Hexadecyltrimethylammonium Ion Research Articles

Cover Feature: Computational Prediction of the Adsorption Equilibrium for Ionic Surfactants at the Electrified Oil/Water Interface (ChemElectroChem 15/2022)

The Cover Feature illustrates a computational prediction of the adsorption equilibrium for ionic surfactants at the electrified oil/water interface. It is shown that a cationic surfactant, hexadecyltrimethylammonium ion, adsorbs at the nitrobenzene/water interface depending on the interfacial potential difference. More information can be found in the Research Article by A. Yamauchi et al.

Computational Prediction of the Adsorption Equilibrium for Ionic Surfactants at the Electrified Oil/Water Interface

AbstractIn a previous study (Somekawa et al., Langmuir 2019, 35, 11345–11350) a non‐Bornian solvation model was successfully applied to computational prediction of the adsorption equilibrium for nonionic surfactants at the oil (O)/water (W) interface. In this study, the method was extended to the adsorption of “ionic” surfactants at the polarized O/W interface. In this extension, the electrostatic potential of an ionic surfactant in the electric double layer formed at the O/W interface was taken into account together with the chemical potential estimated using the non‐Bornian solvation model. The calculation results clearly showed that a cationic surfactant (hexadecyltrimethylammonium ion) was adsorbed at the nitrobenzene/W interface, when the interfacial potential was negative. This prediction was consistent with the previous experimental observation using electrocapillary measurements.

From the outside to the inside: Elucidation of the mechanism of pseudomorphic transformation of SBA-15 into MCM-41 by following its time-resolved conversion

Pseudomorphic transformation of silica materials is a versatile approach for the fabrication of porous phases in which the particle morphology and pore structure can be controlled independently from each other. It has been applied already for a wide variety of different parent silica materials, however, there is still a controversy about the details of the mechanism, about the manner of how the transformation proceeds through the body of the particles. The pure homogeneous distribution model on the one hand, and the core-shell model, on the other hand, are the so-to-speak extreme poles in this controversy, not excluding that a mixed-mode model can be valid for a particular parent silica phase. Herein, the detailed mechanism for the pseudomorphic transformation of ordered mesoporous SBA-15 into MCM-41 is elucidated by following the time-resolved conversion of the parent silica material. Upon pseudomorphic transformation, the characteristic morphology of the parent SBA-15 particles remains unchanged, whereas the original pore structure undergoes a successive restructuring in the presence of hexadecyl-trimethylammonium ions as a structure-directing agent. The inflow of the alkaline transformation solution within the pore system of SBA-15 initiates undirected dissolution and re-condensation processes of the pristine pore walls, resulting in an undulation, a slight shrinkage and a partial obstruction of the original mesopores. Simultaneously small domains of MCM-41 with various spatial orientations are formed on the external particle surface, restricting the access to the undulated mesopores within the particle core. The resulting core-shell structure of the partially transformed materials provides interesting gas physisorption hysteresis phenomena, caused by a cavitation mechanism during the evaporation of adsorbate from partially blocked SBA-15 pores. PXRD reflections that can be assigned to the characteristically large pore spacing of SBA-15 were found within patterns even for materials with a supposedly complete conversion. The occurrence of these reflections can be attributed to inaccessible pore domains of SBA-15. With proceeding transformation, a reduction of the amount of inaccessible SBA-15 pores was observed, finally leading to a material with typical MCM-41 characteristics but with a slightly less pore ordering due to the abrasively conditions during the long hydrothermal treatment. • Time-resolved pseudomorphic transformation of ordered mesoporous SBA-15 into MCM-41. • Original particle morphology of SBA-15 remained unchanged after transformation. • Bimodal mesoporous core-shell structures obtained by partial transformation. • Hysteresis phenomena in partially transformed samples caused by cavitation. • Inaccessibility of SBA-15 pore domains at partially transformed samples proven by nitrogen physisorption and PXRD.

Synthesis of high-saturation magnetization composites by montmorillonite loading with hexadecyl trimethyl ammonium ions and magnetite nucleation for improved effluent sludge handling and dye removal

Organomagnetic clays have been designed and synthesized from montmorillonite loaded with hexadecyl trimethyl ammonium ions (HDTMA+), to be used in water treatment systems to minimize the direct manipulation of effluent sludge dyes. The structural, magnetic, and hyperfine properties have been determined using thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, zeta potential measurement, Mossbauer spectroscopy, and a vibrating sample magnetometer. The Methylene blue and Ponceau 4R (P4R) removal efficiency has been analyzed in batch conditions. The 58% HDTMA+-loaded composite exhibits a saturation magnetization three times higher than the composite without HDTMA+, while the surfactant incorporation improved P4R adsorption. The proper HDTMA+ loading improves the saturation magnetization and the adsorption capacity of the composites, thus yielding added-value materials from two points of view, magnetic response and dye adsorption capacity.

Evanescent-Wave Fiber Optic Sensing of the Anionic Dye Uranine Based on Ion Association Extraction.

Herein, we propose an evanescent-wave fiber optic sensing technique for the anionic dye uranine based on ion association extraction. The sensor was prepared by removing a section of the cladding from a multimode fiber and hydrophobization of the exposed core surface. Uranine was extracted in association along with hexadecyltrimethylammonium (CTA) ion onto the fiber surface and detected via absorption of the evanescent wave generated on the surface of the exposed fiber core. The effect of CTA+ concentration added for ion association was investigated, revealing that the absorbance of uranine increased with increasing CTA+ concentration. A change in the sensor response as a function of the added uranine concentration was clearly observed. The extraction data were analyzed using a distribution equilibrium model and a Freundlich isotherm. The uranine concentration in the evanescent field of the fiber optic was up to 54 times higher than that in the bulk solution, and the limit of detection (3σ) for uranine was found to be 1.3 nM.

Detection of Malachite Green using a colorimetric aptasensor based on the inhibition of the peroxidase-like activity of gold nanoparticles by cetyltrimethylammonium ions.

A specific and sensitive colorimetric aptasensor is described for the determination of Malachite Green (MG). It is exploiting the inhibition of the peroxidase-like activity of gold nanoparticles (AuNPs). The AuNPs act as enzyme mimics that catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to yield a dark blue solution. The catalytic activity is inhibited by hexadecyl trimethyl ammonium ion, specifically by cetyltrimethylammonium bromide (CTAB), which causes the aggregation of AuNPs. If a (negatively charged) RNA-aptamer against MG is added, it binds to the positively charged CTAB and prevents aggregation. This enhances the enzyme mimicking activity of the AuNPs and leads to the formation of a dark blue solution. However, in the presence of MG, the aptamer binds to MG, and leads to the aggregation of AuNPs again. The aggregated AuNPs possess a light blue color. A colorimetric method (best performed at 650nm) was work out that can detect MG in a concentration range from 10 to 500nmolL-1. The detection limit based on 3σ/k criterion is 1.8nmolL-1. The assay is highly specific and accurate. Recoveries from spiked real samples (aquaculture water) ranged from 80% to 120%. Graphical abstract Based on the inhibition of cetyltrimethyal ammonium ion and the enhancement of RNA-aptamer, the differences of the peroxidase-like activities of AuNPs can be greatly enlarged with and without MG, by which a colorimetric aptasensor can be constructed for the detection of Malachite Green (MG).

Seaweed-Liked WS₂/rGO Enabling Ultralong Cycling Life and Enhanced Rate Capability for Lithium-Ion Batteries.

WS2 is considered as a potential anode material for lithium ion batteries (LIBs) with superior theoretical capacity and stable structure with two-dimensional which facilitates to the transportation and storage of lithium ion. Nevertheless, the commercial recognition of WS2 has been impeded by the intrinsic properties of WS2, including poor electrical conductivity and large volume expansion. Herein, a seaweed-liked WS2/reduced graphene oxide (rGO) composites has been fabricated through a procedure involving the self-assembling of WO42−, hexadecyl trimethyl ammonium ion with graphene oxide (GO) and the subsequent thermal treatment. The WS2/rGO nanocomposite exhibited the outstanding electrochemical property with a stable and remarkable capacity (507.7 mAh·g−1) at 1.0 A·g−1 even after 1000 cycles. This advanced electrochemical property is due to its seaweed-liked feature which can bring in plentiful active sites, ameliorate the stresses arisen from volume variations and increase charge transfer rate.

The structure of mesoporous silica obtained by pseudomorphic transformation of SBA-15 and SBA-16

Mesoporous silica with bimodal pore size distributions was prepared by pseudomorphic transformation of SBA-15 and SBA-16 in the presence of hexadecyltrimethylammonium ions as a structure-directing agent. The characteristic particle morphology of the starting materials was retained after the transformation. Analysis of the products by gas sorption and small-angle X-ray scattering (SAXS) revealed hybrid pore structures, which featured – depending on the degree of transformation – variable contributions from the original and the newly introduced pore systems. In the case of SBA-15, it was found that a high degree of transformation leads to a seemingly complete conversion of the original pores with a diameter of 7.1 nm to pores with a diameter of 4.0 nm. The SAXS pattern of the product shows additional peaks that can be assigned to the original SBA-15 pore spacing. Similarly, a cubic phase could be observed in the samples prepared by pseudomorphic transformation of SBA-16, despite an almost complete conversion of the SBA-16 cavities. This leads to the conclusion that the pore structure of the starting material significantly affects the outcome of the pseudomorphic transformation, thus opening possibilities for the synthesis of new porous materials with complex pore systems.

Development of Tetrahydrofuran/Water Optical Waveguide and Its Application to the Observation of Extraction Behavior of 1-Anilino-8-naphtalene Sulfonate at the Tetrahydrofuran/Water Interface.

A stable two-phase sheath flow using tetrahydrofuran (THF) for an inner flow and water for an outer flow was formed in a glass capillary, and worked as a stable liquid-core/liquid-cladding optical waveguide (THF/water LLW). Although THF and water were miscible with any ratio, the length of the stable THF/water LLW at 0.9 - 2.1 cm s-1 reached at least 150 mm. The THF/water LLW was applied to the observation of extraction behavior of solvatochromic fluorescence dye, 1-anilino-8-naphtalene sulfonate (ANS), through the THF/water interface. ANS was added to the water phase (clad solution) and its fluorescence, which was excited with the guided light (355 nm) through the LLW, was observed by changing the position of the detector. While the ANS stayed in the region of 70% THF to the end of the LLW without the addition of cationic surfactant, hexadecyltrimethylammonium ion (CTA+) at pH 3 and 11, the ion-pair of ANS and CTA+ was extracted into the higher concentration region of THF with the addition of CTA+ at pH 11.

Surfactant modified tectosilicates and phyllosilicates for 2,4-D removal and slow release formulation

The removal performance of 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution was investigated by an adsorption process on surfactant modified silicates. Surfactant loaded tectosilicates (clinoptilolite and zeolite Y) and phyllosilicates (bentonite and montmorillonite) have been evaluated as potential adsorption media for this purpose. Complete structural characterizations of surfactant loaded materials were performed by infrared spectroscopy and electron microscopy. Surface modification of selected adsorbents by loading surfactants results in a corresponding increase in the removal of 2,4-D from water. The adsorption data fitted well with the Langmuir adsorption isotherm. Based on the Langmuir adsorption model, the calculated maximum monolayer 2,4-D adsorption capacity values for hexadecyltrimethylammonium ion and dioctadecyldimethylammonium ion loaded montmorillonite (HLM and DLM) at 303 K are found to be 158.73 and 161.29 mg g−1, respectively. The slow release studies have also been performed by a thin layer-funnel analytical test and by a soil column percolating system. The adsorption and desorption results obtained from this reported study prove the surfactant loaded silicates as potential adsorbents for 2,4-D (anionic herbicide) from aqueous solution and can be used as slow release herbicide medium.

Shape and Size Control of Cu Nanoparticles by Tailoring the Surface Morphologies of TiN-Coated Electrodes for Biosensing Applications

A method for controlling the shapes and sizes of Cu nanoparticles during electrodeposition has been developed by tailoring the surface morphologies of TiN-coated electrodes. Larger octahedral Cu NPs grew on a granular TiN film; smaller, irregular Cu NPs formed on a pyramidal TiN film. The surface morphology of the TiN film affected the accumulation of Cu(2+) and hexadecyltrimethylammonium (CTA(+)) ions, leading to the different shapes and sizes of the resulting Cu NPs. The significant steric effect of the CTA(+) ions was confirmed when using the film of pyramidal TiN as the electrode in the CTAB-containing electrolyte; it contributed to the growth of the smaller, irregular Cu NPs. The sensitivity of the smaller, irregular Cu NPs in the detection of glucose was better than that of the larger, octahedral Cu NPs because of the former's greater increase in the Cu(2+)-to-Cu(0) ratio.

Effect of clay surface modification and organoclay purity on microstructure and thermal properties of poly(l-lactic acid)/vermiculite nanocomposites

Vermiculite (VMT) was successfully modified by cationic exchange of hexadecyltrimethyl ammonium ions, covalent grafting of glycidoxypropyl trimethoxy silane, and combining grafting and intercalation. The complete removal of excess surfactant from VMT resulted in a change in the interlayer structure and higher thermal stability of the organoclay mineral. The organosilane grafted on the clay mineral edges improved the thermal stability of the organoclay mineral. The organoclay minerals were melt compounded with poly(l-lactic acid) (PLLA), and the effect of the nanofiller concentration, type of modification and organoclay mineral purity on the nanostructure and thermal properties of nanocomposites was investigated. The removal of excess surfactant and organosilane functionalization enhanced the dispersion level of the organoclay mineral. PLLA degradation that occurred during nanocomposite processing depended on the clay mineral concentration, the extent of clean surface and the clay mineral dispersion state. The removal of excess surfactant and organosilane functionalization improved the thermal stability of nanocomposites.

High-yield, size-controlled synthesis of silver nanoplates and their applications as methanol-tolerant electrocatalysts in oxygen reduction reaction

A novel method for the synthesis of as-prepared Ag nanoplates in high yield and the control of their dimensions has been developed. In this method, hexadecyltrimethyl ammonium ions (CTA +) are used as a trace additive in a seed solution for blocking the seed surface to govern the growth direction on nanoplate in the growth pathway, leading to a high-yield production of the Ag nanoplates with mixed morphologies, mainly triangular nanoplates and nanodisks. The spectra of the obtained nanoplate solution showed a high-intensity peak attributed to the in-plane dipole resonance and a low-intensity peak at 400 nm. By decreasing the amount of CTA +, the mean edge length of triangular nanoplates could be changed from ∼78.7 nm–∼124.8 nm. The in-plane dipole resonance peak corresponding to change in the mean edge length shifted from 630 nm to 785 nm, respectively. The mean edge length of triangular nanoplates could also be controlled from 70 nm to 148 nm by decreasing the CTA +-adsorbed seed amount. To investigate the practical feasibility of application of the proposed method, the prepared nanoplates were used as a methanol-tolerant electrocatalyst in an oxygen reduction reaction (ORR). An analysis conducted using a rotating ring-disk electrode showed that these nanoplates have high activity towards the ORR and that the electron transfer numbers ( n) were 3.85, 3.83, 3.81, and 2.94 for 70 nm, 124 nm, 148 nm nanoplates, and macroscopic Ag electrode, respectively. If the present of methanol, the corresponding n values of 3.82, 3.81, 3.78, and 2.30 were detected. Despite working in the methanol-tolerant solution, the prepared Ag nanoplates still exhibited high electroactivity and their ORR proceeded via an approaching 4-electron pathway.

Novel surfactant selective electrochemical sensors based on single walled carbon nanotubes

New poly(vinyl chloride) PVC membrane electrodes selective to the hexadecyltrimethylammonium ion (CTA +) and sodium dodecyl ion (SD −) have been constructed using a modified single walled carbon nanotube (SWCNT). This sensor was used as a sensing material and incorporated into the plasticized PVC-membrane. The membrane electrodes exhibited a Nernstian response (59.5 mV/decade) for SDS and a near-Nernstian response (57.2 mV/decade) for CTAB over a wide concentration range below their critical micelle concentrations (CMC). The electrodes showed a fast response time (t90% = 30 s) and could be used for 3 months without any divergence in potentials. The SD − ion selective electrode (ISE) can determine monomer units down to concentrations as low as 1.9 × 10 − 6 M and 5.2 × 10 − 6 M for CTA +. The effect of foreign anions along with primary ions on the performance of ion-selective electrode is investigated in terms of potentiometric selectivity coefficients, which were determined using the fixed primary method (FPM) at 5.0 × 10 − 5 M concentration of surfactant ions. The two proposed potentiometric sensors revealed acceptable selectivities for surfactant ions over a wide variety of other common inorganic and organic anions. The lifetime of the sensor is more than three months. This method for determining of anionic surfactants was found to be quite accurate when compared with classical methods.

Effect of the organic groups of difunctional silanes on the preparation of coated clays for olefin polymer modification

AbstractSodium montmorillonite (MMT) was organically modified with hexadecyltrimethyl-ammonium ions and subsequently treated with dichlorosilanes and water, aimed atin situsilane condensation polymerization and modification of clay platelets by polysiloxane coatings. Dimethyldichlorosilane, methylphenyldichlorosilane, and diphenyldichlorosilane were used to produce three siloxane-modified organoclays. The structure and morphology of the clay materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric studies (TG) and scanning electron microscopy (SEM). XRD results showed that the silanes were effectively polymerized in the clay galleries, forming a nanocomposite of intercalated particles. A fraction of the siloxane formed is bonded to the clay surface by covalent siloxane bonds. Strong structural differences in both morphology and thermal stability of the materials may occur when changing methyl or phenyl groups in the siloxane structure. The formation mechanism of these intercalated nanocomposite particles is considered. Finally, these modified clays were incorporated in an olefin polymer and morphological analyses using transmission electron microscope (TEM) images were carried out.

Electrochemical synthesis of hexadecyltrimethylammonium-coated Ag nanopeanuts and their self-assembly to nanonets

A novel and simple electrochemical method for preparing Ag nanopeanuts has been developed. These peanut-shaped nanoparticles are electroreduced in an aqueous solution containing adsorbed hexadecyltrimethylammonium ions (CTA +) without a counter ion, Br −. For electroreduction, the electrical double layer of CTA + micelle has to be regulated. As the aging time increases, the structure of the CTA + micelle changes; this causes the Ag nanopeanuts to assemble via a one-dimensional (1-D) process. Finally, Ag nanonets are obtained. Linear assembly results in a change in the optical properties, such as a red shift in the longitudinal surface plasmon resonance band. Additionally, as an information supported by electrochemical measurement, the newly Ag nanonets as alcohol-tolerant catalysts show high activity toward oxygen reduction.

Organo-inorganic bentonite for simultaneous adsorption of Acid Orange 10 and lead ions

Partial substitution of the interlayer cations of a local bentonite (Bogovina) by hexadecyl trimethylammonium ions (HDTMA) was performed to prepare adsorbents able to simultaneously adsorb toxic metal cations and organic pollutants. Acid Orange10 adsorption increased with increasing HDTMA addition, while the adsorption of Pb 2+ decreased with increasing organophilicity. The adsorption of the dye and Pb 2+ and their mixture onto Na-rich bentonite and HDTMA-bentonites, regardless of adsorbents' organophilicity, obeyed the pseudo-second-order kinetics model.

Adsorption of Dibenzothiophene by Vermiculite in Hydrophobic Form, Impregnated with Copper Ions and in Natural Form

The adsorption capacity of vermiculite, a natural clay, for removing dibenzothiphene (DBTP) from water solutions was investigated. DBTP is an organic compound with sulfur, commonly found in fossil fuels and coal. This compound can also be found in the environment due accidental spills of oil and derivatives. Due to its structure and physical–chemical properties it is considered a persistent compound. Vermiculite (VT) was used as an adsorbent in its natural form, impregnated with copper ions (Cu-VT), and hydrophobically modified (HDTMA-VT) by replacement sodium cations by hexadecyltrimethyl ammonium ion. The results showed that DBTP was adsorbed in considerable amounts by HDTMA-VT; however, the Cu-VT adsorbed DBTP in some proportions of HDTMA-VT. Because of the presence of sulfur atoms in the structure of the molecule, π complexation can be observed. The adsorption isotherms were treated by the Freundlich equation. The values of K f are similar to Cu-VT and HDTMA-VT, showing that the adsorption may be either through hydrophobic interactions or interactions through the formation of π complex. Meanwhile, the results with the VT (natural form) showed a much smaller value of K f. It is believed, compared with the literature, and because of the chemical composition of the vermiculite, that the adsorption mechanism is also conducted by π complexation, considering the absence of organic carbon content.

Insights into Removal of Phenol from Aqueous Solutions by Low Cost Adsorbents: Clays Versus Algae

Exchanged clays and cross-linked algae were compared based on their properties for the removal of phenol from aqueous solutions. Algae Lessonia nigrescens Bory (A1) and Macrocystis integrifolia Bory (A2) were cross-linked with CaCl2 to enhance their physical and mechanical properties. The natural clays were chemically-exchanged with salts of tetramethyl ammonium (B1), hexadecyltrimethyl ammonium (B2), and bencyltriethyl ammonium (B3) ions to increase their affinity towards organic substrates. The effects of pH and adsorbent dose were evaluated. pH exhibited a strong effect mainly on the phenol aqueous chemistry. Sorption isotherm results were modelled on the Langmuir and Freundlich equations and complemented with EDX analysis, indicating that adsorption of phenol from water was mostly driven by hydrophobic forces, with the exchanged bentonites being the adsorbents that reported the maximum adsorption capacities. Conversely, a polar surface adsorption is suggested for algae mostly by means of hydrogen bonding formation. These results provide further insight into the adsorption mechanism of phenol and analogues and their use as powerful and cheap adsorbent for the treatment of phenol-containing real wastewater.

Unusual Vesicle−Micelle Transitions in a Salt-Free Catanionic Surfactant: Temperature and Concentration Effects

The spontaneous formation of vesicles by the salt-free surfactant hexadecyltrimethylammonium octylsulfonate (TASo) and the features of an unusual vesicle-micelle transition are investigated in this work. In a previous work, we have shown that this highly asymmetric catanionic surfactant displays a rare lamellar miscibility gap in the concentrated regime. Here, we analyze in detail the aggregation behavior in the dilute regime (less than 3 wt % surfactant) as a function of both concentration and temperature. The phase diagram is dominated by a two-phase region consisting of a dispersion of a swollen lamellar phase (Lalpha') in the excess solvent phase (L1). Stable vesicles form in this two-phase region, and upon temperature increase, a transition to a single solution phase containing only elongated micelles occurs. The structural characterization of the aggregates and the investigation of their equilibrium properties have been carried out by light microscopy, cryo-TEM, water self-diffusion NMR, and SANS. Similarly to the lamellar-lamellar coexistence, the changes in microstructure at high dilution and high temperature can be understood from solubility differences, electrostatic interactions, and preferred aggregate curvature. Surface charge in the aggregates stems from the higher solubility of the octylsulfonate (So-) ion as compared to that of the hexadecyltrimethylammonium ion (TA+). Upon temperature increase, the ratio of free So(-) relative to the neutral TASo increases. Consequently, the surface charge density of the aggregates increases, and this ultimately induces a transition to a higher-curvature morphology (elongated micelles). Vesicles can also be spontaneously formed by cooling solutions from the micellar region, and the mean size obtained is practically independent of cooling rate, suggesting that dissociation/charge effects also control this process.