Volume Ratio Of Solution Research Articles

The synthesis, characterization of oxidized multi-walled carbon nanotubes, and application to surface acoustic wave quartz crystal gas sensor

Intermetallic alloy catalysts had been prepared by the polyol method, and used for the growth of the individual- or bundle-shaped multi-walled carbon nanotubes (MWCNTs) by thermal chemical vapor deposition method. The purified MWCNTs catalyzed by Mg 28-Ni 68-Mo 4 alloy catalyst were oxidized with the nitric acid/hydrogen peroxide solution (volume ratio = 2/1) to generate carboxylic acid groups. The oxidized MWCNTs (MWCNT-COOH) were further modified with different molecular weights of polyethylene glycols and chloromethyl styrene, respectively, to verify carboxylic acid groups and achieve higher hydrophobic property. Contents of organic functional groups grafted on MWCNTs were estimated with thermogravimetric analysis experiments. In addition, the MWCNT-COOH and poly( n, n-dimethylamino propylsilsesquioxane) (SXNR) were mixed in the THF solvent, and sprayed onto the surface of SAW crystal gas sensor. The MWCNT-COOH were employed to the 156 MHz surface acoustic wave (SAW) quartz crystal sensor for the adsorption of ethanol vapor. The SAW quartz crystal gas sensor coated with the MWCNT-COOH/SXNR was exhibited a high response for ethanol vapor efficiently.

Preparation and Characterization of Cationic Chitosan-modified Poly(D,L-lactide-co-glycolide) Copolymer Nanospheres as DNA Carriers

Chitosan (CS)-modified poly(D,L-lactide-co-glycolide) (PLGA/CS) nanoparticles with cationic surface were prepared by means of emulsion-solvent evaporation technique using polyviny alcohol and chitosan as costabilizers. The preparation conditions of the cationic nanoparticles were optimized by orthogonal factorial design, and the influences of the experiment variables such as polymer concentration, the molecular weight of chitosan, etc., on the size and zeta potential of the nanoparticles were evaluated. It was shown that the diameter of the PLGA/CS nanoparticles can be controlled in the range of 150-200 nm as determined by dynamic light scattering with the optimized conditions. The zeta potential of PLGA/CS nanoparticles increased with increasing the concentration of CS (C(CS)) or decreasing the pH, it was up to 55 mV when C(CS) was 3 mg/mL at pH 4 and inversed around pH 8. The optimization conditions for fabricating the relatively small diameter and high zeta potential cationic nanoparticles were C(CS) 3 mg/mL, C(PLGA) 10 mg/mL, and the volume ratio of organic solution to aqueous medium 1/4. X-ray photo electron spectroscopy and fluorescence inverted microscope observations approved that CS molecules were adsorbed on the surface of PLGA nanoparticles, DNA-condensing ability of the PLGA/CS nanoparticles and cell transfection efficiency of the nanoparticle-DNA complexes were estimated by gel electrophoresis and transfection experiment to 293FT cell, respectively.

Corrosion-induced release of chromium and iron from ferritic stainless steel grade AISI 430 in simulated food contact

Ferritic stainless steel grade AISI 430 with three different surface finishes, glossy, line and abraded has been evaluated regarding changes in metal release rates and corresponding changes in surface composition when immersed in 3 vol% acetic acid at two different temperatures, 40 °C for ten days and 100 °C during three consecutive immersions of 30 min each. Test parameter intervals were set by one of the very few regulatory texts for metal release in food applications, the Italian law text D.M. 21-03-1973, Art. 37. The metal release process was found to be strongly dependent on surface area to solution volume ratio where a specific surface finish would be within the allowed limit, 0.1 mg Cr L −1 for the lowest ratio, 0.5 cm, but exceeded for the highest ratio, 2 cm −1. The amount of released metal increased with increasing temperature and increasing surface roughness (surface finish). Generated data show the regulatory text insufficient and to provide large degrees of freedom, specifically in terms of defining the surface area to solution volume ratio and the acidic cleaning of test vessels, essential parameters to enable reproducible and relevant migration data.

Comparison of Apo- and Heme-bound Crystal Structures of a Truncated Human Heme Oxygenase-2

Heme oxygenase (HO) catalyzes the first step in the heme degradation pathway. The crystal structures of apo- and heme-bound truncated human HO-2 reveal a primarily alpha-helical architecture similar to that of human HO-1 and other known HOs. Proper orientation of heme in HO-2 is required for the regioselective oxidation of the alpha-mesocarbon. This is accomplished by interactions within the heme binding pocket, which is made up of two helices. The iron coordinating residue, His(45), resides on the proximal helix. The distal helix contains highly conserved glycine residues that allow the helix to flex and interact with the bound heme. Tyr(154), Lys(199), and Arg(203) orient the heme through direct interactions with the heme propionates. The rearrangements of side chains in heme-bound HO-2 compared with apoHO-2 further elucidate HO-2 heme interactions.

Reduction of the Total Acid Number of Crude Oil with Basic Solution

Reduction of total acid number (TAN) of crude oil with sodium hydroxide and sodium carbonate solution was investigated. For emulsion emerging in an acid removal process by a sodium hydroxide solution, effects of the volume ratio of sodium hydroxide solution to crude oil and dosage of demulsifiers have been investigated. A model has been engaged to explain the interfacial behavior. When the volume ratio of sodium hydroxide solution (4 wt%) to crude oil exceeds 2, the formed emulsion is an unstable oil-in-water emulsion. When the volume ratio of 4 wt% sodium hydroxide to crude oil reaches 4:1, the total dosage of demulsifiers is 20 mg/l, the weight ratio of non-ion demulsifier LA42 to cationic demulsifier LGA is 1:1, the temperature reaches 40°C, most naphthenic acids were removed from crude oil and the emulsion separated quickly.

Effects of the thermodynamics and rheology of BTDA-TDI/MDI co-polyimide (P84) dope solutions on the performance and morphology of hollow fiber UF membranes

In this work, hollow fiber UF membranes were prepared using BTDA-TDI/MDI co-polyimide (P84, synthesized by the condensation of 2,4-diisocyanato-1-methylbenzene and 1-1′-methylenebis[4-isocyanatobenzene] with 5-5′-carbonylbis[1,3-isobenzofurandione])/ N-methyl-2-pyrrolidone (NMP)/acetone/H 2O/LiCl/polyoxyethylenesorbitan monooleate (Tween80) dope solutions with two approaching ratios ( α = 0, 0.2). The effects of the thermodynamic characteristic (described with the approaching ratio α) of the dope solution, the rheological property (described with shear rate) of the dope solution within the spinneret and other spinning conditions such as air gap, the volume ratio of the dope solution to the bore fluid ( ω) on the structure, morphology and performance of P84 hollow fiber membranes were studied. The hollow fiber membranes spun with the approaching ratio α = 0.2 was found to have a high permeation flux and a large molecular weight cut-off (MWCO) due to the existence of water in the dope solution compared with those spun with the approaching ratio α = 0. The performance of the hollow fiber membranes was dominated by the shear rate of the dope solution within the spinneret according to shear induced molecular orientation. With an increase in shear rate, a low permeation flux and a small MWCO were achieved, and the pore size distribution curve of the membrane shifted to the left, indicating the membrane exhibited a good selectivity. The transition of the spinning process from the wet spinning to the dry-jet wet spinning strongly influenced the performance of the hollow fiber membranes, and a relative low permeation flux and a small MWCO could be obtained when the air gap was not less than 1 cm. With a decrease in the volume ratio of the dope solution to the bore fluid ( ω), the membrane thickness became thinner, resulting in the increase of permeation flux and the MWCO.

Preparation of Ultrafine Beclomethasone Dipropionate Drug Powder by Antisolvent Precipitation

The purpose of this study was to prepare ultrafine beclomethasone dipropionate (BDP) powder via antisolvent precipitation without any surfactants. Various solvents were screened to determine the suitable system for optimum processing while deionized water was kept as the antisolvent. Methanol was selected as the solvent, because a higher degree of supersaturation could be achieved. Several experimental parameters, such as the volume ratio of solution to antisolvent, the concentration of BDP−methanol solution, the temperature, and the stirring speed and time, were investigated in the methanol−deionized water system. The results showed that the yielded powder had a mean particle length of 850 nm and 85% of the particles were distributed in the range of 0.2−1.2 μm, whereas the raw particle size was 2.13 μm, ranging in size from 0.2 μm to 12 μm. Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analysis indicated no change in chemical group structure and crystal structure during the ...

Crystal Structures of Nonoxidative Zinc-dependent 2,6-Dihydroxybenzoate (γ-Resorcylate) Decarboxylase from Rhizobium sp. Strain MTP-10005

Reversible 2,6-dihydroxybenzoate decarboxylase from Rhizobium sp. strain MTP-10005 belongs to a nonoxidative decarboxylase family. We have determined the structures of the following three forms of the enzyme: the native form, the complex with the true substrate (2,6-dihydroxybenzoate), and the complex with 2,3-dihydroxybenzaldehyde at 1.7-, 1.9-, and 1.7-A resolution, respectively. The enzyme exists as a tetramer, and the subunit consists of one (alphabeta)8 triose-phosphate isomerase-barrel domain with three functional linkers and one C-terminal tail. The native enzyme possesses one Zn2+ ion liganded by Glu8, His10, His164, Asp287, and a water molecule at the active site center, although the enzyme has been reported to require no cofactor for its catalysis. The substrate carboxylate takes the place of the water molecule and is coordinated to the Zn2+ ion. The 2-hydroxy group of the substrate is hydrogen-bonded to Asp287, which forms a triad together with His218 and Glu221 and is assumed to be the catalytic base. On the basis of the geometrical consideration, substrate specificity is uncovered, and the catalytic mechanism is proposed for the novel Zn2+-dependent decarboxylation.

Development and optimization of an indirect enzyme-linked immunosorbent assay for the determination of Hexoestrol

An indirect enzyme-linked immunosorbent assay (ELISA) for the detection of hexoestrol (HES) was developed, optimized and validated for the analysis of HES in pork. Many parameters, such as the volume ratio of solution A and solution B, colour developing time, pH value, incubation time, the volume ratio of the standard solution and diluted antiserum, blocking solution, blocking condition, coating solution and coating condition were studied and optimized in the paper. The regression equation of the final inhibition curve is y = − 0.3345x + 1.4955, R2=0.9913. The linear range is 0.1–8.1 ng/ml, and the IC50 is 0.671 ng/ml. The specificity of the assay was evaluated by the cross-reactivity rates of six compounds, of which two structurally related compounds had a relatively higher cross-reactivity rate of 25% and 6%. HES was added into a pork sample at 5 ng/g level and then the sample was extracted. The recovery is between 49.6% and 79.2%, and the variation coefficient is 0.164.

Effects of [formula omitted] on the kinetics of UO 2 oxidation by H 2O 2

The effect of HCO 3 - on the kinetics of UO 2 oxidation by H 2O 2 in aqueous solution has been studied using powder suspensions where the concentration of H 2O 2 was monitored as a function of time. By varying the UO 2 surface to solution volume ratio second order rate constants were obtained for HCO 3 - concentrations ranging from 0 to 100 mM. The second order rate constant increases linearly with HCO 3 - concentration from 0 to approximately 1 mM. Above 1 mM HCO 3 - the rate constant is 4.4 × 10 −6 m min −1 independent of [ HCO 3 - ]. This indicates that the kinetics of the reaction depends on both oxidation and dissolution below 1 mM HCO 3 - while at higher concentrations it is solely governed by oxidation. Hence, the rate constant obtained at HCO 3 - concentrations above 1 mM is the true rate constant for oxidation of UO 2 by H 2O 2. The results also imply that the reaction between HCO 3 - and oxidized UO 2 on the UO 2 surface (i.e. HCO 3 - facilitated dissolution) is limited by diffusion (ca 10 −3 m min −1 in the present system). Furthermore, the experimental results were used to estimate the oxidation site density of the powder used (126 sites nm −1) and the rate constant for dissolution of UO 2 2 + from the UO 2 surface (7 × 10 −8 mol m −2 s −1).

Use of Cyclodextrins as An Environmentally Friendly Extracting Agent in Organic Aged-contaminated Soil Remediation

The removal of Polycyclic Aromatic Hydrocarbons (PAHs) from soil using pure water is quite ineffective due to␣their low aqueous solubility. Most of present processes are based on organic cosolvents or surfactants, leading to potential environmental hazard. Addition of cyclodextrin (CD) in aqueous washing solutions has been shown to␣increase the removal efficiency several times, while being non-toxic agents. Herein are investigated the effectiveness of cyclodextrins to remove PAHs occurring in industrially aged-contaminated soil. β-cyclodextrin (BCD), hydroxypropyl-β-cyclodextrin (HPCD) and methyl-β-cyclodextrin (MCD) solutions were used for soil flushing in column test or batch experiments to evaluate some influent parameters that can significantly increase the removal efficiency. The process parameters chosen were CD concentration, ratio of washing solution volume to soil weight, and temperature of washing solution. These parameters were found to have a significant and almost linear effect on PAHs removal from the contaminated soil, except the temperature where no significant enhancement in PAHs extraction was observed for temperature range from 5 to 35 °C. Removal capacity of HPCD and MCD was higher than BCD one. The PAHs extraction enhancement factor compared to water was about 200.

Study on volume ratio and plasticizer screening of free coating membranes composed of ethyl cellulose and chitosan

AbstractThe aim of this study was to optimize the formula of free blended coating membrane of ethyl cellulose (EC) and chitosan (CS), including their suitable ratio range and the best plasticizer used. The dry films were produced by a casting/solvent evaporation method, with different volume ratio of EC and CS solution plasticized by various plasticizers, respectively. The wet films were prepared by immersing dry films in pH 6.8 phosphate buffer saline (PBS) for 24 h. The promising ratio range of EC/CS was below 20/5 or 20/6 with various plasticizer, which was determined by comparing the viscosity of the blended solutions and the morphology of the blended films. The efficiency of plasticization was evaluated by measuring glass transition temperature (Tg). All the testing plasticizers have good compatibility with EC or CS and dibutyl phthalate (DBP) have the strongest efficiency inducing the lowest Tg (39.9°C) of the film. Mechanical properties were evaluated by the ratio of tensile strength (T) to elastic modulus (E). In the wet state, the films with DBP had the highest T/E value (1.2). The results of leaching of plasticizers also verified that DBP was the most stable plasticizer in the films. The release rates of tetramethylpyrazine phosphate (TMPP) through the pellets coated with the blended films of EC/CS (20 : 6 v/v) plasticized by various plasticizers showed that the more water‐soluble the plasticizer was, the more quickly TMPP dissolved from the coated pellets, which further indicated that the water‐insoluble plasticizers (such as DBP) could be more applicable to keep the sustained or controlled release property of the blended films in wet state. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1932–1939, 2006

Removal of polycyclic aromatic hydrocarbons from aged-contaminated soil using cyclodextrins: Experimental study

The removal of polycyclic aromatic hydrocarbons (PAHs) from soil using water as flushing agent is relatively ineffective due to their low aqueous solubility. However, addition of cyclodextrin (CD) in washing solutions has been shown to increase the removal efficiency several times. Herein are investigated the effectiveness of cyclodextrin to remove PAH occurring in industrially aged-contaminated soil. β-Cyclodextrin (BCD), hydroxypropyl-β-cyclodextrin (HPCD) and methyl-β-cyclodextrin (MCD) solutions were used for soil flushing in column test to evaluate some influent parameters that can significantly increase the removal efficiency. The process parameters chosen were CD concentration, ratio of washing solution volume to soil weight, and temperature of washing solution. These parameters were found to have a significant and almost linear effect on PAH removal from the contaminated soil, except the temperature where no significant enhancement in PAH extraction was observed for temperature range from 5 to 35 °C. The PAHs extraction enhancement factor compared to water was about 200.

Emulsion liquid membranes: Role of internal droplet size distribution on toluene/ n-heptane separation

Using oil/water/oil-type emulsion liquid membranes, batch wise extraction experiments are carried out to separate toluene from a mixture of toluene and n-heptane. In the separation process using emulsion liquid membranes, the internal phase polydispersity affects mass transport of a solute because under steady operating conditions, internal droplet size and size distribution are proportional to the interfacial area. The present study aims to assess the polydispersity character of the internal droplets of emulsion globules. In this paper, the important variables affecting dispersed drop sizes as well as internal droplets mean diameter and size distribution of the emulsion globule, including impeller speed during emulsification, surfactant concentration, volume ratio of surfactant solution, carrier concentration and composition of feed phase are systematically investigated.

Factors Affecting the Adsorption of 60Co onto a Peat from China

The work described was aimed at an analysis of the principal factors affecting the adsorption of 60Co ions onto a peat from Lin Tao County (in the south of Gansu Province, P. R. China). The adsorption of 60Co ions onto the peat was studied as a function of contact time, ratio of solution volume (V) to solid mass (m), pH, ionic strength and the initial concentration of Co ions. It was found that the relative adsorption rate was quite rapid, that adsorption gradually decreased with increasing values of V/m and that ionic strength had a moderate effect on the process. In addition, the pH value strongly influenced the extent of adsorption. Over the high concentration range, the adsorption equilibrium could be described by the Freundlich equation, with this equation being reduced to the Henry equation, i.e. a linear adsorption isotherm, over the low concentration range. No attempt has been made at understanding the mechanism of 60Co ion adsorption onto peat in the present work.

Release of contaminant U(VI) from soils

Summary The retention, mobility, and bio-availability of U(VI) in contaminated soils depend strongly on release of U(VI). Laboratory batch experiments were performed to evaluate the factors (ionic strength of the extraction solution and solution volume to solid mass ratio) controlling the release of U(VI) from contaminated soil at Oak Ridge, Tennessee. Increase in ionic strength shows an evident effect on U(VI) release as indicated by the increase in release rates and associated release mass of U(VI). The ratio of solution volume to solid mass (V/M) has a significant impact on the release of U(VI). Increase in the V/M ratio shows a negligible effect on the U(VI) release over a 4-day period. However, at Day 30 and Day 120, larger V/M ratios cause greater U(VI) release. The maximum U(VI) concentrations observed in the release experiments are in the range of schoepite solubility estimated under conditions relevant to the experiments, suggesting that schoepite solubility primarily controls the U(VI) release, but that solubilization and desorption effects cannot be distinguished using macroscopic methods.

Removal of zinc from dilute aqueous solutions by galvanochemical treatment

The possibility of zinc removal, a common toxic metal, from simulated liquid effluents by the application of a novel treatment method, termed galvanochemical, was investigated. The galvanochemical process is considered as a simple, economic, friendly to the environment, method, which does not create harmful end-products. Synthetic wastewaters were examined, these contained concentrations of zinc commonly found in real wastewaters from small-to-medium size industrial units, such as metal-plating or metal-treatment plants. These liquid wastes pose an important environmental problem, due to the content of heavy metals. The optimization of the main operating parameters was the objective of the study. The galvanic pair scrap ratio iron:coke was used for these investigations. It was found that the use of the galvanic pair mixture of 80 g dm−3 (weight per solution volume ratio), agitated at 160 rpm for 5 h, removed more than 90% of zinc from the initial solution, containing initially 50 mg dm−3 of zinc. The scanning electron microscopy/energy disperse spectrometry (SEM/EDS) analysis performed on the products showed that zinc was adsorbed onto the coke to a small extent and that the zinc removal was mainly based on the adsorption of zinc onto the surface of active iron oxides formed as a result of galvanochemical reactions. Copyright © 2005 Society of Chemical Industry

Development of asymmetric BTDA-TDI/MDI (P84) co-polyimide hollow fiber membranes for ultrafiltration: the influence of shear rate and approaching ratio on membrane morphology and performance

In this paper, the effects of dope composition (especially approaching ratio α), rheology and spinning conditions on the morphology and performance of asymmetric BTDA-TDI/MDI co-polyimide (P84, CAS#: 58698-66-1) hollow fiber membranes spun from P84/N-methyl-2-pyrrolidone (NMP, CAS#: 872-50-4)/H 2O dope solutions were studied. The velocity distribution and rheology of the dope solution within the spinneret were analyzed. The experimental results indicated that the defects on the outer surface of hollow fiber membranes were suppressed by increasing the shear rate of the dope solution within the spinneret. Therefore, membranes with a low flux and a high rejection could be obtained. By changing in shear rate, the hollow fiber membranes ranging from ∼20,000 to >200,000 MWCO can be obtained within a single formulation (such as 21 wt.% P84; H 2O/NMP: 3.6/96.4 (w/w). An increase of shear rate also increased the outer diameter and thickness of the hollow fiber membranes. The approaching ratio α of the dope solution played an important role in determining the membrane structure. The hollow fiber membranes spun at α = 0.45 (21 wt.% P84; H 2O/NMP: 3.6/96.4 (w/w) had a finger-like structure, but sponge-like structure was obtained for α = 0.82 (21 wt.% P84; H 2O/NMP: 6.4/93.6 (w/w). An increase of approaching ratio α resulted in a poor rejection and a high flux. With a decrease in the volume ratio of dope solution to bore fluid, the membrane became thinner and the flux increased. Compared to the dry–jet wet spinning process, the hollow fiber membranes from a wet spinning process had a high flux, a large outer diameter and a poor rejection. For a dry–jet wet spinning process, the increase in the air gap decreased the rejection of the hollow fiber membranes.

Natural Oxidant Demand of Aquifer Materials Using the Push-Pull Technique

The quantification of the natural oxidant demand (NOD) of aquifer materials is required to estimate the fate of reagents injected into contaminated aquifers during in situ chemical oxidation applications. Three push-pull tests were conducted at a horizontal spacing of 12-20 m within an uncontaminated region of the saturated zone in the Canadian Forces Base Borden aquifer located near Alliston, Ont., Canada to estimate the NOD for permanganate. Each test contacted a minimum of 270 kg of aquifer material. Upper estimates of NOD values from the three tests were 0.51-0.75 g/kg based on the initial mass of aquifer material contacted, and lower estimates were 0.29-0.42 g/kg based on additional aquifer material mass contacted during the drift or reaction phase. These results compared favorably to NOD values determined from bench-scale tests with high solids mass to solution volume ratios. If design and operational concerns can be overcome, the push-pull test offers significant advantages over the variety of bench-scale testing methods currently used to determine the NOD of aquifer materials.

Leaching of borosilicate glasses. I. Experiments

The corrosion of sodium borosilicate glasses xNa 2O– yB 2O 3–(1 − x − y)SiO 2 is studied at constant temperature and pH as a function of the glass composition for 0.10 < x ≈ y < 0.25. Two series of experiments are reported with different glass surface area to solution volume ratios ( S/ V = 100 and 2000 m −1). The dissolution kinetics are monitored by following the concentrations of the three cations (Si, B and Na) in solution as a function of time. The altered glasses are characterized by NMR and SAXS. For all glasses, the concentrations of released cations reach a stationary limit. The time required to reach the stationary state decreases from 40 days to a few hours when the content in boron and sodium oxides is increased from 10 to 25 mol.%. The final leached fraction of silicon, LF(Si), is controlled by an apparent silica saturation concentration, which is nearly independent of the initial glass composition. On the contrary, the final leached fraction of boron and sodium, LF(B) and LF(Na), which are always close to each other, show a strong compositional dependence. The LF(B) and LF(Na) are low and nearly equal the LF(Si) for the glasses with boron (and sodium) oxide content less than 15%. This is the mark of a nearly congruent dissolution for these glasses. When the boron (and sodium) oxide content increases from 15% to 20%, there is a sharp increase of LF(B) and LF(Na) in comparison to LF(Si). Above 20%, the LF(B) and LF(Na) saturate to unity, which means that all the soluble cations have been removed, whereas the dissolved fraction of silicon may be less than 10% (depending on the S/ V ratio). 29Si NMR shows a considerable reconstruction of the altered glasses. SAXS puts in evidence the formation of a porous network with a typical pore diameter of 5 nm. The results are qualitatively explained through the competition between (i) the extraction of the soluble boron and sodium, which initiates the formation of a porous network at the nanometer scale, and (ii) the recondensation of silica, which makes the surface layer more polymerized and more resistant than the original glass at the atomic scale.