Formation of Si nanowires by the electrochemical reduction of porous Ni/SiO2 blocks in molten CaCl2

Silicon nanowires (SiNWs) were prepared by the electrochemical reduction of solid Ni/SiO₂ blocks in molten CaCl₂ at 1173 K. The SiNWs have diameter distributions ranging from 80 to 350 nm, and the nickel–silicon droplets are found on the tips of the nanowires. The growth mechanism of SiNWs was investigated, which confirmed that the nano-sized nickel–silicon droplets formed at the Ni/SiO₂/CaCl₂ three-phase interline. The droplets lead to the oriented growth of SiNWs. Formation of nano-sized nickel–silicon droplets suggests that this method could be a potential way to produce nano-sized metal silicides.     

Synthesis and characterization of ZrO2/MnO2/carbon clusters nanocomposite materials

Nano-sized ZrO₂/MnO₂/carbon clusters composite materials has been successfully obtained by the calcination of a Zr(acac)₄/Mn(acac)₃/epoxy resin complex under an oxygen atmosphere. The compositions of the resulting composite materials were determined using inductively coupled plasma (ICP) spectroscopy, elemental analysis and surface characterization by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy (TEM). The ultraviolet–visible (UV–VIS), X-ray photoelectron spectra (XPS) and electron spin resonance (ESR) spectra of the composites were also measured. ESR spectral examinations suggest the possibility of an electron transfer in the process of MnO₂ → carbon clusters → ZrO₂. The visible light-responsive oxidation–reduction ability of the calcined material was also investigated.     

Fabrication and efficient visible light-induced photocatalytic activity of Bi2MoO6/BiPO4 composite

Novel Bi₂MoO₆/BiPO₄ composites with heterojunction structure were fabricated by a one-step hydrothermal method. The photocatalytic properties of Bi₂MoO₆/BiPO₄ composites were evaluated by photocatalytic degradation of rhodamine B (Rh B) under visible light irradiation (λ>420 nm). The results showed that Bi₂MoO₆/BiPO₄ photocatalysts showed much higher photocatalytic activity for the Rh B degradation than the pure BiPO₄ and Bi₂MoO₆ under visible light. The best photocatalytic performance of Bi₂MoO₆/BiPO₄ with about 98.0% Rh B degradation located at molar ratio of 2:1 under visible light illumination for 30 min. The enhanced photocatalytic activity could be mainly ascribed to the formation of heterojunction interface in Bi₂MoO₆/BiPO₄ composites, which is beneficial to the transfer and separation of photogenerated electron–hole pairs, as well as the strong visible light absorption resulting from the sensitization role of Bi₂MoO₆ to BiPO₄. It was also observed that the photodegradation of Rh B is chiefly attributed to the oxidation action of the generated O₂⁻ radicals and the action of h_vb⁺ through direct hole oxidation process.     

The electronic behaviors of TiO2/MnO2/carbon clusters composite materials obtained by the calcination of a TiO(acac)2/Mn(acac)3/epoxy resin complex

The calcination of a TiO(acac)₂/Mn(acac)₃/epoxy resin complex under an oxygen atmosphere successfully produced nano-sized TiO₂/MnO₂/carbon clusters composite material. The surface characterizations of the resulting composites indicate that they are composed of nano-sized particles of TiO₂, MnO₂ and carbon clusters. ESR spectral examination suggests the possibility of an electron transfer in the process of MnO₂ → carbon clusters → TiO₂. The visible light-responsive oxidation–reduction function of the composite materials has also been confirmed.     

Synthesis process and the luminescence properties of rare earth doped NaLa(WO4)2 nanoparticles

Rare earth doped NaLa(WO₄)₂ nanoparticles have been prepared by a simply hydrothermal synthesis procedure. The X-ray diffraction (XRD) pattern shows that the Eu³⁺-doped NaLa(WO₄)₂ nanoparticles with an average size of 10-30 nm can be obtained via hydrothermal treatment for different time at 180 °C. The luminescence intensity of Eu³⁺-doped NaLa(WO₄)₂ nanoparticles depended on the size of the nanoparticles. The bright upconversion luminescence of the 2 mol% Er³⁺ and 20 mol% Yb³⁺ codoped NaLa(WO₄)₂ nanoparticles under 980 nm excitation could also be observed. The Yb³⁺-Er³⁺ codoped NaLa(WO₄)₂ nanoparticles prepared by the hydrothermal treatment at 180 °C and then heated at 600 °C shows a 20 times stronger upconversion luminescence than those prepared by hydrothermal treatment at 180 °C or by hydrothermal treatment at 180 °C and then heated at 400 °C.     

Preparation, conversion, and comparison of the photocatalytic property of Cd(OH)2, CdO, CdS and CdSe

In this paper, we report the hydrothermal preparation of Cd(OH)₂ nanowires and further conversion to CdO nanobelts, CdS nanowires and CdSe nanoparticles through thermal treatment, solvothermal and mixed-solvothermal routes, respectively. The as-obtained products were characterized by means of powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FEMSEM). Research showed that four cadmium compounds were good photocatalysts for the degradation of organic dyes such as Safranine T and Pyronine B, under irradiation of 365 nm UV light. The order of catalytic activity of different materials was found to be Cd(OH)₂<CdO<CdS<CdSe.     

The effect of the Bi source on optical properties of Bi2Te3 nanostructures

nanostructures were synthesized by using different Bi sources via a simple solvothermal process, in which and BiCl₃ were used as the Bi sources. Optical properties of nanostructures prepared with and BiCl₃ as the Bi sources were investigated by micro-Raman spectroscopy. The Raman scattering spectrum of hexagonal nanoplates prepared by using as the Bi source shows that the infrared (IR) active mode A_1u, which must be odd parity and is Raman forbidden for bulk crystal due to its inversion symmetry, is greatly activated and shows up clearly in the Raman scattering spectrum. We attribute the appearance of the infrared active A_1u mode in the Raman spectrum to crystal symmetry breaking of hexagonal nanoplates. However, the Raman scattering spectrum of nanostructures with irregular shape prepared by using as the Bi source only exhibits the two characteristic Raman modes of crystals. Micro-Raman measurements on nanostructures with different morphologies offer us a potential way to tailor optical properties of nanostructures by controlling the morphologies of the nanostructures, which is very important for practical applications of nanostructures in thermoelectric devices.     

Synthesis of nanocrystalline and mesoporous zinc sulphide from a single precursor Zn(SOCCH3)2Lut2 complex

We report the formation of mesoporous zinc sulphide, composed by the fine network of nanoparticles, which was formed via a single precursor Zn(SOCCH₃)₂Lut₂ complex. The complex was chemically synthesized using zinc carbonate basic, 3,5-lutidine and thioacetic acid, in air. The metal precursor complex was characterized using different conventional techniques. Thermogravimetric analysis (TGA) result indicates that the decomposition of the complex starts at 100 °C and continues up to 450 °C, finally yielding ZnS. ZnS nanocrystals were characterized by powder X-ray diffraction (XRD) technique, field emission scanning electron microscopy (FESEM), N₂-sorption isotherm, UV-vis spectroscopy and photoluminescence (PL) spectroscopy. The grain diameter of nanocrystals was found to be 4-5 nm. The material followed Type-IV N₂-sorption isotherm, which is the characteristic of mesoporous materials. The band gap energy, as obtained from optical measurements was around 3.8 eV.     

Chemical reactions in TiO2/SnO2/TiCl4 hybrid electrodes and their impacts to power conversion efficiency of dye-sensitized solar cells

This study examined the applicability of TiO₂/SnO₂/TiCl₄ hybrid electrodes in dye-sensitized solar cells (DSSCs) by combining chemical modeling with experimentation. The interfacial chemical reactions in a TiO₂/SnO₂/TiCl₄ system were simulated using a thermochemistry software package, which led to the design and testing of hybrid working electrodes. Chemical thermodynamic modeling proved that TiCl₄ is an effective agent in removing Tiⁿ⁺ (n<4) and Sn^m+ (m<4) ion impurities from dry-mixed TiO₂/SnO₂ composite particles. Our results demonstrate that the power conversion efficiency of DSSC with a TiO₂/SnO₂/TiCl₄ hybrid electrode exceeds that of the conventional DSSC with a TiO₂ electrode due to the effects of light-scattering and the formation of additional absorbance (SnCl₂), which is an unexpected side effect of TiCl₄ treatment enabling the absorption of visible light. The proposed approach is ideally suited to establishing relationships between chemistry theory and the structure and performance of advanced DSSCs as well as photo-electro-chemical systems.     

Preparation of TiO2 hollow spheres for DSSC photoanodes

High crystallinity mesoporous TiO₂ hollow spheres (MHS-TiO₂) were prepared using the mesoporous carbon hollow sphere template. The MHS-TiO₂ contains mainly nanostructured anatase. The mesopore of the MHS-TiO₂ has a pore opening in the range of 400–600 nm. The refined extended X-ray absorption fine structure spectra indicate that the MHS-TiO₂ possesses less the 1st-shell Ti–O coordination numbers than the nano-TiO₂. More surface active species (A₂ ((Ti=O)O₄)) on the MHS-TiO₂ are also observed by the component fitted X-ray absorption near edge structure spectroscopy. The MHS-TiO₂ photoanode has a better DSSC conversion efficiency than the nano-TiO₂ one by at least 40%. Note that the N3 dye molecules are accessible to the mesopores of the MHS-TiO₂, and the loading time for N3 can be reduced by at least 70% if compared with those of the nano-TiO₂.     

A quantitative study on the effect of nitrogen concentration on two-dimensional electron gas (2DEG) mobility in a dilute nitride GaAsN/AlGaAs heterostructure

Detailed theoretical analysis of the temperature dependence of two-dimensional electron gas mobility data in GaAs_1−xN_x/Al_0.38Ga_0.62As samples (x=0, 0.1% and 0.4%) shows that, as x increases, the dislocation density and the number of ionized impurities in the potential well increase by a factor of ∼ ×300 and ∼ ×500, respectively.     

Bifunctional photocatalysis of TiO2/Cu2O composite under visible light: Ti in organic pollutant degradation and water splitting

Photocatalytic experiment results under visible light demonstrate that both TiO₂ and Cu₂O have low activity for brilliant red X-3B degradation and neither can produce H₂ from water splitting. In comparison, TiO₂/Cu₂O composite can do the both efficiently. Further investigation shows that the formation of Ti³⁺ under visible light has great contribution. The mechanism of photocatalytic reaction is proposed based on energy band theory and experimental results. The photogenerated electrons from Cu₂O were captured by Ti⁴⁺ ions in TiO₂ and Ti⁴⁺ ions were further reduced to Ti³⁺ ions. Thus, the photogenerated electrons were stored in Ti³⁺ ions as the form of energy. These electrons trapped in Ti³⁺ can be released if a suitable electron acceptor is present. So, the electrons can be transferred to the interface between the composite and solution to participate in photocatalytic reaction. XPS spectra of TiO₂/Cu₂O composite before and after visible light irradiation were carried out and provided evidence for the presence of Ti³⁺. The image of high-resolution transmission electron microscopy demonstrates that TiO₂ combines with Cu₂O tightly. So, the photogenerated electrons can be transferred from Cu₂O to TiO₂.     

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.     

Cadmium (II) pyrrolidine dithiocarbamate complex as single source precursor for the preparation of CdS nanocrystals by microwave irradiation and conventional heating process

The complex of cadmium with pyrrolidine dithiocarbamate Cd(pdtc)₂ has been used as single source precursor for the synthesis of CdS nanoparticles. The formation of CdS nanostructures was achieved by thermal decomposition of the complex under microwave irradiation and conventional heating in presence of hexadecylamine. The CdS nanoparticles with disordered close-packed structure were obtained under microwave irradiation, whereas wurtzite hexagonal phase CdS nanorods were obtained by conventional heating method (up to 150 °C). Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and high resolution transmission electron microscopy (HRTEM) studies also were carried out to study the structure and morphology of nanoparticles. The optical property of the CdS nanoparticles was studied by UV-visible and fluorescence emission spectral studies. Fluorescence measurements on the CdS nanoparticles show a strong emission spectrum with two sub bands that are attributed to band-edge and surface-defect emissions. The reduction of a suitable cadmium metal complex is considered to be one of the single pot methods to generate CdS semiconductor nanoparticles with different shapes and high yield.     

A general method for preparing lanthanide oxide nanoparticles via thermal decomposition of lanthanide(III) complexes with 1-hydroxy-2-naphthoic acid and hydrazine ligands

Six new lanthanide(III) complexes (i.e., [Ln(L)₂(NA)_1.5]·3H₂O, where Ln=La(III), Pr(III), Nd(III), Sm(III), Gd(III), and Ce(III) and L and NA indicate N₂H₄ and C₁₀H₆(1-O)(2-COO), respectively) with 1-hydroxy-2-naphthoic acid [C₁₀H₆(1-O)(2-COOH)] and hydrazine (N₂H₄) as co-ligands were characterized by elemental, FTIR, UV-visible, and XRD techniques. In the FT-IR spectra, the N-N stretching frequency in the range of 981–949 cm⁻¹ demonstrates evidence of the presence of coordinated N₂H₄, indicating the bidentate bridging nature of hydrazine in the complexes. These complexes show symmetric and asymmetric COO⁻ stretching from 1444 to 1441 cm⁻¹ and 1582 to 1557 cm⁻¹, respectively, indicating bidentate coordination. TG-DTA studies revealed that the compounds underwent endothermic dehydration from 98 to 110 °C. This was followed by the exothermic decomposition of oxalate intermediates to yield the respective metal oxides as the end products. From SEM images, the average size of the metal oxide particles prepared by thermal decomposition of the complexes was determined to be 39–42 nm. The powder X-ray and SEM coupled with energy dispersive X-ray (EDX) studies revealed the presence of the respective nano-sized metal oxides. The kinetic parameters of the decomposition of the complexes were calculated using the Coats-Redfern equation.     

Improving the visible light photocatalytic activity of mesoporous TiO2 via the synergetic effects of B doping and Ag loading

B-doped together with Ag-loaded mesoporous TiO₂ (Ag/B–TiO₂) was prepared by a two-step hydrothermal method in the presence of boric acid, triblock copolymer surfactant, and silver nitrate, followed by heat treatment. The obtained samples were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption. It was revealed that all samples consist of highly crystalline anatase with mesoporous structure. For Ag/B–TiO₂, B was doped into TiO₂ matrix in the form of both interstitial B and substitutional B while Ag was deposited on the surface of B–TiO₂ in the form of metallic silver. Compared with the single B-doped or Ag-loaded TiO₂ one, mesoporous Ag/B–TiO₂ exhibits much higher visible light photocatalytic activity for the degradation of Rhodamine 6G, which can be ascribed to the synergistic effects of B doping and Ag loading by narrowing the band gap of the photocatalyst and preventing the fast recombination of the photogenerated charge carriers, respectively.     

Hydrothermal synthesis of V O2(B) nanoribbons by a mixed-oxidation state precursor route

Highly crystalline metastable phase V O₂(B) nanoribbons were fabricated on a large scale by hydrothermally treating a mixed-oxidation state vanadium (IV,V) precursor in PEG-600 aqueous solution. The nanoribbons were uniform along the longitudinal direction with a length up to several micrometers, width in the range 50–100 nm, and thickness about 10 nm, respectively. The growth process of nanoribbons and the factors influencing the morphology were also studied in detail. This novel precursor route provided a promising method with less reaction time and mild neutral aqueous environment, and the precursor could be potentially used in the fabrication of other nanostructured vanadium compounds.     

Effects of microwave drying on the microstructure and photocatalytic activity of bimodal mesoporous TiO2 powders

Bimodal nanocrystalline mesoporous TiO₂ powders with highly photocatalytic activity were prepared by a hydrothermal method using tetrabutylorthotitanate as precursor, and then dried in microwave oven. The prepared samples were characterized by XRD, SEM, TEM, HRTEM and N₂ adsorption-desorption measurement. The photocatalytic activity was evaluated by the photocatalytic degradation of acetone in air under UV light irradiation at room temperature. The effects of microwave drying on the microstructures and photocatalytic activity of the TiO₂ powders were investigated and discussed. The results show that microwave drying not only promotes the growth of the pores but also greatly reduces the state of agglomeration within the powders. All the microwave-dried TiO₂ powders show higher photocatalytic activity than Degussa P-25 (P25) and the TiO₂ powders dried by conventional method.     

Characterization of ZnGa2O4:Mn nanophosphor synthesized by the solvothermal method in 1,4-butanediol-water system

We characterized ZnGa₂O₄:Mn²⁺ (ZnGa₂O₄—zinc gallate) nanophosphor synthesized by the solvothermal method in 1,4-butanediol-containing water to increase the amount of Mn²⁺ ions incorporated in the ZnGa₂O₄ matrix without post-heat treatment. We investigated the influence of water content in the solvent on the photoluminescence (PL) intensity and the Mn amount, the latter being measured by X-ray fluorescence analysis and electron paramagnetic resonance spectroscopy. The PL intensity per Mn amount reached the maximum at the 50 wt% water content. The addition of water promotes repeated dissolution and precipitation, resulting in homogeneous Mn²⁺ distribution in the ZnGa₂O₄ matrix. This suggests that the solvothermal method in the 1,4-butanediol-water system is useful for increasing the amount of Mn²⁺ ions incorporated in the ZnGa₂O₄ matrix without post-heat treatment. At the water content >50 wt%, the decrease in PL intensity is attributed to the optical absorption of the by-product, MnOOH.     

The impedance spectroscopic study and dielectric relaxation in A(Ni1/3Ta2/3)O3 [A=Ba,Ca and Sr]

We present the results of impedance spectroscopic study with its analytical interpretations in the framework of electric modulus formalism for Barium Nickel Tantalate Ba(Ni_1/3Ta_2/3)O₃ (BNT), Calcium Nickel Tantalate Ca(Ni_1/3Ta_2/3)O₃ (CNT) and Strontium Nickel Tantalate Sr(Ni_1/3Ta_2/3)O₃ (SNT) synthesized by the solid-state reaction technique. The results of powder X-ray diffraction study reveal that BNT and SNT crystallize in cubic structure with lattice parameter a=4.07 Å and 3.98 Å respectively, whereas CNT crystallizes in monoclinic structure having lattice parameters, a=5.71 Å, b=13.45 Å and c=5.47 Å with β=118.3°. The logarithmic angular frequency dependence of the real part of complex dielectric permittivity and loss tangent as a function of temperature indicate significant dielectric relaxation in the samples, which have been explained by the Debye theory. The frequency dependence of the loss peak and the imaginary part of electrical modulus are found to obey the Arrhenius law. The relaxation mechanism of these samples is modeled by the Cole–Cole equation. This confirms that the polarization mechanism in BNT, CNT and SNT is due to the bulk effect arising in semiconductive grains. The scaling behavior of imaginary part of electric modulus M″ suggests that the relaxation describes the same mechanism at various temperatures but relaxation frequency is strongly temperature dependent. The normalized peak positions of tan δ/tan δ_m and M″/M″_m versus log ω for BNT, CNT and SNT do not overlap completely and are very close to each other. These indicate the presence of both long-range and localized relaxation. Due to their high dielectric constant and low loss tangent, these materials may find several technological applications such as in capacitors, resonators, filters and integrated circuits.