Hexadecyltrimethylammonium Cation Research Articles

Effect of cyclodextrin modification on complexation thermodynamics with hexadecyltrimethylammonium cation with emphasis on subsequent surfactant micellization

Surfactant-cyclodextrin based complexes, are ideal guest-hosts for fundamental studies since both surfactant hydrophobic region with head group, and cyclodextrin cavity can be systematically varied. This allows, better understanding of the contributions that different chemical entities do to the stabilization of the complex and subsequent surfactant micellization. We studied systematically the interaction of hexadecyltrimethylammonium bromide (▪) with native α-, β- and γ-CDs, 2-hydroxypropylated and methylated α- and β-CDs, using isothermal titration calorimetry (ITC), measuring below critical micellization concentration (CMC) at least at three temperatures in the range (288.15 to 318.15) K. Data were treated simultaneously allowing the estimation of thermodynamically consistent temperature dependences of the equilibrium constant, the enthalpy and heat capacity for the inclusion complex formation. The data for cation/CD interaction were analysed mostly by the sequential binding model with 1:1 and 1:2 (cation:CD) stoichiometries, while some cation-CD combinations were examined using only 1:1, or more complicated 1:1, 2:1 and 2:2 stoichiometries. Thermodynamic quantities for complexation are discussed in terms of structural features, their temperature dependence with previous literature being examined. The shift of the CMC in presence of CDs was calculated founding large discrepancies with data in the literature. An extended mass-action chemical equilibrium model is proposed including free surfactant, free CD, complexes of the above mention stoichiometries, also including micelle, surfactant-cyclodextrin complexes of higher order stoichiometry, similar to that found for sodium dodecylsulfate-CDs systems. The new model provides a qualitative match with our own calorimetric titration curves measured above CMC for all studied ▪/CD combinations, and matches quantitatively with literature CMC values.

Electrochemical Sensor for Ascorbic Acid, Acetaminophen and Nitrite Based on Organoclay/Zr‐MOF Film Modified Glassy Carbon Electrode

AbstractA composite (Sa‐HTDMA/UiO‐66) consisting of organoclay (Sa‐HTDMA) and a metal‐organic framework (UiO‐66) was prepared using organically modified natural Cameroonian clay and Zr‐MOF. The organoclay was obtained by intercalating in its interlayer hexadecyltrimethyl ammonium cation (HTDMA). The composite was then used to form a film onto a glassy carbon electrode (GCE) by drop coating (Sa‐HTDMA/UiO‐66/GCE). Electrochemical responses recorded at the as‐prepared modified electrodes for ascorbic acid (AA), acetaminophen (AC) and nitrite (NO2−) were investigated using cyclic and linear sweep voltammetry. The results revealed that Sa‐HTDMA/UiO‐66/GCE exhibited a favorable behavior for individual and simultaneous sensing of AA, AC and NO2−. Additionally, compared with UiO‐66 modified GCE, the composite enabled good performance of the electrode. Under the optimum conditions, the linear calibration curves were attained in the following ranges: 1–650 μM for AA, 1–700 μM for AC and 1–600 μM for NO2− with the respective detection limits of 0.01, 0.19 and 0.33 μM. Application of the sensors to determine AA and AC in pharmaceutical preparations, and NO2− in tap water, was successful.

Sorption of phenols on hexadecyltrimethylammonium- modified bentonite: Application of Polanyi−Manes potential theory

This study investigated the sorption of phenol and 4-chlorophenol (4-CP) on natural bentonite modified with hexadecyltrimethylammonium (HDTMA) cation. The Freundlich, Langmuir, Dubinin−Radushkevich (DR), Sips, and Polanyi−Dubinin−Manes (PDM) models fitted the sorption data well (R2 > 0.92). The Freundlich coefficient and the maximum sorbed amount of the Langmuir and PDM models of 4-CP were higher than phenol because of higher hydrophobicity (log Kow = 2.39 for 4-CP and 1.46 for phenol). The PDM model that includes solubility and molar volume was highly useful in predicting the sorption of phenols having widely different hydrophobicity and solubility. The characteristic curves, the plot of sorbed volume ( qv) versus the sorption potential per molar volume ( ε/ Vm) of 4-CP and phenol were distinctly different although they have similar chemical compositions. The selectivity of 4-CP (3.72) was higher than that of phenol (0.27) in binary sorption systems. The sorbed volume ( qv) in the binary sorption was remarkably reduced and the characteristic curve had wider distribution owing to competition in pore-filling. The sorption behaviors were elucidated by partitioning and pore-filling mechanisms. Among the tested binary sorption models, the modified Langmuir competitive model was the best in the prediction of the binary sorption (R2 > 0.98).

Corrosion Inhibition of Mild Steel by Cetrimonium trans-4-Hydroxy Cinnamate: Entrapment and Delivery of the Anion Inhibitor through Speciation and Micellar Formation.

Chemical inhibitors are widely used to protect metallic alloys from corrosion in aqueous environments. This Letter investigates the possible synergistic behavior of a quaternary ammonium carboxylate compound toward the development of a new system taking advantage of the surface activity of a known antimicrobial surfactant molecule, hexadecyl trimethylammonium cation, combined with a known organic corrosion inhibitor, the trans-4-hydroxy-cinnamate anion. Short-term potentiodynamic polarization (PP) studies combined with immersion in aqueous chloride solutions demonstrated the high inhibition efficiency of the combination of ions, and NMR pfg-diffusion measurements revealed micellar formation that was concentration- and pH-dependent. The NMR data suggest that speciation changes occur in the solution that correlate with enhanced corrosion inhibition efficiency at higher pH and at concentrations above the CMC of the compound. This new contribution may provide a rational molecular design toward delivering corrosion inhibitors to a metal surface through controlled speciation in solution.

Modification of Egyptian clay by different organic cations

Nowadays, clay minerals are used extensively in a wide range of applications as nano additives for polymeric materials. Nevertheless hydrophilic characteristics of the nano additives reduce their degree of compatibility with polymeric chains. To overcome this problem it is necessary to modify the clay in order to render its surface more organophilic prior to the intercalation of the polymeric chains between its layers. In this work the Egyptian natural clay mineral montmorillonite (MMT) was modified with two cationic organic modifiers, namely hexadecyltrimethylammonium (HDTMA) and tributyl hexadecyl phosphonium using two different procedures. The first, using the magnetic stirrer while the second using a high speed mixer at different mixing times from 0.5 up to 2.5 hr. The samples with and without organic modifiers were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and transmission electron microscope (TEM). XRD results revealed that the basal spacing of the organo-montmorillonite (OMMT) prepared using high speed mixer was larger than that using magenetic stirrer. The best result was obtained after 1.5 hr stirring in the high speed mixer. The modification of MMT was confirmed by FTIR as determined from –CH2 stretching vibration of the organic modifiers. The TGA analysis revealed that the MMT modified with tributyl hexadecyl phosphonium cation had high thermal stability than that modified with hexadecyl trimethyl ammonium cation. The amount of surfactants within organoclays were found to be found to be about 19 and 24%, respectively, for hexadecyl trimethyl ammonium bromide and tributyl hexadecyl phosphonium bromide. SEM demonstrated that the modified MMT exhibited a massive thin layered structure with some large flacks and some interlayer spaces. TEM images of the prepared organoclays showed exfoliated structure. This work proved to enhance the economical value of the Egyptian natural resources.

Organic modification of bentonite and its application for perrhenate (an analogue of pertechnetate) removal from aqueous solution

Technetium-99 (99Tc) is an important fission product of nuclear industry. Its characteristics can be predicted by studying rhenium (Re), a chemical analogue of technetium, thus avoiding the use of radioactive elements at high concentrations. The present work focused on the sorption of Re(VII) by hexadecyl trimethylammonium cation (HDTMA) modified bentonite. Our experimental results show that the bentonite sample has been successfully modified. The stability of HDTMA in the sample is satisfactory with the increasing of calcination temperature (<200°C). The uptake rate of Re(VII) is relatively rapid and the sorption kinetics of Re(VII) can be successfully described by the pseudo-second-order model. Thermodynamic studies reveal that the sorption process is more favorable at low temperature. The uptake ratio of Re(VII) on HDTMA modified bentonite was enhanced significantly compared with the unmodified one, the surface precipitate between HDTMA and Re(VII) is the main mechanism for Re(VII) uptake by HDTMA modified bentonite.

A hybrid of hexakis(hexyloxy) triphenylene and synthetic saponite

A novel hybrid of a triphenylene–based liquid crystal molecule, hexakis(hexyloxy) triphenylene, and synthetic saponite, was prepared by the reaction between colloidally dispersed synthetic saponite in the presence of a cationic surfactant, hexadecyltrimethylammonium cation, and hexakis(hexyloxy) triphenylene to improve the thermal and/or optical properties of hexakis(hexyloxy) triphenylene by the host-guest interactions. Judging from the expansion of the interlayer space (0.60nm) and the molecular sizes of hexakis(hexyloxy) triphenylene and hexadecyltrimethylammonium cation, they were expected to be incorporated in the interlayer space. The changes in the phase transition of hexakis(hexyloxy) triphenylene in saponite (from 69–99°C to be 65–105°C) and optical properties of the hybrid were due to the interactions of the liquid crystal and the hexadecyltrimethylammonium cation in the interlayer space.

Effects of ion pairing on the capillary electrophoretic separation and ultraviolet-absorption detection of quaternary ammonium cations using meso-octamethylcalix[4]pyrrole as the background electrolyte additive.

Five quaternary ammonium cations, including tetramethylammonium, tetraethylammonium, hexadecyltrimethylammonium, benzyltrimethylammonium, and 1-butyl-3-methylimidazolium, have been separated by capillary electrophoresis. A direct ultraviolet method has been achieved when tetrabutylammonium fluoride was the background electrolyte and meso-octamethylcalix[4]pyrrole was the background electrolyte additive. The ultraviolet spectra of meso-octamethylcalix[4]pyrrole and cation mixtures showed that redshifts can be attributed to the size of cations, and the maximum absorption wavelength shifted from 218 to 230 nm when tetrabutylammonium cation was substituted with tetramethylammonium cation or tetraethylammonium cation. Conductivity measurements were performed to evaluate the ion-pairing effect of tetrabutylammonium fluoride in a mixture of acetonitrile/ethanol (80:20, v/v), and the ion-pairing formation constant, Kip, was calculated (Kip = 14.8 ± 0.3 L/mol) using the Fuoss extended model. Ion pairing also occurs between cations of the analytes and counterion, a fluoride complex of meso-octamethylcalix[4]pyrrole. The tetramethylammonium cations associate more strongly with this counterion than the tetraethylammonium cation that contributes to the change of selectivity in capillary electrophoresis separation. The effective mobilities of the cations with trimethyl groups, such as tetramethylammonium cation, benzyltrimethylammonium cation, and hexadecyltrimethylammonium cation, decreased faster than others with the increase of meso-octamethylcalix[4]pyrrole concentration, highlighting the fact that the ion-pairing effect played an important role in this method.

Efficient stabilization of Saccharomyces cerevisiae external invertase by immobilisation on modified beidellite nanoclays

The external invertase isoform 1 (EINV1) was immobilised on eight differently modified beidellite nanoclays. Modifications were composed of organo-modification with different amounts of surfactant – hexadecyl trimethylammonium cation (HDTMA), pillaring with Al/Fe containing polyhydroxy cations and acid modification of Na-enriched and pillared clays. The modified nanoclays were characterised by XRD, N2-physisorption, SEM and FT-IR spectroscopy. The amount of bound enzyme activity was significantly influenced by the modification of beidellite ranging from 50 to remarkable 2200U/g. Biochemical characterization was performed for five modified nanoclays showing the highest enzyme activity after invertase immobilisation. The investigation demonstrated that after immobilisation the structure and the catalytic properties of invertase were preserved, while Km values were slightly increased from 26 to 37mM. immobilisation significantly improved thermal and storage stability of EINV1. Results indicate that beidellite nanoclays obtained by low cost modifications can be applied as a suitable support for the immobilisation of invertase. The immobilizate can be efficiently engaged in sucrose hydrolysis in batch reactor.

Thermodynamics of the adsorption of different dyes onto bentonite modified with hexadecyltrimethylammonium cation

Removal of two different dyes: Acid Orange 10 (AO10) and Reactive Black 5 (RB5) from their aqueous solutions using organobentonite as adsorbent was investigated. The experiments were carried out at different temperatures (298, 313, 323, and 333 K) in order to obtain thermodynamic parameters for adsorbate/adsorbent system i.e., activation energy, Gibbs free energy, enthalpy and entropy. The results of thermodynamic studies indicated that the adsorption of both dyes onto organobentonite is an endothermic process, while the values for activation energies (76 kJ mol−1 for AO10 and 51 kJ mol−1 for RB5) indicated that chemisorption occurred.

Identification and Quantification of the Interaction Mechanisms Between the Cationic Surfactant HDTMA-Br and Montmorillonite

AbstractSeveral detailed studies have been done on the characterization of organoclays and the type of structures developed when they interact with alkylammonium molecules. Few published contributions exist, however, on the distribution of surfactant within the organoclays and the mechanism by which they are intercalated. Also, although X-ray photoelectron spectroscopy (XPS) is a suitable technique for the study of the surface characteristics of organoclays, very few such XPS studies have been carried out. With the aim of contributing to a better understanding of the intercalation process, a series of organoclays was synthesized using a montmorillonite and the cationic surfactant hexadecyltrimethylammonium bromide (HDTMABr), with an increasing surfactant load of between 0.2 and 4.0 times the cation exchange capacity of the starting clay. By means of XPS, zeta potential, and thermal analysis techniques, distinguishing the strongly interacting fraction from the weakly interacting fraction of the adsorbed surfactant molecules was possible. Adsorption isotherms of each of these processes were constructed and then adjusted using the Langmuir and Dubinin-Radusquevich adsorption models. Three types of interaction between the surfactant and the clay were identified and described qualitatively and quantitatively. Two of these interactions, strong and weak, involved the hexadecyltrimethylammonium cation (HDTMA+). The third was a weak interaction involving the ion pair HDTMA+Br−. The results of this study may be useful for the comprehensive design of organoclays with specific physicochemical properties according to the application for which they are destined.

Adsorption of thorium from aqueous solution by HDTMA+-pillared bentonite

The ability of hexadecyltrimethylammonium cation pillared bentonite (HDTMA+-bentonite) has been explored for the removal and recovery of thorium from aqueous solutions. The adsorbent was characterized using small-angle X-ray diffraction, high resolution transmission electron microscopy and Fourier transform infrared spectroscopy. The influences of different experimental parameters such as solution pH, initial thorium concentration, contact time and temperature on adsorption were investigated. The HDTMA+-bentonite showed the highest thorium sorption capacity at initial pH of 3.5 and contact time of 60 min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir isotherm. The thermodynamic parameters, ∆G° (298 K), ∆H° and ∆S° were determined to be −31.78, −23.71 kJ/mol and 27.10 J/mol K, respectively, which demonstrated the sorption process of HDTMA+-bentonite towards Th(VI) was feasible, spontaneous and exothermic in nature. The adsorption on HDTMA+-bentonite was more favor than Na-bentonite, in addition the saturated monolayer sorption capacity increased from 17.88 to 31.20 mg/g at 298 K after HDTMA+ pillaring. The adsorbed HDTMA+-bentonite could be effectively regenerated by 0.1 mol/L HCl solution for the removal and recovery of Th(VI). Complete removal (99.9 %) of Th(VI) from 1.0 L industry wastewater containing 16.8 mg Th(VI) ions was possible with 7.0 g HDTMA+-bentonite.

Molecular Dynamics Simulation of Secondary Sorption Behavior of Montmorillonite Modified by Single Chain Quaternary Ammonium Cations

Organoclays synthesized from single chain quaternary ammonium cations (QAC) ((CH(3))(3)NR(+)) exhibit different mechanisms for the sorption of nonpolar organic compounds as the length of the carbon chain is increased. The interaction between a nonpolar sorbate and an organoclay intercalated with small QACs has been demonstrated to be surface adsorption, while partitioning is the dominant mechanism in clays intercalated with long chain surfactants. This study presents the results of a molecular dynamics (MD) simulation performed to examine the sorption mechanisms of benzene in the interlayer of three organoclays with chain lengths ranging from 1 to 16 carbons: tetramethylammonium (TMA) clay; decyltrimethylammonium (DTMA) clay; and hexadecyltrimethylammonium (HDTMA) clay. The basis of the overall simulation was a combined force field of ClayFF and CVFF. In the simulations, organic cations were intercalated and benzene molecules were introduced to the interlayer, followed by whole system NPT and NVT time integration. Trajectories of all the species were recorded after the system reached equilibrium and subsequently analyzed. Simulation results confirmed that the arrangement of the surfactants controlled the sorption mechanism of organoclays. Benzene molecules were observed to interact directly with the clay surface in the presence of TMA cations, but tended to interact with the aliphatic chain of the HDTMA cation in the interlayer. The simulation provided insight into the nature of the adsorption/partitioning mechanisms in organoclays, and explained experimental observations of decreased versus increased uptake capacities as a function of increasing total organic carbon (TOC) for TMA clay and HDTMA clay, respectively. The transition of sorption mechanisms was also quantified with simulation of DTMA clay, with a chain length between that of TMA and HDTMA. Furthermore, this study suggested that at the molecular level, the controlling factor for the ultimate sorption capacity is available surface sites in the case of TMA clay, and density of aliphatic chains within the interlayer space for HDTMA clay.

Adsorption of uranium from aqueous solution using HDTMA+-pillared bentonite: isotherm, kinetic and thermodynamic aspects

The ability of hexadecyltrimethylammonium cation pillared bentonite (HDTMA+-bentonite) has been explored for the removal and recovery of uranium from aqueous solutions. The adsorbent was characterized using small-angle X-ray diffraction, high resolution transmission electron microscopy, and Fourier transform infrared spectroscopy. The influences of different experimental parameters such as solution pH, initial uranium concentration, contact time, dosage and temperature on adsorption were investigated. The HDTMA+-bentonite exhibited the highest uranium sorption capacity at initial pH of 6.0 and at 80 min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir isotherm. The thermodynamic parameters, △G° (308 K), ΔH°, and ΔS° were determined to be −31.64, −83.84 kJ/mol, and −169.49 J/mol/K, respectively, which demonstrated the sorption process of HDTMA+-bentonite towards U(VI) was feasible, spontaneous, and exothermic in nature. The adsorption on HDTMA+-bentonite was more favor than Na-bentonite, in addition the saturated monolayer sorption capacity increased from 65.02 to 106.38 mg/g at 298 K after HDTMA+ pillaring. Complete removal (≈100%) of U(VI) from 1.0 L simulated nuclear industry wastewater containing 10.0 mg U(VI) ions was possible with 1.5 g HDTMA+-bentonite.

Batch-wise nitrate removal from water on a surfactant-modified zeolite

Nitrate adsorption kinetics were determined in batch-wise experiments on a surfactant-modified zeolite (SMZ), prepared by treatment of a clinoptilolite sample by HDTMABr (HDTMA + being the hexadecyltrimethylammonium cation). The influence of various parameters was studied, namely initial nitrate concentration (0.08–8.06 mmol/L), liquid/solid weight ratio (L/S = 5–50 mL/g) and presence of Cl −, SO 4 2 - and HCO 3 - competing anions (at the same equimolar concentration equal to 1.61 mmol/L). The equilibrium time for nitrate uptake is short (0.5–1 h), with a maximal removal value R max. at equilibrium ( R max(%) = 100 × ( C i − C e )/ C i , where C i and C e are the initial and equilibrium NO 3 - concentrations in solution) of about 80% for initial nitrate concentrations ([ NO 3 - ] i ) in the 0.08–2.42 mmol/L range. For higher concentrations (4.83 and 8.06 mmol/L), R max. decreases significantly to 58% and 40% values, respectively. The sorption equilibrium data are in good agreement with the Langmuir isotherm model. On the other hand, the R max. value decreases with the increase of adsorbent mass. Under the used experimental conditions, the presence of competing anions does not change the nitrate R max.value, but slows down the exchange kinetics, the increasing affinity order towards the SMZ being the following: Cl − ≪ HCO 3 - # SO 4 2 - < NO 3 - .

Partial Exchange of Fe(III) Montmorillonite with Hexadecyltrimethylammonium Cation Increases Catalytic Activity for Hydrophobic Substrates

Fe(III) montmorillonite clay that was partially exchanged with hexadecyltrimethylammonium (HDTMA(+)) cations achieved increased catalytic activity for the oxidative coupling of hydrophobic organic substrates. A series of mixed-cation organoclays were produced, where the organic cation content ranged from 6 to 50% relative to the cation-exchange capacity (CEC) of the clay, and were tested for catalytic activity using different Fe(III)-mediated oxidative coupling reactions. Enhanced catalytic activity by Fe(3+)/HDTMA(+) montmorillonite for coupling hydrophobic substrates was observed, with maximum catalytic activity in the oxidative coupling of 2-naphthol observed at 6% HDTMA(+) coverage. However, maximum catalytic activity with a more hydrophobic substrate, anthrone, was achieved with 50% HDTMA(+) coverage, indicating that matching levels of organic modification to substrate hydrophobicity improves catalytic activity. The organization of the organic cations at the clay surfaces proved to be heterogeneous, as determined by scanning transmission X-ray microscopy (STXM) and powder X-ray diffraction. Results from molecular dynamics simulations supported the heterogeneous nature of the catalysts but also pointed toward large regions within the interlayers that may be filled with nonreactive hydrated Fe oxides resulting from the organic cation treatment. The exchangeable Fe content of the organic treated clays, as determined by AAS and ICP measurements, was observed to be higher than expected relative to that of Fe-saturated clay, substantiating this hypothesis. These findings have implications for the development of substrate-specific clay catalysts, where the composition and configuration of exchangeable cations can be matched to a particular substrate or reaction.

Spectral and equillibrium properties of phenol–HDTMA- and phenol–BDMHDA-bentonite as a response to the molecular arrangements of surfactant cations

The FT-IR and XRD: spectra of HDTMA-bentonite and BDMHDA-bentonite loaded with phenol were registered. As follows from the spectra and the equillibrium data phenol sorption on the clay modified by hexadecyltrimethylammonium cation (HDTMA +) or benzyldimethylhexadecylammonium cation (BDMHDA +) is satisfactory. The distribution constants of phenol K d(phen) and phenolate anion K d(phen) − are higher in the case of BDMHDA-bentonite than HDTMA-bentonite. This fact can be explained from the viewpoint of different arrangements of surfactant cations in the interlamellar space of bentonite, i.e. vertical and parallel arrangements in BDMHDA- and HDTMA-bentonite, respectively.

A Comparative Study of the Use of Organoclay‐Based Formulations and Organic Amendment to Reduce the Leaching of the Herbicide MCPA in Soil

AbstractMCPA (4‐chloro‐2‐methylphenoxyacetic acid) is an acidic herbicide widely used on olive crops in Spain. Due to its anionic form at natural soil pH, there is high risk of leaching and groundwater contamination by the use of this herbicide. The aim of this work was to study the effects of organoclay‐based formulations of MCPA and olive oil waste amendment on MCPA leaching in a sandy loam soil. For this purpose, batch adsorption and column leaching studies were performed. The organoclays used to prepare the clay‐based formulations of MCPA were obtained by treating Wyoming montmorillonite (SWy‐2) and Arizona montmorillonite (SAz‐1) with an amount of hexadecyltrimethylammonium (HDTMA) cation equal to 100% of the CEC of the montmorillonites. The organic residue used in this study was a solid waste from olive oil production (olive oil waste, OOW). The soil was amended with the organic residue at the rate of 10% (w/w). Batch release and column leaching studies indicated that organoclay‐based formulations of MCPA reduced the release rate and the leaching of the herbicide as compared to the use of a conventional formulation containing the herbicide in an immediately available form. The increase in soil organic matter of the soil upon amendment with the organic residue also resulted in greater adsorption and reduced leaching of MCPA in the soil. Accordingly, both the use of organoclay‐based formulations and the amendment of soil with OOW are proposed as efficient strategies to reduce extensive leaching losses associated with the application of MCPA in high‐risk scenarios, such as Mediterranean olive groves.

A novel flow battery—A lead-acid battery based on an electrolyte with soluble lead(II): Part VI. Studies of the lead dioxide positive electrode

The structure of thick lead dioxide deposits (approximately 1 mm) formed in conditions likely to be met at the positive electrode during the charge/discharge cycling of a soluble lead-acid flow battery is examined. Compact and well adherent layers are possible with current densities >100 mA cm −2 in electrolytes containing 0.1–1.5 M lead(II) and methanesulfonic acid concentrations in the range 0–2.4 M; the solutions also contained 5 mM hexadecyltrimethylammonium cation, C 16H 33(CH 3) 3N +. From the viewpoint of the layer properties, the limitation is stress within the deposit leading to cracking and lifting away from the substrate; the stress appears highest at high acid concentration and high current density. There are, however, other factors limiting the maximum current density for lead dioxide deposition, namely oxygen evolution and the overpotential associated with the deposition of lead dioxide. A strategy for operating the soluble lead-acid flow battery is proposed.

A novel flow battery—A lead-acid battery based on an electrolyte with soluble lead(II): V. Studies of the lead negative electrode

The structure of lead deposits (approximately 1 mm thick) formed in conditions likely to be met at the negative electrode during the charge/discharge cycling of a soluble lead-acid flow battery is examined. The quality of the lead deposit could be improved by appropriate additives and the preferred additive was shown to be the hexadecyltrimethylammonium cation, C 16H 33(CH 3) 3N +, at a concentration of 5 mM. In the presence of this additive, thick layers with acceptable uniformity could be formed over a range of current densities (20–80 mA cm −2) and solution compositions. While electrolyte compositions with lead(II) concentrations in the range 0.1–1.5 M and methanesulfonic acid concentrations in the range 0–2.4 M have been investigated, the best quality deposits are formed at lower concentrations of both species. Surprisingly, the acid concentration was more important than the lead(II) concentration; hence a possible initial electrolyte composition is 1.2 M Pb(II) + 5 mM C 16H 33(CH 3) 3N + without added acid.