Pseudo-Second-Order Kinetic Equation for Describing the Effect of Sorbent and Sorbate Concentrations.

The sorbent concentration (Cs) effect and sorbate initial concentration (C0) effect are common phenomena observed in the study of adsorption kinetics at solid-liquid interfaces. That is, adsorption rate constants simulated with classical kinetic equations, such as the pseudo-second-order (PSO) model, for a given system vary with Cs and C0. The classical kinetic equations cannot predict or describe the "Cs-effect" and "C0-effect" (called "C-effects" here). In the current work, the dynamic partition coefficient of sorbate between solid and liquid phases (Kt) was used to describe the adsorption kinetic processes. Based on the surface component activity (SCA) model, which assumes the activity coefficients of the surface components (fs) are not equal to unity but rather a function of Cs and the adsorption capacity (or C0) and referring to the classical PSO model, a new kinetic equation was established, called the "SCA-PSO kinetic model", and its two parameters, the intrinsic equilibrium partition coefficient (Ke0) and the intrinsic rate constant (k20), are independent of Cs and C0. In addition, the new model relates Kt and the rate constant (k2) to Cs and C0 via fs, and can thus describe the C-effects. The fs can be estimated from the change of equilibrium partition coefficient (Ke) with Cs and C0. The new model predicts that with the increase of Cs and C0, Ke decreases while k2 increases. Its rationality was confirmed by the literature-reported adsorption kinetic data of heavy metals on inorganic and biomass sorbents with the C-effects.

A Fusion-Growth Protocell Model Based on Vesicle Interactions with Pyrite Particles.

Protocell models play a pivotal role in the exploration of the origin of life. Vesicles are one type of protocell model that have attracted much attention. Simple single-chain amphiphiles (SACs) and organic small molecules (OSMs) possess primitive relevance and were most likely the building blocks of protocells on the early Earth. OSM@SAC vesicles have been considered to be plausible protocell models. Pyrite (FeS2), a mineral with primitive relevance, is ubiquitous in nature and plays a crucial role in the exploration of the origin of life in the mineral-water interface scenario. "How do protocell models based on OSM@SAC vesicles interact with a mineral-water interface scenario that simulates a primitive Earth environment" remains an unresolved question. Hence, we select primitive relevant sodium monododecyl phosphate (SDP), isopentenol (IPN) and pyrite (FeS2) mineral particles to build a protocell model. The model investigates the basic physical and chemical properties of FeS2 particles and reveals the effects of the size, content and duration of interaction of FeS2 particles on IPN@SDP vesicles. This deepens the understanding of protocell growth mechanisms in scenarios of mineral-water interfaces in primitive Earth environments and provides new information for the exploration of the origin of life.

Correlations of Surface Free Energy and Solubility Parameter with Dielectric Constant and Density for Inorganic Solids.

There should be some intrinsic correlations between the surface free energy (γ) and solubility (δ) parameters, called characteristic parameters here, of substances with their basic physical properties such as the relative dielectric constant (εr) and density (ρ), because they are all related to intermolecular interactions. Several correlations have been proposed empirically (or semiempirically) for liquids, but not for solids. It is essential to establish such correlations for solids because the estimation of γ and δ for solids is difficult and/or time-consuming. In the current work, the γ, δ, εr, and ρ data of 34 inorganic solids were chosen, and possible relationships between the characteristic parameters (γ and δ) and the physical quantities (εr and ρ) were explored by a trial-and-error fitting method based on the data of the solids. Six equations relating γ and δ to εr and δ were established. The γ parameters include total (γt), dispersive (γd), and polar (γp) ones, and the δ parameters include the Hildebrand parameter (δt) and the Hansen-dispersive (δd), polar (δp), and hydrogen-bonding (δh) ones. The empirical equations can be used to estimate the characteristic parameters of inorganic solids from their easily measurable physical quantities.

General Adsorption Model to Describe Sigmoidal Surface Tension Isotherms of Binary Liquid Mixtures.

Surface tension (σ) isotherms of liquid mixtures can be divided into Langmuir-type (L-type, including LI- and LII-type) and sigmoid-type (S-type, including SI- and SII-type). Many models have been developed to describe the σ-isotherms. However, the existing models can well describe the L-type isotherms, but not the S-type ones. In the current work, a thermodynamic model, called the general adsorption model, was developed based on the assumption of surface aggregation occurring in the surface layers, to relate the surface composition with the bulk one. By coupling the general adsorption model with the modified Eberhart model, a two-parameter equation was developed to relate the σ with the bulk composition. Its rationality was examined using the σ data of 10 binary mixtures. The results indicate that the new model can accurately describe the S- and L-type isotherms of binary liquid mixtures, showing a good universality. One advantage of the model is that its two parameters, i.e., the adsorption equilibrium constant (K) and the average aggregation number (n), can be estimated by linear fitting experimental σ data, thereby obtaining unique values. This model suggests that the S- and LII-type isotherms arise from the surface aggregation (n ≠ 1). In addition, the standard molar Gibbs free energy of surface adsorption (ΔG̃ad0) and the apparent surface layer thickness (τ) were analyzed for 10 binary mixtures. The ΔG̃ad0 data suggest that the order of adsorption tendency is LI-type ≫ SI-type ≈ SII-type > LII-type, and the strong adsorption usually corresponds to large τ. This work provides a feasible model for describing the S-type isotherms and a better understanding of the surface properties of liquid mixtures.

Preparation of hydrogels based on poplar cellulose and their removal efficiency of Cd(II) from aqueous solutions.

Industrial heavy metal-contaminated wastewater is one of the main water pollution problems. Adsorbents are a promising method for the removal of heavy metal contaminants. Herein, polyaspartic acid/carboxymethyl poplar sawdust hydrogels (PASP/CMPP) and ascorbic acid/carboxymethyl poplar sawdust hydrogels (VC/CMPP) were prepared by aqueous polymerization using alkalized poplar sawdust (CMPP) as the substrate and PASP and vitamin C (VC) as modifiers. The effective results, provided by the characterization analysis of SEM and BET, indicate that the surface of the PASP/CMPP hydrogel has a larger number of loose pores and a larger pore volume than the VC/CMPP hydrogel. The treatment effects of the two hydrogels on simulated wastewater containing Cd(II) were investigated by a batch of experiments. The results showed that PASP/CMPP had a better adsorption effect than VC/CMPP under the same adsorption conditions. Interestingly, the solid concentration effect was found in the process of sorption kinetics and sorption isotherms. The sorption kinetic curves of Cd(II) on PASP/CMPP were well-fitted by the quasi-second-order kinetics under different adsorbent concentrations. The adsorption conforms to Langmuir and Freundlich adsorption isotherm models. More importantly, PASP/CMPP composites are expected to be used as a new kind of environmental adsorbent for wastewater treatment.

Stability and Crystallinity of Sodium Poly(Heptazine Imide) in Photocatalysis.

Poly(heptazine imide) (PHI) salts, as crystalline carbon nitrides, exhibit high photocatalytic activity and are being extensively researched, but its photochemical instability has not drawn researchers' attention yet. Herein, sodium PHI (PHI-Na) ultrathin nanosheets with increased crystallinity, synthesized by enhancing contact of melamine with NaCl functioning as a structure-induction agent and hard template, exhibits improved photocatalytic hydrogen evolution activity, but low photochemical stability, owing to Na+ loss in the photocatalytic process, which, interestingly, can be enhanced by the common ion effect, e.g., addition of NaCl that is also able to remarkably increase the photoactivity with the apparent quantum yield at 420 nm reaching 41.5 %. This work aims at attracting research peers' attention to photochemical instability of PHI salts and provides a way to enhance their crystallinity.

A Model for the Structure of Adsorbed Layers at Solid/Liquid Interfaces.

Understanding the structure of adsorbed layers, including their composition (the mole fraction of sorbate, xA) and thickness (dal), is of great significance for revealing the nature of adsorption and guiding its applications. Many techniques have been used to estimate the structure of adsorbed layers of organics at solid/liquid interfaces. However, there is still a lack of feasible thermodynamic models to describe the correlation between the structure (more precisely, xA and dal) and the equilibrium adsorption amount (Γe). Herein, a thermodynamic model, called the dynamic bonding equilibrium (DBE) model, was developed on the basis of the adsorption equilibrium thermodynamics with an assumption that, at adsorption equilibrium, the sorbate and solvent within the adsorbed layer both exist in different bonding states. The DBE model relates xA and dal with Γe and thus can predict or describe the structure (xA and dal) of adsorbed layers from Γe. Its rationale was confirmed by the literature-reported adsorption data of organics, including surfactants, proteins, and polymers, on hydrophilic and hydrophobic surfaces in water. This work provides a feasible approach for obtaining information about the structure of adsorbed layers at solid/liquid interfaces.

Adsorption of Cetylpyridinium Chloride at Silica Nanoparticle/Water Interfaces (II): Dependence of Surface Aggregation on Particle Size.

Herein, we report a thermodynamic model that relates the adsorption (aggregation) parameters of surfactants at solid/liquid interfaces to particle radius (r). The adsorption (aggregation) parameters include adsorption amounts, equilibrium constants (or the standard Gibbs free energy changes), the critical surface micelle concentration (csmc), and the average aggregation number of surface micelles (n). The model predicts the size dependence of the surface aggregation of surfactants, which is determined by the changes in the interfacial tension and the molar volume of surface components caused by adsorption. In addition, the adsorption of cetylpyridinium chloride (CPyCl), a cationic surfactant, on silica nanoparticles with different r values (ca. 6-61 nm) was determined at 298 K and pH 4, showing an obvious size dependence, consistent with the prediction of the model. With an increase in r, the adsorption isotherm changes from the double-plateau type to the Langmuir type, accompanied by obvious changes in the adsorption parameters. The size-dependent adsorption data can be well described using the model equations, indicating that the model presented here is acceptable. In addition, the model can extract information on the interfacial tensions from adsorption data. We think that the model deepens the understanding of the aggregation phenomena of surfactants at solid/liquid interfaces.

Vesicle formation of single-tailed amphiphilic alkyltrimethylammonium bromides in water induced by dehydration-rehydration.

We recently found that rough glass surfaces (RGSs) can in situ mediate the micelle-to-vesicle transition in single-component solutions of simple single-tailed amphiphiles (STAs), but only result in a relatively small number of vesicles coexisting with a large number of micelles. In the current work, a dehydration-rehydration (DHRH) method was used to induce the formation of vesicles in the single-component aqueous solutions of alkyltrimethylammonium bromides (CnTABs, n = 12, 14, and 16), a kind of typical cationic STAs. That is, a CnTAB micelle solution dropped on smooth glass surfaces (SGSs) was first dried, and the dried CnTAB aggregates were then rehydrated in a monomer solution of CnTAB. A large population of vesicles and even pure vesicle (or vesicle-dominated) systems were obtained, indicating that the DHRH process could more effectively induce the formation of STA vesicles than RGS in situ mediation. The so-obtained vesicles were characterized using DLS, FF-/cryo-TEM, AFM, SAXS, and fluorescence techniques, and their stability was determined. In addition, the effects of the conditions of DHRH and the chain length of CnTABs on the vesicle formation were examined. It was demonstrated that the vesicles can be formed as long as the concentrations of CnTABs in the rehydrated systems are higher than their critical micelle concentrations. The size and wall thickness of vesicles increase with an increase in chain length. A possible mechanism for the DHRH-induced vesicle formation is proposed: bilayer sheets are formed on SGSs during dehydration, and then detached from the SGSs to form vesicles during rehydration. A highly interdigitated structure of alkyl chains between two leaflets was identified in the bilayers, which probably is the origin of the formation and stability of STA vesicles.

MnOx Film-Coated NiFe-LDH Nanosheets on Ni Foam as Selective Oxygen Evolution Electrocatalysts for Alkaline Seawater Oxidation.

Compared to freshwater electrolysis, seawater electrolysis to produce hydrogen is preferable and more promising, but this technology is plagued by the electrode's corrosion and oxidative reactions of the competitive Cl- ion on the anode. To develop efficient oxygen evolution reaction (OER) catalysts for seawater electrolysis, the ultrathin MnOx film-covered NiFe-layered double-hydroxide nanosheet array is directly assembled on Ni foam (MnOx/NiFe-LDH/NF) by hydrothermal and electrodeposition in turn. This catalyst demonstrates excellent OER-selective activity in alkaline saline electrolytes. In 1 M KOH/0.5 M NaCl and 1 M KOH/seawater electrolytes, MnOx/NiFe-LDH/NF exhibits lower overpotentials at 100 mA cm-2 (η100 values of 265 and 276 mV, respectively) and Tafel slopes (73 and 77 mV decade-1, respectively) than does the NiFe-LDH/NF electrode (η100 values of 298 and 327 mV and Tafel slopes of 91 and 140 mV decade-1, respectively). In alkaline saline solutions, the stability and durability of the former are also better than those of the latter. The good OER selectivity and catalytic performance are attributed to the MnOx overlayer that selectively blocks Cl- anions from approaching catalytic centers, and the good conductivity, fast kinetics, more oxygen vacancies, and abundant active sites of MnOx/NiFe-LDH/NF. The robust stability is due to the enhanced resistance for Cl- corrosion stemming from the MnOx protective film. Hence, MnOx/NiFe-LDH/NF can act as a promising OER electrocatalyst for alkalized natural seawater electrolysis.

Adsorption of Cetylpyridinium Chloride at Silica Nanoparticle/Water Interfaces (I): Dependence of Adsorption Equilibrium on Particle Size.

In the current work, a size-effect model was developed to describe the particle size-dependence of adsorption at solid/liquid interfaces. A parameter, ΔQad, was introduced, defined as the change of the product of the solid/liquid interfacial tension and the molar volume of solid surface components caused by adsorption. The model predicts that with a decrease in particle radius (r), the saturation adsorption amount per unit area (Γm, mol/m2) decreases, while the change of the adsorption equilibrium constant (Kad) is determined by the ΔQad, namely, it decreases if ΔQad > 0 but increases if ΔQad < 0. There exists a critical r at which the saturation adsorption amount per unit mass (Γmg, mol/g) attains a maximum. In addition, the adsorption of cetylpyridinium chloride (CPyCl), a cationic surfactant, on silica nanoparticles with different r (ca. 6-61 nm) values was determined at 298 K and pH 9, showing an obvious size-dependence. With a decrease in r, Kad and Γm decrease, indicating a decrease in the affinity of silica particles toward CPyCl. The size-dependent adsorption data can be well described using our model. Adsorption can affect the molar volume of the solid surface phase, which plays an important role in the size-dependence of adsorption. This work provides a better understanding of the size-dependent adsorption phenomenon at solid/liquid interfaces.

Spontaneous vesicle formation and vesicle-to-α-gel transition in aqueous mixtures of sodium monododecylphosphate and guanidinium salts.

Monoalkyl phosphates (MAPs) are one kind of important single-chain weak acid/salt type surfactants, but the understanding of their aggregation behavior in water is very limited due to their insolubility at room temperature. In the current work, the effect of guanidinium salts (GuSalts) on the solubility of sodium monododecylphosphate (SDP), a typical MAP, in water was determined at 25.0 °C, and the aggregation behavior of SDP in the GuSalt/water mixtures was investigated. The solubility of SDP is significantly improved by GuSalts including GuCl, GuSO4, GuSO3, GuPO4, and GuCO3 at 25.0 °C, resulting in an isotropic phase. SDP vesicles are spontaneously formed in the isotropic phase, with a critical vesicle concentration of ∼1.0 mM independent of the type of GuSalts. A "bridging dimer" mechanism is proposed to explain the formation of SDP vesicles. The SDP vesicles have a unilamellar structure with a size of ∼80 nm and an alkyl interdigitated degree of ∼25%, and exhibit size-selective permeability. Interestingly, a temperature-induced reversible transition between vesicles and α-gels was observed for the SDP/GuSalt/H2O systems when the SDP content is higher than 20 mM. The α-gels obtained are composed of vesicles and bilayer sheets, showing similar viscoelasticity to conventional gels, although their water content is as high as ∼98 wt%. The microviscosity of SDP vesicle membranes (ca. 35.79-49.34 mPa s at 25.0 °C) and the transition temperature between vesicles and α-gels (ca. 21.0-22.8 °C) are all dependent of the type of GuSalts. This work deepens the understanding of the aggregation behavior of MAPs and also provides valuable information for their practical applications.

Vesicle formation of single-chain amphiphilic 4-dodecylbenzene sulfonic acid in water and micelle-to-vesicle transition induced by wet-dry cycles.

Simple single-chain amphiphiles (SCAs) can form vesicular structures in their single-component aqueous solutions, which has attracted great attention, but the understanding of their aggregation behavior is still limited. In this work, the aggregation behavior of 4-dodecylbenzene sulfonic acid (DBSA), a typical simple SCA, in water was investigated. The structure and properties of the aggregates formed were determined. In particular, the effect of wet-dry cycles on the structures of aggregates was examined. The mechanisms of aggregate formation and structural transition were discussed. It was found that the increase of DBSA concentration can drive the occurrence of a micelle-to-vesicle transition, showing a critical micelle concentration and critical vesicle concentration of ∼0.53 and 2.14 mM, respectively. The vesicles formed coexist with micelles in solution, with a unilamellar structure and ∼80 nm size, and exhibit size-selective permeability. In addition, the vesicles show remarkable stability upon long-term storage, exposure to high temperature, and freeze-thaw cycles. The H-bonding interaction between DBSA species and the interdigitated structure of alkyl chains in bilayers play a key role in the formation and stability of DBSA vesicles. Interestingly, it was found that the wet-dry cycle can induce a micelle-to-vesicle transition and an obvious increase in the size of the original vesicles, accompanied by the formation of some multilamellar vesicles. This work provides a better understanding of the aggregation behavior of simple SCAs in their single-component aqueous solutions.

Specific Ion Effects on the Colloidal Stability of Layered Double Hydroxide Single-layer Nanosheets.

The surface charge properties and aggregation behavior of positively charged Mg-Al-NO3 layered double hydroxide (LDH) single-layer nanosheets dispersed in water were investigated in the presence of K+ salts with different mono-, di-, and trivalent anions, using electrophoresis and dynamic light scattering techniques. An increase in the salt concentration can significantly decrease the effective surface charge density (σeff) of LDHs, leading to the aggregation of nanosheets. The critical coagulation concentration (CCC) or ionic strength (CCIS) of salts for nanosheets significantly decreases with an increase in the valence of anions. Specific ion effects, with a partially reverse Hofmeister series, are observed. On the basis of the Stern model and the DLVO theory, the relationship of CCC with σeff and the ionic valences of salts (zi) is theoretically analyzed, which can accurately describe the dependence of CCC on the σeff and zi but cannot explain the origin of specific ion effects. To explore the origin of specific ion effects, a correlation between CCIS and the specific adsorption energy (Esc) of anions within the Stern layer is developed. Especially, an empirical relationship of Esc with the characteristic physical parameters of anions is proposed. Our model can accurately predict the CCISs of at least monovalent anions and divalent anions (CO32- and SO42-), demonstrating that the specific ion effects observed can be attributed to the differences in ionic size, polarizability, and hydration free energy (or the formation capacity of anion-cation pairs) of different anions. This work not only deepens the understanding of specific ion effects on the colloidal stability but also provides useful information for the potential applications of LDH single-layer nanosheets.

Predicting Points of Zero Net Charge of Layered Double Hydroxides.

Many models such as electrostatic and crystallographic models have been developed to predict the point of zero net charge (PZNC) of (hydr)oxides without structural charges. Nevertheless, there is still a lack of feasible models for the prediction of the PZNC of structurally charged (hydr)oxides such as layered double hydroxides (LDHs), a large class of lamellar inorganic materials possessing positive structural charges. Herein, a modified electrostatic model is proposed by taking the structural charge (σst) and the Pauling's electrostatic valence principle into account, to correlate the PZNC with the characteristic physical constants of (hydr)oxides. The new model suggests that the PZNC of structurally charged (hydr)oxides is proportional to their σst, which was confirmed by the PZNC data of 28 LDH samples. The model can be used to describe or predict the PZNC of LDHs and also may provide guidance for the designed synthesis and application of LDH materials.

Surfactant-Free Microemulsions of 1-Butyl-3-methylimidazolium Hexafluorophosphate, Diethylammonium Formate, and Water.

Surfactant-free microemulsions (SFMEs) are a unique kind of microemulsion, which form from immiscible fluids (i.e., oil and water phases) in the presence of amphi-solvents rather than traditional surfactants. In comparison with traditional surfactant-based microemulsions (SBMEs), SFMEs have received much less attention, and the current understanding of the unique system is very limited. Herein, we report a SFME consisting of the hydrophobic ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), the protic IL diethylammonium formate (DEAF), and water, in which the bmimPF6 and DEAF are used as the oil phase and amphi-solvent, respectively. Three kinds of microstructures, namely, water-in-bmimPF6 (W/IL), bicontinuous (BC), and bmimPF6-in-water (IL/W), are identified for the SFME, using cyclic voltammetry, cryo-TEM, and DLS techniques. Especially, the volumetric and surface free energy properties of the SFME are investigated by excess molar volume ( VmE) and surface tension (γ) measurements, and they are found to be similar to those of SBMEs. Discontinuous changes in VmE and γ with the system compositions are observed as the system microstructures change, which can be used to identify the structural transition of SFMEs. We think this study provides a better understanding of SFME features.

Analysis of Adsorbed Layers of Benzyldimethyldodecylammonium Bromide on Silica Particles in Water Using the Sorbent Mass Variation Method.

A "sorbent mass variation" (SMV) method has been suggested to investigate the adsorption at solid-liquid interfaces, which can provide information on the adsorbed layer structure including its thickness and composition. However, there has been little research focused on the method, and therefore, it is essential to examine its general applicability. Herein, the adsorption of benzyldimethyldodecylammonium bromide (BDDABr), a cationic surfactant, on silica (SiO2) nanoparticles (with ∼12 and 24 nm in size, denoted as S-SiO2 and L-SiO2, respectively) in water was investigated using the SMV method. The adsorption isotherms all show a linearly declining tendency in the saturated adsorption regime, consistent with the prediction of the SMV model. The adsorption is interpreted to form noncomplete bilayers (or isolated admicelles). The thicknesses of the adsorbed bilayers on S-SiO2 and L-SiO2 are estimated to be ∼2.9 and 2.7 nm, respectively, and the volume fractions of BDDABr in the saturated adsorbed layers are 0.63 and 0.68, respectively. In addition, the change in the Gibbs free energy of the adsorption process is also analyzed, showing its spontaneous nature. This work demonstrates that the SMV method is available for investigation on the adsorption of surfactants at solid-liquid interfaces, which can provide information on the structure and formation thermodynamics of adsorbed layers.

Synthesis of layered double hydroxide/poly(N-isopropylacrylamide) nanocomposite hydrogels with excellent mechanical and thermoresponsive performances.

Nanocomposite (NC) hydrogels of positively charged layered double hydroxide (LDH) single-layer nanosheet (SLNS) cross-linked poly(N-isopropylacrylamide) (PNIPAM) were synthesized. Especially, the LDH SLNSs used here were pre-synthesized via an aqueous synthetic route without using organic solvents and modifiers. The obtained LDH/PNIPAM NC hydrogels were characterized using XRD, SEM, TEM, and DSC. The mechanical and thermoresponsive properties were determined using tensile, compression, and swelling/deswelling tests. Interestingly, different network structures are observed for the NC hydrogels along the horizontal and vertical directions; those along the horizontal direction exhibit a fine and uniform sponge-like network structure while those along the vertical direction exhibit a hierarchical layered architecture. Compared with the conventional N,N'-methylene bisacrylamide cross-linked PNIPAM hydrogel, the NC hydrogels exhibit extraordinary deformability and stretchability and obviously improved thermoresponsive swelling/deswelling characteristics. Furthermore, the fracture elongation observed here is obviously higher than those reported for negatively charged clay/PNIPAM NC hydrogels. With the increase in the LDH content from 0.8 to 2.0 wt%, the fracture strength and the compressive strength at an 85% strain increase from 23.5 to 37.2 kPa and from 0.15 to 0.57 MPa, respectively, while the fracture elongation decreases from 2689 to 2202%. The mechanism for the improved mechanical performances of the NC hydrogels is discussed. To the best of our knowledge, this is the first report on LDH/PNIPAM hydrogels. This work provides a green synthesis route for LDH-containing NC hydrogels. The new NC hydrogels may have great potential applications such as in tissue engineering, drug vehicles, and sorbents.

Correction: Model of protocell compartments - dodecyl hydrogen sulfate vesicles.

Correction for 'Model of protocell compartments - dodecyl hydrogen sulfate vesicles' by Bin Liu et al., Phys. Chem. Chem. Phys., 2018, DOI: .

Model of protocell compartments - dodecyl hydrogen sulfate vesicles.

Dodecyl hydrogen sulfate (DHS), a simple single-alkyl sulfonic acid, can form vesicles spontaneously in water without any additives close to its apparent pKa. Interestingly, DHS vesicles show typical characteristics of primitive cell membranes in respect of selective permeability, fast exchange, self-reproduction and stability under primordial environments.