Fabrication and photocatalytic activity of LaFeO3 ribbon-like nanofibers

LaFeO₃ ribbon-like nanofibers were synthesized via a sol–gel-assisted electrospinning method. The differences in morphology and photocatalytic property of LaFeO₃ nanofibers prepared through different needles were investigated. At the same time, the morphology and photocatalytic activity of porous LaFeO₃ nanobelts formed at different calcination temperatures were also investigated. Scanning electron microscopy results revealed that the obtained ribbon-like LaFeO₃ nanofibers made using a coaxial needle contained a large number of pores. Moreover, with the increase of calcination temperature, the morphology of the fibers also changed. X-ray diffraction analysis showed a series of fibers all in orthorhombic LaFeO₃ phase but no other impurities. In addition, the photocatalytic activity of LaFeO₃ nanofibers was studied for the degradation of methylene blue under visible light. The results demonstrated that ribbon-like nanofibers exhibited excellent photocatalytic activity compared with the others and the LaFeO₃ nanobelts calcined at 500°C had the best photocatalytic activity. Based on the experimental results, possible forming mechanisms involving in LaFeO₃ nanofibers through different needles are also discussed.     

Synthesis and formation mechanism of TiO2/Al2O3 nanobelts by electrospinning

Poly(vinyl pyrrolidone) (PVP)/[Ti(SO₄)₂ + Al(NO₃)₃] composite nanobelts were prepared via electrospinning technology, and TiO₂/Al₂O₃ nanobelts were fabricated by calcination of the prepared composite nanobelts. The samples were characterized by thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). XRD results show that the composite nanobelts were amorphous in structure, and pure phase TiO₂/Al₂O₃ nanobelts were obtained by calcination of the relevant composite nanobelts at 950°C for 8 h. SEM analysis indicates that the surface of as-prepared composite nanobelts was smooth, the widths of the composite fibers were in narrow range, and the mean width was ca. 8.9 ± 2.1 μm, thickness was about 255 nm, and there is no cross-linking among nanobelts. The width of TiO₂/Al₂O₃ nanobelts was ca. 1.3 ± 0.1 μm and the thickness was about 105 nm. TG-DTA analysis reveals that the N,N-dimethylformamide (DMF), organic compounds and inorganic salts in the composite nanobelts were decomposed and volatilized totally, and the weight of the sample kept constant when sintering temperature was above 900°C, and the total weight loss percentage was 81%. FTIR analysis manifests that crystalline TiO₂/Al₂O₃ nanobelts were formed at 950°C. The possible formation mechanism of the TiO₂/Al₂O₃ nanobelts was preliminarily discussed.     

Structure,optical and magnetic properties of LaFeO3 nanoparticles prepared by polymerized complex method

This work reports the study the structure, optical and magnetic properties of LaFeO₃ nanoparticles synthesized by the polymerized complex method. The LaFeO₃ nanoparticles were successfully obtained from calcination of the precursor at different temperatures from 750 to 1,050 °C in air for 2 h. The calcined LaFeO₃ nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–Visible spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge spectroscopy (XANES) and vibrating sample magnetometry. The XRD and TEM results showed that all LaFeO₃ samples had a single phase nature with the orthorhombic structure. The estimated crystallite sizes were in the range of 44.5 ± 2.4–74.1 ± 4.9 nm. UV–Vis spectra showed strong UV and Vis absorption with small band gap energy. The valence states of Fe ions were in the Fe³⁺ and Fe⁴⁺ state, as confirmed by XPS and XANES results. The weak ferromagnetic behavior with specific saturation magnetization of 0.1 emu/g at 10 kOe was obtained for the small particle of 44.5 ± 2.4 nm. The uncompensated spins at the surface was proposed as playing a part in the magnetic properties of small sized LaFeO₃.     

Synthesis and characterization of LaFeO3 powders prepared by a mixed mechanical/thermal processing route

Lanthanum ferrite, LaFeO₃ (LF), has raised considerable interest since it can be used in many applications such as solid-oxide fuel cell electrode, sensor material (H₂O and ethanol) and catalyst. Since the conventional ceramic route of synthesis has some disadvantages, mainly related to an exaggerated grain growth, LF has been prepared by different methods including combustion synthesis, sol–gel, hydrothermal processes, polymerizable complex method and mechanochemistry. As concerns this last method, a problem occurs due to the moisture sensitivity of La2O₃. To overcome the problem, we used lanthanum acetate sesquihydrate [La(CH₃COO)₃·1.5H₂O] and iron (II) oxalate dehydrate [FeC₂O₄·2H₂O] as precursors. The mechanism of the solid-state reactions in the mixtures has been studied by TG–DSC and XRPD. Synthesis of LaFeO₃ has been realized by annealing the mechanically activated mixtures for 3 h at temperatures between 500 and 800 °C. While LF prepared at 500 °C < T < 600 °C has an amorphous character, LF obtained at T ≥ 600 °C is free from carbonaceous impurities as it is shown by FT-IR and TG measurements. The specific area of the LaFeO₃ powders obtained starting from the mechanically activated mixture is decreasing by increasing the annealing temperature. On the contrary, the annealing on samples of physical mixture at temperatures up to 800 °C only yields a mixture of LaFeO₃, La₂O₃ and Fe₂O₃.

     

A highly sensitive nonenzymatic glucose sensor based on nickel oxide–carbon nanotube hybrid nanobelts

In this study, we demonstrated a highly sensitive electrochemical sensor for the determination of glucose in alkaline aqueous solution by using nickel oxide single-walled carbon nanotube hybrid nanobelts (NiO–SWCNTs) modified glassy carbon electrode (GCE). The hybrid nanobelts were prepared by the deposition of SWCNTs onto the Ni(SO₄)_0.3(OH)_1.4 nanobelt surface, followed by heat treatment at different temperatures ranging from 400 °C to 600 °C. The NiO–SWCNTs hybrid nanobelts modified electrode prepared at 500 °C displays enhanced electrocatalytic activity towards glucose oxidation, revealing a synergistic effect between the NiO and the deposited SWCNTs. The as-fabricated nonenzymatic glucose sensor exhibits excellent glucose sensitivity (2,980 μA cm^?2 mM^?1), lower detection limit (0.056 μM, signal/noise [S/N] ratio?=?3), and wider linear range (0.5–1,300 μM). Moreover, the sensor has been successfully used for the assay of glucose in serum samples with good recovery, ranging from 96.4 % to 102.4 %.     

Mn掺杂SnO_2一维纳米结构的制备、形貌及光学性质

用化学气相沉积(CVD)法制备了Mn掺杂的SnO2一维纳米结构(纳米线及纳米带),X射线衍射(XRD)显示样品为金红石型SnO2晶体,其生长机理可分别归结为气-液-固(VLS)和气-固(VS)机理,生长温度和气态原料浓度的差别是造成样品形貌及生长机理不同的主要原因.样品的拉曼谱出现了500、543、694和720cm-1四个新拉曼谱峰,分别是由活性的红外模和表面模引起的.纳米线及纳米带发光峰位于520nm处,发光强度随样品中氧空位的增减出现由强到弱的变化.     

Microwave synthesis of LaBO3 (B = Co,Fe) perovskites using graphite and citric acid additions

We studied the effects of graphite and citric acid additions on the formation of LaFeO₃ and LaCoO₃ perovskites upon microwave treatment of crystalline hydrates or nitrate solutions, respectively. The addition of graphite was shown to increase the yield of LaCoO₃ perovskite and to result in the formation of crystalline LaFeO₃ perovskite even at the microwave treatment stage. Subsequent thermal treatment at 800°C yields single-phase lanthanum ferrite with a high specific surface area (11 m²/g). Due to the addition of citric acid to nitrate solutions, a highly viscous gel forms, which allows preparation of single-phase perovskites with a high specific surface area (up to 34 m²/g) after microwave treatment and calcination. The samples obtained using the admixtures are characterized by a high catalytic activity in methane oxidation. No single-phase oxides form without introduction of these admixtures.     

A simple route to obtain TiO2 nanowires by the sol–gel method

In this work, titanium dioxide (TiO₂) nanowires were synthesized by the sol–gel method, without using any kind of templates, instead of that acetic acid was used as morphological modifier. In order to control crystalline phases and crystal size, TiO₂ was calcinated at 400, 500 and 600 °C during 1 h. The resulting morphology was nanowires, which diameter was maintained constant after calcination at different temperature (about 76 nm). Moreover, crystalline phases in order of predominance were anatase, anatase–rutile and rutile–anatase at 400, 500 and 600 °C, respectively. Additionally, the crystallite size increases with respect to temperature from 13 to 75 nm.     

The particle dimension controlling synthesis of α-MnO2 nanowires with enhanced catalytic activity on the thermal decomposition of ammonium perchlorate

Hydrothermal method synthesis of α-MnO₂ nanowires has been achieved at different temperatures in this work. X-ray diffraction and transmission electron microscopy confirmed the pure phase of the α-MnO₂ nanowires. All of the samples crystallized in a single-phase nanowires shape. The α-MnO₂ nanowires diameter increased from 11 nm to 21 nm with the increase in hydrothermal temperature from 120 °C to 200 °C. The α-MnO₂ catalytic activity on the decomposition of ammonium perchlorate (AP) was characterized through thermogravimetric analysis. The decomposition rate of AP with the addition of α-MnO₂ was size relative. The 11 nm MnO₂ nanowires exhibited the best catalytic activity, which lowered the high-temperature peak of AP by 130 °C.     

Wavelength dependence in photochemical vapor deposition of aluminum film using dimethylaluminum hydride

In photochemical vapor deposition of aluminum film on silicon using dimethylaluminum hydride, (CH₃)₂AlH, a surface reaction dominated below a (CH₃)₂AlH pressure of 0.3 m Torr at 200°C, which was induced only with the 160 nm band emitted from a deuterium lamp. A gas-phase reaction occurred above 0.3 mTorr at 200°C, which could be induced by both 160 nm and 240 nm emission bands from the lamp. To distinguish between surface ad gas-phase reactions, a thickness profile was used. At 240°C the surface reaction could be induced even by the 240 nm band, while the deposits formed under illumination of the two bands were thinner than those obtained with only the 240 nm band, indicating occurrence of vacuum ultraviolet (VUV)-enhanced desorption. The mechanism responsible for the observed wavelength dependence in unclear. The electrical resistivity of the films deposited at 200°C was 4.5 μΩ cm, which did not change with wavelength.     

Thermal and morphological study of Al2O3 nanofibers derived from boehmite precursor

The boehmite nanofibers were prepared by using NaAlO₂ and Al₂(SO₄)₃ as the starting materials without any surfactant. The phase transitions of the boehmite nanofibres against different temperature were studied and various phases were derived from well-crystallized boehmite nanofibers. All these phases had the same morphology even after high temperature calcination. In addition, the retention of specific surface area of the samples were very high because of the limited aggregation occurred in calcinations for each sample. For instance, the ??-Al₂O₃ obtained at 500?°C had the specific surface area (208.56?m²/g) with an average pore diameter of 6.0?nm. With the further increase of the calcination temperature, the nanofibers became shorter and coarsening, which resulted in the decrease of the specific surface area. It is worthwhile to notice that the BET surface areas (40.97?m²/g) and the pore volume (0.27?cm³/g) of the fibrous structures obtained after 1200?°C calcination are substantially higher than that of the non-fibrous alumina because of the morphology maintenance.     

Preparation and Studies of ZnO:Al Films and Powders

ZnO:Al (0–10 at% Al) films and powders were produced using acac-modified methoxy-ethoxide precursors, obtained from Zn(C₂H₅)₂ and Al₄(OPr ⁱ )₁₂. The conversion to oxide powders was monitored with TGA and DSC, and the phase development was investigated with XRD, FT-IR spectroscopy, and TEM-EDS. The gels obtained by air-hydrolysis contained ca 0.5 acac/(Zn + Al) and a small amount of water and hydroxyls. All residual groups were removed to yield ZnO:Al by heating to ca 400°C. The powders obtained at 400 and 500°C were elementally homogeneous, and consisted of hex-ZnO:Al as ca 3–5 (10 at% Al) or 20–30 (3 at% Al) nm sized crystalline particles. Spin-coating on quartz, Si/SiO₂, and window glass, followed by heating to 500°C resulted in 150–200 nm thick films of hex-ZnO:Al. 500 nm thick films were obtained by repeating the deposition and heat-treatment twice. The films were visually very clear and the measured transmittance high over the 400–800 nm range (91–93% at 800 nm) for ca 300 nm thick films.     

Synthesis and characterization of perovskite-type La1-yCayMn1-xB″xO3±δ nanomaterials (B″ = Ni,Fe; x = 0.2, 0.5; y = 0.4, 0.25)

Perovskite-type nanomaterials of the compositions La_1-yCa_yMn_1-xB″_xO_3±δ with B’’ = Ni, Fe; x = 0.2, 0.5 and y = 0.4, 0.25 were prepared using two different preparation routes (synthesis by precipitation and the PVA/sucrose method) at 500 °C–700 °C. The calcined products of the syntheses were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and physisorption measurements. The materials from the PVA/sucrose method contain particles with diameters from 33 nm to 48 nm, generate specific surface areas up to 33 m²/g and form pure compared to 45 nm–93 nm and up to 18 m²/g from precipitation method which contain a significant amount of sodium ions. The agglomeration process was analyzed for one nanomaterial (B’’ = Fe, x = 0.2, y = 0.4) from the PVA/sucrose method using temperature dependent XRD showing only a slight growth (4.3%) of nanoparticles at 600 °C. The materials from the PVA/sucrose method turned out to be more suitable as electrode materials in electrochemical applications (SOFC, sensors) because of smaller particle sizes, higher specific surface areas and purity.     

Hydrothermal Synthesis of Na0.28V2O5 Nanobelts and their Electrochemical Behavior in Lithium Batteries

A simple low temperature hydrothermal method was found to yield Na_0.28V₂O₅ nanobelts after two days at 130 °C in acidic medium (H₂SO₄) without using any surfactant. The obtained products were characterized by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), and Raman spectroscopy. Their morphology was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Additionally, their electrochemical behavior in a lithium battery was investigated. The XRD pattern shows that the product is composed of monoclinic Na_0.28V₂O₅ nanobelts. From the FTIR spectrum, the band centered at 961 cm^–1 is assigned to V=O stretching vibration, which is sensitive to intercalation and suggests that Na⁺ ions are inserted between the vanadium oxide layers. SEM/TEM analyses reveal that the products consist of a large quantity of nanobelts which have a thickness of 60–150 nm and a length of several tens of micrometers. The electrochemical results show that the nanobelts exhibit an initial discharge specific capacity of 390 mAh · g^–1, and its stabilized capacity still remained around 200 mAh · g^–1 after the 18th cycle.     

Synthesis of nanosized BaSnO3 powders from metal isopropoxides

Nanocrystalline BaSnO₃ with a primary particle size of 40–60 nm was prepared through hydrolysis of a barium tin isopropoxide and following crystallization. The thermal decomposition, the crystallization and the microstructure of the obtained powders were investigated with the help of TG-DTA, IR, XRD, HRSEM and HRTEM. The organic rest groups in the as-prepared powder decompose thermally at 350°C, which is accompanied by the building of BaCO₃ that disappear again at 600°C. The crystallization of BaSnO₃ takes place at 500–600°C. Single-phase BaSnO₃ powders have been obtained at a temperature as low as 600°C. The amorphous as-prepared powder shows a cluster structure. Nucleation of BaSnO₃ beginning at 350°C was observed under HRTEM, and the spherical nano-particles of BaSnO₃ calcined at 760°C crystallize well and are strongly aggregated. The presented results indicate a heterogeneous nucleation and growth mechanism by the formation of BaSnO₃.     

Mass production of very thin single-crystal silicon nitride nanobelts

We report the large-scale synthesis of very thin single-crystalline Si₃N₄ nanobelts with high yield via catalyst-assisted pyrolysis of polymeric precursors. The obtained nanobelts, which show a perfect crystal structure and smooth surface, are up to several millimeters in length with typical width and thickness of ∼800 nm and tens of nanometers, respectively. It is believed that the nanobelts were grown via a vapor-solid process, in which Al catalyst played a key role. This result provides a possibility for mass producing high quality, very thin Si₃N₄ nanobelts.     

氧化铟八面体、纳米带、锯齿状纳米线和纳米链的可控合成

在N₂/H₂O混合气流中将硅片上金覆盖的金属铟颗粒加热到800 ℃制备出了不同形貌的In₂O₃纳米结构, 在距铟源不同距离处依次得到In₂O₃的八面体、纳米带、锯齿状纳米线和纳米链. 采用拉曼光谱、扫描电镜、X射线衍射和透射电镜对产物进行了表征分析. 结果表明, 八面体、纳米带、锯齿状纳米线和纳米链均为立方相单晶结构的In₂O₃. 基于气-固和气-液-固生长机理详细分析了八面体、纳米带、锯齿状纳米线和纳米链的生长过程, 提出了不同形貌In₂O₃纳米结构的生长模式.     

Effect of thermal treatment on the structure and texture of differently impregnated NiO/SiO2 catalysts

NiO/SiO₂ catalysts were prepared with Ni contents ranging from 2–15% using a microporous silica support at pH ~11.5. The role of the method of preparation on the resulting catalyst is also investigated. Structural and textural changes were followed using X-ray diffraction, TG and DTA techniques—the surface area measurements were carried out on the parent catalysts and those produced in the temperature range 250–1000°C.Impregnation of the silica gel in the nickel ammine complex solution (catalyst series 1N–4N) with subsequent drying at 80°C overnight produced crystalline catalysts with two distinct peaks at d-spacings of 2.035 and 2.349 Å resulting from a surface silicate. This is easily destroyed by thermal treatment at 250°C for Ni contents ? 10% but is stable to this temperature for the higher Ni content. Drying the catalyst at room temperature (3N_b) gives rise to an amorphous product. A non-crystalline catalyst is also obtained when concentrated ammonia solution is added to the adsorbed nickel salt (3N_c). At high Ni content, the hydroxo ligand becomes significant and results in a surface compound in which one silanol group is attacked. This gives rise to a crystalline product at 500°C with characteristic d-spacings at 2.201 and 2.049 Å which, subsequently, produces a poorly crystalline NiO product at 1000°C. The presence of this hydroxo ligand is manifested by a small endotherm at 260°C.At Ni contents below 15% but greater than 2% a small exotherm is observed at ~ 500°C resulting from a reduction process. Entrained SO₄^2? ions present as an impurity are evolved at temperatures & > 750°C and can be estimated by TG analysis.The specific surface area decreases with Ni contents ? 5% but increases for higher Ni contents. Catalyst samples containing 15% Ni possess the highest specific area at all temperatures.Pore structure analysis showed that microporosity increased with increase in Ni content for the catalyst series 1N–4N. Samples from preparations 3N_b and 3N_c showed more mesoporosity than that of 3N. Thermal treatment causes widening of the pores for catalysts 1N–3N becoming predominantly mesoporous, co-existing with some micropores. Catalyst samples with 15% Ni remained predominantly microporous-mesoporosity increasing only at 1000°C.     

Development and investigation of the flexible hydrogen sensor based on ZnO-decorated Sb2O3 nanobelts

Hydrogen is regarded as the next-gen fuel for vehicles to avoid the emission of toxic gases, which needs a continuous monitoring of the concentration level. In the design of the H₂ sensor, especially of flexible type, a sensing layer will be blended, which affects the sensing performance of the device. Based on this concern, the present investigation is carried out to understand the effect of the bending angle toward the sensing performance of bare and ZnO (n-type)-decorated Sb₂O₃ (p-type) nanobelt–based sensors for hydrogen gas. The sensing element was prepared by the thermal chemical vapor deposition followed by the drop-casting method. Furthermore, the role of the zinc precursor (molar concentration—1 M–3 M) on the preparation of ZnO-decorated Sb₂O₃ nanobelts was studied. Various techniques were used to confirm the formation of ZnO-decorated nanobelts such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), and Fourier transform infrared spectroscopy (FTIR). From these analyses, 1 M concentration of the zinc precursor shows uniform distribution of nanoparticles over the surface of Sb₂O₃ nanobelts. However, agglomeration was observed when the concentration of the zinc precursor increases from 1 M to 3 M. Later, the prepared nanobelts were deposited on the OverHead Projector (OHP) sheet by the doctor blade method for sensing hydrogen gas at 100 °C at a concentration of 1000–3000 ppm. In addition to it, the effect of the substrate bending angle (0°, 45°, 60°, and 90°) was analyzed at a fixed concentration of H₂ gas (1000 ppm). From this study, it is clear that the highest sensing response was achieved for 1 M decorated nanobelts compared with bare as well as other concentrations because of uniform distribution of nanoparticles on the surface of nanobelts. Moreover, the prepared sample demonstrates better sensing performance with the bending of substrates, which suggests that the prepared sensor could be used for flexible electronic devices. The prepared nanobelts show a good H₂ gas–sensing response even with bending of the substrates. The work suggests that the prepared sensor is applicable for flexible electronic devices.     

Synthesis of nanosized zinc and magnesium chromites starting from PVA–metal nitrate solutions

In this article, we present a detailed study regarding the preparation of nanosized zinc and magnesium chromites starting from a 4% poly(vinyl)alcohol (PVA) aqueous solution and metal nitrates. The controlled thermal treatment of these solutions has permitted the isolation of an intermediary solid product, used as precursor of the preferred mixed oxides: zinc and magnesium chromites. The as-obtained precursors were characterized by FT-IR spectrometry and thermal analysis. FT-IR spectrometry has evidenced the disappearance of the NO₃ ^? anions at 140?°C, due to the redox interaction with PVA. The thermal decompositions of the synthesized precursors were different, as resulted from both thermal analysis and FT-IR spectrometry. Thus, while ZnCrPVA precursor decomposes up to 400?°C with formation of zinc chromite, the precursor MgCrPVA decomposes up to 500?°C, with formation of MgCrO₄ as intermediary amorphous phase. By thermal decomposition of MgCrO₄ at 500?°C, weakly crystallized MgCr₂O₄ powder is obtained. The obtained chromite powders consist of fine nanoparticles with diameters ranging from 10 to 30?nm at 500?°C; on raising the annealing temperature to 1000?°C, chromite particles become octahedral, with diameter up to 500?nm, but with no sign of sintering.