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21.
Takunda Muzvidziwa Jonathan O. Okonkwo Munyaradzi Shumba Tichaona Nharingo Upenyu Guyo 《International journal of environmental analytical chemistry》2017,97(7):623-636
We report on the development of an electrochemical sensor based on electrodepositing zinc oxide on multiwalled carbon nanotube-modified glassy carbon electrode for the detection of caffeine in pharmaceutical wastewater effluents. The measurements were carried out using cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperometry and differential pulse voltammetry (DPV). DPV measurements showed a linear relationship between oxidation peak current and concentration of caffeine in 0.1 M HClO4 (pH 1.0) over the concentration range 0.00388–4.85 mg/L and a detection limit of 0.00194 mg/L. The diffusion coefficient and Langmuir adsorption constant for caffeine were calculated to be 3.25 × 10?6 cm2 s?1 and 1.10 × 103 M?1, respectively. The sensor showed satisfactory results when applied to the detection of caffeine in wastewater effluents. 相似文献
22.
Ion association and hydration clusters in aqueous lithium borate solution are extremely important to understand some extraordinary properties of lithium borates. In the present work, polyborate distribution in aqueous LiBO2 solution was investigated through Raman and thermodynamics equilibrium analysis. Geometry and stability of hydrated clusters LiB(OH)4(H2O)n up to n = 8 were calculated at the B3LYP/aug-cc-pVDZ level. Three different types of ion association, namely, contact ion pairs (CIP), solvent-shared ion pairs (SIP) and solvent separated ion pairs (SSIP) were obtained; characteristics of all of these stable configurations were determined, and the most stable hydrated clusters were chosen. Then the mechanisms of ion aggregation and crystal nuclei formation in the LiB(OH)4 solution were proposed. The tight four-hydrated sphere of Li+ makes it difficult for the dehydrated form of its first hydration sphere to from a CIP, which is the passible reason that lithium borate always has a large super-saturation degree. 相似文献
23.
《Comptes Rendus Chimie》2017,20(7):704-709
Aluminophosphate and silicoaluminophosphate molecular sieves with both five (AFI) and eleven (AEL) type structures are synthesized by hydrothermal crystallization at 473 K, using tripropylamine and dipropylamine as a structure-directing template. The as-prepared AFI and AEL sieves are characterized and then assessed as sorbents for uranium (VI) from radioactive effluents. The sorption process is used to reduce the volumes of effluents and convert them into a stable solid waste. The batch experimental studies are carried out to evaluate the AEL and AFI structure effect on the removal of uranium. The AlPO4-5, SAPO-5, AlPO4-11 and SAPO-11 are applied to radioactive effluents with different activities obtained from Nuclear Research Center of Draria, Algeria. Important decontamination factor values are obtained for AFI sorbents. Thermodynamic parameters, namely, the enthalpy (ΔH), entropy (ΔS) and free energy (ΔG) for each sorption process are calculated. The collected results indicated that sorbents are effective materials for the removal of uranium (VI) ions, the sorbent with AFI structure being a highly effective material for the removal of uranium (VI) ions from nuclear effluents. 相似文献
24.
《化学:亚洲杂志》2017,12(10):1052-1056
The β‐cyclodextrin‐assisted aqueous‐exfoliation method was used to prepare transition‐metal dichalcogenide (TMD) nanosheets, in a cheap, highly efficient, scalable and environmentally friendly manner. As study cases, MoS2 and ReS2 nanoflakes were prepared according to this method. Particularly, the effective exfoliation of ReS2 crystals in an aqueous environment was observed for the first time. Moreover, exfoliated nanomaterials can be readily utilized in hydrogen evolution reactions (HERs) as noble‐metal‐free catalysts. This work provides new opportunities for highly efficient exfoliation of TMDs and other 2D nanomaterials into few‐layer nanosheets in aqueous media. Their production process showed high biocompatibility, broad applicability and excellent sustainability. 相似文献
25.
26.
不同水介质润滑下GCr15钢的微动磨损特性 总被引:6,自引:4,他引:6
采用液压高精度材料试验机考察了平面-球面接触GCr15钢摩擦副在海水、酸性水和洁净水等3种不同水介质润滑下的微动磨损性能.用激光扫描显微镜(LSM)观察了磨痕表面形貌.结果表明:3种水介质对钢-钢摩擦副具有明显的润滑作用,其中酸性水的润滑作用最明显;磨损体积损失同介质的润滑作用和腐蚀作用相关,在洁净水和海水介质润滑下的磨损体积损失较小,在酸性水介质润滑下的磨损体积损失较大;在海水润滑下的GCr15钢磨损表面呈现明显的点蚀特征. 相似文献
27.
Summary A three-parameter model is introduced to describe the shear rate — shear stress relation for dilute aqueous solutions of polyacrylamide (Separan AP-30) or polyethylenoxide (Polyox WSR-301) in the concentration range 50 wppm – 10,000 wppm. Solutions of both polymers show for
a similar rheological behaviour. This behaviour can be described by an equation having three parameters i.e. zero-shear viscosity
0, infinite-shear viscosity
, and yield stress
0, each depending on the polymer concentration. A good agreement is found between the values calculated with this three-parameter model and the experimental results obtained with a cone-and-plate rheogoniometer and those determined with a capillary-tube rheometer.
a Pa–1 physical quantity defined by:a = {1 – ( / 0)}/ 0 - c l concentration (wppm) - D m capillary diameter - L m length of capillary tube - P Pa pressure drop - R m radius of capillary tube - u m s–1 average velocity - v r m s–1 local axial velocity at a distancer from the axis of the tube - shear rate (–dv r /dr) - local shear rate in capillary flow - s–1 wall shear rate in capillary flow - Pa s dynamic viscosity - a Pa s apparent viscosity defined by eq. [2] - ( a ) Pa s apparent viscosity in capillary tube at a distanceR from the axis - 0 Pa s zero-shear viscosity defined by eq. [4] - Pa s infinite-shear viscosity defined by eq. [5] - l ratior/R - kg m– density - Pa shear stress - 0 Pa yield stress - r Pa local shear stress in capillary flow - R Pa wall shear stress in capillary flow R = (PR/2L) - v m3 s–1 volume rate of flow With 8 figures and 1 table 相似文献
Zusammenfassung Der Zusammenhang zwischen Schubspannung und Schergeschwindigkeit von strukturviskosen Flüssigkeiten wird durch ein Modell mit drei Parametern beschrieben. Mit verdünnten wäßrigen Polyacrylamid-(Separan AP-30) sowie Polyäthylenoxidlösungen (Polyox WSR-301) wird das Modell experimentell geprüft. Beide Polymerlösungen zeigen im untersuchten Schergeschwindigkeitsbereich von ein ähnliches rheologisches Verhalten. Dieses Verhalten kann mit drei konzentrationsabhängigen Größen, nämlich einer Null-Viskosität 0, einer Grenz-Viskosität und einer Fließgrenze 0 beschrieben werden. Die Ergebnisse von Experimenten mit einem Kegel-Platte-Rheogoniometer sowie einem Kapillarviskosimeter sind in guter Übereinstimmung mit den Werten, die mit dem Drei-Parameter-Modell berechnet worden sind.
a Pa–1 physical quantity defined by:a = {1 – ( / 0)}/ 0 - c l concentration (wppm) - D m capillary diameter - L m length of capillary tube - P Pa pressure drop - R m radius of capillary tube - u m s–1 average velocity - v r m s–1 local axial velocity at a distancer from the axis of the tube - shear rate (–dv r /dr) - local shear rate in capillary flow - s–1 wall shear rate in capillary flow - Pa s dynamic viscosity - a Pa s apparent viscosity defined by eq. [2] - ( a ) Pa s apparent viscosity in capillary tube at a distanceR from the axis - 0 Pa s zero-shear viscosity defined by eq. [4] - Pa s infinite-shear viscosity defined by eq. [5] - l ratior/R - kg m– density - Pa shear stress - 0 Pa yield stress - r Pa local shear stress in capillary flow - R Pa wall shear stress in capillary flow R = (PR/2L) - v m3 s–1 volume rate of flow With 8 figures and 1 table 相似文献
28.
This paper is focused on the capabilities of gas–liquid foams to attenuate acoustic waves. It is postulated that the sound attenuation phenomenon in foams is largely governed by the hydrodynamic resistance of the Plateau-Gibbs channels (PGC) to the flow of liquid through them. It is shown that the addition of solid particles to gas–liquid foams has opposite effects depending on the concentration of the added solid particles. As long as the concentration of the added solid particles is smaller than a certain critical value the sound attenuation coefficient increases and as a result in the sound velocity decreases. However, if the concentration of the added solid particles becomes larger than this critical value the attenuation coefficient decreases and the sound velocity increases. When the concentration of the solid particles reaches some critical value, the particles block the Plateau-Gibbs channels and stop the filtration. As a result the attenuation coefficient of the sound wave decreases while the sound velocity, in such three-phase foams, increases. The point at which the sound wave stops attenuating and its velocity starts to increase is known as the point of self-clarification. Based on this postulate and on the results of our preliminary tests the present study provides a plausible explanation to the above-mentioned contradicting effect, and the self- clarification phenomenon. 相似文献
29.
Hongni Teng Ning Li Xixi Zhu Yong Chen 《Journal of Dispersion Science and Technology》2013,34(6):828-833
Aqueous two-phase systems (ATPS) are formed in mixtures of sodium dodecylsulfate (SDS), cetyltrimethyl ammonium bromide (CTAB), and sodium bromide (NaBr). Two different kinds of ATPS appear when CTAB and SDS surfactants are in excess, respectively. Such ATPS may provide a new, useful partitioning system for separation of bovine serum albumin (BSA). The partitioning of BSA was studied in these systems. The results show that the partitioning is affected by the electrical property, the hydrophobicity and the structure of liquid crystal (LC), which exists in the top phase of the ATPS. BSA is extracted into the top phase with higher distribution coefficient when LC and BSA are oppositely charged. The hydrophobicity of LC, which can be improved by increasing the length of alkyl group, enhances the distribution coefficient. The hydrophobicity of lamellar LC and hexagonal LC is stronger than that of cubic LC, which causes extractive capability of the former is higher than the latter. 相似文献
30.
The indium-mediated Barbier-type allylation reaction of aldehydes with allyl bromide, which gives corresponding homoallyl alcohols, was investigated. The reaction medium and the effects of substituents were discussed in detail. The results showed that various aldehydes, including aromatic, heterocyclic, and aliphatic aldehydes, with different substituents could all react well with excellent yields of 91–97% in aqueous tetrahydrofuran at room temperature within about 1 h.