Sulfated TiO2 Decontaminate 2-CEES and DMMP in Vapor Phase

A hybrid complex Zr(PO₄)(AgHPO₄) was prepared by ion-exchange and its activity was examined on the allylic oxidation of cycloolefins using tert-butylhydroperoxide (TBHP) as oxidant under argon atmosphere. Under these reaction conditions, attack of the activated C–H bond was preferred instead of the epoxidation of C=C bond, yielding enols as the main products, this is a novel highly active/selective and reusable heterogeneous catalyst.     

Correlation between acidic properties of nickel sulfate supported on TiO2-ZrO2 and catalytic activity for ethylene dimerization

A series of catalysts, NiSO₄/TiO₂-ZrO₂, for ethylene dimerization was prepared by the impregnation method using an aqueous solution of nickel sulfate. For NiSO₄/TiO₂ -ZrO₂ sample, no diffraction line of nickel sulfate was observed up to 30 wt%, indicating good dispersion of nickel sulfate on the surface of TiO₂-ZrO₂. The addition of nickel sulfate to TiO₂-ZrO₂ shifted the phase transition of TiZrO₄ from amorphous to orthorhombic to a higher temperature because of the interaction between nickel sulfate and TiO₂-ZrO₂. The number of acid sites of NiSO₄/TiO₂-ZrO₂ increased in proportion to the nickel sulfate content up to 20 wt% of NiSO₄. Nickel sulfate supported on TiO₂-ZrO₂ was found to be very active even at room temperature, giving a maximum in both activity and acidity when the catalyst containing 20% NiSO₄ was calcined and evacuated at 500°C The asymmetric stretching frequency of the S=O bonds for NiSO₄/TiO₂-ZrO₂ samples was related to the acidic properties and catalytic activity. That is, the higher the frequency, the higher both the number of acid sites and the catalytic activity for ethylene dimerization.     

Acidity studies of titania-silica mixed oxides

A series of titania-silica mixed oxides were prepared by co-precipitation and sol-gel methods. The mole fraction of titanium was varied from 0 to 1. The effects of preparation method and chemical composition on the physical properties and acidity profiles of mixed oxides were examined. While pure silica was non-acidic and titania contained only Lewis acid sites, Brønsted acidity was created by the Ti-O-Si interaction in the binary oxides. Samples containing a titania: silica mole ratio of 9 1 possessed the largest amount of Brønsted acidity. The generation of acid sites and the stability of the oxide was a strong function of preparation method. With all preparation methods, higher calcination temperatures increased crystallinity and decreased the total number of acid sites.     

Sulfated SnO2-SiO2 superacid catalysts by Sol-Gel method

A series of sulfated SnO₂-SiO₂ binary oxides were prepared by the Sol-Gel method with different SnO₂ molar content. Tin chloride and tetraethylorthosilicate were used as precursors. The resulting solids were characterized by Fourier Transform Infrared spectroscopy (FTIR), ammonia thermodesorption, surface area measurements and also titrated using Hammett indicators. To correlate the acidic properties with catalytic activity, solids were tested in the 2-propanol decomposition reaction. SnO₂ addition to SiO₂ produce a twofold synergetic effect: an increase in the surface area in most of the resulting mixed oxides and high catalytic activities for the dehydration reaction. The titrated materials, using Hammett indicators, are of superacid nature (Ho –13.7).     

Efficient synthesis of titania nanotubes and enhanced photoresponse of Pt decorated TiO2 for water splitting

We investigated the effect of HMT (hexamethylenetetraamine) on the anodic growth of TiO₂ nanotube arrays. The tube length increases to 4.3 μm with HMT concentration increasing to 0.04 mol·L⁻¹. Adsorption of HMT on the TiO₂ surface is shown to markedly decrease the chemical dissolution rate of tube mouth, resulting in longer nanotube length. Furthermore, Pt nanoparticles were successfully deposited on the surface of TiO₂ nanotubes by ac electrodeposition method. The TiO₂/Pt composites were characterized by field emission scanning electron microscope (FESEM), X-ray photoelectron spectra (XPS), and photoelectrochemistry. An enhancement in photocurrent density has been achieved upon modification of TiO₂ nanotubes with Pt nanoparticles.     

Selective Catalytic Reduction of NOx with CH4 over the In/Sulfated TiO2 Catalyst

Tungstated TiO₂ (WTi), tungstated Fe₂O₃ (WFe), tungstated SnO₂ (WSn), sulfated TiO₂ (STi), sulfated Fe₂O₃ (SFe), and sulfated SnO₂ (SSn) are used as the support for the In and Pd catalysts for the SCR of NO with methane. It was found that the In/STi catalyst with a 2% indium loading showed the highest NO_x conversion (39% at 450 °C and 12,000 h⁻¹) among all of the catalysts studied. The acid strength of the STi support was very important for the formation of the InO⁺ site, which was thought to be the active site for NO reduction. The activity of the In/STi catalyst can be improved by increasing the surface area of the STi support. The most attractive feature of the In/STi catalyst is its high resistance for SO₂.     

Surface modification of TiO2/SiO2 composite hydrosol stabilized with polycarboxylic acid on Kroy-process wool fabric

Self-cleaning of wool fabric has been of increasing interest due to availability and practicability. In this paper, two kinds of wool fabrics, including raw wool and Kroy-process wool fabric, were successfully modified by TiO₂/SiO₂ gel stabilized by 1,2,3,4-butanetetracarboxylic acid (BTCA) and citric acid (CA), respectively. The optimum concentration of carboxylic acids and TiO₂/SiO₂ gel was decided by the crease recovery angles and total color difference (ΔE) values, respectively. The results revealed that wool fabrics treated with BTCA and TiO₂/SiO₂ had better wrinkle resistance in comparison with CA and TiO₂/SiO₂ treated samples. The decomposition of stains was studied using UV irradiation and the presence of TiO₂/SiO₂ gel demonstrated obvious self-cleaning property, in which the color of wool fabric was unchangeable. The hydrophilicity of Kroy-process wool fabric increased relative to raw ones. In addition, Scanning Electron Microscope images demonstrated the layer of TiO₂/SiO₂ nanoparticles coated on treated samples. In general, the adhesion properties coated to the fabric surface showed a slight loss even at harsh processing conditions, however, the anti-UV properties obviously increased due to the decrease in the fabric porosity. And the linkages between carboxylic acid and wool fibers were illustrated using FTIR pattern.     

Photoassisted mineralization of remazole red F3B over NiO/TiO2 and CdO/TiO2 nanoparticles under simulated sunlight

In this work, a series of titania-supported NiO and CdO materials were synthesized by a modified sol-gel process. The prepared photocatalysts were characterized by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), and transmission electron microscopy (TEM). The activities of titania-supported NiO and CdO photocatalysts for photocatalytic degradation of Remazole Red F3B (RR) dye, under simulated sunlight, were investigated. The photocatalytic mineralization of an RR dye solution over various NiO-x/TiO₂ and CdO-x/TiO₂ photocatalysts under simulated sunlight was investigated. It was worthy noticing that the photocatalytic activity of titania improved using the prepared catalysts. The prepared TiO₂, NiO-5/TiO₂, and CdO-2/TiO₂ photocatalysts exhibited higher photocatalytic activity under simulated sunlight than did commercial TiO₂. The prepared photocatalysts were stable after photocatalytic degradation of the dye. The observed photocatalytic mineralization of the dye was 51 and 71% over NiO-10/TiO₂ and CdO-2/TiO₂ after 180 min of irradiation, respectively. Juxtaposing a p-NiO-5/TiO₂ semiconductor provided a potential approach for decreasing charge recombination. The prepared photocatalystsNiO-5/TiO₂ and CdO-2/TiO₂ are promising composites for the solar detoxification of textile wastewater.     

Photocatalytic Properties of Silica-supported TiO2

TiO₂ supported on SiO₂ surface is effective on the recovery of photocatalyst, morphological control, and coating on the substrate. Furthermore, it shows much higher photocatalytic activity than pure TiO₂. The silica support is quite influential on the surface properties of TiO₂ supported on SiO₂. The enhanced photocatalytic activity of TiO₂–SiO₂ could be explained by the effects of surface area, adsorption, band-gap energy and local structure. However, it is difficult to say which one is the most important factor responsible for the photocatalytic property of TiO₂–SiO₂. For example, the reduction of particle size could effect on both of the surface area and band-gap energy. And, Ti–O–Si bonds could modify the band-gap energy and local structure. Therefore, the photocatalytic properties of TiO₂–SiO₂ should be expressed by sum of many factors such as surface area, adsorption, band-gap energy and local structure.     

Preparation and characterization of SO42-/TiO2 and S2O82-/TiO2 catalysts

Nanosized solid superacids SO₄ ²⁻/TiO₂ and S₂O₈ ²⁻/TiO₂, as well as MCM-41-supported SO₄ ²⁻/ZrO₂, were prepared. Their structures, acidities, and catalytic activities were investigated and compared using XRD, N₂ adsorption-desorption, and in situ FTIR-pyridine adsorption, as well as an evaluation reaction with pseudoionone cyclization. The results showed that SO₄ ²⁻/TiO₂ and S₂O₈ ²⁻/TiO₂ possess not only nanosized particles with diameters < 7.0 nm, a BET surface greater than 140 cm²/g and relatively regular mesostructures with pores around 4.0 nm, but also a pure anatase phase and strong acidity. Different from the Lewis acid nature of SO₄ ²⁻/ZrO₂/MCM-41, SO₄ ²⁻/TiO₂ and S₂O₈ ²⁻/TiO₂ exhibit mainly Bronsted acidities. The strongest Bronsted acid sites were produced on SO₄ ²⁻/TiO₂ promoted with H₂SO₄, while Lewis acid sites on S₂O₈ ²⁻/TiO₂ even stronger than those on SO₄ ²⁻/ZrO₂/MCM-41 were generated when persulfate solution was used as sulfating agent. Because of their distinct acid natures, SO₄ ²⁻/TiO₂ and S₂O₈ ²⁻/TiO₂ exhibited catalytic activities for the cyclization of pseudoionone that were much higher than that of SO₄ ²⁻/ZrO₂/MCM-41. It can be concluded that the existence of more Br?nsted acid sites was favorable for proton participation in the cyclization reaction. Translated from Journal of Chemical Engineering of Chinese Universities, 2006, 20(2): 239–244 [译自: 高校化学工程学报]     

Surface modification of TiO2 nanoparticles with silane coupling agent for nanocomposite with poly(butyl acrylate)

Abstract

In order to enhance the compatibility of TiO₂ nanoparticles in poly(butyl acrylate) (PBA) matrix, surface modification of TiO₂ was conducted using 3-methacryloxypropyl-trimethoxysilane (MPS). To improve the effect of surface modification, TiO₂ was predispersed in ethanol via ultrasonic waves. The process was investigated in detail to obtain the optimum condition of ultrasonic dispersion. The dispersion of TiO₂ in ethanol was evaluated via sedimentation rate. Fourier transform infrared spectroscopy and thermogravimetric analysis were performed to investigate the effect of surface modification. It was found that the organic functional groups of MPS had been successfully grafted onto the surface of TiO₂ nanoparticles. Finally, both neat PBA film and TiO₂/PBA composite film were prepared and characterised. The modified TiO₂ presented good compatibility in PBA matrix.     

On the effects of the sol-gel synthesis parameters on textural and structural characteristics of TiO2

The effects of alcohol/alkoxide, water/alkoxide molar ratios, acid addition, type of solvent, reaction temperature and calcination temperature on textural, structural and morphological characteristics of TiO₂ were studied. The results show that surface area, pore size distribution and crystalline phases were very sensitive to preparation conditions.     

Sulfated and Persulfated TiO2/MCM-41 Prepared by Grafting Method and their Acid-catalytic Activities for Cyclization of Pseudoionone

Solid acid catalysts of SO₄²⁻/TiO₂/MCM-41 and S₂O₈²⁻/TiO₂/MCM-41 were prepared via grafting method and sulfate/persulfate promotion. The catalysts exhibited desirable activity and better selectivity for cyclization reaction of pseudoionone compared to traditional SO₄²⁻/TiO₂. A combination of XRD, N₂ adsorption–desorption and FTIR spectroscopy indicated that the catalysts possess well-ordered mesostructure, and the grafted TiO₂ are in highly dispersed amorphous form rather than crystalline phase. For S₂O₈²⁻/TiO₂/MCM-41 higher S content and more Br?nsted acid sites can be achieved by persulfation, which is favorable for the protons participated cyclization reaction. The similar Si–O–Ti–O–S=O structure of all acid sites on pore surface of the catalysts is attributed to the improvement of selectivity in comparison with SO₄²⁻/TiO₂.     

The relationship between the structure and electrocatalytic properties of TiO2 electrodes doped with CeO2

This paper describes the study of the preparation of Ti/Ti_1-xCe_xO₂ electrodes using the Pechini method and their application for the electroreduction of nitrobenzene in aqueous acid medium. The electrodes were studied using X-ray diffraction, and scanning electron microscopy and it was found that the electrocatalytic properties are influenced by the microstructure and morphology of the electrodes. All doped electrodes presented an enhanced performance for nitrobenzene electroreduction when compared to pure TiO₂. The Ti_0.995Ce_0.005O₂ electrode presented the best performance, with an increase of 58% in the aniline yield under galvanostatic electrolysis conditions.     

BisGMA/TiO2 Organic-Inorganic Hybrid Nanocomposite

BisGMA (Bisphenol-A-glycidyldimethacrylate) resin had been modified by incorporating TiO₂ nanoparticles (0.5–2% by weight). An ultrasonic mixing process was used to disperse the particles into the resin system prior to casting and curing test specimens. TEM investigation showed that the particles were nano size (5–60 nm) and dispersed throughout the entire volume of the resin. In dynamic mechanical analysis, nanophase resin showed increase in storage modulus and glass transition temperature from neat resin system. Thermogravimetric analysis revealed better thermal stability. Flexural loading, T _g and flexural modulus of the nanocomposites were enhanced as the particle volume fraction was enhanced and than decreased.     

Carbon-modified TiO2 for photocatalysis

ABSTRACT: Here we present a method to produce TiO2 nanocrystals coated by thin layer of graphitic carbon. The coating process was prepared via chemical vapor deposition (CVD) with acetylene used as a carbon feedstock with TiO2 used as a substrate. Different temperatures (400°C and 500°C) and times (10, 20, and 60 s) of reaction were explored. The prepared nanocomposites were investigated by means of transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy/diffuse reflectance spectroscopy and ultraviolet-vis (UV-vis)/diffuse reflectance spectroscopy. Furthermore, photocatalytic activity of the materials was investigated under visible and UV-vis light irradiation in the process of phenol decomposition. It was found that TiO2 modification with carbon resulted in a significant increase of photoactivity under visible irradiation and decrease under UV-vis light irradiation. Interestingly, a shorter CVD time and higher process temperature resulted in the preparation of the samples exhibiting higher activity in the photocatalytic process under visible light irradiation.     

Improved Catalyst for Photocatalytic Oxidation of Acetaldehyde Above Room Temperature

Sulfated TiO₂ was more active and deactivated more slowly than Degussa P-25 TiO₂ during PCO of acetaldehyde above 373 K. Thermal catalytic reactions appear to poison both catalysts. Sulfating TiO₂ increased surface area by 60% and increased the number of acetaldehyde adsorption sites by a factor of 1.7.     

Effect of the Acidity of TiO2 Surface on Its Photocatalytic Activity in Acetone Gas-Phase Oxidation

The effect of the surface acidity of modified TiO₂ samples on the rate of photocatalytic decomposition of acetone vapor was studied. The TiO₂ activity was shown to depend strongly on the concentration of acid and basic sites on the surface. It was 1.23 times greater for TiO₂ treated with 10 M H₂SO₄ solution than for the untreated sample. This dependence may be related to changes in the adsorption energy of the reagents.     

Catalytic Activities of Al2O3-promoted NiSO4/TiO2 for Acid Catalysis

A series of catalysts, NiSO₄/Al₂O₃–TiO₂, for acid catalysis was prepared by the impregnation method, where support, Al₂O₃–TiO₂ was prepared by the coprecipitation method using a mixed aqueous solution of titanium tetrachloride and aluminum nitrate solution followed by adding an aqueous ammonia solution. The addition of nickel sulfate (or Al₂O₃) to TiO₂ shifted the phase transition of TiO₂ from amorphous to anatase to higher temperature because of the interaction between nickel sulfate (or Al₂O₃) and TiO₂. 15-NiSO₄/5-Al₂O₃–TiO₂ containing 15 wt% NiSO₄ and 5 mol% Al₂O₃, and calcined at 400°C exhibited maximum catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation. The catalytic activities for both reactions were correlated with the acidity of catalysts measured by the ammonia chemisorption method. The charge transfer from Ti atoms to the neighboring Al atoms strengthens the Al–O bond between Al and the surface sulfate species. The addition of Al₂O₃ up to 5 mol% enhanced the acidity, thermal property, and catalytic activities of NiSO₄/Al₂O₃–TiO₂ gradually due to the interaction between Al₂O₃ and TiO₂ and consequent formation of Al–O–Ti bond.     

Mechanism of degradation of nitrilotriacetic acid by heterogeneous photocatalysis over TiO2 and platinized TiO2

TiO₂-heterogeneous photocatalysis of nitrilotriacetic acid (NTA) at pH 2.5 was studied to establish the kinetic regime and the reaction mechanism. Pure Degussa P-25 and Hombikat UV100 commercial samples were compared. A Langmuirian behavior was observed over P-25. Platinization of the Hombikat sample (0.5 wt.%) caused an important increase on the photocatalytic rate with a change in the kinetics from zero order in the pure precursors to first order in the platinized sample. The nature of the intermediates and their evolution with time were compared on all systems. Glycine, iminodiacetic and oxamic acids have been identified in different proportions, together with ammonium and glycolic acid, depending on the catalyst used. The rapid depletion of NTA was not accompanied by a corresponding total organic carbon (TOC) reduction, but 84% of TOC decrease was obtained on P25 after 24 h, a very reasonable result for refractory compounds. A detailed mechanism is proposed for the photocatalytic reaction, suggested to be the same over the three catalysts here tested.