Cationic Cetyltrimethylammonium Bromide Research Articles

Effect of CTAB on the surface resonance plasmon intensity of silver nanoparticles: Stability and oxidative dissolution

Stable silver nanoparticles (AgNPs) were prepared from the reduction of silver ions by sodium borohydride in presence of shape controlling cationic cetyltrimethylammonium bromide (CTAB) at room temperature. The intensity and position of surface plasmon resonance (SRP), morphology depends on the concentrations of CTAB. The complex forming tendency of CTAB with positive head group of surfactant and borohydride anion (BH4−) was responsible for pre-, and post-micellar effect. The values of BH4−-CTAB binding constant (Ks = 33.6 × 104 mol−1 dm3) and rate constant in micellar pseudo phase (km = 5.5 × 10−5 s−1) were calculated. Catalytic role of CTAB discussed in term of pseudo-phase model. The silver soles were unstable at higher [BH4−] (≥14.0 × 10−5 mol/L). Transmission electron microscopic images indicate that the AgNPs are roughly spherical and poly dispersed. The oxidative dissolution of silver nanoparticles was very slow. The [BH4−] has significant impact on the sensing properties of AgNPs. The dissolution rate increases drastically by adding hydrogen peroxide. Scavengers quenched the oxygen radical reactive species (hydroxy radical and superoxide) and decreased the hydrogen peroxide catalyses rate of AgNPs.

Magnetic Solid-Phase Extraction and Fluorimetric Determination of Some Fluoroquinolones

An approach to estimating the concentration of fluoroquinolones based on their sorption and preconcentration by magnetic solid-phase extraction on magnetite nanoparticles modified with cetyltrime-thylammonium bromide cations (CTAB) or polyethyleneimine cationic polyelectrolyte (PEI), and the fluorimetric determination of these preparations is proposed. The optimal conditions for the modification of magnetite nanoparticles by PEI and CTAB cations are found. Using examples of enrofloxacin, levofloxacin, and pefloxacin, patterns of their sorption and preconcentration on modified magnetite nanoparticles are found. Fluorimetric procedures for the determination of enrofloxacin and levofloxacin in river water, a plasma substitute, and veterinary preparations are tested.

Sensitivity of Extracellular Vesicles from Human Blood Serum to Various Detergents

Blood exosomes and microvesicles, collectively known as small extracellular vesicles (sEV), are vesicles about 100-150 nm in size. Small EV are involved in various aspects of signaling in the body; in addition, they can serve as markers of various pathologies. For biochemical studies, vesicle solubilization is often required. We tested the ability of various detergents to dissolve membranes of the sEV. Small EV were isolated from the blood serum of healthy volunteers by gel filtration on Sepharose CL-2B and tried to solubilize them using the anionic detergent DOC (sodium deoxycholate), non-ionic detergent Brij 35 (polyoxyethyleneglycol dodecyl ether), zwitterionic detergent CHAPS (3 - [(3-chloramidopropyl) dimethylammonio] -1-propanesulfonate), and cationic detergent CTAB (cetyl trimethylammonium bromide). The concentration of sEV in the solution was determined by dynamic light scattering. We find DOC is the most effective for sEV solubilization.

Promising Route for the Development of a Computational Framework for Self-Assembly and Phase Behavior Prediction of Ionic Surfactants Using MARTINI.

Surfactants are amphiphilic molecules with multiple uses and industrial applications as detergents, wetting agents, emulsifiers, and so forth. They can be divided into three main categories: nonionic, ionic, and zwitterionic. The development of a universal computational framework able to predict key properties such as their critical micelle concentration (cmc) and the size of the micelles they form and to ultimately extract phase diagrams for their aqueous solutions, possibly in the presence of salts and oils, using their chemical constitution as input, would provide valuable information for the design and the production of these materials. In this work, we focus on ionic surfactants and investigate a possible route toward the development of such a framework based on coarse-grained simulations using the MARTINI forcefield in two versions: its implicit solvent version, called Dry MARTINI, and its explicit solvent version, called Wet MARTINI. The surfactants considered in our efforts are the anionic sodium dodecyl sulfate (SDS) and the three cationic cetyl, dodecyl, and octyl trimethyl ammonium bromide (CTAB, DTAB, and OTAB, respectively). First, we choose their mapping onto coarse-grained MARTINI beads. Next, we estimate their cmc's, their peak aggregation numbers, Nagg, and in the case of SDS, its small angle neutron scattering pattern at low concentrations, applying the Dry MARTINI forcefield. With a single modification to the Lennard-Jones energy parameter between hydrophobic beads and invoking Ewald summation with a physically meaningful dielectric constant for electrostatic interactions, our estimates are in very good agreement with experimental results. Furthermore, we predict the phase behavior of SDS/water and CTAB/water binary solutions using Wet MARTINI and find semiquantitative agreement with experimental phase diagrams. We conclude that the MARTINI forcefield, with careful treatment of electrostatic interactions and appropriate modification of parameters for some key functional groups, can be a powerful ally in the quest for a universal computational framework for the design of new surfactants with improved properties.

Adsorption of Fluoroquinolone Antibiotics at the Gas-Liquid Interface Using Ionic Surfactants.

The overuse of antibiotics in today's society has resulted in high concentrations of pharmaceutical contaminants in the natural environment. In this work, we investigated the surfactant-mediated adsorption of fluoroquinolone (FQ) antibiotics at the gas-liquid interface and their separation using a semi-batch foam fractionation process. FQs being a zwitterionic compound have an affinity to bind with both cationic and anionic surfactants. The adsorption of FQs to the gas-liquid interface was investigated using a cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS) surfactant. Ciprofloxacin (CF) was chosen as a model FQ antibiotic. The adsorption properties of the surfactant systems and CF were characterized using pendant-drop tensiometry and surface excess analysis. It was found that CF partitions to the gas-liquid interface more readily in the presence of SDS compared to CTAB. This was also corroborated in the foam fractionation experiments. At optimum operating conditions, CF showed a higher removal efficiency with SDS (96.3%) compared to CTAB (52%). In spite of strong molecular interactions between CTAB and CF, the preferential adsorption of DS--CF complexes was far greater than CTA+-CF complexes. At optimized operating conditions, using SDS as the surfactant, other FQs such as norfloxacin, levofloxacin, and ofloxacin were recovered up to 97.9, 91.7, and 96.7%, respectively, with effluent concentration less than 100 nM. Overall, the work demonstrates foam fractionation as a novel and environment-friendly gas-liquid separation technique for the targeted removal of FQ antibiotics from waterbodies.

In Silico Characterization of the Binding Modes of Surfactants with Bovine Serum Albumin

The binding interactions of the surfactants: anionic sodium dodecyl sulphate (SDS), cationic cetyltrimethylammonium bromide (CTAB), non-ionic octyl glucoside (OG), and zwitterionic 3-[Hexadecyl(dimethyl)ammonio]-1-propanesulfonate (HPS), with bovine serum albumin (BSA) were investigated by computer simulation. The results disclosed that the surfactants bound stably between hydrophobic subdomain IIA and IIIA where tryptophan-213 residue, an important intrinsic fluorophore in BSA is housed. The interactions of the surfactants with the BSA were electrostatic and hydrophobic interactions. The head-groups of SDS, HPS and OG formed hydrogen bonds with the BSA, while that of CTAB was shielded from intermolecular hydrogen-bonding due to intervening methyl groups. Subsequently, molecular dynamics (MD) simulation of the protein-surfactant complexes revealed that hydrogen bonds formed by OG were stronger than those of SDS and HPS. However, the decomposed force-field energies showed that OG had the least interaction energy with the BSA. In addition to MD simulation, it was found by density functional theory (DFT) that the differences in the coulomb interaction energies can be attributed to charge distribution in the surfactants. Overall, free energies calculated by linear interaction energy (LIE) proved that the binding of each surfactant was dominated by differences between van der Waals interactions in bound and free states.

Kinetic and mechanistic investigations of [Zn (II)‐Trp]+ and ninhydrin in aqueous and cationic CTAB surfactant

AbstractKinetic and mechanistic investigations of [Zn (II)‐Trp]+ and ninhydrin in aqueous and cationic cetyltrimethylammonium bromide (CTAB) surfactant have been executed in CH3COOH‐CH3COONa buffers of pH 5.0. Spectrophotometric as well as conductometric techniques were employed to carry out the study at experimental temperature. The values of rate constant (kobs in aqueous and kψ in CTAB surfactant) and binding parameters (KB for [Zn (II)‐Trp]+ and KN for ninhydrin) have been determined by the means of a computer program referred to as linear least squares technique. Fractional‐ and first‐order kinetics were found in ninhydrin and [Zn (II)‐Trp]+, respectively, in aqueous and cationic CTAB. Study was catalyzed and accelerated by CTAB surfactant. An increase in CTAB surfactant concentration from 0 to 45 mmol kg−1 resulted to an increase in kψ from 2.5 × 10−5 s−1 to 22.7 × 10−5 s−1. Surfactant concentration beyond 45 mmol kg−1 had a slow decreasing effect in kψ. In order to elucidate CTAB effect on kψ, a pseudo‐phase model of micelles was applied.

Dielectric relaxation studies of collagen – surfactant complexes in aqueous buffer solution

Dielectric relaxation studies of rat tail tendon collagen with anionic sodium dodecyl sulphate (SDS), cationic cetyltrimethyl ammonium bromide (CTAB) and nonionic Tween 80 in aqueous buffer solutions at four different temperatures have been carried out in the frequency range 1 GHz to 25 GHz using time domain dielectric spectroscopy. The frequency dependent normalized dielectric modulus function P of the collagen and surfactant solutions show up as peaks around 1–2 GHz which is due to the bound water around collagen macromolecule and surfactant micelles. For the collagen – surfactant complexes, the peak in normalized dielectric modulus function P is shifted towards high frequency side near 2–3 GHz upon addition of surfactants to collagen in buffer solution. The water structure around collagen is altered in the presence of micelle forming surfactant additives and this change may affect the degrees of freedom of their motion. Hence the significant changes are observed in the relaxation time of bound water around collagen macromolecule in the presence of surfactants. Further, it was observed that no considerable change in relaxation time of hydration water of the complexes with respect to change in temperature within the studied temperature range. The activation enthalpy and activation entropy for the dipolar orientation corresponding to the free water for the surfactants and their complexes with collagen have been calculated from the Arrhenius plot. Our thermodynamic results suggest that the two‑hydrogen-bonded model may be possible in SDS and Tween 80 environments, whereas the one‑hydrogen-bonded model is likely to be possible in buffer and CTAB environments.

The effects of surfactants on the heterogeneous uptake of sulfur dioxide on hematite

Surfactants are often found to be associated with atmospheric particles. They can change the physicochemical properties of these particles, and thereby impact their chemical reactivity. However, their influences on heterogeneous reactions of atmospheric trace gases have not been paid much attention. In this study, the impacts of different surfactants on the heterogeneous conversion of SO2 on hematite were investigated by using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), including cationic cetyltrimethylammonium bromide (CTAB), anionic sodium dodecyl sulfate (SDS) and nonionic polyethylene glycol tert-octylphenyl ether (Triton X-100). Results indicated that heterogeneous reactivities of hematite-surfactant mixtures were significantly different due to the presence of different surfactants. Under dry conditions, heterogeneous reactivities decreased with the increase of their concentrations, but the higher reactivities were observed at an appropriate concentration range of CTAB and SDS when compared to pure hematite, showing their promoting effects at this concentration range. Under the condition of 58% relative humidity, the heterogeneous reactivities increased first and then decreased with the increasing mass fractions of CTAB and SDS, but pure hematite showed the highest reactivity. While the mixtures containing Triton X-100 had stronger ability to suppress sulfate formation under 58% RH than under dry condition, though these mixtures under 58% RH presented same trend as under dry condition. Water molecules can renew surface reactive sites and promote sulfate formation at an appropriate mass fraction of CTAB or SDS, water molecules can also promote the adsorption mode transition of Triton X-100 from adsorption through terminal OH groups to adsorption through ethoxyl groups, resulting in more surface active sites being covered and a drastically decrease in the reactivity. A possible mechanism for the impact of surfactants on the heterogeneous conversion of SO2 on hematite is proposed, and atmospheric implications based on these results are discussed.

Colorimetric Sensing of Nitroaromatic Energetic Materials Using Surfactant-Stabilized and Dithiocarbamate-Functionalized Gold Nanoparticles

There is an increasing need for sensitive/selective determination of explosive traces in soil and post-blast debris for environmental and criminal investigations. A colorimetric sensor was developed to detect and quantify trinitrotoluene (TNT) and tetryl by the use of surfactant-stabilized and dithiocarbamate-functionalized gold nanoparticles (AuNPs). The sensor was manufactured by modifying the nanoparticles with the cationic surfactant cetyl trimethyl ammonium bromide and incorporating diethyldithiocarbamate (DDTC) in the AuNPs synthesis. DDTC firmly bound to AuNPs may show charge-transfer interactions with the —NO2 groups of the analytes, and a color change proportional to analyte concentration accompanied the agglomeration of nanoparticles, at which the absorbances were recorded at 534 nm and 458 nm for TNT and tetryl, respectively. Although the limit of detection was 8 mgL−1 (3.52 × 10−5 molL−1) for TNT and 0.8 mgL−1 (2.78 × 10−6 molL−1) for tetryl, providing moderate sensitivity, the cost was greatly reduced compared to those of other thiol-functionalized AuNPs sensors. Possible interferences of other energetic substances in synthetic mixtures, of camouflage materials used in passenger belongings (e.g., detergent, sugar, caffeine, and paracetamol) and common soil ions were also examined. The method was statistically validated against a reference gas chromatography/mass spectrometry method. This sensor may pave the way for the manufacture of novel low-cost nitroaromatic explosive sensors made of DDTC-based pesticides.

Comparative studies of natural and synthetic surfactants for dyes interactions at their second point of micellisation

ABSTRACT The presented work describes the interaction behaviour of natural and synthetic ionic surfactants with the oppositely charged dyes at the point of second critical micellar concentration (CMC). These interactions were monitored at different times, with additive at varying temperatures. The surfactant changes its shape at second CMC and therefore the interactional changes occurred owing to its structural changes. The obtained second CMC for the natural surfactant (NS) was 6.6 mM, whereas the counter, synthetic surfactants (SS) like cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) possess 20 and 65 mM, respectively. The cationic CTAB showed a red shift, whereas the anionic SDS showed hypochromic shift and comparable results with NS. The interactions were found to be spontaneous at all monitored temperatures. The studied NS provides a suitable replacement to the SS. This interactional study will be helpful in various applications, such as soil washing, oil recovery and in different medicinal uses, and found to be economical.

Initiator Based on the Cu(II) and Cetyl Trimethyl Ammonium Bromide Compounds that Generates Free Radicals in the Decomposition of tert-Butyl Hydroperoxide in Optimum Temperature Conditions

The two-component composition consisting of complex copper Cu(II) compounds and cationic surface-activated substance cetyl trimethyl ammonium bromide (CTAB) exhibits high catalytic reactivity during decomposition of tert-butyl hydroperoxide. One specific characteristic of the effects of the Cu(II) + CTAB binary system consists in its high rate of processing without visible signs of deactivation in the transformation of significant amounts of the reagent in optimum temperature conditions.

Tunable size and shape of conductive poly(N‐methylaniline) based on surfactant template and doping

AbstractPoly(N‐methylaniline) (PNMA) is one of the polyaniline derivatives with N‐substituted position. Polyaniline derivatives have attracted attention due to their higher solubility in common solvents than pristine polyaniline, but they still possess lower electrical conductivity. In this work, PNMA was synthesized via chemical oxidative polymerization in an ethanol–water system. The effect of surfactant type, namely anionic sodium dodecylbenzenesulfonate (SDBS), cationic cetyltrimethylammonium bromide and non‐ionic Tween20, on the electrical conductivity, doping level and morphology was investigated. PNMA prepared with the SDBS system possessed the highest electrical conductivity among the obtained PNMAs with and without surfactants. The effect of /NNMA dopant mole ratios on the re‐doping, crystallinity, morphology and particle size was also examined. Using an /NNMA mole ratio of 10:1 in the re‐doping process provided the highest electrical conductivity of 15.53 ± 2.5 S cm−1, a doping level of 55.59%, along with hollow spherical particles with the thinnest membrane. Electron microscopy images revealed that the morphology of PNMA particles depended mainly on the surfactant type but not the /NNMA mole ratio. © 2019 Society of Chemical Industry

Multi-shaped cationic gold nanoparticle-l-cysteine-ZnSeS quantum dots hybrid nanozyme as an intrinsic peroxidase mimic for the rapid colorimetric detection of cocaine

Current presumptive tests for illicit drugs can suffer from false positive results and poor selectivity, and consequentially there is a need to develop new colour spot tests specifically designed to circumvent these existing challenges. In this work, we report on a new fluorescent hybrid nanozyme peroxidase-like catalytic colorimetric sensor and demonstrate proof of concept of this novel colorimetric-specific presumptive test for cocaine. A novel peroxidase-mimic hybrid nanozyme was developed based on the localized surface plasmon resonance-enhanced fluorescence interaction between multi-shaped cationic cetyltrimethylammonium bromide (CTAB)-functionalized gold nanoparticles (AuNPs) and anionic non-cadmium fluorescent-emitting L-cysteine-capped ZnSeS alloyed quantum dots (QDs). The affinity-based interaction of cocaine with the QDs-CTAB-AuNP surface was induced by its distinct structural conformation and this forms the basis for the selective recognition. Thus, the hybrid nanozyme could function both as a catalytic affinity-based receptor and as an optical signal transducer based on the catalysed oxidation of 3,5,5-tetramethylbenzidine by H2O2. A positive bluish-green colour, specific to cocaine recognition, was colorimetrically obtained under optimum catalytic conditions. The optimized assay system detected cocaine within two minutes with unique specificity and distinct colour reaction. Under the optimum cocaine reaction conditions, the analysis of other substances and drugs on the colorimetric response of the QDs-CTAB-AuNP hybrid nanozyme revealed no colour interference, thus demonstrating that the developed probe could be utilized as a presumptive colour spot test for cocaine.

Eco-friendly walnut shell powder based facile fabrication of biogenic Ag-nanodisks, and their interaction with bovine serum albumin

Walnut shell biomass was used for the extraction of juglone by water as a solvent at room temperature. Upon addition of AgNO3 to a dye solution, prefect transparent pale brown color develops within the reaction time. UV–visible spectroscopy revealed the appearance of surface plasmon absorption (SRP) peak at 410 nm for spherical silver nanoparticles (AgNPs). Transmission electron microscopy suggested the formation of spherical and truncated triangular nano-plate geometry of AgNPs with average diameter 25 nm. Juglone-surfactant interactions (micellization and incorporation) have been studied spectrophotometrically by using cationic cetyltrimethylammonium bromide (CTAB). The presence of CTAB has significant impacts on size, shape and the size distribution of AgNPs. The nucleation, growth, and adsorption processes depend on the [CTAB]. It also catalyzes the Ag+ ions reduction by juglone with a rate enhancement of ca. 100-fold. Activation parameters (activation energy, enthalpy of activation and entropy of activation) were evaluated to the synthesis of silver nano-disks. Antioxidant activity of juglone was accessed by the scavenging effect on DPPH radical. Silver nanoparticles was also used as quencher to determine their interaction with bovine serum albumin (BSA). The quenching constant were found to be 1.4 × 103 M−1 L s−1 and 4.8 × 103 M−1 L s−1 for two BSA concentrations.

Cationic-Surfactant-Coated Mica Surfaces below the Critical Micellar Concentration: 1. Patchy Structures As Revealed by Peak Force Tapping AFM Mode.

The morphology and structure of the self-assembled surfactant aggregates at the solid-liquid interface remain controversial. For the well-studied system of cationic cetyltrimethylammonium bromide (C16TAB) adsorbed onto the opposite negatively charged, atomically smooth mica surface, a variety of surface aggregates have been previously reported: AFM imaging pointing to cylinders and surface micelles as opposed to mono/bilayer-like structures revealed by neutron and X-ray reflectometry, NMR, spectroscopic techniques, and numerical simulations. To reconcile with the latter results, we revisit the morphometry of the C16TAB-coated mica surfaces using the recent peak force tapping (PFT-AFM) mode that allows fragile structures to be imaged with the lowest possible applied force. The evolution of the structural organization at the mica-water interface is investigated above the Krafft boundary over a wide concentration range (from 1/1000 to 2 cmc) after long equilibration times to ensure thermodynamic equilibrium. A complex but fairly complete picture has emerged: At very low concentrations, the C16TAB surfactants adsorb as isolated molecules before forming small clusters. Above 1/140 cmc, monolayer-like stripes are formed. As the concentration is increased, a connected network of these patches progressively covers the mica substrate. Above 1/80 cmc, bilayer-like patches build on top of the underlying monolayer, and ultimately a complete bilayer (at about half the cmc) covers the entire mica substrate. Thanks to the less invasive PFT-AFM imaging mode, our observations not only agree with the theoretical predictions and numerical simulations but also reconcile, at last, the direct observations by means of the AFM imaging technique with the results obtained with other techniques.

Correlation between Photoelectrochemical and Spectrophotometric Study of Dye-Surfactant Combination in Photogalvanic Cell

The photogalvanic cells are rechargeable device with the sun light in which surfactant solutions are potentially important for efficient energy conversion and storage. Here, effect of cationic cetyltrimethyl ammonium bromide (CTAB), anionic sodium dodecyl sulphate (SDS) and non ionic tween 80 surfactants on the electrical output of the cationic oxazine dye brilliant cresyl blue (BCB)-fructose (redox couple) system in photogalvanic cells have been studied. For this, the photopotential and photocurrent for different cells having BCB-fructose system without and with surfactant (CTAB, SDS and tween 80) in the alkaline medium have been measured. The total 30 different cells have been prepared for optimizing the concentration of electrolytes corresponding to the higher electrical out put. Generally, the electrical output increases in presence of a particular surfactant, due to increase in solubilization and stabilization properties of dye molecules in the water. The amount of enhancement in electrical output of BCB-fructose system was highest with SDS and lowest with tween 80, i.e. the order for BCB-fructose system with different surfactants in photogalvanic cells is: BCB-fructose-SDS > BCB-fructose-CTAB > BCB-fructose-tween 80. This order for electrical output was good agreement with the stability order of BCB-SDS/CTAB/tween 80 system, on the basis of spectrophotometric study. Hence, among these surfactants, SDS has stronger capacity, (due to opposite charge on BCB and SDS) to stabilize the BCB-fructose system leads to enhancement in electrical output of photogalvanic cells. Therefore, dye and surfactant, having chemical structure, like BCB and SDS, has a great importance of improvement of electrical performance to photogalvanic cells in the future.

Influence of Cationic Cetyltrimethylammonium Bromide on Rate of Zn(II)-Histidine Complex and Ninhydrin.

Paper analyses the influence of cationic cetyltrimethylammonium bromide on rate of Zn(II)-histidine and ninhydrin. UV-visible spectroscopy was applied to note absorbance of Zn(II)-histidine complex with ninhydrin at the end of reaction in the two systems. Rate constant, kobs, (in aqueous) and rate constant, kψ, (in cetyltrimethylammonium bromide, CTAB) were determined by computer software. Reactions depict first-order in Zn(II)-histidine concentration and fractional-order in ninhydrin concentration in aqueous and micellar media. The results achieved indicate that the reactions take place principally by the same reaction mechanism in both the media. Critical micelle concentration of CTAB surfactant was calculated by recording the conductivity as a function of surfactant concentrations. Influence of various amounts of surfactant on Zn(II)-histidine complex and ninhydrin reaction was performed under different reaction conditions. Reaction was catalyzed and accelerated efficiently by surfactant medium compared to aqueous medium. The observed influence of surfactant on rate has been mentioned in details and their quantitative treatment of kinetic results have been deduced by the means of Menger and Portnoy model for micellar catalysis.

The effects of surfactants (sodium dodecyl sulfate, triton X-100 and cetyl trimethyl ammonium bromide) on the dewaterability of microalgae biomass using pressure filtration

The application of pressure filtration in microalgae harvesting requires chemical pretreatment in order to reduce membrane fouling and to increase water flux. Surfactants have shown potential to enhance microalgae dewaterability by charge neutralization, bridging and releasing extracellular polymeric substances (EPS) and bound water. In this study, the effect of three surfactants including anionic sodium dodecyl sulfate (SDS), non-ionic triton X-100 and cationic cetyl trimethyl ammonium bromide (CTAB) on the dewaterability of Chlamydomonas sp. was investigated. Filtration fluxes and biomass concentrations were used to evaluate the microalgae dewaterability. Based on the results, SDS and Triton X-100 had a negative effect on the dewaterability of microalgae biomass. However, CTAB improved the dewaterability by decreasing the reversible and irreversible fouling resistance. The optimum dosage of CTAB was found to be 1500 mg/L, and resulted in 95.8% and 140% improvement on average water flux and biomass recovery efficiency, respectively.

Kinetics of alkaline fading of methyl violet in micellar solutions of surfactants: Comparing Piszkiewicz's, Berezin's, and pseudophase ion‐exchange models

AbstractThe micellar effect of surfactants of various types on the rate of the reaction between methyl violet and hydroxide ion is studied. The absorption spectra show that the cation of methyl violet is bound by micelles of all types at proper concentrations of surfactants. The observed rate constant in micellar systems containing nonionic Brij‐35, zwitterionic 3‐(dimethyldodecylammonio)‐propanesulfonate, cationic cetyltrimethylammonium bromide and hydroxide surfactants is higher, whereas in solutions of the anionic surfactant sodium dodecylsulfate is lower than that one in the surfactant‐free system. Piszkiewicz's, Berezin's, and pseudophase ion‐exchange models of the kinetic micellar effect are used for the treatment of the dependences of the above‐mentioned constants on the surfactant concentration. The values of the corresponding kinetic parameters are compared and discussed. The influence of nonionic, zwitterionic, and anionic micelles on the reaction rate is discussed on the basis of medium and concentration kinetic effects.The character of the cationic micelles effect is somewhat paradoxical. Although the observed pseudo–first‐order reaction rate constant substantially increases in the presence of such micelles, the second order‐rate constant in these micelles is lower than the corresponding value in surfactant‐free aqueous solution. As a possible explanation, the decrease in the reactivity of the HO– ions is proposed, owing to their electrostatic association with the cationic headgroups (“diverting effect”).