Rapid synthesis of MXenes at room temperature

Ti₃C₂, one of the most studied MXenes (M is an early transition metal, and X is either C or N), has attracted considerable attention due to their excellent electrical conductivity, hydrophilicity, and catalytic activity. To date, most MXenes are prepared from powders and chemical etching under conditions of either long duration (generally ≥8?h) or high temperature (generally ≥35°C). In this study, Ti₃C₂ with –F and –O/–OH terminal groups was successfully obtained by electrochemically etching porous Ti₃AlC₂ sheet electrodes in NH₄HF₂ solution at room temperature. The reaction mechanism and the effect of voltage were demonstrated. Electrochemical etching could induce subsequent over-etching to generate carbide-derived carbons.     

Size control of magnetite nanoparticles by organic solvent-free chemical coprecipitation at room temperature

This study provides a facile single-step coprecipitation method for preparing size-controlled high crystalline magnetite nanoparticles in water system without using any organic solvents. In this method, an iron ions solution and an alkaline solution are simply mixed at room temperature without using any additional heating treatment. The size of obtained magnetite nanoparticles greatly depended on the coexisting anionic species in the starting solution because the coexisting anions greatly influenced both the formation of crystal nuclei and the dispersion stabilisation of formed precipitates. The size control of magnetite nanoparticles having high crystallinity and ferromagnetic property could be successfully achieved by using the effects of coexisting anions. For synthesising finer magnetite nanoparticles, the presence of lactate ion in the starting solution was effective, and coarser ones could be synthesised under higher ferrous/ferric ions molar ratios.     

Desulfurization from thiophene by SO(4)(2-)/ZrO(2) catalytic oxidation at room temperature and atmospheric pressure

Thiophene, due to its poison, together with its combustion products which causes air pollution and highly toxic characteristic itself, attracted more and more attention to remove from gasoline and some high concentration systems. As the purpose of achieving the novel method of de-thiophene assisted by SO(4)(2-)/ZrO(2) (SZ), three reactions about thiophene in different atmosphere at room temperature and atmospheric pressure were investigated. SO(4)(2-)/ZrO(2) catalyst were synthesized and characterized by X-ray photoelectron spectroscopy (XPS), Fourier transformation infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscope (SEM). The products were detected by gas chromatography-mass spectrometry (GC-MS). XP spectra show that ozone-catalyst system (SZO) have two forms of sulfur element (S(6+) and S(2-)) on the catalyst surface, which distinguished from that of air-catalyst system (SZA) and blank-catalyst system (SZB) (S(6+)). And the results of GC-MS exhibited that some new compounds has been produced under this extremely mild condition. Especially, many kinds of sulfur compounds containing oxygen, that is easier to be extracted by oxidative desulfurization (ODS), have been detected in the SZA-1.5h and SZB-3h system. In addition, some long chain hydrocarbons have also been detected. While in SZO-0.5h system, only long chain hydrocarbons were found. The results show that total efficiency of desulfurization from thiophene with ozone near to 100% can be obtained with the SO(4)(2-)/ZrO(2) catalytic oxidation reaction.     

Self-propagating high temperature synthesis of high purity single-crystalline SnO2 nanobelts

A new application of conventional self-propagating high temperature synthesis technology was developed to synthesise high purity single-crystalline SnO₂ nanobelts through a simple, convenient and efficient method. The outcome of the research, for which an experimental setup was designed and manufactured, turned out to be successful and propagable. High purity SnO₂ nanobelts could be obtained within minutes. The growth mechanism of these SnO₂ nanobelts is discussed in this article.     

Investigation of SiOxCy film as the encapsulation layer for full transparent OLED using hollow cathode discharge plasma at room temperature

The plasma polymer of SiO_xC_y film has attracted much attention because it could possess both the organic and inorganic properties simultaneously for wide range applications. In this work, a SiO_xC_y film with a gradient composition through tuning the N₂O/N₂O + Ar ratio from 0% to 100% was used for TOLED encapsulation using hollow cathode discharge plasma. In order to confirm whether the plasma damage was caused during the PECVD process, a ZnO buffer layer prepared using RF sputtering was deposited before encapsulation. Furthermore, the reference samples with glass lid encapsulation were also used for comparison. The results showed that the SiO_xC_y film with a gradient composition cooperated with the sputtering ZnO buffer layer was a simple and effective method for TOLED encapsulation.     

Controlled synthesis and photoluminescence properties of hierarchical BaXO4 (X = Mo, W) nanostructures at room temperature

Controlled synthesis of hierarchical Barium molybdate (BaMoO₄) nanostructures with different morphologies, such as peanut-like, cube-like and flower-like, was successfully achieved in aqueous solution at room temperature. The obtained products were characterized by a scanning electron microscope (SEM) and an X-ray power diffractometer (XRD). The morphologies of the obtained products were found to be greatly dependent on reaction time, EDTA concentration and the [Ba²⁺]/[MoO₄²⁻] ratio. This controllable method could be readily extended to produce hierarchical Barium tungstate (BaWO₄) nanostructures with peanut-like, dumbbell-like, sphere-like and flower-like morphologies. The photoluminescence (PL) properties of the obtained BaMoO₄ and BaWO₄ nanostructures exhibited strong dependence on the morphologies and sizes, respectively.     

Self-generation of three-dimensional hierarchical Cu2S architectures at room temperature

A simple approach is proposed to realize the three dimensional (3D) hierarchical Cu₂S architectures at room temperature in this letter. The 3D Cu₂S architectures are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectrum (XPS). The effects of synthetic conditions, such as reaction time and the amount of reagents, on the morphology of the product are investigated. The growth mechanism of the product is proposed, based on the evolution of the morphologies with the increasing of reaction time. Our work provides a facile and easy method on designing for the fabrication of 3D hierarchical architecture materials.     

Conversion of V2O5·xH2O into orthorhombic V2O5 single-crystalline nanobelts

Orthorhombic V₂O₅ single-crystalline nanobelts have been synthesized by hydrothermal treating V₂O₅·xH₂O precipitate derived from aqueous solution of V₂O₅ and H₂O₂. The synthetic method is facile, fast, environmental friendly, and easy to scale up. The V₂O₅ single-crystalline nanobelts are 30-80 nm in width, 30-40 nm in thickness, and lengths up to several tens of micrometers. The V₂O₅·xH₂O precursor is crucial for the formation of orthorhombic V₂O₅ single-crystalline nanobelts. The influences of synthetic parameters, such as reaction time and reaction temperature, on the crystal structures and morphologies of the resulting products have been investigated. Time-dependent experiments show that V₂O₅·xH₂O are dehydrated gradually and converted into orthorhombic V₂O₅ single-crystalline nanobelts. High reaction temperature also favors the formation of orthorhombic V₂O₅ nanobelts.     

Preparation and characterization of poly(o-phenylenediamine) microrods using ferric chloride as an oxidant

Microrods of poly(o-phenylenediamine) (PoPD) were synthesized by a templateless method using ferric chloride as an oxidant. The microrod morphologies of the resulting PoPD were confirmed by scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images. When the concentration of o-phenylenediamine (oPD) was 0.03 M, the microrods of PoPD had a diameter in the range of 0.5-2 μm and a length from 2 μm to 20 μm. It was found that the concentration of oPD monomer had much influence on the morphology of the obtained PoPD. When the concentration of oPD was lower than 0.03 M, long microrods could be observed. However, when the concentration of oPD monomer was higher than 0.12 M, the length of the microrods became very short and the diameter became bigger. Fourier transform infrared spectroscopy (FTIR), UV-vis absorption spectra and X-ray diffraction (XRD) were used to characterize the structure of the obtained PoPD microrods.     

Varistor performance of nanocrystalline Zn-Bi-O thin films prepared by reactive RF magnetron sputtering at room temperature

The Zn-Bi-O films were deposited by reactive radio frequency magnetron sputtering in oxygen atmosphere from ZnBi alloy target (wt% ratio Zn:Bi=9:1) on glass substrate at room temperature. The XRD patterns show that the films deposited on tin-doped indium oxide/glass substrates were nanocrystalline. The microstructure of Bi-doped ZnO films was studied by scanning electron microscopy in combination with energy dispersive X-ray spectroscopy. All the obtained layers had varistor-type non-linear current-voltage (I-V) characteristics with low breakdown voltage varying from few tenths of a volt to few volts.     

Preparation and characterization of single-crystalline gallium oxide nanobelts

Single-crystalline β-Ga₂O₃ nanobelts were synthesized by a simple physical evaporation method in argon atmosphere with the starting materials of Ga. The β-Ga₂O₃ nanobelts have a width of 50-100 nm and width-to-thickness ratios of 5-10, and length of up to a few millimeters, which may have potential applications in nanosize sensors or optoelectronic nanodevices.     

Fast response detection of H2S by CuO-doped SnO2 films prepared by electrodeposition and oxidization at low temperature

Fast response detection of H₂S by CuO-doped SnO₂ films prepared was prepared by a simple two-step process: electrodeposition from aqueous solutions of SnCl₂ and CuCl₂, and oxidization at 600 °C. The phase constitution and morphology of the CuO-doped SnO₂ films were characterized by X-ray diffraction and scanning electron microscopy. In all cases, a polycrystalline porous film of SnO₂ was the product, with the CuO deposited on the individual SnO₂ particles. Two types of CuO-doped SnO₂ films with different microstructures were obtained via control of oxidation time: nanosized CuO dotted island doped SnO₂ and ultra-uniform, porous, and thin CuO film coated SnO₂. The sensor response of the CuO doped SnO₂ films to H₂S gas at 50–300 ppm was investigated within the temperature range of 25–125 °C. Both of the CuO-doped SnO₂ films show fast response and recovery properties. The response time of the ultra-uniform, porous, and thin CuO coated SnO₂ to H₂S gas at 50 ppm was 34 s at 100 °C, and its corresponding recovery time was about 1/3 of the response time.     

UV-enhanced atomic layer deposition of ZrO2 thin films at room temperature

A UV-enhanced atomic layer deposition (UV-ALD) process was developed to deposit ZrO₂ thin films on poly(ethylene terephthalate) (PET) polymer substrates using zirconium tetra-tert-butoxide (ZTB) and H₂O as precursors with UV light. In the UV-ALD process, the surface reactions were found to be self-limiting and complementary enough to yield uniform, conformal, and pure ZrO₂ thin films on polymer substrates at room temperature. The UV light was very effective to obtain the high-quality ZrO₂ thin films with good adhesive strength on polymer substrates. The ZrO₂ thin films exhibit large-scale uniformity, sharp interfaces, and unique electrical properties.     

基于质谱诊断的C4H8/H2等离子体状态在放电腔室的径向分布研究

利用质谱研究了不同工艺参数下C_4H_8/H_2等离子体的离子组分和能量的径向分布规律,并分析了CH片段的裂解与聚合过程。结果表明,当工作压强较低时(≤7Pa),小分子CH片段的相对密度随径向距离的增大而逐渐减小,大分子CH片段则逐渐增多;随着工作压强的增大,CH片段的相对密度达到极值所对应的径向距离逐渐增大。当射频功率一定时,小分子CH片段的相对密度随径向距离增大而减小,大分子CH片段则逐渐增多。此外,离子能量随径向距离的增大均呈现出逐渐减小的趋势。当工作压强为3Pa、射频功率为20 W时,C_4H_8/H_2等离子体中CH片段的径向分布最均匀,有利于提高辉光放电聚合物薄膜结构与组分的均匀性。     

Solvothermal synthesis of Co/CoFe2O4 nanobelts

A facile solvothermal route is used for the synthesis of Co/CoFe₂O₄ nanobelts by rationally manipulating the dosages of a surfactant Poly(vinylpyrrolidone) (PVP, MW 40000). PVP plays a pivotal role in preparing the Co/CoFe₂O₄ nanobelts. The optimal dosage for the synthesis of the Co/CoFe₂O₄ nanobelts is 0.5 g. Lower than this value, octahedral particles and nanobelts were coexistent; higher than this value, octahedral particles were obtained. Furthermore, the possible formation mechanism of Co/CoFe₂O₄ nanobelts was proposed. A small quantity of Co²⁺ ions are reduced by glycerol, which is the reason for the presence of metallic Co in the CoFe₂O₄ ferrite. The Co/CoFe₂O₄ nanobelts may be very attractive for potential applications because of their outstanding magnetic properties (Ms = 110 emu/g, Hc = 387 Oe).     

Fracture behavior and mechanism of 2D C/SiC-BCx composite at room temperature

2D C/SiC composite was modified with partial BC_x matrix by low pressure chemical vapor infiltration technique (LPCVI), which was named as 2D C/SiC-BC_x composite. The flexural fracture behavior, mechanism, and strength distribution of 2D C/SiC-BC_x composite are investigated. The results indicate that the flexural strength, fracture toughness, and fracture work are 442.1 MPa, 22.84 MPa m^1/2, and 19.2 kJ m⁻², respectively. The flexural strength of C/SiC-BC_x composite decrease about 20% than that of C/SiC composite. However, the fracture toughness and fracture work increase about 19% and 18.5%, respectively. The properties varieties between C/SiC-BC_x composite and C/SiC composite can be attributed to the weak-bonding interface between BC_x/SiC matrices according to the results of detailed microstructure analysis. The strength distribution of 2D C/SiC-BC_x composite follows as Normal distribution or Weibull distribution with σ_u = 0, and m = 8.1393. The mean value of flexural strength for 2D C/SiC-BC_x composite is 443 MPa obtained by theory calculation, which is consistent with experiment result (442.1 MPa) very well.     

Effect of pulse voltage and aluminum purity on the characteristics of anodic aluminum oxide using hybrid pulse anodization at room temperature

Most of the anodic aluminum oxide (AAO) templates are performed by potentiostatical method at 0-10 °C to inhibit the Joule's heat enhanced dissolution in aluminum oxide for well-ordered cell configuration. In this article, we propose the hybrid pulse anodization (HPA) method with effective suppression of Joule's heat generation to fabricate AAO at room temperature. Effects of purity of aluminum (Al) foils and pulse voltage on the evolution of pore characteristics have been investigated. The AAO morphology is captured by scanning electron microscope and analyzed via gray-scale imaging in order to identify the pore size distribution. The increased applied potential results in the widened pores and non-uniform cell arrangement due to the increased current density and variation. Moreover, low-purity Al foils lead to the reduced AAO distribution uniformity owing to the uneven electric field induced pits on the Al surface for inferior pore arrangement. Extending both the positive and negative pulse period from 1 s to 5 s during HPA can enhance the distribution uniformity of AAO from high-purity Al by up to about 95%. In addition, the relationship between AAO configuration and Al purity and pulse voltage is further discussed and established.     

Tensile strength of fibrous composites at elevated temperature

Abstract

This paper describes an analysing methodology to simulate the tensile strength of a unidirectional fibrous composite under thermomechanical loads using properties of constituent fibre and matrix materials and fibre volume fraction only. The stress states in the constituent phases at every mechanical load level are explicitly determined by making use of a bridging matrix, whereas the thermal stresses in the constituents are obtained based on Schepery's formulae. A composite failure is assumed when any constituent material attains its ultimate stress state. The maximum normal stress theory of isotropic materials is used to detect the constituent failure. A unidirectional alumina fibre reinforced aluminium matrix composite at a number of temperatures from room temperature to 773 K subjected to off axial loads has been analysed. The predicted off axial strengths are comparable with the experiments of Mutsuda and Matsuura.     

Influence of oxygen/argon pressure ratio on the morphology, optical and electrical properties of ITO thin films deposited at room temperature

Transparent conductive oxides (TCOs) such as indium tin oxide (ITO) thin films onto glass substrates are widely used as transparent and conductive electrodes for a variety of technological applications including flat panel displays, solar cells, smart windows, touch screens, etc.ITO films on glass and polycarbonate (PC) substrates were prepared at room temperature (RT) and at different PO₂. The films were characterized in terms of the surface roughness (δ), sheet resistance, the refractive index (n) and extinction coefficient (k). The free carrier density (n_c) and the carrier mobility (μ) of the ITO (In₂O₃:Sn) films were measured and studied. The n_c and μ values vary in different ratio of oxygen partial pressure (PO₂) of ITO deposition. The observed changes in the ITO film resistivity are due to the combined effect of different parameter values for n_c and μ. From AFM analysis and spectra calculations, the surface roughness values of the ITO films were studied and it was observed that the δ values were lower than 15 nm. The energy band gap E_g ranges from 3.26 eV to 3.66 eV as determined from the absorption spectrum. It was observed an increase on the energy band gap as the PO₂ decrease in the range of 20-2% PO₂. The Lorentz oscillator classical model has also been used to fit the ellipsometric spectra in order to obtain both refractive index n and extinction coefficient κ values.     

Novel properties of AZO film sputtered in Ar+H2 ambient at high temperature

AZO (ZnO:Al) transparent conductive thin film was prepared by RF magnetron sputtering with a AZO (98 wt% ZnO 2 wt% Al₂O₃) ceramic target in the same Ar+H₂ ambient at different substrate temperatures ranging from 100 to 300 °C. The minimum resistivity of AZO films was 7.9×10⁻⁴ Ω cm at the substrate temperature of 200 °C. The average transmission in the visible rang was more than 90%. Scanning electron microscopy and XRD analyses showed that the surface morphology of the AZO samples altered with the increasing of the substrate temperature. AZO film prepared at 200 °C in the pure Ar ambient was also made as comparison about the resistivity, carrier concentration and the average crystallite size. The resistivity became about 3 times higher. The carrier concentration became lower and the average crystallite size was smaller.