Nucleation of Surfactant–Alkane Mixed Solid Monolayer and Bilayer Domains at the Air–Water Interface

We investigated the wetting transitions of tetradecane and hexadecane droplets in dodecyltrimethylammonium bromide (C12TAB), tetradecyltrimethylammonium bromide (C14TAB), and hexadecyltrimethylammonium bromide (C16TAB) aqueous solutions. By varying the surfactant concentration, the formation of mixed monolayers of a surfactant and an alkane was observed at the air–water interface. Depending on the combination of surfactant and alkane, these wetting monolayers underwent another thermal phase transition upon cooling either to a frozen mixed monolayer (S1) or a bilayer structure composed of a solid monolayer of a pure alkane rested on a liquid-like mixed monolayer (S2). Based on the phase diagrams determined by phase modulation ellipsometry, the difference in the morphology of the nucleated S1 and S2 phase domains was also investigated using Brewster angle microscopy. Domains of the S1 phase were relatively small and highly branched, whereas those of the S2 phase were large and circular. The difference in domain morphology was explained by the competition of the domain line tension and electrostatic dipole interactions between surfactant molecules in the domains.

Physico-chemical and spectroscopic investigation of flavonoid dispersed C n TAB micelles

In this study, kaempferol (0.2 m/mmol kg −1 ) dispersed cationic surfactant micelles were prepared as a function of alkyltrimethylammonium bromide (C n TAB) hydrophobicity (C = 12 to C = 16). The dispersion study of kaempferol in different C n TAB, i.e. dodecyltrimethylammonium bromide (C = 12), tetradecyltrimethylammonium bromide (C = 14) and hexadecyltrimethylammonium bromide (C = 16), was conducted with the physico-chemical properties of density, sound velocity, viscosity, surface tension, isentropic compressibility, acoustic impedance, surface excess concentration and area occupied per molecule and thermodynamic parameters Gibbs free energy, enthalpy and activation energy measured at 298.15 K. These properties were measured with varying concentration of C n TAB from 0.0260 to 0.0305 mol kg −1 in a 10% (w/w) aqueous dimethyl sulfoxide solvent system. The variations in these measured properties have been used to infer the kaempferol dispersion stability via hydrophobic–hydrophilic, hydrophilic–hydrophilic, van der Waals, hydrogen bonding and other non-covalent interactions.

Functionalization of Zeolite NaP1 for Simultaneous Acid Red 18 and Cu(II) Removal

The efficiency of azo dye Acid Red 18 (AR18) and Cu(II) ions simultaneous removal from an aqueous solution on NaP1CS and NaP1H was investigated, taking into account the effect of the phase contact time, pH, initial concentration, temperature, and interfering ions presence. Zeolite denoted as NaP1CS was modified by chitosan (CS) and zeolite denoted as NaP1H was modified by hexadecyltrimethylammonium bromide (HDTMA). In order to characterize sorption properties of NaP1CS, the obtained sorbent was characterized using Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption/desorption (ASAP). The kinetic parameters were determined by means of the pseudo first order (PFO), pseudo second order (PSO), and intraparticle diffusion (IPD) kinetic models. To present the adsorption data, three different isotherm models (Langmuir, Freundlich and Dubinin-Radushkevich) were used. The desorption process was also examined. It was found that for sorbent NaP1CS the pseudo second order (PSO) kinetic model and the Langmuir isotherm fitted best the experimental data. Moreover, it was noted that the acidic pH is appropriate to achieve the best sorption properties of NaP1CS for Cu(II) and NaP1H for AR18 and Cu(II). The thermodynamic parameters indicate an endothermic process. The most effective solution for the desorption process was found to be 1 M HCl. The results indicate that simultaneous removal of dye AR18 and Cu(II) on modified zeolite NaP1CS or NaP1H is possible and proceeds with a very good efficiency. The obtained zeolites could effectively adsorb AR18 an Cu(II) simultaneously, but their adsorption abilities were rather different.

Hybrid materials precursor to natural bentonite in the decontamination of Alizarin Yellow from aqueous solutions

The present study aims to investigate the insights of Alizarin Yellow removal by hybrid materials precursor to natural bentonite. The hybrid materials employed are bentonite modified with hexadecyltrimethylammonium bromide (HDTMA) (BnH) and aluminium pillared HDTMA bentonite (BnAH). Surface morphology of materials are obtained with scanning electron microscopy-Energy dispersive X-ray analysis (SEM-EDX). The batch reactor operations conducted in the removal of Alizarin Yellow by these solids for various parametric studies which enabled to deduce the mechanism involved at solid/solution interface. Sorption capacity and selectivity was increased significantly using hybrid materials in the removal of AY. Hybrid materials showed very high removal capacity of AY and apparently unaffected at varied pH (4.0−10.0) and sorptive concentrations 1.0 to 25.0 mgL^-1. Kinetic studies indicated that an apparent equilibrium occurred within 5–10 min of contact and the kinetic data was better fitted to the pseudo-second-order kinetic model. The percent removal of AY was not affected by increasing the background electrolyte (NaCl) concentration to 0.1 molL^-1 and in presence of several co-existing ions. It is revealed that the hybrid materials are found more organophilic and AY molecule bound with strong forces at the surface of hybrid materials.

Fixed-Bed Modification of Zeolitic Tuffs and Their Application for Cr(VI) Removal

Natural clinoptilolite tuff (CL) and chabazite-clinoptilolite tuff (CH) were modified in fixed-bed column by immobilization of hexadecyltrimethylammonium bromide (HDTMA-Br), then investigated as a sorbent for inorganic anions of Cr(VI). The proposed modification technique combined with surfactant solution batching allows minimizing the surfactant loses through foaming and crystallization and creation of stable organic coverage. The HDTMA loading depended on the mineral composition of the zeolitic tuff, the topology of its external surface, and process conditions. The maximum surface coverage was obtained by gradually dosing surfactant solution in the smallest volume of batches and corresponded up to 100% and 182% of external cation exchange capacity (ECEC) for mono and double layer coverage, respectively. In case of mono layer coverage, modification proceeds until the exhaustion of surfactant in supply solution, while in the double layer one, until equilibrium of HDTMA concentration in both zeolitic and liquid phases was established. The efficiency of Cr(VI) uptake by prepared surface modified zeolites (SMZs) increased with increasing of HDTMA loading. In the case of mono layer SMZs, the capacities of CH-HDTMA and CL-HDTMA were 10.3 and 5.4 mg/g, respectively, while in the case of double layer SMZs, the amount of Cr uptake on CH-HDTMA and CL-HDTMA were 16.8 and 15 mg/g, respectively. Ion exchange is the predominant mechanism of Cr(VI) sorption but it takes place only if modification resulted in at least partial double layer coverage. The XPS analysis reveals Cr(VI) reduction to a less-toxic Cr(III) by the electron donating N-containing groups and by reaction with Fe+2 ions on the zeolite external surface.

Micro-structural investigations on oppositely charged mixed surfactant gels with potential dermal applications

Dicarboxylic amino acid-based surfactants (N-dodecyl derivatives of -aminomalonate, -aspartate, and -glutamate) in combination with hexadecyltrimethylammonium bromide (HTAB) form a variety of aggregates. Composition and concentration-dependent mixtures exhibit liquid crystal, gel, precipitate, and clear isotropic phases. Liquid crystalline patterns, formed by surfactant mixtures, were identified by polarizing optical microscopy. FE-SEM studies reveal the existence of surface morphologies of different mixed aggregates. Phase transition and associated weight loss were found to depend on the composition where thermotropic behaviours were revealed through combined differential scanning calorimetry and thermogravimetric studies. Systems comprising more than 60 mol% HTAB demonstrate shear-thinning behaviour. Gels cause insignificant toxicity to human peripheral lymphocytes and irritation to bare mouse skin; they do not display the symptoms of cutaneous irritation, neutrophilic invasion, and inflammation (erythema, edema, and skin thinning) as evidenced by cumulative irritancy index score. Gels also exhibit substantial antibacterial effects on Staphylococcus aureus, a potent causative agent of skin and soft tissue infections, suggesting its possible application as a vehicle for topical dermatological drug delivery.

Synthesis of Hierarchical MOR-Type Zeolites with Improved Catalytic Properties

Hierarchical MOR-type zeolites were synthesized in the presence of hexadecyltrimethylammonium bromide (CTAB) as a porogen agent. XRD proved that the concentration of CTAB in the synthesis medium plays an essential role in forming pure hierarchical MOR-type material. Above a CTAB concentration of 0.04 mol·L−1, amorphous materials are observed. These hierarchical mordenite possess a higher porous volume compared to its counterpart conventional micrometer crystals. Nitrogen sorption showed the presence of mesoporosity for all mordenite samples synthesized in the presence of CTAB. The creation of mesopores due to the presence of CTAB in the synthesis medium does not occur at the expense of zeolite micropores. In addition, mesoporous volume and BET surface seem to increase upon the increase of CTAB concentration in the synthesis medium. The Si/Al ratio of the zeolite framework can be increased from 5.5 to 9.1 by halving the aluminum content present in the synthesis gel. These synthesized hierarchical MOR-type zeolites possess an improved catalytic activity for n-hexane cracking compared to large zeolite crystals obtained in the absence of CTAB.

Binary Surfactant–Mediated Tunable Nanotip Growth on Gold Nanoparticles and Applications in Photothermal Catalysis

Plasmonic nanostructures with sharp tips are widely used for optical signal enhancement because of their strong light-confining abilities. These structures have a wide range of potential applications, for example, in sensing, bioimaging, and surface-enhanced Raman scattering. Au nanoparticles, which are important plasmonic materials with high photothermal conversion efficiencies in the visible to near-infrared region, have contributed greatly to the development of photothermal catalysis. However, the existing methods for synthesizing nanostructures with tips need the assistance of poly(vinylpyrrolidone), thiols, or biomolecules. This greatly hinders signal detection because of stubborn residues. Here, we propose an efficient binary surfactant–mediated method for controlling nanotip growth on Au nanoparticle surfaces. This avoids the effects of surfactants and can be used with other Au nanostructures. The Au architecture tip growth process can be controlled well by adjusting the ratio of hexadecyltrimethylammonium bromide to hexadecyltrimethylammonium chloride. This is due to the different levels of attraction between Br−/Cl− and Au3+ ions. The surface-enhanced Raman scattering and catalytic abilities of the synthesized nanoparticles with tips were evaluated by electromagnetic simulation and photothermal catalysis experiments (with 4-nitrothiophenol). The results show good potential for use in surface-enhanced Raman scattering applications. This method provides a new strategy for designing plasmonic photothermal nanostructures for chemical and biological applications.