Stability for solutions to nonlinear nonautonomous evolution equations

In this paper, we find an estimate on d(u(t), K(t)), where u is a mild solution to the nonautonomous Cauchy problem \({\dot{u}(t) + A(t)u(t) \ni 0,\, t \geq s, u(s) = u_0}\) . Here, A(t) is a family of nonlinear multivalued, ω-accretive operators in a Banach space X, with D(A(t)) possibly depending on t, and K(t) a family of closed subsets in X.     

Modification of a steel fiber with a graphene based bucky gel for headspace solid-phase microextraction of volatile aromatic hydrocarbons prior to their quantification by GC

A graphene based bucky gel-coated stainless steel fiber was prepared and applied to headspace solid phase microextraction of volatile organic compounds. Graphene was mixed with an ionic liquid to produce a bucky gel that displays the attractive features of both compounds. It can be directly deposited on an etched stainless steel wire to give the fiber for use in extraction of benzene, toluene, ethylbenzene and xylene (BTEX) isomers. The presence of graphene favors the π-interaction between the sorbent and aromatic analytes. The sorbent is thermally stable up to 300 °C and can be used more than 50 times. It was characterized by field emission scanning electron microscopy, FT-IR spectroscopy and thermogravimetric analysis. Under optimized conditions, linear responses were found in the range of 0.11–5000 μg L^?1 for toluene, 0.15–5000 for benzene and o-xylene, 0.17–5000 for m- and?p-xylene and 0.20–5000 for ethylbenzene. Limits of detection are between 0.03 and 0.06 μg L^?1 (at an S/N ratio of 3). The run-to-run RSDs are <5.8% (for n =?6), and fiber-to-fiber RSDs are 4.1–9.2% (n =?4). The method was successfully applied to the extraction of BTEX isomers in spiked urine samples and gave recoveries between 88 and 105%.

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Graphical abstract Graphene based bucky gel (G-BG) was prepared by mixing an ionic liquid with graphene. It was physically deposited on stainless steel wire. The fiber was applied to the headspace solid phase microextraction (HS-SPME) of benzene, toluene, ethylbenzene and xylenes.

     

Nano titania-supported sulfonic acid (n-TSA) as an efficient,inexpensive, and reusable catalyst for one-pot synthesis of 1, 8-dioxo-octahydroxanthene and tetrahydrobenzo[<Emphasis Type="Italic">b</Emphasis>]pyran derivatives

This paper explains how with the help of nano titania-supported sulfonic acid (n-TSA), new 1,8-dioxo-octahydroxanthene and tetrahydrobenzo[b]pyran derivatives can be produced. To do this, at first n-TSA, which is relatively cheap, easy separable and reusable was made. Next, using this nano catalyst,1,8-dioxo-octahydroxanthene and tetrahydrobenzo[b]pyran derivatives were synthesized from di-ketones and various aromatic aldehydes/or malononitrile without using solvent. Appropriate one-pot operation using different aromatic aldehydes with both electron donating and withdrawing groups have resulted in the best yields. Reusability of the nano catalyst, environmental friendliness, reduced reaction time, non-toxic reaction medium and catalyst high activity are substantial advantages of this work. Nowadays, it is really important that the catalyst can be recovered easily and reused five times while maintaining catalytic activity.     

Green Synthesis of New Boron-Containing Quinazolines: Preparation of Benzo[d][1,3,2]diazaborinin-4(1H)-one Derivatives

A series of new boron-containing quinazolinones, benzo[d][1,3,2]diazaborinin-4(1H)-one derivatives, were synthesized by the sequential one-pot reaction of isatoic anhydride, amines, and arylboronic acids in the absence of a catalyst and solvent. Heating isotoic anhydride and amines led to the formation of 2-aminobenzamide intermediates, which reacted easily with boronic acids to obtain the title compounds in good yields. Solvent-free conditions provided a unique procedure because the corresponding products were not obtained using various solvents either under reflux conditions or at room temperature.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details.]     

Carbon nanotube-based magnetic bucky gels in developing dispersive solid-phase extraction: application in rapid speciation analysis of Cr(VI) and Cr(III) in water samples

In this work, we developed dispersive solid-phase extraction method with the use of carbon nanotube based magnetic bucky gels. The hydrophilic carbon nanotube (CNT)-based magnetic bucky gels (M-BGs) were developed with the features of magnetic susceptibility to permit fast injection of sorbent, rapid retrieval of the sorbent and high dispersion of MWCNT in the aqueous sample. We combined magnetic multi-wall carbon nanotube nanocomposite (MMWCNTs) with hydrophilic ionic liquids in order to prepare highly stable carbon nanotube-based magnetic bucky gels. The hydrophilic ILs act simultaneously as modifier and disperser for MMWCNTs and reduce the agglomeration of sorbent in water .Consequently they enhance the extraction efficiency. We used the unique features of this responsive gel (fluidity, stability, magnetic properties, and strong sorbing ability) in developing a new, fast, sensitive, simple, and environmental-friendly magnetic bucky gel-based dispersive solid-phase extraction method (M-BG-dSPE) combined with fibre optic linear array detection spectrophotometer (FO-LADS) for preconcentration and speciation of Cr(VI) and Cr(III) in water samples. The properties of MMWCNT and magnetic bucky gels were characterised by scanning electron microscopy (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and Fourier transform infrared spectrophotometer (FT-IR). Under the optimised conditions, the enrichment factor of the method was 318, the limit of detection was 0.1 ng mL^?1 and the repeatability of the method, expressed as the relative standard deviation (RSD, n = 5), varies between 3.2% and 2.5% in different concentrations. The proposed procedure has been applied for speciation of Cr(VI) and Cr(III) in water samples with good recoveries in the range from 90 to 105%. Validation of the method was carried out by comparison of the obtained results with results obtained by the ET-AAS and spiking-recovery method.     

Ca掺杂的氧化铍纳米管吸附H2O和NH3的选择传感特

通过密度泛函计算, 借助NH₃和H₂O分子对未掺杂以及钙掺杂的BeO碳纳米管的结构和电传导性进行了研究. 结果发现,NH₃和H₂O分子可以吸附在纳米管侧壁的Be原子上,吸附能分别为约36.1和39.0 kcal/mol. 态密度分析显示BeO纳米管的电传导性在吸附后稍有变化. 对于NH₃和H₂O分子,纳米管表面的钙原子替换Be原子可使吸附能分别增加约7.4和14.7 kcal/mol. 与未掺杂纳米管不同的是,钙掺杂BeONT吸附NH₃和H₂O分子的电传导性更加敏感,且H₂O分子比NH₃分子更敏感.     

A mild and clean Baeyer–Villiger oxidation of ketones using sodium peroxydisulfate as oxidant catalyzed by silica-supported aluminum chloride

Sodium peroxydisulfate was used as the oxidant for Baeyer?CVilliger oxidation of a variety of cyclic and acyclic ketones at room temperature in the presence of Silica-supported aluminum chloride (silica-AlCl₃) as catalyst. The catalyst was prepared by a simple procedure, which exhibited high catalytic activity for the Baeyer?CVilliger oxidation of ketones using environmental friendly sodium peroxydisulfate as oxidizing agent.     

Rhodium(III) and cadmium(II) complexes based on the polypyridyl ligand 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz)

Tppz (2,3,5,6-tetrakis(2-pyridyl)pyrazine) complexes [Rh(tppz)(bpy)Cl][PF₆]₂.acetylacetone (bpy = 2,2′-bipyridine) and [{CdCl₂}₂(μ-tppz)].ethylene glycol have been synthesized and characterized by elemental analyses, IR, ¹H NMR, cyclic voltammetry, photoluminescence and electronic spectral studies. Solid state structures of both complexes have been determined by single-crystal X-ray crystallography. The structural determination shows that the dinuclear Cd(II) complex, [{CdCl₂}₂(μ-tppz)], is a 1D coordination polymer. An ORTEP drawing of [Rh(tppz)(bpy)Cl][PF₆]₂.acetylacetone shows that the coordination geometry around the Rh(III) center is a distorted octahedron. [{CdCl₂}₂(μ-tppz)] displays intraligand ¹(π–π^*) fluorescence and can potentially serve as a photoactive material. For the mononuclear Rh(III) complex, only a two-electron reduction process occurs at the metal with the elimination of Cl⁻ ligand. The emission of this complex is assigned as πd^* phosphorescence.