A method for the trace determination of cadmium ions in water, human urine and human blood serum samples using ultrasonic‐assisted dispersive micro‐solid‐phase extraction (UA‐D‐μSPE) was developed. Silica‐coated magnetic nanoparticles were coated with polythiophene, and the resulting sorbent was characterized using thermogravimetry, differential thermal analysis, scanning electron microscopy, Fourier transform infrared spectrometry and X‐ray diffraction. Following UA‐D‐μSPE, cadmium ions were quantified using graphite furnace atomic absorption spectrometry. A Box–Behnken design was used for optimization of important sorption and desorption parameters in UA‐D‐μSPE: in the sorption step, pH of solution, sorption amount and sonication time for sorption; in the desorption step, concentration of eluent, volume of eluent and sonication time. The optimum conditions for the method were: pH of solution, 7.5; sonication time for sorption, 3 min; sorption amount, 35 mg; type and concentration of eluent, HCl and 1.1 mol l?1; volume of eluent, 360 μl; sonication time for desorption, 110 s. Under the optimized conditions the limit of detection and relative standard deviation for the detection of cadmium ions by UA‐D‐μSPE were found to be 0.8 ng l?1 and <6%, respectively. 相似文献
Pressure drop behaviour of ice slurry based on ethanol–water mixture in circular horizontal tubes has been experimentally investigated. The secondary fluid was prepared by mixing ethyl alcohol and water to obtain initial alcohol concentration of 10.3% (initial freezing temperature ?4.4 °C). The pressure drop tests were conducted to cover laminar and slightly turbulent flow with ice mass fraction varying from 0% to 30% depending on test conditions. Results from flow tests reveal much higher pressure drop for higher ice concentrations and higher velocities in comparison to the single phase flow. However for ice concentrations of 15% and higher, certain velocity exists at which ice slurry pressure drop is same or even lower than for single phase flow. It seems that higher ice concentration delay flow pattern transition moment (from laminar to turbulent) toward higher velocities. In addition experimental results for pressure drop were compared to the analytical results, based on Poiseulle and Buckingham–Reiner models for laminar flow, Blasius, Darby and Melson, Dodge and Metzner, Steffe and Tomita for turbulent region and general correlation of Kitanovski which is valid for both flow regimes. For laminar flow and low buoyancy numbers Buckingham–Reiner method gives good agreement with experimental results while for turbulent flow best fit is provided with Dodge–Metzner and Tomita methods.Furthermore, for transport purposes it has been shown that ice mass fraction of 20% offers best ratio of ice slurry transport capability and required pumping power. 相似文献
The polythiophene nanoparticles (nano-PT) were prepared with average diameter of 20–35 nm. The nanostructurals of polythiophene were confirmed by TEM and SEM analyzes. The kinetics of the thermal degradation and thermal oxidative degradation of nano-PT were investigated by thermogravimetric analysis. Kissinger method, Flynn–Wall–Ozawa method, and advanced isoconversional method have been used to determine the activation energies of nano-PT degradation. The results showed that the thermal stability of nano-PT in pure N2 is higher than that in air atmosphere. The analyzes of the solid-state processes mechanism of nano-PT by Criado et al. method showed: the thermal degradation process of nano-PT goes to a mechanism involving second-order (F2 mechanism); otherwise, the thermo-oxidative degradation process of nano-PT is corresponding to a phase boundary controlled reaction mechanism (R2 mechanism). 相似文献
Three tetra‐amine compounds 2‐((2‐(2‐aminobenzylamino)ethylamino)methyl)benzenamine ( L1 ), 2‐((3‐(2‐aminobenzylamino)propylamino)methyl)benzenamine ( L2 ), and 2‐((4‐(2‐aminobenzylamino)butylamino)methyl)benzenamine ( L3 ) were synthesized and then their reaction with 2‐hydroxybenzaldehyde, 2‐nitrobenzaldehyde, and 2‐hydroxy‐3‐methoxybenzaldehyde were investigated. Treatment of L1 , L2 , and L3 with the former aldehydes gave derivatives of quinazolines in a good yield. The products have been studied with IR, 1H NMR, 13C NMR, COSY, HMQC, and microanalysis. 相似文献
The zwitterionic intermediate generated from the reaction of triphenylphosphine with electron deficient acetylenic compounds was trapped by various NH acids. The synthesis resulted in a new class of highly functionalized heterocyclic compounds. Some of the reactions produced E and Z isomers. And the stability and transformation of them were studied by dynamic 1H NMR and density functional theory (DFT) calculations. 相似文献
In this numerical study, laminar flow of water nanofluid/GNP–SDBS (graphene nanoplatelet–sodium dodecylbenzene sulfonate) for 0–0.1% solid nanoparticles mass fraction was investigated for Reynolds numbers of 50–1000 in 3D space via finite volume method. In the newly proposed microchannel design, the cooling fluid is moving in countercurrent in the upper and lower layers of the microchannels, and there are cavities and sinusoidal routes on the solid walls of the microchannel, and the presence of rectangular ribs on the flow centerline along the fluid path enhances mixing for cooling fluid and creates better heat transfer for warm surfaces. The results of this study show that this special design of the microchannel can have a substantial increase in Nusselt number and heat transfer so that in the considered geometry by adding solid nanoparticles mass fraction it is possible to increase average Nusselt number for each Reynolds number by approximately 20%. Also, the mixing of the fluid because of formation of secondary flows has a strong effect on making the temperature distribution uniform in the cooling fluid and solid bed (wall) of the microchannel, especially in the lower layer. The upper layer of the microchannel always has a lower temperature due to indirect contact with heat flux compared with the lower layer. In this study, by increasing Reynolds number and mass fraction of solid nanoparticles the Nusselt number is increased and heat resistance of the lower wall of the microchannel is reduced. Based on the investigation of flow field and heat transfer, the use of the proposed design of the microchannel is recommended for Reynolds number less than 300.
The production and properties of a biosurfactant, synthesized by a member of the Bacillus subtilis group (PTCC 1696) which was isolated from an Iranian oil field, have been investigated. The biosurfactant, which was produced as a primary metabolite associated with the growth of PTCC 1696, was able to reduce the surface and interfacial tension of media to 26.7 and 0.1 mN/m, respectively. Crude biosurfactant and acid precipitated biosurfactant have critical micelle concentrations of 10 and 100 mug/ml, respectively. The stability of the biosurfactant at different salinities, pH and temperature and also its emulsifying activity have been investigated. It is an effective surfactant at very low concentrations over a wide range of temperatures, pHs and salt concentrations and also has the ability to emulsify oil, which is essential for enhanced oil recovery. 相似文献
Polythiophene nanoparticles as a conductive filler was prepared with average diameter of 20-35 nm and its molecular structure was confirmed by the FT-IR, TEM, XRD and UV-vis analysis. A new conductive epoxy nanocomposite was synthesized by curing of diglycidyl ether of bisphenol A/4,4′-(4,4′ Isopropylidenediphenoxy) bis (Phthalic Anhydride) involving various percentages of polythiophene nanoparticles. DSC and DMTA studies revealed that low percentage of the polythiophene nanoparticles, i.e. 1%, results in improved crosslink density as evidenced by increasing in the glass transition temperature. The addition of polythiophene nanoparticles into the epoxy matrix resulted in a significant increment in the electrical conductivity, mechanical properties, thermal stability and activation energy of thermal degradation. The advanced isoconversional method is utilized to describe the curing behavior and thermal degradation process of the neat epoxy and epoxy nanocomposite. We have utilized the Coats-Redfern and Criado methods to find the solid state thermal degradation reaction mechanism. For the nanocomposite, the mechanism was recognized to be two-dimensional diffusion (D2) reaction and it changes to a nucleation and growth (A4) for pure epoxy system. 相似文献