Effect of Ag addition on the properties of Pd–Ag/TiO2 catalysts containing different TiO2 crystalline phases

Anatase and rutile TiO₂ were used for preparation of the TiO₂ supported Pd and Pd–Ag catalysts for selective hydrogenation of acetylene. It was found that Pd/TiO₂-anatase exhibited higher acetylene conversion and ethylene selectivity than rutile TiO₂ supported ones. However, addition of Ag to Pd/TiO₂-anatase catalyst resulted in lower ethylene selectivity while that of Pd/TiO₂-rutile increased. It is suggested that Ag addition suppressed the beneficial effect of the Ti³⁺ sites presented on the anatase TiO₂ during selective acetylene hydrogenation whereas without Ti³⁺, Ag promoted ethylene selectivity by blocking sites for over-hydrogenation of ethylene to ethane.     

TiO2 nanoceramic films prepared by ion beam assisted evaporation for optical application

A TiO₂ nanoceramic film was prepared as an alternative absorber layer for infrared thermal detectors. The TiO₂ film was amorphous, and its grain size increased with the ion anode voltage and oxygen flow rate. Moiré deflectometry was applied for measuring the nonlinear refractive indices of TiO₂ films on polycarbonate (PC) substrates. The nonlinear refraction index was measured to be of the order of 10⁻⁸ cm² W⁻¹ and the change in refractive index was of the order of 10⁻⁵. The linear refractive index was correlated with the porosity. Denser TiO₂ films exhibited higher linear refractive indices, obvious red-shifts and narrower absorption bands in the near-IR region.     

CO hydrogenation to iso-C4 hydrocarbons over CeO2–TiO2 catalysts

CeO₂–TiO₂ (Ce:Ti = 0.25–9, molar ratio) catalysts were synthesized by a sol–gel method and the catalytic performances were evaluated in the selective synthesis of isobutene and isobutane from CO hydrogenation under the reaction conditions of 673–748 K, 1–5 MPa and 720–3000 h⁻¹. The physical properties, such as specific surface area, cumulative pore volume, average pore diameter, crystal phase and size, of the catalysts were characterized by N₂ adsorption/desorption and XRD. All the CeO₂–TiO₂ composite oxides showed higher surface areas than pure TiO₂ and CeO₂. No TiO₂ phase was detected on the samples of CeO₂–TiO₂ in which TiO₂ contents were in the range of 10–50 mol%. Crystalline Ce₂O₃ was detected in CeO₂–TiO₂ (8:2). The reaction conditions, temperature, pressure and space velocity, had obvious influences on the CO conversion and distribution of the products over CeO₂–TiO₂ (8:2) catalyst.     

Direct synthesis of mesoporous silicalite-1 supported TiO2–ZrO2 for the dehydrogenation of EB to styrene with CO2

Direct synthesis route was developed to support TiO₂–ZrO₂ binary metal oxide onto the carbon templated mesoporous silicalite-1 (CS-1). Metal hydroxide modified carbon particles could play a role as hard template and simultaneously support metal components on the mesopores during the crystallization of zeolites. Such supported TiO₂–ZrO₂ binary metal oxides (TZ/CS-1) showed better resistance to deactivation in the oxidative dehydrogenation of ethylbenzene (ODHEB) in the presence of CO₂. These catalysts were found to be active, selective and catalytically stable (10 h of time-on-stream) at 600 °C for the dehydrogenation of ethylbenzene (EB) to styrene (Sty).     

Excellent antimicrobial properties of mesoporous anatase TiO2 and Ag/TiO2 composite films

Optically transparent, crack-free, mesoporous anatase TiO₂ thin films were fabricated. The Ag/TiO₂ composite films were prepared by incorporating Ag in the pores of TiO₂ films with an impregnation method via photoreduction. The as-prepared composite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectronic spectra (XPS) and N₂ adsorption. The release behavior of silver ions in the mesoporous composite film was also studied. Moreover, the antimicrobial behaviors of the mesoporous film were also investigated by confocal laser scanning microscopy. The antibacterial activities of the composite films were studied by a fluorescence label method using Escherichia coli (E. coli) as a model. The as-prepared mesoporous TiO₂ films showed much higher antimicrobial efficiency than that of glass and commercial P25 TiO₂ spinning film. The facts would result from the high surface area, small crystal size and more active sites for the mesoporous catalysis. After the doping of Ag, a significant improvement for the antimicrobial ability was obtained. To elucidate the roles of the membrane photocatalyst and the doped silver in the antimicrobial activity, cells from a silver-resistant E. coli were used. These results indicated that Ag nanoparticles in the mesoporous were not only an antimicrobial but also an intensifier for photocatalysis. The as-prepared mesoporous composite film is promising in application of photocatalysis, antimicrobial and self-clean technologies.     

Effect of ceria on the structure and catalytic activity of V2O5/TiO2–ZrO2 for oxidehydrogenation of ethylbenzene to styrene utilizing CO2 as soft oxidant

The present study was undertaken to investigate the influence of ceria on the physicochemical and catalytic properties of V₂O₅/TiO₂–ZrO₂ for oxidative dehydrogenation of ethylbenzene to styrene utilizing CO₂ as a soft oxidant. Monolayer equivalents of ceria, vanadia and ceria–vanadia combination over TiO₂–ZrO₂ (TZ) support were impregnated by a coprecipitation and wet impregnation methods. Synthesized catalysts were characterized by using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, temperature programmed reduction, transmission electron microscopy and BET surface area methods. The XRD profiles of 550 °C calcined samples revealed amorphous nature of the materials. Upon increasing calcination temperature to 750 °C, in addition to ZrTiO₄ peaks, few other lines due to ZrV₂O₇ and CeVO₄ were observed. The XPS V 2p results revealed the existence of V⁴⁺ and V⁵⁺ species at 550 and 750 °C calcinations temperatures, respectively. TEM analysis suggested the presence of nanosized (<7 nm) particles with narrow range distribution. Raman measurements confirmed the formation ZrTiO₄ under high temperature treatments. TPR measurements suggested a facile reduction of CeO₂–V₂O₅/TZ sample. Among various samples evaluated, the CeO₂–V₂O₅/TZ sample exhibited highest conversion and nearly 100% product selectivity. In particular, the addition of ceria to V₂O₅/TZ suppressed the coke deposition and allowed a stable and high catalytic activity.     

TiO2, TiO2/Ag and TiO2/Au photocatalysts prepared by spray pyrolysis

TiO₂, TiO₂/Ag and TiO₂/Au photocatalysts exhibiting a hollow spherical morphology were prepared by spray pyrolysis of aqueous solutions of titanium citrate complex and titanium oxalate precursors in one-step. Effects of precursor concentration and spray pyrolysis temperature were investigated. By subsequent heat treatment, photocatalysts with phase compositions from 10 to 100% rutile and crystallite sizes from 12 to 120 nm were obtained. A correlation between precursor concentration and size of the hollow spherical agglomerates obtained during spray pyrolysis was established. The anatase to rutile transformation was enhanced with metal incorporations and increased precursor concentration. The photocatalytic activity was evaluated by oxidation of methylene blue under UV-irradiation. As-prepared TiO₂ particles with large amounts of amorphous phase and organic residuals showed similar photocatalytic activity as the commercial Degussa P25. The metal incorporated samples showed comparable photocatalytic activity to the pure TiO₂ photocatalysts.     

Photocatalytic properties of TiO2 sol-gel modified nanocomposite films

TiO₂ nanocomposite films with different concentrations of TiO₂ MT-150A nanoparticles were immobilized on glass substrates using a dip coating process. The crystalline structure and surface chemical state of nanocomposite film properties were examined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The specific surface area and morphology of TiO₂ MT-150A nanoparticles were evaluated by the BET method and Field Emission Scanning Electron Microscopy (FE-SEM). The photocatalytic activities of films were evaluated by the methyl orange decoloring rate. XPS measurements showed that the oxygen amount (%) was related to the film composition. The composite film with 10 g/L MT-150A loading yielded the highest amount of surface oxygen (26.82%) and TiO₂ rutile showed the lowest amount of surface oxygen (13.67%) in the form of surface hydroxyl groups. The remaining oxygen was identified as lattice oxygen. In addition, the nanocomposite film with 10 g/L MT-150A loading yielded the highest photocatalytic activity.     

Solid acidities of SiO2–TiO2/montmorillonite composites synthesized under different pH conditions

SiO₂–TiO₂/montmorillonite composites were prepared under acidic, neutral and basic conditions and the solid acidity of the resulting composites were determined. All the SiO₂/TiO₂ ratio of the colloidal particles was set at 10 but the resulting SiO₂/TiO₂ ratios were significantly richer in TiO₂. The XRD patterns of the acidic composite showed expanding and broadening of the (001) reflection by intercalation of colloidal SiO₂–TiO₂ particles, but the neutral and basic composites showed only broadening of the reflections and no intercalation. The specific surface areas of the acidic, neutral and basic composites (375, 237 and 247 m²/g, respectively) were much larger than of montmorillonite (6 m²/g). The average pore sizes were about 4, 15 and 50 nm, and the amounts of solid acidic sites measured by the NH₃-TPD were 178, 95 and 86 µmol/g for the acidic, neutral and basic composites, respectively. The solid acid amount of the acidic composite was twice that of a commercial catalyst, K-10, (85 µmol/g) and much higher than the guest phase SiO₂–TiO₂ gel (16 µmol/g) or the host phase montmorillonite (6 µmol/g). The TPD peak temperatures reflect the acid strength, and were similar in all the samples, ranging from 175° to 200 °C.     

Preparation of TiO2 nanofilm via sol–gel process and its photocatalytic activity for degradation of methyl orange

The preparation of TiO₂ nanofilm was conducted on common glass via the sol–gel process. Glacial acetic acid and diethanolamine were used as inhibitors to prepare acidic and alkaline TiO₂ sol, respectively. XRD, SEM, and EDS characterization showed that the film prepared from acidic TiO₂ sol had a narrow particle size distribution of 15–30 nm and relatively poor particle crystallization while in the case of the film from alkaline TiO₂ sol the nanoparticles were in a wide range of 10–80 nm and well crystallized. The photolysis evaluation through MO degradation revealed that the film from acidic sol possessed apparently better photocatalytic activity than that from alkaline sol. Heat treatment with longer time led to a 50% increase of the photocatalytic activity for the film.     

TiO2 nanotubes and CNT–TiO2 hybrid materials for the photocatalytic oxidation of propene at low concentration

In this work, we investigated titanium dioxide (TiO₂) nanotubes and CNT–TiO₂ hybrid materials for the photocatalytic oxidation (PCO) of propene at low concentration (100 ppmv) in gaseous phase. The materials were prepared via sol–gel method using sacrificial multi-walled carbon nanotubes (CNT) as templates and subsequent heat treatments to obtain the desired crystalline phase (anatase, rutile or a mixture of both) and eventually to remove the carbon template. We also studied rutile nanotubes for the first time and demonstrate that the activity strongly depends on the crystalline composition, following rutile < anatase < anatase/rutile mixture. The enhanced activity of the anatase–rutile mixture is attributed to the decrease in the electron–hole pair recombination due to the multiphasic nature of the particles. The key result of this work is the exceptional performance of the CNT–TiO₂ hybrid, which yielded the highest observed photocatalytic activity. The improved performance is attributed to synergistic effects due to the hybrid nature of the material, resulting in small anatase crystalline sizes (CNT act as heat sinks) and a reduced electron–hole pair recombination rate (CNTs act as electron traps). These results demonstrate the great potential of hybrid materials and stimulate further research on CNT-inorganic hybrid materials in photocatalysis and related areas.     

NOx storage behavior and sulfur-resisting performance of the third-generation NSR catalysts Pt/K/TiO2–ZrO2

The NO_x storage and reduction (NSR) catalysts Pt/K/TiO₂–ZrO₂ were prepared by an impregnation method. The techniques of XRD, NH₃-TPD, CO₂-TPD, H₂-TPR and in situDRIFTS were employed to investigate their NO_x storage behavior and sulfur-resisting performance. It is revealed that the storage capacity and sulfur-resisting ability of these catalysts depend strongly on the calcination temperature of the support. The catalyst with theist support calcined at 500 °C, exhibits the largest specific surface area but the lowest storage capacity. With increasing calcination temperature, the NO_x storage capacity of the catalyst improves greatly, but the sulfur-resisting ability of the catalyst decreases. In situ DRIFTS results show that free nitrate species and bulk sulfates are the main storage and sulfation species, respectively, for all the catalysts studied. The CO₂-TPD results indicate that the decomposition performance of K₂CO₃ is largely determined by the surface property of the TiO₂–ZrO₂ support. The interaction between the surface hydroxyl of the support and K₂CO₃ promotes the decomposition of K₂CO₃ to form –OK groups bound to the support, leading to low NO_x storage capacity but high sulfur-resisting ability, while the interaction between the highly dispersed K₂CO₃ species and Lewis acid sites gives rise to high NO_x storage capacity but decreased sulfur-resisting ability. The optimal calcination temperature of TiO₂–ZrO₂ support is 650 °C.     

Effect of molar ratio of TiO2/SiO2 on the properties of particles synthesized by flame spray pyrolysis

Titania (TiO₂)–silica (SiO₂) nanoparticles were synthesized from sprayed droplets of a mixture of TEOS and TTIP by flame spray pyrolysis (FSP). The effect of molar ratio between TEOS and TTIP in the mixture on the particle properties such as particle morphology, average particle diameter, specific surface area, crystal structure, etc., were determined using TEM, XRD, BET, and FT-IR. A UV-spectrometer was also used to measure the absorption spectrum and the band gap energy of the product particles. As the molar ratio of TEOS/TTIP increased by increasing TEOS concentration at the fixed TTIP concentration, the average particle diameter of the mixed oxide nanoparticles increased with maintaining uniform dispersion between TiO₂ and SiO₂, and crystal structure was transformed from anatase to amorphous. The band gap energy of the TiO₂–SiO₂ nanoparticles increased with respect to the increase of the molar ratio due to the decrease of width of UV-absorption spectrum. Photocatalytic activity of TiO₂–SiO₂ composite particles decreased with the concentration of TEOS.     

TiO2 as a sintering additive for KNbO3 ceramics

Improved densification during the conventional sintering of KNbO₃ ceramics was achieved by using small additions of TiO₂. This improved densification can be explained on the basis of high-temperature chemical reactions in the system. X-ray diffractometry and electron microscopy were used in combination with diffusion-couple experiments in order to elucidate the chemical reactions between KNbO₃ and TiO₂. TiO₂ reacts with KNbO₃ forming KNbTiO₅, and a low concentration of Ti incorporates in the KNbO₃ structure resulting in the formation of oxygen vacancies and, consequently, in an improvement in the densification. At ∼1037 °C eutectic melting between the KNbO₃ and the KNbTiO₅ further improves the densification of the KNbO₃ ceramics.     

Semiconducting properties of self-organized TiO2 nanotubes

The semiconducting properties of anodic grown TiO₂-nanotubes were analyzed by means of the potential dependence of the interfacial capacity under different electrolyte and illumination conditions. The experimental results offer evidence for a duplex oxide film conformed by the bottom and wall of pores with different density of donors and concentration of surface states. The surface extension offered by the walls of oxide tubes is manifested in surface related effects such as the shift of the flat band potential and trapping of photoelectrons.     

Synthesis and electrochemiluminescence of the CeO2/TiO2 composite

CeO₂/TiO₂ composite with kernel–shell structure was synthesized by a sol–gel process. The characterization results show that the composite is made up of anatase phase TiO₂ and cubic system CeO₂. The electrochemiluminescence (ECL) behavior of the CeO₂/TiO₂ composite was studied by a cyclic voltammetry in the presence of persulfate, and the effect factors on ECL emission were discussed. Based on a series of experiments, it is proposed that the strong dual ECL emission produced by the CeO₂/TiO₂ composite resulted from the benefit ECL effect of interface heterojunction in composite.     

Combined TiO2/SiO2 mesoporous photocatalysts with location and phase controllable TiO2 nanoparticles

Combined TiO₂/SiO₂ mesoporous materials were prepared by deposition of TiO₂ nanoparticles synthesised via the acid-catalysed sol–gel method. In the first synthesis step a titania solution is prepared, by dissolving titaniumtetraisopropoxide in nitric acid. The influences of the initial titaniumtetraisopropoxide concentration and the temperature of dissolving on the final structural properties were investigated. In the second step of the synthesis, the titania nanoparticles were deposited on a silica support. Here, the influence of the temperature during deposition was studied. The depositions were carried out on two different mesoporous silica supports, SBA-15 and MCF, leading to substantial differences in the catalytic and structural properties. The samples were analysed with N₂-sorption, X-ray diffraction (XRD), electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) to obtain structural information, determining the amount of titania, the crystal phase and the location of the titania particles on the mesoporous material (inside or outside the mesoporous channels). The structural differences of the support strongly determine the location of the nanoparticles and the subsequent photocatalytic activity towards the degradation of rhodamine 6G in aqueous solution under UV irradiation.     

Synthesis and electrochemical properties of CeO2 nanoparticle modified TiO2 nanotube arrays

In this paper, a cerium dioxide (CeO₂) modified titanium dioxide (TiO₂) nanotube array film was fabricated by electrodeposition of CeO₂ nanoparticles onto an anodized TiO₂ nanotube array. The structural investigation by X-ray diffraction, scanning electron microscopy and transmission electron microscopy indicated that the CeO₂ nanoparticles grew uniformly on the walls of the TiO₂ nanotubes. The composite was composed of cubic-phase CeO₂ crystallites and anatase-phase TiO₂ after annealing at 450 °C. The cyclic voltammetry and chronoamperometric charge/discharge measurement results indicated that the CeO₂ modification obviously increased the charge storage capacity of the TiO₂ nanotubes. The charge transfer process at the surface, that is, the pseudocapacitance, was the dominate mechanism of the charge storage in CeO₂-modified TiO₂ nanotubes. The greater number of surface active sites resulting from uniform application of the CeO₂ nanoparticles to the well-aligned TiO₂ nanotubes contributed to the enhancement of the charge storage density.     

Electrochemical deposition of p-type CuSCN in porous n-type TiO2 films

We present an energy band model and a method for filling p-type CuSCN in n-type porous TiO₂ film. The energy band model is based on the interface energy levels between TiO₂/CuSCN heterojunction and the aqueous electrolyte. The whole deposition process is divided into three stages: the uniform nucleation on the internal surface at positive potential, the crystal growth with the cathodic potential shifting negatively and the thermal activated growth at constant potential. This was demonstrated by the electrochemical experiment combining the hydrothermal process. It was found that the obtained TiO₂/CuSCN heterojunction exhibited good rectification characteristics, indicating that an intimate electrical contact was formed between the large internal surface of TiO₂ film and CuSCN. This novel hydrothermal-electrochemical method may be valuable for fabricating extremely thin absorber (eta)-solar cells and other semiconductor devices.