Amount Of Cationic Surfactant Research Articles

The preparation of stimulus-responsive Pickering emulsion and its application in preparing microspheres

In this paper, we report a novel redox responsive water-in-oil Pickering emulsion stabilized by negatively charged SiO2 nanoparticles hydrophobized with a trace amount of cationic surfactant 3-pyridyl-5-ferrocenyl-2-pyrazoline (PFP), in which ferrocene serves as a redox-sensitive group. The stability of Pickering emulsion can be modulated by adding oxidant and reducing agent alternatively, which leads to the change of amphiphilicity of SiO2 nanoparticles because of the adsorption of PF+P and desorption of PFP. This destabilization-stabilization behavior can be cycled at least three times, demonstrating that the Pickering emulsion is switchable. At the same time, polyacrylamide@SiO2-PF+P microspheres are prepared using Pickering emulsion as template, which can be used for the detection of Fe3+. Interestingly, when extremely small amounts of microspheres are placed in Fe3+ solution and left overnight, the limit of detection (LOD) decreases significantly because of the synergistic effect of enrichment and fluorescent probe for polyacrylamide and PF+P respectively. Moreover, the fluorescence intensity increased when EDTA was added to the solution containing microspheres and Fe3+, and a decrease of fluorescence intensity was observed when Fe3+ was added again, indicating that the composite microspheres could be reused. This work provides a promising way to construct novel fluorescent probes.

Application of Surfactant Modified Natural Zeolites for the Removal of Salicylic Acid—A Contaminant of Emerging Concern

This work aimed to test composites (surfactant modified zeolites prepared by treatment of natural zeolites—clinoptilolite (IZ CLI) and/or phillipsite (PHIL75)-rich tuffs with two different amounts of cationic surfactants: cetylpyridinium chloride (CPyCl) and Arquad® 2HT-75 (ARQ)) for the adsorption of salicylic acid (SA)—a common contaminant of emerging concern. Adsorption of SA was studied at different initial drug concentrations (in the range of 2–100 mg/L) in water solution. The Langmuir isotherm model showed the highest adsorption was achieved by bilayer composite of IZ CLI and CPyCl—around 11 mg/g. Kinetic runs were performed by using the initial drug concentration of 20 mg/L in the time interval from 0 to 75 min and pseudo-second order had good correlation with experimental data. The influence of the four different temperatures on the SA adsorption was also investigated and thermodynamic parameters suggested that the adsorption drug onto composites is an exothermic and nonspontaneous process, followed by the decrease of randomness at the solid/liquid interface during the adsorption. Zeta potential and Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) had been performed for the characterization of composites after adsorption of SA confirming the presence of the drug at composite surfaces.

Compaction and decompaction of DNA dominated by the competition between counterions and DNA associating with cationic aggregates

A systematic work concerning the DNA compaction and decompaction controlled by cationic surfactants, cetyltrimethylammonium with [FeCl3Br]− (CTAFe), Br− (CTABr) and Cl− (CTACl) as counterions, respectively, was performed. We discovered that cationic surfactants with complex counterions, [FeCl3Br]−, cannot promote the decompaction of DNA like those with Br− and Cl− as counterions. The rod-like CTAFe micelles were found to remain free in supernatants and cannot directly promote any redissolution or decompaction of DNA. These interesting findings could provide a better understanding of the interaction behavior of DNA and cationic surfactants. We conclude that the fundamental reason of the DNA decompaction lies upon the electrostatic competition between the counterions and DNA for associating with the cationic aggregates. At a high concentration, the binding of counterions to cationic CTA+ aggregates is promoted, which weakens and screens the electrostatic attraction between DNA and cationic aggregates. This could cause the decompaction of DNA as the cases of CTABr/DNA and CTACl/DNA mixtures. Our data revealed the fundamental reason of the compaction and decompaction behavior of DNA induced by cationic surfactants independently, a reasonable three-step model of the conformational changes of DNA controlled by different amounts of cationic surfactants was presented. The current work could provide a clear guidance in gene delivery, gene therapy and biomedicine fields.

Evaluation of ultrasound-assisted in situ sorbent formation solid-phase extraction method for determination of arsenic in water, food and biological samples

A simple and rapid ultrasound-assisted in situ sorbent formation solid-phase extraction (UAISFSPE) coupled with electrothermal atomic absorption spectrometry detection (ET-AAS) was developed for preconcentration and determination of arsenic (As) in various samples. A small amount of cationic surfactant is dissolved in the aqueous sample containing As ions, which were complexed by ammonium pyrrolidinedithiocarbamate After shaking, a little volume of hexafluorophosphate (NaPF6) as an ion-pairing agent was added into the solution by a microsyringe. Due to the interaction between surfactant and ion-pairing agent, solid particles are formed. The alkyl groups of the surfactant in the solid particles strongly interact with the hydrophobic groups of analytes and become bound. Sonication aids the dispersion of the sorbent into the sample solution and mass transfer of the analyte into the sorbent, thus reducing the extraction time. The solid particles are centrifuged, and the sedimented particles can be dissolved in an appropriate solvent to recover the absorbed analyte. After separation, total arsenic (As(III) and As(V)) was determined by ET-AAS. Several experimental parameters were investigated and optimized. A detection limit of 7 ng L−1 with preconcentration factor of 100 and relative standard deviation for 10 replicate determinations of 0.1 µg L−1 As(III) were 4.5% achieved. Consequently, the method was applied to the determination of arsenic in certified reference materials, water, food and biological samples with satisfactory results.

Combination of In Situ Surfactant-based Solid Phase Extraction and Central Composite Design for Preconcentration and Determination of Manganese in Food and Water Samples

A new kind of solid phase extraction (SPE), which we named in situ surfactant-based solid phase extraction (ISS-SPE), represents a simple, selective and rapid method for preconcentration and determination of manganese from food and water samples. This method has distinct advantages: extraction times are short and recoveries are high; further, we can see formation of fine particles of large specific surface and their good dispersion in the solution. In this work, a small amount of cationic surfactant, n-dodecyltrimethylammonium bromide (DTAB) was injected into the water sample containing Mn ions, which were complexed by 1-(2-pyridylazo)-2-naphthol (PAN). After shaking, a little volume of NaPF6 as an ion-pairing agent was added into the solution by a microsyringe. After preconcentration, the settled phase was dissolved in a specific volume of ethanol and then aspirated into the flame atomic absorption spectrometer by using a homemade microsample introduction system. The effective parameters such as pH, concentration of surfactant, concentration of chelating agent, concentration of ion-pairing agent and effect of salt concentration were optimized by a fractional factorial design to identify the most important parameters and their interactions, and central composite methodology was used to achieve the optimum point of effective parameters to the response. Under the optimum conditions, preconcentration of 10 ml of the sample solution permitted detection of 0.88 μg l−1 with enhancement factor of 45.6, and the relative standard deviation (RSD) for five determinations of Mn ions was 3.5%. The developed method was applied to the determination of trace manganese in various real samples with satisfactory results.

Synthesis of walnut-like hierarchical structure with superhydrophobic and conductive properties

Walnut-like structures made up of a polyaniline (PANI) nanofiber network and polystyrene (PS) microspheres are successfully fabricated by a novel approach, “competitive adsorption–restricted polymerization”. In the reaction system, PS microspheres are simultaneously encapsulated by cationic surfactant and aniline hydrochloride. Just this cationic surfactant molecule affects the nucleation model and second growth of PANI via electrostatic interactions and steric hindrance, which accounts for the formation of a PANI nanofiber network coating on the PS surface. The size, ordering and amount of PANI nanofibers on the three-dimensional surface can be particularly controlled by altering a variety of synthetic conditions, such as the amount of cationic surfactant, temperature and concentration. A superhydrophobic and conductive surface is obtained by drop-casting a suspension of these walnut-like PS/PANI particles onto a substrate.

Effect of surfactant on reductive dechlorination of trichloroethylene by zero-valent iron

Trichloroethylene (TCE) is a representative dense nonaqueous phase liquid (DNAPL) in groundwater. TCE as a form of free fluid has been treated by surfactant-enhanced aquifer remediation (SEAR). After application of SEAR, groundwater contains little amount of residual TCE and surfactant. Residual TCE could be treated by zero-valent iron (ZVI). However, surfactant might modify the surface property of ZVI. As a result, the reduction of TCE on the surface of ZVI might be affected by the presence of surfactant. In this study, the effect of surfactant types on reductive dechlorination of TCE was investigated using zero-valent iron. Cationic surfactant enhanced the dechlorination rate of TCE at a concentration below the critical micelle concentration (CMC) compared to pure ZVI. Electrostatic interaction between electronegative chloride group of TCE and positive head group of cationic surfactant was increased sorption of TCE on the surface of ZVI. However, anionic and nonionic surfactants inhibited the reductive dechlorination of TCE because of the decrease of TCE sorption on the surface of ZVI. The reduction rate of TCE in the presence of nonionic surfactant is dependent on the length of hydrophobic carbon chain in nonionic surfactant. Little amount of cationic surfactant could enhanced the reductive dechlorination rate of TCE. As a result, the time to treat TCE in groundwater will be shortened.

Spectrofluorimetric Assay of Cationic Surfactants by Fluorescence Quenching of 9-Anthracenecarboxylic Acid

A new simple, selective and sensitive fluorescence quenching method was developed to determine cationic surfactants with the 9-anthracenecarboxylic acid (ACA). The fluorescence intensity of ACA was decreased by addition of trace amounts of cationic surfactants. Under optimum conditions, the ratio of fluorescence intensity in the absence and presence of cationic surfactants was proportional to the concentration of cationic surfactants over the range of 0.3–4.5 × 10−5 mol L−1 for cetylpyridinium chloride (CPC) and 0.4–6.0 × 10−5 mol L−1 for cetyl trimethyl-ammonium bromide (CTAB). The detection limits are 1.0 × 10−6 mol L−1 for CPC and 1.2 × 10−6 mol L−1 for CTAB, respectively. Based on this approach, this paper presents a new quantitative method for cationic surfactants assay.

Sorption study of 2,4-dichlorophenol on organoclays constructed for soil bioremediation

The role of the type and amount of cationic surfactant in the sorption behaviour of partially modified clays was studied and the applicability of a partially modified organoclay for bioremediation was demonstrated. Partially modified surfactant/clay complexes (“organoclays”) were prepared from Na-montmorillonite by using monoalkyl-(dodecyltrimethylammonium and octadecyltrimethylammonium) and dialkylammonium (didodecyldimethylammonium and dioctadecyldimethylammonium) bromides. The degree of modification was varied between 35 and 89% of the cation exchange capacity of montmorillonite (MM). The sorption of 2,4-dichlorophenol (DCP) on organoclays was studied by using the batch technique. The intercalation of DCP into the interlayers of organo-MM was detected by X-ray diffraction. The adsorption isotherms found were non-linear indicating that the sorption is not only based on a simple partition mechanism. The adsorption coefficients K d calculated from the initial isotherm slope turned out to be exponential with the organic carbon content of organo-MM ( f oc). In particular, dialkylammonium-modified MM revealed outstanding sorption characteristics for DCP. The comparison of partially modified organo-MMs with similar f oc and volume fraction of surfactant indicated that the surfactant arrangement in the interlayers significantly influences the DCP adsorption. It could be assumed that both the kind and degree of exchanged surfactant play a decisive role in the adsorption of DCP on the organoclays. By performing biodegradation experiments in the presence of dioctadecyldimethylammonium montmorillonite, the complete biodegradation of DCP was achieved demonstrating the applicability of partially modified organoclays for bioremediation.

Chemical and physical factors affecting the extractability of methidathion from soil samples.

Determination of methidathion in soil samples using Soxhlet extraction has been studied. Several factors were investigated for their effect on methidathion recovery. Some were related to the extraction procedure, for example solvent type used for the extraction (acetone or hexane/toluene), extraction time, soil humidity, and type of sterilisation system employed. Other factors tested included the addition of organic matter to the soil, for example urban sewage sludge and the cationic surfactant TDTMA. Experimental designs were used to determine the effects of the different factors. Acetone resulted in higher recoveries and was less affected by the presence of water. Autoclaving was the most appropriate sterilisation method. Thimerosal resulted in a decrease in insecticide recovery. Methidathion recovery increased as the amount of cationic surfactant was increased, but decreased as the amount of sewage sludge added to the soil was increased. In general, because the factors studied were not always independent of each other, a clear description of the methodology used is needed when analysing pollutants in environmental samples.

Adsorption Mechanism of Chloroacetanilide Herbicides to Modified Montmorillonite

This study was undertaken to characterize the adsorption mechanism of alachlor and metolachlor on montmorillonite modified with cationic surfactants. Adsorbed amounts of cationic surfactant on montmorillonite surfaces were determined by CNHSO analyzer. Equilibrium concentrations of alachlor and metolachlor were determined by GC and adsorption results were fit to a linear regression equation. The slope of the isotherms (Kd) was normalized to the fraction of organic carbon on montmorillonite complexes to produce corresponding Koc. Adsorption of surfactants fit very well to Langmuir equation. Increased basal spacing indicates that surfactant molecules could penetrate through the interlayer spacing and arrange themselves in different ways. Equilibrium data of alachlor and metolachlor suggest that adsorption may occur via physical or chemical bonds. Koc values of alachlor or metolachlor decreased as the fraction of the organic carbon increased in montmorillonite complexes indicating independent adsorption process. Changes of the molar free energy of the adsorption reactions were in the range of physical adsorption, indicating that adsorption reactions are spontaneous and the molecules either adsorb on the surface or penetrate into the inter‐layers of montmorillonite‐surfactant complex. Careful investigation of the adsorption data suggests that interaction may occur via the active groups such as carbonyl group (–C˭O), anilidic (C–N) group and/or phenyl rings. This information may provide better understanding on adsorption mechanism and be useful in designing ecologically acceptable herbicide formulations.

Glucose‐6‐phosphate dehydrogenase partitioning in two‐phase aqueous mixed (nonionic/cationic) micellar systems

The enzyme glucose-6-phosphate dehydrogenase (G6PD) plays an important role in maintaining the level of NADPH and in producing pentose phosphates for nucleotide biosynthesis. It is also of great value as an analytical reagent, being used in various quantitative assays. In searching for new strategies to purify this enzyme, the partitioning of G6PD in two-phase aqueous mixed (nonionic/cationic) micellar systems was investigated both experimentally and theoretically. Our results indicate that the use of a two-phase aqueous mixed micellar system composed of the nonionic surfactant C(10)E(4) (n-decyl tetra(ethylene oxide)) and the cationic surfactant C(n)TAB (alkyltrimethylammonium bromide, n = 8, 10, or 12) can improve significantly the partitioning behavior of G6PD relative to that obtained in the two-phase aqueous C(10)E(4) micellar system. This improvement can be attributed to electrostatic attractions between the positively charged mixed (nonionic/cationic) micelles and the net negatively charged enzyme G6PD, resulting in the preferential partitioning of G6PD to the top, mixed micelle-rich phase of the two-phase aqueous mixed micellar systems. The effect of varying the cationic surfactant tail length (n = 8, 10, and 12) on the denaturation and partitioning behavior of G6PD in the C(10)E(4) /C(n)TAB/buffer system was investigated. It was found that C(8)TAB is the least denaturing to G6PD, followed by C(10)TAB and C(12)TAB. However, the C(10)E(4)/C(12)TAB/buffer system generated stronger electrostatic attractions with the net negatively charged enzyme G6PD than the C(10)E(4)/C(10)TAB/buffer and the C(10)E(4)/C(8)TAB/buffer systems, when using the same amount of cationic surfactant. Overall, the two-phase aqueous mixed (C(10)E(4)/C(10)TAB) micellar system yielded the highest G6PD partition coefficient of 7.7, with a G6PD yield in the top phase of 71%, providing the optimal balance between the denaturing effect and the electrostatic attractions for the three cationic surfactants examined. A recently developed theoretical framework to predict protein partition coefficients in two-phase aqueous mixed (nonionic/ionic) micellar systems was implemented, and the theoretically predicted G6PD partition coefficients were found to be in reasonable quantitative agreement with the experimentally measured ones.

Stability and Adsorption Properties of Suspensions of Finely Dispersed Silica in the Presence of Cationic Surfactants

Interrelation between the coagulation rate, adsorption and electrokinetic properties of silica polydisperse suspensions in the presence of cationic surfactants is studied. The highest coagulation rate is observed in a certain concentration range of the cationic surfactants. When pH values increases, an increasing amount of cationic surfactant is required to achieve maximal coagulation rate. For bisquaternary cationic surfactants, ethonium and decamethoxine, maximal coagulation rate is observed at concentrations by an order of magnitude lower than for monoquaternary cetyltrimethylammonium bromide. It is concluded that the suspensions lost their stability as a result of both neutralization of particle surface charge and flocculating effect of the cationic surfactants. Moreover, the flocculation mechanism depends on the cationic surfactant nature and physicochemical parameters of the medium, ionic strength and pH.

Synthesis of mesoporous MCM-48 with a mixed nonionic-cationic surfactant templating pathway

In a hydrothermal system, we studied the influence of nonionic surfactant poly(ethylenglycol) monooctylphenyl ether (OP-10) on the self-assembling process of mesoporous molecular sieve MCM-48 and found that OP-10 can decrease the amount of cationic surfactant needed for the preparation of MCM-48 further by its stronger van der Waals force, shorten the synthetic period and produce MCM-48 with more extensive cross-linked framework. By altering the ratio of nonionic surfactant to cationic surfactant, we could obtain the mesoporous molecular sieves with different structures. When the crystallization temperature exceeded 140°C, OP-10 would separate from micelle, lose its amphiphilic character, and then hamper the conversion of lamellar mesoporous molecular sieves into microporous materials.