High performance H2 sensor based on rGO-wrapped SnO2–Pd porous hollow spheres

Hydrogen (H₂) sensors based on metal oxide semiconductors (MOS) are promising for many applications such as a rocket propellant, industrial gas and the safety of storage. However, poor selectivity at low analyte concentrations, and independent response on high humidity limit the practical applications. Herein, we designed rGO-wrapped SnO₂–Pd porous hollow spheres composite (SnO₂–Pd@rGO) for high performance H₂ sensor. The porous hollow structure was from the carbon sphere template. The rGO wrapping was via self-assembly of GO on SnO₂-based spheres with subsequent thermal reduction in H₂ ambient. This sensor exhibited excellently selective H₂ sensing performances at 390 °C, linear response over a broad concentration range (0.1–1000 ppm) with recovery time of only 3 s, a high response of ～8 to 0.1 ppm H₂ in a minute, and acceptable stability under high humidity conditions (e. g. 80%). The calculated detection limit of 16.5 ppb opened up the possibility of trace H₂ monitoring. Furthermore, this sensor demonstrated certain response to H₂ at the minimum concentration of 50 ppm at 130 °C. These performances mainly benefited from the special hollow porous structure with abundant heterojunctions, the catalysis of the doped-PdO_x, the relative hydrophobic surface from rGO, and the deoxygenation after H₂ reduction.     

Analysis of nitrogen oxide emissions from modern vehicles using hydrogen or other natural and synthetic fuels in combustion chamber

The paper presents a calculated analysis of the equilibrium emission of nitrogen oxides on the exhaust of carburetor and diesel internal combustion engines. The temperature of fuel oxidation is assumed to be 1,400 °C while the pressure for carburetor and diesel engines is assumed to be 60 atm and 80 atm respectively. The studies have been carried out for natural and synthetic fuels such as hydrogen, ethanol, methanol, petroleum, diesel fuel and methane at the excess air coefficient corresponding to the fuel oxidation temperature of 1,400 °C. In the paper, the method for calculating the equilibrium composition based on the equilibrium constant and mass conservation equations has been applied. It is shown that with an increase in pressure from 1 atm to 60 atm for carburetor engines and up to 80 atm for diesel engines, the reaction of nitrogen dioxide formation may shift towards an increase in NO₂. The formation of NO may be not affected by the increase in pressure by virtue of the fact that the reaction proceeds without changes in the amount. It has been determined that NO is the major atmospheric pollutant. However, it would be advisable to use more extensively the fuels characterized by the lowest output of nitrogen dioxide (methane and methanol), since nitrogen dioxide (NO₂) related to the 2nd hazard class is appeared to be the most dangerous to humans. It has been revealed that the reduction in oxidation temperature using hydrogen as a fuel for electrochemical current generators may allow reducing nitrogen oxide emissions by more than an order of magnitude as compared to the best results for ICE.     

Synthesis of Ionic Ultramicroporous Polymers for Selective Separation of Acetylene from Ethylene

The design of highly stable and efficient porous materials is essential for developing breakthrough hydrocarbon separation methods based on physisorption to replace currently used energy-intensive distillation/absorption technologies. Efforts to develop advanced porous materials such as zeolites, coordination frameworks, and organic polymers have met with limited success. Here, a new class of ionic ultramicroporous polymers (IUPs) with high-density inorganic anions and narrowly distributed ultramicroporosity is reported, which are synthesized by a facile free-radical polymerization using branched and amphiphilic ionic compounds as reactive monomers. A covalent and ionic dual-crosslinking strategy is proposed to manipulate the pore structure of amorphous polymers at the ultramicroporous scale. The IUPs exhibit exceptional selectivity (286.1–474.4) for separating acetylene from ethylene along with high thermal and water stability, collaboratively demonstrated by gas adsorption isotherms and experimental breakthrough curves. Modeling studies unveil the specific binding sites for acetylene capture as well as the interconnected ultramicroporosity for size sieving. The porosity-engineering protocol used in this work can also be extended to the design of other ultramicroporous materials for the challenging separation of other key gas constituents.     

Synthesis of magnetically recoverable ferrite (MFe2O4, M Co,Ni and Fe)-supported TiO2 photocatalysts for decolorization of methylene blue

Effects of ferrite materials as supports (CoFe₂O₄, NiFe₂O₄, and Fe₃O₄) on nano-TiO₂ were elucidated by their use in the oxidation of methylene blue. These photocatalysts, which were synthesized by co-precipitation, were characterized by XRD, SEM, EDS and VSM. The crystalline phase of TiO₂ onto magnetic MFe₂O₄ was formed by anatase and rutile. TiO₂/CoFe₂O₄ exhibited the strongest magnetic property of the prepared catalysts, and the photocatalytic efficiencies followed the order TiO₂/CoFe₂O₄ > TiO₂/NiFe₂O₄ > TiO₂/Fe₃O₄. MB decolorization was enhanced with the amount of TiO₂ on the photocatalyst, and was moderately affected by the extent of structural distortion of ferrite supports.     

密度泛函理论研究金属镧离子的水合团簇

Y型分子筛具有许多工整均匀的孔道结构,经常作为酸催化剂、双功能助推剂和择形催化剂,被广泛应用于干燥、洁净过滤、吸附分离和催化等领域。工业生产中稀土Y型分子筛的制备一般选用稀土离子水溶液与NaY型分子筛通过离子交换置换制取,但稀土离子水合结构以及通过分子筛孔的微观机理仍不清楚。本工作采用密度泛函理论(DFT)在M06-2X-D3/def2-SVP计算水平下,La3+采用LANL2DZ赝势基组,采用SMD=water隐式溶剂模型研究了La3+水合团簇及其不同价态时的结构性质,对水合团簇结构尺寸、Mulliken电荷、结合能以及能量分解进行了分析。结果表明,La3+水合团簇结构柔性较大,并非大于某个水合数无法通过分子筛孔;随水合数目的增大,La-O(H2O)平均半径有着增大的趋势,La3+在水溶液中总是趋于更稳定的多水合团簇结构;La-O(OH-)形成的键能比La-O(H2O)强;在[La(H2O)n]3+水合数目小于等于9时,团簇结构中以静电为主导作用,其次是诱导作用和交换互斥作用,色散作用所占比例最小;当水合数目大于9时,诱导作用所占比例升高,静电作用所占比例降低。研究结果对于深入认识稀土水合结构和分子筛制备机理具有重要理论指导意义。     

Room-temperature hydrogenation of halogenated nitrobenzenes over metal–organic-framework-derived ultra-dispersed Ni stabilized by N-doped carbon nanoneedles

Ultra-dispersed Ni nanoparticles (7.5 nm) on nitrogen-doped carbon nanoneedles (Ni@NCNs) were prepared by simple pyrolysis of Ni-based metal–organic-framework for selective hydrogenation of halogenated nitrobenzenes to corresponding anilines. Two different crystallization methods (stirring and static) were compared and the optimal pyrolysis temperature was explored. Ni@NCNs were systematically characterized by wide analytical techniques. In the hydrogenation of p-chloronitrobenzene, Ni@NCNs-600 (pyrolyzed at 600 °C) exhibited extraordinarily high performance with 77.9 h^–1 catalytic productivity and > 99% p-chloroaniline selectivity at full p-chloronitrobenzene conversion under mild conditions (90 °C, 1.5 MPa H₂), showing obvious superiority compared with reported Ni-based catalysts. Notably, the reaction smoothly proceeded at room temperature with full conversion and > 99% selectivity. Moreover, Ni@NCNs-600 afforded good tolerance to various nitroarenes substituted by sensitive groups (halogen, nitrile, keto, carboxylic, etc.), and could be easily recycled by magnetic separation and reused for 5 times without deactivation. The adsorption tests showed that the preferential adsorption of –NO₂ on the catalyst can restrain the dehalogenation of p-chloronitrobenzene, thus achieving high p-chloroaniline selectivity. While the high activity can be attributed to high Ni dispersion, special morphology, and rich pore structure of the catalyst.     

Rational design on photoelectrodes and devices to boost photoelectrochemical performance of solar-driven water splitting: a mini review

As an eco-friendly, efficient, and low-cost technique, photoelectrochemical water splitting has attracted growing interest in the production of clean and sustainable hydrogen by the conversion of abundant solar energy. In the photoelectrochemical system, the photoelectrode plays a vital role in absorbing the energy of sunlight to trigger the water splitting process and the overall efficiency depends largely on the integration and design of photoelectrochemical devices. In recent years, the optimization of photoelectrodes and photoelectrochemical devices to achieve highly efficient hydrogen production has been extensively investigated. In this paper, a concise review of recent advances in the modification of nanostructured photoelectrodes and the design of photoelectrochemical devices is presented. Meanwhile, the general principles of structural and morphological factors in altering the photoelectrochemical performance of photoelectrodes are discussed. Furthermore, the performance indicators and first principles to describe the behaviors of charge carriers are analyzed, which will be of profound guiding significance to increasing the overall efficiency of the photoelectrochemical water splitting system. Finally, current challenges and prospects for an in-depth understanding of reaction mechanisms using advanced characterization technologies and potential strategies for developing novel photoelectrodes and advanced photoelectrochemical water splitting devices are demonstrated.     

miR-145通过调节SOD活性介导人参皂苷Rb1对脑缺血再灌注损伤大鼠的脑保护作用

目的: 探讨人参皂苷Rb1是否通过减少miR-145含量来上调脑缺血再灌注损伤大鼠脑组织SOD活性发挥脑保护作用。方法: 将60只SD大鼠按随机数字表法分成模型组、生理盐水对照组、人参皂苷Rb1组、人参皂苷Rb1+miR-145模拟物组、人参皂苷Rb1+miR-145质控品组,每组12只。采用大脑中动脉闭塞（MCAO）法建立大鼠脑缺血再灌注损伤模型。人参皂苷Rb1组和生理盐水对照组大鼠在制模后即刻分别腹腔注射人参皂苷Rb1（40 mg/kg）和等量生理盐水;人参皂苷Rb1+miR-145模拟物组和人参皂苷Rb1+miR-145质控品组大鼠在制模前2 d分别侧脑室注射miRNA 145模拟物和miRNA 145质控品,其他操作同人参皂苷Rb1组。再灌注损伤后24 h测各组大鼠神经行为学评分,其中6只大鼠测量脑梗死体积;另6只大鼠取大脑皮质,测定miR-145、超氧化物歧化酶（SOD）含量。结果: 与模型组比较,人参皂苷Rb1组大鼠行为学评分明显降低（P＜0.05）,脑梗死体积明显减小（P＜0.05）,miR-145含量明显减少（P＜0.05）,SOD活性明显增加（P＜0.05）。与人参皂苷Rb1组,人参皂苷Rb1+miR-145模拟物组大鼠行为学评分明显升高（P＜0.05）,脑梗死体积明显增加（P＜0.05）,miR-145含量明显增加（P＜0.05）,SOD活性显著下降（P＜0.05）。结论: 人参皂苷Rb1可以通过减少miR-145含量来上调脑缺血再灌注损伤大鼠脑组织SOD活性发挥脑保护作用。     

Deploy Efficiency Driven k-Barrier Construction Scheme Based on Target Circle in Directional Sensor Network

Journal of Computer Science and Technology - With the increasing demand for security, building strong barrier coverage in directional sensor networks is important for effectively detecting...