N-doped NaTaO3: novel visible-light-driven photocatalysts synthesised by a sol–gel method

N-doped NaTaO₃ catalysts were synthesized via a sol–gel method followed by a subsequent calcination process under NH₃ atmosphere. The as prepared samples were characterized by XPS, XRD, UV–Vis DRS, and BET analyses. All XRD peaks of the sample calcined at 900 °C matched with pure perovskite NaTaO₃ while peaks of TaON and Na₂Ta₄O₁₁ were found for that calcined at 1,000 °C. The DRS of samples shown cutoff edge has red shifted, from 315 nm of pure to 391 nm of N-doped NaTaO₃. N-doping helps to narrow the band gap, and the prepared sample was visible light sensitive. The XPS spectrum of Ta4p3&N1s shown two new peaks at 398.3 and 401.4 eV appear in the N-doped sample corresponding to Ta–N bonds and adsorption nitride, respectively. Photocatalytic activity of the catalysts was evaluated using Rhodamine B dye. The result demonstrated that the sample calcined under NH₃ had a higher photocatalytic activity than that of P25 under visible light. The NaTaO₃/TaON heterojunction played an important role on promoting photoactivity.     

Synthesis of highly pure nanocrystalline and mesoporous CaTiO3 by a particulate sol–gel route at the low temperature

The low temperature perovskite-type calcium titanate (CaTiO₃) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol–gel route. The prepared sol had a narrow particle size distribution about 17 nm. X-ray diffraction and Fourier transform infrared spectroscopy revealed that, the synthesized powders had highly pure and crystallized CaTiO₃ structure with preferable orientation growth along (1 2 1) direction at 400–800 °C. The activation energy of crystal growth was calculated 5.73 kJ/mol. Furthermore, transmission electron microscope images showed that the average crystallite size of the powders annealed at 400 °C was around 3.5 nm. Field emission scanning electron microscope analysis and atomic force microscope images revealed that, the deposited thin films had uniform, mesoporous and nanocrystalline structure with the average grain size in the range 33–39 nm depending on annealing temperature. Based on Brunauer–Emmett–Teller (BET) analysis, the synthesized powders showed mesoporous structure with BET surface area in the range 51–21 m²/g at 400–800 °C. One of the smallest crystallite size and one of the highest surface areas reported in the literature is obtained which can be used in many applications, such as photocatalysts.     

Low temperature nanostructured lithium titanates: controlling the phase composition, crystal structure and surface area

Low temperature lithium titanate compounds (i.e., Li₄Ti₅O₁₂ and Li₂TiO₃) with nanocrystalline and mesoporous structure were prepared by a straightforward aqueous particulate sol–gel route. The effect of Li:Ti molar ratio was studied on crystallisation behaviour of lithium titanates. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders were crystallised at the low temperature of 500 °C and the short annealing time of 1 h. Moreover, it was found that Li:Ti molar ratio and annealing temperature influence the preferable orientation growth of the lithium titanate compounds. Transmission electron microscope (TEM) images showed that the average crystallite size of the powders annealed at 400 °C was in the range 2–4 nm and a gradual increase occurred up to 10 nm by heat treatment at 800 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 21–28 nm at 600 °C and 49–62 nm at 800 °C depending upon the Li:Ti molar ratio. Moreover, atomic force microscope (AFM) images confirmed that the lithium titanate films had columnar like morphology at 600 °C, whereas they showed hill-valley like morphology at 800 °C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure containing pores with needle and plate shapes. The surface area of the powders was enhanced by increasing Li:Ti molar ratio and reached as high as 77 m²/g for the ratio of Li:Ti = 75:25 at 500 °C. This is one of the smallest crystallite size and the highest surface areas reported in the literature, and the materials could be used in many applications such as rechargeable lithium batteries and tritium breeding materials.     

Effects of Ag–La codoping on structure and electrical properties of BaTiO3 powder

Ag–La codoped BaTiO₃ powders were prepared by sol–gel technology after the preparation of Ag-doped and La-doped BaTiO₃ powders. Variations in the structure, constitution, morphology, and electrical properties of the modified BaTiO₃ powders were characterized. It can be concluded that Ag–La codoping decreases the resistivity of the modified powders more significantly than Ag doping and La doping, respectively. The sample with the lowest resistivity was obtained by codoping with 0.1 at.% Ag and 0.3 at.% La, where the resistivity decreased to 7.13 × 10² Ω m from the value of 4.30 × 10⁹ Ω m of the undoped powder. X-ray diffractometry (XRD) and Fourier-transform infrared (FTIR) analyses indicate that the main phase of the codoped powders transitions from tetragonal to cubic with increasing La doping content. Scanning electron microscopy (SEM) observations illustrate that codoping makes the particles distribute more equably. The relationship between the resistivity and the structure of the doped BaTiO₃ powders is discussed based on defect chemistry.     

Preparation and characterization of CaCu3Ti4O12 powders by non-hydrolytic sol–gel method

CaCu₃Ti₄O₁₂ (CCTO) powders were prepared via a non-hydrolytic sol–gel (NHSG) method by using acetylacetone as chelating agent and ethylene glycol as solvent. The samples were characterized by TG–DSC, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscope. The dielectric properties of ceramics were also measured. The pure perovskite-like CCTO powders were obtained by heat treatment at 800 °C for 2 h. The average particle sizes of CCTO powders calcined at 800 °C were approximately 350–450 nm. The samples sintered at 1,000 °C showed the mean grain size of 2.5–4 μm. Specially, the ceramics exhibited high dielectric constant (1.19 × 10⁵–1.40 × 10⁵) and low dielectric loss (0.051–0.1) in the temperature range of 30–110 °C. Moreover, with the NHSG method the period of synthesis process was greatly shortened.     

Deactivation and Regeneration of NaTaO3 Photocatalyst in Cooperating Dehydrogenation Coupling of Isopropanol and Hydrogenation Coupling of Acetone Reaction System

Photocatalyst activity is influenced by many factors, such as adsorption of by‐products, runoff of surface hydroxyl groups and carriers. In this study, a simple and efficient photocatalyst regeneration method was developed. Results indicated that NaTaO₃ photocatalyst lost its photoactivity after three cycles of reaction that involves coupling of isopropanol and hydrogenation coupling of acetone reaction system. Runoff of Na on the surface was the main reason for the deactivation of NaTaO₃ photocatalyst. After hydrothermal treatment of the deactivated NaTaO₃ with 10 m NaOH at 180°C for 12 h, its photocatalytic activity was restored to the original level. The photocatalytic activity remained stable even after 10 cycles.     

Sol–gel synthesized vanadium doped TiO2 photocatalyst: physicochemical properties and visible light photocatalytic studies

Vanadium doped titanium dioxide (V–TiO₂) photocatalyst was synthesized by the sol–gel method using ammonium vanadate as vanadium source. The prepared samples were characterized by XRD, N₂ adsorption–desorption method, UV–Vis DRS, Fourier transform infrared (FTIR), scanning electron microscope–energy dispersive X-ray and photoluminescence (PL) analysis. The results show that V⁵⁺ ions were successfully incorporated into the crystal lattice of TiO₂ as a consequence, not only an obvious decrease in the band gap and a red shift of the absorption threshold into the visible light region was recorded for the V modified TiO₂, but, also a decrease in photogenerated electrons and holes recombination rate was observed as demonstrated by PL analysis. FTIR study indicated that in undoped TiO₂ sample the acetate group favored a bidentate bridging mode of binding with titanium atoms, whereas a bidentate chelating mode of linkage was observed in V–TiO₂ powders. The crystallite size of the samples calcined at 300 and 500 °C were decreased beyond the molar ratio of 200:1 (V:Ti), this may be due to dopant presence in the grain boundaries hindering the crystal growth. The photocatalytic activities for both pure and vanadium doped TiO₂ powders were tested in the discoloration of a reactive dyestuff, methylene blue, under visible light. The 100:1 (V:Ti) doped photocatalyst, calcined at 300 °C showed enhanced photocatalytic activity under visible light with a rate constant (k_obs) of 5.024 × 10^?3 min^?1 which is nearly five times higher than that of pure TiO₂, as result of low band gap value, high specific surface area and a decrease in recombination rate.     

Synthesis of nanosized NaTaO3 in low temperature and its photocatalytic performance

A simple synthetic route in mild condition to obtain nanosized NaTaO₃ powder with cubic morphology is reported in which the compound was hydrothermally prepared at 120 °C for 12 h. The cubic crystalline structure of this nanosized NaTaO₃ product was ensured by using XRD and TEM. The band gap of the nanosized NaTaO₃ was 3.96 eV based on UV spectrum. The hydrothermal process probably follows the dissolution-precipitation mechanism. Also this NaTaO₃ powder showed high photoreactivity under UV light in gas phase and liquid phase photoreactions.     

Sensor Performance of Nanostructured TiO<Subscript>2</Subscript>–SnO<Subscript>2</Subscript> Films Prepared by an Aqueous Sol–Gel Process

Nanostructured TiO₂–SnO₂ thin films and powders were prepared by a facile aqueous particulate sol–gel route. The prepared sols showed a narrow particle size distribution with hydrodynamic diameter in the range 17.2–19.3 nm. Moreover, the sols were stable over 5 months, since the constant zeta potential was measured during this period. The effect of Sn:Ti molar ratio was studied on the crystallisation behaviour of the products. X-ray diffraction analysis revealed that the powders were crystallised at the low temperature of 400 °C containing anatase-TiO₂, rutile-TiO₂ and cassiterite-SnO₂ phases, depending on annealing temperature and Sn:Ti molar ratio. Furthermore, it was found that SnO₂ retarded the anatase to rutile transformation up to 800 °C. The activation energy of crystallite growth was calculated in the range 0.96–6.87 kJ/mol. Transmission electron microscope image showed that one of the smallest crystallite sizes was obtained for TiO₂–SnO₂ binary mixed oxide, being 3 nm at 600 °C. Field emission scanning electron microscope analysis revealed that the deposited thin films had nanostructured morphology with the average grain size in the range 20–40 nm at 600 °C. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO gas at low operating temperature of 200 °C, resulting in increased thermal stability of sensing films as well as a decrease in their power consumption.     

Direct electrochemical sensing of ο-phenylendiamine based on perovskite-type nanomaterial LaNiTiO3–Fe3O4

An electrochemical sensor is developed in this work based on the new perovskite-type nanomaterial LaNiTiO₃–Fe₃O₄ for sensitive determination of o-phenylenediamine (OPD). As-synthesized materials and the surface of as-fabricated electrochemical sensor are characterized by X-ray diffraction, atomic force microscope, and electrochemical impedance spectroscopy, respectively. The results of characterizations depict that the sample is of nanoscaled complex oxides consisting of perovskite structure and spinel structure, and has good conductive properties. The construction and experimental conditions of the electrochemical sensor are also optimized. The electrochemical properties of OPD at glassy carbon electrode modified with LaNiTiO₃–Fe₃O₄ are investigated in alkaline solution (NaOH). The new electrochemical sensor exhibits high electrocatalytic activity and stability in NaOH, and a promotion of electrochemical oxidation of OPD at low potentials can be obviously observed. A wide linear range is obtained from 1.0?×?10^?6 to 7.0?×?10^?3 M with a relative low detection limit of 0.15 μM (S/N?=?3) under optimal conditions. Furthermore, the sensor exhibits reliable results for the determination of OPD in commercial samples.     

Synthesis and characterization of CaTiO3-(Sm,Nd)AlO3 microwave ceramics via sol–gel method

0.65CaTiO₃–0.35Sm_0.9Nd_0.1AlO₃ (CTSA) ceramic nanopowders were synthesized via sol–gel method using the ethylene diamine tetraacetic acid as a chelating agent. Thermal analysis, Fourier transform infrared spectroscopy and X-ray diffraction were used to character the decomposition of precursor and phase transformation process of derived oxide powders. Single phase and well-crystallized 0.65CaTiO₃–0.35Sm_0.9Nd_0.1AlO₃ powders with particle size of 30–40 nm were obtained by calcination at 800 °C. Dense ceramic was successfully obtained from the ultrafine powders sintered at 1,325 °C, almost 100 °C lower than 1,415 °C required for conventional powders. Compared with those prepared by conventional solid-state method, the CTSA ceramics derived from sol to gel process sintered at a lower temperature showed better microwave dielectric properties of ε_r ~ 39, Q × f over 50,000 GHz and small τ_f ~ ?7.1 ppm/K.     

Switchable Spherical-Wormlike Micelle Transition in Sodium Oleate/N-(3-(Dimethylamino)propyl)-Octanamide Aqueous System Induced by Carbon Dioxide Stimuli and pH Regulation

The structure transitions of the aggregates in the sodium oleate (NaOA)/N-(3-(dimethylamino)propyl)-octanamide (DPOA) aqueous system was investigated upon CO₂ stimuli. During the process of bubbling of CO₂, three appearance states of sol, gel, and emulsion with little white precipitate were observed continuously. The cryo-transmission electron microscope characterization and rheological measurements exhibited that the sol–gel transition was attributed to a spherical-wormlike micelle transition. Moreover, this transition was switchable at least three cycles in the pH range of 10.91–9.56 by CO₂ stimuli and pH regulation (adding NaOH), which could be explained by the protonation of DPOA and deprotonation of DPOA · H⁺. Bubbling of CO₂ resulted in protonation of DPOA, which not only inserted into the OA^– as a co-surfactant but also screened the electrostatic repulsion among OA^–, corporately leading to the spherical-wormlike micelle transition. Adding NaOH caused the deprotonation of DPOA · H⁺ and hence reversed this transition. This surfactant system with switchable micelle transition not only displays tremendous application potential in various fields but also is of key importance in cyclic utilization of surfactant.     

Synthesis and visible light photocatalytic activity of Ag spot-coated TiO2–60 wt% SrO composite powders

Nano-sized TiO₂–60 wt% SrO composite powders were synthesized from titanium isopropoxide and Sr(OH)₂·8H₂O by use of a sol–gel method. Ag spot-coated TiO₂–60 wt% SrO composite powders containing 3, 5, or 7 wt% Ag were synthesized by hydrothermal-assisted attachment, by use of Ag hydrosol in a high-pressure bomb at 250 °C and 450 psi. Nano-sized Ag particles approximately 5–25 nm in diameter adhered to the TiO₂–60 wt% SrO₂ composite powders. The photocatalytic activity of Ag spot-coated TiO₂–SrO powders in the degradation of phenol showed that all were highly active when irradiated with UV light. TiO₂–60 wt% SrO composite powder spot-coated with 5 wt% Ag was more photocatalytically active under visible light than TiO₂–SrO composite powder.     

The study on microstructure and electrochemical properties of Al–Mg–Sn–Ga–Pb alloy anode material for Al/AgO battery

The microstructure of Al–Mg–Sn–Ga–Pb quinary aluminum alloy anode material and the influences of its electrochemical properties and self-corrosion rate in 4 mol/l NaOH +10 g/l Na₂SnO₃ medium were studied. The microstructure and morphology were characterized by metallographic microscope, transmission electron microscope, and scanning electron microscopy. The electrochemical properties were tested by electrochemical workstation, and the self-corrosion rate of Al alloy anode was studied by methods of recovery H₂ gas by discharge water. The results show that homogenization has not much impact on the electrochemical properties and the corrosion rate of the cast aluminum alloy anode material; besides, return annealing treatment of the cold-rolled Al–Mg–Sn–Ga–Pb quinary aluminum alloy anode material can reduce the rate of self-corrosion and make Al anodic potential shift negative steadily and improve the properties of the material.

     

Synthesis of CaWO4:Er3+@SiO2 and CaWO4:Tm3+@SiO2 nano-particles via a combustion pathway and study of their optical properties

Use of citric acid as a chelating agent and fuel, ammonium nitrate as fuel, boric acid as flux material and silica as supports, CaWO₄:Ln³⁺@SiO₂ (Ln = Er and Tm) nanoparticles were synthesized via a combustion reaction at 800 °C. Characterization of the samples was performed by X-ray diffractometer (XRD), reflectance UV–Vis spectrophotometer, fluorescence spectrophotometer (PL) and transmission electron microscope (TEM). XRD patterns showed that tetragonal crystalline structure of scheelite and silica supports were formed, and that the formation of a silica support could enhance the luminescence intensity of CaWO₄:Ln³⁺. The reflectance UV–Vis and PL spectra indicated the broad absorption band of WO₄ ^2? groups about 240 nm, the WO₄ ^2? wide excitation band with maximum at 240 nm, a broad emission band of WO₄ ^2? with maximum about 420 nm, and characteristic emissions of Ln³⁺ ions. According to the TEM analysis, CaWO₄:Er³⁺@SiO₂ and CaWO₄:Tm³⁺@SiO₂ nanoparticles have almost the same morphology with average particle sizes about 50 nm.     

Control of nitrogen doping in NaTaO3 synthesized by hydrothermal reaction and chemical state of nitrogen

Nitrogen-doped NaTaO₃ was synthesized through 1-pot reaction, hydrothermal process using Ta₃N₅ as precursor. Changing concentration and amount of NaOH aqueous solution influenced nitrogen content in NaTaO₃. Absorption edge of nitrogen-doped NaTaO₃ was extended at 570 nm, and absorbance in visible light region depended on nitrogen content in NaTaO₃. Anodic photocurrent measured under visible light irradiation became larger with increasing nitrogen content in NaTaO_3-xN_y. Under ultraviolet light irradiation (λ ≤ 400 nm), the highest anodic photocurrent was observed when nitrogen concentration was y = 0.024. It was possible to expand the wavelength range that can be effectively utilized for the photoelectrochemical reaction.     

Synthesis, structural and photocatalytic studies of Mn-doped CdS nanoparticles

Mn-doped CdS nanoparticles (Cd_1?x Mn _x S; where x = 0.00–0.10) were synthesized by a chemical precipitation method. The synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscope, transmission electron microscope (TEM), and UV–Vis spectrometer. The XRD and TEM measurements show that the size of crystallites is in the range of 10–40 nm. Optical measurements indicated a red shift in the absorption band edge upon Mn doping. The direct allowed band gaps of undoped and Mn-doped CdS nanoparticles measured by UV–Vis spectrometer were 2.3 and 2.4 eV at 400 °C, respectively. Photocatalytic activities of CdS and Mn-doped CdS were evaluated by irradiating the solution to ultraviolet light and taking methyl orange (MO) as organic dye. It was found that 5 mol% Mn-doped CdS bleaches MO much faster than undoped CdS upon its exposure to the ultraviolet light. The experiment demonstrated that the photo-degradation efficiency of 5 mol% Mn-doped CdS was significantly higher than that of undoped CdS.     

Rapid calcination of ferrite Ni0.75Zn0.25Fe2O4 by microwave energy

Ferrites Ni_0.75Zn_0.25Fe₂O₄ were obtained by polymeric precursor method and calcined in a short time with microwave energy to assess the morphological and microstructural characteristics. Samples were calcined at 500, 650, 800, and 950 °C for 30 min in a microwave oven. The resulting powders were characterized by thermal analysis (TG/DSC), X-ray diffraction (XRD), Fourier transform infrared spectrometer, field-emission gun scanning electron microscope (FEG-SEM), and energy-dispersive X-ray spectroscopy. The XRD results showed the formation of single ferrite phase at temperature of 500 °C for 30 min. The FEG-SEM analysis showed agglomerated particles with formation of non-dense longitudinal plates, with interparticle porosity and agglomerated fine particles. The rapid calcination by microwave energy demonstrated satisfactory results in relatively low temperature of 500 °C for 30 min and appeared to be a promising technique for obtaining nickel–zinc ferrite powders.     

Effect of synthesis duration on the morphological and structural modification of the sea urchin-nanostructured γ-MnO2 and study of its electrochemical reactivity in alkaline medium

Single-crystalline nanorods and sea urchin-like morphology of the γ-MnO₂ nanostructures were successfully synthesized by hydrothermal method at different synthesis durations. The as-synthesized products were characterized by the techniques X-ray powder diffraction (XRD), field emission gun-scanning electron microscope (FEG-SEM) coupled with energy-dispersive X-ray elemental analysis (EDX), transmission electron microscope (TEM), isotherms of N₂ adsorption/desorption and BET-BJH models. The effect of synthesis duration on the morphology, porous structure, and crystallographic form of MnO₂ powders was studied. The electrochemical reactivity of as-prepared powders was investigated in 1 mol L^?1 KOH by both cyclic voltammetry and impedance spectroscopy by using a micro-cavity electrode. The results show that the best electrochemical reactivity of the MnO₂ powder was obtained with synthesis duration of 24 h.     

Synthesis of sodium titanium phosphate at ultra-low temperature

Powders of the Nasicon material NaTi₂(PO₄)₃ were directly synthesized at ultra-low temperature. NaTi₂(PO₄)₃ was obtained by mixing the initial reagents titanium hydroxide, 85 % H₃PO₄, and NaH₂PO₄·2H₂O at 85 °C for 3.5 h or at 125 °C for 1.5 h. The raw materials and synthesized products were characterized for purity, crystal structure, particle size, and powder morphology by thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy, scanning electron microscopy (SEM), and UV–visible diffuse reflectance spectroscopy. XRD results revealed that NaTi₂(PO₄)₃ powders with rhombohedral crystal structure were synthesized at 85 and 125 °C. SEM patterns showed that the as-prepared products were agglomerated and that each of the agglomerations consisted of many small grains 50–80 nm in diameter.