Increase In Ion Strength Research Articles

Ultrasonic‐assisted activation of clay for efficient removal of U(VI) and Cr(VI)

AbstractThe natural clay mineral was activated using the acid treatment under ultrasonic conditions to improve its adsorption performance. The acid‐activated clay (AAC) was investigated to remove Cr(VI) from wasted lubricant and U(VI) from aqueous solution by batch, spectroscopy, and modeling. Batch experiments showed that the isotherms and adsorption kinetics of Cr(VI)/U(VI) on AAC were satisfactorily followed by Frenudlich and the pseudo‐second‐order model, respectively. The decreased adsorption of U(VI) on AAC with the increase of ion strength indicated the outer surface complexation of U(VI) on AAC. The interaction mechanism of Cr(VI)/U(VI) on AAC was demonstrated to be surface complexation by oxygenated functional groups (e.g., hydroxyl) according to X‐ray photoelectron spectroscopy (XPS) analysis. According to fitting of surface complexation models using three approaches, the adsorption of U(VI) on AAC at different pH can be better fitted by the double‐layer model compared to the constant‐capacitance model and triple‐layer model. These findings are great important for the application of acid activated clay in the removal of heavy metals and radionuclides from the environment.

A literature review on thermodynamic sorption models of radionuclides with some selected granitic minerals

The literature for radionuclide sorption on four common granitic minerals have been surveyed. Mainly, such studies were modelling using Thermodynamic Sorption Models were investigated. Although the studies give a far from concerted results, they agree on the necessity to model radionuclide uptake by granitic minerals with a combination of ion exchange and surface complexation reactions. For the sheet-silicates biotite and chlorite alkaline and alkaline earth mainly bind by ion exchange but there is also a clear pH effect for this, which shows the importance of protons competing with metal cations for the exchange sites. For multivalent metal cations, surface complexation is the model of choice since the binding to mineral surfaces seems to be strongly dependent on pH and to be little affected by an increase in ion strength. Anion sorption seems to be taking place also by surface complexation, where the sorption mainly takes place at low pH. For the feldspar minerals K-feldspar and plagioclase the sorption is also modelled by the two reaction mechanisms ion exchange and surface complexation. Surface complexation seems to be especially prevalent for the M(III) and M(VI) state, while ion exchange probably dominates M (II) uptake. Although the literature on these minerals is sparse, the studies show that also these minerals have considerable sorption capacity and must be considered if sorption onto granite is to be modelled from single mineral data. What is usually missing from these studies are more systematic variations in pH, ion strength and temperature. Instead, there is a certain overemphasis on the establishment of sorption isotherms.

Influence of Soil Colloids on Ni Adsorption and Transport in the Saturated Porous Media: Effects of pH, Ionic Strength, and Humic Acid

Natural colloids are widely distributed in soil and groundwater. Due to their specific characteristics, colloids can actively involve various transport contaminants, resulting in a complicated fate and the transport of heavy metals to the environment. This study investigated the effects of soil colloids on the adsorption and transport of Ni2+ in saturated porous media under different conditions, including pH, ion strength (IS), and humic acid (HA), because these indexes are non-negligible in the fates of various organic or inorganic matters in the subsurface environment. The results indicate that Ni2+ adsorption by soil colloids slightly increased from 17% to 25% with the increase of pH from 5.5 to 7.5 at the IS of 30 mmol·L−1, whilst it significantly reduced from 55% to 17% with the increase of IS from 0 to 30 mmol·L−1 at a pH of 5.5. Both Langmuir and Freundlich models can fit the adsorption isotherms of Ni2+ on soil colloids and quartz sand. According to the column experiment, the presence of soil colloids increased the initial penetration rate, but could not increase the final transport efficiency of Ni2+ in the effluent. The presence of soil colloids has weakened the effect of IS on Ni2+ transport in the sand column. Moreover, this experiment implies that HA remarkably decreased the Ni2+ transport efficiency from 71.3% to 58.0% in the presence of soil colloids and that there was no significant difference in the HA effect on the Ni2+ transport in the absence of soil colloids.

Adsorption of benzene on soils under different influential factors: an experimental investigation, importance order and prediction using artificial neural network

The adsorption of benzene on soils is specifically associated with its migration and transformation. Although previous studies have proved that the adsorption of benzene is affected by various factors, studies simultaneously considering the effects of multiple factors are rare. This study aimed to identify the qualitative and quantitative relationships between multiple influential factors and the adsorption capacity of benzene (BC). Batch adsorption experiments considering different influential factors, including initial concentration (IC), pH, temperature (T), ion strength (IS) and organic matter content (OMC), were conducted in three kinds of soils collected in a chemical industry park. The correlation analysis between different influential factors and BC was carried out based on the experimental data. The artificial neural network (ANN) was applied to predict BC. The results showed that BC increased with the increase of T. As the pH increased, BCs on silty loam and loam increased, while that on sandy loam decreased. Besides, BCs on silty loam and loam raised with increasing OMC, while that on sandy loam remained unchanged. BCs on all three kinds of soils attained their peaks when IS was small and then become stable with an increase in IS. The sequence of correlation between BC and influential factors is listed as IC > OMC > T > IS > pH for silty loam, OMC > IC > T > IS > pH for loam and IC > T > IS > pH > OMC for sandy loam. ANN analysis showed satisfactory accuracy in predicting BC under different influential factors. These results help us understand the important factors affecting benzene adsorption and provide a tool to get the adsorption information easily in complex site conditions.

Controlled Crystallization of Sodium Chloride Nanocrystals in Microdrop­lets Produced by Electrospray from an Ultra‐Dilute Solution

AbstractControlled crystallization is very important for crystal growth. The electrospray (ES) technique has attracted great interest thanks to its advantages of facile manipulation of micrometer droplets and the generation of fine and charged droplets with very narrow size dispersion. In this work, nanocrystals with cubic shapes with 32 nm edges were successfully grown from ultra‐dilute NaCl solution (1 µg mL–1) on a millisecond timescale by an ES technique. Dispersed and charged microdroplets were created by ES. In the process, an increase in ion strength and built‐in electric field in microdroplets promoted nucleation and growth. Moreover, solvent evaporation increased solute and charge concentration and decreased the size of the microdroplets, which had a further effect on nucleation and growth. The morphologies of crystals were the competitive results of ion strength and evaporation. Fortunately, these physicochemical properties can be controlled facilely by adjusting the ES parameters. This report suggests potential application of ES technology for controllable crystallization of pharmaceuticals, proteins, etc.

Presentation of a nano-based tag for immunoassay, based on amine-modified bovine serum albumin nanoparticles.

The aim of this study was to evaluate four immunoassays, based on amine-modified bovine serum albumin nanoparticles (AMBSANPs). First, the capability of nitrate absorption by AMBSANPs under different conditions was evaluated. Then, serial concentrations of pure βHCG were added to wells coated with βHCG antibody for immunoassays 1 and 2, and wells coated with βHCG aptamer for immunoassays 3 and 4. Next, AMBSANPs conjugated with βHCG antibody was added for immunoassays 1 and 3, and AMBSANPs conjugated with βHCG aptamer were added for immunoassays 2 and 4. Finally, the optical density (OD) of each well was read at 340 nm, and compared with controls. Moreover, the concentration of βHCG in the clinical samples was quantified by immunoassays 1, 2, 3, 4 and ELISA, and then compared. The effect of some serum interferences on these immunoassay methods was evaluated. The authors observed that the amount of nitrate absorption by AMBSANPs increased with an increase in H+ ion concentration and temperature, and decreased with an increase in ion strength. The correlation (R2) between ELISA and immunoassays 1, 2, 3 and 4 were 0.97, 0.97, 0.98, 0.99, respectively. It was found that the increase in the serum interferences led to a decrease in the measured βHCG concentration.

Comparative adsorption of Eu(III) and Am(III) on TPD.

Comparative adsorption behaviors of Eu(III) and Am(III) on thorium phosphate diphosphate (TPD), i.e., Th4(PO4)4P2O7, have been studied using a batch approach and surface complexation model (SCM) in this study. The results showed that Eu(III) and Am(III) adsorption increased to a large extent with the increase in TPD dose. Strong pH-dependence was observed in both Eu(III) and Am(III) adsorption processes, suggesting that inner-sphere complexes (ISCs) were possibly responsible for the adsorption of Eu(III) and Am(III). Meanwhile, the adsorption of Eu(III) and Am(III) decreased to a different extent with the increase in ion strength, which was possibly related to outer-sphere complexes and/or ion exchange. In the presence of fulvic acid (FA), the adsorption of Eu(III) and Am(III) showed high enhancement mainly due to the ternary surface complexes of TPD-FA-Eu(3+) and TPD-FA-Am(3+). The SCM showed that one ion exchange (≡S3Am/Eu) and two ISCs (≡(XO)2Am/EuNO3 and ≡(YO)2Am/EuNO3) seemed more reasonable to quantitatively describe the adsorption edges of both Eu(III) and Am(III). Our findings obviously showed that Eu(III) could be a good analogue to study actinide behaviors in practical terms. However, it should be kept in mind that there are still obvious differences between the characteristics of Eu(III) and Am(III) in some special cases, for instance, the complex ability with organic matter and adsorption affinity to a solid surface.

Adsorption of nickel ions from seawater by modified chitosan

Chitosan (CS) was modified by using sodium chloride as the porogen agent to remove nickel ions in seawater. The modified CS was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and pHpzc analysis. The influence of pH, background electrolyte concentrations on nickel ions adsorption by CS and modified CS was investigated. The results showed that nickel ions adsorption capacity by CS and modified CS are greatly improve when background electrolyte concentration increase from 0 to 0.8556 mol/L, indicating the modified CS could be an excellent adsorbent to remove nickel ions from seawater. Langmuir, Freundlich, Redlich–Peterson, and Langmuir–Freundlich models were used to illustrate the isotherms of the adsorption process. The mechanism of the adsorption was a combination of electrostatic interaction and chemical adsorption. The nickel species distribution was predicted by Visual MINTEQ program, and the total content of Ni2+, NiOH+, and NiCl+ cation species increased with the increase of ion strength in aqueous, which could demonstrate the adsorption mechanism is dominantly an electrostatic interaction as well. The modified CS could be a potential material to remove nickel ions in pretreatment of seawater for mariculture or industrial applications.

Adsorption Behaviors of Arsenic(V) onto Fe-Based Backwashing Sludge Produced from Fe(II)-Removal Plants

This study investigates the adsorption characteristics of As(V) onto the Fe-based backwashing sludge (FBBS), which was produced in the Fe(II) removal process. FBBS exhibits rough surfaces and shows high BET surface area of 148.41 m2/g. According to the results of EDS and XRD, the main constituents include sulfate inter-layered Fe hydroxide [Fe(SO4)OH], ferric oxhydroxide (γ-FeOOH), quartz (SiO2), and calcium carbonate (CaCO3). The adsorption kinetics data were well described by the Elovich model (r2 = 0.993), indicating the highly heterogeneous adsorption. The maximum adsorption capacity of As(V) increased from 40.04 to 88.76 mg/g as temperatures increased from 298 to 318 K, suggesting an endothermic process. The removal of As(V) was inhibited with elevated solution pH, especially from pH 7.0 to pH 10.0. Moreover, the removal of As(V) was enhanced with an increase in ion strength (0.01-1 M NaNO3), implying that the adsorption of As(V) was mainly through inner-sphere complexes mechanism.

Enhanced Adsorption of Malachite Green by EDTAD-modified Sugarcane Bagasse

Ethylenediaminetetraacetic dianhydride (EDTAD) modified sugarcane bagasse (SB) was prepared and characterized by Fourier transform infrared spectroscopy (FTIR). Due to the presence of a large number of carboxyl groups, the adsorption capacity of the EDTAD modified SB (EDTAD-SB) for malachite green (MG) showed a significant increase compared with SB. Increase in ion strength of solution-induced decline of MG sorption. The maximum adsorption capacities were 157.2 mg g−1 for MG, according to the Langmuir equation. Kinetic studies showed better correlation coefficients for a pseudo-second-order kinetic model, confirming that the sorption rate was controlled by a chemisorption process.

Studies on Interaction of CdTe Quantum Dots with Bovine Serum Albumin Using Fluorescence Correlation Spectroscopy

Luminescent quantum dots (QDs) have widely used in some biological and biomedical fields due to their unique and fascinating optical properties, meanwhile the interaction of QDs with biomolecules recently attract increasing attention. In this paper, we employed fluorescence correlation spectroscopy (FCS) to investigate the nonspecific interaction between CdTe QDs and bovine serum albumin (BSA) as a model, and evaluate their stoichiometric ratio and association constant. Our results documented that BSA was able to bind to CdTe QDs and form the QD-BSA complex by a 1:1 stoichiometric ratio. The association constant evaluated is 1.06+/-0.14x10(7) M(-1) in 0.01 M phosphate buffer (pH=7.4). Furthermore, we found that QD-BSA complex dissociated with increase of ion strength, and we speculated that the interaction of CdTe QDs with BSA was mainly attributed to electrostatic attraction. Our preliminary results demonstrate that fluorescence correlation spectroscopy is an effective tool for investigation of the interaction between quantum dots (or nanoparticles) and biomolecules.

Nucleation kinetics of calcium phosphate nanoparticles in reverse micelle solution

Abstract The nucleation kinetics of calcium phosphate nanoparicles in the reverse micelle solution was investigated in the present experiment. The reaction system consisted of cetyltrimethylammonium bromide (CTAB), cyclohexane, n -pentanol and reactant solution. The amorphous nuclei were mainly composed of dicalcium phosphate (DCPA, monetite) rather than hydroxyapatite (HA) because of the kinetic favor of DCPA. Nucleation kinetic parameters – the nucleation free energy Δ G C , the critical nucleus radii and critical nucleation number – were calculated with the model based on classical nucleation theory and UV–vis absorption spectra. The nucleation rate equation of nanoparticles prepared in reverse micelles solution was developed. Comparisons with classical nucleation equation showed that nucleation rate in reverse micelle solution was lower than those conducted in aqueous solution. A rational reason for this result is as follows: reverse micelles might condense reaction solution thus increasing its concentration. An increase in ion strength makes reverse micelles invulnerable which might disfavor the effective coalescence and the nucleation process as well.

Preparation of Amphoteric Microgels of Poly(acrylamide/methacrylic acid/dimethylamino ethylene methacrylate) with a Novel pH−Volume Transition

Amphoteric microgels consisting of poly(AAm/MAc/DMAEMA/MB) were prepared by semicontinuous polymerization in ethanol. Scanning electron microscopy (SEM) and dynamic light scattering (DLS) were employed for evaluating the microspheres and their pH−volume transitions in the aqueous solution, respectively. Monodispersed amphoteric microgels with a U-type of pH−volume transition, i.e., volume contracted in the pH range 6.5−7.5 and expanded beyond this, were prepared by adding MAc dropwise at a certain rate (20 g/80 min, standard recipes). It was observed that increasing [NaCl] or [CaCl2] served to decrease the hydrodynamic diameter of amphoteric microgels, irrespective of pH. Moreover, in the region of pH 2−3, the pH of amphoteric microgels increased with the increase of ion strength, whereas inversely, for pH 9−10, the pH decreased with an increase of ion strength, regardless of the types of salts. The U-type curve of diameter vs pH could be replaced along with the pH axis by adjusting the charged amount of DMAEMA. Control-releasing behavior of amphoteric microgels was also investigated. It was observed that the dye was released to the same extent when the pH was changed from 6.8 to either acidic or basic conditions.

Thermochemical esterifying citric acid onto lignocellulose for enhancing methylene blue sorption capacity of rice straw

In this paper, rice straw was esterified thermochemically with citric acid (CA) to produce potentially biodegradable cationic sorbent. The modified rice straw (MRS) and crude rice straw (CRS) were evaluated for their methylene blue (MB) removal capacity from aqueous solution. The effects of various experimental parameters (e.g., initial pH, sorbent dose, dye concentration, ion strength, and contact time) were examined. The ratio of MB sorbed on CRS increased as the initial pH was increased from pH 2 to 10. For MRS, the MB removal ratio came up to the maximum value beyond pH 3. The 1.5 g/l or up of MRS could almost completely remove the dye from 250 mg/l of MB solution. The ratio of MB sorbed kept above 98% over a range from 50 to 450 mg/l of MB concentration when 2.0 g/l of MRS was used. Increase in ion strength of solution induced decline of MB sorption. The isothermal data fitted the Langmuir model. The sorption processes followed the pseudo-first-order rate kinetics. The intraparticle diffusion rate constant ( k id) was greatly increased due to modification.

Preparation and utilization of rice straw bearing carboxyl groups for removal of basic dyes from aqueous solution

One kind of potentially biodegradable cationic sorbent with high sorption capacity of basic dyes was prepared by thermochemically esterifying oxalic acid onto rice straw, and then the esterified rice straw was further loaded with sodium ion for enhancing its cationic sorption capacity. The sorption of two basic dyes, basic blue 9 (BB9) and basic green 4 (BG4), from aqueous solutions onto modified product was investigated. The effects of various experimental parameters (e.g. initial pH, sorbent dosage, dye concentration, ion strength, contact time) were examined and optimal experimental conditions were decided. The BB9 and BG4 removal ratios came up to the maximum value beyond pH 6. The 2.0 g/l or above of sorbent could almost completely remove BB9 and BG4 from 250 mg/l of dye solution. The ratios of BB9 and BG4 sorbed kept above 97% over a range from 50 to 250 mg/l of dye concentration when 2.0 g/l of sorbent was used. Increase in ion strength of solution induced decline of BB9 and BG4 sorption. The isothermal data fitted well to the Langmuir and Freundlich models. The sorption processes could be described by the pseudo-second-order kinetic model. The results in this research confirmed that the OA-modified rice straw was an excellent basic dye sorbent.

Removal of basic dyes from aqueous solution by sorption on phosphoric acid modified rice straw

In this article, rice straw was chemically modified by means of phosphorylation, and then the phosphoric acid modified rice straw was further loaded with sodium ion in order to yield potentially biodegradable cationic sorbent. The feasibility of the modified product as cationic dye sorbent for removing basic dyes from aqueous solution was investigated. Two basic dyes, basic blue 9 (BB9) and basic red 5 (BR5), were used as sorbates. The effects of various experimental parameters (e.g. initial pH, sorbent dosage, dye concentration, ion strength, contact time) were examined and optimal experimental conditions were decided. The BB9 and BR5 removal ratios came up to the maximum value beyond pH 4. The 1.5 g/l or more sorbent could almost completely remove BB9 and BR5 from 250 mg/l of dye solution. The ratios of BB9 and BR5 sorbed were kept above 96% over a range from 50 to 350 mg/l of dye concentration when 2.0 g/l of sorbent was used. Increase in ion strength of solution induced decline of BB9 and BR5 sorption. The isothermal data fitted the Langmuir model. The sorption processes followed the pseudo-first-order rate kinetics. The results in this research confirmed that the phosphoric acid modified rice straw was an excellent basic dye sorbent.