Enhanced dielectric constant and breakdown strength in dielectric composites using TiO2@HfO2 nanowires with gradient dielectric constant

To investigate the influence of modification of ceramic fillers on the dielectric properties of polymer-based composites, TiO₂ and core-shell structured TiO₂@HfO₂ nanowires were synthesized, and investigated in this study. TiO₂ nanowires/polyvinylidene fluoride (PVDF) and TiO₂@HfO₂ nanowires/PVDF nanocomposites were prepared using the solution casting method. The experimental results showed that the TiO₂@HfO₂ nanowires/PVDF composites had improved dielectric properties compared with that of the TiO₂ nanowires/PVDF composites. Owing to the enhanced interfacial polarisation by the multilevel interface, the composites with 10 wt % TiO₂@HfO₂ nanowires achieved the highest permittivity of 12.56 at 1 kHz, which was enhanced by ～72% compared to the PVDF matrix. The electric field was evenly distributed by building the fillers with a gradient dielectric constant. The characteristic breakdown strength of the composite with 5 wt % TiO₂@HfO₂ reached 377.76 kV/mm, compared with that of 334.37 kV/mm for the composite with 5 wt % TiO₂ nanowires. This study initiated a novel strategy for preparing dielectrics with high dielectric constant and improved breakdown strength.     

Preparation and characterisation of mixed matrix Al2O3- and TiO2-based ceramic membranes prepared using polymeric synthesis route

Al₂O₃- and TiO₂-based ceramic membranes prepared using polymeric synthesis route were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and gas permeability tests. The influence of the final calcination temperature and the systematic investigation of the properties of the membranes are provided. The calcination temperature affected morphological, structural and chemical properties, as well as the gas permeability of the ceramic membranes. XRD analysis revealed rhombohedral and tetragonal structures of Al₂O₃ and TiO₂-based ceramic, respectively, prepared at calcination temperatures of 1100 and 1200 °C. The TiO₂-based ceramic matrix calcined at temperatures of 1100 and 1200 °C exhibited a well-defined crystalline microstructure with the grains increasing in size as a function of temperature. FTIR analysis revealed that phosphorus additives in orthoclase clay tend to form phosphonate groups during the calcination process. The decomposition of organic source was not fulfilled as tested at calcination temperatures of 1000, 1100 and 1200 °C.     

Vapor-phase selective hydrogenation of maleic anhydride to succinic anhydride over Ni/TiO2 catalysts

A series of supported Ni/TiO₂ catalysts were prepared by incipient wetness impregnation method under different calcination temperatures, and the as-prepared catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic properties of these Ni/TiO₂ catalysts were investigated in the vapor phase hydrogenation of maleic anhydride (MA) to succinic anhydride (SA). The results showed that the catalytic activity and the selectivity of the Ni/TiO₂ catalysts were strongly affected by the calcination temperature. The catalyst calcined at 1023 K showed a relatively higher SA selectivity of 96% at high MA conversion (96%) under the tested conditions (493 K and 0.2 MPa). The improvement of SA selectivity could be mainly assigned to the presence of suitable metal–support interaction, which can play a role in catalytic property of active nickel species as electron promoter. Besides, the change of surface properties of TiO₂ support with the increasing calcination temperatures, e.g., the decrease of Lewis acid sites, might also have some positive role in reducing the side-products like γ-butyrolacetone (GBL).     

Effect of calcination temperature on the structural properties and photocatalytic activities of solvothermal synthesized TiO2 hollow nanoparticles

TiO₂ hollow nanoparticles were prepared by the solvothermal method, calcined at different temperatures and characterized by XRD, BET, SEM, PL and FT-IR. The effects of morphology, size and calcination temperature on the photocatalytic activity of the prepared materials were discussed in detail. It was found that the calcination temperature altered the crystallinity, morphology, surface area, and the porous structure. The photocatalytic activity of the TiO₂ powders evaluated through photocatalytic degradation of gaseous acetone under UV-light irradiation, showed TiO₂ calcined at 250 °C to exhibit a higher photocatalytic activity than commercial powders (Degussa P25).     

Effect of MnOx/TiO2 Oxidation State on Ozone Concentration in a Nonthermal Plasma-Driven Catalysis Reactor

Manganese oxides on titanium dioxide were prepared by impregnation method at various calcination temperatures and by deposition-precipitation method and the catalysts were characterized using TG-DTA, XRD, XPS, and N₂ adsorption. Various oxidation states for manganese were obtained and activity towards ozone decomposition inside a nonthermal plasma catalysis reactor was investigated. Activity tests show that with increasing manganese oxidation state, the greater the degree of ozone decomposition inside the reactor. MnOx/TiO₂ prepared by impregnation method calcined at 350 °C showed the highest decrease in ozone concentration.     

Effect of calcination temperature on the catalytic activity of Au colloids mechanically mixed with TiO2 powder for CO oxidation

In order to elucidate the role of the contact structure between gold and metal oxide support in low-temperature CO oxidation, a mechanical mixture of colloidal gold with TiO₂ powder was prepared and calcined at different temperatures. The sample calcined at 473 K, which is composed of spherical gold particles with a mean diameter of 5.1 nm and TiO₂ powder, is poorly active for CO oxidation at temperatures up to 473 K. The catalytic activity appreciably increases with an increase in calcination temperature up to 873 K even though gold particles grow to larger ones, reaching a level with almost the same turnover frequency as that of Au/TiO₂ prepared by a deposition–precipitation method. This revised version was published online in July 2006 with corrections to the Cover Date.     

Immobilization of TiO2 into Self‐Supporting Photocatalytic Foam: Influence of Calcination Temperature

Immobilization of photocatalytic powder is crucial to obtain industrially relevant purification processes. To achieve this goal, self‐supporting TiO₂ foams were manufactured by a polyacrylamide gel process. These gels were calcined at different temperatures to study the effect of the calcination temperature on foam characteristics (rigidity, crystallinity, and porosity) and its influence on photocatalytic activity. The results show that an optimal degradation is achieved for those foams calcined between 700 and 800°C. Calcination at higher temperatures results in a steep decrease in activity, explained by stability issues of the material due to formation of Na₂SO₄ phases and a larger rutile fraction.     

Preparation of calcined hydrotalcite/TiO2-Ag composite and enhanced photocatalytic properties

A series of calcined hydrotalcite/TiO₂-Ag (HTC/TiO₂-Ag) composites with different silver (Ag) contents were successfully prepared and investigated as a catalyst for the photodegradation of phenol using UV–vis light (λ>300 nm). The Ag nanoparticles were deposited on the surface of TiO₂ (TiO₂-Ag) through photodeposition method. The TiO₂-Ag nanoparticles were supported on hydrotalcite (HT) by the co-precipitation method at variable pH (HT/TiO₂-Ag), and then calcined at 500 °C to obtain the HTC/TiO₂-Ag composites. The composites were characterized by inductively coupled plasma mass spectrometry (ICP-MS), N₂ adsorption/desorption (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and diffuse reflectance spectra (DRS). Results show that there is an optimum silver ratio to obtain the highest photocatalytic performance in the HTC/TiO₂-Ag photocatalyst which is 2 wt%, and is assigned as HTC/TiO₂-Ag(2). The association of silver nanoparticles on TiO₂ enhanced photocatalytic activity of the bare semiconductor composite. Only 56% of phenol was photodegraded when photodegradation was performed with HTC/TiO₂, whereas ~100% was photodegraded using HTC/TiO₂-Ag(2). The data gathered from the photocatalytic degradation of phenol were successfully fitted to Langmuir-Hinshelwood model, and can be described by pseudo-first order kinetics. The results showed the HTC/TiO₂-Ag(2) as efficient photocatalyst, low cost, separable from solution by sedimentation, and reusable. The superior performance of HTC/TiO₂-Ag(2) composite photocatalyst may be attributed to the synergic catalytic effect between silver and TiO₂, dispersion of TiO₂-Ag(2) nanoparticles supported on calcined hydrotalcite, and the calcined hydrotalcite like photocatalyst.     

Adsorption and photodegradation of methylene blue on TiO2-halloysite adsorbents

TiO₂-halloysite (TiO₂-HNT) composites were fabricated by depositing anatase TiO₂ on the halloysite (HNT) surfaces with calcination treatment at 100, 200, 300 and 500 °C. The obtained composites were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-Ray diffraction (XRD). HNT was attached with TiO₂ particles or clusters in sizes of 10–30 nm. With the increasing of calcination temperature, the crystalline of anatase became more perfect, but the structure of HNT could be destroyed at 500 °C. The adsorption and photodegradation of methylene blue (MB) by TiO₂-HNTs were investigated. The kinetic adsorption fit the pseudo second-order, and the isotherm data followed the Langmuir model. The maximum adsorption capacities of MB were in the range of 38.57 to 54.29 mg/g. TiO₂-HNTs exhibited an efficient photocatalytic activity in the decomposition of MB. For TiO₂-HNT calcined at 300 °C, 81.6% MB were degraded after 4 h treatment of UV irradiation.     

Design of TiO2 nanocrystals with enhanced sunlight photocatalytic activity by exploring calcining conditions

As a promising inorganic semiconductor photocatalyst, TiO₂ has been widespread concerned since 1972. However, its practical application is limited due to its low efficiency for utilizing solar light and rapid recombination of photo-generated charges. Here, we report a way to solve these problems by calcining TiO₂ samples under different conditions. It was found that the catalytic performance of TiO₂ catalysts was closely related to calcination temperature and calcination atmosphere. The XRD, Raman spectra, BET, UV–vis spectra, SEM and TG-DTA investigations of the catalysts revealed that the crystal structure of TiO₂, the specific surface area, and abundant oxygen vacancies were the primary factors influencing the performance of TiO₂ catalysts. Consequently, the TiO₂ nanocrystal calcined in a nitrogen/hydrogen mixed atmosphere at 300 °C for 3 h exhibited higher catalytic activity than others. These results demonstrated that annealing conditions can play an important role in catalyst activity.     

Synthesis and characterization of CuO/TiO2 catalysts for low-temperature CO oxidation

In this paper, the CuO/TiO₂ catalysts prepared by the deposition–precipitation (DP) method were extensively investigated for CO oxidation reaction. The structural characters of the CuO/TiO₂ catalysts were comparatively investigated by TG-DTA, XRD, and XPS measurements. It was shown that the catalytic behavior of CuO/TiO₂ catalysts greatly depended on the TiO₂-support calcination temperature, the CuO loading amount and the CuO/TiO₂ catalysts calcination temperature. CuO supported on the anatase phase of TiO₂-support calcined at 400 °C showed better catalytic activity than those supported on TiO₂ calcined at 500 and 700 °C. Among all our investigated catalysts with CuO loading from 2% to 12%, the catalyst with 8 wt% CuO loading exhibited the highest catalytic activity. The optimum calcination temperature of the CuO/TiO₂ catalysts was 300 °C. The XRD results indicated that the catalytic activity of the CuO/TiO₂ catalysts was related to the crystal phase and particle size of TiO₂ support and CuO active component.     

Photostabilization of polypropylene by surface modified rutile‐type TiO2 nanorods

Rutile‐type titanium dioxide (TiO₂) nanorods were prepared, superficially modified and tested for the protection of polypropylene (PP) from the UVB and UVC irradiations. The silica coating blocked the active sites on the nanorods and the following calcination further reduced the amount of surface hydroxyl groups and thus, made the TiO₂ nanorods more efficient against the photodegradation. Compared with spherical TiO₂ nanoparticles, the calcined silica‐coated TiO₂ nanorods demonstrated good photostabilization efficiency due to the excellent shielding effect and the improved dispersion of the nanoparticles in PP matrix. When used in combination with the conventional hindered amine light stabilizer (HALS), CHIMASSORB^® 944, the surface modified TiO₂ nanorods revealed strong synergistic effect during the photo‐oxidation of the PP composites. The capacity of photostabilization was much higher than the combination with the commercial spherical TiO₂ nanoparticles and even higher than the typical HALS photostabilization system containing hindered phenol TINUVIN^® 328. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40601.     

Solid‐state synthesis and characterization of polyaniline/nano‐TiO2 composite

Polyaniline/nano‐TiO₂ composites with the content of nano‐TiO₂ varying from 6.2 wt % to 24.1 wt % were prepared by using solid‐state synthesis method at room temperature. The structure and morphology of the composites were characterized by the Fourier transform infrared (FTIR) spectra, ultraviolet‐visible (UV–vis) absorption spectra, X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The electrochemical performances of the composites were investigated by galvanostatic charge–discharge measurement, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results from FTIR and UV–vis spectra showed that the composites displayed higher oxidation and doping degree than pure PANI. The XRD and morphological studies revealed that the inclusion of nano‐TiO₂ particles hampered the crystallization of PANI chains in composites, and the composites exhibited mixed particles from free PANI particles and the nano‐TiO₂ entrapped PANI particles. The galvanostatic charge–discharge measurements indicated that the PANI/nano‐TiO₂ composites had higher specific capacitances than PANI. The composite with 6.2 wt % TiO₂ had the highest specific capacitance among the composites. The further electrochemical tests on the composite electrode with 6.2 wt % TiO₂ showed that the composite displayed an ideal capacitive behavior and good rate ability. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation,structural and photocatalytic activity of Sn/Fe co-doped TiO2 nanoparticles by sol-gel method

Pure and Sn/Fe co-doped (0.2 at.% Sn and 0.6 at.% Fe, 0.6 at.% Sn and 0.2 at.% Fe, 1.0 at.% Sn and 1.0 at.% Fe) TiO₂ nanoparticles were synthesized via a sol-gel method and subsequently calcined at different temperatures. Furthermore, the particles were analyzed by TG-DSC, XRD, TEM, HRTEM, EDS, SAED and UV–Vis for investigating the influences of dopant and calcination temperature on the thermal effect, composition, morphology, energy band gap (E_g) and the degradation efficiency of methyl orange (MO) under various light irradiations respectively. Results indicated that Sn/Fe co-doping inhibited the crystallization transformation from anatase to rutile phase of TiO₂ and decreased the E_g. The increased calcination temperature and Sn/Fe co-doped effect brought about the abnormal grain growth of TiO₂ nanoparticles. 0.6 at.% Sn/0.2 at.% Fe and 1.0 at.% Sn/1.0 at.% Fe co-doped TiO₂ nanoparticles presented better photocatalytic performance than pure and 0.2 at.% Sn/0.6 at.% Fe co-doped TiO₂ nanoparticles under visible light irradiation mainly due to the decreased E_g. On the contrary, 0.2 at.% Sn and 0.6 at.% Fe co-doped TiO₂ nanoparticles calcined at 650 °C showed the most excellent photocatalytic performance under UV light irradiation, which was about twice as large as that of pure TiO₂ possibly due to the formed hybrid structure of anatase and rutile phase as well as the h⁺-mediated decomposition pathway.     

Ultrasonic-assisted pH Swing Method for the Synthesis of Highly Efficient TiO2 Nano-size Photocatalysts

A new route for the preparation of nanocrystalline TiO₂ particles based on the pH swing method assisted by ultrasonic irradiation in the presence of a surfactant (Pluronic P-123) has been successfully achieved. The prepared TiO₂ catalysts were calcined from 400 to 800 °C and characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transformed infra-red spectroscopy (FTIR), gas adsorption measurements (BET) and thermogravimetirc measurements (TAG/DTA) analyses. Characterization results revealed that the enhancement in the particle size of TiO₂ by the pH swing method could be controlled by combining the pH swing with ultrasonic irradiation. Increasing the calcination temperatures led to an increase in both the particle and pore size, whereas the surface area and pore volume gradually decreased. A synergistic effect was observed in the combined process of pH swing with ultrasonication, yielding small TiO₂ particles as well as high surface area, pore volume, pore diameter, and crystalline anatase phase. The activity of the catalysts was investigated for the oxidation of 4-chlorophenol (4-CP). TiO₂ prepared with 15 times pH swing and calcined at 700 °C was found to show the highest rate for the oxidative degradation of 4-CP when compared to the TiO₂ sample prepared with just 1 time pH swing and to the commercial P-25 TiO₂ Degussa photocatalyst. Thus, a novel approach in controlling the various physico-chemical parameters of TiO₂ nanoparticles was developed.     

Synthesis and Characterization of Lead-Free Ferroelectric 0.5[Ba(Zr0.2Ti0.8)O3]–0.5[(Ba0.7Ca0.3)TiO3]—Polyvinylidene Difluoride 0–3 Composites

0.5[Ba(Zr_0.2Ti_0.8)O₃]–0.5[(Ba_0.7Ca_0.3)TiO₃]/[BZT–BCT]–polyvinylidene difluoride/[PVDF] 0–3 composites were prepared by uniaxial hot-press method for different volume fractions of BZT–BCT ceramic powder in a PVDF polymer matrix. The structural, microstructural and dielectric properties were investigated and discussed. There was an increase in relative permittivity (ε_r) and dielectric loss (tan δ) of the composites with increase in the volume fraction of the ceramics. At room temperature and at 1 kHz frequency, 0.25[BZT–BCT]–0.75[PVDF] composite showed a highest relative permittivity (ε_r) ~41.     

Synthesis,analysis and characterization of ordered mesoporous TiO2/SBA-15 matrix: Effect of calcination temperature

Mesoporous TiO₂/SBA-15 matrix was prepared by the sol–gel synthesis of TiO₂ in previously prepared SBA-15 particles. Nonionic surfactant was used as liquid template and Na₂SiO₄ as SiO₂ precursor for the synthesis of mesoporous silica SBA-15 with high specific surface area. Different calcination temperature was used for the synthesis and analysis of TiO₂/SBA-15 matrix. The synthesized titania/silica composites were characterized by X-ray diffraction, FTIR, TEM, UV–vis spectroscopy, etc. TEM micrographs showed titania is successfully embedded in SBA-15 channel. Different calcination temperature indicates different size of particle formation and different photocatalytic properties. The activity test indicated that TiO₂/SBA-15 composite prepared by this method had better photocatalytic performance than pure TiO₂. The preparation method and the textural characteristics of mesoporous materials have great influence for the photocatalytic activity.     

Electrospun Sn-doped TiO2: Synthesis,structural, optical and catalytic performance as a function of Sn loading and calcination temperatures

A series of tin (Sn)-doped titania (TiO₂) composites were prepared by electrospinning and then calcined at temperatures of 500 °C, 600 °C, and 700 °C. The morpho-structural and optical properties of the resulting composites were assesed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. In this way, the effect of the dopant amounts and calcination temperatures on the composition, morphology, band gap energy (E_g) of the prepared composites was established, as well as their photocatalytic activity towards ciprofloxacin (CIP) photodegradation. The kinetics of ciprofloxacin photodecomposition reactions was analyzed. Herein, it is reported that the nanostructured material based on ([1.5%]Sn:TiO₂) sintered at 500 °C shows a remarkable photocatalytic activity with a removal efficiency of about 100% and a rate constant of 9.685 × 10^?2 min^?1. The photocatalytic stability of this material was evaluated by reusability tests with five cycles under identical conditions for CIP photodegradation. In-depth structural investigations were undertaken to explain this remarkable photocatalytic activity towards water decontamination.     

Preparation of nanosized anatase TiO2-coated kaolin composites and their pigmentary properties

Nanosized anatase TiO₂-coated kaolin composites were prepared by the chemical deposition method starting from calcined kaolin and TiCl₄. The resultant TiO₂ nanoparticles on the kaolin surfaces existed in anatase phase after calcination at 200, 400, and 900 °C for 1 h, respectively. The surfaces of the kaolin powders were uniformly coated by a monolayer of TiO₂ nanoparticles. The higher calcination temperature was beneficial to formation of well crystallized anatase TiO₂ nanoparticles. The light scattering indexes of the TiO₂-coated calcined kaolin composites were two times higher than that of the kaolin substrate. XPS analysis shows that TiO₂ coating layers anchored at the kaolin surfaces via the Ti-O-Si and Ti-O-Al bonds.     

Structural,dielectric and mechanical behaviors of (La,Nb) Co-doped TiO2/Silicone rubber composites

Ceramic/polymer composites have great potential to achieve the concomitant enhancement of both dielectric constant and breakdown field while maintaining other superior properties of the polymer matrix, ideal for elastomer sensors, actuators, capacitive energy storage, and many other applications. However, material incompatibility between the ceramic filler and the polymer matrix often leads to void formation, particle aggregation and phase separation, with significantly degraded performance. Herein, through surface modification, co-doped TiO₂ particles were uniformly dispersed and bridged onto the silicone rubber matrix via a silane coupling agent for fabricating composites via mechanical mixing and hot-pressing. The synthesized composites exhibit enhanced dielectric constant, increased from 2.78 to 5.06 when 50 wt% co-doped TiO₂ particles are incorporated. Their dielectric loss is less than 0.001 in a broad frequency range. Theoretical modelling and experimental results reveal that the morphology and dispersion state of co-doped TiO₂ particles were crucial to the dielectric properties of the silicone rubber-based composites. Besides, the composites are thermally stable up to 400 °C. Significantly increased tensile strength (612 kPa) and elongation at break (330%) were obtained for the composite incorporated with 30 wt% co-doped TiO₂ particles, accompanied by a moderate increased elastic module (540 kPa). Such composites have the potential for different applications.