V-doped In2O3 nanofibers for H2S detection at low temperature

Pristine and vanadium-doped In₂O₃ nanofibers were fabricated by electrospinning and their sensing properties to H₂S gas were studied. X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the inner structure and the surface morphology. The H₂S-sensing performances were characterized at different temperatures ranging from 50 to 170 °C. The sensor based on 6 mol% V-doped In₂O₃ nanofibers exhibit the highest response, i.e. 13.9–50 ppm H₂S at the relatively low temperature of 90 °C. In addition, the fast response (15 s) and recovery (18 s) time, and good selectivity were observed.     

Structural and electrochemical behaviors of metastable Li2/3[Ni1/3Mn2/3]O2 modified by metal element substitution

Layered metastable lithium manganese oxides, Li_2/3[Ni_1/3−xMn_2/3−yM_x+y]O₂ (x = y = 1/36 for M = Al, Co, and Fe and x = 2/36, y = 0 for M = Mg) were prepared by the ion exchange of Li for Na in P2-Na_2/3[Ni_1/3−xMn_2/3−yM_x+y]O₂ precursors. The Al and Co doping produced the T^#2 structure with the space group Cmca. On the other hand, the Fe and Mg doped samples had the O6 structure with space group R-3m. Electron diffraction revealed the 1:2 type ordering within the Ni_1/3−xMn_2/3−yM_x+yO₂ slab. It was found that the stacking sequence and electrochemical performance of the Li cells containing T^#2-Li_2/3[Ni_1/3Mn_2/3]O₂ were affected by the doping with small amounts of Al, Co, Fe, and Mg. The discharge capacity of the Al doped sample was around 200 mAh g⁻¹ in the voltage range between 2.0 and 4.7 V at the current density of 14.4 mA g⁻¹ along with a good capacity retention. Moreover, for the Al and Co doped and undoped oxides, the irreversible phase transition of the T^#2 into the O2 structure was observed during the initial lithium deintercalation.     

Effect of TiO2 on phase evolution and microstructure of MgAl2O4 spinel in different atmospheres

The effect of TiO₂ on the formation and microstructure of magnesium aluminate spinel (MgAl₂O₄) at 1600 °C in air and reducing conditions were investigated. Under reducing conditions, stoichiometric MgAl₂O₄ spinel shifted toward alumina-rich types owing to volatilization of MgO, resulting in an increase in the porosity of fired samples. Addition of graphite to mixtures of MgO and Al₂O₃ intensified the reducing conditions and accelerated the formation of non-stoichiometric MgAl₂O₄. For TiO₂-containing samples on addition of MgAl₂O₄, magnesium aluminum titanium oxide (Mg_xAl_2(1−x)Ti_(1+x)O₅, x = 0.2 or 0.3) was detected as a minor phase. Under reducing conditions, XRD peak shifts were smaller for TiO₂-containing samples than for samples without TiO₂ owing to the formation of a solid solution of TiO₂ in MgAl₂O₄ and establishment of alumina-rich spinel, which have opposite effects on increasing the lattice parameter. In bauxite-containing samples, MgAl₂O₄ spinel, corundum, magnesium orthotitanate spinel (Mg₂TiO₄) and amorphous phases were identified. Mg₂TiO₄ spinel formed a complete solid solution with MgAl₂O₄ spinel but Mg₂TiO₄ remained as a distinct phase owing to the heterogeneous microstructure of bauxite-containing samples. Also dense microstructure established in air fired TiO₂ containing samples. The results are discussed with emphasis on the application and design of alumina-magnesia-carbon refractory materials, which are used in the steel industry.     

Synthesis of a TiO2 ceramic membrane containing SrCo0.8Fe0.2O3 by the sol-gel method with a wet impregnation process for O2 and N2 permeation

A SrCo_0.8Fe_0.2O₃ impregnated TiO₂ membrane (TiO₂-SrCo_0.8Fe_0.2O₃ membrane) was successfully prepared using a sol-gel method in combination with a wet impregnation process. The membrane was subjected to a single gas permeance test using oxygen (O₂) and nitrogen (N₂). The TiO₂ membrane was immersed in the SrCo_0.8Fe_0.2O₃ solution, dried and then calcined to affix SrCo_0.8Fe_0.2O₃ into the membrane. The effect of the acid/alkoxide (H⁺/Ti⁴⁺) molar ratio of the TiO₂ sol on the TiO₂ phase transformation was investigated. The optimal molar ratio was found to be 0.5, which resulted in nanoparticles with a mean size of 5.30 nm after calcination at 400 °C. The effect of calcination temperature on the phase transformation of TiO₂ and SrCo_0.8Fe_0.2O₃ was investigated by varying the calcination temperature from 300 to 500 °C. X-ray diffraction spectroscopy (XRD) and Fourier transform infrared (FTIR) analysis confirmed that a calcination temperature of 400 °C was preferable for preparing a TiO₂-SrCo_0.8Fe_0.2O₃ membrane with fully crystallized anatase and SrCo_0.8Fe_0.2O₃ phases. The results also showed that polyvinyl alcohol (PVA) and hydroxypropyl cellulose (HPC) were completely removed. Field emission scanning electron microscopy (FESEM) analysis results showed that a crack-free and relatively dense TiO₂ membrane (∼0.75 μm thickness) was created with a multiple dip-coating process and calcination at 400 °C. The gas permeation results show that the TiO₂ and TiO₂-SrCo_0.8Fe_0.2O₃ membranes exhibited high permeances. The TiO₂-SrCo_0.8Fe_0.2O₃ membrane developed provided greater O₂/N₂ selectivity compared to the TiO₂ membrane alone.     

Effect of TiO2 supporting layer on Fe2O3 photoanode for efficient water splitting

For an electrochemical water splitting system, titanate nanotubular particles with a thickness of ∼700 nm produced by a hydrothermal process were repetitively coated on fluorine-doped tin oxide (FTO) glass via layer-by-layer self-assembly method. The obtained titanate/FTO films were dipped in aqueous Fe solution, followed by heat treatment for crystallization at 500 °C for 10 min in air. The UV–vis absorbance of the Fe-oxide/titanate/FTO film showed a red-shifted spectrum compared with the TiO₂/FTO coated film; this red shift was achieved by the formation of thin hematite-Fe₂O₃ and anatase-TiO₂ phases verified using X-ray diffraction and Raman results. The cyclic voltammetry results of the Fe₂O₃/TiO₂/FTO films showed distinct reversible cycle characteristics with large oxidation–reduction peaks with low onset voltage of I–V characteristics under UV–vis light illumination. The prepared Fe₂O₃/TiO₂/FTO film showed much higher photocurrent densities for more efficient water splitting under UV–vis light illumination than did the Fe₂O₃/FTO film. Its maximum photocurrent was almost 3.5 times higher than that obtained with Fe₂O₃/FTO film because of the easy electron collection in the current collector. The large current collection was due to the existence of a TiO₂ base layer beneath the Fe₂O₃ layer.     

Selective oxidation of methanol to dimethoxymethane over acid-modified V2O5/TiO2 catalysts

Selective oxidation of methanol to dimethoxymethane (DMM) was conducted in a fixed-bed reactor over an acid-modified V₂O₅/TiO₂ catalyst. The influence of the acid modification on its structure, redox and acidic properties, and catalytic performance for methanol oxidation were investigated. The results indicated that the content of vanadia in the catalyst exhibits a vital influence on the dispersion of vanadium species, while the acid modification can enhance its surface acidity. Proper amounts of the acid (W() = 15%) and V₂O₅ (W(V₂O₅) = 15%) components loaded in the acid-modified V₂O₅/TiO₂ catalyst are able to build a bi-functional circumstance that is favorable for the formation of DMM with high activity and selectivity. As a result, for the selective oxidation of methanol, the H₂SO₄-modified V₂O₅/TiO₂ catalyst gives a much higher DMM yield at 150 °C than the unmodified one.     

Particle size effect of Li[Ni0.5Mn0.5]O2 prepared by co-precipitation

Spherical (Ni_0.5Mn_0.5)(OH)₂ with different secondary particle size (3 μm, 10 μm in diameter) was synthesized by co-precipitation method. Mixture of the prepared hydroxide and lithium hydroxide was calcined at 950 °C for 20 h in air. X-ray diffraction patterns revealed that the prepared material had a typical layered structure with space group. Spherical morphologies with mono-dispersed powders were observed by scanning electron microscopy. It was found that the layered Li[Ni_0.5Mn_0.5]O₂ delivered an initial discharge capacity of 148 mAh g⁻¹ (3.0-4.3 V) though the particle sizes were different. Li[Ni_0.5Mn_0.5]O₂ having smaller particle size (3 μm) showed improved area specific impedance due to the reduced Li⁺ diffusion path, compared with that of Li[Ni_0.5Mn_0.5]O₂ possessing larger particle size (10 μm). Although the Li[Ni_0.5Mn_0.5]O₂ (3 μm) was electrochemically delithiated to Li_0.39[Ni_0.5Mn_0.5]O₂, the resulting exothermic onset temperature was around 295 °C, of which the value is significantly higher than that of highly delithiated Li_1−δCoO₂ (∼180 °C).     

Effect of fluorine in the preparation of Li(Ni1/3Co1/3Mn1/3)O2 via hydroxide co-precipitation

Uniform and spherical Li(Ni_1/3Co_1/3Mn_1/3)O_(2−δ)F_δ powders were synthesized via NH₃ and F⁻ coordination hydroxide co-precipitation. The effect of F⁻ coordination agent on the morphology, structure and electrochemical properties of the Li(Ni_1/3Co_1/3Mn_1/3)O_(2−δ)F_δ were studied. The morphology, size, and distribution of (Ni_1/3Co_1/3Mn_1/3)(OH)_(2−δ)F_δ particle diameter were improved in a shorter reaction time through the addition of F⁻. The study suggested that the added F improves the layered characteristics of the lattice and the cyclic performance of Li(Ni_1/3Co_1/3Mn_1/3)O₂ in the voltage range of 2.8-4.6 V. The initial capacity of the Li(Ni_1/3Co_1/3Mn_1/3)O_1.96F_0.04 was 178 mAh g⁻¹, the maximum capacity was 186 mAh g⁻¹ and the capacity after 50 cycles was 179 mAh g⁻¹ in the voltage range of 2.8-4.6 V.     

All-solid-state lithium battery with a three-dimensionally ordered Li1.5Al0.5Ti1.5(PO4)3 electrode

To fabricate all-solid-state Li batteries using three-dimensionally ordered macroporous Li_1.5Al_0.5Ti_1.5(PO₄)₃ (3DOM LATP) electrodes, the compatibilities of two anode materials (Li₄Mn₅O₁₂ and Li₄Ti₅O₁₂) with a LATP solid electrolyte were tested. Pure Li₄Ti₅O₁₂ with high crystallinity was not obtained because of the formation of a TiO₂ impurity phase. Li₄Mn₅O₁₂ with high crystallinity was produced without an impurity phase, suggesting that Li₄Mn₅O₁₂ is a better anode material for the LATP system. A Li₄Mn₅O₁₂/3DOM LATP composite anode was fabricated by the colloidal crystal templating method and a sol-gel process. Reversible Li insertion into the fabricated Li₄Mn₅O₁₂/3DOM LATP anode was observed, and its discharge capacity was measured to be 27 mA h g⁻¹. An all-solid-state battery composed of LiMn₂O₄/3DOM LATP cathode, Li₄Mn₅O₁₂/3DOM LATP anode, and a polymer electrolyte was fabricated and shown to operate successfully. It had a potential plateau that corresponds to the potential difference expected from the intrinsic redox potentials of LiMn₂O₄ and Li₄Mn₅O₁₂. The discharge capacity of the all-solid-state battery was 480 μA h cm⁻².     

Amorphous Ru1−yCryO2 loaded on TiO2 nanotubes for electrochemical capacitors

Amorphous Ru_1−yCr_yO₂/TiO₂ nanotube composites were synthesized by loading different amount of Ru_1−yCr_yO₂ on TiO₂ nanotubes via a reduction reaction of K₂Cr₂O₇ with RuCl₃·nH₂O at pH 8, followed by drying in air at 150 °C. Cyclic voltammetry and galvanostatic charge/discharge tests were applied to investigate the performance of the Ru_1−yCr_yO₂/TiO₂ nanotube composite electrodes. For comparison, the performance of amorphous Ru_1−yCr_yO₂ was also studied. The results demonstrated that the three dimensional nanotube network of TiO₂ offered a solid support structure for active materials Ru_1−yCr_yO₂, allowed the active material to be readily available for electrochemical reactions, and increased the utilization of active materials. A maximum specific capacitance 1272.5 F/g was obtained with the proper amount of Ru_1−yCr_yO₂ loaded on the TiO₂ nanotubes.     

Zr-doped Li[Ni0.5−xMn0.5−xZr2x]O2 (x = 0, 0.025) as cathode material for lithium ion batteries

Layered Li[Ni_0.5−xMn_0.5−xZr_2x]O₂ (x = 0, 0.025) have been prepared by the mixed hydroxide and molten-salt synthesis method. The individual particles of synthesized materials have a sub-microsize range of 200-500 nm, and LiNi_0.475Mn_0.475Zr_0.05O₂ has a rougher surface than that of LiNi_0.5Mn_0.5O₂. The Li/Li[Ni_0.5−xMn_0.5−xZr_2x]O₂ (x = 0, 0.025) electrodes were cycled between 4.5 and 2.0 V at a current density of 15 mA/g, the discharge capacity of both cells increased during the first ten cycles. The discharge capacity of the Li/LiNi_0.475Mn_0.475Zr_0.05O₂ cell increased from 150 to 220 mAh/g, which is 50 mAh/g larger than that of the Li/LiNi_0.5Mn_0.5O₂ cell. We found that the oxidation of oxygen and the Mn³⁺ ion concerned this phenomenon from the cyclic voltammetry (CV). Thermal stability of the charged Li[Ni_0.5−xMn_0.5−xZr_2x]O₂ (x = 0, 0.025) cathode was improved by Zr doping.     

Phase relations and electrical properties in the pseudo-ternary La2O3–TiO2–Mn2O3 system in air

Scanning electron microscopy (SEM), electron-probe microanalysis, energy- and wavelength-dispersive X-ray analysis and X-ray powder diffraction were used to investigate the subsolidus phase relations in the pseudo-ternary La₂O₃–TiO₂–Mn₂O₃ system in air (oxygen partial pressure p_O2=0.21   atm) at 1275 °C. The addition of Mn₂O₃ to the starting La₂O₃:3TiO₂ mixture led to the formation of a La-deficient perovskite La_2/3TiO₃ compound. The oxides form two new compounds with the proposed compositions: (i) La_1.7Ti_13.0Mn_6.3O_38−x, with a davidite-like crystal structure, and (ii) La₄₉Ti₁₈Mn₁₃O₁₂₉. There were also several solid solutions existing over a wide range of concentrations.     

Novel synthesis of layered LiNi1/2Mn1/2O2 as cathode material for lithium rechargeable cells

A new solution combustion synthesis of layered LiNi_0.5Mn_0.5O₂ involving the reactions of LiNO₃, Mn(NO₃)₂, NiNO₃, and glycine as starting materials is reported. TG/DTA studies were performed on the gel-precursor and suggest the formation of the layered LiNi_0.5Mn_0.5O₂ at low temperatures. The synthesized material was annealed at various temperatures, viz., 250, 400, 600, and 850 °C, characterized by means of X-ray diffraction (XRD) and reveals the formation of single phase crystalline LiNi_0.5Mn_0.5O₂ at 850 °C. The morphology of the synthesized material has been investigated by means of scanning electron microscopy (SEM) and suggests the formation of sub-micron particles. X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) studies on the synthesized LiNi_0.5Mn_0.5O₂ powders indicate that the oxidation states of nickel and manganese are +2 and +4, respectively. Electrochemical galvanostatic charge-discharge cycling behavior of Li//LiNi_0.5Mn_0.5O₂ cell using 1 M LiPF₆ in EC/DMC as electrolyte exhibited stable capacities of ∼125 mAh/g in the voltage ranges 2.8-4.3 V and 3.0-4.6 V and is comparable to literature reports using high temperature synthesis route. The capacity remains stable even after 20 cycles. The layered LiNi_0.5Mn_0.5O₂ powders synthesized by this novel route have several advantages as compared to its conventional synthesis techniques.     

Microwave dielectric properties of the (1 − x)Mg2TiO4-xCaTiO3-y wt.% ZnNb2O6 ceramics system

Composite ceramics based on (1 − x)Mg₂TiO₄-xCaTiO₃-y wt.% ZnNb₂O₆ (x = 0.12-0.16, y = 0-8) were prepared by a conventional mixed-oxide route. Zn²⁺ partially replaced Mg²⁺ in Mg₂TiO₄ and formed the spinel-structured (Mg_1−δZn_δ)₂TiO₄ phase. Nb²⁺, is known to be solid soluble in CaTiO₃, was found to change its shape from cubic to pliable. A bi-phase system (Mg_1−δZn_δ)₂TiO₄ and CaTiO₃ exhibited in all samples, where a small amount of second phase Mg_1−δZn_δTiO₃ was also detected. The microwave dielectric properties of specimens were strongly related to ZnNb₂O₆ and CaTiO₃ content. As y increased, ?_r and τ_f decreased, however, Q × f decreased to a minimum value and started to increase thereafter. It was also found that ?_r and τ_f increased and Q × f decreased with increasing x. The optimized microwave dielectric properties with ?_r = 18.37, Q × f = 31,027 GHz (at 6 GHz), and τ_f = 0.51 ppm/°C were achieved for (1 − x)Mg₂TiO₄-xCaTiO₃-y wt.% ZnNb₂O₆ (x = 0.12, y = 4) sintered at 1360 °C for 6 h.     

Electrochemical and thermal studies of Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 (x = 1/12, 1/4, 5/12, and 1/2)

Samples of the layered cathode materials, Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ (x = 1/12, 1/4, 5/12, and 1/2), were synthesized at 900 °C. Electrodes of these samples were charged in Li-ion coin cells to remove lithium. The charged electrode materials were rinsed to remove the electrolyte salt and then added, along with EC/DEC solvent or 1 M LiPF₆ EC/DEC, to stainless steel accelerating rate calorimetry (ARC) sample holders that were then welded closed. The reactivity of the samples with electrolyte was probed at two states of charge. First, for samples charged to near 4.45 V and second, for samples charged to 4.8 V, corresponding to removal of all mobile lithium from the samples and also concomitant release of oxygen in a plateau near 4.5 V. Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ samples with x = 1/4, 5/12 and 1/2 charged to 4.45 V do not react appreciably till 190 °C in EC/DEC. Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ samples charged to 4.8 V versus Li, across the oxygen release plateau, start to significantly react with EC/DEC at about 130 °C. However, their high reactivity is similar to that of Li_0.5CoO₂ (4.2 V) with 1 μm particle size. Therefore, Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ samples showing specific capacity of up to 225 mAh/g may be acceptable for replacing LiCoO₂ (145 mAh/g to 4.2 V) from a safety point of view, if their particle size is increased.     

One-step synthesis and improved electrochemical performance of Li(Ni1/3Co1/3Mn1/3)O2 by a modified radiated polymer gel method

We present the mechanism for the synthesis of a layered Li(Ni_1/3Co_1/3Mn_1/3)O₂ compound by a modified radiated gel method. Pure-phase Li(Ni_1/3Co_1/3Mn_1/3)O₂ material was achieved when the polymer gel was calcined at 900 °C between 15 and 30 h. The unit cell parameter c decreased, and a varied slightly with increased sintering time. Electrochemical characterization revealed that the optimized sample (25 h) had a high initial discharge capacity of 188 mAh/g (2.8-4.5 V, 20 mA/g), an excellent capacity retention of 90.1% after 30 cycles and a good rate performance.     

TiO2-V2O5纳米纤维光催化氧化烟气中的Hg0

对静电纺丝法制备的TiO₂和TiO₂-V₂O₅纳米纤维进行光催化脱除模拟烟气中Hg⁰的研究。对纳米纤维进行了SEM、TEM、XRD、BET和UV-Vis检测。结果表明TiO₂-V₂O₅纳米纤维为锐钛矿,V₂O₅高度分散在TiO₂中。纤维直径在200 nm左右,由粒径为10 nm左右的微粒组成。掺杂V₂O₅后,纤维的吸光范围扩大,在可见光范围内的吸光度比纯TiO₂时有了很大提高。实验研究了不同光照条件、V₂O₅的掺杂量和循环次数对脱汞的影响,分析了TiO₂-V₂O₅催化脱汞的机理。当V₂O₅的质量含量为3%时,TiO₂-V₂O₅在可见光下的脱汞率可达到66%,比纯TiO₂时的7%有了显著提高;纤维的脱汞性能稳定,多次循环后紫外光和可见光下的脱汞率仍分别保持在80%和65%左右。电子的跃迁和电子、空穴的快速分离是TiO₂-V₂O₅在可见光下脱汞率提高的主要原因。     

The first cycle characteristics of Li[Ni1/3Co1/3Mn1/3]O2 charged up to 4.7 V

In this research, we studied the first cycle characteristics of Li[Ni_1/3Co_1/3Mn_1/3]O₂ charged up to 4.7 V. Properties, such as valence state of the transition metals and crystallographic features, were analyzed by X-ray absorption spectroscopy and X-ray and neutron diffractions. Especially, two plateaus observed around 3.75 and 4.54 V were investigated by ex situ X-ray absorption spectroscopy. XANES studies showed that the oxidation states of transition metals in Li[Ni_1/3Co_1/3Mn_1/3]O₂ are mostly Ni²⁺, Co³⁺ and Mn⁴⁺. Based on neutron diffraction Rietveld analysis, there is about 6% of all nickel divalent (Ni²⁺) ions mixed with lithium ions (cation mixing). Meanwhile, it was found that the oxidation reaction of Ni²⁺/Ni⁴⁺ is related to the lower plateau around 3.75 V, but that of Co³⁺/Co⁴⁺ seems to occur entire range of x in Li_1−x[Ni_1/3Co_1/3Mn_1/3]O₂. Small volume change during cycling was attributed to the opposite variation of lattice parameter “c” and “a” with charging-discharging.     

C2H2 gas sensor based on Ni-doped ZnO electrospun nanofibers

Pure and Ni-doped ZnO nanofibers were synthesized using the electrospinning method. The morphology, crystal structure and optical properties of the nanofibers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy, respectively. It is found that Ni doping does not change the morphology and crystal structures of the nanofibers, and the ultraviolet emissions of ZnO nanofibers present red shift with increasing Ni doping concentration. C₂H₂ sensing properties of the sensors based on the nanofibers were investigated. The results show that the C₂H₂ sensing properties of ZnO nanofibers are effectively improved by Ni doping, and 5 at% Ni-doped ZnO nanofibers exhibit a maximum sensitivity to C₂H₂ gas.     

SnO2 nanoparticle embedded TiO2 nanofibers — Highly efficient photocatalyst for the degradation of rhodamine B

SnO₂ nanoparticle embedded TiO₂ nanofibers were fabricated by a simple electrospinning method. The relationship between the SnO₂/TiO₂ weight ratio and photocatalytic efficiency was investigated from the view point of Rhodamine B decomposition. In addition, electron microscopic analysis, energy dispersive analysis, X-ray diffraction analysis, and photoluminescence study demonstrated that SnO₂ nanoparticle was successfully embedded in TiO₂ nanofibers. TiO₂ nanofibers containing SnO₂ nanoparticle provided an enhanced interfacial region between TiO₂ and SnO₂. SnO₂ nanoparticles embedded TiO₂ nanofibers exhibited highly efficient photocatalytic activity under UV light irradiation due to high charge separation of electron–hole pairs.