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This study investigated the adsorption of methyl orange (MO) from aqueous solutions using a novel MnFe₂O₄/GO nanocomposite coated with cetyltrimethylammonium bromide (CTAB). The dual-layer surfactant modification facilitates both electrostatic and lipophilic interactions. This enhancement significantly improves dye removal efficiency. The adsorption process was monitored using spectrophotometry at 464 nm, with various characterization techniques confirming the structural and magnetic properties of the nanocomposite. The optimized parameters for maximum adsorption include a 2-minute ultrasonic dispersion, pH 6.8, and a surfactant-to-adsorbent ratio of 1, achieving a maximum adsorption capacity of 285.7 mg/g. The kinetic data followed a pseudo-second-order model, whereas the adsorption isotherm aligned with the Freundlich model, indicating multilayer adsorption. Thermodynamic analysis revealed the spontaneous and exothermic nature of the process. Additionally, the magnetic properties of the nanocomposite enabled efficient separation and reusability over three cycles without significant loss of performance. This study demonstrates the potential of MnFe₂O₄/GO coated with CTAB for rapid, efficient, and reusable removal of anionic dyes from wastewater through a combined mechanism of electrostatic and hydrophobic interactions.

An in-line sample concentration method for capillary electrophoresis called admicelle to solvent microextraction was proposed. In this technique, analytes were trapped in the cetyltrimethylammonium bromide admicelles formed in situ on the negatively charged capillary surface. A solvent plug was then partially injected hydrodynamically to collapse the admicelles, which liberated and focused the analytes at the solvent front. Voltage was applied across the capillary, completing the stacking process. Various solvents, namely, methanol, ethanol, and acetonitrile, were investigated. The optimal solvent for solvent to admicelle microextraction was 30% acetonitrile in 24 mM sodium tetraborate (pH 9.2). Sample injection time and solvent to sample injection ratio were also optimised. For this demonstration, the optimum sample injection time and solvent to sample injection ratio were 320 s and 1:2, respectively. Using the optimum conditions, UV detection sensitivity was enhanced 132–176-fold for the model anions. The LOQ, %intra-/inter-day (n = 6/n = 12, 2 days) repeatability, and linearity (R2) of admicelle to solvent microextraction were 0.08–2 µg/mL, 1.9–3.9%, 2.8–4.9%, and 0.992, respectively. Admicelle to solvent microextraction was applied to the analysis of various fortified water samples, with good repeatability (%RSD = 0.5–3.6%), and no matrix interferences.

Adsorption isotherms of single and double chain cationic surfactants with different chain length (cetyltrimethyl-, didodecyl- and dihexadecyl ammonium bromide) onto cellulose nanofibrils were determined. Nanofibrillated cellulose, also known as microfibrillated cellulose (MFC), with varying contents of carboxyl groups (different surface charge) was prepared by TEMPO-mediated oxidation followed by mechanical fibrillation. The fibril charge was characterized by potentiometric and conductometric titration. Surfactant adsorption was verified by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). Wetting and adhesion of water onto fibril films was determined by contact angle measurements. Small aggregates (admicelles) of surfactant were shown to form on the nanofibril surfaces, well below critical micelle concentrations. The results demonstrate the possibility of using cationic surfactants to systematically control the degree of water wettability of cellulose nanofibrils.

Adsolubilization of contaminants by surfactant-modified material is an important phenomenon for surfactant-based environmental technologies. Recently, extended surfactants have been shown to enhance the adsolubilization capacity of organic solutes. In this study, two extended surfactants (ethoxy propoxylated carboxylate extended surfactant—C16PO4EO5C and propoxylate extended sulfate surfactant—C16PO4S) were selected for modifying positively charged alumina surfaces with the aim of enhancing adsolubilization of organic solutes with varying degrees of polarity (phenanthrene, styrene, and phenylethanol). The nature of the charged surface as a function of extended surfactant adsorption was evaluated through the zeta potential measurements. The results showed that at maximum bilayer coverage, the zeta potential of the alumina surface remained constant and was oppositely charged (negative) to the unmodified alumina (positive). Zeta potential measurements showed that the adsorbed bilayer of carboxylate-based extended surfactant produced more negatively charged surface. Surfactant desorption results showed that the surfactant-modified surface retained their negatively charge, albeit reduced, indicating that partial desorption occurred but not to the point that the positively charged alumina surface was realized. The adsolubilization results suggest a benefit of the ethoxy groups in adsolubilizing the polar phenylethanol in the palisade layer.

Adsolubilization reaches its maximum when a surfactant adsorbed onto the solid–liquid interface achieves complete bilayer or maximum adsorption. The attempt to enhance the adsolubilization of organic solute is accomplished by increasing interaction between the hydrophobic core of adsorbed admicelles and the organic solute. Solubilization and adsolubilization were studied with linker-based and extended-surfactant-based systems. Extended surfactants have propylene oxide (PO) groups of intermediate polarity inserted between hydrophobic and lipophilic moieties in the surfactant molecule. This study evaluated the adsolubilization of polar (phenylethanol) and nonpolar (ethylcyclohexane) solutes into conventional linker-based and extended-surfactant-based admicelles. The results demonstrated that the extended-surfactant-based systems showed higher solubilization capacity than the conventional sodium dodecyl sulfate alone or with linker. For the polar solute, the presence of PO group has a greater effect than the number of PO groups or the tail length, while for the nonpolar solute as the number of POs groups and the tail length increased, the adsolubilization capacity also increased. Preliminary explanations for these observations are provided.

The micellar, adsorption, and adsolubilization properties of a novel ethoxy carboxylate extended surfactant are measured and compared to an extended sulfate surfactant. The critical micelle concentration (CMC) of the ethoxy carboxylate extended surfactant is measured to be 0.02 mM while it is 0.07 mM for the extended sulfate surfactant. Adsorption and adsolubilization studies are carried out on alumina oxide surfaces. The extended sulfate surfactant has a higher maximum adsorption capacity onto the aluminum than the ethoxy carboxylate extended surfactant (0.47 vs. 0.14 mmol/g, respectively). For adsolubilization, the extended sulfate surfactant shows a slightly higher phenanthrene adsolubilization compared to the ethoxy carboxylate extended surfactant (log K adm of 6.15 vs. 5.71, respectively). In contrast, for solubilization, the ethoxy carboxylate extended surfactant exhibits higher phenanthrene solubilization capacities than the extended sulfate surfactant (log K mic of 5.61 vs. 5.42, respectively). Relative to surfactant loss from the solid surface, the ethoxy carboxylate extended surfactant shows a higher desorption capacity as compared to the extended sulfate surfactant. From these measurements, the ethoxy carboxylate extended surfactant has better properties for micellar applications (lower CMC, higher K mic ), while the extended sulfate surfactant has better properties for admicellar applications (higher q max and K adm values, and less desorption).

Anionic and cationic surfactant mixtures exhibit desirable synergism, but are limited by their tendency to form precipitates. This research evaluates the adsorption, adsolubilization and desorption of mixtures of carboxylate-based anionic extended surfactants and a pyridinium-based cationic surfactant. The mixture of cetylpyridinium chloride (CPC), selected as the cationic surfactant, with four anionic extended surfactants were studied. The anionic surfactants studied were alkyl propoxylated ethoxylated carboxylate with average number of carbon chain length of 16 and 17 or 16 and 18 with 4 mol of propylene oxide groups and either 2 or 5 mol of ethylene oxide groups. The adsorption of anionic extended and cationic surfactant mixtures onto a negatively charged metal oxide surface (silica dioxide) was evaluated. The adsolubilization of phenylethanol, styrene and ethylcyclohexane were evaluated for these mixed surfactant systems. The desorption potential of individual and mixed surfactant systems was also evaluated by varying the number of washing (desorption) steps. It was found that the plateau adsorption of mixed anionic extended surfactant and cationic surfactant occurred at lower surfactant concentration than that of the CPC alone, although the maximum adsorption capacity of CPC was not enhanced in our mixed surfactant systems. Adsolubilization capacities of these mixed surfactant systems are higher than that of the individual surfactant system. For desorption studies, these mixed surfactant systems showed lower stability than the individual surfactant system.

The impact of lipophilic linker and extended surfactant properties on admicelle formation and styrene adsolubilization were evaluated through adsorption and adsolubilization studies on aluminum oxide. While linker-based systems achieved a higher maximum adsorption than extended surfactants, the extended surfactants reached maximum adsorption at a lower aqueous surfactant concentration. Results of solubilization and adsolubilization studies are summarized by the extent of solute solubilization into micelles and admicelles, as captured through the micellar partition coefficient, K mic , and the admicellar partition coefficient, K adm . The extended-surfactant-based micelles showed greater solubilization capacity than linker-based micelles. Relative to the effect of the number of propoxy groups for extended surfactants with the same alkyl chain length, the results show that the solubilization capacity increases when the PO number increases for both C12,13- and C14,15-based surfactant series. Thus, adsolubilization using extended-surfactant-based admicelles showed adsolubilization enhancement but required lower amounts of surfactants to form admicelles. These results thus provide insights into external and internal linker-based and extended-surfactant-based admicellar systems and highlight the differences observed between them and admicelles based on conventional surfactant systems.

Hemimicelle-based and/or admicelle-based solid-phase extraction (SPE) has recently been proved to be a fruitful strategy for the extraction and concentration of a wide variety of organic pollutants. This research focus on the effect of river and wastewater matrix components on the adsorption of sodium dodecyl sulfate (SDS) onto alumina, which is the most-used sorbent in hemimicelle-based and/or admicelle-based SPE, and we discuss the analytical consequences of the modifications observed. The effect of electrolytes (0.1 M NaCl), precipitating agents (127 and 333 mg L-¹ CaCl₂) and major organic components in wastewater (19.8 mg L-¹ carbohydrates, proteins and fats and 10 mg L-¹ linear alkylbenzene sulfonates (LAS) and rivers (8 mg L-¹ humic acid) on the SDS adsorption isotherm was investigated. Also, the global effect of matrix components was assessed using a river sample. Three types of sorbents were considered (hemimicelles, mixed hemimicelles/admicelles and admicelles). Electrolytes were found to compete with surfactant molecules for charge surface sites in the early part of the hemimicellar region; precipitating agents yield insoluble salts with the aqueous surfactant in equilibrium with admicelle-based sorbents; and organic matter did not have any influence at all. The matrix component concentrations investigated were above the usual range present in rivers and wastewater, which makes this study applicable to a wide number of environmental water samples. From the results obtained, simple rules were established to prevent and detect matrix-induced surfactant adsorption modifications, which permits us to know, a priori, the suitability of these sorbents for a specific application and allows the development of more straightforward and robust methods.

The electrochemical polymerization of aniline was studied in sodium dodecyl sulfate (SDS) admicelles. The results demonstrate that electrochemical polymerization of aniline can be catalyzed by admicelles. The catalytic efficiency in SDS solutions increased slowly with SDS concentration when the SDS concentration was very low, but increased rapidly when SDS admicelles formed on the electrode surface. The catalytic efficiency decreased with the addition of n-pentanol. The polyaniline films formed in SDS admicelles were nanometer films and the size of particles in the films increased with SDS concentration, but decreased with the addition of n-pentanol. Therefore, n-C^sub 5^H^sub 11^OH can be used to regulate the electrochemical polymerization of aniline in SDS admicelles.[PUBLICATION ABSTRACT]