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.     

Self-assembled Nafion–silica nanoparticles for elevated-high temperature polymer electrolyte membrane fuel cells

In this paper, a novel Nafion/SiO₂ nanocomposite membrane based on the self-assembled Nafion–SiO₂ nanoparticles was developed. The average particle size of Nafion–SiO₂ nanoparticles prepared by self-assembly process was 2.8 ± 0.5 nm. The self-assembled Nafion–SiO₂ nanoparticles significantly enhance the durability of the Nafion/silica nanocomposite membrane as compared to that of conventional Nafion/silica composite and Nafion 212 membranes under wet/dry cyclic tests at 90 °C. With an addition of 5 wt% self-assembled Nafion–SiO₂ nanoparticles, the Nafion/SiO₂ nanocomposite membrane shows a significantly improved performance stability at cell/humidifying temperatures of 100 °C/60 °C under a current density of 600 mA/cm², and the degradation rate is 0.12 mV/min, almost 20 times lower than 2.33 mV/min measured on the pristine Nafion 212 membrane under the same conditions. The present results demonstrate the promises of the self-assembled Nafion/SiO₂ nanocomposite membrane for elevated-high temperature PEM fuel cells applications.     

Mesoporous TiO2 nano networks: Anode for high power lithium battery applications

Anatase phase mesoporous TiO₂ with I41/amd space group was synthesized via the urea assisted hydrothermal method. The existence of mono phasic TiO₂ sub-microspheres of uniform particle size (ca. 400 nm) encompassing an average crystallite size of 14 nm was demonstrated using the XRD, FE-SEM and TEM analysis. Surface area of ca. 116.49 m²/g along with a pore size of 7 nm was calculated using the BET and adsorption isotherm measurements which authenticated the mesoporous nature of the synthesized material. Suitable calcination temperature for the better electrochemical property was established via the optimization process. Accordingly, the mesoporous TiO₂ calcined at 400 °C displayed improved cycleability with excellent rate capability ever reported, even at 20 C-rate of discharge. The reason for the superior rate capability is corroborated to the highly mesoporous nature of the TiO₂ sub-microspheres that has imparted desirable surface area apposite for enhanced ionic and electronic diffusion.     

Fabrication and magnetic properties of electrospun copper ferrite (CuFe2O4) nanofibers

Tetragonal copper ferrite (CuFe₂O₄) nanofibers were fabricated by electrospinning method using a solution that contained poly(vinyl pyrrolidone) (PVP) and Cu and Fe nitrates as alternative metal sources. The as-spun and calcined CuFe₂O₄/PVP composite samples were characterized by TG-DTA, X-ray diffraction, FT-IR, and SEM, respectively. After calcination of the as-spun CuFe₂O₄/PVP composite nanofibers (fiber size of 89 ± 12 nm in diameter) at 500 °C in air for 2 h, CuFe₂O₄ nanofibers of 66 ± 13 nm in diameter having well-developed tetragonal structure were successfully obtained. The crystal structure and morphology of the nanofibers were influenced by the calcination temperature. After calcination at 600 and 700 °C, the nature of nanofibers changed which was possibly due to the reorganization of the CuFe₂O₄ structure at high temperature, and a fiber structure of packed particles or crystallites was prominent. Crystallite size of the nanoparticles contained in nanofibers increases from 7.9 to 23.98 nm with increasing calcination temperature between 500 and 700 °C. Room temperature magnetization results showed a ferromagnetic behavior of the calcined CuFe₂O₄ samples, having their specific saturation magnetization (M_s) values of 17.73, 20.52, and 23.98 emu/g for the samples calcined at 500, 600, and 700 °C, respectively.     

Formation and characterization of magnetic barium ferrite hollow fibers with high specific surface area via sol–gel process

The magnetic barium ferrite (BaFe₁₂O₁₉) hollow fibers with a high specific surface area about 22–38 m² g^?1, diameters around 1 μm and a ratio of the hollow diameter to the fiber diameter estimated about 1/2–2/3 have been prepared by the gel-precursor transformation process. The precursor and resulting ferrite hollow fibers were analyzed by thermo-gravimetric and differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy and X-ray diffraction. The specific surface area was measured by the Brunauer–Emmett–Teller method. The gel formed at pH 5.5 has a good spinnability. A pure barium ferrite phase is formed after calcined at 750 °C for 2 h and fabricated of nanograins about 38 nm with a hexagonal plate-like morphology, which are increased to about 72 nm with the calcination temperature increased up to 1050 °C. The barium ferrite hollow fibers obtained at 750 °C for 2 h have a specific surface area 38.1 m² g^?1 and average pore size 6.5 nm and then the specific surface area and average pore size show a reduction tendency with the calcination temperature increasing from 750 to 1050 °C owing to the particle growth and fiber densification. These barium ferrite hollow fibers exhibit typical hard-magnetic materials characteristics and the formation mechanism for hollow structures is discussed.     

The effect of silver doping on photocatalytic properties of titania multilayer membranes

In this investigation an Ag doped titania multilayer membrane is successfully fabricated via the sol–gel processing method. The doped membrane is characterized via X-ray Diffraction and N₂-sorption techniques and the photocatalytic properties of the membrane are investigated via methyl orange degradation. The properties included high surface area (101 m²/g), small pore size (3.1 nm), and active anatase crystal phase. The prepared titania membrane has a high photocatalytic activity and decomposes methyl orange by 50% after 9 h of UV irradiation. The prepared membrane can be applied in the development of efficient photocatalytic systems for the treatment of water. Due to the high photoactivity of the prepared titania membrane, this study reveals the possibility of combining two processes for removal of organic pollutants: the photocatalytic process and the membrane separation process. In the combining process the lifetime of the membrane increases and the quality of water is enhanced.     

Electrocatalytic oxidation of nitric oxide at TiO2–Au nanocomposite film electrodes

Structured films of TiO₂ (anatase) nanoparticles (ca. 6 nm diameter) and gold nanoparticles (nominal 20 nm diameter) are formed via a layer-by-layer deposition procedure. TiO₂ nanoparticles are deposited with a Nafion polyelectrolyte binder followed by calcination to give a mesoporous thin film electrode. Gold nanoparticles are incorporated into this film employing a poly(diallyldimethylammonium chloride) polyelectrolyte binder followed by calcination to give a stable mesoporous TiO₂–gold nanocomposite. This methodology allows well-defined and structured films to be formed which are re-usable after a 500 °C heat treatment in air.Electrochemical experiments are performed in aqueous KCl and buffer solutions and for the oxidation of nitric oxide, NO, and nitrite in phosphate buffer solution. It is shown that the NO oxidation occurs as a highly effective electrocatalytically amplified process at the surface of the gold nanocomposite probably with co-evolution of oxygen, O₂. In contrast, the oxidation of nitrite to nitrate occurs at the same potential but without oxygen evolution. A mechanistic scheme for the amplified NO detection process is proposed.     

Thermal stability of TiO2-anatase: Impact of nanoparticles morphology on kinetic phase transformation

TiO₂ is a material of great interest for many technological applications among which, as catalyst support. As this specific application requires a good thermal stability of the material, the phase transition between the two most commonly used titania polymorphs, anatase and rutile, has been extensively studied over the past decade. However not much importance has been given to the initial and final particles morphologies. In this study, anatase nanoparticles with an elongated shape were synthesized and their kinetic phase transformation was studied. The thermal treatments were conducted at temperatures ranging from 500 to 700 °C. The morphology evolution and the phase transition were characterized by X-ray diffraction and transmission electron microscopy. The phase transformation kinetics is best described by the interface nucleation models. The values of the measured kinetic parameters are significantly lower than those proposed in the literature for isotropic particles, with an activation energy of E_a = 345 kJ mol^?1. The influence of morphology and, as a consequence, the influence of exposed faces on anatase particles, are presented and discussed.     

Novel core–shell SDC/amorphous Na2CO3 nanocomposite electrolyte for low-temperature SOFCs

Novel core–shell SDC (Ce_0.8Sm_0.2O_1.9)/amorphous Na₂CO₃ nanocomposite was prepared for the first time. The core–shell nanocomposite particles are smaller than 100 nm with amorphous Na₂CO₃ shell of 4–6 nm in thickness. The nanocomposite electrolyte shows superionic conductivity above 300 °C, where the conductivity reaches over 0.1 S cm⁻¹. Such high conductive nanocomposite has been applied in low-temperature solid oxide fuel cells (LTSOFCs) with an excellent performance of 0.8 W cm⁻² at 550 °C. A new potential approach of designing and developing superionic conductors for LTSOFCs was presented to develop interface as ‘superionic highway’ in two-phase materials based on coated SDC.     

Novel synthesis of high-surface-area ordered mesoporous TiO2 with anatase framework for photocatalytic applications

Ordered mesoporous TiO₂ materials with an anatase frameworks have been synthesized by using a cationic surfactant cetyltrimethylammonium bromide (C₁₆TMABr) as a structure-directing agent and soluble peroxytitanates as Ti precursor through a self-assembly between the positive charged surfactant S⁺ and the negatively charged inorganic framework I^? (S⁺I^? type). The low-angle X-ray diffraction (XRD) pattern of the as-prepared mesoporous TiO₂ materials indicates a hexagonal mesostructure. XRD and transmission electron microscopy results and nitrogen adsorption–desorption isotherms measurements indicate that the calcined mesoporous TiO₂ possesses an anatase crystalline framework having a maximum pore size of 6.9 nm and a maximum Brunauer–Emmett–Teller specific surface area of 284 m² g^?1. This ordered mesoporous anatase TiO₂ also demonstrates a high photocatalytic activity for degradation of methylene blue under ultraviolet irradiation.     

Titania nanotube supported tin anodes for lithium intercalation

A new type of nanostructured titania nanotube supported tin anode was prepared for lithium ion batteries. The as-prepared titania nanotubes are in the anatase phase with diameters of about 12 nm. Tin nanoparticles are dramatically decorated on the titania nanotubes and have a particle size of about 10 nm. This new structure promises good retention of reversible capacity on cycling for lithium intercalation. By charge/discharge measurements, the reversible capacity of the titania nanotubes supported tin anode for lithiation and de-lithiation was found to be 312 mA h/g (cycled between 0.05 and 2.0 V) and 203 mA h/g (cycled between 0.05 and 1.3 V) after 50 cycles with around 100% columbic efficiency.     

Préparation et caractérisation des catalyseurs Rh/Al2O3 et Rh/ZnO–Al2O3

A series of rhodium (1 and 5 wt%) deposited on alumina and alumina modified by Zn was prepared by impregnation of Al₂O₃ and ZnO–Al₂O₃ with two different precursors, Rh(NO₃)₂·xH₂O and RhCl₃, followed by calcination at 723 K, and characterized after reduction at different temperatures, in the range 500–800 °C. Catalysts were analysed by Hydrogen Chemisorption (Hc), Temperature-Programmed Reduction (TPR), Temperature-Programmed Desorption (TPD), X-ray diffraction (RDX), and Scanning Electron Microscopy methods. The results show that the metal dispersion depends strongly on the Zn/Rh atomic ratio and on the metal loading. The presence of Zn and high reduction temperature decrease the capacity to chemisorb hydrogen, whereas the metal particles' size increase is probably due to the sintering effect. Temperature-programmed studies (TPR) of catalysts show that the temperature of maximal reduction is lower with nitrate-prepared catalysts, which is explained by metal–support interactions.     

Chrysanthemum-like Co3O4 architectures: Hydrothermal synthesis and lithium storage performances

Three-dimensional chrysanthemum-like Co₃O₄ was prepared via a facile hydrothermal route without any template, and a subsequent calcination process. With a controlled concentration of the homogeneous precipitation agent, urea, a chrysanthemum-like precursor was hydrothermally obtained at 120 °C for 20 h, and the morphology was kept for Co₃O₄ after a subsequent calcination at 300 °C for 2 h. Co₃O₄ chrysanthemum-like architectures are assemblies of nanorods radiating from a common centre, and the nanorods consisted of interconnected nanoparticles with the size of about 30 nm. When tested as an anode material of Li-ion batteries, chrysanthemum-like Co₃O₄ presented a discharge capacity of ∼450 mA h/g after 50 discharge/charge cycles.     

Investigation of Mg modified mesoporous silicas and their CO2 adsorption capacities

CO₂ adsorption properties on Mg modified silica mesoporous materials were investigated. By using the methods of co-condensation, dispersion and ion-exchange, Mg²⁺ was introduced into SBA-15 and MCM-41, and transformed into MgO in the calcination process. The basic MgO can provide active sites to enhance the acidic CO₂ adsorption capacity. To improve the amount and the dispersion state of the loading MgO, the optimized modification conditions were also investigated. The XRD and TEM characteristic results, as well as the CO₂ adsorption performance showed that the CO₂ adsorption capacity not only depended on the pore structures of MCM-41 and SBA-15, but also on the improvement of the dispersion state of MgO by modification. Among various Mg modified silica mesoporous materials, the CO₂ adsorption capacity increased from 0.42 mmol g⁻¹ of pure silica SBA-15 to 1.35 mmol g⁻¹ of Mg–Al–SBA-15-I1 by the ion-exchange method enhanced with Al³⁺ synergism. Moreover, it also increased from 0.67 mmol g⁻¹ of pure silica MCM-41 to 1.32 mmol g⁻¹ of Mg–EDA–MCM-41-D10 by the dispersion method enhanced with the incorporation of ethane diamine. The stability test by 10 CO₂ adsorption/desorption cycles showed Mg–urea–MCM-41-D10 possessed quite good recyclability.     

Visible light photocatalysis by a Titania–Rhodium(III) complex

Titania hybrid photocatalysts containing 0.5, 1.0, 2.0, and 5.0 wt% of rhodium(III) were prepared by chemisorption of RhCl₃ × 3H₂O onto anatase hydrate powder (TH). Analytical data suggest that a titania–trichlororhodate complex is produced containing a [TiO₂]–O–Rh bond.Similar results are found in the case of modification by RhBr₃ × 3H₂O. Diffuse reflectance spectra exhibit an absorption shoulder throughout the visible region down to 700 nm. Photoelectrochemical measurements indicate that the quasi-Fermi level of electrons is gradually shifted to more anodic potentials with increasing rhodium loading reaching a value of ?0.34 V at pH 7 (vs. NHE) in the case of 5.0%RhCl₃/TH. This is more anodic by 210 mV as compared to unmodified TH. Upon visible light irradiation this photocatalyst induces a fast mineralization of 4-chlorophenol whereas cyanuric acid, which is known to be mineralized in the presence of the analogous Pt(IV) modified titania, is not degraded.     

Quantum-dots containing Fe/SBA-15 silica as “green” catalysts for the selective photocatalytic oxidation of alcohol (methanol,under visible light)

Fe/SBA-15 catalysts containing iron oxide nanoparticles confined inside silica pores (replicated, internal, poorly crystalline) and grown outside silica grains (external, mainly crystalline hematite) in different proportions are prepared using a single silica support. Fe-species are deposited by the two-solvent technique with two iron salts precursors (Fe(NO₃)₃·9H₂O, FeCl₃·6H₂O) and two solvents (cyclohexane, hexane) for 11 wt% of iron. Calcination is performed in reproducible conditions (700 °C, 2 °C/min, thin bed, in air). SAXS measurements are used to show that the 2D hexagonal structure of the used silica is maintained after Fe-loading and calcination. Ar sorption measurements show that the pores are partially plugged. The oxidation of pure methanol is used as a test reaction to compare photocatalytic properties. H₂O₂ and visible light both activate the reaction. More active catalysts are formed with hexane associated with FeCl₃·6H₂O than with Fe(NO₃)₃·9H₂O. A reversed situation is observed with cyclohexane. Iron leaching (after 1 h 30 of test, up to 3 mg of Fe by mL) is important. These results are expected to be of interest in the exploration of size and shape “nanocatalysis” and to provide a further understanding for the reactions that take place when porous silicas are used as supports.     

RuO2-wired high-rate nanoparticulate TiO2 (anatase): Suppression of particle growth using silica

To enhance the high-rate capability (up to 120 C, 20 A/g) of nanoparticulate TiO₂ (anatase) formed by thermal treatment of protonated TiO₂ nanotubes, we used two types of additives: RuO₂ as an electron-conductive material [Y.-G. Guo, Y.-S. Hu, W. Sigle, J. Maier, Adv. Mater. 19 (2007) 2087] and silica as a suppressant of particle growth during heat treatment. We show systematically that both additives, when used separately, improve the high-rate performance of anatase by 25–55 mA h/g at 60 C. The combined use of both additives in a total amount of merely 2.5 wt.% leads to an improvement of more than 70 mA h/g at 60 C. The underlying mechanisms for these significant effects are briefly discussed.     

Effects of calcination and activation temperature on dry reforming catalysts

The effect of calcination temperatures on dry reforming catalysts supported on high surface area alumina Ni/γ-Al₂O₃ (SA-6175) was studied experimentally. In this study, the prepared catalyst was tested in a micro tubular reactor using temperature ranges of 500, 600, 700 and 800 °C at atmospheric pressure, using a total flow rate of 33 ml/min consisting of 3 ml/min of N₂, 15 ml/min of CO₂ and 15 ml/min of CH₄. The calcination was carried out in the range of 500–900 °C. The catalyst is activated inside the reactor at 500–800 °C using hydrogen gas. It was observed that calcination enhances catalyst activity which increases as calcination and reaction temperatures were increased. The highest conversion was obtained at 800 °C reaction temperature by using catalyst calcined at 900 °C and activation at 700 °C. The catalyst characterization conducted supported the observed experimental results.     

Net-structured NiO–C nanocomposite as Li-intercalation electrode material

Net-structured NiO was prepared by urea-mediated homogeneous hydrolysis of Ni(CH₃COO)₂ under microwave radiation followed by a calcination at 500 °C. NiO–C nanocomposite was prepared by dispersing the as-prepared net-structured NiO in glucose solution and subsequent carbonization under hydrothermal conditions at 180 °C. The carbon in the composite was amorphous by the X-ray diffraction (XRD) analysis, and its content was 15.05 wt% calculated according to the energy dispersive X-ray spectroscopy (EDX) result. Transmission electron microscopy (TEM) image of the NiO–C nanocomposite showed that the NiO network was homogeneously filled by amorphous carbon. The reversible capacity of NiO–C nanocomposite after 40 cycles is 429 mAh g⁻¹, much higher than that of NiO (178 mAh g⁻¹). These improvements are attributed to the carbon, which can enhance the conductivity of NiO, suppress the aggregation of active particles, and increase their structure stability during cycling.     

Novel nano-structured Pd+yttrium doped ZrO2 cathodes for intermediate temperature solid oxide fuel cells

Novel nano-structured Pd+yttrium doped ZrO₂ (YSZ) electrodes have been developed as cathodes of intermediate temperature solid oxide fuel cells (IT-SOFCs). Nano-sized Pd particles were introduced into the rigid and porous YSZ structure by PdCl₂ solution impregnation. The results show that Pd nanoparticles (20–80 nm) were uniformly distributed in the porous YSZ structure; and such nano-structured composite cathodes were highly active for the O₂ reduction reaction, with polarization resistances (R_E) of 0.11 and 0.22 Ω cm² at 750 and 700 °C and activation energy of 105 kJ mol⁻¹ that is significantly lower than those for the conventional perovskite-based cathodes (130–201 kJ mol⁻¹).