalysis of silver. When compared to PD method, the SCR produced more homogeneous and smaller silver particles with a better dispersion than photodeposition that results in a relative increase of material activity in the photocatalytic degradation of dye pollutant.     

Effect of hydrolysis catalyst and thermal treatment on titania synthesis via sol-gel

The effect of acidic and basic catalysts and of thermal treatment on the preparation of TiO₂ by the sol-gel method has been studied. The resultant solids were characterized by UV-Vis spectroscopy. A displacement of the band due to a fundamental transition to lower energies was observed when acid catalysts were used.

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, TiO₂ - . . .

     

Preparation of MEH‐PPV/nanosized titania hybrids via in situ sol–gel reaction of titanium alkoxide: Optical property

Homogenously dispersed organic (MEH‐PPV)/inorganic (nanosized titania) hybrids were successfully synthesized. The method of preparation was based on a simple one‐step in situ sol–gel technique using titanium isopropoxide (TIP) as the precursor. The key benefit of this preparation was that TIP interacted with both 2‐chlorophenol and MEH‐PPV, so that the degree of aggregation and phase separation could be kept to a minimum with a suitable recipe. MEH‐PPV/TIP/H₂O/2‐chlorophenol of various weight ratios were synthesized to examine the morphology as well as optical properties of the MEH‐PPV/TIP(titania) hybrid. The observation of MEH‐PPV gelation and Fourier transform infrared results verified the interaction existing between MEH‐PPV and TIP. SEM photographs showed that TIP(titania) were homogenously dispersed in the MEH‐PPV film if the hybrid solution was clear from the use of a suitable recipe. UV–vis absorption measurements showed that the addition of TIP decreased the conjugation length of MEH‐PPV. A redshift in the photoluminescence (PL) emission was observed in almost all the hybrids in the solution state, because of the aggregation of MEH‐PPV. However, it was found that spinning destroyed the aggregation of MEH‐PPV, resulting in a blueshift in the PL emission of the hybrids. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 515–529, 2008     

Influence of synthesis methods on zirconium doped titania photocatalysts

Synthesis of various zirconium doped titania based photocatalysts were carried out by adapting different synthetic strategies. Doping is done on commercially available anatase titania, sol-gel titania and template mediated sol gel titania. A comparative study of the various prepared photocataysts was done using physico-chemical characterization techniques such as X-ray diffraction (XRD), surface area- pore volume measurements, UV-VIS Diffuse reflectance spectra (DRS), elemental analysis (XRF) and transmission electron microscopic (TEM) studies. The effect of zirconium and preparation methods on the photocatalytic degradation of methylorange is studied extensively. Both the surface properties and photo activity of zirconium doped titania were found to have a great dependence on the preparation methods. Among the different photocatalytic systems, the catalyst prepared by doping in the presence of urea template was found to produce a maximum photodegradation of 97.5%.     

Electrochemical analysis of the sol-gel synthesis of phosphonate-modified titania through the diffusion of a functionalised ferrocene

Titanium oxide/phenylphosphonate hybrids were prepared by a two-step sol-gel processing, in the presence of ferrocenylphosphonic acid as an electrochemical probe. We showed that as expected the diffusion of the redox species was related to the kinetics of the sol-gel polymerization. The probable passage through cluster Ti₄O(OⁱPr)₈(PhPO₃)₃ has been confirmed by the electrochemical response under partial hydrolysis conditions.     

Effect of phosphate ions in the properties of titania sol-gel

Sol-gel titania was phosphated in two different ways: i) “in situ” phosphation using phosphoric acid as hydrolysis catalyst in the titanium butoxide gelling system, and ii) gelling with nitric acid and impregnation with ammonium phosphate solution. In calcined samples at 600°C a positive effect on the specific surface area for the “in situ” phosphated sample was found. X-ray diffraction patterns showed that the presence of phosphates ions stabilized the anatase phase. FTIR-pyridine adsorption identified only Lewis acid sites in phosphated samples. In the isopropanol decomposition for “in situ” phosphated titania, the activity was six times higher than that obtained for titania phosphated by impregnation, showing strong acidity for the in situ phosphated TiO₂ catalyst.     

Heteroleptic metal alkoxide "oxoclusters" as molecular models for the sol-gel synthesis of perovskite nanoparticles for bio-imaging applications

Systematic structural study of the molecules, resulting from microhydrolysis of heterometallic beta-diketonate alkoxides of barium and strontium (single-source precursors of perovskite oxide materials), demonstrates that the structures of these products result from a thermodynamically driven self-assembly of metal cations and ligands directed towards the most densely packed cores. The ratio between metal cations, and of the cations to bidentate heteroligands, is easily changed to enable the highest packing density. The key to the application of single-source precursors appears to be the use of stoichiometric or superstoichiometric water amounts together with solvents preventing diffusion of possible homometallic intermediates. Eu-doped BaTiO3 nanoparticles have been successfully obtained and characterized.     

Effects of annealing treatment on the properties of MEH-PPV/titania hybrids prepared via in situ sol-gel reaction

A uniform poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV)/titania hybrid film was successfully prepared by an in situ sol-gel reaction of titanium isopropoxide (TIP) in the presence of MEH-PPV/2-chlorophenol solution. The annealing treatment increased the conversion of TIP to titania as determined from evidence of the formation of Ti-O-Ti bonds in the Fourier transform infrared (FTIR) spectrum. Scanning electronic microscope (SEM) photographs showed that the morphology and distribution of titania in the hybrid film were strongly related to the amount of water in the in situ sol-gel reaction. The thermal stability of MEH-PPV/titania hybrids was enhanced by the annealing treatment. Small angle X-ray scattering (SAXS) and X-ray diffraction (XRD) analyses indicated that annealing treatment promoted the ordered aggregation of the MEH-PPV chains and crystallization of titania to a certain extent. The blue shift in Ultraviolet-visible (UV-vis) absorption of pure MEH-PPV after annealing was ascribed to the small extent of decomposition and coil conformation which occurred at high temperature. A more-obvious blue shift for the hybrids was observed, which resulted from irregular aggregation and coil conformation of the MEH-PPV chains induced by heterogeneous point, TIP (titania). The red shift in the photoluminescent (PL) emission for pure MEH-PPV resulted from a certain extent of ordered aggregation after annealing. However, only a slight red shift in the PL emission peak for the hybrids was found due to the hindrance of ordered aggregation of MEH-PPV chains in the presence of TIP (titania).     

Template synthesis of titania on polysaccharides

Template synthesis of titania was conducted in solutions of polysaccharides, xanthan and sodium hyaluronan, prepared in ethylene glycol and on cellulose fibrils placed in ethylene glycol. The process was controlled by the addition of water in amounts sufficient only for the hydration of polysaccharides. When the precursor of TiO₂, tetra(isopropyl) orthotitanate, was added, the fast reactions of hydrolysis and condensation were triggered only after its contact with water, which provided the precipitation of titania on xanthan and sodium hyaluronan macromolecules or on cellulose fibrils. The morphology of the synthesized TiO₂ samples depended on the reagent concentrations in a reaction mixture. Amorphous titania was transformed by calcination into the crystalline state. Some of the obtained TiO₂ samples have rather high photocatalytic activity comparable to that of the commercial photocatalysts.     

Determination of the conditions of the sol-gel synthesis of biosorbents for water treatment

The feasibility of sol-gel synthesis of a series of biosorbents with encapsulated starches, intended for water treatment, was elucidated. The factors governing the morphology of the resulting materials were examined. The performance of the composites synthesized in sorption removal of polyvalent metal ions from water was estimated.     

Amperometric biosensor for hydrogen peroxide based on hemoglobin entrapped in titania sol-gel film

Hemoglobin (Hb) was entrapped in a titania sol-gel matrix and used as a mimetic peroxidase to construct a novel amperometric biosensor for hydrogen peroxide. The Hb entrapped titania sol-gel film was obtained with a vapor deposition method, which simplified the traditional sol-gel process for protein immobilization. The morphologies of both titania sol-gel and the Hb films were characterized using scanning electron microscopy (SEM) and proved to be chemically clean, porous, homogeneous. This matrix provided a biocompatible microenvironment for retaining the native structure and activity of the entrapped Hb and a very low mass transport barrier to the substrates. H₂O₂ could be reduced by the catalysis of the entrapped hemoglobin at −300 mV without any mediator. The reagentless H₂O₂ sensor exhibited a fast response (less than 5 s) and sensitivity as high as 1.29 mA mM⁻¹ cm⁻². The linear range for H₂O₂ determination was from 5.0×10⁻⁷ to 5.4×10⁻⁵ M with a detection limit of 1.2×10⁻⁷ M. The apparent Michaelis-Menten constant of the encapsulated hemoglobin was calculated to be 0.18±0.02 mM. The stability of the biosensor was also evaluated.     

Effect of ultraviolet irradiation on crystallization behavior and surface microstructure of titania in the sol-gel process

Nanosized titania was prepared at various hydrolysis ratios (r=H₂O/Ti) by photo-assisted and conventional sol-gel methods. It was found that hydrolysis ratio and ultraviolet irradiation greatly affect the titania crystallization behavior. The introduction of photo-irradiation benefits anatase formation throughout a wide range of hydrolysis ratio. XPS results show that hydrolysis reaction was promoted by ultraviolet irradiation. In addition, photo-irradiation was also verified to be in favor of the generation of large specific surface area and high crystallinity, which resulted in relative high photocatalytic activity of TiO₂ prepared by a photo-assisted sol-gel method.     

Monolayer vanadia on titania systems from alkoxide precursors. Part III. Activity in secondary alcohol oxidation

The activity of V⁵⁺ ion monolayer supported on anatase, rutile, and anatase-rutile mixed carrier and of bulk V₂O₅ was examined in isopropyl alcohol and cyclohexanol oxidation. Catalysts exhibited remarkable activity in ketone formation. At higher temperatures benzene was the predominant product of cyclohexanol reaction.

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V⁵⁺, , - V₂O₅, . . .

     

Monolayer vanadia on titania systems from alkoxide precursors. Part II. Activity in primary alcohol oxidation

The activity of V⁵⁺ ion monolayers supported on anatase, rutile and anatase-rutile mixed carrier and of bulk V₂O₅ has been studied in ethanol and n-propanol oxidation. Catalysts exhibited remarkable activity in aldehyde formation. Reaction selectivity was diminished by low temperature combustion.

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V⁵⁺, , -, V₂O₅ -. . .

     

New crystalline aluminum alkoxide oxide fluorides: evidence of the mechanism of the fluorolytic sol-gel reaction

This study reports three new crystalline aluminum isopropoxide oxide fluorides with molar ratios of Al:F equal to 1:1 and 1:1.25. These are the first three representatives isolated without the incorporation of external donor molecules. Compound 1 Al(4)F(4)(μ(4)-O)(μ-O(i)Pr)(5)[H(O(i)Pr)(2)] contains a tetranuclear unit consisting of two different five fold coordinated AlFO(4)-units, with F exclusively in the terminal position. Compound 2, Al(4)F(4)(μ(4)-O)(μ-O(i)Pr)(5)[H(O(i)Pr)(2)]·Al(5)F(5)(μ(5)-O)(μ-O(i)Pr)(8), contains both a tetranuclear unit (as in 1) and a pentanuclear Al-unit. Al-atoms in the latter are five- and six fold coordinated. Compound 3, Al(16)F(20)(μ(4)-O)(4)(μ-O(i)Pr)(20)·2((i)PrOH), exhibits a slightly higher fluorination degree and contains an oligomeric chain of four F-linked tetranuclear Al-units. In addition to X-ray structure analysis, compound 1 was characterized by different solid state MAS NMR techniques, including (27)Al triple quantum MAS NMR and (1)H, (1)H→(13)C CP, (19)F and (27)Al MAS NMR. On the basis of the collected data, a reliable decomposition of (27)Al single pulse MAS NMR spectra and an unambiguous assignment of the resonances to the respective structural AlFO(4)-units are given. The new crystalline aluminum isopropoxide oxide fluorides are direct evidence of the fluorolytic sol-gel mechanism previously discussed.     

制备条件对稀土掺杂TiO2物理性质和光催化降解吡唑草胺性能的影响

多相光催化是一种非常有效的降解各种水污染物的方法.本文以稀土(镝和镨)掺杂的TiO2为光催化剂,考察了制备条件对其物理性质和光催化性能的影响.采用溶胶-凝胶法和不同条件(反应温度450,550,650oC;反应时间4,8,12 h)的固态反应法制备了TiO2样品.运用X射线衍射分析了该样品的晶相,发现只存在锐钛矿相,并得到Raman光谱的证实.同时采用扫描电镜观察了样品的结构和粒径;以BET法计算了其比表面积;运用紫外-可见光漫反射光谱测得了样品的带隙能量.通过测量紫外光照射下常用除草剂吡唑草胺的降解速率评价了样品的光催化活性,反应过程中吡唑草胺的浓度用高效液相色谱分析.结果表明,稀土掺杂使得TiO2吸收边红移,并提高了其光催化活性;制备时最优的固态反应条件为550oC反应8 h.     

Hemoglobin/colloidal silver nanoparticles immobilized in titania sol-gel film on glassy carbon electrode: direct electrochemistry and electrocatalysis

By vapor deposition method, both hemoglobin (Hb) and colloidal silver nanoparticles (CSNs) were entrapped in a titania sol-gel matrix on the surface of a glassy carbon electrode (GCE). CSNs could greatly enhance the electron transfer reactivity of Hb and its catalytic ability toward nitrite. Direct fast electron transfer between Hb and the GCE was achieved, and a pair of well-defined, quasi-reversible redox peaks was observed. The anodic and cathodic peak potentials are located at -0.298 V and -0.364 V (vs. Ag/AgCl), respectively. The dependence of the formal potential on solution pH indicated that the direct electron transfer reaction of Hb was a one-electron transfer coupled with a one-proton transfer reaction process. Meanwhile, the catalytic ability of Hb toward the reduction of NO2- was also studied. Accordingly, a NO2- biosensor was prepared, with a linear range from 0.2 mM to 6.0 mM and a detection limit of 34.0 microM. The apparent Michaelis-Menten constant was calculated to be 7.48 mM. Moreover, the biosensor had good long-term stability.     

Sulfated titania catalyzed water mediated efficient synthesis of dicoumarols—a green approach

An efficient, mild, and environmental friendly method has been developed for the synthesis of dicoumarols in water over Lewis and Bronsted acid catalyst sulfated titania (TiO₂/SO₄²⁻). The method involves the condensation of various aromatic and aliphatic aldehydes with 4-hydroxycoumarin. It affords the corresponding product in high yield with short reaction times employing a very low loading of catalyst. The catalyst was reused several times without significant change in activity.     

Effect of the Al/Si atomic ratio on surface and structural properties of sol-gel prepared aluminosilicates

A series of aluminosilicates with an Al/Si ratio ranging from 0 to ∞ (0 for pure silica and ∞ for pure alumina) was prepared by sol-gel process and characterized by surface and structure techniques. Aluminum trisecbutoxide and tetramethylorthosilicate were used as precursors for the sol-gel synthesis. The acidic properties of the oxides were studied by determination of the zero point charges, through mass titration method, and, for selected samples, by FT-IR spectroscopy of adsorbed pyridine used as a probe for both Brønsted and Lewis acidity. A dependence of the acidity on the Al/Si atomic ratio was found. According to the X-ray diffraction patterns, all the oxides have an amorphous structure except pure alumina exhibiting a γ-alumina pattern. The surface areas of the mixed oxides increase with increasing amount of alumina and are higher as compared to the individual oxides. The surface elemental distribution and electronic properties were investigated by X-ray photoelectron spectroscopy. According to the results, good agreement between the surface Al/Si atomic ratio and the analytical ratio is obtained.