Hydrothermal synthesis of hierarchical SnO2 nanomaterials for high-efficiency detection of pesticide residue

Acephate pesticide contamination in agricultural production has caused serious human health problems. Metal oxide semiconductor (MOS) gas sensor can be used as a portable and promising alternative tool for efficiently detection of acephate. In this study, hierarchical assembled SnO₂ nanosphere, SnO₂ hollow nanosphere and SnO₂ nanoflower were synthesized respectively as high efficiency sensing materials to build rapid and selective acephate pesticide residues sensors. The morphologies of different SnO₂ 3D nanostructures were characterized by various material characterization technology. The sensitive performance test results of the 3D SnO₂ nanomaterials towards acephate show that hollow nanosphere SnO₂ based sensor displayed preferable sensitivity, selectivity, and rapid response (9 s) properties toward acephate at the optimal working temperature (300 °C). This SnO₂ hollow nanosphere based gas sensor represents a useful tool for simple and highly effective monitoring of acephate pesticide residues in food and environment. According to the characterization results, particularly Brunauer-Emmett-Teller (BET) and Ultraviolet-Visible Spectroscopy (UV–vis), the obvious and fast response can be attributed to the mesoporous hollow nanosphere structure and appropriate band gap of SnO₂ hollow nanosphere.     

Low-temperature and stable CO oxidation of Co3O4/TiO2 monolithic catalysts

Highly efficient Co₃O₄/TiO₂ monolithic catalysts with enhanced stability were in-situ grown on Ti mesh for CO oxidation,which could completely oxidize CO at 120℃.The comprehensive catalytic performance is competitive to some noble metal catalysts and conventional Co₃O₄ powder catalysts,which holds great potential toward industrial applications.Meanwhile,the in-situ synthesis strategy of Co₃O₄/TiO₂ monolithic catalysts on flexible mesh substrate in this work can be extended to the development of a variety of oxide-based monolithic catalysts towards diverse catalysis applications.     

β-环糊精修饰碳糊电极测定盐酸青藤碱

研究盐酸青藤碱在β-环糊精(β-CD)修饰碳糊电极上的电化学行为,在此基础上建立了测定盐酸青藤碱的电化学新方法。盐酸青藤碱在β-CD修饰碳糊电极上是受吸附控制的电化学反应过程,在p H 6.6的柠檬酸–柠檬酸钠底液中,盐酸青藤碱在β-CD修饰碳糊电极上产生一对良好的氧化还原峰,峰电位分别为0.458 V和0.086 V。氧化峰电流与盐酸青藤碱的质量浓度在3.658 5~91.462 5 mg/L范围内呈良好线性关系,线性相关系数为0.995 4,检出限为1.229 3 mg/L。该方法应用于正清风痛宁片中盐酸青藤碱含量的测定,测定结果的相对标准偏差为5.82%(n=7),回收率在95.7%~107.4%之间。该方法简便、快速,结果准确,可用于盐酸青藤碱的测定。     

A novel strategy for boosting the photoluminescence quantum efficiency of CdSe nanocrystals at room temperature

Highly luminescent colloidal nanocrystals have wide applications in bioimaging and various optoelectronic devices.Herein we report a facile and mild procedure by combining S2-treatment and binary ligand passivation,which can efficiently enhance the luminescent property of CdSe nanocrystals at room temperature.The photoluminescence quantum yield of as-treated CdSe nanocrystals exhibits drastic enhancement(e.g.,188 times for CdSe nanorods)after this dual-passivation treatment.The methodology proposed here can be applied to various CdSe nanocrystals,regardless of their sizes,shapes,and crystal structures.     

Dispersion of carbon nanotubes by carbazole-tailed amphiphilic imidazolium ionic liquids in aqueous solutions

Spectrophotometric, kinetic, and transmission electron microscopic (TEM) data for the formation of Ag-nanoparticles using aspartic acid (Asp) as reductant are reported for the first time. In the formation of transparent silver sols, an alkaline medium is required. The silver nanoparticles are spherical, uniform particle size, and strongly depend on the [Asp]. The apparent rate constant decreases with [Asp] (from 4.0 to 24.0×10(-4)moldm(-3), the rate constants decreased from 2.6×10(-4) to 0.3×10(-4)s(-1)). For a certain reaction time, i.e., 30min, the absorbance of the silver sol first increased until it reached a maximum, and then decreased with [Asp]. Kinetic and TEM results indicate that the size of the Ag-nanoparticles depends on the [Asp]. It is proposed that the oxidation of Asp occurs by the adsorbed Ag(+) ions on the surface of Ag(2)O particles.     

Heterogeneous interaction between zwitterions of amino acids and glycerol in aqueous solutions at 298.15 K

The enthalpies of mixing of six kinds of amino acid (glycine, L-alanine, L-valine, L-serine, L-threonine, and L-proline) with glycerol in aqueous solutions and the enthalpies of diluting of amino acid and glycerol aqueous solutions have been determined by flow microcalorimetry at 298.15 K. Employing McMillan–Mayer theory, the enthalpies of mixing and diluting have been used to calculate heterogeneous enthalpic pairwise interaction coefficients (h _xy ) between amino acids and glycerol in aqueous solutions. Combining h _xy values of amino acids with glycol in the previous study, the variations of the h _xy values between amino acids and glycerol have been interpreted from the point of view of solute–solute interactions.     

Regioselective oxyalkylation of vinylarenes catalyzed by diatomite-supported manganese oxide nanoparticles

A regioselective oxyalkylation reaction of vinylarenes with cyclic ethers was developed under the catalysis of a new heterogeneous catalyst, the diatomite-supported Mn(3)O(4) nanoparticles (SMONP-1). The use of this heterogeneous catalyst provided a novel approach for the synthesis of α-carbonyled β-alkylated aryl derivatives via a sp(3) C-H bond functionalization under mild aerobic conditions.     

Two new diterpenoids from the buds of Wikstroemia chamaedaphne

Two new diterpenoids, wikstroelide Q (1) and prostratin Q (5), together with three known diterpenoids, pimelea factors P? (2), P? (3), and prostratin (4), and five known lignans, (+)-epipioresinol (6), (+)-isolariciresinol (7), (?)-lariciresinol (8), (+)-epi-sesaminone (9), and prestegane B (10), were isolated from the buds of Wikstroemia chamaedaphne Meissn. Their structures were elucidated by a combination of spectroscopic analyses. Compounds 1–10 were evaluated for their cytotoxicities against HL-60, SMMC-7721, A549, MCF-7, SW480, and BEAS-2B cell lines in vitro.     

Rh(111)及Rh@Cu(111)表面乙烯氢甲酰化反应选择性的理论研究

采用密度泛函理论对比研究了Rh(111)表面与Rh@Cu(111)表面合金上乙基加氢反应及CO插入反应过程.结果发现,与Rh(111)表面相比,Rh@Cu(111)表面合金的集团效应和配体效应使得加氢反应的能垒降低了0.12eV,而CO插入反应的却显著降低了0.78eV.这表明RhCu合金催化剂可以有效地提高氢甲酰化反应的选择性.     

Constrained Markov decision processes with first passage criteria

This paper deals with constrained Markov decision processes (MDPs) with first passage criteria. The objective is to maximize the expected reward obtained during a first passage time to some target set, and a constraint is imposed on the associated expected cost over this first passage time. The state space is denumerable, and the rewards/costs are possibly unbounded. In addition, the discount factor is state-action dependent and is allowed to be equal to one. We develop suitable conditions for the existence of a constrained optimal policy, which are generalizations of those for constrained MDPs with the standard discount criteria. Moreover, it is revealed that the constrained optimal policy randomizes between two stationary policies differing in at most one state. Finally, we use a controlled queueing system to illustrate our results, which exhibits some advantage of our optimality conditions.