Green synthesis of α-Fe2O3 nanoparticles for photocatalytic application

In this study, the preparation of α-Fe₂O₃ nanoparticles using curcuma and tea leaves extract are reported. The curcuma and tea leaves are acted as a reductant and stabilizer. The crystal structure and particle size of the as-synthesized materials were measured through X-ray diffraction. X-ray diffraction patterns revealed that the as-prepared samples were α-Fe₂O₃ nanoparticles with well-crystallized rhombohedral structure and the crystallite sizes of the α-Fe₂O₃ nanoparticles are 4 and 5 nm. Scanning electron microscopy images showed that the prepared samples have spherical shape. The purity and properties of the as-synthesized α-Fe₂O₃ nanoparticles were measured by Raman spectroscopy. The chemical compositions of the as-prepared α-Fe₂O₃ nanoparticles have been analyzed by Fourier transform infrared spectroscopy. The absorption edge of the α-Fe₂O₃ nanoparticles are 561 and 551 nm. The photocatalytic activity of the α-Fe₂O₃ nanoparticles was measured by degradation of methylene orange and the α-Fe₂O₃ nanoparticles showed the excellent photocatalytic performance.     

Fabrication of shape-controlled α-Fe2O3 nanostructures by sonoelectrochemical anodization for visible light photocatalytic application

In this study, various α-Fe₂O₃ (hematite) nanostructures were prepared on Fe foils by sonoelectrochemical anodization method. The principal component of the electrolyte was ethylene glycol contained 0.3 wt.% NH₄F. The α-Fe₂O₃ surface shapes have been controlled by varying the water volume ratios (WVR) in electrolyte solution. The α-Fe₂O₃ samples were characterized by field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, grazing incidence x-ray diffraction, and UV-vis absorbance spectra. As the variation of WVR, the α-Fe₂O₃ samples showed different surface morphologies of nanoparticles, nanorods, nanoporous, and nanoleaflets. The visible light photocatalytic activity of the α-Fe₂O₃ nanostructures was investigated by degradation of methylene blue, and the α-Fe₂O₃ nanoporous sample showed the best photocatalytic performance.     

Hybrid effect of an in situ multilayer Zn–ZnO–Cr2O3 electrodeposited nanocomposite coatings for extended application

Multifunctional composite coatings of Zn?ZnO?Cr₂O₃ were deposited electrolytically on prepared carbon mild steel (CS) from Zn electrolyte, having Zn²⁺ ions and uniformly dispersed nano ZnO?Cr₂O₃ particulates. The corrosion resistance characteristics of the deposited coatings were evaluated using the linear polarization measurement method in 3.65% NaCl. The microstructural properties of the produced multilayered coatings were evaluated by scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), x-ray diffraction (XRD), and atomic force microscope (AFM). Thermal deformations were observed after 4 h at 250°C and the mechanical response of the coated samples was investigated using a diamond-based Dura Scan microhardness tester and a MTR-300dry abrasive wear tester. From the results, a significant improvement in the corrosion performance of coatings was observed with bath containing less than 2 g/L. The microhardness, thermal stability, and anti-wear properties of Zn?ZnO?Cr₂O₃ shows improved performance against Zn?ZnO coating matrixes, which was attributed to dispersive strengthening effect and grain induced effect of the ZnO/Cr₂O₃ particulate.     

Polycrystalline t′-ZrO2(Ln2O3) formed by displacive transformations

ZrO₂ (3 mol% Y₂O₃) tetragonal and t-ceramics (displacively formed ceramics) were compared with ZrO₂ ceramics (3 mol% Ln₂O₃, where Ln=La, Pr, Nd, Sm, Gd, Tb, Dy, Er, or Yb) processed in an identical manner. Sintering at 1500 °C for 2 h produced mainly tetragonal polytypes for the dopants with smaller ionic radii than Dy(i.e., Er, Y and Yb) but when ZrO₂ was reaction sintered with dopants with larger ionic radii excessive monoclinic phase transformation and associated microcracking resulted. High-temperature annealing in the cubic stability regime and rapid cooling through the tetragonal stability regime was used to fabricate t-composites of ZrO₂ doped with Y, Yb, Er or Dy. Room-temperature fracture toughness and strength values are explained on the basis of a ferroelastic-cubic-to-tetragonal transformation. The domain structure was viewed by transmission optical microscopy (TOM) or transmission electron microscopy (TEM).     

Uniform α-Fe2O3 nanotubes fabricated for adsorption and photocatalytic oxidation of naphthalene

Uniform α-Fe₂O₃ nanotubes with small aspect ratio were successfully fabricated by a hydrothermal method. In situ Fourier-transform infrared spectroscopy was used to study the mechanistic details of adsorption and photocatalytic oxidation of naphthalene over theα-Fe₂O₃ nanotubes. A possible degradation mechanism of naphthalene was proposed.     

Nanoscale (EOT = 5.6 nm) nonvolatile memory characteristics using n-Si/SiO(2)/HfAlO nanocrystal/Al(2)O(3)/Pt capacitors

The charge storage characteristics of the high-κ HfAlO nanocrystal memory capacitors prepared by atomic layer deposition in an n-Si/SiO(2)/HfAlO/Al(2)O(3)/Pt structure have been investigated after high-temperature annealing treatment. The high-resolution transmission electron microscopy image shows that the diameter of high-κ HfAlO nanocrystal is<2?nm. The high-κ HfAlO nanocrystals have been also confirmed by x-ray photoelectron spectroscopy measurement. Due to the formation of high-κ HfAlO nanocrystals with the high-temperature (～900?°C) annealing treatment, a large hysteresis memory window of 3.7?V at a sweeping gate voltage <10?V is observed as compared to that of the as-deposited memory capacitors. A hysteresis memory window of ～1.7?V with a small sweeping gate voltage of ± 5?V is also observed. A small equivalent oxide thickness (EOT) of 5.6?nm is obtained due to the high-κ memory structure design. A significant memory window of ΔV≈0.7?V at 20?°C and ΔV≈0.6?V at 85?°C is observed after 10(4)?s of retention time, due to the charge confinement in the high-κ HfAlO nanocrystals.     

Dielectric enhancement of BaTiO3/BaSrTiO3/SrTiO3 multilayer thin films deposited on Pt/Ti/SiO2/Si substrates by sol–gel method

Polycrystalline BaTiO₃/Ba_0.6Sr_0.4TiO₃/SrTiO₃ (BT/BST/ST) multilayer thin films with different periodicities have been deposited on Pt/Ti/SiO₂/Si substrates by using a sol–gel method. The multilayer thin films were crack free, compact and crystallized in a perovskite structure. The dielectric constant of the multilayer thin films was significantly increased and the dielectric loss was almost the same as those of uniform BT, ST and BST thin films. The dielectric constant increased with increasing stacking periodicity as the thickness of each individual layer decreased. The multilayer thin films showed excellent dielectric properties and can be promisingly used for the dielectric layer of silicon-based embedded capacitors in package substrate.     

A study of the physical,chemical and biological properties of TiO2 coatings produced by micro-arc oxidation in a Ca–P-based electrolyte

In this work, a porous and homogeneous titanium dioxide layer was grown on commercially pure titanium substrate using a micro-arc oxidation (MAO) process and Ca–P-based electrolyte. The structure and morphology of the TiO₂ coatings were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, and profilometry. The chemical properties were studied using electron dispersive X-ray spectroscopy (SEM–EDS) and X-ray photoelectron spectroscopy. The wettability of the coating was evaluated using contact angle measurements. During the MAO process, Ca and P ions were incorporated into the oxide layer. The TiO₂ coating was composed of a mixture of crystalline and amorphous structures. The crystalline part of the sample consisted of a major anatase phase and a minor rutile phase. A cross-sectional image of the coating–substrate interface reveals the presence of voids elongated along the interface. An osteoblast culture was performed to verify the cytocompatibility of the anodized surface. The results of the cytotoxicity tests show satisfactory cell viability of the titanium dioxide films produced in this study.     

(WO3)x–(TiO2)1−x nano-structured porous catalysts grown by micro-arc oxidation method: Characterization and formation mechanism

Very recently, we fabricated (WO₃)_x–(TiO₂)_1−x layers via micro-arc oxidation process under different applied voltages. Morphological and topographical studies, accomplished by SEM and AFM techniques, revealed that the pores size as well as the surface roughness increased with the voltage. Phase structure and chemical composition of the layers were also investigated by XRD and XPS and the results showed the grown layers consisted of titanium and tungsten oxides. It was found that WO₃ dispersed in the TiO₂ matrix and also doped into the TiO₂ lattice. In addition, optical properties of the synthesized layers were studied employing a UV–vis spectrophotometer. Band gap energy of the layers was approximately determined as 2.87 eV. Finally, methylene blue was selected as a model material and its degradation rate on the surface of the layers was measured to determine the photocatalytic efficiency. The degradation rate constants were measured as 2.2 × 10⁻² and 0.9 × 10⁻² min⁻¹ under ultraviolet and visible irradiations.     

Fe2O3 hexagonal nanosheets assembled with NiS formed p–n heterojunction for efficient photocatalytic hydrogen evolution

Journal of Materials Science - In the field of photocatalysis, the recombination of photogenerated holes and electrons is still an urgent problem to be solved. Among many measures, constructing...     

Enhanced energy-storage properties of SrTiO3 doped (Bi1/2Na1/2)TiO3–(Bi1/2K1/2)TiO3 lead-free antiferroelectric ceramics

The energy-storage properties of SrTiO₃-doped (15, 20, 25, and 30 mol%) 0.80Bi_1/2Na_1/2TiO₃–0.20Bi_1/2K_1/2TiO₃ lead-free antiferroelectric ceramics were investigated by two-step sintering method. The ceramics with higher SrTiO₃ content had smaller grain sizes and a more homogeneous distribution. About 25 mol% SrTiO₃ doping induced antiferroelectric properties, showing a typical double hysteresis loops, accompanied by a large energy density. The first sintering temperature of the ceramics had main impact on the relative density, and the high relative density possessed large external breakdown strength. The optimum electrical performances with a low remanent polarization (P_r = 1.9 μC/cm²), a low coercive field (E_c = 1.7 kV/cm) and a large energy density (W = 0.97 J/cm³) at 10 Hz were obtained at 1,190 °C for a SrTiO₃ content of 25 mol%.     

Self-diffusion in α-Al2O3 and growth rate of alumina scales formed by oxidation: effect of Y2O3 doping

In many cases, alumina scales are assumed to grow predominantly by oxygen diffusion, but some authors have found that the growth can be controlled by aluminium diffusion. These mechanisms can be modified by active elements. The problem with alumina is that there is a lack of data about self-diffusion coefficients, and, due to the stoichiometry of alumina, diffusion data correspond to an extrinsic diffusion mechanism so that it is not possible to compare oxygen and aluminium diffusion coefficients. In order to obtain information about the alumina scale growth mechanism, oxygen (¹⁸O) and aluminium (²⁶Al) self-diffusion coefficients in Al₂O₃ were determined in the same materials and in the same experimental conditions, thus allowing a direct comparison. For both isotopes, bulk and sub-boundary diffusion coefficients were determined in single crystals of undoped alumina. Grain-boundary diffusion coefficients have been computed only for oxygen diffusion in polycrystals. Oxygen diffusion has been also studied for yttria-doped -alumina in the lattice, sub-boundaries and grain boundaries. Oxygen and aluminium bulk diffusion coefficients are of the same order of magnitude. In the sub-boundaries, aluminium diffusion is slightly faster than oxygen diffusion. Yttria doping induces a slight increase of the oxygen bulk diffusion, but decreases the grain-boundary diffusion coefficients on account of segregation phenomena. These results are compared with the oxidation constants of alumina former alloys (alloys which develop an alumina scale by oxidation). It appears that neither lattice self-diffusion nor grain boundary self-diffusion can explain the growth rate of alumina scales. Such a situation is compared to the case of Cr₂O₃.     

Synthesis of (Zn,Mg)TiO3–TiO2 composite ceramics for multilayer ceramic capacitors

(Zn_0.8Mg_0.2)TiO₃–xTiO₂ composite ceramics has been prepared via the solid-phase synthesis method. TiO₂ was employed to tone temperature coefficient of resonant frequency (τ_f) and stabilize hexagonal (Zn, Mg)TiO₃ phase. 3ZnO–B₂O₃ was effective to promote sintering. The movement of grain boundary was obvious because of the liquid phase sintering. The scanning electron microscope (SEM) photographs and energy dispersive spectrometer (EDS) patterns showed that segregation and precipitation of dissociative (Zn, Mg)TiO₃ grains occurred at grain boundary during sintering. SnO₂ was used as inhibitor to prevent the grain boundary from moving. The dielectric behaviors of specimen strongly depended on structural transition and microstructure. We found that 1.0 wt.% 3ZnO–B₂O₃ doped (Zn, Mg)TiO₃–0.25TiO₂ ceramics with 0.1 wt.% SnO₂ additive displayed excellent dielectric properties (at 1000 °C): ?_r = 27.7, Q × f = 65,490 GHz (at 6.07 GHz) and τ_f = −8.88 ppm °C⁻¹. The above-mentioned material was applied successfully to make multilayer ceramic capacitors (MLCCs), which exhibited an excellent electrical property. The self-resonance frequency (SRF) and equivalent series resistance (ESR) of capacitor decreased with capacitance increasing, and the quality factor (Q) of capacitor reduced as frequency or capacity increased.     

(La2/3Ca1/3)(Mn(3-x)/3)Fex/3)O3体系磁电阻行为的研究

通过系统地测量（La_2/3Ca_1/3）（Mn_{（3-x）／3}Fe_x／3）O₃（x＝0、0.1、0．2、0．3的体系样品的电阻率-温度关系以及一定温度下磁电阻率与磁场的关系,发现随x的变化其磁电阻率峰和电阻率峰均发生位移,磁电阻率峰值增大,并伴生磁电阻率峰展宽效应．作者认为由于Fe的替代,引起体系中Mn³⁺／Mn⁴⁺比率及磁矩的变化,加之外场对磁有序结构的调制作用,从而影响了Mn³⁺－O^－Mn⁴⁺的双交换作用,最终导致磁电阻行为发生变化．     

Nanostructured Cu–Al2O3 composite produced by thermochemical process for electrode application

Nanostructured Cu–Al₂O₃ composite powders were synthesized by thermochemical process. The synthesis procedures are (1) preparation of precursor powder by spray-drying of solution made from water-soluble copper and aluminum nitrates, (2) air heat treatments to evaporate volatile components in the precursor powder and synthesis of nanostructured CuO+Al₂O₃, and (3) CuO reduction by hydrogen into pure Cu. The suggested procedures stimulated the formation of the γ-Al₂O₃, and different alumina formation behaviors appeared with various heat-treating temperatures. The mean particle size of the final Cu–Al₂O₃ composite powders produced was 20 nm, and the electrical conductivity and hardness in the hot-extruded bulk were competitive with Cu–Al₂O₃ composite by the conventional internal oxidation process.     

Co-catalysis effect of different morphological facets of as prepared Ag nanostructures for the photocatalytic oxidation reaction by Ag–TiO2 aqueous slurry

This paper highlights the comparative co-catalytic efficiency of different shapes of prepared Ag nanoparticles of size much larger as well as smaller than titania for the Ag–TiO₂ photocatalysis. Quantum sized Ag nanospheres (4^_8 nm), nanorod (length 70–75 nm and width 30–38 nm), polygonal nanosphere (80–120 nm) and truncated triangles (side length 70–140 nm) are prepared by solvothermal process. The co-catalytic activities of these Ag nanostructures were investigated by mixing them with TiO₂ for the photocatalytic degradation of aqueous salicylic (0.5 mM) and benzoic acid (0.5 mM) under UV light (125 W-Hg arc, 10.4 mW cm⁻²) irradiation. The Ag co-catalysis effect imparted to TiO₂ follows as polygonal nanosphere > nanorod > truncated triangle > small nanosphere due to the formation of many Ag–TiO₂ interfaces by a single large-sized Ag nanoparticle than smaller one. As the surface coverage of Ag particles by TiO₂ decreases, the Ag–TiO₂ photoactivity is decreased accordingly. The efficient adsorption of salicylic acid to TiO₂ surface through –COOH and –OH groups render its higher photodegradation rate (1.8–2.7 × 10⁻² μmol min⁻¹) than benzoic acid (1.5–2.5 × 10⁻² μmol min⁻¹) having one chelating –COOH group. Zeta potential and conductance measurement of photoreaction mixture were carried out to investigate the ionic interaction-adsorption of reactant substrates over Ag–TiO₂ surface.     

Synthesis of poly-(3-hydroxybutyrate-co-12 mol % 3-hydroxyvalerate) by Bacillus cereus FB11: its characterization and application as a drug carrier

The synthesis of microbial polyhydroxyalkanoate is investigated in this work for it potential application as drug carrier for cancer therapy. The bacterial isolate Bacillus cereus FB11 has synthesized poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer under nutrient stress conditions using glucose as a sole carbon source. The FTIR spectrum of the purified copolymer showed the characteristic absorption bands at 1,719, 1,260 and 2,931 cm^?1 attributing to C=O, C–O stretching and C–H vibrations, respectively. The result of ¹H-NMR confirmed that it was composed of 88 mol % of 3-hydroxybutyrate and 12 mol % of 3-hydroxyvalerate monomeric subunits. The nanoparticles were fabricated from copolymer and used as a carrier for anticancer drug ellipticine. The in vitro drug release studies showed that % inhibition of A549 cancer cell line receiving ellipticine loaded poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) nanoparticles was two-fold higher in comparison to ellipticine alone. This drug delivery system offers exciting possibilities for cancer therapy by increasing the bioavailability of anti-neoplastic drug to the tumor site.     

La(2-x)/3(Ag(0)1-2x/3Ag(I)x)TiO3光致变色粉体的制备与表征

通过固相反应法合成了具有光致变色性质的La(2-x)/3(Ag(0)1-2x/3Ag(I)x)TiO3(简称Ag-LST)钙钛矿结构复合氧化物粉体,采用XRD、XPS、ICP和SEM等实验技术对Ag-LST进行了表征.结果表明,Ag-LST具有立方晶相钙钛矿结构,其表面层元素组成为Ag:La:Ti=0.45:0.60:1.00.研究了Ag-LST的光致变色性质,在紫外光(300W汞灯)下照射Ag-LST 1min,样品的颜色从棕黄色转变为蓝紫色;在可见光(500W氙灯)下照射Ag-LST 1h,样品恢复为原来的棕色.Ag-LST的光致变色性质可能与Ag(0)-Ag(I)相互转换有关.     

Oxidation behaviour of TiAlYN/CrN and CrAlYN/CrN nanoscale multilayer coatings with Al2O3 topcoat deposited on γ-TiAl alloys

Abstract

TiAlYN/CrN and CrAlYN/CrN nanoscale multilayer coatings were deposited on γ-TiAl specimens using magnetron sputtering techniques. The nitride layers were manufactured by unbalanced magnetron sputtering (UBM) and high power impulse magnetron sputtering (HIPIMS). The CrAlYN/CrN coatings had an oxy-nitride overcoat. On some of the coated samples an additional alumina topcoat was deposited. The oxidation behaviour of the different coatings was investigated at 750 and 850°C performing quasi-isothermal oxidation tests in laboratory air. Mass change data were measured during exposure up to failure or the maximum exposure length of 2500 h. When exposed to air at 750°C, the Ti-based nitride films exhibited higher oxidation resistance than the Ti – 45Al –8Nb substrate material. The alumina topcoat enhanced the oxidation protection of this coating system, acting as diffusion barrier to oxygen penetration. At 850°C, the TiAlYN/CrN films exhibited poor stability and rapidly oxidised, and therefore were not applicable for long-term protective coatings on γ-TiAl alloys. The beneficial effect of the additional Al₂O₃ layer was less pronounced at this exposure temperature. The Cr-based nitride films exhibited high oxidation resistance during exposure at 850°C. HIPIMS deposition improved the oxidation behaviour of the CrAlYN/CrN nanoscale multilayer coatings in comparison to UBM coatings. For these coatings, the decomposed and partially oxidised nitride films were an effective barrier to oxygen inward diffusion. The alumina topcoat did not significantly increase the oxidation resistance of the γ-TiAl alloy coated with Cr-based nitride films.     

Electro-codeposition of Al2O3-Y2O3 composite thin film coatings and their high-temperature oxidation resistance on γ-TiAl alloy

In this paper, electro-codeposition based on electrophoretic deposition and electrolytic deposition was developed to prepare Al₂O₃-Y₂O₃ composite thin film coatings on a γ-TiAl based alloy. Scanning electron microscope observations showed that the Al₂O₃-Y₂O₃ composite coatings were very compact and consisted of uniform nano-particles after microwave sintering. Cyclic oxidation at 900 °C indicated that the Al₂O₃-Y₂O₃ composite thin film coatings improved the oxidation and scale spallation resistance of the γ-TiAl alloy significantly. The superior oxidation and spallation resistance of the coatings were attributed to the suppression of outward diffusion of Ti and Al and inward diffusion of O, the promoted selective oxidation of Al in the γ-TiAl alloy, and the improved adhesion of oxide scale induced by the Al₂O₃-Y₂O₃ composite thin film coatings.