Combustion Synthesis and Catalytic Activity of LaCoO3 for HMX Thermal Decomposition

Perovskite‐type LaCoO₃ was prepared by stearic acid solution combustion method and characterized by XRD, DSC‐TG, and XPS techniques. The catalytic activities of LaCoO₃ for HMX (octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine) thermal decomposition were investigated. The as‐prepared LaCoO₃ shows higher activity than the calcined one. This could be due to higher concentration of surface‐adsorbed oxygen and hydroxyl species as well as higher BET surface area of the as‐prepared LaCoO₃.     

铁酸铋/石墨烯纳米复合材料的制备及其对高氯酸铵热分解的催化作用

为了提高纳米复合金属氧化物对高氯酸铵(AP)热分解的催化作用,以Bi(NO₃)₃·5H₂O、Fe(NO₃)₃·9H₂O和GO为前驱体,采用水热法制备了铁酸铋/石墨烯(BiFeO₃/rGO)纳米复合材料;利用XRD、FT-IR、XPS、TGA、SEM和TEM等对所制备样品的结构、粒径及形貌进行了表征;采用差热分析研究了不同添加量的BiFeO₃/rGO纳米复合材料对AP热分解过程的影响,分析了BiFeO₃/rGO对AP热分解的催化机理及其对AP热分解动力学的影响。结果表明,rGO的引入有效阻止了纳米BiFeO₃颗粒的团聚,大大增加了比表面积;当BiFeO₃/rGO纳米复合材料的质量分数为4%时,AP的高温分解峰降低最多,达167℃,表观分解热增加了1631J/g,达2518J/g,表观活化能从172.07kJ/mol降低至128.35kJ/mol,表明所制备的BiFeO₃/rGO纳米复合材料能有效催化AP的热分解。     

Hybrid Microwave Sintering of Infrared Transparent Nano‐Y3Al5O12 Synthesized by a Modified Combustion Technique

Infrared transparent ceramics found to have numerous civilian and defense applications. In the present work, Y₃Al₅O₁₂ nanoparticles were synthesized by an auto‐igniting modified single‐step combustion method. The structure and morphology of the as‐prepared powder revealed the phase purity and ultrafine nature of the powder having an average crystallite size of 16 nm and well‐defined lattice planes. Coupling of the resistive and microwave heating at precise proportion leads to a sintered density of the powder with 99.3% of the theoretical density at a temperature as low as 1470°C for a soaking duration of just 20 min. Marked reduction in grain size and the porosity was also observed for the hybrid sintered pellets. An average grain size of 167 nm was measured for the sintered pellets, which also showed a high transmittance of 80% in the UV–vis region and 82.5% in the mid‐IR region.     

溶胶-凝胶燃烧法制备SmBO3粉体的工艺条件及其光吸收性能

研究了溶胶-凝胶燃烧法制备SmBO3前驱体过程中的各种影响因素,考察了煅烧温度及煅烧时间对所合成的SmBO3粉体光吸收性能的影响. 结果表明,当加热温度为80℃、H2O/(Sm+B)摩尔比为30、pH值为2、柠檬酸/(Sm+B) 摩尔比为1:1时获得的凝胶在180℃下发生稳定的自燃烧反应,得到白色蓬松的前驱体. 前驱体经750℃煅烧2 h后得到的SmBO3粉体平均颗粒尺寸为100 nm. 在1.05~1.15 mm波长范围,SmBO3粉体对光存在较强的吸收,在1.07 mm波长附近反射率达最低值,约为0.41%,而在1.06 mm波长处反射率约为0.6%.     

Catalytic Decomposition of Airborne Ozone by MnCO3 and its Mechanism

Ozone is an ubiquitous air pollutant. To develop a new kind of catalyst besides the usually used MnO₂ for ozone decomposition, the sub-micrometer spherical MnCO₃ was prepared via a facile co-precipitation method without additive agents at room temperature and characterized by XRD, BET, SEM, TGA, XPS and H₂-TPR. As-prepared MnCO₃ showed better catalytic activity for ozone decomposition than that of α-MnO₂, which is frequently studied in the literature. Amorphous MnO_x was found on the MnCO₃ surface, and it further formed when MnCO₃ was exposed to the ozone flow. The MnO_x layer is regarded as the active component in the catalytic ozone decomposition and crystalline MnCO₃ serves as the support-stabilizing MnO_x surface phase. Then MnCO₃ powder was supported on non-woven fabrics through a simple and low-cost impregnation method. The MnCO₃-based non-woven fabrics exhibited 100% ozone conversion over 8 days at 25 °C with inlet ozone concentration 14 ppm and space velocity 42,000 h^?1. This provides an alternative material for ozone-induced air cleaning.     

Degradation of Refractory Organic Pollutants by Catalytic Ozonation—Activated Carbon and Mn-Loaded Activated Carbon as Catalysts

A novel catalyst for the ozonation process was prepared by loading manganese on the granular activated carbon (GAC). Nitrobenzene was used as a model refractory organic micropollutant in this study. The catalytic activity of GAC and the Mn-loaded GAC were studied respectively. The removal efficiency of nitrobenzene by Mn-loaded GAC catalyzed ozonation could reach 34.2–49.9%, with the oxidation efficiency being about 1.5–2.0 times higher than that achieved in GAC catalyzed ozonation and 2.0–3.0 times higher than that achieved by ozonation alone. The effect of pH and the t -butanol on the GAC/ozone process was discussed. The optimum condition for preparing the catalyst was studied.     

草酸盐热分解法制备介孔CeO_2催化剂及其脱硝性能研究

用热分解法,对草酸铈进行缓慢热分解,制备出比表面积较高,孔道分布均匀的介孔结构CeO2材料。此法无需引入表面活性剂做造孔模板,步骤简单,成本较低。通过TG-DSC,XRD,N2吸附-脱附,扫描电镜和透射电镜等法对材料的结构和形貌进行表征。此外,还对在不同焙烧温度下制备的介孔CeO2材料进行了氨气选择性催化还原(SCR)脱硝性能测试,结果表明500℃焙烧制备的介孔CeO2的催化活性最好,在275~425℃温度范围之间,NO的转化率维持在100%。     

Characterization of Combustion Aerosol Produced by a Mini-CAST and Treated in a Catalytic Stripper

We characterized the properties of combustion aerosol produced at different operating conditions of a mini-CAST burner that was treated in a Catalytic Stripper (CS) operating at 300°C. The goal was to establish a methodology for the production of soot particles resembling those emitted from internal combustion engines. Thermo-optical analysis of samples collected on Quartz filters revealed that the particles contained semi-volatile material that survived the CS. The amount of semi-volatile species strongly depended on the operating conditions ranging from less than 10% to as high as 30% of the particle mass. The mini-CAST operating conditions were also found to have a strong effect on the effective particle density (ρ_e ). The ρ_e , for example, ranged from as low as 0.3 to 1.05 g/cm³ for mondisperse 80 nm particles, although the mass-mobility exponent remained relatively constant (2.1–2.25). These differences are indicative of differences in the primary particle diameter, which was estimated to range between 8.5 and 34 nm depending on the operating conditions. The different types of particles produced were also found to exhibit different affinities for butanol but also different light absorption per mass of elemental carbon which can, therefore, lead to inconsistencies in aerosol instrumentation calibrations (e.g., condensation and optical particle counters, photoacoustic sensors). The work highlights the importance of establishing a detailed and well-defined method in using the mini-CAST-CS approach for instrument calibration in ways mimicking various engine combustion sources.

Copyright 2013 American Association for Aerosol Research     

Enhanced Permeability and Dielectric Constant of NiZn Ferrite Synthesized in Nanocrystalline Form by a Combustion Method

The performance parameters of Ni_0.5Zn_0.5Fe₂O₄, synthesized in the nanocrystalline form by an autocombustion method, have been investigated. The sample sintered at 1200°C, with Bi₂O₃ as additive shows a very high value of initial permeability μ' _i of >400 at 1 MHz, with low loss. Similarly, a very high dielectric constant is obtained at lower frequencies. The results show that optimum magnetic and electrical properties can be achieved for the NiZn ferrite nanocrystalline powders synthesized by the present autocombustion method and sintered at a relatively lower temperature of 1200°C when compared with a temperature of 1400°C required for the materials synthesized by the conventional ceramic method.     

Combustion Synthesis and Enhancement of BiOCl by Doping Eu3+ for Photodegradation of Organic Dye

Eu³⁺‐doped BiOCl with different doping concentrations was synthesized by a simple combustion method. The as‐synthesized photocatalysts were characterized by X‐ray diffraction, scanning electron microscope, transmission electron microscope, Raman spectroscopy, X‐ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, and UV–vis diffuse reflectance spectroscopy. The experimental results show that Eu³⁺ was successfully doped into the lattice of BiOCl. The as‐synthesized Eu³⁺‐doped BiOCl photocatalysts show a more intense continuous absorption in UV light region, accompanied with decreased energy band gap. Moreover, the Eu³⁺ doping leads to the formation of oxygen vacancies, small crystallite size, and high specific surface areas. Compared with pure BiOCl, the Eu³⁺‐doped BiOCl photocatalysts exhibits much higher photocatalytic activity for Rhodamine B (RhB) under UV light irradiation. As‐obtained Eu³⁺‐doped BiOCl can be easily reused with excellent stability. In addition, the mechanism of the improved photocatalytic properties of Eu³⁺‐doped BiOCl was discussed in detail.     

DC Electrical Resistivity and Magnetic Property of Single-Phase α-Fe2O3 Nanopowder Synthesized by a Simple Chemical Method

Nanocrystalline pure α-Fe₂O₃ powder, with an average particle size of 35 nm, has been synthesized by using an aqueous solution-based synthetic route. DC electrical resistivity of the synthesized material was measured with respect to temperature by the two-probe method from 28° to 225°C. Room temperature resistivity of the nanopowder was ∼10⁸Ω·cm. Magnetic hysteresis measurement revealed that the synthesized α-Fe₂O₃ nanopowder exhibited ferromagnetic behavior at room temperature. The hysteretic features are high saturation magnetization of 5.1 emu/g, high remanence of 2.2 emu/g, and coercivity of 200.5 Oe.     

Removal Characteristics of Organic Pollutants in Sewage Treatment by a Pre-Coagulation,Ozonation and Ozone/Hydrogen Peroxide Process

The applicability of a sequential process of ozonation and ozone/hydrogen peroxide process for the removal of soluble organic compounds from a pre-coagulated municipal sewage was examined. 6–25% of initial T-COD_Cr was removed at the early stage of ozonation before the ratio of consumed ozone to removed T-COD_Cr dramatically increased. Until dissolved ozone was detected, 0.3 mgO₃/mgTOC₀ (Initial TOC) of ozone was consumed. When an ozone/hydrogen peroxide process was applied, additional COD_Cr was removed. And we elucidated that two following findings are important for the better performance of ozone/hydrogen peroxide process; those are to remove readily reactive organic compounds with ozone before the application of ozone/hydrogen peroxide process and to avoid the excess addition of hydrogen peroxide. Based on these two findings, we proposed a sequential process of ozonation and multi-stage ozone/hydrogen peroxide process and the appropriate addition of hydrogen peroxide. T-COD_Cr, TOC and ATU-BOD₅ were reduced to less than 7 mg/L, 6 mgC/L and 5 mg/L, respectively after total treatment time of 79 min. Furthermore, we discussed the transformation of organic compounds and the removal of organic compounds. The removal amount of COD_Cr and UV₂₅₄ had good linear relationship until the removal amounts of COD_Cr and UV₂₅₄ were 30 mg/L and 0.11 cm^?1, respectively. Therefore UV₂₅₄ would be useful for an indicator for COD_Cr removal at the beginning of the treatment. The accumulation of carboxylic acids (formic acid, acetic acid and oxalic acid) was observed. The ratio of carbon concentration of carboxylic acids to TOC remaining was getting higher and reached around 0.5 finally. Removal of TOC was observed with the accumulation of carboxylic acids. When unknown organic compounds (organic compounds except for carboxylic acids) were oxidized, 70% was apparently removed as carbon dioxide and 30% was accumulated as carboxylic acids. A portion of biodegradable organic compounds to whole organic compounds was enhanced as shown by the increase ratio of BOD/COD_Cr.     

Emulsifying Activity and Stability of a Non-Toxic Bioemulsifier Synthesized by Microbacterium sp. MC3B-10

A previously reported bacterial bioemulsifier, here termed microbactan, was further analyzed to characterize its lipid component, molecular weight, ionic character and toxicity, along with its bioemulsifying potential for hydrophobic substrates at a range of temperatures, salinities and pH values. Analyses showed that microbactan is a high molecular weight (700 kDa), non-ionic molecule. Gas chromatography of the lipid fraction revealed the presence of palmitic, stearic, and oleic acids; thus microbactan may be considered a glycolipoprotein. Microbactan emulsified aromatic hydrocarbons and oils to various extents; the highest emulsification index was recorded against motor oil (96%). The stability of the microbactan-motor oil emulsion model reached its highest level (94%) at 50 °C, pH 10 and 3.5% NaCl content. It was not toxic to Artemia salina nauplii. Microbactan is, therefore, a non-toxic and non-ionic bioemulsifier of high molecular weight with affinity for a range of oily substrates. Comparative phylogenetic assessment of the 16S rDNA gene of Microbacterium sp. MC3B-10 with genes derived from other marine Microbacterium species suggested that this genus is well represented in coastal zones. The chemical nature and stability of the bioemulsifier suggest its potential application in bioremediation of marine environments and in cosmetics.     

Microstructural,Optical, Morphological,Luminescence and Electrical Properties of a CdO Nanocomposite Synthesized by a Chemical Route Assisted Microwave Irradiation Technique

This article reports a CdO nanocomposite successfully synthesized by a chemical route assisted microwave irradiation technique. Sodium dodecyl benzene sulfonate (SDBS) is a good surfactant and it is used in forming the nanocomposite. The microwave irradiation technique is simple and less time consuming for preparing a nanocomposite. The obtained products were characterized by different techniques such as X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), UV-Vis DRS, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), room temperature photoluminescence (PL), and DC electrical conductivity. The grain size determined by the XRD pattern was found to be 20–40 nm. The lattice fringes and nanocomposite morphology particle size were obtained by TEM. The room temperature PL spectra reveal blue and red emissions. The calculated average electrical conductivity was around 5.1 × 10⁻⁸ to 2.02 × 10⁻⁸ S/cm.

     

Structural,dielectric, vibrational and magnetic properties of Sm doped BiFeO3 multiferroic ceramics prepared by a rapid liquid phase sintering method

Rare earth Sm substituted Bi_1−xSm_xFeO₃ with x=0, 0.025, 0.05, 0.075 and 0.10 polycrystalline ceramics were synthesized by a rapid liquid phase sintering method. The effect of varying composition of Sm substitution on the structural, dielectric, vibrational, optical and magnetic properties of doped BiFeO₃ (BFO) ceramics have been investigated. X-ray diffraction patterns of the synthesized rare earth substituted multiferroic ceramics showed the pure phase formation with distorted rhombohedral structure with space group R3c. Good agreement between the observed and calculated diffraction patterns of Sm doped BFO ceramics in Rietveld refinement analysis of the X-ray diffraction patterns and Raman spectroscopy also confirmed the distorted rhombohedral perovskite structure with R3c symmetry. Dielectric measurements showed improved dielectric properties and magnetoelectric coupling around Néel temperature in all the doped samples. FTIR analysis establishes O–Fe–O and Fe–O stretching vibrations in BiFeO₃ and Sm-doped BiFeO₃. Photoluminescence (PL) spectra showed visible range emissions in modified BiFeO₃ ceramics. The magnetic hysteresis measurements at room temperature and 5 K showed the increase in the magnetization with the increase in doping concentration of Sm which is due to the structural distortion and partial destruction of spin cycloid caused by Sm doping in BFO ceramics.     

Catalytic Production of Carbon Nanotubes by Decomposition of CH4 over the Pre-reduced Catalysts LaNiO3, La4Ni3O10, La3Ni2O7 and La2NiO4

A large amount of more graphitic carbon nanotubes with a narrow size distribution was produced from catalytic decomposition of CH₄ over pre-reduced LaNiO₃, La₄Ni₃O₁₀, La₃Ni₂O₇ and La₂NiO₄. The structure and component of fresh and reduced LaNiO₃, La₄Ni₃O₁₀, La₃Ni₂O₇ and La₂NiO₄ were determined by X-ray diffraction (XRD). The carbon nanotubes obtained were characterized by means of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Thermal oxidation of carbon nanotubes in air was made by thermogravimetric experiments (TG). The results revealed that the value of La/Ni in different catalyst precursors influences the diameter distribution and graphitic degree of carbon nanotubes. Lower La/Ni leads to wider diameter and higher graphitic degree of carbon nanotubes.     

Aerosol Generation by a Spray-Drying Technique Under Coulomb Explosion and Rapid Evaporation for the Preparation of Aerosol Particles for Inhalation Tests

In this study, nanosized (<100 nm) aerosol particles with high mass concentrations for inhalation tests were generated by a spray-drying technique with combining Coulomb explosion and rapid evaporation of the droplets. Under typical spray-drying conditions, aerosol particles with average diameter of 50–150 nm were prepared from a suspension of NiO nanoparticles with a primary diameter of 15–30 nm. Under the Coulomb explosion method, the sprayed droplets were charged by being mixed with unipolar ions to break up the droplets, which resulted in the generation of smaller aerosol particles with diameters of 15–30 nm and high number concentrations. Under the rapid evaporation method, the droplets were heated immediately after being sprayed to avoid inertial impaction on the flow path due to shrinkage of the droplet, which increased the mass concentration of the aerosol particles. The combination of the Coulomb explosion and rapid evaporation of droplets resulted in the generation of aerosol particles with sizes less than 100 nm and mass concentrations greater than 1 mg/m³; these values are often necessary for inhalation tests. The aerosols generated under the combined method exhibited good long-term stability for inhalation tests. The techniques developed in this study were also applied to other metal oxide nanoparticle materials and to fibrous multiwalled carbon nanotubes.

Copyright 2014 American Association for Aerosol Research     

微电解-生物膜复合工艺净化含重金属离子的有机废水

A complex process of micro electrolysis and biofilm was developed to continuously treat organic wastew-aters containing heavy metal ions such as Cu^2 and Cr^3 ,and the relevant purifying mechanism was also addressed. In detail,organic materials in wastewater could be consumed as nutritious source by biofilm composed of aerobes and anaerobes,However,for heavy metal ions (Cu^2 ,Cr^3 ),part was removed by electrodeposition,and some was adorbed on biofilm.In order to compare with the combined process of micro electrolysis and biofilm,the experimental data of micro electrolysis process (intermittent )or biofilm process (continuous)were provided,and the kinetic data of C6H12O6(glucose)biodegradation by cultured microbes or acclimated microbes were also obtained,These experimental results indicated that for wastewater initially consisted of C6H12O6(500 mg.L^-1),Cu^2 and Cr^3 (10mg.L6-1),after treatment,its concentrations of C6H12O6,Cu^2 and Cr^3 were lowered to the leve of 55-65 mg.L^-1),after treatment,its concentrations of C6H12O6,Cu^2 and Cr^3 were lowered to the level of 55-65 mg.L^-1,and less than 1mg.L^-1,respectively,And the industrial reused water standards could be met by treated wastewater.     

Structural,dielectric, magnetic,and ferroelectric properties of bismuth ferrite (BiFeO3) synthesized by a solvothermal process using hexamethylenetetramine (HMTA) as precipitating agent

Multiferroic BiFeO₃ (BFO) has been synthesized by the solvothermal technique for 4 h at 180 °C using Hexamethylenetetramine (HMTA) as a precipitating agent. Optimizations on HMTA concentration were performed to attain BFO in a narrow possible time using the solvothermal method. The effect of HMTA concentration on structural properties was investigated by XRD, FE-SEM, FT-IR, and Raman techniques. Moreover, the magnetic, ferroelectric, dielectric, and optical properties were studied by VSM, Ferroelectric analyser, Dielectric spectrometer, and UV–Vis–NIR spectrometer, respectively. The XRD data has unveiled the significant role of HMTA, as a precipitating agent, in obtaining the pure phase BFO at a particular concentration. A high concentration of HMTA (6 M) is found to be more favourable for producing pure phase BFO within the short reaction time of 4 h without any impurity phase formations. The FE-SEM images have shown the formation of granular structures that are inhomogeneously distributed throughout the powdered BFO with porosities. In addition, the magnetic measurements confirmed that the BFO synthesized with varying HMTA concentration exhibits a reasonable week ferromagnetic behaviour. However, the pure BFO powder synthesized at 6 M HMTA shows high magnetization value (0.72 emu/g) compared to the other samples synthesized at low concentrations of HMTA. Further, the dielectric measurements of all the synthesized BFO samples have shown a decrease in dielectric loss with an increase in frequency. Whereas the dielectric behaviour exhibited by the pure BFO synthesized at 6 M HMTA has shown a high dielectric constant value with moderate dielectric loss. A ferroelectric analyser studies the ferroelectric behaviour of BFO powder. The study revealed that pure phase BFO synthesized with 6 M HMTA exhibits a high value of remanent polarization with unsaturated P-E loops due to the high leakage current in the sample. The UV–Vis data shows that the BFO samples exhibited an excellent optical absorption in the visible range with narrow optical band gaps. Therefore, all the characterizations related to magnetic, structural, dielectric, ferroelectric, and optical properties of synthesized pure BFO have proven the significance of precipitating agent HMTA in the solvothermal synthesis method. Based on our findings, the synthesized pure phase BFO can be an excellent semiconducting photocatalyst for multiferroic based photocatalysis applications.