Synergistic solubilization of polycyclic aromatic hydrocarbons by mixed micelles composed of a photoresponsive surfactant and a conventional non-ionic surfactant

Synthesis and Surface Properties of Photoresponsive Gemini Surfactants: Implication for Remediating PAHs-Contaminated Groundwater

The efficient utility of surfactants remains a daunting task for groundwater remediation. In this study, we have synthesized a conventional photoresponsive surfactant 4-[4-[(4-butylphenyl)azo]phenoxy]butyldimethylethylammonium bromide (AzoPB) and a gemini photoresponsive surfactant N¹,N²-bis[4-[4-[(4-butylphenyl)azo]phenoxy]butyl]-N¹,N²-tetramethylethane-1,2-diammonium bromide (AzoPBT) for solubilizing PAHs in groundwater. The two surfactants' photosensitivity, surface properties, and solubilization/release ability for phenanthrene (Phe) and acenaphthylene (Ace) were studied in detail. Under UV-light irradiation for 15-20 s, the two surfactants can be converted from trans to cis, while cis-to-trans isomerization can be achieved under visible-light irradiation for 1 min. Compared to AzoPB, AzoPBT exhibited strong surface properties such as lower critical micelle concentration (0.52 mM), surface tension (γ, 28.94 mN·m^-1), minimum area (A_min, 1.72 × 10^-8 nm²), and higher maximum adsorption (Γ_max, 96.55 mol·m^-2). The solubility of Phe and Ace in the AzoPBT aqueous solution (12.84 and 14.27 mg/L) was much higher than that in the AzoPB aqueous solution (7.51 and 8.77 mg/L) and gradually increased as the surfactant concentration increased in both aqueous solutions. Compared to AzoPB, gemini surfactant AzoPBT exhibited stronger solubilization ability. After four cycles of cis-trans isomerization conversion, AzoPBT could still reduce the hydrophobicity of Phe in natural groundwater, although the solubility of Phe decreased slightly. Additionally, the release capacity of AzoPBT was significantly higher than that of AzoPB during the cyclic solubilization-release process. The results indicated that gemini photoresponsive surfactants should be preferable to conventional photoresponsive surfactants for groundwater remediation due to their higher solubilization and release efficiency for Phe in the cyclic solubilization and release process, which can improve repair efficiency, minimize secondary pollution, and reduce remediation costs.

Interaction quantitative modeling of mixed surfactants for synergistic solubilization by resonance light scattering

In situ flushing through surfactant-enhanced aquifer remediation (SEAR) technology has long been recognized as a promising technique for NAPL removal from contaminated aquifers. However, there have been few studies on the choice of surfactants. In this work, the interaction quantitative model between resonance light scattering intensity and the concentration of binary surfactant mixtures NP-10+SDBS and NP-10+CTAB was established, and the mechanism of binary surfactant interaction was explored through the model by the resonance light scattering method. The relationship between the model constants and NAPL solubilization was also investigated to better address the application of surfactants in practical NAPL-contaminated site remediation. The critical micelle concentrations (CMCs) of nonylphenol ethoxylate (NP-10), dodecyl benzene sulfonate (SDBS), hexadecyl trimethyl ammonium bromide (CTAB), and the binary surfactant mixtures were measured by resonance light scattering (RLS), which were consistent with those obtained from surface tension measurements. In all cases, the RLS signals exhibited similar variations with surfactant concentration. A quantitative calculation model based on the RLS measurement data was established, and the binding constants K_NP-10+SDBS and K_NP-10+CTAB were calculated to be 0.66 and 1.51 L·mmol^-1, respectively, according to the equilibrium equations. The results showed that the binding constants have a significant positive correlation with NAPL solubilization.

Growth and antioxidant response in Spirodela polyrrhiza under linear alkylbenzene sulfonate, naphthalene and their joint stress

The synthetic organic surfactants linear alkylbenzene sulfonate (LAS) and polycyclic aromatic hydrocarbon naphthalene (NAP), two common organic pollutants, are frequently detected in freshwater environments. However, the combined ecotoxicological risks associated with these pollutants have not been fully elucidated. The present study investigated the effects of individual and combined treatments of LAS and NAP on the growth and physiological responses of Spirodela polyrrhiza. The results showed that LAS was the main compound toxic to S. polyrrhiza in a dose-dependent manner. The peroxidase (POD) enzyme and catalase (CAT) enzyme are the main antioxidant enzymes protecting S. polyrrhiza from LAS stress. When exposed to NAP stress alone, only slightly reversible damage was observed as the exposure time was extended (14 days). The antioxidant enzyme systems (including superoxide dismutase (SOD), CAT and POD) showed positive responses. Synergistic effects were induced with LAS-NAP mixtures (≥ 5 + 5 mg L^-1), and LAS played a major toxic role. The POD enzyme was a sensitive protective enzyme in duckweed during the joint exposure to LAS + NAP. The results indicate that LAS or NAP may cause serious damage to S. polyrrhiza and aggravate ecotoxicity in aquatic ecosystems.

Predicting Leachables Solubilization in Polysorbate 80 Solutions by a Linear Solvation Energy Relationship (LSER)

PURPOSE

A linear solvation energy relationship (LSER) was developed to predict the partitioning of neutral chemicals from polysorbate 80 (PS 80) micelles to water. Predicted partition coefficients were converted to a concentration dependent solubilization strength of aqueous PS 80 solutions. This solubilization strength represents a key parameter to project equilibrium levels of leaching from pharmaceutical plastic materials.

METHODS

To construct the LSER model equation, partition coefficients between PS 80 micelles and water were measured via a reference phase method or collected from the literature. Multiple linear regression of partition coefficients against five publicly available solute parameters was used to obtain the LSER system parameters.

RESULTS

112 chemically diverse compounds were incorporated for LSER model regression. The model equation shows a very good fit (R² = 0.969, SD = 0.219) for the entire dataset. The accuracy of the multi-parameter LSER model was proven to be substantially better in comparison to a single-parameter log-linear model based on the octanol-water partition coefficient.

CONCLUSION

PS 80 solubilization strength in water can expediently and accurately be calculated for neutral organic compounds with the proposed LSER model. LSER system parameters provide insightful chemical information with respect to solubilization in aqueous solutions of PS 80.

Strong synergistic effect of cationic hydrocarbon surfactant and novel nonionic tri-block short-chain fluorocarbon surfactant mixtures on surface activity, wettability and solubilization

Abstract

Mixing hydrocarbon surfactants with fluorocarbon surfactants is still an important strategy to improve the economic benefits and performances of fluorocarbon surfactants and expand their range of application. Herein, we prepared a novel kind of hydrocarbon-fluorocarbon surfactant mixtures via mixing a cationic surfactant, cetyltrimethylammonium bromide (CTAB), with a tri-block nonionic short-chain fluorocarbon surfactant (F9EG13F9) in aqueous solution. The results showed that adding a small CTAB amount to F9EG13F9 (the molar fraction of CTAB in the mixture (x1) was 0.2) could greatly reduce its critical micelle concentrations (cmc) from 0.408 mmol/L to 0.191 mmol/L. At this x1, the contact angle of the mixture was the minimum (57.7 °) at 100 s on polytetrafluoroethylene film, which was even lower than that of F9EG13F9. Besides, CTAB/F9EG13F9 mixtures possessed better colloidal stability and solubilization ability toward hydrophobic dye (Sudan І) than F9EG13F9. The outstanding performances of binary surfactant mixtures benefited from the non-ideal mixing and strong synergistic effect evidence that CTAB/F9EG13F9 surfactant mixtures could be used in practical applications instead of individual F9EG13F9, thereby reducing the used cost of F9EG13F9.

Graphical abstract

The Total Solubility of the Co-Solubilized PAHs with Similar Structures Indicated by NMR Chemical Shift

The synergism/inhibition level, solubilization sites and the total solubility (S_t) of co-solubilization systems of phenanthrene, anthracene and pyrene in Tween 80 and sodium dodecyl sulfate (SDS) are studied by ¹H-NMR, 2D nuclear overhauser effect spectroscopy (NOESY) and rotating frame overhauser effect spectroscopy (ROESY). In Tween 80, inhibition for phenanthrene, anthracene and pyrene is observed in most binary and ternary systems. However, in SDS, synergism is predominant. After analysis, we find that the different synergism or inhibition situation between Tween 80 and SDS is related to the different types of surfactants used and the resulting different co-solubilization mechanisms. In addition, we also find that three polycyclic aromatic hydrocarbons (PAHs) have similar solubilization sites in both Tween 80 and SDS, which are almost unchanged in co-solubilization systems. Due to the similar solubilization sites, the chemical shift changes of surfactant and PAH protons follow the same pattern in all solubilization systems, and the order of chemical shift changes is consistent with the order of changes in the St of PAHs. In this case, it is feasible to evaluate S_t of PAHs by chemical shift. In both Tween 80 and SDS solutions, the ternary solubilization system has relatively high S_t rankings. Therefore, in practical applications, a good overall solubilization effect can be expected.

Electrochemically reversible foam enhanced flushing for PAHs-contaminated soil: Stability of surfactant foam, effects of soil factors, and surfactant reversible recovery

Although surfactant foams enhanced-remediation for PAHs-contaminated soil has been proved to be an effective method, lack of simple/economic surfactant recovery methods from the eluent solutions limit its further remediation application for organic contaminated soil. Here, we prepared a electrochemically reversible ferrocene surfactant FcCH₂N⁺(CH₃)C₁₂H₂₅ (Fc12), then investigated the foaming ability and foam stability of Fc12 under its reduced (active state) and oxidation (inactive state) states and explored the flushing efficiency of reduced Fc12 foam for PAHs-contaminated soil and the recovery efficiency of collected eluent solution. The results showed that the foaming ability and foam stability of reduced Fc12 are greatly higher than those of oxidized Fc12, which is indicative of a well reversibly switchable characteristic of Fc12. The contaminated soil flushing efficiencies of reduced Fc12 for phenanthrene and pyrene were 65.28% and 46.45%. The respective desorption efficiency of phenanthrene and pyrene from collected eluent solutions were calculated to be 74.94% and 72.75% by electrochemical oxidation control, which indicates that Fc12 can be well recovered by simple electrochemical control. This study provides a feasible method for the recovery of surfactants from surfactant-enhanced remediation processes by simply electrochemical control.

Nonionic and anionic surfactant-washing of polycyclic aromatic hydrocarbons in estuarine sediments around an industrial harbor in southern Taiwan

Various surfactants, such as nonionic Triton X-100 and Simple Green™ (SG), and anionic sodium dodecylsulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS) were utilized to remove polycyclic aromatic hydrocarbons (PAHs) from heavily contaminated harbor sediments dredged from Kaohsiung Harbor in Taiwan. Desorption/re-sorption equilibrium, kinetics, and washability of PAHs using the selected surfactant were evaluated under different critical micelle concentrations (CMC). Experimental results revealed that the desorption rate of high molecular weight PAHs was greater than those of low molecular weight PAHs, and the anionic SDS was relatively effective in the removal of total PAHs (>50%) compared to the other surfactants. The correlation between the effectiveness of the surfactant washing processes and the physicochemical properties of individual PAH was statistically analyzed. The resulting data suggested that hydrophobic factors (K_ow, K_oc and S_w) affected PAH treatability more than the reactivity of PAH (electron affinity and ionization potential). Since the adsorption of anionic surfactant altered the hydrophobicity of organic matter in the sediment, PAHs preferred transferring from the sediment to the hydrophobic core of micelles in aqueous solution. Nevertheless, the nonionic surfactant enhanced the PAH partition in the aqueous phase, thus increasing the micellar solubilization of PAH.

Synergistic Solubilization of Phenanthrene by Mixed Micelles Composed of Biosurfactants and a Conventional Non-Ionic Surfactant

This study investigated the solubilization capabilities of rhamnolipids biosurfactant and synthetic surfactant mixtures for the application of a mixed surfactant in surfactant-enhanced remediation. The mass ratios between Triton X-100 and rhamnolipids were set at 1:0, 9:1, 3:1, 1:1, 1:3, and 0:1. The ideal critical micelle concentration values of the Triton X-100/rhamnolipids mixture system were higher than that of the theoretical predicted value suggesting the existence of interactions between the two surfactants. Solubilization capabilities were quantified in term of weight solubilization ratio and micellar-water partition coefficient. The highest value of the weight solubilization ratio was detected in the treatment where only Triton X-100 was used. This ratio decreased with the increase in the mass of rhamnolipids in the mixed surfactant systems. The parameters of the interaction between surfactants and the micellar mole fraction in the mixed system have been determined. The factors that influence phenanthrene solubilization, such as pH, ionic strength, and acetic acid concentration have been discussed in the paper. The aqueous solubility of phenanthrene increased linearly with the total surfactant concentration in all treatments. The mixed rhamnolipids and synthetic surfactants showed synergistic behavior and enhanced the solubilization capabilities of the mixture, which would extend the rhamnolipids application.

Co-solubilization of polycyclic aromatic hydrocarbon mixtures in aqueous micellar systems and its correlation with FRET for enhanced remediation processes

Surfactant enhanced remediation (SER) is an effective approach for decontaminating the PAH polluted soils. Solubilization and Cosolubilization of Phenanthrene (Ph), Pyrene (Py) and Perylene (Pe) as single, binary and ternary mixtures have been studied employing cationic (CTAB), anionic (SDS), non-ionic surfactant (Brij 30) and block copolymer (P123) micelles. In the single solute solubilization studies, solubility of Pe follows the order Brij 30 > CTAB > SDS whereas Ph or Py followed the order of CTAB > Brij 30 > SDS. In the cosolubilization studies, an increase, decrease or no change in the mutual solubility of PAHs was observed. Synergism in solubilization was observed most in P123 in both binary and ternary PAH mixture where more PAHs could get solubilized in the dense micellar shell region, thereby enhancing the micellar core volume leading to enhanced solubilization of PAHs. The solubilizates as pairs (Ph-Pe and Py-Pe) were further tested for any possible energy transfer in presence of surfactant based restricted host environments using spectrofluorometry and spectrophotometry. Based on the solubilization and cosolubilization an efficient non-radiative energy transfer (FRET) was observed between Ph/Py (donor) and Pe (acceptor) in the non-ionic surfactant system as well as in CTAB-Brij 58 mixed system. The results of this work may improve the effective utilization of surfactants in their correct evaluation for the removal of PAHs from contaminated soils or aquifers treated with SER technology.

Optimization of β-cyclodextrin consolidated micellar dispersion for promoting the transcorneal permeation of a practically insoluble drug

Development of efficient ocular drug delivery system for antifungal drugs becomes a must nowadays to face and eradicate the widely spread ophthalmic fungal infections. Itraconazole, a triazole antifungal, is struggling to penetrate the cornea and subsequently, its efficacy is limited. The aim of this study was to enhance itraconazole corneal penetration through utilizing the minimum surfactant amount in presence of β-cyclodextrin which acted as a dissolution and permeation enhancer. β-Cyclodextrin consolidated micellar dispersions (CCMD) were prepared after an initial screening to select the composition of surfactant(s). The preparation was done according to a modified melt dispersion technique. The prepared CCMD were characterized through the analysis of their particle size, zeta potential and solubilization efficiency. The optimum formula was chosen based on a factorial response surface analysis and it was composed of 17:1 w/w surfactant/drug, 30:1 w/w cyclodextrin/drug ratios and 0.02% polyethylene oxide. This formula was subjected to in vitro characterization including release, imaging by transmission electron microscope, mucoadhesion, stability, in addition to the determination of the minimum inhibitory concentration. Moreover, the ex vivo/in vivo permeation, safety and efficacy profiles were determined. The optimized CCMD formula was found to be significantly safe, stable, mucoadhesive and efficient to permeate the drug through rabbits' corneas. Consequently, the optimized CCMD formulation can be a promising, safe and efficient platform for the transcorneal delivery of lipophilic drugs including most antifungals.

Surfactant-enhanced remediation of polycyclic aromatic hydrocarbons: A review

Polycyclic aromatic hydrocarbons (PAHs) are toxic, mutagenic and carcinogenic organic compounds that are widely present in the environment. The bioremediation of PAHs is an economical and environmentally friendly remediation technique, but it is limited because PAHs have low water solubility and fewer bioavailable properties. The solubility and bioavailability of PAHs can be increased by using surfactants to reduce surface tension and interfacial tension; this method is called surfactant-enhanced remediation (SER). The SER of PAHs is influenced by many factors such as the type and concentration of surfactants, PAH hydrophobicity, temperature, pH, salinity, dissolved organic matter and microbial community. Furthermore, as mixed micelles have a synergistic effect on PAH solubilisation, selecting the optimum ratio of mixed surfactants leads to effective PAH remediation. Although the use of surfactants inhibits microbial activities in some cases, this could be avoided by choosing an optimum combination of surfactants and a proper microbial community for the targeted PAH(s), resulting in up to 99.99% PAH removal. This article reviews the literature on SER of PAHs, including surfactant types, the synergistic effect of mixed micelles on PAH removal, the impact of surfactants on the PAH biodegradation process, factors affecting the SER process, and the mechanisms of surfactant-enhanced solubilisation of PAHs.