Highly sensitive and selective trimethylamine sensors based on WO3 nanorods decorated with Au nanoparticles

One-dimensional tungsten oxide (WO₃) gas sensing materials have been widely used for the detection of trimethylamine (TMA) gas. Furthermore, it is believed that an effective method to improve the gas sensing performance is to introduce noble metals into sensing materials. In this work, a novel gas sensing material was prepared by decorating Au nanoparticles on WO₃ nanorods. Based on field emission scanning electron microscopy (FESEM/EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM), the morphology and microstructure of as-prepared samples were characterized. Results show that Au nanoparticles with diameter of 13–15 nm are loaded on the surface of WO₃ nanorods with length of about 1–2 µm and width of 50–80 nm. Gas sensing tests reveal that the Au@WO₃ sensor has remarkably enhanced response to TMA gas compared with pure WO₃ nanorods. In addition, and the gas sensing mechanism has been investigated based on the experimental results. The superior sensing features indicate the present Au@WO₃ nanocomposites are promising for gas sensors, which can be used in the detection of the trimethylamine gas and this work provides insights and strategies for the fabrication of sensing materials.     

Hydrothermal preparation and luminescence property of MWO4:Sm3+ (M = Ca,Sr, Ba) red phosphors

MWO₄:Sm³⁺ (M = Ca, Sr and Ba) red phosphors with spherical microparticles were successfully prepared via a mild and facile hydrothermal route. The crystal structure and particle morphology were investigated by the X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. Photoluminescence excitation and emission spectra and decay curve were used to characterize the luminescence properties of the MWO₄:Sm³⁺ phosphors. The excitation spectra indicate that MWO₄:Sm³⁺ phosphors can be excited effectively by the UV InGaN light-emitting diode (LED), and the emission spectra show that the phosphors can emit strong red light from 600 to 650 nm. Therefore, it is considered to be a new promising red phosphor for white LED application.     

Ultrasound-assisted mineralization of organic contaminants using a recyclable LaFeO3 and Fe3+/persulfate Fenton-like system

A recyclable heterogeneous catalyst has been successfully developed for application in a Fenton-type advanced oxidation process without adding external H₂O₂. LaFeO₃ was prepared from Fe(NO₃)₃·9H₂O and La(NO₃)·6H₂O by a simple sol-gel method and its catalytic efficiency was evaluated for mineralization of 4-chlorophenol using a Fenton-like process. The mineralization process was carried out under ultrasonication in presence of heterogeneous LaFeO₃ catalyst with H₂O₂ that was produced during ultrasonication. The mineralization process was monitored through total organic carbon (TOC) analysis. Very importantly, utmost 5-fold synergism was evidenced by the ultrasound mediated LaFeO₃-catalyzed system. Besides, more than twofold synergism was observed by combining the ultrasound assisted LaFeO₃ catalytic process and potassium persulfate (KPS) assisted advanced oxidation process. It is worth to mention that complete mineralization (∼96%) of 4-chlorophenol (initial concentration of 1.25 × 10⁻⁴ M) was observed within 1 h in the presence of LaFeO₃ (0.5 g L⁻¹) and KPS (1.0 mmol) under ultrasonication (40 kHz). Even after four cycles, the activity of LaFeO₃ remained intact which proved its recyclability. Extremely reusable heterogeneous LaFeO₃ catalyst makes the system more interesting from both economic and environmental points of view.     

DFT-GGA study of NO adsorption on the LaO (001) surface of LaFeO3

In order to demonstrate the adsorption of the nitrogen monoxide molecule (NO) on the LaO (001) surface of LaFeO₃, we perform simulations based on density functional theory. The generalized gradient approximation (GGA) for the exchange-correlation energy functional indicates that the electronic state of the LaFeO₃ bulk is an anti-ferromagnetic insulator with a local magnetic moment of 4.1 μ_B at each Fe atom. Using the ultrasoft pseudo-potential method with spin-polarized GGA, fully optimized internal parameters as well as charge and spin density are determined for the NO-adsorbed structure prepared in a slab model. The calculated adsorption energy of NO is around ? 1.4 eV on the LaO (001) surface of LaFeO₃. This value decreases down to ? 4.46 eV at an oxygen vacancy site, where the nitrogen atom of NO is embedded in the 1st LaO layer forming a bond with Fe in the 2nd FeO layer.     

Nanocrystalline SnO2–TiO2 thin film deposited on base of equilateral prism as an opto-electronic humidity sensor

Present paper reports the synthesis of SnO₂–TiO₂ nanocomposite, its characterization and performance as opto-electronic humidity sensor. Nanocrystalline SnO₂–TiO₂ film was deposited on the base of an equilateral prism using a photo resist spinner and the as prepared film was annealed at 200 °C for 2 h. The crystal structure of the prepared film was investigated using X-ray diffraction (XRD). Minimum crystallite size of the material was found 7 nm. Surface morphology of the film was investigated by Scanning electron microscope (SEM LEO-0430, Cambridge). SEM image shows that the film is porous. Differential scanning calorimetry (DSC) of as synthesized material shows two exothermic peaks at about 40 and 110 °C, respectively which are due to the evaporation of chemical impurities and water. Further the prepared film was investigated through the exposure of humidity and relative humidity (%RH) was measured directly in terms of modulation in the intensity of light recorded on a digital power meter. The maximum sensitivity of sensor was found 4.14 μW/%RH, which is quite significant for sensor fabrication purposes.     

Biomolecule-assisted hydrothermal synthesis and properties of manganese sulfide hollow microspheres

Gamma-manganese sulfide (γ-MnS) hollow microspheres have been successfully synthesized via a biomolecule-assisted hydrothermal process in the presence of l-cysteine and urea at 180 °C for 24 h. In the synthesis system, l-cysteine was employed as not only a sulfur source, but also a coordination agent. The structure, morphology and optical properties of as-prepared products have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and photoluminescence (PL) spectrum. Reaction parameters such as ratio of l-cysteine to urea, surfactants and reaction time played a significant role in controlling the morphology of as-prepared products. The probable formation mechanism of the γ-MnS hollow microsphere was proposed on the basis of the experimental results.     

Temperature sensing performance of dysprosium doped aluminum oxide powders

Dy³⁺-doped Al₂O₃ powders were prepared by combustion synthesis. Down-converted luminescence lines peaked at 451 and 471, 572, 660, 708 and 752 nm were obtained under 355 nm pulsed laser irradiation for as-prepared Dy³⁺ doping concentrations of 0.5, 1.0 and 2.0 wt.%. The fact that the relative intensities of the 451 and 471 nm luminescence bands changed with the samples temperature allowed the use of these emission lines for temperature sensing. We found that the maximum sensitivity of the temperature sensor based on the luminescence intensity ratio of those transitions changed with Dy³⁺ doping concentration indicating different coupling strengths between the crystal field and the rare-earth.     

Photocatalytic activities for water splitting of La-doped-NaTaO3 fabricated by microwave synthesis

The microwave synthesis was used to fabricate the La_0.02Na_0.98TaO₃ photocalyst. Using X-ray diffraction (XRD) and scanning electron microscope (SEM), we have investigated phase formation and crystal morphology of La_0.02Na_0.98TaO₃ powders prepared by microwave heating. The grains with an average size of 63 nm were easily obtained due to the fast reaction under microwave irradiation. The as-prepared La_0.02Na_0.98TaO₃ powders have high photocatalytic activities for water splitting owing to good crystallinity and high surface area compared to traditional La_0.02Na_0.98TaO₃ powders.     

Cation self-diffusion in LaFeO3 measured by the solid state reaction method

Cation diffusion in LaFeO₃ has been studied using the solid state reaction between sintered bodies of La₂O₃ and Fe₂O₃ at 950–1350 °C in air or O₂–N₂ mixtures. LaFeO₃ was the only product formed. The growth was parabolic and demonstrated to take place predominantly by diffusion of Fe³⁺ through the LaFeO₃ layer. The self-diffusion coefficient of Fe³⁺ was accordingly calculated from the parabolic rate constant, and at constant activity of La₂O₃, a_La2O3 = 1, it shows Arrhenius-type behaviour with activation energy 320 ± 20 kJ/mol. It appeared to be independent of the surrounding pO₂, but this was ascribed to lack of equilibrium with the atmosphere during growth of the LaFeO₃ layer. Correspondingly, the product LaFeO₃ is probably stoichiometric, and differences between our diffusivity and activation energy and those in the literature are discussed in view of this.     

Optical study of rare earth activated NaBa0.45Sr0.55PO4 phosphor

Dy³⁺ and Eu²⁺ activated triple phosphate NaBa_0.45Sr_0.55PO₄ phosphors were prepared by facile combustion synthesis. Excellent emission observed when NaBa_0.45Sr_0.55PO₄:Dy³⁺ and NaBa_0.45Sr_0.55PO₄:Eu²⁺ excited at 348 nm and 354 nm wavelength respectively. From a powder X-ray diffraction (XRD) analysis, the formation of compound with a trigonal–hexagonal scalenohedral structure was confirmed. In the photoluminescence spectra, the NaBa_0.45Sr_0.55PO₄:Dy³⁺ phosphor emits two distinctive colours: a blue band centred at 482 nm and a yellow band at 576 nm originating from Dy³⁺ whereas NaBa_0.45Sr_0.55PO₄:Eu²⁺ emits blue colour at 470 nm. Also, surface morphology has been studied by scanning electron microscope (SEM). Phosphors exhibit a strong absorption in the range of 340–400 nm and chromatic properties indicated that present phosphor is a hopeful candidate for near ultra violet light emitting diodes (nUV LEDs).     

Synthesis of nickel nanoparticles supported on hollow samaria-doped ceria particles via the solution-spray plasma technique: Anode catalysts for SOFCs

Aiming at SOFC anode applications, we have synthesized nanometer-sized nickel catalysts supported on hollow spherical particles of samaria-doped ceria (Ni/SDC) by spraying a mixed solution of nickel, samarium, and cerium nitrates into an atmospheric pressure plasma. The as-prepared particles consisted of SDC (average diameter d_SDC = ca. 0.8 µm) and uniformly dispersed nanometer-sized NiO particles. When reduced in H₂ at 800 °C or 1000 °C, Ni nanoparticles (average diameter d_Ni = 34 nm) were found to be embedded uniformly into the SDC surface.     

Mixed oxygen ion and electron conducting hollow fiber membranes for oxygen separation

Phase inversion spinning technique was employed to prepare dense perovskite hollow fiber membranes made from composition BaCo_xFe_yZr_zO_3−δ (BCFZ, x + y + z = 1.0). Scanning electron microscope (SEM) shows that such hollow fibers have an asymmetric structure, which is favored to the oxygen permeation. An oxygen permeation flux of 7.6 cm³/min cm² at 900 °C under an oxygen gradient of 0.209 × 10⁵ Pa/0.065 × 10⁵ Pa was achieved. From the Wagner Theory, the oxygen permeation through the hollow fiber membrane is controlled by both bulk diffusion and surface exchange. The elements composition of fresh fiber and the fiber after long-term experiments were analyzed by energy-dispersive X-ray spectra (EDXS). Compared to the fresh fiber, sulphur was found on the tested hollow fiber membrane surface exposed to the air side and in the bulk, and Ba segregations occur on the tested hollow fiber membrane surface exposed to the air side. A decrease of the oxygen permeation flux was observed, which was probably due to the sulphur poisoning.     

Growth of single wall carbon nanotubes using PECVD technique: An efficient chemiresistor gas sensor

In this work, the uniform and vertically aligned single wall carbon nanotubes (SWCNTs) have been grown on Iron (Fe) deposited Silicon (Si) substrate by plasma enhanced chemical vapor deposition (PECVD) technique at very low temperature of 550 °C. The as-grown samples of SWCNTS were characterized by field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM) and Raman spectrometer. SWCNT based chemiresistor gas sensing device was fabricated by making the proper gold contacts on the as-grown SWCNTs. The electrical conductance and sensor response of grown SWCNTs have been investigated. The fabricated SWCNT sensor was exposed to ammonia (NH₃) gas at 200 ppm in a self assembled apparatus. The sensor response was measured at room temperature which was discussed in terms of adsorption of NH₃ gas molecules on the surface of SWCNTs. The achieved results are used to develope a miniaturized gas sensor device for monitoring and control of environment pollutants.     

Synthesis of nanoparticles of CoxFe(3−x)O4 by combustion reaction method

Nanocrystalline magnetic particles of Co_xFe_(3−x)O₄, with x ranging from 0.79 to 1.15, has been synthesised by combustion reaction method using iron nitrate Fe(NO₃)₃.9H₂O, cobalt nitrate Co(NO₃)₂·6H₂O, and urea CO(NH₂)₂ as fuel without template and subsequent heat treatment. The process is quite simple and inexpensive since it does not involve intermediate decomposition and/or calcining steps. The maximum reaction temperature ranged from 850 to 1010 °C and combustion lasted less then 30 s for all systems. X-ray diffraction patterns of all systems showed broad peaks consistent with cubic inverse spinel structure of CoFe₂O₄. The absence of extra reflections in the diffraction patterns of as-prepared materials ensures phase purity. The average crystallite sizes determined from the prominent (3 1 1) peak of the diffraction using Scherre's equation and TEM micrographs consisted of ca. 27 nm in spherical morphology. FTIR spectra of the as-prepared material showed traces of organic and metallic salts byproducts. However, when the same material was washed with deionised water the byproducts were rinsed off, resulting in pure materials. Magnetic properties such as saturation magnetisation, remanence magnetisation and coercivity field measured at room temperature were 48 emu/g, 15 emu/g and 900 Oe, respectively.     

CuGaS2 hollow spheres from Ga–CuS core–shell nanoparticles

A liquid gallium emulsion was prepared as a starting material using ultrasound treatment in ethylene glycol. Core–shell particles of Ga@CuS were successfully synthesized by deposition of a CuS layer on gallium droplets through sonochemical deposition of copper ions and thiourea in an alcohol media. The core and shell of Ga@CuS products were composed of amorphous gallium metal and covellite phase CuS, which transformed into chalcopyrite CuGaS₂ hollow spheres after sulfurization at 450 °C, which was the lowest crystallization temperature. The formation of hollow nanostructures was ascribed to the Kirkendall mechanism, in which liquid gallium particles play an important role as reactive templates. In conclusion, we obtained CuGaS₂ hollow spheres with a 430 nm outer diameter and 120 nm shell thickness that had the same crystal structure and electrical properties as bulk CuGaS₂.     

Preparation and photoluminescence properties of the Sr1.56Ba0.4SiO4:0.04Eu2+ phosphor

The Sr_1.56Ba_0.4SiO₄:0.04Eu²⁺ phosphors were prepared via a combustion reaction and following the calcination method at low temperature. The influences of the amount of the uncommonly used SrCl₂ flux, different calcination temperatures and time on the structure and the photoluminescence (PL) properties of the phosphors were investigated. Under the excitation of 450 nm blue light, the phosphor shows the intense broad emission band from 490 nm to 650 nm, and the emission peak is centered at 553 nm. The luminescence intensity of Sr_1.56Ba_0.4SiO₄:0.04Eu²⁺ was very sensitive to the crystallinity and morphology characteristics of the phosphor. The phosphor calcined at 950 °C for 3 h in 20%H₂/80%Ar atmosphere exhibits improved PL properties due to its high crystallinity and excellent morphology characteristics. The use of the SrCl₂ flux provides a novel way to improve the crystallinity of the silicates phosphors at low preparation temperature.     

Self-assembly of well-ordered and highly uniform nanoripples induced by focused ion beam

Well-ordered and highly uniform nanoripple structures on the surface of single crystal LaAlO₃ (1 0 0), SrTiO₃ (1 0 0) and Al₂O₃ (0 0 0 1) were formed via self-assembly (not by beam writing) by focused ion-beam bombardment. The morphology and topography of nanoripple structures were characterized using in-situ focused ion-beam/scanning electron microscope, as well as ex-situ atomic force microscopy. Under off-normal bombardment without sample rotation, the characteristic wavelength of nanoripples varying from 248 to 395 nm on the LaAlO₃ (1 0 0) surface can be obtained by changing ion fluence and incident angle. When all sputtering parameters except the ion fluence are constant, the wavelength of nanoripples is increased with the enhanced ion fluence. These results demonstrate the potential application of using ion sputtering method for fabricating the well-ordered and highly uniform nanoripples which can be used in nanodevices.     

Self assembled V2O5 nanorods for gas sensors

Hollow spheres of vanadium pentoxide made up of self assembled nanorods have been prepared successfully by solvothermal method. The calcinated samples of V₂O₅ nanorods exhibit orthorhombic structure as determined through XRD analysis. The nanorods are found to self assemble into hollow sphere like structures which can be clearly seen in SEM images. The diameter of the hollow spheres were around 2–3 μm, while the nanorods forming the micro spheres were with diameters in the range of 100–200 nm and are of few hundreds of nanometers in length. The change in the resistance of the V₂O₅ nanorod sensing element with respect to the test gas concentration was measured by noting down the resistance at each concentration for various time intervals. Sensitivity of the material linearly increased with different concentration of ethanol and ammonia. It is clearly seen that the V₂O₅ nanorods have more sensing response for ethanol when compared to that of ammonia.     

Electrochemical properties of spinel-type manganese oxide/porous carbon nanocomposite powders in 1 M KOH aqueous solution

Spinel-type manganese oxide/porous carbon (Mn₃O₄/C) nanocomposite powders have been simply prepared by a thermal decomposition of manganese gluconate dihydrate under an Ar gas flow at above 600 °C. The structure and texture of the Mn₃O₄/C nanocomposite powders are investigated by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) equipped scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), selected area-electron diffraction (SA-ED), thermogravimetric and differential thermal analysis (TG-DTA) and adsorption/desorption of N₂ gas at ?196 °C. The electrochemical properties of the nanocomposite powders in 1 M KOH aqueous solution are studied, focusing on the relationship between their structures and electrochemical capacitance.In the nanocomposite powders, Mn₃O₄ nano particles approximately 5 nm in size are dispersed in a porous carbon matrix. The nanocomposite powders prepared at 800 °C exhibit a high specific capacitance calculated from cyclic voltammogram of 350 and 600 F g^?1 at a sweep rate of 1 and 0.1 mV s^?1, respectively. The influence of the heating temperature on the structure and the electrochemical properties of nanocomposite powders is also discussed.     

TiO2(110)-(1 × 1) supported Cu particles: An FT-RAIRS investigation

The morphology of TiO₂(110)-(1 × 1) supported Cu particles has been investigated by Fourier Transform Reflection Absorption Infrared Spectroscopy (FT-RAIRS), employing adsorbed CO as a probe molecule sensitive to local surface structure. For Cu coverage (deposited at 300 K) less than 2.85 MLE nucleated Cu particles in the range 2 nm–4 nm are formed, as indicated by a final state shift in the core level Cu(2p_3/2) binding energy and by the existence of only transmission bands in the FT-RAIRS spectra for adsorbed CO. ν_S(CO) indicates that these small particles expose sites similar to those of the stepped Cu surfaces Cu(211), Cu(311), and Cu(755). At Cu coverages in the range of 6 MLE and above, corresponding to particle sizes above 4.6 nm, ν_S(CO) indicates the predominance of (110), (100) and (111) adsorption sites. Annealing the Cu layers to 650 K results in the slight growth of the particle sizes, and transformation of the CO adsorption sites corresponding to the close packed facets. The transformation of the local dielectric from that of titania to that dominated by the Cu particle is shown to take place between 3.7 and 4.2 nm, and this change is also to a smaller extent sensitive to the dispersion of the particles.