Limonene in Arizona liquid systems used in countercurrent chromatography. I Physicochemical properties

Limonene is a biorenewable cycloterpene solvent derived from orange peel waste. Its potential as a “green” solvent to replace heptane was recently evaluated. Countercurrent chromatography (CCC) is a preparative separation technique using biphasic liquid systems. One liquid phase is the mobile phase; the other liquid phase is the stationary phase held in place by centrifugal fields. A particular range of special proportions of the heptane/ethyl acetate/methanol/water system is called the Arizona (AZ) liquid system when the heptane/ethyl acetate ratio is exactly the same as the methanol/water ratio. A continuous polarity decrease is obtained between the most polar A composition (ethyl acetate/water or 0/1/0/1 v/v) and the least polar Z composition (heptane/methanol or 1/0/1/0 v/v), replacing heptane by limonene and methanol by ethanol produce biphasic liquid systems much more environmentallyfriendly than the original AZ compositions. The chemical compositions of the two liquid phases of 12 AZ limonene/ethyl acetate/ethanol/water proportions were fully determined by Karl-Fisher titration of water and by gas chromatography for the organic solvents. The results were compared with the compositions of the corresponding AZ mixtures containing heptane and methanol. Significant differences in ethyl acetate and ethanol distribution between phases of the two systems with identical volume proportions were established. The ratio of the upper phase over the lower phase volumes and the phase density difference are important in CCC, there are also significant differences between the classic and “green” AZ systems that are discussed.     

Characterization of crystalline and amorphous content in pharmaceutical solids by dielectric thermal analysis

Morphological and thermodynamic transitions in drugs as well as their amorphous and crystalline content in the solid state have been distinguished by thermal analytical techniques, which include dielectric analysis (DEA), differential scanning calorimetry (DSC), and macro-photomicrography. These techniques were used successfully to establish a structure versus property relationship with the United States Pharmacopeia standard set of active pharmaceutical ingredient (API) drugs. A distinguishing method is the DSC determination of the amorphous and crystalline content which is based on the fusion properties of the specific drug and its recrystallization. The DSC technique to determine the crystalline and amorphous content is based on a series of heat and cool cycles to evaluate the drugs ability to recrystallize. To enhance the amorphous portion, the API is heated above its melting temperature and cooled with liquid nitrogen to ?120 °C (153 K). Alternatively a sample is program heated and cooled by DSC at a rate of 10 °C min^?1. DEA measures the crystalline solid and amorphous liquid API electrical ionic conductivity. The DEA ionic conductivity is repeatable and differentiates the solid crystalline drug with a low conductivity level (10^?2 pS cm^?1) and a high conductivity level associated with the amorphous liquid (10⁶ pS cm^?1). The DSC sets the analytical transition temperature range from melting to recrystallization. However, analysis of the DEA ionic conductivity cycle establishes the quantitative amorphous and crystalline content in the solid state at frequencies of 0.10–1.00 Hz and to greater than 30 °C below the melting transition as the peak melting temperature. This describes the “activation energy method.” An Arrhenius plot, log ionic conductivity versus reciprocal temperature (K^?1), of the pre-melt DEA transition yields frequency dependent activation energy (E _a, J mol^?1) for the complex charging in the solid state. The amorphous content is inversely proportional to the E _a where the E _a for the crystalline form is higher and lower for the amorphous form with a standard deviation of ±2%. There was a good agreement between the DSC crystalline melting, recrystallization, and the solid state DEA conductivity method with relevant microscopic evaluation. An alternate technique to determine amorphous and crystalline content has been established for the drugs of interest based on an obvious amorphous and crystalline state identified by macro-photomicrography and compared to the conductivity variations. This second “empirical method” correlates well with the “activation energy” method.     

Morphological changes of sterically stabilized nanocrystalline cellulose after periodate oxidation

Periodate oxidation breaks the C2–C3 bond in the glucose repeat units of cellulose, forming two vicinal aldehyde groups. When the cellulose is partially oxidized, three products were generated after periodate oxidation: fibrous cellulose, sterically stabilized nanocrystalline cellulose (SNCC) and dialdehyde modified cellulose. Thus, by periodate oxidation alone, we can produce nanocellulose. SNCCs were produced after 26, 42 and 84 h periodate oxidation. Their morphologies were examined by transmission electron microscopy, which show that the three SNCCs have similar diameters (5–10 nm). In contrast, the average length of SNCC decreases with aldehyde content: from approximately 590 nm after 26 h of oxidation to 100 nm for an oxidation period of 84 h. It indicates that the morphology of SNCC can be well controlled by the degree of periodate oxidation, which depends on the amount of periodate and the reaction time. Equivalent spherical diameters of SNCCs were also examined by dynamic light scattering, and the results correspond closely to the ones observed by TEM. The viscosities of SNCCs were measured by an Ubbelohde viscometer and compared with theory. Because the length of SNCC particles gradually reduces while their diameters remain almost the same, we propose that periodate reacts preferentially with the amorphous region of cellulose. After most of the amorphous regions have reacted, the reaction proceeds at the boundary of amorphous and crystalline regions, creating a reaction front that advances towards the crystalline regions, thus continually shortening them. Dynamic light scattering experiments on SNCC suspensions when adding cosolvents into them proved that SNCCs were sterically stabilized in water.     

Interface characteristics of a Zr‐based BMG/copper laminated composite

Diffusion bonding of metallic glasses and crystalline metals utilizing excellent superplasticity of monolithic bulk metallic glasses (BMGs) within supercooled liquid region has been found to be an efficient method to improve the room temperature plasticity and fracture toughness of metallic glass. A Zr‐based BMG/copper laminated composite was fabricated by copressing method, and the interface bonding status was characterized by scanning electron microscopy (SEM) and high‐resolution transmission electron microscopy. No void or crack is detected, and the interface is a metallurgical bonding of atomistic level. Although the BMG retains amorphous state after copressing at 390 °C, the region of the amorphous‐crystalline mixture structure with the width of 30–40 nm occurred within the diffusion zone. Copyright © 2013 John Wiley & Sons, Ltd.     

Reaction sintering and microstructural evolution in metakaolin-metastable alumina composites

Fine needles of mullite grains were obtained successfully in a compact and low porous matrix using solid state sintering. We treated high-grade kaolin and sand-rich kaolin at 750 °C to amorphous metakaolins, and bauxite at 1,000 °C to metastable alumina. By designing a stochiometric composition of mullite, each amorphous metakaolin was added to metastable alumina. Fine grains of mullite with almost complete crystallization were obtained from 1,350 °C in a case of amorphous metakaolin from high-grade kaolin and at 1,550 °C in the other case where amorphous metakaolin is from sand-rich kaolin. The difference in the temperatures of mullitization was linked to the late dissolution of silica from the cristobalite and quartz phases which were still present in the sand-rich metakaolin sample at 1,350 °C. The use of metastable alumina and metakaolin instead of kaolin to design the mullite matrix allows the increase in number of mullite nucleation sites. This results to high densification and crystallization, fine grain size, and high mechanical properties of the final matrix.     

Nitric Oxide Conversion and Ozone Synthesis in a Shielded Sliding Discharge Reactor with Positive and Negative Streamers

Positive and negative streamer discharges in atmospheric pressure air were generated in a shielded sliding discharge reactor at operating voltages as low as 5 kV for a gap length of 1.6 cm. In this reactor, electrodes are placed on top of a dielectric layer and one of the electrodes, generally the one on ground potential, is connected to a conductive layer on the opposite side of the dielectric. The energy per pulse, at the same applied voltage, was more than a factor of seven higher than that of pulsed corona discharges, and more than a factor of two higher than that of sliding discharges without a shield. It is explained on the basis of enhanced electric fields, particularly at the plasma emitting electrode. Specific input energy required for 50 % removal from ~1,000 ppm initial NO could be reduced to ~18 eV/molecule when ozone in the exhaust of negative streamers was utilized. For sliding discharges and pulsed corona discharges this value was ~25 eV/molecule and it was 35 eV/molecule for positive shielded sliding discharges. Also, the ozone energy yield from dry air was up to ~130 g/kW h and highest for negative streamer discharges in shielded sliding discharge reactors. The high energy density in negative streamer discharges in the shielded discharge reactor at the relatively low applied voltages might not only allow expansion of basic studies on negative streamers, but also open the path to industrial applications, which have so far been focused on positive streamer discharges.     

Oxidation of wood cellulose using 2-azaadamantane N-oxyl (AZADO) or 1-methyl-AZADO catalyst in NaBr/NaClO system

A wood cellulose was oxidized with catalytic amounts of 2-azaadamantane N-oxyl (AZADO) or 1-methyl-AZADO, in an NaBr/NaClO system, in water at pH 10. The oxidation efficiency, carboxylate/aldehyde contents, and degree of polymerization (DP_v) of the oxidized celluloses thus obtained were evaluated in terms of the amount of AZADO or 1-methyl-AZADO catalyst added, in comparison with those prepared using the TEMPO/NaBr/NaClO system. When the AZADO/NaBr/NaClO and 1-methyl-AZADO/NaBr/NaClO oxidation systems were applied to wood cellulose using the same molar amount of TEMPO, the oxidation time needed for the preparation of oxidized celluloses with carboxylate contents of 1.2–1.3 mmol/g was reduced from ≈80 to 10–15 min. Moreover, the molar amounts of AZADO and 1-methyl-AZADO that had to be added for the preparation of oxidized celluloses with carboxylate contents of 1.2–1.3 mmol/g were reduced to 1/32 and 1/16 of the amount of TEMPO added, respectively. The DP_v values for the AZADO- and 1-methyl-AZADO-oxidized celluloses after NaBH₄ treatment were in the range of 600–800. This indicated that not only C6-carboxylate groups but also C2/C3 ketones were formed to some extent on the crystalline cellulose microfibril surfaces during the AZADO- and 1-methyl-AZADO-mediated oxidation. When the AZADO-oxidized wood cellulose, which had a carboxylate content of 1.2 mmol/g, was mechanically disintegrated in water, an almost transparent dispersion consisting of individually nano-dispersed oxidized cellulose nanofibrils was obtained, with a nanofibrillation yield of 89 %.     

Electrical Features of Radio-frequency,Atmospheric-pressure,Bare-metallic-electrode Glow Discharges

Radio-frequency (RF), atmospheric-pressure glow discharge (APGD) plasmas with bare metallic electrodes have promising prospects in the fields of plasma-aided etching, deposition, disinfection and sterilization, etc. In this paper, an induced gas discharge approach is proposed for obtaining the RF, atmospheric-pressure, γ-mode, glow discharges with pure nitrogen or air as the primary plasma-working gas using bare metallic electrodes. The discharge characteristics, including the discharge mode, the breakdown voltage and discharge voltage for sustaining α mode and/or γ mode discharges, of the RF APGD plasmas of helium, argon, nitrogen, air or their mixtures using a planar-type plasma generator are presented in this study. The uniformity (no filaments) of the discharges is confirmed by the images taken by an iCCD with a short exposure time (10 ns). The effects of different gap spacings and electrode materials on the discharge characteristics, the variations of the sheath thickness and the electron number density are also studied in this paper.     

Internally dispersed synthesis of uniform silver nanoparticles via in situ reduction of [Ag(NH3)2]+ along natural microfibrillar substructures of cotton fiber

Silver nanoparticles (Ag NPs) are known to have efficient antimicrobial properties, but the direct application of Ag NPs onto the surface of textiles has shown to be ineffective and raise environmental concerns because Ag NPs leach out during washing. In this study, non-leaching and stable Ag-cotton nanocomposite fiber was produced by the in situ formation of Ag NPs inside the cotton fiber. The reported method is to introduce a nanofluidic system in alkali-swollen cotton fiber. Sequential flows of [Ag(NH₃)₂]⁺ and reductant aqueous fluids into the opened microfibrillar channels yielded a self-assembly of Ag ions on the deprotonated cellulose and subsequent nucleation and particle growth on the microfibrils. Transmission electron and field emission scanning electron microscopy images showed Ag NPs evenly dispersed throughout the entire cross-section of the fiber and their fixation onto the isolated secondary cell wall, respectively. Despite the rapid reduction reaction and the absence of a stabilizing agent, the successful formation of monodispersed Ag NPs (12 ± 3 nm) was attributed to the self-controlled function of the highly organized microfibrillar substructures, which regulated the transport and mixing of reactants. Incorporation of Ag NPs into the internal structure of the cotton fiber did not significantly influence the cotton crystalline structure.     

Tunable mixed amorphous–crystalline cellulose substrates (MACS) for dynamic degradation studies by atomic force microscopy in liquid environments

Atomic force microscopy in liquid environments (L-AFM) became a state of the art technique in the field of enzymatic cellulose degradation due to its capability of in situ investigations on enzymatic relevant scales. Current investigations are however limited to few substrates like valonia cellulose, cotton linters and processed amorphous cellulose as only these show required flatness and purity. Structurally monophasic, these substrates confine conclusions regarding enzymatic degradation of mixed amorphous–crystalline substrates as commonly found in nature. To exploit the full potential of the technique, cellulose substrates with multiphase properties, flat topology and purity are therefore absolutely required. In this study we introduce a special preparation route based on highly crystalline Avicel PH101^® cellulose and the ionic liquid 1-butyl-3-methylimmidazolium chloride as dissolution reagent. As comprehensively shown by atomic force microscopy, wide angle X-ray scattering, Raman spectroscopy and electron microscopy, the developed material allows precise control of its polymorphic composition by means of cellulose types I and II embedded in an amorphous matrix. Together with the tunable composition and flat topology over large areas (>10 × 10 µm²) the material is highly suited for L-AFM studies.     

偶氮苯型侧链液晶聚合物的阻隔特性研究

合成了偶氮苯侧链液晶聚合物聚甲基丙烯酸(3-[4-(4′-氰基偶氮苯)苯氧基]丙酯)(PM3ABCN),采用原位掠入射X射线衍射(GIXRD)方法研究了该聚合物膜在向列相和各向同性态(无定形相)时对气体的阻隔特性.并采用X射线能谱仪(EDS)分析铁片氧化后的氧含量,计算得到渗透通过聚合物膜的氧气的量.结果表明,当PM3ABCN膜处于各向同性态时,通过聚合物膜的氧气平均渗透量为1.92×10-3cm3 day-1m-2;而处于液晶态的膜对氧气的阻隔性提高了4.4倍,氧气平均渗透量为4.38×10-4 cm3day-1 m-2.结合样品表面的显微分析结果,探讨了液晶凝聚相结构对气体小分子的阻隔机理.     

Linen fiber template-assisted preparation of TiO2 nanotubes: palladium nanoparticle coating and electrochemical applications

TiO₂ nanotubes were fabricated from TiF₄ precursors within the pore channels of the linen fiber templates, resulting in crystalline fabricated titanate nanotubes (f-TNTs) upon removal by calcination at 500–600 °C. The f-TNTs were formed by the aggregation of TiO₂ nanoparticles (NPs) with a diameter of 80 nm; the wall thickness and size of the f-TNTs can be controlled by adjusting the concentration of the TiF₄ precursor, time, temperature, and the size of the linen fibers respectively. After that, palladium (Pd⁽⁰⁾) NPs were coated on the surface of the f-TNTs (Pd/f-TNTs) by the chemical reduction method, using NaBH₄ as a reducing agent. The size of the Pd⁽⁰⁾ NPs is about 10–13 nm. The Pd/f-TNT nanocomposite is systematically characterized by X-ray diffraction, high-resolution transmission electron microscopy, and field emission scanning electron microscopy. The Pd/f-TNT nanocomposite-modified glassy carbon electrodes exhibited excellent electrocatalytic activity as well as amperometric determination of hydrazine, ascorbic acid, and dopamine; these electrochemical applications were carried out by cyclic voltammetry.     

Pre-Column Derivatization HPLC Procedure for the Quantitation of Aluminium Chlorohydrate in Antiperspirant Creams Using Quercetin as Chromogenic Reagent

This article describes the development and validation of a selective high-performance liquid chromatography method that allows, after liquid–liquid extraction and pre-column derivatization reaction with quercetin, the quantification of aluminium chlorohydrate in antiperspirant creams. Chromatographic separation was achieved on an XTerra MS C18 analytical column (150 × 3.0 mm i.d., particle size 5 μm) using a mobile phase of acetonitrile:water (15:85, v/v) containing 0.08 % trifluoroacetic acid at a flow rate of 0.30 mL min^?1. Ultraviolet spectrophotometric detection at 415 nm was used. The assay was linear over a concentration range of 3.7–30.6 μg mL^?1 for aluminium with a limit of quantitation of 3.74 μg mL^?1. Quality control samples (4.4, 17.1 and 30.6 μg mL^?1) in five replicates from five different runs of analysis demonstrated intra-assay precision (% coefficient of variation <3.8 %), inter-assay precision (% coefficient of variation <5.4 %) and an overall accuracy (% recovery) between 96 and 101 %. The method was used to quantify aluminium in antiperspirant creams containing 11.0, 13.0 and 16.0 % (w/w) aluminium chlorohydrate, respectively.     

Effect of silica surface coating on the luminescence lifetime and upconversion temperature sensing properties of semiconductor zinc oxide doped with gallium(III) and sensitized with rare earth ions Yb(III) and Tm(III)

Optical sensing of temperature by measurement of the ratio of the intensities of the 700 nm emission and the 800 nm emission of Ga(III)-doped ZnO (GZO) nanoparticles (NPs) and of GZO NPs coated with a silica shell are demonstrated at 980 nm excitation. It is found that the relative sensitivity of SiO₂@Yb/Tm/GZO is 6.2% K^?1 at a temperature of 693 K. This is ~3.4 times higher than that of Yb/Tm/GZO NPs. Obviously, the SiO₂ shell structure decreases the rate of the nonradiative decay. The decay time of the 800 nm emission of the Yb/Tm/GZO NPs (15 mol% Ga; 7 mol% Yb; 0.5 mol% Tm) displays a biexponential decay with a dominant decay time of 148 μs and a second decay time of ~412 μs. The lifetime of the Yb/Tm/GZO NPs at 293 K, and of the SiO₂@Yb/Tm/GZO NPs are ~412 μs. Both the Yb/Tm/GZO and SiO₂@Yb/Tm/GZO can be used up to 693 K. These results indicate that the SiO₂ shell on the Yb/Tm/GZO is beneficial in terms of sensitivity and resolution.

Open image in new window

Graphical abstract The enhancement the decay time and thermal sensitivity in the SiO₂@Yb/Tm/GZO shell@core structure have been studied compared to the Ga(III)-doped Yb/Tm-doped ZnO (Yb/Tm/GZO). The SiO₂@Yb/Tm/GZO have good thermal accuracy up to 693 °C.

     

Hydration of NaCl on glassy, supercooled-liquid, and crystalline water

Interactions of sodium chloride with amorphous and crystalline water films, leading to the possible formation of a dilute NaCl solution, were investigated using time-of-flight secondary ion mass spectrometry as a function of temperature. A monolayer of NaCl tends to remain on the surface or in subsurface sites of thick amorphous solid water films (200 monolayers); the Na+ ion is hydrated preferentially, whereas the Cl- ion is segregated at the surface. The hydration structure of NaCl is fundamentally unchanged for viscous liquid water that appears at temperatures higher than 136 K. The solubility of NaCl increases abruptly at 160 K because of the evolution of supercooled liquid water, which can hydrate the Cl- ion efficiently. However, the diffusion of the ions toward the bulk of supercooled liquid water is interrupted by crystallization; therefore, the dilute NaCl solution that is characterized by completely separated Na+-Cl- pairs may not be formed. When NaCl is deposited on the crystalline ice film, hydration of NaCl is enhanced above 160 K as well, indicating that a liquidlike phase coexists with crystals.     

以无机铝盐为前驱体用溶胶凝胶法合成中孔氧化铝

以水合硝酸铝(Al(NO3)3·9H2O)为前驱体, 通过乙醇介质中环氧丙烷的开环反应促使形成了透明的块状氧化铝凝胶. 凝胶在常压下干燥并于700 ℃焙烧后得到中孔无定型氧化铝. 通过改变环氧丙烷的加入量实现了氧化铝孔径和孔体积等宏观结构性能的调节. 用扫描电镜(SEM)、傅立叶变换红外光谱(FI-IR)和差热分析(DTA)等方法对样品进行了表征. 由于合成中存在环氧丙烷开环产物作为液体模板剂的造孔作用, 在氧化铝凝胶中造成了孔分布曲线具有双峰分布的墨水瓶状孔. 反应过程中pH值的测定和红外光谱的表征结果都证明环氧丙烷是一种很好的质子消耗剂, 其开环促使铝离子水解聚合并形成凝胶网络结构. 同时根据表征结果对环氧丙烷参与的溶胶凝胶氧化铝的合成机理进行了探讨.     

Surface characterization of adsorbents in ultrasound-assisted oxidative desulfurization process of fossil fuels

Surface properties of two different phases of alumina were studied through SEM images. Characterization of amorphous acidic alumina and crystalline boehmite by XRD explains the differences in adsorption capacities of each sample. Data from small angle neutron scattering (SANS) provide further results regarding the ordering in amorphous and crystalline samples of alumina. Quantitative measurements from SANS are used for pore size calculations. Higher disorder provides more topological traps, irregularities, and hidden grooves for higher adsorption capacity. An isotherm model was derived for adsorption of dibenzothiophene sulfone (DBTO) by amorphous acidic alumina to predict and calculate the adsorption of sulfur compounds. The Langmuir-Freundlich model covers a wide range of sulfur concentrations. Experiments prove that amorphous acidic alumina is the adsorbent of choice for selective adsorption in the ultrasound-assisted oxidative desulfurization (UAOD) process to produce ultra-low-sulfur fuel (ULSF).     

Molecular aggregation in the ternary system deca glycerol dioleate/heptane/water

The phase diagram for the ternary system deca glycerol dioleate(DGD)/heptane/water was established at 25 °C. In this phase diagram it was seen that the reverse micellar solution phase extends in its area until the water content reaches 35–45 wt%, at which a liquid crystalline phase begins to appear. On the basis of the experimental results of specific conductivity, viscosity, etc. for the samples containing a definite amount of DGD (0,1 M), and varying relative amounts of heptane and water, the mechanism of the transition of reverse micellar structures to liquid crystalline phase is discussed.     

Effect of phenyl group on the structure and formation of transitional alumina from Al (OPh)<Subscript>3</Subscript>

The structure of freshly prepared Al(OPh)₃, its decomposition product, the hydrolyzed products and their structural evolution were investigated employing ²⁷Al MAS NMR spectroscopy, PXRD, TGA/DTA/DSC/FTIR techniques. In the ²⁷Al MAS NMR spectrum of the aluminium phenoxide, three signals with the chemical shift at 3.78, 21 and 45 ppm were observed. The chemical shift at 3.78 and 45 ppm revealed the presence of four and sixfold coordinated aluminum. The signal at 21 ppm corresponded to fivefold coordinated aluminium. When the aluminium phenoxide was directly decomposed in air at 600 °C, it resulted in amorphous product as evidenced from the PXRD pattern. The observed signals with chemical shifts at 10.1, 42, 73.6 ppm in the ²⁷Al MAS NMR spectrum indicated the presence of 6, 5 and 4 coordination for the aluminium atoms suggesting disordered transitional γ-alumina to be the product. The hydrolysis studies of Al(OPh)₃ with excess of water at 70 °C yielded bohemite (γ-AlOOH). The alumina obtained after dehydration at 600 °C was X-ray amorphous. The dehydrated product at 600 °C showed the presence of four and six coordinated aluminium atoms in the ²⁷Al MAS NMR spectrum confirming it to be ordered γ-Al₂O₃. Crystalline γ-Al₂O₃ was obtained on further heating at 800 °C.     

Synthesis of FeNi3 nanoparticles in benzyl alcohol and their electrical and magnetic properties

Pure and highly crystalline FeNi₃ alloy nanoparticles (NPs) were synthesized via sol–gel route with benzyl alcohol, using hydrazine as a reduction reagent without the usage of additional surfactant molecules nor further annealing processes. The structural studies revealed that the particle size is of ca. 200 nm, whose structure consisted on aggregation of small crystallites of about 13 nm. The magnetic properties of the as-synthesized NPs were similar to the bulk with a saturation magnetization of 95 emu g^?1. Moreover, the coercive field was ca. 50 G, exhibiting a M _r /M _s ratio of 0.03, indicative of soft ferromagnetism. The electrical transport in the temperature range 2–300 K exhibits a typical ferromagnetic metallic behaviour. Finally, similar FeNi₃ NPs were synthesized in EtOH/H₂O mixtures in the presence of sodium dodecyl sulphate molecules as surfactant for comparative purposes, exhibiting a typical half hard magnetic behaviour, highlighting the interest of the reported benzylic route.