Adsorption Of Cetyltrimethylammonium Bromide Research Articles

Surfactant-mediated transport behavior of zinc oxide nanoparticles in porous media

Nanomaterials and surfactants are widely detected in soil-groundwater environments, while the surfactant-mediated transport behavior of nanoparticles has not been sufficiently investigated. In this study, the transport of ZnO nanoparticles (nZnO) in quartz sand (QS) in the presence of cetyltrimethylammonium bromide (CTAB) is investigated by adsorption and column experiments in combination with XDLVO analysis and numerical simulation. The adsorption of nZnO on QS is investigated by adsorption experiments under the environmental concentration of CTAB (50 mg·L−1). The results of adsorption experiments indicate that the adsorption efficiency of QS is related to the concentration of nZnO and primarily exhibits multilayer adsorption, and the Freundlich model can effectively fit the experimental data of isothermal adsorption. Additionally, the adsorption process is dominated by several factors, among which chemical adsorption is the primary controlling factor. The column experiment results indicate that at higher initial concentrations, the transport capacity of nZnO is weakened due to the occupation of adsorption sites on the QS and the increased collision opportunities between particles. The addition of ionic strength promotes the aggregation of nZnO by reducing electrostatic repulsion, thus inhibiting nZnO transport. Significantly, the inhibition of divalent Ca2+ is stronger than that of monovalent Na+. Interestingly, HA binds mainly to CTAB to form a hydrophobic complex, which reduces the repulsive force between nZnO and QS and inhibits the transport of nZnO. Increasing the pH, nZnO mobility first increases and then decreases, and begins to be inhibited at pH= 9 near the zero-point charge of nZnO. Moreover, at pH= 10, nZnO particles acquire a positive charge due to the adsorption of CTAB, and consequently, they are retained by QS through the hydrophobic interaction between the adsorbed CTABs. In addition, nZnO transport capacity does not increase with CTAB concentration. When a certain concentration of nZnO is reached, nZnO transport capacity is inhibited with CTAB concentration.

The effect of charge screening for cationic surfactants on the rigidity of interfacial nanoparticle assemblies

HypothesisFunctionalizing colloidal particles with oppositely charged surfactants is crucial for stabilizing emulsions, foams, all-liquid structures, and bijels. However, surfactants can reduce the attachment energy, the driving force for colloidal self-assembly at interfaces. An open question remains on how the inherent interfacial activity of cationic surfactants influences the interfacial rigidity of particle-laden interfaces. We hypothesize that charge screening among cationic surfactants regulates the rigidity of oil/water interfaces by reducing the attachment energy of nanoparticles. ExperimentsWe investigate the interfacial rigidity of cetyltrimethylammonium bromide (CTAB) functionalized silica nanoparticles (Ludox® TMA) by analyzing the shape deformation of 1,4-butanediol diacrylate (BDA) droplets under varying salt and alcohol concentrations. The nanoparticle packing density is assessed using scanning electron microscopy. Attachment energy is characterized through interfacial tension measurements, three-phase contact angle analysis, and CTAB adsorption studies. We also examine the effects of interfacial rigidities on the structure of bijel films formed via roll-to-roll solvent transfer-induced phase separation (R2R-STrIPS) using confocal laser scanning microscopy. FindingsIncreasing salt and alcohol concentrations decrease the interfacial rigidity of CTAB-functionalized nanoparticle films by reducing the interfacial tension. The contact angle has a minor influence on the rigidity. These results indicate that CTAB charge screening weakens the nanoparticle attachment energy to the interface. Controlling the rigidity enables the mass production of bijel sheets with consistent flatness, which is crucial for their potential applications in catalysis, energy storage, tissue engineering, and filtration membranes.

Application of a novel mixed anionic/cationic collector in the selective flotation separation of lepidolite and quartz

A novel mixed anionic/cationic collector of sodium dodecyl sulfonate (SDS) and cetyltrimethylammonium bromide (CTAB) was applied in the flotation separation of lepidolite from quartz. The micro-flotation experiment proved that the obvious floatability difference between lepidolite and quartz can achieve their flotation separation in this mixed collector system. The optimum dosage of SDS and CTAB were 60 mg/L and 10 mg/L respectively, and the optimal pulp pH was 7.0. Zeta potential analyses showed that the further adsorption of CTAB affects a positive shift of 17.14 mV in the potential of lepidolite after the pre-adsorption of SDS, while quartz shifted positively by only 4.89 mV. Fourier transform infrared analyses indicated that CTAB and SDS can co-adsorb on the surface of lepidolite to enhance its hydrophobicity. X-ray photoelectron spectroscopy analyses further demonstrated that the mixed collector of SDS and CTAB had a stronger selectivity for adsorption on the lepidolite surface than that of quartz. The adsorption strength of SDS on lepidolite was greater than that of quartz, and the co-adsorption of SDS and CTAB on the surface of lepidolite can additionally enlarge their differences in flotation behavior. These may be the essence of achieving the selective separation of the two minerals.

Interaction of crude oil with halogen-free ionic liquid-based catanionic surfactants

Chemical injection has proved to have superior performance in improving oil recovery. The injected chemicals are typically designed to participate in interfacial interactions at liquid–liquid and rock-liquid interfaces while having minimum adsorption onto the rock surface. This study endeavors to investigate the interfacial activity of several environmentally-friendly halogen-free ionic liquid-based catanionic surfactants synthesized via an ion exchange reaction between cationic imidazolium-based ionic liquids, [Cnmim][Cl] (n = 4,8,12), and anionic surfactants, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and dioctyl sodium sulfosuccinate. Results revealed that the catanionic surfactant synthesized with medium-chain ionic liquid (n = 8) and sodium dodecyl sulfate exhibited higher interfacial activity, demonstrating a minimum crude oil-brine interfacial tension of 0.17 mN/m and wettability alteration index of 0.79. The results of the adsorption study also revealed the adsorption density of 2.19 mg/g onto the dolomite surface for 2000 mg/L of catanionic surfactant in seawater, which was considerably lower than cetyltrimethylammonium bromide adsorption (11.55 mg/g) in the control experiment. Finally, the surface energy analysis of liquid-rock interactions was conducted using the concept of work of adhesion to scrutinize the wettability alteration and adsorption processes, where a direct relationship between work of adhesion and adsorption density was proposed. According to the results of this study, medium chain ionic liquid-based catanionic surfactant containing dodecyl sulfate anion, exhibiting excellent interfacial activity and low adsorption tendency onto the dolomite surface, could be considered in future chemical enhanced oil recovery applications.

Studying the effect of various surfactants on the possibility and intensity of fine migration during low-salinity water flooding in clay-rich sandstones

In the majority, sandstone reservoirs contain clay particles. When such reservoirs are exposed to low-salinity water, multi-ion exchange (MIE) and electrical double layer (EDL) expansion result in fine migration, which sweeps residual oil in the porous media while imposing damage and permeability reduction.This research investigates the effect of surfactants on the possibility and intensity of fine migration in clay-rich sandstones. First, the impact of these surfactants on the surface charge of quartz and clay particles was investigated. The results showed that both CTAB (CetylTrimethylAmmonium Bromide) and QS (Quillaja Saponin) lower the magnitude of fine particles' zeta potential from −40 mv to 2 and -18 mv, respectively, The zeta potential compensation weakens the repulsive forces. However, SDS (Sodium Dodecyl Sulfate), and TX (Triton X-100) do not change the magnitude of zeta potential. The surfactants were injected at a concentration of 10 g/L into sandpacks containing 5 wt% of kaolin. SDS and TX couldn't prevent fine migration, and sandpack permeability decreased from 65 md to about 8. CTAB completely prevented fine migration (permeability reduction from 66 to 62md). Meanwhile, QS reduced the intensity of fine migration and the permeability decreased to 30 md. Post-flushing diluted surfactant solutions showed that CTAB loses its ability to control fine migration and the magnitude of permeability drops to 8 md. However, QS still controlled the intensity of fine migration.CTAB, QS, SDS, and TX-100 adsorption on oil-aged sandstone rocks lower the contact angle from 1290 to 21.20, 69.50, 52.70, and 62.10, respectively. It should be noted that the aging time for this experiment was 14 days, which was conducted at 60 °C. contact angel studies illustrated that EDL compaction by surfactants can cause wettability alteration toward water wet conditions, through adsorption in the stern layer, which results in oil desorption. BET analysis showed that the kaolinite particles are mesoporous with weak interaction, which are covered by CTAB or QS adsorption. However, after lowering the surfactant concentration in the bulk fluid, CTAB is desorbed, resulting in the revival of pores. In contrast, desorption in QS dilution was negligible. The behavior difference is related to the adsorption mechanism. CTAB is absorbed on the particle surface based on cation exchange and QS due to hydrogen bonding. In QS, the hydrophilic part is adsorbed on the particles, and the hydrophobic part forms the external surface, which prevents water from reaching the hydrophilic part.

The effects of growth modifiers on the catalytic performance of hierarchical Pd/ZSM-23 bifunctional catalysts for n-hexadecane hydroisomerization

Hydroisomerization of n-alkanes catalyzed by metal-zeolite bifunctional catalysts is an important process to produce clean biofuels. The employment of appropriate growth modifiers during the synthesis of hierarchical zeolites to increase the iso-alkane yield has captured much attention. In this work, cetyltrimethylammonium bromide (CTAB) and polydiallyl dimethyl ammonium chloride (PDDA), representatives of cationic surfactants and cationic polyelectrolytes, are added to the initial gel to one-pot synthesize hierarchical ZSM-23 zeolites (Z23-xPC and Z23-yPP) via the bottom-up strategy. The corresponding Pd/ZSM-23 catalysts are prepared by loading 0.5 wt% Pd on microporous and hierarchical ZSM-23 and tested for the hydroisomerization of n-hexadecane. Due to the cationic adsorption of CTAB or steric hindrance effect of PDDA, Z23-xPC and Z23-yPP samples all demonstrate enhanced mesoporosity compared with the conventional microporous Z23-P sample. The diffusivity experiments indicates that the D/L2 values decrease in the order of Pd/Z23-5PP > Pd/Z23-3PC > Pd/Z23-P, suggesting that the hydrocarbons diffusion in the channel of hierarchical ZSM-23 samples is evidently improved. In addition, the Brønsted acid densities of the Z23-xPC and Z23-yPP samples are also evidently reduced compared to that of the microporous Z23-P sample because of the proportion decreases of framework Al atoms at T2-T5 sites. Compared with the microporous Pd/Z23-P catalyst, the appropriate addition amount of growth modifiers can evidently improve the yield of iso-hexadecane products and limit the cracking process. Especially for the Pd/Z23-5PP catalyst, the cracking process is effectively limited and the maximum iso-hexadecane yield of 75.4% is obtained at an n-hexadecane conversion of 88.8% at 290 °C, which is the highest among all catalysts. Therefore, this work has provided an effective method for the simple preparation of bifunctional catalysts with improved diffusion performance and more favorable metal–acid balance.

Adsorptive removal of dichlorophenoxyacetic acid (2,4-D) using novel nanoparticles based on cationic surfactant-coated titania nanoparticles.

A novel nanomaterial based on cationic surfactant-coated TiO2 nanoparticle (CCTN) was systematically fabricated in this work. Synthesized titania nanoparticles were thoroughly characterized by XRD, FT-IR, HR-TEM, TEM-EDX, SEM with EDX mapping, BET, and ζ potential measurements. The adsorption of cationic surfactant, cetyltrimethylammonium bromide (CTAB), on TiO2 was studied under various pH and ionic strength conditions. Adsorption of CTAB on TiO2 increased with ionic strength increment in the presence of hemimicelle monolayer structure, indicating that nonelectrostatic and electrostatic forces control CTAB uptake. CTAB adsorption isotherms on TiO2 were according to a two-step model. Potential application in pesticide removal of 2,4-dichorophenoxy acetic acid (2,4-D) using CCTN was also studied. Optimum parameters for 2,4-D treatment through adsorption technique were pH 5, adsorption time of 120min, and CCTN dosage of 10mg·mL-1. Very low 2,4-D removal efficiency using TiO2 without CTAB coating was found to be approximately 28.5% whereas the removal efficiency was up to about 90% by using CCTN under optimum conditions, and the maximum adsorption capacity of 12.79mg·g-1 was found. Adsorption isotherms of 2,4-D on CCTN were more suitable with the Langmuir model than Freundlich. Adsorption mechanisms of 2,4-D on CCTN were mainly governed by Columbic attraction based on isotherms and surface charge changes.

Effect of surfactant on the attachment between coal particles and bubbles: An experimental and molecular dynamics simulation study

Surfactant plays a vital role in flotation, especially in the adsorption of particle and bubble surface. From macroscopic to atomic scales, the effects of surfactant on the attachment between coal particles and bubbles were investigated by the induction time measurements, bubble-particle wrap angle measurements, thin liquid films measurements and molecular dynamics (MD) simulation. The three surfactants are Cetyltrimethylammonium bromide (CTAB), Sodium dodecylbenzene sulfonate (SDBS), and Methyl isobutyl carbinol (MIBC). Macroscopically, the coal particles could be more easily attached to a bubble surface in three solutions, particularly in CTAB solution. This was because the speed of thinning and rupture of thin liquid film between coal-particles and bubbles was faster in CTAB solution than that in other solutions. MD simulation findings show that the adsorption of CTAB significantly improves the water molecule migration rate. In addition, the CTAB promotes the attachment efficiency in floatation.

Application of graphene oxide and its derivatives on the adsorption of a cationic surfactant (interaction mechanism, kinetic, isotherm curves and thermodynamic studies)

In this research, the adsorption of a cationic surfactant, Cetyl Trimethyl Ammonium Bromide (CTAB), on graphene oxide-based adsorbents was investigated. The adsorbents consist of graphene oxide (GO), reduced graphene oxide (rGO), functionalized graphene oxid by humic acid (GO-HA), and functionalized reduced graphene oxid by thionine acetate (rGO-Th) that are characterized by the Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectrophotometry (FT-IR), X-ray Diffraction (XRD) and Brunauer-Emmett-Teller (BET) analysis. Examine factors affecting the adsorption of CTAB such as pH, contact time, adsorbent dosage, and agitation speed were investigated. Based on the results, the optimum pH for GO, rGO, GO-HA, and rGO-Th were 7, 8, 6.5, and 10, respectively and the optimum contact time and agitation speed were 30 min and 450 rpm, respectively. Also, kinetic, isothermal, and thermodynamic studies were done and the results indicated that the pseudo-second-order kinetic model fitted on experimental data for all of adsorbents. Under the optimum conditions, the maximum adsorption capacity of GO, rGO, GO-HA, and rGO-Th were 2000, 238, 3333, and 159 mg/g, and the fitted isotherm models were BET, Langmuir, Freundlich, and Langmuir, respectively. The adsorption thermodynamic suggested that CTAB adsorption on GO and GO-HA are exothermic and on rGO and rGO-Th are endothermic processes. The results indicated that physical properties of adsorbents such as surface area do not play a significant role and the electrostatic interaction between CTAB molecules and the functional groups of adsorbents plays a key role in CTAB adsorption on GO-based adsorbents.

Adsorption of CTAB on Sapphire-c at High pH: Surface and Zeta Potential Measurements Combined with Sum-Frequency and Second-Harmonic Generation.

The adsorption of cetyltrimethylammonium bromide (CTA+Br-) on sapphire-c surfaces was studied at pH 10 below the surfactants' critical micelle concentration. The evolution of interfacial potentials as a function of CTAB concentration was characterized by surface and zeta potential measurements and complemented by molecular dynamic (MD) simulations as well as by second-harmonic (SHG) and vibrational sum-frequency generation (SFG) spectroscopy. The changes in interfacial potentials suggest that the negative interfacial charge due to deprotonated surface aluminols groups is neutralized and can be even overcompensated by the presence of CTA+ cations at the interface. However, SFG intensities from strongly hydrogen-bonded interfacial water molecules as well as SHG intensities decrease with both increasing CTAB concentration and the magnitude of the surface potential. They do not suggest a charge reversal at the interface, while the change in zeta potential is actually consistent with an apparent charge inversion. This can be qualitatively explained by results from MD simulation, which reveal adsorbed CTA+ cations outside a first strongly bound hydration layer of water molecules, where they can locally distort the structural order and replace some of the interfacial water molecules adjacent to the first layer. This is proposed to be the origin for the significant loss in SFG and SHG intensities with increasing CTAB concentration. Moreover, we propose that CTA+ can act as a counterion and enhance the occurrence of deprotonated surface aluminols that is consistent with the decrease in surface potential.

Adsorption of cetyltrimethyl ammonium bromide surfactant for organophilization of palygorskite clay

AbstractThis work determines the optimal palygorskite (Plg) content (maximum surfactant adsorption point) to achieve organophilization using the cationic surfactant cetyltrimethyl ammonium bromide (CTAB) at various concentrations. Adsorption assays were carried out in a finite bath after varying the content of Plg and CTAB in solution. In those assays, the effects of time, temperature, pH and thermodynamic characteristics were studied. The results were analysed using the Langmuir, Freundlich, Dubinin–Radushkevich and Tempkin adsorption models. The increase in clay content in the dispersion leads to a decrease in adsorption of surfactant on the clay. It was possible to obtain the optimal Plg content to achieve organophilization at various concentrations of CTAB surfactant. The experimental data fitted well to the Freundlich model. The Dubinin–Radushkevich and Tempkin isotherms confirmed the chemical adsorption of CTAB on Plg clay.

Synthesis of low-cost bentonite/Duranta erecta's fruit powder imbedded alginate beads and its application in surfactant removal.

High industrialization and improved medical facilities are deteriorating aquatic bodies through untreated effluents. This study is aimed to design and characterize the bentonite, Duranta erecta, and their hybrid-alginate beads for the removal of cetyltrimethylammonium bromide (CTAB) from its aqueous solution. D. erecta's seed powder was treated by using a sonochemical method and embedded into alginate beads. All designed beads were characterized by using physicochemical methods, Fourier-transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) technique. Hybrid beads were found to form an appropriate hydrogel structure with maximum surface area per unit gram (544 cm2 g-1), 0.42 mg dry weight, and 2.70 mm diameter. Kinetics and intraparticle diffusion models were fitted where involvement of both chemisorption and intraparticle diffusion was observed during the initial 30 and post-30-min phase, respectively. Thermodynamic studies corroborated the spontaneity of the CTAB adsorption process. Bentonite alginate beads showed the highest adsorption capacity of 97.06 mg g-1 in 100 mg L-1 CTAB solution at optimized conditions, while hybrid-alginate beads showed excellent efficiency with a wide range of physicochemical conditions frame. Conclusively, designed beads can be used to remove the surfactant, i.e., CTAB, from industrial waste effluents for the betterment of water reservoirs.

Tuning Cationic Micelle Properties with an Antioxidant Additive: A Molecular Perspective.

In this work, we characterize the micellization and morphology transition induced in aqueous cetyltrimethylammonium bromide (CTAB) solution by the addition of the antioxidant propyl gallate (PG) using tensiometry, rheology, and small-angle neutron scattering (SANS) techniques combined with the molecular dynamics (MD) simulation approach. The adsorption of CTAB at the air-water interface in the presence of varying [PG] revealed a progressive decrease in the critical micelle concentration (CMC), while the changes in different interfacial parameters indicated enhancement of the hydrophobicity induced by PG in the CTAB micellar system. The dynamic rheology behavior indicated an increase in the flow viscosity (η) as a function of [PG]. Moreover, the rheological components (storage modulus, G', and loss modulus, G″) depicted the viscoelastic features. SANS measurements depicted the existence of ellipsoidal micelles with varying sizes and aggregation number (Nagg) as a function of [PG] and temperature. Computational simulation performed using density functional theory (DFT) calculations and molecular dynamics (MD) provided an insight into the atomic composition of the examined system. The molecular electrostatic potential (MEP) analysis depicted a close proximity of CTAB, i.e., emphasized favorable interactions between the quaternary nitrogen of CTAB and the hydroxyl group of the PG monomer, further validated by the two-dimensional nuclear Overhauser enhancement spectroscopy (2D-NOESY), which showed the penetration of PG inside the CTAB micelles. In addition, various dynamic properties, viz., the radial distribution function (RDF), the radius of gyration (Rg), and solvent-accessible surface area (SASA), showed a significant microstructural evolution of the ellipsoidal micelles in the examined CTAB-PG system, where the changes in the micellar morphology with a more elongated hydrophobic chain and the increased Rg and SASA values indicated the notable intercalation of PG in the CTAB micelles.

Adsorption complexes ‘zeolite–cationic surfactant’: properties and surface activity in a polymer composite material based on ultra-high-molecular-weight polyethylene

We investigated the adsorption of the cationic surfactant cetyltrimethylammonium bromide (CTAB) to zeolite from premicellar and micellar solutions, as well as some properties of the organically modified zeolite surface and the nature of its interfacial interaction with ultra-high-molecular-weight polyethylene (UHMWPE) in a UHMWPE-based polymer composite material (PCM). The formation mechanism of mono- and bimolecular adsorption layers of cetyltrimethylammonium cation and bromide anion to the clinoptilolite (Cli) surface was proposed, and the thermodynamic and kinetic characteristics of adsorption were determined. The surface texture of organically modified zeolite was studied by instrumental methods; the thermal stability limits of CTAB adsorption layers to zeolite surface and their decomposition behavior in inert and oxidizing media were established. The evaluation of the deformation and strength properties, the study of the supramolecular structure, and the calculation of the thermodynamic and kinetic parameters of the PCM crystallization process revealed that the filing with organically modified Cli increases the UHMWPE surface activity and improves their compatibility.

CTAB adsorption onto dolomite in the presence of ionic liquid and deep eutectic solvent: Experimental and theoretical studies

Surfactant adsorption onto reservoir rock surfaces would undesirably influence its functionality from standpoint of enhanced oil recovery (EOR). This study investigates the performance of an imidazolium-based ionic liquid (IL) and a choline chloride-based deep eutectic solvent (DES) as additives to inhibit cetyltrimethylammonium bromide (CTAB) adsorption onto dolomite rock surface from experimental and theoretical perspectives. In the experimental part, static adsorption tests were conducted using UV–Vis spectrophotometer to find the adsorption density of the chemicals in both single (e.g. only CTAB) and combination modes (CTAB-IL and CTAB-DES). In addition, Langmuir and Freundlich isotherms were used to fit the experimental data and also to discern the adsorption patterns. In the theoretical part, interaction energies were determined using the XDLVO theory. The experimental results revealed lower adsorption of IL and DES in comparison with CTAB. Moreover, the addition of IL and DES, as potential adsorption inhibitors, effectively reduced CTAB adsorption where almost 73% reduction was observed when 1000 ppm of the IL was added to 2000 ppm of CTAB in seawater. From theoretical investigation, it was found that among different interaction energies, Lewis acid-base interaction was primarily dominant. The consistency between the experimental and theoretical results was further confirmed when the work of adhesion was calculated and compared for different chemicals investigated in this study.

Reorganization of Interfacial Water By an Amphiphilic Cationic Surfactant Promotes CO2 Reduction

The presence of cetyltrimethylammonium bromide (CTAB) near the surface of a Cu electrode promotes the electrochemical reduction of CO2-to-fuels. The presence of CTAB increases the CO2 reduction rate by as much as 10x and decreased the HER rate by 4x, leading to ~75% selectivity towards the reduction of CO2. We utilized Surface Enhanced Infrared Absorption Spectroscopy (SEIRAS) to probe the dynamics of CTAB adsorption on the structure of interfacial water and CO2 reduction intermediates. HER suppression was found to arise from the displacement of interfacial water molecules from the presence of CTAB in the double layer. The enhanced CO2 reduction rate can be correlated to an increased population of atop bound CO and the emergence of a low frequency atop CO band. These results unravel the role of additives in improving CO2-to-fuels electrocatalysis and establishing this as a powerful methodology for directing product selectivity.

Cetyl Trimethyl Ammonium Bromide as Anti-Pit Agent for Mild Steel in Sulfuric Acid Medium

Aim: Pitting corrosion is a very serious problem for mild steel when it comes in contact with the dilute sulfuric acid medium. Specialized corrosion inhibitors are essentially required to minimize pitting and uniform types of corrosion in mild steel. Background: Most of the corrosion inhibitors discovered so far protects the mild steel from uniform type of corrosion. But pitting corrosion is more fatal than a uniform type of corrosion because it immediately makes mild steel unfit for use as leakage starts from the pit. Objective: The objective was to protect the mild steel alloys from pitting corrosion when comes in contact with dilute sulfuric acid by the use of organic corrosion inhibitor. Methods: Cetyl Trimethyl Ammonium Bromide (CTAB) is tested as a corrosion inhibitor for mild steel in 0.1 N H2SO4 as corroding medium at 25.0, 30.0 and 35.0°C by weight loss, electrochemical polarization, and Impedance spectroscopy methods. Surface study of corroded and un-corroded specimens of mild steel was carried out by Metallurgical Research Microscopy (MRM) and Scanning Electron Microscopy (SEM) techniques. Results: Surface study confirms that the adsorption of CTAB takes place through nitrogen atom resulting in the formation of uniform, nonporous, passive film confirmed by decrease in Warburg Impedance (Zw), decrease in Faradaic current, increase in Capacitive current, an increase in charge transfer resistance, Rct (41 to 401 Ω cm2) and significant increase in capacitive loop in Nyquist plot with increase in concentration of CTAB which results in significant decrease in corrosion rate of mild steel in 0.1N H2SO4 medium (percentage corrosion inhibition efficiency: 95.0%) especially eradicating pitting type of corrosion. Conclusion: CTAB was proved to be a very good anti-pit agent for mild steel in 0.1N sulfuric acid medium. Pitting and uniform type of corrosion was significantly reduced by the use of CTAB as corrosion inhibitor for mild steel in the dilute sulfuric acid medium at 25.0, 30.0 and 35.0°C.

Separation performances of a multi-stage continuous bubble cap foam fractionation column

ABSTRACT A multi-stage continuous bubble cap foam fractionation column was developed to achieve high separation performance using cetyltrimethyl ammonium bromide (CTAB) as a model surfactant. The effect of design and operating parameters on the overall performances was investigated at a steady state. The results illustrated that with increasing the airflow rate, the enrichment ratio of CTAB was decreased and its recovery percentage increased. When the feeding concentration of CTAB was greater than 0.2 g/L, the adsorption of CTAB at the gas-liquid interface was closed to equilibrium. Based on mass balances and equilibrium relationships, a new method of the number of theoretical stages by stage-to-stage calculation and graphics were presented on the foam fractionation column.

Reductive degradation of chlorinated organophosphate esters by nanoscale zerovalent iron/cetyltrimethylammonium bromide composites: Reactivity, mechanism and new pathways

Chlorinated organophosphate esters (Cl-OPEs), e.g., tris(2-chloroethyl) phosphate (TCEP), tris(2-chloro-2-propyl) phosphate (TCPP) and tris(1,3-dichloro-2-propyl) phosphate (TDCPP), are widely used as additive flame retardants in commercial and building products. They have potential persistent organic pollutant properties and are frequently detected in various waters, especially in wastewaters. Nanoscale zerovalent iron (nZVI)-based method is an efficient reductive technology for treating waters polluted by halogenated organic pollutants (HOCs). Cetyltrimethylammonium bromide (CTAB) is a ubiquitous surfactant in wastewaters and can favorably affect the interaction between HOCs and nZVI. However, its effect on the Cl-OPEs removal by nZVI-based materials still remains unknown. Herein, the adsorption and degradation efficiencies of Cl-OPEs by nZVI and sulfidated nZVI (S-nZVI) in the presence or absence of CTAB were quantified based on the decreasing concentrations of Cl-OPEs in reaction systems. Our results showed that TDCPP and TCPP were adsorbed onto the nZVI or S-nZVI surface and subsequently degraded. In contrast, TCEP was just adsorbed onto the particle surface without further degradation. The addition of CTAB significantly enhanced the hydrophobic adsorption between Cl-OPEs and nZVI or S-nZVI, leading to increased degradation of Cl-OPEs (especially TCEP). CTAB adsorption isotherms indicated that S-nZVI had a higher adsorption capacity for CTAB than nZVI. The S-nZVI/CTAB composite exhibited a better performance than nZVI/CTAB composite. When S-nZVI was combined with 100.0 mg L−1 CTAB, 100% of TDCPP, TCPP and TCEP was degraded within 3 hours, 5 and 14 days, respectively. As the concentration of CTAB was increased up to 335.0 mg L−1, TCEP could be completely degraded within 3 days by S-nZVI. Five degradation products of TCEP were identified, of which O,O-di-(2-chloroethyl) O-ethyl phosphate (DCEEP) and ethane were reported for the first time. We propose that TCEP is dechlorinated by nZVI or S-nZVI through the electron attack at the ethyl-chlorine group to form bis(2-chloroethyl) phosphate, DCEEP, chloride, ethene and ethane, representing previously unknown degradation pathways.

Dynamics of Competitive Adsorption of Lipase and Ionic Surfactants at the Water-Air Interface.

Lipase is one of the most important enzymes playing a key role in many biological and chemical processes, in particular for fat hydrolysis in living systems and technological applications such as food production, medicine, and biodiesel production. As lipase is soluble in water, the major hydrolysis process occurs at the water-oil interface, where lipase can get in contact with the oil. To provide optimum conditions, the emulsification of the oil is essential to provide a large interfacial area which is generally done by adding surfactants. However, the presence of surfactants can influence the lipase activity and also cause competitive adsorption, resulting in a removal of lipase from the interface or its conformational changes in the solution bulk. Here we have studied the dynamics of competitive adsorption and interfacial elasticity of mixed solutions containing lipase and the anionic surfactant sodium dodecyl sulfate (SDS) or the cationic surfactant cetyltrimethylammonium bromide (CTAB), respectively, at the water-air interface. The experiments were performed with a special coaxial double capillary setup for drop bulk-interface exchange developed for the drop profile analysis tensiometer PAT with two protocols: sequential and simultaneous adsorption of single components and mixed systems. The results in terms of dynamic surface tension and dilational viscoelasticity illustrate fast and complete desorption of a preadsorbed CTAB and SDS layers via subphase exchange with a buffer solution. In contrast, the preadsorbed lipase layer cannot be removed either by SDS or CTAB from the interface during drop bulk exchange with a buffer solution due to the unfolding process and conformation evolution of the protein molecules at the interface. In the opposite case, lipase can remove preadsorbed SDS and CTAB. The dynamic surface tension and viscoelasticity data measured before and after subphase exchange show joint adsorption of lipase and CTAB in the form of complexes, while SDS is adsorbed in competition with lipase. The results are in good correlation with the determined surface charges of the lipase gained by computational simulations which show a dominant negatively charged surface for lipase that can interact with the cationic CTAB while partial positively charged regions are observed for the interaction with the anionic SDS.