Enhanced visible light-induced photoelectrocatalytic degradation of phenol by carbon nanotube-doped TiO2 electrodes

We used a modified sol-gel method to prepare titanium dioxide and multi-walled carbon nanotube (CNT) composites that we subsequently deposited onto indium tin oxide (ITO) conductive glass plates. We characterized these CNT-doped TiO₂ (CNT-TiO₂) films using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance UV-vis spectroscopy. The photoelectrocatalytic (PEC) activity of the composites was evaluated through their ability to mediate the degradation of phenol. XRD measurements indicated that the TiO₂ component existed solely in the anatase phase and that the crystallinity of the CNTs was low. XPS indicated that carbon atoms could substitute for both oxygen and titanium atoms in the TiO₂ lattice to form Ti-C and Ti-O-C structures, which were responsible for the extra photoabsorption and PEC activity under illumination with visible light, in addition to those provided by the CNTs and carbonaceous and Ti³⁺ species. An interphase interaction between TiO₂ and the CNTs elevated the photoabsorbance of the composites in the visible light region. A sample of TiO₂ doped with 10% CNTs and calcined at 400 °C exhibited the highest photocurrent and PEC efficiency. We systematically investigated the effects of several parameters of the PEC process, including the applied potential and pH, on the phenol conversion.     

Structural characterization of barium titanate-cobalt ferrite composite powders

Barium titanate-cobalt ferrite composite powders prepared by sol-gel method and by mixing of precursors were characterized by Raman spectroscopy, scanning electron microscopy and Rietveld refinement of XRD data. Ba vacancies and BaTiO₃-CoFe₂O₄ interfacial stress were associated to lowering of tetragonal distortion in the ferroelectric structure. Raman spectroscopy suggested the encapsulation of ferrite inside clusters of particles in the sol-gel composite.     

EIS analysis of hydrophobic and hydrophilicTiO2 film

Titanium oxide films were formed on metallic titanium substrates by employing a thermal treatment at 800 °C under air atmosphere. Component and microstructure of the oxide films were characterized by XRD and SEM method. Water contact angles on titanium oxide film surface were measured in both dark and sunlight illumination condition. Corrosion tests were carried in seawater solution under different illuminate conditions. Electrochemical impedance spectroscopy (EIS) techniques were used to study the changes on TiO₂ film. Results indicated that: hydrophilic TiO₂ film suffered a severe photo-corrosion effect in seawater due to their semiconductor properties under sunlight condition, but the hydrophobic TiO₂ film under dark condition exhibited a good corrosion resistance.     

Characterization of electrodeposited WO3 films and its application to electrochemical wastewater treatment

WO₃ films have been prepared on to IrO₂-coated Ti substrate by cathodic deposition, and as-deposited and annealed films have been characterized using XRD, TEM, Raman and FT-IR spectroscopy. The as-deposited film consists of nanocrystalline, orthorhombic WO₃·H₂O and this phase transforms to amorphous WO₃ by annealing at 250 °C and to monoclinic WO₃ by annealing at and above 350 °C. The as-deposited and annealed films have been used as anodes for electrochemical decomposition of phenol in aqueous solutions with and without chloride ions. The monoclinic WO₃ anodes prepared by annealing at 350 and 400 °C show relatively high electrochemical activity in the chloride-containing solution. In addition, the anodes possess high chemical and physical stabilities: very low dissolution rate of WO₃ during the electrolysis and good adhesion to the substrate. Thus, WO₃ anodes may be promising materials for anodic oxidation of bio-refractory organics in wastewater, although further improvement of electrochemical activity is needed for more effective decrease in total organic carbons in wastewater.     

Preparation, cross-linking and ceramization of AHPCS/Cp2ZrCl2 hybrid precursors for SiC/ZrC/C composites

SiC/ZrC/C composites were prepared via pyrolysis of a polymeric precursor, namely AHPCS/Cp₂ZrCl₂ hybrid precursor prepared by the blend of allylhydridopolycarbosilane (AHPCS) and bis(cyclopentadienyl) zirconium dichloride (Cp₂ZrCl₂). The cross-linking and polymer-to-ceramic conversion of as-synthesized AHPCS/Cp₂ZrCl₂ were characterized by means of FTIR, ¹³C NMR, TGA, EDS, Raman spectroscopy and XRD. It is suggested that dehydrocoupling, hydrosilylation and dehydrochlorication are involved in the cross-linking of the hybrid precursor, which is responsible for a relatively high ceramic yield of 75.5% at 1200 °C. The polymer-to-ceramic conversion is complete at 900 °C, and it gives an amorphous ceramic. Further heating at 1350 °C induces partial crystallization, and then the characteristic peaks of β-SiC and cubic ZrC appear at 1600 °C. The effect of the composition of the hybrid precursor is also studied in the work.     

Deposition of thin TiO2 layers on platinum by means of cyclic voltammetry of selected complex Ti(IV) media leading to anatase

Thin layers of anatase TiO₂, up to 1 μm, were produced on the surface of a platinum electrode by means of cycling voltammetry from the aqueous solutions of the peroxo-oxalate complexes and the oxalate complexes of titanium(IV). Mechanisms of TiO₂ electrodeposition as well as different electrochemical reactions causing pH changes at the electrode were studied. The electroreduction processes of hydrogen peroxide and nitrite ion on platinum cause the highest pH changes. Values of the molar ratio of Ti(IV)/H₂O₂ should be kept closely to 0.5.In all cases studied, the electrodeposition led to the partially decomposed amorphous oxalate compounds of titanium(IV), which can be converted into crystalline anatase above 500 °C in air. The thermal behaviour of TiO₂ precursor compounds was examined by DRIFTS and TG-DTA methods. Strong effects of K⁺ and NH₄⁺ ions on the electrodeposition process were found by using of the EQCM technique, Raman spectroscopy and XRD measurements. The ammonium electrolyte warrants purity of the anatase phase.Morphology of the oxide films produced in different solvents was examined by SEM.     

On the formation of an oxycarbonate intermediate phase in the synthesis of BaTiO3 from (Ba,Ti)-polymeric organic precursors

The study of BaTiO₃ crystallization from X-ray amorphous (Ba,Ti) polymeric organic powders has been carried out on a (Ba,Ti)–citrate polymeric resin heat-treated in air at 250 °C. From thermal analysis, X-ray diffraction, infrared and Raman spectroscopies, and ¹³C NMR spectroscopy, it has been concluded that an intermediate oxycarbonate phase was formed prior to the formation of BaTiO₃ above 550 °C. Although not well crystallized, thermoanalytical measurements, the unique XRD pattern, and new IR, Raman, and ¹³C NMR structural features revealed that such a metastable intermediate oxycarbonate phase has a stoichiometry close to Ba₂Ti₂O₅CO₃, which is characterized by having CO₃^2- groups different to those of pure BaCO₃ located, probably, in an open interlayer BaTiO₃ metastable structure. A tentative structure for the oxycarbonate phase is proposed. From the XRD crystal size measurements and Raman spectra, it was suggested that the thermal decomposition of the (Ba, Ti) citrate polymeric organic precursor above 550 °C led to the formation of a mixture of tetragonal and hexagonal BaTiO₃ polymorphs rather than cubic. Despite the specific surface of the synthesized BaTiO₃ powders up to 700 °C, higher than 40 m²/g and an equivalent particle size smaller than 25 nm, Raman spectra indicated asymmetry inside the TiO₆ octahedra of the BaTiO₃ structure.     

Catalytic performance of Ti-SBA-15 prepared by chemical vapor deposition for propylene epoxidation

Ti-SBA-15C catalysts were prepared by supporting Ti on SBA-15 with chemical vapor deposition (CVD) using TiCl₄ as titanium source, and were characterized by XRD, N₂ adsorption, FT-IR and ICP. The results show that SBA-15E prepared by ethanol solution extracting template has higher concentration of surface Si-OH groups than SBA-15 calcined at 550 °C, resulting in high Ti content on Ti-SBA-15EC prepared by CVD. The temperature and time of TiCl₄ deposition affect the Ti content and catalytic activity of Ti-SBA-15EC for the epoxidation of propylene with cumene hydroperoxide (CHP). Ti-SBA-15EC prepared by CVD at 700 °C for 1.5 h exhibits more excellent performance than Ti-SBA-15C, Ti-SBA-15 prepared hydrothermally and Ti/SBA-15 (impregnation method), and the 87.3% conversion of CHP and 96.4% selectivity to propylene oxide can be obtained at 80 °C for 4 h. The performance of Ti-SBA-15EC is decreased hardly for the epoxidation of propylene after used repeatedly 6 times.     

Oxidative coupling of methane catalyzed by Li, Na and Mg doped BaSrTiO3

The XBaSrTiO₃ (X = Li, Na, Mg) with perovskite structure was prepared by impregnation of LiCl, NaCl or MgCl₂ solution on BaSrTiO₃ (BST) surface. The products were characterized with XRD, SEM, UV, FT-IR and Raman spectroscopy. Determination of band gap, conduction and basicity of the prepared catalysts revealed that NaBST exhibits the lowest band gap and the most conduction and basicity. The catalytic performances of XBSTs for the oxidative coupling of methane (OCM) in a tubular continuous flow reactor were evaluated. The NaBST showed the maximum catalytic effect on methane conversion (47%), C₂₊ selectivity (51%) and ethylene yield (24%) at the temperature of 800 °C.     

The synthesis of carbon nanotubes at low temperature via carbon suboxide disproportionation

Carbon nanotubes were synthesized via a novel route using an iron catalyst at the extremely low temperature of 180 °C. In this process, carbon suboxide was used as carbon source, which changed to freshly formed free carbon clusters through disproportionation. The carbon clusters can grow into nanotubes in the presence of Fe catalyst, which was obtained by the decomposition of iron carbonyl Fe₂(CO)₉ at 250 °C under nitrogen atmosphere. The products were characterized with XRD, TEM, HRTEM and Raman spectroscopy.     

Synthesis and characterization of electrodeposited samaria and samaria-doped ceria thin films

Samaria (Sm₂O₃) and samaria-doped ceria (SDC) films are electrochemically deposited on stainless steel in view of a potential use in solid oxide fuel cells. As it is possible to deposit separately pure ceria (CeO₂) and pure samaria (Sm₂O₃) in similar conditions, SDC films were successfully obtained in one electrochemical conditions set. Thin films have been fabricated at low-temperature (30 °C) by applying a cathodic potential of −0.8 V/SCE, for 2 h. Structural and morphological properties of electrodeposited films have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), techniques and Raman spectroscopy. Special attention has been focused on the Raman spectroscopy study to emphasize the effect of heat treatment and samarium doping. Despite cracks, single SDC phase was obtained crystallizing in a cubic symmetry.     

Cycling-induced degradation of LiCoO2 thin-film cathodes at elevated temperature

The cycle life of LiCoO₂-based all solid-state thin-film cells has been studied at room temperature, and at elevated temperatures of 50, 100, and 150 °C. X-ray diffraction, as well as Raman analysis, has been used to complement the electrochemical data in examining structural and chemical changes. XRD and Raman spectroscopy data indicate that elevated temperature soaks of the thin-film batteries in the quiescent state causes no discernable changes in the LiCoO₂ cathode layer. However, when the thin-film batteries are cycled at elevated temperatures, decreases in average grain size of the LiCoO₂ film occur with dramatic concomitant charge and discharge capacity loss.     

Synthesis and Characterization of Bowl-Like Single-Crystalline BaTiO3 Nanoparticles

Novel bowl-like single-crystalline BaTiO₃ nanoparticles were synthesized by a simple hydrothermal method using Ba(OH)₂·8H₂O and TiO₂ as precursors. The as-prepared products were characterized by XRD, Raman spectroscopy, SEM and TEM. The results show that the bowl-like BaTiO₃ nanoparticles are single-crystalline and have a size about 100–200 nm in diameter. Local piezoresponse force measurements indicate that the BaTiO₃ nanoparticles have switchable polarization at room temperature. The local effective piezoelectric coefficient d₃₃ ^* d_{33}^{ * } is approximately 28 pm/V.     

V-doped In2O3 nanofibers for H2S detection at low temperature

Pristine and vanadium-doped In₂O₃ nanofibers were fabricated by electrospinning and their sensing properties to H₂S gas were studied. X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the inner structure and the surface morphology. The H₂S-sensing performances were characterized at different temperatures ranging from 50 to 170 °C. The sensor based on 6 mol% V-doped In₂O₃ nanofibers exhibit the highest response, i.e. 13.9–50 ppm H₂S at the relatively low temperature of 90 °C. In addition, the fast response (15 s) and recovery (18 s) time, and good selectivity were observed.     

Low-temperature synthesis of Bi2Fe4O9 nanoparticles via a hydrothermal method

Bi₂Fe₄O₉ (BFO) nanoparticles were successfully synthesized by a hydrothermal method at a temperature as low as 100 °C. The as-prepared powders, characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM) and physical property measurement system (PPMS), exhibited a pure BFO phase about 100 nm size with uniform sheet-like shape and exhibited an AF order at room temperature. It was found that high alkali concentration and alkali ion Na⁺ played a key role in the formation of BFO nanoparticles at a low temperature of 100 °C.     

Microstructure and ionic conductivity properties of gadolinia doped ceria (GdxCe1−xO2−x/2) electrolytes for intermediate temperature SOFCs prepared by the polyol method

Gd_0.1Ce_0.9O_1.95 and Gd_0.2Ce_0.8O_1.9 powders were prepared through the polyol process without using any protective agent. Microstructural and physical properties of the samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG) and impedance analysis methods. The results of the thermogravimetry/differential thermal analysis (TG/DTA) and XRD indicated that a single-phase fluorite structure formed at the relatively low calcination temperature of 500 °C. The XRD patterns of the samples revealed that the crystallite size of the samples increased as calcination temperatures increased. The sintering behavior and ionic conductivity of pellets prepared from gadolinia doped ceria (GDC) powders, which were calcined at 500 °C, were also investigated. The relative densities of the pellets, which were sintered at temperatures above 1300 °C, were higher than 95%. The results of the impedance spectroscopy revealed that the GDC-20 sample that was sintered at 1400 °C exhibited an ionic conductivity of 3.25×10⁻² S cm⁻¹ at 800 °C in air. This result clearly indicates that GDC powder with adequate ionic conductivity can be prepared through the polyol process at low temperatures.     

Synthesis of La2NiO4 via a PVA-based route

Single-phase La₂NiO₄ has been prepared using polyvinyl alcohol (PVA) as a complexing agent. Thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were used to characterize precursor and derived oxide powders. The particle size and morphologies of La₂NiO₄ crystallites were characterized by field emission scanning electron microscope (FSEM). The effect of the mol ratios of metal ion to hydroxyl groups in polyvinyl alcohol on the formation of La₂NiO₄ was investigated. XRD analysis showed that single-phase and well-crystallized La₂NiO₄ was obtained from precursor with M/OH = 1:3 at 900 °C. The La₂NiO₄ ceramics sintered at 1300 °C for 4 h exhibits an electrical conductivity of 42.5 Ω⁻¹ cm⁻¹ at room temperature.     

Effects of PVA content on the synthesis of LaFeO3 via sol-gel route

LaFeO₃ were synthesized via a sol-gel route based on polyvinyl alcohol (PVA). Differential scanning calorimetry (DSC), Thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM) techniques were used to characterize precursors and derived oxide powders. The effect of the ratios of positively charged valences to hydroxyl groups of PVA (Mⁿ⁺/-OH) on the formation of LaFeO₃ was investigated. XRD analysis showed that single-phase and well-crystallized LaFeO₃ was obtained from the Mⁿ⁺/-OH = 4:1 molar ratio precursor at 700 °C. For the precursor with Mⁿ⁺/-OH = 2:1, nanocrystalline LaFeO₃ with average particle size of ∼50 nm was formed directly in the charring procedure. With increase of PVA content to Mⁿ⁺/-OH = 1:1, phase pure LaFeO₃ was obtained at 500 °C.     

Raman studies of peroxide formation,decomposition, and reduction on Ba/MgO

Ba/MgO is an active catalyst for the oxidative coupling of methane to form ethane and ethylene. It has been proposed that activation of methane occurs via reaction with peroxide species present at the surface of the catalyst. In the present work, Raman spectroscopy has been used to investigate the formation, decomposition, and reduction of BaO₂ on 4 mol% Ba/MgO. The presence of BaO₂ is evidenced by the presence of a band at 842 cm^–1. The peroxide forms above 300°C but is stable to decomposition at temperatures up to 500°C. Reduction of BaO₂ to BaO proceeds via Ba(OH)₂. BaCO₃ forms when either BaO or BaO₂ is exposed to CO₂. Once formed, BaCO₃ is stable to decomposition in He or O₂ at temperatures up to 500°C. Only BaCO₃ is observed when a mixture of CH₄ and O₂ is passed over the catalyst at 500°C.     

Synthesis of carbon nanotubes by pyrolysis of solid Ni(dmg)2

We describe the high yield synthesis of multi-walled carbon nanotubes (MWCNTs) and the determination of the optimum production conditions. The method involves the catalytic pyrolysis of solid Ni(dmg)₂ under an Ar atmosphere. The obtained materials were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy and thermogravimetry analysis (TGA). The data revealed the formation of MWCNTs surrounded by a varying quantity of byproducts such as amorphous carbon and metallic particles, depending mainly on the reaction temperature. Pyrolysis of Ni(dmg)₂ at 900 °C results in the production of nanotube material with the highest degree of crystallinity.