Anionic Surfactant Sodium Dodecyl Sulfate Research Articles

Novel quaternary ammonium compounds derived from aromatic and cyclic amino acids: Synthesis, physicochemical studies and biological evaluation

Novel quaternary ammonium surfactants (QUATs) derived from phenylalaninyl-proline dipeptide with chain length C12 and C14 were synthesised as potential active ingredients to be used in body cleansing formulations. The physicochemical properties and biological activities of the QUATs were determined in both single and in mixed surfactant system with either the conventional anionic surfactant sodium dodecyl sulphate (SDS) or sodium N-dodecyl prolinate. The C12 QUAT derivative showed antagonistic behaviour in both SDS and sodium N-dodecyl prolinate mixed surfactant system. Comparing the mixed system of the C12 QUAT with SDS and sodium N-dodecyl prolinate, it was found that the latter displayed better antibacterial activity together with the lower ocular irritation. The C12 QUAT-sodium N-dodecyl prolinate mixture were non cytotoxic at a concentration corresponding to its MIC value, showing that the mixture was selective towards bacterial cells rather than mammalian cell lines. Diffusion measurements showed that the sodium N-dodecyl prolinate surfactant consisted of 26 molecules per micelle in water but only 3 molecules per micelle in DMSO/water (1:1). On the other hand, C12 QUAT did not form a micelle in DMSO/Water. Membrane permeability studies of the C12 QUAT and sodium N-dodecyl prolinate showed that these surfactants are capable to penetrate into deeper skin layers to exert their antibacterial and cleansing action and hence can be used as a promising candidate as active ingredients in body wash formulations.

Interfacial and Aggregation Behaviour of Sodium Dodecyl Sulphate Induced by Ionic Liquids.

Aggregation studies of anionic surfactant sodium dodecyl sulphate (SDS) was investigated in aqueous 1-butyl-3-methylimidazolium chloride [bmim]Cl and N-butyl-N-methyl pyrrolidinium tetrafluoroborate [bmp]BF4 ionic liquid (IL) solutions respectively. Systems were studied by surface tension, conductance, UV-VIS absorption/emission spectroscopy and dynamic light scattering. Critical micelle concentration (CMC) values gradually decreased with increasing IL concentration which indicates synergistic interaction between ILs and SDS. Gibbs free energy change results demonstrated spontaneous micellization induced by ILs; however the effect of ILs were not similar to the corresponding regular salts (NaCl and NaBF4). Aggregation number (n) of micelles, determined by fluorescence quenching method, indicate that the 'n' values increase with increasing ILs concentration, induced by the oppositely charged IL cation. Size of the micelles, determined by dynamic light scattering studies, increased with increasing ILs concentration, which were due to the formation of larger aggregates; the aggregates are considered to be comprised of the anionic surfactant with a substantial proportion of ILs cation as the bound counter ions. Such studies are considered to shed further light in the fundamentals of IL induced micellization as well as in different practical applications.

Antiwear nano-lubricants of calcium-doped zinc oxide: Applicable to tribological activities

The tribological properties of zinc oxide (ZnO) and 12% calcium doped zinc oxide nanoparticles (ZCOs) have been investigated by performing standard tests, ASTM D4172 and D5183on a four-ball tester. All the nanoparticles were synthesized through auto combustion method. Calcium doped zinc oxide nanoparticles of different size were prepared by varying the calcination temperature as 600 °C (ZCO-1) and 1000 °C (ZCO-2) respectively. The synthesized nanoparticles have been characterized by different techniques such as powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM) coupled with energy-dispersive X-ray (EDX). Incorporation of calcium as a dopant was found to enhance the antiwear and antifriction behavior of the ZnO nanoparticles. The nanoparticles ZCO-1 with smaller size, 25 nm provided much better results as compared to ZCO-2, 35 nm. Furthermore, a stable suspension of the synthesized nanoparticles was prepared with an anionic sodium dodecylsulphate surfactant (0.25% w/v with 0.1% SDS) which increased substantially the antiwear properties and reduced simultaneously the friction between moving metal surfaces. Thus, the enhanced tribological properties may result in the commercial deployment of these nano-lubricants in lubrication industries.

Influence of electron accelerator irradiation on epoxy nanocomposites materials for spacecraft structure

Different types of surfactants; nonionic, anionic and cationic represented by Polyoxyethylene sorbitan monooleate (Tween 80), sodium dodecyl sulfate (SDS), and cetyltrimethylammonium bromide (CTAB) respectively were used to select a proper type of surfactant enhancing dispersion quality of multiwall carbon nanotubes (MWCNTs) in the epoxy resin. Hereinafter, the effect of one of the most severe space environment threats which are an electron beam on the candidate material used as a structural space material. The candidate material is characterized by furrier transformation infrared spectroscopy (FTIR), mechanical properties, surface tension, and electrical dispersion measurement. The mechanical results revealed that the strength increases by 10% while adding the CTAB surfactant, while decreases by 27% and 32% by adding tween-80 and SDS respectively. The anionic surfactant SDS, despite keeping the stiffness the reference sample it is the lower strength and elongation. The CTAB improves the mechanical properties by improving the strength and stiffness while elongation is significantly decreased by adding any of the surfactants. The surface tension of Tween 80 and anionic surfactant; SDS,  = 24.4 mN/m while the surface tension in case of the CTAB is  = 25.4 mN/m. Surface tension and electrical dispersion measurement results reveal that the nonionic surfactant Tween 80 led to a uniform dispersion of MWCNTs in the epoxy than other surfactants. The effect of 100-kGy irradiation via electron beam on the structure and its electrical properties of the epoxy composites was studied. Improving the dispersion quality of the MWCNTs in epoxy nanocomposites materials for spacecraft structure occurred.

Influence of surfactants on a pre-adsorbed cationic layer: Removal and modification

Removal of organic species from solid surfaces is a crucial process. The use of oppositely charged surfactants provides a potential method for enhanced removal. Neutron reflectometry has been used to investigate the complex behaviour of a pre-adsorbed and tenacious layer of the cationic surfactant didodecyldimethylammonium bromide (DDAB) on a mica surface, during exposure to different organic species in solution. The anionic surfactant sodium dodecylsulfate (SDS) was shown to be able to remove the cationic layer, but only if anionic micelles were present in solution. To facilitate comparison with the behaviour of a non-ionic surfactant, the direct adsorption of pentaethylene glycol monododecyl ether (C12E5) to mica was also studied; low surface coverage adsorption was seen at the critical micelle concentration and above. C12E5 was then found not to remove the cationic layer, but did include into the layer to some degree. The presence of cationic surfactant on the mica was however shown to significantly modify the adsorption behaviour of the non-ionic surfactant.

Effect of mixed cationic/anionic surfactants on the low-rank coal wettability by an experimental and molecular dynamics simulation

Mixed surfactants consisting of the cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and the anionic surfactant sodium dodecyl sulfate (SDS) demonstrated high floatability of low-rank coal, and the optimal molar ratio of CTAB and SDS was 1:9. The surface and thermodynamic parameters (CMC, γCMC, Γmax, Amin, ΔGm0) obtained from surface measurements indicated higher surface activity and denser molecular arrangement in the mixed CTAB/SDS surfactants than in single CTAB or SDS. The contact angle of the coal sample increased from 38.9° to 73.7°, and the wetting heat of the coal became less negative, which showed a better positive effect on enhancing the contact angle and restricting the hydrophilicity of the coal surface. Molecular dynamics (MD) simulations were carried out to investigate the influence on the wettability of low-rank coal. The results indicated a significant increase in hydrophobicity of the low-rank coal. Furthermore, the combustible recovery was enhanced significantly by up to 47.67%, and the concentrated ash value was increased by up to 3.63%.

Study on extraction of anthocyanin from pericarp waste by SDS precipitation

In recent years, our country (China) has invested more and more in environmental protection, and resource recycling concept is also gaining in popularity. The free throw of the peel wastes both increases the load on the environment and wastes the useful ingredients in the peel. It is a natural pigment anthocyanin, not only has the natural colorants function but also has a high biological value and medicinal value. Useful anthocyanin extracted from the peel waste is a manifestation of the principle of “turning waste into treasure and utilization”. The Surfactant precipitation technique is a relatively new plant anthocyanin extraction method. Anionic surfactant-sodium dodecyl sulfate was selected to experiment, and the extraction efficiency of sodium dodecyl sulfate precipitation technique peel waste anthocyanin was discussed. Parameters such as surfactants, potassium chloride, sodium chloride concentration pH, and other factors on the recovery of the solvent category extraction affect the results. The results showed that optimal experimental conditions for 3mL crude extract solution, as follows: pH is 2, using 4mL5mmol/L of SDS, 1.5mL 6mmol/L of KCl,1mL AR acetone, 1mL 0.25mol/L of NaCl, under the best condition, the rate of anthocyanin extraction was up to 60.81%.

Electrodeposition of Nickel/Graphene Oxide Particle Composite Coatings: Effect of Surfactants on Graphene Oxide Dispersion and Coating Performance

The dispersibility of graphene oxide particles (GOs) in nickel electrolytes is critical for its uniform incorporation in the nickel matrix during the electrodeposition process. In this study, we study the fundamental interaction of surfactants and nickel ionic strength for uniform and stable incorporation of GOs in nickel electrolytes and their effect on coating performance. The results indicate that the non-ionic surfactant Polyethylene glycol (PEG) has the optimal dispersibility of GOs in nickel electrolyte, followed by the cationic surfactant Cetyltrimethylammonium bromide (CTAB) and the anionic surfactant Sodium dodecyl sulfate (SDS). It is also noted that the increasing nickel ionic strength would deteriorate the stability of GOs, attributing to the generation of cross-linking of high strength divalent nickel ions with dispersed graphene oxide. The electrodeposited coatings show that more incorporation of graphene oxide in the coating is achieved when the PEG surfactant is used, which leads to an increased hardness by 146% and a decreased friction coefficient by 72.7% under low nickel sulfamate concentration (200 g l−1), compared to pure nickel coating. Eventually, the study shows that higher nickel ionic strength would deteriorate the performance of the coatings, while the selection of proper surfactant can compensate for it.

Physico-chemical characterization of biosurfactant from Pseudomonas aeruginosa PU1 and its application in microbial enhance oil recovery.

Biosurfactant-producing bacteria were isolated from transformer oil-contaminated soil. The strain was identified as Pseudomonas aeruginosa PU1 based on its molecular characterization by 16S rRNA gene sequencing. The extraction of biosurfactant was done by acid precipitation method using 2 N hydrochloric acid and further purified by silica-gel column chromatography. The highest rhamnolipid biosurfactant production (8.92 ± 0.08 g/L) was obtained using molasses (6%, w/v) and ammonium nitrate (5%, w/v). The purified biosurfactant showed a reduction of surface tension of water from 70.23 mN/m to 29.77 mN/m at a concentration of 30 mg/L. The functional groups were characterized by fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR). The liquid chromatography-mass spectrometry (LC-MS) analysis showed six different rhamnolipid congeners with psuedomolecular ions (m/z) of 305, 361, 451, 505, 532 and 621. X-ray diffraction (XRD) analysis and the thermal analysis showed crystalline nature and thermal stability of the biosurfactant. The stability study of the biosurfactant reveals that the emulsifying activity was much stable at various ranges of temperature (4-120 °C), pH (2-12), and NaCl concentration (2-10%, w/v) even on the 7th day. The purified biosurfactant PU1 was found to be effective in oil recovery and showed 68.53 ± 3.07% of oil recovery in the sand pack column under saline condition, which was higher than anionic surfactant sodium dodecyl sulphate (SDS). The physico-chemical properties and the stability studies of the biosurfactant suggested that it has enormous potential in oil recovery in the soil contaminated with the oils.

Determining binding of polycyclic aromatic hydrocarbons to micelles formed by SDS and SOL using semi-equilibrium dialysis

Micellar enhanced ultra-filtration (MEUF) is a modified ultrafiltration (UF) method that can remove small molecules that are not effectively removed by UF alone. In this work we used a similar semi-equilibrium dialysis (SED) method to characterize two anionic surfactants, sodium dodecyl sulfate (SDS) and sodium laurate (SOL), as MEUF candidates to remove several polycyclic aromatic hydrocarbon (PAH) compounds. These anionic surfactants have low toxicity and are more biodegradable compared to the fairly toxic and persistent cetyltrimethylammonium bromide (CTABr) and similar cationic surfactants, which is important as MEUF surfactants may be present in the treated effluent. The log binding constants (Log KB) of the PAHs naphthalene, phenanthrene, pyrene and fluorene to SDS ranged from 3.07 to 4.48, which compared well with the previous results for CTABr and indicated that SDS is an excellent candidate for MEUF. The log binding constants for the same PAHs with SOL micelles ranged from 2.11 to 3.53, which suggested that SOL might be adequate for stronger-binding PAH like pyrene and fluorene but less suitable for naphthalene and phenanthrene. The results demonstrated a strong correlation between the Log KB with one micelle type and the Log KB with the other, suggesting a common set of properties and interactions are responsible for the binding. Similar to the previous results for CTABr, a significant correlation between Log KB and Log KOW values indicates that hydrophobic character is the main driving force for PAH binding with these anionic micelles. This may also be useful for predicting MEUF performance for various compound/surfactant combinations where Log KB is not known.

Performance and modelling of retention in microemulsion liquid chromatography

The capability of liquid chromatography with microemulsions (MEs) as mobile phases was studied for the analysis of four parabens (butylparaben, ethylparaben, methylparaben, and propylparaben) and seven β-adrenoceptor antagonists (acebutolol, atenolol, carteolol, metoprolol, oxprenolol, propranolol, and timolol). MEs were formed by mixing aqueous solutions of the anionic surfactant sodium dodecyl sulphate, the alcohol 1-butanol that played the role of co-surfactant, and octane as oil. In order to guarantee the formation of stable MEs, a preliminary study was carried out to determine the appropriate ranges of concentrations of the three components. For this purpose, mixtures of variable composition were prepared, and the possible separation of two phases (formation of an emulsion) was visually detected. The advantage offered by the addition of octane to micellar mobile phases, inside the concentration range that allows the formation of stable MEs, was evaluated by comparing the retention behaviour, peak profile and resolution of mixtures of the probe compounds, in the presence and absence of octane. The final aim of this work was the proposal of a mathematical equation to model the retention behaviour in microemulsion liquid chromatography. The derived global model that considered the three factors (surfactant, alcohol and oil) allowed the prediction of retention times at diverse mobile phase compositions with satisfactory accuracy (in the 1.1‒2.5% range). The behaviour was compared with that found with mobile phases without octane. The model also yielded information about the retention mechanism and revealed that octane, when inserted inside the micelle, modifies the interaction between solutes and micelles.

Study of conductivity, contact angle and surface free energy of anionic (SDS, AOT) and cationic (CTAB) surfactants in water and isopropanol mixture

The thermodynamic properties of cationic surfactant CTAB (cetyltrimethylammonium bromide), anionic surfactant SDS (sodium dodecyl sulfate), and AOT (Aerosol OT) in pure water and 0.1, 0.2, 0.3, and 0.4 volume fraction of isopropanol were observed by measuring the conductivity at 298.15 K. Various physicochemical properties like CMC, α and the thermodynamic properties like standard free energy of micellization (∆Gmo), the free energy of surfactant tail transfer (∆Gtranso) were calculated. Also, (log S1 and log S2), α, CMC, K0KCMC, ∆Gmo and ∆Gtranso are correlated with the volume fraction of isopropanol. The result revealed a sharp increase in conductivity with an increase in surfactant concentration. With the increasing isopropanol content in the solvent composition, the critical micelle concentration (CMC) of the CTAB and SDS increased. The degree of micellar dissociation (α) as well as the Gibbs' free energy was found to be increased with the increasing volume fraction of isopropanol. The correlation of ∆Gmo with the solvent parameters and the solvophobic parameter were also included. The contact angle and surface free energies over the aluminum foil surface were also evaluated using a drop shape analyzer (DSA-25E).

MWNT-Based Electrode for the Voltammetric Quantification of Carvacrol

Glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWNTs) dispersed in anionic surfactant sodium dodecylsulfate (MWNTs/GCE) has been developed for the carvacrol quantification. The electrode modification provides electrocatalytic effect to carvacrol oxidation (the cathodic shift of the oxidation potential on 121 mV and 1.7-fold increase of the oxidation currents vs. GCE). The electrodes are characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The 8.4-fold higher effective surface area has been obtained for the modified electrode (75 ± 2 mm2 for MWNTs/GCE vs. 8.9 ± 0.2 mm2 for GCE). EIS data have shown 6-fold lower charge transfer resistance in comparison to GCE. The irreversible diffusion-controlled oxidation of carvacrol with participation of one electron and one proton has been proved. The parameters of electrooxidation have been calculated. Differential pulse voltammetric quantification in phosphate buffer pH 6.5 can be performed in the ranges of 0.1–25 and 25–150 μM of carvacrol. The detection limit of 0.075 μM has been achieved. The method developed has been successfully applied for the determination of total isopropylmethylphenols in oregano spices. The results obtained have been compared to independent spectrophotometric method data.

Oxidative stress in benthic oligochaete worm, Tubifex tubifex induced by sublethal exposure to a cationic surfactant cetylpyridinium chloride and an anionic surfactant sodium dodecyl sulfate

The present study was assessed to determine the in vivo toxic effects of a cationic surfactant, cetylpyridinium chloride (CPC), and an anionic surfactant, sodium dodecyl sulfate (SDS) in terms of oxidative stress biomarkers in benthic oligochaete worm Tubifex tubifex for 14 days. The investigation demonstrated that sublethal concentrations of CPC (0.0213, and 0.0639 mg L−1) and SDS (1.094 and 3.092 mg L−1)induced paramount alterations in the oxidative stress enzymes in Tubifex tubifex. Superoxide dismutase (SOD), glutathione S-transferase (GST), reduced glutathione (GSH), and glutathione peroxidase (GPx) exhibited an initial notable increase in their activities in the surfactants exposed worms at 1d and 7d of exposure period followed by consequential reduction at 14d exposure period with respect to control, while catalase (CAT) and malondialdehyde (MDA) activities markedly incremented gradually throughout the exposure periods. Through the construction of the correlation matrix and integrated biomarker response (IBR), the effects of CPC and SDS on Tubifex tubifex were distinguished. These results indicate that exposure to these cationic and anionic surfactants modulates the levels of oxidative stress enzymes in Tubifex tubifex.

Removal of hydrocarbon from soils possessing macro-heterogeneities using electrokinetics and surfactants

The removal of n-hexadecane from soil in two-dimensional (vertical) setups was investigated using electrokinetics (EK), hydraulic gradient (HG), and anionic surfactant SDS (Sodium Dodecyl Sulfate) and nonionic surfactant Tween 80. The investigation relied on creating a two-dimensional block containing 3 × 3 cells each 3 cm in dimension. The soils in the blocks were created by mixing loamy sand soil (LSS) with kaolinite (clay) at three proportions: 100% LSS + 0% clay, 95% LSS + 5% clay and 90% LSS + 10% clay. This approach is very different from existing approaches where heterogeneity is layered. The surfactant concentration exhibited a large variability in space, including in the sand around the soil which highlights the limitations of one-dimensional investigations. In general, HG delivered surfactant more uniformly in the sand, but not in the soil. The performance of Tween 80 with EK was slightly higher than that of SDS, as the removal was 64% to 51%, respectively; and was better than SDS when HG was used, 65% to 46%. Another set of experiments was conducted using one cell made of 20% LSS + 80% clay with Tween 80. The EK provided a much higher removal efficiency (77%) than HG (43%), which indicates that EK performs better than HG for clayey soils. Overall, the study indicates that for both anionic and nonionic surfactant, the removal of n-hexadecane using EK was comparable to or better than HG, and that EK is capable of delivering the surfactants in two-dimensional systems.

Experimental synthesis and performance comparison analysis of high-efficiency wetting enhancers for coal seam water injection

To improve the wettability effect of coal seam water injection, and reduce dust production from the source, this paper proposes the preparation of three kinds of high-efficiency wetting enhancers. In this study, 2-acrylamide-2-methylpropionic sulfonic acid and itaconic acid were introduced into the polymer chain of sodium alginate in different combinations. Anionic surfactant sodium dodecyl sulfate and nonionic surfactant aliphatic alcohol polyoxyethylene ether were added in different proportions to obtain three kinds of enhancers. The three kinds of enhancers have good viscosity and fluidity, and the optimal emulsifier additive is determined by a surface tension test. The hydrophilic hydroxyl, carboxyl or sulfonic groups of enhancers were obtained by a Fourier-transform infrared experiment, which was beneficial to water absorption. The contact effect of different solutions on coal block was studied by a scanning electron microscopy experiment. An energy dispersive spectrometry experiment proved that the solution was well dispersed. Through reverse osmosis experiment and contact angle analysis, the wettability of different solutions was compared, and the best enhancers was obtained. The molecular dynamics simulation was used to verify the relationship between them, and finally the mechanism of action was deduced. It was proved that AMPS-IA/SA+SDS/AEO had better wettability. Thus, AMPS-IA/SA+SDS/AEO is an ideal enhancer for coal seam water injection.

PH-Dependent surface charge at the interfaces between aluminum gallium nitride (AlGaN) and aqueous solution revealed by surfactant adsorption

HypothesisThe net surface charge of AlGaN/GaN structures, where AlGaN is in contact with the solution, is controlled by the pH-dependent protonation and deprotonation of the surface hydroxyl groups and possibly the electron-deficient surface electronic states. We hypothesize that atomic force microscopy (AFM) force measurements of ionic surfactant adsorption can reveal how the AlGaN surface properties vary with pH. ExperimentsAFM force curves and images were used to probe the AlGaN/solution interface in water as a function of pH, and with added cationic surfactant cetyltrimethylammonium bromide (CTAB) or anionic surfactant sodium dodecylsulfate (SDS). FindingsThe AlGaN/solution interface is negatively charged at pH 12, has an isoelectric point near pH 5.5, and is positively charged at pH values less than 5.5. Surfactant adsorption data suggests AlGaN surface is somewhat hydrophobic at acidic pH. Compared to gallium nitride (GaN), at pH 2, AlGaN has a lower charge density and hydrophobicity, but at other values of pH, the surface properties of AlGaN and GaN are similar.

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.

Applicability of an anionic-nonionic surfactant in p-cresol contaminated soil washing: Finding the optimal mixing ratio.

In this study, the parameters influencing p-cresol removal efficiency in soil washing method were investigated. Primarily, extraction efficiencies of three Tween series surfactants (Tween 20, Tween 60, Tween 80) with 10mM concentration were compared. Tween 80 showed the best results since its value (55%) was 4% and 13% higher than that of Tween 60 and Tween 20. The impact of mixed surfactant on extraction rate was examined by employing a mixture of Tween 80 and one anionic surfactant (sodium dodecyl sulfate) with different molar ratio as the main washing solution. The results denoted that the molar ratio of 3:2 (SDS:Tween80) could enhance the extraction rate up to 38% compared to using SDS and Tween 80 alone. Regarding the initial p-cresol concentration in the collected sample, the cleanup level (390mg/kg) could only be achieved using the mixed-surfactant. Thus, the minimum required surfactant concentrations to hit the target level was calculated to be 3.54g/L of Tween 80 and 2.105g/L of SDS (molar ratio of 0.27 SDS:Tween80). Studying the role of surfactant concentration indicated that its increment from 10mM to 20mM, which is way above all the reagents' critical micelle concentration (CMC), does not affect the removal rate considerably. The same results were obtained comparing the effect of washing time in three different levels (30min, 60min and 90min). However, temperature showed to be a more significant parameter as it could enhance the results up to 20% (for SDS).

Comparison of Same Carbon Chain Length Cationic and Anionic Surfactant Adsorption on Silica

Adsorption of a cationic surfactant dodecyl pyridinium chloride (DPC) on silica was studied to show a comparison with the adsorption of an anionic surfactant sodium dodecyl sulfate (SDS), whose carbon chain length is the same and on the same silica. Results provided a better understanding of the adsorption mechanism of cationic and anionic surfactant on negatively charged silica. The experiment covered different electrolyte concentrations and pH values. Results indicated that at the same pH, the DPC adsorption amounts are higher when the electrolyte concentration is higher; at a higher DPC equilibrium concentration, the adsorption amount difference is larger than that at low DPC equilibrium concentration, and when DPC equilibrium concentration is lower than 0.1 mmol/L, the adsorption amount difference cannot be observed. At charge compensation point (CCP, 0 zeta potential), the negative surface charge of silica was compensated by DP+, a continuous increasing zeta potential indicated a bilayer adsorption of DPC on silica. The adsorption amount increased with increasing pH. The calculated lines by Gu and Zhu model show a two-step property, including a bilayer and hemi-micelle adsorption. DPC adsorbed more strongly on silica than SDS due to the combination of electrostatic and hydrophobic attraction.