Solutions Of Hexadecyltrimethylammonium Bromide Research Articles

Improving household water treatment: using zeolite to remove lead, fluoride and arsenic following optimized turbidity reduction in slow sand filtration

Despite the United Nations 2030 agenda, large number of both urban and rural dwellers in low-income countries continue to lack access to improved water. Thus, increased effort is required towards enhancing low-cost drinking water treatment technologies especially for developing countries. Slow sand filter (SSF) is one of the most commonly used low-cost and efficient technologies for treating household drinking water. However, effectiveness of SSF is substantially affected by very high turbidity and relatively large amounts of dissolved heavy metals. To enhance removal of both turbidity and heavy metals, this study optimized sand bed depth (SBD) of SSF and investigated the potential of natural zeolite from Uganda for removal of lead, arsenite (As(III)) and fluoride ions from water. To remove lead ions, the zeolite was used in its natural form. However, to remove As(III) and fluoride, the natural zeolite was modified using hexadecyltrimethylammonium bromide solution. Removal of high turbidity was found to require a large optimal SBD. Furthermore, efficiency of treating synthetic turbid water increased with increasing initial turbidity. Variation of final turbidity with SBD was found to be best described by an exponential function. Optimal SBDs on top of an underdrain gravel layer of 0.2 m were 453, 522, 561, and 580 mm for turbidity of 60, 80, 100, and 120 NTU, respectively. Optimized SBD used achieve at least 95% efficiency in removing suspended particles from water with turbidity 120 NTU was found to save up to 35% of the total cost for acquiring sand volume required by a conventional SSF. For a particular zeolite mass, removal efficiencies of lead, As(III) and fluoride generally increased with increasing contact time. Removal efficiencies of lead, As(III), and fluorides were also shown to increase with increasing zeolite mass. Lead removal efficiencies using natural zeolite were 75 and 98% under 20 and 40 min, respectively. Removal of As(III) using modified zeolite mass was 91% within contact time of 10 min. Adsorption of fluoride on modified zeolite was 80% within 5 min. Adsorption of lead, As(III), and fluorides indicated promising potential of natural zeolites from Uganda for treating polluted water.

Electroosmotic flow assisted pseudophase to pseudophase microextraction for stacking in capillary zone electrophoresis

A stacking technique is proposed to improve the poor detection sensitivity of capillary zone electrophoresis (CZE) with UV detection. A long injection (e.g., 12.4 cm plug) of model anionic analytes prepared in a dilute solution of hexadecyltrimethylammonium bromide (CTAB) was enriched 26–34-x (compared to a typical or 2.1 mm sample injection) via the injection of a micellar solution of sodium dodecyl sulfate (SDS) prior to CZE separation. During sample injection, the CTAB formed a stationary pseudophase coating, which trapped the analytes at the inner walls of a fused silica capillary. The SDS micelles then released the CTAB admicelles via the formation of solution CTAB-SDS catanionic micelles during SDS plug injection and voltage application. As the SDS micelles moved through the sample zone, the formation of the catanionic micelles then released and accumulated the analytes at the front of the injected SDS zone. The stacking technique is called electroosmotic flow (EOF) assisted pseudophase to pseudophase microextraction because the EOF was essential for the formation of CTAB-SDS catanionic micelles for microextraction. Also, the CTAB and SDS aggregates are both pseudophases, which were used to retain and release the analytes from the capillary wall, respectively.

Morphology of surfactant mixtures at solid/liquid interfaces: High-speed AFM observation

We characterized time-dependent morphological changes in cationic monomeric/gemini surfactant mixtures adsorbed on silica using high-speed atomic force microscopy (HS-AFM). The gemini surfactant employed in this study was 1,2-bis(dodecyldimethylammonio)ethane dibromide (12-2-12). This surfactant was mixed with a monomeric surfactant, hexadecyltrimethylammonium bromide (HTAB), in the presence of a background electrolyte. The HS-AFM measurements revealed that wormlike surface aggregates that formed in an HTAB solution transformed into a bilayer within a few hundred seconds after the HTAB solution was replaced by an HTAB + 12-2-12 mixed solution. This morphological change was reversed within a few hundred seconds after this solution was replaced by the initial HTAB solution. These time-dependent morphological changes were supported by simultaneous quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry measurements. The energy dissipation, monitored by QCM-D, changed reversibly in response to the solution exchanges.

Non-enzymatic colorimetric sensor for cardiac Troponin I (cTnI) based on self-assembly of gold nanorods on heparin

The paper reports a simple enzyme-free colorimetric sensor for the detection of cardiac marker, Troponin I (cTnI) based on the self-assembly of gold nanorods (AuNRs) on heparin. The sensing system consists of a purple colour solution of Hexadecyltrimethylammonium bromide (CTAB) stabilised AuNRs self-assembled in presence of heparin due to the electrostatic interaction resulting in the reduction of surface plasmon absorption (SPR) of AuNRs and hence colour quenching/change of solution from red to blue. However, in the presence of cTnI, the electrostatic balance was disturbed due to the strong complex forming tendency between heparin and cTnI which was attributed due to the stronger complex forming tendency between the sulphate and carboxylate group of glycosaminoglycans and heparin binding proteins present in cTnI. Hence, the AuNRs are left free in the solution and retains the native red colour of the solution. As the concentration of cTnI in the solution was increased, the colour gradually changes from blue to red there by enabling the sensing of cTnI. The above mechanisms were confirmed by transmission electron microscopy. The AuNR aggregation was found to be inversely proportional to the concentration of cTnI. The change in absorbance of AuNRs with different concentrations of cTnI was monitored by UV-Visible spectroscopy. Using this sensor system, cTnI in the range of 0.5–15 ng/mL could be measured with a detection limit of 0.4 ng/mL. The system also showed good selectivity in presence of different competing substances under the same experimental conditions. The method appears to be simple, cost effective, and would be highly be beneficial in rural health care centres where high tech diagnostic aids are inaccessible.

Facilely-fabricated smart hydroxyl-surfaces with rapidly switchable wettability for water and oil: Reversibility between superoleophilicity and near superoleophobicity

Abstract Smart surfaces with switchable wettability for both aqueous and non-aqueous drops have aroused much interest because of their potential applications. In this work, a facile approach for the creation of tunable surface wettability on hydroxyl surfaces with rapid switch at ambient temperature is developed. Both surface hydrophobicity and oleophobicity are enhanced after a fluoro-surfactant solution rinse which acts as a stimulus. The reversal of surface wettability can be achieved simply by a rinse of aqueous solution of hexadecyltrimethylammonium bromide. This rapid wettability-switching property may be attributed to surface modification by physisorbed monolayer of fluoro-surfactant. When adopting a simple but effective pretreatment associated with surface roughening and oxidation, an extreme wettability change (between superhydrophilicity and superhydrophobicity) for both water and hexadecane drops can be achieved. This novel route is found to be durable and can be applied to a variety of surface materials including metal, ceramics, and polymer.

Solid Film Formation at the Tetradecane/Aqueous Hexadecyltrimethylammonium Bromide Solution Interface Studied by Interfacial Tensiometry and X-ray Reflectometry.

The effect of oil on condensed film formation in the adsorbed film of hexadecyltrimethylammonium bromide (C16TAB) at the tetradecane (C14)/water (W) interface was examined by interfacial tension and X-ray reflectivity measurements. The interfacial tension vs temperature curves have break point due to the expanded?condensed phase transition of the adsorbed film. The partial molar entropy of C16TAB at the interface changes discontinuously, whereas the interfacial density changes almost continuously at the phase transition point. The electron density profile normal to the interface manifested that the condensed film is regarded as a two-dimensional (2D) solid rotator phase in which C16TAB and C14 molecules are densely packed with perpendicular orientation. Combining the interfacial tension and X-ray reflectivity data, the mixing ratio of C16TAB to C14 in the solid film was determined to be 2:3 and thus the film is enriched in oil molecules than surfactant ones. Furthermore, the partial molar entropy change of C14 associated with solid film formation was found to be largely negative and very close to that of surface freezing of liquid alkane, manifesting that C14 molecules are well ordered to form a 2D solid film by mixing with C16TAB molecules at the interface. The solid film formation of the present system is driven by effective vdW interactions between adsorbed C16TAB and intercalated C14 molecules. The morphology of the condensed domain observed during phase transition suggested that the contact energy is more predominant than the dipole repulsion at the domain boundary, which promotes coalescence of small domains into large ones during phase transition.

A new approach about the intercalation of hexadecyltrimethylammonium into halloysite: preparation, characterization, and mechanism

Three organoclays were prepared by mixing an Algerian halloysite with a solution of hexadecyltrimethylammonium bromide (HDTMA-Br) equivalent to six times the cation-exchange capacity of our clay. Unlike a majority of studies which were focused on the initial concentration of the intercalating agent, this paper investigates the influence of the reaction time for a given initial concentration. Three intercalation times were examined: 2, 7, and 14 days. The resulting organoclays were analyzed by XRD, FTIR, TG–DTA, TEM, and N2 adsorption–desorption. The intercalation of HDTMA+ cations begins by a latency period up to 2 days, during which these cations interact with the external surface of halloysite. From 2 to 7 days, they migrate into the interlayer spaces, leading to an expansion of the basal distance from 7.3 to 26.0 A. Between 7 and 14 days, the expansion remains unchanged for an intercalation rate around 42%. FTIR analysis proved that the surfactant interacts with the inner surface hydroxyl groups. From 200 °C, thermal analysis highlighted a succession of stages linked to the removal of HDTMA+. The TEM images showed a decrease in the outer diameter of the intercalated nanotubes with an enlargement of lumen diameter up to 20 nm. The arrangement of HDTMA+ species into interlayer spaces reflected a paraffin-type monolayer configuration. Knowing that the intercalation of organic compounds into the clay minerals changes their behavior from hydrophilic to hydrophobic, a nanotubular organohalloysite with a basal expansion of 26.0 A could be a highly effective adsorbent for wastewater decontamination.

Antibiotic-affinity strategy for bioluminescent detection of viable Gram-positive bacteria using daptomycin as recognition agent

A bioluminescent method was proposed for rapid detection of viable Gram-positive bacteria based on a novel antibiotic-affinity strategy on a magnetic beads (MBs) platform. Daptomycin, a highly efficient lipopeptide antibiotic for Gram-positive bacteria, was used as a recognition agent to functionalize MBs. The daptomycin-functionalized MBs showed high capture and concentration efficiency for Gram-positive bacteria due to the strong binding between daptomycin and bacterial cell membrane in the presence of Ca2+ ion. The captured bacteria were lysed by hexadecyl trimethyl ammonium bromide solution, followed by a bioluminescent detection of the released intracellular adenosine triphosphate. Four Gram-positive bacteria, including Staphylococcus aureus, Streptococcus mutans, Bacillus subtilis and Staphylococcus epidermidis, were detected as model bacteria by this method. Under the optimal conditions, the bacteria could be detected within a linear range of 1.0 × 102–3.0 × 106 CFU mL−1, with a detection limit of 33 CFU mL−1. The whole detection procedure could be completed within 20 min. Gram-negative bacteria and dead Gram-positive bacteria showed negligible interference to the detection of viable Gram-positive bacteria. The proposed method was successfully applied to quantify the amount of viable Gram-positive bacteria in cheese, milk, lake water, human urine and physiological saline injection with acceptable recovery values ranging from 75.0% to 120.0%. The strategy possessed some advantages such as high sensitivity, short assay time and simple operation, thus showed great promise for food hygiene, environment monitoring, clinical diagnosis and drug safety.

Foaming in aqueous solutions of hexadecyltrimethylammonium bromide and silica nanoparticles: Measurement and analysis of rheological and interfacial properties

ABSTRACTThe properties of aqueous foams stabilized by a mixture of negatively charged silica nanoparticles and hexadecyltrimethylammonium bromide were studied in this work. Rheological properties of the foams were studied. The interaction between nanoparticles and surfactant molecules in the bulk phase was studied by zeta potential and size measurements of the particles. The interaction at the interface was studied by means of interfacial shear rheology, surface pressure measurement, and atomic force microscopy. It was found that foams were more stable at low surfactant concentrations, though the foamability was low. This was due to the formation of a strong viscoelastic film of surfactant-laden particles at the air–water interface. A suitable mechanism has been proposed to explain the stability of foams in the presence of nanoparticles at different surfactant concentrations.

Calculation aspects of diffusion coefficients in micellar solutions of ionic surfactants

Results of calculating diffusion coefficients of ionic surfactants as functions of their concentration in micellar solutions have been analyzed within the framework of the quasi-chemical variant of the law of mass action. Diffusion coefficients have been evaluated for an ideal mixture of monomeric molecules and micelles, as well as taking into account the correction for the variability of the aggregation number of a surfactant using aqueous solutions of hexadecyltrimethylammonium bromide, hexadecylpyridinium chloride and bromide, and alkyltriphenylphosphonium bromides as examples.

Ion-pair amphiphile: a neoteric substitute that modulates the physicochemical properties of biomimetic membranes.

Ion-pair amphiphiles (IPAs) are neoteric pseudo-double-tailed compounds with potential as a novel substitute of phospholipid. IPA, synthesized by stoichiometric/equimolar mixing of aqueous solution of hexadecyltrimethylammonium bromide (HTMAB) and sodium dodecyl sulfate (SDS), was used as a potential substituent of naturally occurring phospholipid, soylecithin (SLC). Vesicles were prepared using SLC and IPA in different ratios along with cholesterol. The impact of IPA on SLC was examined by way of surface pressure (π)-area (A) measurements. Associated thermodynamic parameters were evaluated; interfacial miscibility between the components was found to depend on SLC/IPA ratio. Solution behavior of the bilayers, in the form of vesicles, was investigated by monitoring the hydrodynamic diameter, zeta potential, and polydispersity index over a period of 100 days. Size and morphology of the vesicles were also investigated by electron microscopic studies. Systems comprising 20 and 40 mol % IPA exhibited anomalous behavior. Thermal behavior of the vesicles, as scrutinized by differential scanning calorimetry, was correlated with the hydrocarbon chain as well as the headgroup packing. Entrapment efficiency (EE) of the vesicles toward the cationic dye methylene blue (MB) was also evaluated. Vesicles were smart enough to entrap the dye, and the efficiency was found to vary with IPA concentration. EE was found to be well above 80% for some stable dispersions. Such formulations thus could be considered to have potential as novel drug delivery systems.

Chromium VI adsorption from sodium chromate and potassium dichromate aqueous systems by hexadecyltrimethylammonium-modified zeolite-rich tuff

In the present investigation, zeolite-rich tuff from the state of Chihuahua, which was conditioned with a sodium chloride solution and subsequently modified with a hexadecyltrimethylammonium bromide solution, was used to evaluate the removal of Cr(VI) from aqueous systems prepared with Na2CrO4, K2Cr2O7 or a mixture of both Na2CrO4 and K2Cr2O7 salts. The zeolitic materials were characterized by scanning electron microscopy and X-ray diffraction, and their surface area was also determined. These experiments were performed in a batch system in which the influences of the pH, contact time between phases, and concentration of Cr(VI) in solution on the adsorption of Cr(VI) by surfactant-modified zeolite-rich tuff were investigated. The removal efficiency of chromium ions from aqueous solution is influenced by pH and the specific chromium species involved plays an important role in the adsorption process. The Cr(VI)-Na2CrO4 and Cr(VI)-K2Cr2O7 adsorption kinetics data were fit to a pseudo-second-order model, and the Langmuir isotherm adequately described the experimental results of these mono-component systems. In the Cr(VI)-Na2CrO4:Cr(VI)-K2Cr2O7 mixture, the surfactant-modified zeolite-rich tuff adsorbed more Cr(VI) depending on the initial ratio of Na2CrO4:K2Cr2O7 salts in the bi-component aqueous system.

Synthesis and characterization of modified UZM-5 as adsorbent for nitrate removal from aqueous solution

This article introduces synthesis and characterization of UZM-5 and its surfactant modification by using solutions of hexadecyltrimethylammonium bromide (CH3(CH2)15N(Br)(CH3)3, HDTMABr). Potential application of produced surfactant modified UZM-5 (SMU) as adsorbent for nitrate removal from aqueous solution were investigated. The effect of HDTMABr concentration on its adsorption on UZM-5 was studied by FTIR, TGA, N2 adsorption–desorption, and XRD techniques. Intense reduction in surface area, total pore volume of the UZM-5 sample upon alkyl chain attachment was observed by the BET method. From the TGA results, the electrostatic interactions were proved to be the main mechanisms that govern the adsorption of HDTMA cation on UZM-5. Adsorption isotherms of nitrate on SMU were measured at aqueous concentration range of 30–100mgL−1. The adsorption data was fitted by the Langmuir, Freundlich and Dubinin–Redushkevich (D–R) isotherms. The maximum monolayer sorption capacity of SMU for nitrate removal was found to be 18.62mgg−1 at 298K. Thermodynamic study of nitrate sorption on SMU was performed based on ΔHo, ΔGo and ΔSo. The results showed that nitrate sorption on SMU were strongly affected by pH, initial ion content and rival anions.

X-ray Reflectivity Measurements for Freezing Transitions of Alkane Wetting Film on Surfactant Solution Surface

Abstract X-ray reflectivity measurements were applied to hexadecane wetting film on aqueous solutions of hexadecyltrimethylammonium bromide (CTAB) and tetradecyltrimethylammonium bromide (TTAB). In both cases, the monolayers in which oil molecules are penetrated from hexadecane droplets into surfactant-adsorbed films were found at room temperature. Upon cooling, they showed first-order freezing transitions, however, it was also confirmed that the structures of freezing films were qualitatively different: hexadecane molecules were frozen together with CTAB to form mixed solid monolayer in CTAB–hexadecane while the frozen hexadecane monolayer wetted mixed liquid monolayer in TTAB–hexadecane.

Time-dependent Dynamic Receding Contact Angles Studied during the Flow of Dilute Aqueous Surfactant Solutions through Fluorinated Microtubes

Abstract We report on the time-dependent dewetting behavior of dilute surfactant solutions of hexadecyltrimethylammonium bromide (CTAB) during forced flow in fluorinated ethylene–propylene (FEP) microtubes. The dynamic receding contact angle of the solution at a given velocity decreased as the solid–liquid contact time increased. Kinetics with long relaxation time of several hundred seconds led to a final state displaying a 0° dynamic receding contact angle. This effect was absent in the case of 2-propanol, where the dynamic receding contact angle did not depend on the contact time.

Effect of precursor solution dark incubation on gold nanorods morphology

Gold nanorods were synthesized in an aqueous solution of hexadecyltrimethylammonium bromide via a combination of chemical reduction and UV photoirradiation. Gold ligand complexes, present in the stock solution, are initially reduced, by ascorbic acid as mild reducing agent. The gold ions nucleation and colloid growth proceeds then by subsequent UV irradiation of the so-obtained precursor solution. We present a systematic study of the effect of incubation of the precursor solution on the dispersion state and aspect ratio of the produced nanorods. Incubation of the precursor solution allows the synthesis of higher aspect ratio nanorods with narrower size distribution compared to those obtained without incubation. We propose a mechanism for the gold nanorods formation including two stages, a nucleation and a diffusive growth. This allows us to explain the synthesis improvement as a consequence of the increase in the size of the gold ligand complexes aggregates, leading to a decrease of the nanorods growth rate.

Structural Transitions of CTAB Micelles in a Protic Ionic Liquid

Micellar solutions of hexadecyltrimethylammonium bromide (CTAB) in a protic ionic liquid, ethylammonium nitrate (EAN), are studied by shear rheology, polarizing optical microscopy (POM), conductivity measurements, and small angle neutron scattering (SANS). Three concentration regimes are examined: A dilute regime (with concentrations [CTAB] < 5 wt %) consisting of noninteracting spherical micelles, a semidilute regime (5 wt % ≤ [CTAB] ≤ 45 wt %) where micelles interact via electrostatic repulsions, and a concentrated regime (45 wt % < [CTAB] ≤ 62 wt %) where a reversible, temperature-dependent isotropic (L(1)) to hexatic (Hex) phase transition is observed. The L(1)-Hex transition, which has been predicted but not previously observed, is characterized by (1) a sharp increase in the shear viscosity, (2) the formation of focal conical birefringence textures (observed by POM), and (3) enhancement of the crystalline order, evidenced by the appearance of Bragg reflections in the SANS profiles. Ionic conductivity is not sensitive to the L(1)-Hex transition, which corroborates the absence of topological transitions.

Halide Anions as Shape-Directing Agents for Obtaining High-Quality Anisotropic Gold Nanostructures

The fundamental role of halide anions in the seed-mediated synthesis of anisotropic noble metal nanostructures has been a subject of debate within the nanomaterials community. Herein, we systematically investigate the roles of chloride, bromide and iodide anions in mediating the growth of anisotropic Au nanostructures. A high-purity surfactant solution of hexadecyltrimethylammonium bromide (CTABr) is used to reliably probe the role of each halide anion without interference from impurities. Our investigation reveals that bromide anions are required for the formation of Au nanorods, while the controlled combination of both bromide and iodide anions are necessary for the production of high-quality Au nanoprisms. Chloride anions, however, are ineffective at promoting anisotropic architectures and are detrimental to nanorod and/or nanoprism growth at high concentrations. We examine the seed structure and propose a growth model based on facet-selective adsorption on low-index Au facets to rationalize the nanost...

Synthesis and surfactant modification of clinoptilolite and montmorillonite for the removal of nitrate and preparation of slow release nitrogen fertilizer

This article introduces the synthesis of clinoptilolite and montmorillonite, and their surfactant modification by using solutions of hexadecyltrimethylammonium bromide (CH3(CH2)15N(Br)(CH3)3, HDTMAB) and dioctadecyldimethylammonium bromide ((CH3(CH2)17)2N(Br)(CH3)2, DODMAB). The feasibility of using surfactant modified silicates (SMSs) as a potential adsorbent for nitrate and for slow release of nutrient has been investigated. Adsorption isotherms of NO3− on SMSs have been measured at aqueous concentration of 160–280mgL−1. The SMSs show much higher adsorption capacity than the unmodified materials as determined by Langmuir adsorption isotherm. The surfactant modification and increased surfactant loading concentration enhance the nitrate anion retaining capacity of silicates (montmorillonite (16.05mgg−1)<clinoptilolite (30.58mgg−1)<DODMAB loaded clinoptilolite (75.19mgg−1)<DODMAB loaded montmorillonite (76.92mgg−1)<HDTMAB loaded montmorillonite (80.65mgg−1)<HDTMAB loaded clinoptilolite (125.00mgg−1)). The adsorption data fitted well with the Langmuir and Freundlich isotherms. The slow nutrient release studies have been performed by thin layers-funnel analytical test and soil column percolating system. The obtained results indicate that SMSs are very good adsorbent for NO3− and a slow release of nitrogen is achievable as it releases NO3− still after 15–20 days of leaching study.

Convenient approaches for the synthesis of gold nanowires by successive utilization of two kinds of reducing agents in the solution of hexadecyl-trimethylammonium bromide

In spite that several empirical approaches for the synthesis of gold nanowires have been reported, there still remains ambiguity and controversy for their mechanisms. In this study, we report very easy and highly-reproducible synthetic method of gold (Au) nanowires with the size and the length of 40–50 nm and several micrometers, respectively. The method includes an extremely higher concentration of hexadecyl-trimethylammonium bromide (CTAB) at room temperature. We successively used two kinds of reducing agents, firstly sodium borohydride for the reduction of Au(III) ion into mostly Au(I) ion, and secondly triethylamine (TEA) leading Au(I) ion to Au(0) and its growth to Au nanowires. The former should be added very slowly, while the latter at once. Effects of oxygen were crucial for the growth to nanowires, and copper ion was quite effective for reductive scavenging of unwanted oxygen. It is strongly suggested that Cu(I) ion first generates the complex with TEA and then reduces Au(I) ion to Au(O). Thus, the Au nanowires grow in higher concentrations of Cu(I) ion. The concentration of CTAB was also found to be very important for the generation of Au nanowires.