Comparative study of K0.5Bi0.5TiO3 nanoparticles derived from sol-gel-hydrothermal and sol-gel routes

A kind of novel lead-free ferroelectrics, potassium bismuth titanate, K_0.5Bi_0.5TiO₃ (KBT), has been prepared by sol-gel-hydrothermal and sol-gel routes, respectively, and the structural characters of as-synthesized powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results indicated that sol-gel-hydrothermal route led to the formation of KBT nanowhiskers with diameters of 20 nm and lengths of 1 μm, and the processing temperature was as low as 160 °C, but the normal sol-gel route tended to form KBT cubic particles of about 100-200 nm, and the processing temperature was higher than 700 °C. It is believed that the gel precursor and hydrothermal environment play an important role in the formation of the nanowhiskers at low temperature. Due to the good sinterability of nanowhiskers, the ferroelectric and dielectric properties of KBT ceramics prepared by sol-gel-hydrothermal route were super to that prepared by sol-gel route.     

Preparation and characterization of SrSnO3 nanorods

Perovskite strontium stannate (SrSnO₃) nanorods were prepared by annealing the precursor SnSr(OH)₆ nanorods at 600 °C for 3 h. The precursor nanorods were hydrothermally synthesized at 160 °C for 16 h using Sr(NO₃)₂ and SnCl₄·5H₂O as starting materials in the presence of surfactant cetyltrimethyl ammonium bromide (CTAB). As-prepared samples were characterized by X-ray diffraction (XRD), thermogravimetric-differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and infrared ray spectroscopy (IR). The results show that the as-synthesized powders are made of SrSnO₃ one-dimensional nanorods of about 0.2-1 μm length and 100-150 nm diameter. Possible formation mechanism of SrSnO₃ with nanorod structure under certain conditions was preliminarily analyzed, in which it was thought that CTAB played an important role in the formation process of the nanorod structure. Electrochemical performance of the samples versus Li metal was also evaluated for possible use in lithium-ion batteries.     

Synthesis of nanometer Bi2WO6 synthesized by sol-gel method and its visible-light photocatalytic activity for degradation of 4BS

Nanometer Bi₂WO₆ catalyst with visible-light responsive was prepared by a sol-gel method in the presence of EDTA. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectrum, Fourier transform infrared (FTIR) spectrum, Brunauer-Emmet-Teller (BET). The UV-vis diffuse reflectance spectrum of the as-prepared sample shows a markedly blue-shift as compared to that of the sample obtained by a solid-state reaction. The as-prepared samples exhibited higher activities than that synthesized by the solid-state reaction for 4BS photodegradation under visible-light irradiation (λ>400 nm) and the sample prepared at 450 °C exhibited the highest photocatalytic activity.     

Preparation and photocatalytic property of α-Fe2O3 hollow core/shell hierarchical nanostructures

We report the preparation of a novel kind of α-Fe₂O₃ hollow core/shell hierarchical nanostructures self-assembled by nanosheets. A green precursor powder is first prepared using nontoxic and inexpensive FeCl₃ and urea in ethylene glycol by a surfactant-free solvothermal method at 160 °C for 15 h. The α-Fe₂O₃ hollow core/shell hierarchical nanostructures are obtained by the thermal treatment of the green precursor powder. The as-prepared α-Fe₂O₃ hollow core/shell hierarchical nanostructures are porous, and exhibit a good photocatalytic activity for the degradation of phenol. The samples are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).     

Growth and structure of Bi0.5(Na0.7K0.2Li0.1)0.5TiO3 thin films prepared by pulsed laser deposition technique

Bi_0.5(Na_0.7K_0.2Li_0.1)_0.5TiO₃ (BNKLT) thin films were prepared on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition (PLD) technique. The films prepared were examined by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effects of the processing parameters, such as oxygen pressure, substrate temperature and laser power, on the crystal structure, surface morphology, roughness and deposition rates of the thin films were investigated. It was found that the substrate temperature of 600 °C and oxygen pressure of 30 Pa are the optimized technical parameters for the growth of textured film, and all the thin films prepared have granular structure, homogeneous grain size and smooth surfaces.     

Preparation of alkaline solid polymer electrolyte based on PVA-TiO2-KOH-H2O and its performance in Zn-Ni battery

A novel composite alkaline polymer electrolyte based on poly(vinyl alcohol) (PVA) polymer matrix, titanium dioxide (TiO₂) ceramic fillers, KOH, and H₂O was prepared by a solution casting method. The properties of PVA-TiO₂-KOH alkaline polymer electrolyte films were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and AC impedance techniques. DSC and XRD results showed that the domain of amorphous region in the PVA polymer matrix augmented when TiO₂ filler was added. The SEM result showed that TiO₂ particles dispersed into the PVA matrix although some TiO₂ aggregates of several micrometers were formed. The alkaline polymer electrolyte showed excellent electrochemical properties. The room temperature (20 °C) ionic conductivity values of typical samples were between 0.102 and 0.171 S cm⁻¹. The Zn-Ni secondary battery with the alkaline polymer electrolyte PVA-TiO₂-KOH had excellent electrochemical property at the low charge-discharge rate.     

Elaboration and characterization of TiO2 nanoparticles incorporated in SiO2 host matrix

Nanometer-scale TiO₂ particles have been synthesized by sol-gel method. It was incorporated in a glass-based silica aerogel. The composite was characterized by various techniques such as particle size analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and photoluminescence (PL). The bulk glass presents a strong luminescence at wavelengths ranging from 750 to 950 nm. This PL was attributed to various non-bridging oxygen hole centers (NBOHCs) defects resulting from thermal treatment and crystallization of TiO₂ at the interface between titania nanoparticles and silica host matrix.     

Mesoporous TiO2-B nanowires synthesized from tetrabutyl titanate

Ultralong mesoporous TiO₂-B nanowires were synthesized via a hybrid hydrothermal-ion exchanging-thermal treatment using tetrabutyl titanate (TBOT) as a raw material. The phase transformations and porous structures of TiO₂-B nanowires were characterized and studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and N₂ adsorption-desorption measurement. Mesoporous TiO₂-B nanowires showed a length of several micrometers and diameter of about 25 nm. The porous structures of obtained TiO₂-B nanowires were demonstrated by BJH pore distribution measurement. The wirelike morphologies and porous structures of monodisperse nanowires calcined at 600 °C showed little change, which indicated that such nanowires possessed high thermal stability. The formation mechanism of TiO₂-B nanowires with mesoporous structures were also discussed based on our experimental results.     

Multilayer Bi1.5Zn1.0Nb1.5O7/Ba0.6Sr0.4TiO3/Bi1.5Zn1.0Nb1.5O7 thin films for tunable microwave applications

Bi_1.5Zn_1.0Nb_1.5O₇/Ba_0.6Sr_0.4TiO₃/Bi_1.5Zn_1.0Nb_1.5O₇ tunable multilayer thin film has been fabricated by pulsed laser ablation and characterized. Phase composition and microstructure of multilayer films were characterized by X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The film has very smooth surface with RMS roughness of 1.5-2 nm and grain size of 100-150 nm. Total film thickness has been measure to be 375 nm. The BZN thin films at 300 K, on Pt(1 1 1)/SiO₂/Si substrate showed zero-field dielectric constant of 105 and dielectric loss tangent of 0.002 at frequency of 0.1 MHz. Thin films annealed at 700 °C shows the dielectric tunability of 18% with biasing field 500 kV/cm at 0.1 MHz. The multilayer thin film shows nonferroelectric behavior at room temperature. The good physical and electrical properties of multilayer thin films make them promising candidate for tunable microwave device applications.     

Properties of K0.5Bi0.5TiO3 thin films deposited on different substrates

K_0.5Bi_0.5TiO₃ thin films were deposited on fused quartz, n-type Si(100) and Pt/TiO₂/SiO₂/Si substrates by repeated coating/dying cycles. X-ray diffraction analysis shows that the films annealed at 700 °C for 10 min present perovskite phase. Atomic force microscopy reveals that the surface morphology is smooth, the grain sizes of the films on Si(100) are quite larger than on fused quartz. The capacitance-voltage hysteresis loops at various sweeping speed are collected as are polarization types. The films in the ON and OFF states are relatively stable. The films also exhibit a hysteresis loop at an applied voltage of 4 V, with a remanent polarization of 9.3 μC/cm² and a coercive voltage of 2 V. The insulating property of negative bias voltage is better than that of positive bias voltage. The transmittance of the films is between 74 and 82% in the wavelength range of 200-2000 nm.     

Preparation, characterization and photocatalytic activity of polycrystalline Bi2O3/SrTiO3 composite powders

Bi₂O₃/SrTiO₃ composite powders have been prepared and their photocatalytic activities were investigated by photooxidation of methanol. These powders were characterized by UV-Visible diffuse reflectance spectra, SEM and X-ray diffraction (XRD). The results revealed that all the Bi₂O₃/SrTiO₃ composite powders exhibited higher photocatalytic activity than pure SrTiO₃, Bi₂O₃ and TiO₂ (P25) under visible light irradiation (λ>440 nm). The effects of the Bi₂O₃ contents on the photocatalytic activities of the composite powders were examined, the photocatalytic activities increased with the content of Bi₂O₃ increasing to a maximum of 83% and then decreased under visible light irradiation. The effects of the calcination temperatures on the photocatalytic activities of the composite powders were also investigated.     

A facile and environmentally friendly chemical route for the synthesis of metastable VO2 nanobelts

Metastable VO₂ nanobelts, designated as VO₂ (B), were successfully fabricated by a facile hydrothermal route in the presence of V₂O₅ and glucose. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), transmission electron microscopy (TEM), selected area electronic diffraction (SAED), high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) techniques. The main synthesis parameters such as temperature, reaction time and molar ratio of the starting materials have been also discussed. The results showed that pure B phase VO₂ nanobelts with high crystallinity can be prepared easily at 180 °C in 24 h at the molar ratio of V₂O₅:glucose=1:1. Typically, the belt-like products were 0.6-1.2 μm long, 80-150 nm wide and 20-30 nm thick. It is noted that the whole process is free of any harmful reducing reagents and surfactants, and valuable gluconic acid can be formed as the main by-product. From an economic and environmental point of view, the present approach is particularly fit for the synthesis of VO₂ (B) nanobelts on a large scale.     

Some studies about the green and red light emitting structures in NaCl1−xBrx:Mn

In this work we present the results obtained from the luminescence spectra and X-ray diffraction as well as transmission electron microscopy, at room temperature on crystals of NaCl_1−xNaBr_x:MnCl₂:0.3% (x=0.00, 0.05, 0.25, and 0.50). The results suggest the existence of structures between the crystal planes (1 1 1) and (2 0 0), which may be associated with different types of Mn²⁺ arrangements, such as dipole complexes, octahedral and rhombohedral structures as well as other possible nanostructures that include mixtures of bromine/chlorine ions. These are responsible for the emission spectra of “as grown” crystals consisting of maxima around 500 nm and 600 nm. The green emission has been usually attributed to rhombohedral/tetrahedral symmetry sites; the present results point out that this is due to Mn–Cl/Br nanostructures with rhombohedral structure. On the other hand when the crystals are thermally quenched from 500 °C to room temperature the structures previously detected present changes. Only a red band appears around 620 nm if the samples are later annealed at 80 °C.     

Photo(electro)catalytic Activity of Cu-Modified TiO2 Nanorod Array Thin Films under Visible Light Irradiation

In the present study, a two-step method was applied to synthesise Cu²⁺-modified TiO₂ nanorod array thin films for photocatalytic processes. TiO₂ nanorod array thin films were synthesised by a hydrothermal method and then modified with an ultrasonic-assisted sequential cation adsorption method. The samples were characterised by X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (DRS), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy and inductively coupled plasma mass spectroscopy (ICP-MS) analysis. The photoelectrochemical properties of the samples were evaluated by linear sweep voltammetry and Mott–Schottky analysis; photocatalytic activities were tested by methylene blue degradation under visible light. The photocurrent density of the TiO₂/FTO sample modified with 50 mM Cu²⁺ solution was 26 times higher than that of the unmodified TiO₂/FTO sample. Additionally, methylene blue degradation efficiency under visible light was increased 40% with respect to the efficiency of the unmodified sample. The mechanism of the photocatalytic activity enhancement of Cu²⁺-modified TiO₂ nanorod films was discussed.     

Fabrication and characterization of CuO-core/TiO2-shell one-dimensional nanostructures

We have fabricated CuO-core/TiO₂-shell one-dimensional nanostructures by coating the CuO nanowires with MOCVD-TiO₂. The structure of the core/shell nanowires has been investigated by using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis techniques. The CuO-cores and the TiO₂-shells of the as-synthesized nanowires have been found to have crystalline monoclinic CuO and crystalline tetragonal anatase TiO₂ structures, respectively. The CuO-core/TiO₂-shell nanowires are winding and has rougher surface, whereas the CuO nanowires are straight and have smoother surface.Influence of the substrate temperature and the growth time on the structure such as the morphology, size, and crystallographic orientation of CuO nanowires synthesized by thermal oxidation of Cu foils have also been investigated. All the nanowires have only the CuO phase synthesized at 600 °C, whereas those synthesized at 400 °C have both CuO and Cu₂O phases. The highest density of CuO nanowires with long thin straight morphologies can be obtained at 600 °C. In addition, the growth mechanism of the CuO nanowires has been discussed.     

Magnetic and transport properties of Mn-doped Bi2Se3 and Sb2Se3

We report on the single crystal growth and thermoelectric and magnetic properties of Mn-doped Bi₂Se₃ and Sb₂Se₃ single crystals prepared by the temperature gradient solidification method. The composition and crystal structure were determined using electron probe microanalysis and θ–2θ powder X-ray diffraction studies, respectively. The lattice constants of several percent Mn-doped Bi₂Se₃ and Sb₂Se₃ were slightly smaller than those of the undoped sample due to the smaller Mn atomic radius (1.40 Å) than those of Bi (1.60 Å) and Sb (1.45 Å). Mn-doped Bi₂Se₃ and Sb₂Se₃ showed spin-glass and paramagnetic properties, respectively.     

Solvothermal preparation and characterization of nanocrystalline Bi2Te3 powder with different morphology

Bi₂Te₃-based alloys are currently best-known, technological important thermoelectric materials near room temperature. In this paper, nanocrystalline Bi₂Te₃ with different morphologies was synthesized by a solvothermal process based on the reaction between BiCl₃, Te, and KBH₄ in N,N-dimethylformamide at 100-180 °C. KBH₄ was used as a reducing agent. The products were characterized by X-ray diffraction and transmission electron microscopy (TEM). The particle morphologies and size are dependent on the reaction temperature and time. A possible formation mechanism is proposed.     

Third-order nonlinear optical properties of Bi2S3 and Sb2S3 nanorods studied by the Z-scan technique

Bismuth sulfide (Bi₂S₃) and antimony sulfide (Sb₂S₃) nanorods were synthesized by hydrothermal method. The products were characterized by UV-vis spectrophotometer, X-ray powder diffraction (XRD) and transmission electron microscope (TEM). Bi₂S₃ and Sb₂S₃ nanorods were measured by Z-scan technique to investigate the third-order nonlinear optical (NLO) properties. The result of NLO measurements shows that the Bi₂S₃ and Sb₂S₃ nanorods have the behaviors of the third-order NLO properties of both NLO absorption and NLO refraction with self-focusing effects. The third-order NLO coefficient χ⁽³⁾ of the Bi₂S₃ and Sb₂S₃ nanorods are 6.25×10⁻¹¹ esu and 4.55×10⁻¹¹ esu, respectively. The Sb₂S₃ and Bi₂S₃ nanorods with large third-order NLO coefficient are promising materials for applications in optical devices.     

Applications of vertically oriented TiO2 micro-pillars array on the electrode of dye-sensitized solar cell

In this research, dye-sensitized solar cells based on TiO₂ micro-pillars fabricated by inductive couple plasma etcher were investigated by analyses of X-ray diffraction (XRD), scanning electron microscopy (SEM), contact angle, ultraviolet-visible absorption spectra (UV-vis), and current-voltage characteristics. X-ray diffraction patterns show that the TiO₂ anatase phase forms while sintering at 450 °C for 30 min. The SEM images reveal that the diameter and height of TiO₂ micro-pillars are about 3 and 0.8 μm, respectively. The measurements of contact angle between TiO₂ micro-pillars and deionized water (DI water) reveal that the TiO₂ micro-pillars is super-hydrophilic while annealed at 450 °C for 30 min.The absorption spectrum of TiO₂ micro-pillars is better than TiO₂ thin film and can be widely improved in visible region with N3 dye adsorbed. The results of current-voltage (I-V) characteristics analysis reveal that dye-sensitized solar cell with TiO₂ micro-pillars electrode has better I-V characteristics and efficiency than TiO₂ film electrodes. This result may be due to the annealed TiO₂ micro-pillars applied on the electrode of dye-sensitized solar cell can increase the contact area between TiO₂ and dye, resulting in the enhancement of I-V characteristics and efficiency for dye-sensitized solar cell.     

Synthesis of anatase TiO2 nanowires by modifying TiO2 nanoparticles using the microwave heating method

Anatase TiO₂ nanowires with a diameter of 5-10 nm and length of 500 nm to 2 μm have been successfully synthesized by modifying TiO₂ nanoparticles (P25) using the microwave heating method. The microwave power, reaction pressure, and reaction time for the synthesis of TiO₂ nanowires were 500 W, 0.5-3.0 MPa (corresponding to a temperature range of 175-260), and 40-70 min, respectively. X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and the BET techniques were used to investigate the phase structures, morphologies, and specific surface areas of the TiO₂ nanowires. The effects of reaction time, pressure, and different post-treatment processes on the microstructures of TiO₂ nanowires were discussed. It has been shown that the microwave heating method is efficient in transforming TiO₂ nanoparticles to anatase TiO₂ nanowires.