Surfactant Loading Research Articles

Mechanism and performance for adsorption of 2-chlorophenol onto zeolite with surfactant by one-step process from aqueous phase.

To decrease the power, material, and time consumption in wastewater treatment, a one-step process was performed to remove 2-chlorophenol (2-CP) from aqueous phase using zeolite and cetyltrimethylammonium bromide (CTAB). Compared with the traditional two-step process, the one-step process used in this study achieved almost eight times higher 2-CP adsorption capacity within a shorter time and maintained high removal efficiencies (around 65%) in reuse tests, thus becoming an efficient and economically acceptable alternative process. For the one-step process, the kinetic data fitted well with a nonlinear pseudo-second-order model, and the isotherm data fitted well with the Dubinin-Astakhov (DA) model. The uptake of 2-CP was highly dependent on pH, increasing in the pH range of 3-6. The enhanced 2-CP removal in a one-step adsorption process can be explained by the larger amount of surfactant loading (≥0.056mmol/g), as determined from the total organic carbon (TOC) and zeta potential. Due to the formation of a loose CTAB bilayer, the hydrophobic partition and the interaction with the positively charged "head" of CTAB bilayers were decisive for the enhancement of pollutant adsorption. Therefore, organic pollutants could be removed from water alongside the synthesis of hydrophobic zeolite in a one-step process, which is a promising technology for the in-situ treatment of organic wastewater.

Organoclay-based nanoparticles from montmorillonite and natural clay deposits: Synthesis, characteristics, and application for MTBE removal

This study introduces organoclay-based submicron- and nanosized particles prepared from montmorillonite (SWy2) and naturally occurring clay deposits using sequential steps of wet ball milling, ultrasonication and sedimentation followed by an ion exchange process using two surfactants, long alkyl chain HDTMA+ (hexadecyltrimethylammonium bromide) and short alkyl chain TMA+ (tetramethylammonium bromide). The resultant organoclay-based nanoparticles were characterized using X-ray diffraction (XRD), thermogravimetric-differential thermal analysis (TG-DTA) and Fourier-transform infrared (FTIR) spectroscopy. The adsorption of MTBE (methyl tert-butyl ether) by organo-montmorillonite with different surfactant loadings (0.5–2.0 CEC) in aqueous solution was also investigated. The results of XRD analysis for organoclay-based nanoparticles showed that the value of d (001) increased with increasing alkyl chain length and surfactant loading. FTIR results showed that the functional groups of the organoclays changed due to the intercalation of the long alkyl chain surfactant HDTMA+ between clay layers. The removal of MTBE is highly dependent upon surfactant type and loading. The results indicated that the organo-montmorillonite-based nanoparticles prepared from HDTMA+ have a higher affinity for MTBE in aqueous solution than the organo-montmorillonite prepared from TMA+. Therefore, long alkyl chain HDTMA+ can be considered to be the most suitable organo-modifier for enhancing the adsorption characteristics of montmorillonite for MTBE removal.

Chromium immobilization in soil using quaternary ammonium cations modified montmorillonite: Characterization and mechanism

The potential risk of heavy metal in soil can be reduced by stabilization techniques. Stabilizing amendments, montmorillonites modified with tetramethylammonium (TMA) and hexadecyltrimethylammonium (HDTMA) at different loadings were prepared, characterized and assayed for remediation of hexavalent chromium contaminated soil. Characterization results demonstrated that TMA modification resulted in increased surface area and pore volume, whereas HDTMA modification resulted in decreased surface area and pore volume. For HDTMA modified montmorillonites (H-Monts), the arrangement model of surfactant molecules and the structural characteristics strongly depended on the surfactant loading density. Less pronounced packing density dependence was observed for TMA modified montmorillonites (T-Monts). Modified toxicity characteristic leaching procedure (TCLP) was utilized to evaluate the chromium immobilizing capacity of the prepared organo-montmorillonites, and the results revealed that both T-Monts and H-Monts can be reasonably effective in chromium stabilization under different leaching condition. The comparison of chromium leaching behavior manifested by T-Monts and H-Monts suggested that mechanisms for chromium immobilization by organo-montmorillonites amendment proceeded via two adsorption approaches. Each approach involves different functional groups, depending on the leaching pH and surfactant loading concentration. In addition, the effect of HDTMA loading concentration, amendment dosage, initial chromium concentration and incubation time on the immobilizing efficiency of H-Monts was investigated.

Effect of various surfactants on the stability time of kerosene–boron nanofluids

Nanofluid fuels, a new class of nanotechnology-based fluids, are liquid fuels with a stable suspension of nanometre-sized particles. The preparation of fuel mixtures and achieving to a stable and long-term suspension is the key step in nanofluid synthesis. The idea of this work is to suspend nano- and micron-sized boron particles in kerosene, exploring the differences between the complete sedimentation times of particles in fuel at various weight fractions of surfactants and investigating the viscosity of nanofluid at low weight concentration of nanoparticles. Various surfactants including oleic acid, propylene glycol, sorbitan oleate, Tween 85 and CTAB were used to prepare stable kerosene/boron slurries. Suspensions were prepared with varying surfactant loadings of 0.1–2.0% by weight, in steps, for the same particle loading of 0.5 wt%. The results showed that sorbitan oleate was the best surfactant and the optimum weight ratio of boron particle to sorbitan oleate for enhanced stability of nanofluid was determined to be 2. The complete sedimentation time of nanoparticles at the most stable nanofluid was ∼57 h. At low temperature and high weight fraction of particles, nanofluids showed similar 67% enhancement in viscosity properties.

Synthesis and Characterization of Aviation Turbine Kerosene Nanofluid Fuel Containing Boron Nanoparticles

The present work studies the thermal and physical properties of aviation turbine kerosene (ATK)–boron nanofuels, including stability time, viscosity, thermal behavior, and energy content. Also, this study tries to explore the effects of the size and concentration of boron particles, surfactant type, and temperature on the stability and viscosity of nanofuel. Nanofuel samples were prepared and characterized at 0.5–4 wt % of particle loading and 0.1–2 wt % of surfactant loading ranges, for micro- and nanosized boron particles. Various surfactants, such as oleic acid, propylene glycol (PG), sorbitan oleate, Tween 85, and cetyltrimethylammonium bromide (CTAB), were used to stabilize the nanofluids. The results showed that sorbitan oleate was the best surfactant and the best weight ratio of boron particles/sorbitan oleate was about 2. With the increase of the nanoparticle concentrations from 2 to 4 wt % at 5 °C, the nanofuel viscosity was increased 24%, and with the increase of the temperature from 5 to 40 °C ...

Stability and Aggregation Kinetics of Titania Nanomaterials under Environmentally Realistic Conditions.

Nanoparticle morphology is expected to play a significant role in the stability, aggregation behavior, and ultimate fate of engineered nanomaterials in natural aquatic environments. The aggregation kinetics of ellipsoidal and spherical titanium dioxide (TiO2) nanoparticles (NPs) under different surfactant loadings, pH values, and ionic strengths were investigated in this study. The stability results revealed that alteration of surface charge was the stability determining factor. Among five different surfactants investigated, sodium citrate and Suwannee river fulvic acid (SRFA) were the most effective stabilizers. It was observed that both types of NPs were more stable in monovalent salts (NaCl and NaNO3) as compared with divalent salts (Ca(NO3)2 and CaCl2). The aggregation of spherical TiO2 NPs demonstrated a strong dependency on the ionic strength regardless of the presence of mono or divalent salts; while the ellipsoids exhibited a lower dependency on the ionic strength but was more stable. This work acts as a benchmark study toward understanding the ultimate fate of stabilized NPs in natural environments that are rich in Ca(CO3)2, NaNO3, NaCl, and CaCl2 along with natural organic matters.

Measurements of the stabilisation of liquid film flow by the soluble surfactant sodium dodecyl sulfate (SDS)

Gravity-driven film flow of aqueous solutions of SDS is studied experimentally and the evolution of small-amplitude, regular inlet disturbances is investigated. With the addition of SDS, strong attenuation of non-linear growth is observed, with traveling waves remaining relatively small in height and near-sinusoidal over an impressive parametric range. The critical Reynolds number of the primary instability rises by an order of magnitude. Maximum stabilization is observed at small surfactant loadings (characterized by surface tension 60–65mN/m) and the critical Reynolds number gradually decreases with further addition of surfactant. Observations are interpreted by the competing effects of surface elasticity -which increases with the adsorbed SDS and intensifies Marangoni stresses- and surfactant mass transfer between bulk and interface -which also increases with the amount of SDS and mitigates interfacial gradients and Marangoni stresses.

The study of an azo dye removal from liquid medium by modified clay

In this batch study, montmorillonite was modified by a cationic surfactant [hexadecyltrimethylammonium bromide (HDTMA-MMT)] and used as sorbent to remove bromocresol green (BCG) from aqueous solutions. The effect of several factors such as surfactant loading rate onto the clay, contact time, pH, adsorbent dosage, dye concentration, and ion strength were investigated on the sorption. The equilibrium time for BCG sorption was reached at contact time of 20 minutes. Fitting the experimental data to different kinetic and isotherm models showed that the experimental data are well described by pseudo-second-order kinetic (R2 > 0.99) and Freundlich isotherm (R2 > 0.99) models. According to the results of this study, HDTMA-MMT can be considered as a low-cost, eco-friendly, and highly effective option for the sorption of BCG from aqueous solutions.

Structure of Hybrid Materials Based on Halloysite Nanotubes Filled with Anionic Surfactants

The structures of pristine halloysite nanotubes (HNTs) and ones functionalized by anionic surfactants (sodium dodecanoate and sodium dodecyl sulfate) were investigated by small angle neutron scattering (SANS). These experiments evidenced the structural organization of the surfactants adsorbed onto the HNT cavity and the importance of the surfactant headgroup. Contrast matching experiments were employed in order to mask the dominant scattering effect of the clay hollow nanotubes and to focus on the surfactant organization within the lumen. Further investigation on the mesoscopic structure of the investigated materials was carried out by electric birefringence (EBR), which allowed study of the rotational mobility of both pristine and functionalized HNTs. The gained structural insights were used to deduce some relevant properties of the hybrids, such as their surfactant loading, charge, and solubilization ability toward hydrophobic compounds. For the latter, the HNT lumen hydrophobization was straightforward...

Surfactant modification and adsorption properties of clinoptilolite for the removal of pertechnetate from aqueous solutions

Natural clinoptilolite modified with a cationic surfactant stearyldimethylbenzylammonium chloride (SDBAC) was used as an adsorbent for the removal of pertechnetate from aqueous solutions. Adsorption studies were performed in a batch system. The effects of various experimental parameters (amount of surfactant loading, contact time, solution pH, competing anions) on the removal efficiency of TcO4− were investigated. SDBAC-clinoptilolite with organo-bilayer was successfully used to remove TcO4− from aqueous solutions in the pH range of 5.0-8.0. ReO4− as an analogue of TcO4− was used to model the isotherms. Adsorption capacity of the SDBAC-clinoptilolite and the mechanism of ReO4− (TcO4−) sorption were also determined.

Determination of the critical micelle concentration in simulations of surfactant systems.

Alternative methods for determining the critical micelle concentration (cmc) are investigated using canonical and grand canonical Monte Carlo simulations of a lattice surfactant model. A common measure of the cmc is the "free" (unassociated) surfactant concentration in the presence of micellar aggregates. Many prior simulations of micellizing systems have observed a decrease in the free surfactant concentration with overall surfactant loading for both ionic and nonionic surfactants, contrary to theoretical expectations from mass-action models of aggregation. In the present study, we investigate a simple lattice nonionic surfactant model in implicit solvent, for which highly reproducible simulations are possible in both the canonical (NVT) and grand canonical (μVT) ensembles. We confirm the previously observed decrease of free surfactant concentration at higher overall loadings and propose an algorithm for the precise calculation of the excluded volume and effective concentration of unassociated surfactant molecules in the accessible volume of the solution. We find that the cmc can be obtained by correcting the free surfactant concentration for volume exclusion effects resulting from the presence of micellar aggregates. We also develop an improved method for determination of the cmc based on the maximum in curvature for the osmotic pressure curve determined from μVT simulations. Excellent agreement in cmc and other micellar properties between NVT and μVT simulations of different system sizes is observed. The methodological developments in this work are broadly applicable to simulations of aggregating systems using any type of surfactant model (atomistic/coarse grained) or solvent description (explicit/implicit).

Ultrasound-assisted preparation of ZnO nanostructures: understanding the effect of operating parameters

AbstractThe present work deals with the use of ultrasound atomization for the preparation of zinc oxide nanostructures. The focus of the work is to understand the effect of different operating parameters, such as ultrasonic power dissipation, flow rate, concentration, and surface tension, on the final particle morphology obtained during the synthesis. The prepared nanostructures were observed under scanning electron microscope to understand the morphology of the synthesized nanostructures. It was established that the final characteristics of the nanostructures, in terms of shape and size, can be effectively controlled by controlling flow rate, precursor concentration, surface tension, and ultrasonic power dissipation. The droplet size was found to increase with an increase in the flow rate of an aqueous solution of zinc nitrate, ultrasonic power, and decrease in the loading of surfactant (polyvinylpyrrolidone). The present work has clearly established the utility of ultrasound-assisted synthesis of nanoparticles with clear evidence for obtaining desired characteristics based on controlled application.

Structure and performance of anionic–cationic-organo-montmorillonite in different organic solvents

With an increase of polarity and surfactant loading, the dispersibility of ACOMt in organic solvents increased.

Hexadecyl Trimethyl Ammonium Bromide-Modified Montmorillonite as a Low-Cost Sorbent for the Removal of Methyl Red from Liquid-Medium

In this study, montmorillonite (MMT) modified by a cationic surfactant (Hexadecyltrimethyl ammonium bromide, HDTMA) was used as adsorbent to the removal of methyl red (MR) from aqueous solution. The effect of different parameters includes surfactant loading rate, contact time, pH, adsorbent dosage, and initial MR content was investigated on the sorption. The sorption capacity was increased by increasing the surfactants loading rate up to 120% cation exchange capacity (CEC) of the clay. The contact time 30 min and pH of 6 were selected as the optimum for the uptake of MR. The maximum uptake capacity was obtained 1428.5 mg/g. The experimental data of the sorption was well fitted by pseudo-second-order kinetic and Freundlich isotherm models. The results show that the HDTMA-modified MMT can be applied as an effective and low cost sorbent for the removal of MR dye from aqueous solution.

Ionic dye–surfactant nanoassemblies: interplay of electrostatics, hydrophobic effect, and π–π stacking

The interplay of several non-covalent interaction forces is used as key to supramolecular structures. Combining cationic alkyltrimethylammonium bromide surfactants and the divalent anionic azo dye Acid Red 26 (Ar26) as small building blocks in aqueous solution, electrostatic interactions of the oppositely charged building blocks in combination with hydrophobic effect and π–π interactions play a major role in aggregate formation. Static and dynamic light scattering and small-angle neutron scattering (SANS) revealed different sizes of aggregates in the range of 2 nm ≤ R H ≤ 420 nm depending on surfactant length, concentration and of dye to surfactant loading ratio. A strong relationship of assembly size with surfactant concentration has been found, where initial surfactant monomers and micelles influence the aggregate formation differently. The stability of dye–surfactant aggregates which also shows a dependency on surfactant tail length has been related to ζ-potential measurements. Small-angle neutron scattering elucidated that dye–surfactant aggregates possess cylindrical shapes with different aspect ratios. UV/Vis spectroscopy gave information on the dye–dye π–π stacking geometry and extent, while the thermodynamic parameters for micellization and dye–surfactant binding ΔH, ΔG, and ΔS as well as stoichiometry and binding constant obtained by isothermal titration calorimetry revealed insight into the interplay of interactions.

Optimization of diacylglycerol production by glycerolysis of fish oil catalyzed by Lipozyme TL IM with Tween 65.

The diacylglycerols (DAG) are emulsifiers with high added value used as functional additives in food, medicine, and cosmetic industries. In glycerolysis of oils for the production of DAG, the immiscibility between the substrates (glycerol and oil phases) has to be overcome, for example, by the addition of a food grade surfactant like Tween 65. The main objective of this work was to optimize the process conditions for obtaining diacylglycerols rich in the omega-3 eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, through the enzymatic glycerolysis of fish oil, in systems with Tween 65 and without this surfactant, using Lipozyme TL(®) IM as biocatalyst. The experiments were performed according to predetermined conditions varying the temperature, enzyme load, the oil to glycerol molar ratio and, when added, the surfactant load. After 6 h of reaction, it was possible to produce up to 20.76 and 13.76% of diacylglycerols from fish oil in the reactions with and without Tween 65, respectively.

Influence of synthesis method in preparation of HDTMA+- and HDPy+-illites/smectites

Intercalation of cationic surfactants hexadecylpyridinium (HDPy+) and hexadecyltrimethylammonium (HDTMA+) into the interlayer space of homoionic (Na+-, Ca++- and Zn++-) illites/smectites using three methods (solution intercalation, solid–solid reaction and microwave irradiation) was investigated in this study. The changes in the surfaces and structures of the organo-illites/smectites with cationic surfactant were characterized using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR).The results showed that the intercalation of surfactant cations was complete within 24h, 15min and 2min by conventional method, solid–solid reaction and microwaves irradiation, respectively. HDPy+t and HDTMA+ surfactants were retained by Zn++-illites/smectites suggesting important surface properties (CEC=80meq/100g clay, SBET=116.5m2/g) and developed acid–base properties (point of zero proton charge PZC, density charge σH). HDPy+ cation loading was effective suggesting that the aromatic polar group is favored for intercalation. Different configurations of surfactants within interlayer space of clay mineral were proposed based on the basal spacings which increased with surfactant loading. The presence of symmetrical and asymmetrical vibration bands of the –CH2 group in the IR spectrum of the modified illites/smectites and the variation of their frequencies and their intensities confirmed the results obtained by XRD.

Surfactant modified montmorillonite as a low cost adsorbent for 4-chlorophenol: Equilibrium, kinetic and thermodynamic study

Chlorophenols are toxic, mutagenic and carcinogenic compounds that must be removed before discharging into the environment. In this study, montmorillonite (Mt) modified with two cationic surfactants (hexadecyl trimethyl ammonium bromide, HDTMA, and tetradecyl trimethyl ammonium bromide, TTAB) was used to remove 4-chlorophenol (4-CP) from aqueous solutions. The influence of various factors such as surfactant loading rate, contact time, pH, adsorbate content, solution ion strength and temperature was investigated on the sorption. The sorption uptake of 4-CP was increased by increasing the surfactants loaded onto the Mt up to 150% CEC (cation exchange capacity) of the clay. The contact time of 10 min and 45 min and pH of 11 were found to be as the optimum for the sorption of 4-CP by HDTMA-Mt and TTAB-Mt, respectively. The sorption capacity of 4-CP by the sorbents at the equilibrium was 29.96 mg/g for HDTMA-Mt and 25.90 mg/g for TTAB-Mt. The results also indicated that the Freundlich isotherm model and pseudo-second order kinetic model well described the sorption process than other models. It is obvious that the surfactant modified montmorillonite, especially HDTMA type, in comparison with raw Mt was more efficient sorbent to remove 4-CP from aqueous solutions.

Modeling Aggregation of Ionic Surfactants Using a Smeared Charge Approximation in Dissipative Particle Dynamics Simulations.

Using dissipative particle dynamics (DPD) simulations, we explore the specifics of micellization in the solutions of anionic and cationic surfactants and their mixtures. Anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant cetyltrimethylammonium bromide (CTAB) are chosen as characteristic examples. Coarse-grained models of the surfactants are constructed and parameterized using a combination of atomistic molecular simulation and infinite dilution activity coefficient calibration. Electrostatic interactions of charged beads are treated using a smeared charge approximation: the surfactant heads and dissociated counterions are modeled as beads with charges distributed around the bead center in an implicit dielectric medium. The proposed models semiquantitatively describe self-assembly in solutions of SDS and CTAB at various surfactant concentrations and molarities of added electrolyte. In particular, the model predicts a decline in the free surfactant concentration with the increase of the total surfactant loading, as well as characteristic aggregation transitions in single-component surfactant solutions caused by the addition of salt. The calculated values of the critical micelle concentration reasonably agree with experimental observations. Modeling of catanionic SDS-CTAB mixtures show consecutive transitions to worm-like micelles and then to vesicles caused by the addition of CTAB to micellar solution of SDS.

Simultaneous removal of ammonium and nitrate by HDTMA-modified zeolite.

In this study, surfactant (hexadecyltrimethylammonium, HDTMA) modified zeolite (clinoptilolite) (SMZ) was used for simultaneous removal of ammonium and nitrate in wastewater, and the sorption properties of SMZ were determined. Results showed that natural clinoptilolite had good affinity for ammonium, but low sorption ability for nitrate, and the ammonium sorption process was well described by the pseudo-second order kinetic model. The SMZ had a significant enhancement on nitrate sorption and could simultaneously remove ammonium and nitrate at specific conditions, with removal efficiency up to 93.6% and 81.8%, respectively. The sorption process fitted well with the Langmuir isotherm. Orthogonal experiments showed that ammonium concentration was the most important factor for ammonium sorption on SMZ. However, surfactant loading was the major factor for nitrate sorption. Meanwhile, phosphate did not interfere with nitrate removal. Semi-empirical quantum mechanics molecular simulation indicated that electrostatic attraction existed between HDTMA and nitrate. Results of this study demonstrated that SMZs may have great potential for removing cations and anions simultaneously in the aquatic environment.