Anionic Sulfonate Research Articles

The Effects of Dynamic Noncovalent Interaction between Surfactants and Additional Salt on the pH‐Switchable Interfacial Tension Variations

AbstractThe dynamic noncovalent interaction between the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and 1,3‐diphenylguanidine (DPG) was employed to control the interfacial activity of the surfactant. At high HCl concentration (1000 mg L−1), the SDBS/DPGn+ system could reduce the water/oil interfacial tension (IFT) to 10−4 mN m−1 order of magnitude, which was much lower than the IFT values in the SDBS/DPG+ system with a low HCl concentration (100 mg L−1) and the individual SDBS system by three and four orders of magnitude, respectively. The pH‐switchable protonation of amido groups in DPG molecules determines the SDBS/DPG molecular interaction and the amplitude of IFT reduction, which was confirmed by control experiments using two other surfactants (sodium dodecyl sulfate [SDS] and dodecyl trimethylammonium bromide [DTAB]). Moreover, the investigation of the NaCl and temperature effects on the IFT indicated the intensity of mixed SDBS/DPGn+ adsorption layers at the water/oil interface.

Synergistic effects of anionic surfactants on adsorption of norfloxacin by magnetic biochar derived from furfural residue

Norfloxacin (NOR) is a persistent organic pollutant and can be effectively removed from effluent by adsorption of biochar. However, the presence of other emerging contaminants, such as surfactants, will potentially alter adsorption performance of norfloxacin by biochar and the molecular-scale mechanisms of the interaction between surfactants and biochar remain poorly understood. In this study, adsorption of norfloxacin on magnetic biochar prepared with iron-containing furfural residue (FRMB) in the presence or absence of anionic surfactants was investigated. The adsorption of NOR was significantly affected by the initial pH and anionic surfactants-sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS). In the presence of SDS and SDBS, the maximum sorption capacities of NOR were 2.33 and 1.97 times higher than that in the absence of surfactants, reached to 698.6 mg g−1 and 589.9 mg g−1, respectively. The optimal pH condition which was 4 indicated that electrostatic adsorption played a decisive role in the adsorption process after introduction of SDS/SDBS. The adsorption data were fitted well by the Elovich model and Freundlich model at the optimal conditions in which both SDS and SDBS were hemimicelle (0.8 mM SDS or 0.4 mM SDBS), indicating surface heterogeneity of FRMB and the adsorption mechanism was related to the assembly of surfactants on biochar. FTIR results showed that FRMB and SDS/SDBS interacted through hydrophobic action, and more complex or aggregates were formed between the NOR and biochar/SDS/SDBS. This work highlights the synergistic enhancement effects of tested surfactants on the removal of NOR by magnetic biochar from aqueous systems.

Surface-Charged Zirconia Nanoparticles Prepared by Organophosphorus Surface Functionalization with Ammonium or Sulfonate Groups.

Organophosphorus coupling agents bearing permanently charged functional groups (either cationic quaternary ammonium or anionic sulfonates) were synthesized and used for the modification of zirconia nanoparticles with a diameter <10 nm. Surface functionalization was confirmed by FTIR and solid-state NMR spectroscopy. Surface coverages up to 2.3-2.4 molecules/nm2 were achieved for modification with these charged coupling agents. The pH-dependent charge measurements of homogeneously modified particles showed stable surface charges over a wide range of pH for both ammonium- and sulfonate-functionalized particles. Surface charge measurements of particles co-functionalized with charged coupling molecules and uncharged methyl phosphonic acid revealed a decreasing charge density with increasing amount of uncharged coupling agent. Thus, an adjustment of charges by co-functionalization was obtained on the particle surface. The thus-formed surface-charged colloids were used in a second step for electrostatic-driven aggregation phenomena necessary for layer-by-layer processes. Sulfonate-modified negatively charged SiO2 submicrometer particles of 506 nm in diameter were decorated with ammonium-modified ZrO2 nanoparticles. In addition, a layer-by-layer deposition of alternating charge-modified TiO2 nanoparticles was proven by optical spectroscopy. Due to the broad applicability of organophosphorus coupling agents for surface modification, particularly for transition-metal oxides, the shown route represents a general method for the creation of almost pH-independent charges on the surface of nanoparticles.

High energy density of two-dimensional MXene/NiCo-LDHs interstratification assembly electrode: Understanding the role of interlayer ions and hydration

The application of two-dimensional layered hybrid materials in supercapacitor electrodes has high energy density. However, the hybrid assembly and electrochemical energy storage mechanism of multifarious layered electrode materials are still unclear. In this work, a two-dimensional interstratification assembly hybrid electrode by using electrostatic assembly between MXene modified with cetyl trimethylammonium bromide cation (CTAB) and NiCo-LDHs modified with dodecyl benzene sulfonic acid anion (DBS) is presented. As a result, the self-restacking of MXene and NiCo-LDHs nanosheets are effectively prevented, leading to a regular interstratification structure and large interlayer spacing, which accelerate diffusion of electrolyte ions and possess more electrochemical activity sites. The freestanding MXene/NiCo-LDHs electrode displays a much higher specific capacitance of 1207 F g−1 at a scan rate of 0.5 A g−1, an impressive rate capability with 93% capacitance retention after 5000 cycles. Moreover, it shows maximum energy density of 107.3 Wh kg−1 (98.5 mWh cm−3) at a power density of 571 W kg−1 (524 mW cm−3), which is among the highest values reported for MXene and NiCo-LDHs based materials in aqueous electrolytes. This significant electrochemical performance is mainly attributed to hydration of two-dimensional electrodes and exchange or adsorption of interlayer anion-cation.

Binary mixtures of anionic double-chain sulfonate emulsifiers in VCM emulsion polymerization with high solid content: effect of emulsifier’s combination ratio and concentration

Binary mixtures of anionic double-chain sulfonate emulsifiers, sodium di-isodecyl sulfosuccinate and sodium pentadecan-sulfonate (SPS) were employed in batch reactor at different combination ratios and concentration for vinyl chloride emulsion polymerization. Reaction performances were evaluated by monitoring conversion rate and molecular weight by K-value parameter. Particle size and its distribution were investigated as a criterion for particle nucleation and the growing process by calculating the number of latex particles and the average number of growing chains per particle, respectively. The final latexes were evaluated by means of the coarse matter content as a qualitative character of the latex. The results showed that the overall reaction rate increases by high amount of SPS. Also, by increasing SPS content in binary mixture, coarse particle formation decreased and latex stability and particle size distribution increased. Furthermore, it has been found that the particle size was nonlinearly dependent on the combined ratio and amount of emulsifier and has shown a minimum within the scope of the study.

Topically Applied Etamsylate: A New Orphan Drug for HHT-Derived Epistaxis (Antiangiogenesis through FGF Pathway Inhibition).

Hereditary hemorrhagic telangiectasia (HHT) is a vascular dysplasia characterized by recurrent and spontaneous epistaxis (nose bleeds), telangiectases on skin and mucosa, internal organ arteriovenous malformations, and dominant autosomal inheritance. Mutations in Endoglin and ACVRL1 / ALK1 , genes mainly expressed in endothelium, are responsible in 90% of the cases for the pathology. These genes are involved in the transforming growth factor-β(TGF-β) signaling pathway. Epistaxis remains as one of the most common symptoms impairing the quality of life of patients, becoming life-threatening in some cases. Different strategies have been used to decrease nose bleeds, among them is antiangiogenesis. The two main angiogenic pathways in endothelial cells depend on vascular endothelial growth factor and fibroblast growth factor (FGF). The present work has used etamsylate, the diethylamine salt of the 2,5-dihydroxybenzene sulfonate anion, also known as dobesilate, as a FGF signaling inhibitor. In endothelial cells, in vitro experiments show that etamsylate acts as an antiangiogenic factor, inhibiting wound healing and matrigel tubulogenesis. Moreover, etamsylate decreases phosphorylation of Akt and ERK1/2. A pilot clinical trial (EudraCT: 2016–003982–24) was performed with 12 HHT patients using a topical spray of etamsylate twice a day for 4 weeks. The epistaxis severity score (HHT-ESS) and other pertinent parameters were registered in the clinical trial. The significant reduction in the ESS scale, together with the lack of significant side effects, allowed the designation of topical etamsylate as a new orphan drug for epistaxis in HHT (EMA/OD/135/18).

Effect of different concentrations of surfactant on the wettability of coal by molecular dynamics simulation

Anionic surfactant sodium dodecyl benzene sulfonate (SDBS) at varying concentrations was selected to investigate the influence on the wettability of Zhaozhuang Coal by molecular dynamics simulation. Six groups of water/surfactant/coal systems with different concentrations were constructed. The influence of surfactant with different concentrations on the wettability of coal was concluded by analyzing various properties from the energetic behaviors to the dynamic characteristics. The results show that the interfacial tension decreases sharply and then rises slowly with the increase of SDBS surfactant concentration, obtaining that surfactants can obviously reduce the interfacial tension. The surfactant molecules could be detected at the water/coal interface through analyzing the system’s relative concentration distribution. In addition, the difference in the wettability of surfactants on coal surfaces is caused by the spatial distribution differences of alkyl chains and the benzene ring of the surfactant molecules. And the negative interaction energy between SDBS and the coal surface indicates that adsorption process is spontaneous. Furthermore, it is of great practical significance for improving the dust reduction effect and reducing the disaster of coal dust by exploring the effects of surfactant molecules on the wettability of coal.

Evaluating ferrocene ions and all-ferrocene salts for electrochemical applications

The success of applications such as redox flow battery (RFB) technologies is highly dependent on the development of new molecular strategies, and much work has focused on the chemistry of ferrocene compounds as RFB components. This report presents four “all-ferrocene” salts comprised of ferrocene anions and cations and evaluates their solubility and electrochemical properties. The four salts are formed via metathesis reactions employing the (ferrocenemethyl)trimethylammonium cation and mono and bis sulfonate or carboxylate ferrocene anions. We observed that the potentials of the ferrocene components was not only dependent on the substituent, but also on the solvent medium. In particular, the sulfonate and carboxylate ferrocene anions exhibited significant shifts in redox potential between water, propylene carbonate (PC), and DMF. Most notably, in (ferrocenemethyl)trimethylammonium 1,1′-bis(sulfonato)ferrocene, the potentials of the cation and anion reverse, with the anion having a lower potential in aqueous solution and a more positive potential in organic media.

One-Step Synthesis and Functionalization of High-Salinity-Tolerant Magnetite Nanoparticles with Sulfonated Phenolic Resin.

Superparamagnetic nanoparticles are being actively developed for various applications in oil fields. A key requirement for such nanoparticles is the long-term stability of their dispersion under harsh subsurface conditions such as high salinity and high temperature. In this study, through functionalization of the surface of the magnetite nanoparticles with a sulfonated phenolic resin, stable dispersions of the nanoparticles in 5 wt % NaCl solution at neutral to basic pH were achieved. Sulfonated phenolic resin is aromatic in nature and can endure high temperatures; moreover, the strongly anionic sulfonate groups facilitate sufficient electrostatic repulsion between the particles even in a highly saline environment. Sulfonated phenolic resin was synthesized by heating a mixture of 4-hydroxybenzenesulfonic acid and formaldehyde at 1:1 molar ratio. Then, by synthesizing magnetite nanoparticles by a co-precipitation process in a solution of sulfonated phenolic resin, one-pot synthesis/surface functionalization was accomplished, which not only simplifies the manufacturing process but also can potentially lower the cost of production owing to the use of readily available phenolic resins. The reliability of the technique was confirmed by the detailed characterization of the nanoparticle through size distribution analysis, thermogravimetric analysis, ζ-potential measurements, transmission electron microscopy imaging, and energy-dispersive X-ray spectroscopy mapping. Further, Langevin curve was generated for evaluating the superparamagnetism of the nanoparticles.

An investigation on the stability of the hazelnut oil-water emulsion

In this study, the stability of the emulsion of two immiscible liquids, including the effect of surfactants and agitation systems has been evaluated. The working fluid was hazelnut oil in water. Three different surfactants—two anionic sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS) and a nonionic (Tween-20) — were tested. To assess the effect of surfactant type and agitation speed on droplet size distribution, focused beam reflectance measurement (FBRM) was employed. Emulsions prepared with both surfactant types, that is, anionic and nonionic, were better stabilized than emulsions with no surfactant. Droplet size decreased when the surfactant concentration was increased, until critical micelle concentration (CMC) of surfactants was reached. Once the CMC was reached, the variation in droplet size was significantly reduced or eliminated with any further increase in its concentration. The interfacial tension (IFT) was found to be a function of surfactant concentrations: with an increase in the surfactant concentration, the adsorption of surfactant molecules increased at the oil-water interface. The IFT remained unchanged when the micelles formed in the aqueous phase above CMC. Data analysis from FBRM revealed that higher agitation speed produced finer droplets. The destabilization time scale of emulsions in the presence of different surfactants was also assessed using electrical resistance tomography (ERT).

Fly ash based geopolymer for the adsorption of anionic surfactant from aqueous solution

Contamination of the world's water resources is a growing issue and its remediation requires the development of highly efficient, environmentally friendly and economical processes. Water contaminated with surfactants can cause detrimental health effects in humans and aquatic animals. Removing surfactants using adsorption is effective, simple and economical. This paper describes the development of a fly ash based geopolymer (FAGP) adsorbent for adsorbing the anionic surfactant sodium dodecyl benzene sulfonate (SDBS). The adsorption parameters of the geopolymers were optimized using batch adsorption. The adsorption kinetics, isotherms and thermodynamics were also determined. The FAGP had an amorphous morphology and a surface area of 31.873 m2/g. The optimum parameters for adsorbing the SDBS using FAGP were pH 2, contact time 180 min, adsorbent dosage 1 g/L for an initial SDBS concentrations of 880 mg/L. The maximum adsorption capacity of 714.3 mg/g was obtained. The adsorption followed pseudo second order kinetics and Langmuir isotherm models suggesting that the adsorption process was chemisorption with monolayer adsorbate coverage. SDBS was adsorbed onto FAGP by electrostatic interactions between the positively charged FAGP and negatively charged SDBS. The activation energy of adsorption was 4.052 kJ/mol and the Gibbs free energy was negative, suggesting the adsorption process was physisorption, endothermic, spontaneous and more favorable at a temperature of 65 °C. The adsorption of SDBS onto FAGP occurs through both physisorption and chemisorption. FAGP was proven as a low-cost adsorbent to remove SDBS and could be potentially used for the adsorption of other water contaminating surfactants.

Systematically quantifying oil–water microemulsion structures using (spin-echo) small angle neutron scattering

Microemulsion systems consisting of D2O, an alkane, an anionic internal olefin sulfonate surfactant, salt and secondary butyl alcohol (SBA) as co-solvent are studied in a systematic way. In four different sample sets, either the salt content, SBA content or alkane carbon number was varied in order to study the effects of the individual compounds on the structure sizes making up the microemulsion. Using complementary small-angle neutron scattering techniques SANS and Spin-Echo SANS, it was found that the microemulsion systems exhibit the largest structures in the optimum state (domain size of d/2 =144 nm in the model by Teubner and Strey), where the structure is considered bicontinuous. In comparison, at under- and over-optimum states where the structures consist of emulsified spherical droplets, the smallest measured diameter was 2R = 44 nm. Furthermore, the structure sizes in bicontinuous microemulsions decrease exponentially (down to d/2 =15 nm for pentadecane and 5 wt% SBA) as function of both SBA content and alkane carbon number. The observed trends in structure sizes combined with the trends observed in the area per surfactant molecule, are qualitatively explained with the extended Winsor R-ratio, the HLD-NAC model and surfactant film flexibility arguments.

Impact of molecular structure, headgroup and alkyl chain geometry, on the adsorption of the anionic ester sulfonate surfactants at the air-solution interface, in the presence and absence of electrolyte

The transition from monolayer to multilayer adsorption at the air-water interface in the presence of multivalent counterions has been demonstrated for a limited range of anionic surfactants which exhibit increased tolerance to precipitation in the presence of multivalent counterions. Understanding the role of molecular structure in determining the transition to surface ordering is an important aspect of the phenomenon. The focus of the paper is on the alkyl ester sulfonate, AES, surfactants; a promising group of anionic surfactants, with the potential for improved performance and biocompatibility. Neutron reflectivity measurements were made in aqueous solution and in the presence of NaCl, CaCl2, MgCl2 and AlCl3, for a range of alkyl ester sulfonate surfactants, in which the headgroup and alkyl chain geometries were manipulated.In the regions of monolayer adsorption changing the AES headgroup and alkyl chain geometries results in an increased saturation adsorption and in a more gradual decrease in the adsorption at low concentrations, consistent with a greater adsorption efficiency. Changing the AES headgroup and alkyl chain geometries also results in changes in the transition from monolayer adsorption to more ordered surface structures with the addition of AlCl3 and mixed multivalent electrolytes. A more limited surface layering is observed for the ethyl ester sulfonate, EES, with a C14 alkyl chain. Replacing the C14 alkyl chain with a C18 isostearic chain results in only monolayer adsorption.The results demonstrate the role and importance of the surfactant molecular structure in determining the nature of the surface adsorption in the presence of different electrolytes, and in the tendency to form extended surface multilayer structures.

Effect of sodium dodecyl benzene sulfonate (SDBS) on the performance of anaerobic co-digestion with sewage sludge, food waste, and green waste

The anionic detergent sodium dodecyl benzene sulfonate (SDBS) inhibits anaerobic solid waste fermentation process in mesophilic anaerobic digesters. In this study, the effect SDBS on the performance of anaerobic digestion (AD) of mixture of sewage sludge, food waste, and green waste serving as substrate was investigated. The batch experiments were conducted with five SDBS concentrations namely 0, 0.01, 0.02, 0.05, 0.1, and 0.2 g/g (SDBS/dry sludge) under mesophilic condition (37 ± 1 °C) and lasted for 63 days. The results showed that the presence of SDBS remarkably increased the release of protein and carbohydrate, and resulting in the serious accumulation of volatile fatty acids (VFAs), especially for propionate accumulation. Likewise, the observed variations in enzyme activities associated with different stage of AD revealed that methanogenesis was quite sensitive to SDBS and inhibited by the increase of SDBS addition. Meanwhile, the presence of SDBS decreased the pH value and the concentration of free ammonia, but increased the concentration of NH4+-N. Furthermore, the production of biogas was reduced by SDBS. In conclusion, SDBS addition has a negative impact on anaerobic co-digestion. On the one hand, methanogens were severely inhibited and biogas yield decreased remarkably, on the other hand, the accumulation of VFAs was excessive. Thus, the presence of surfactant (SDBS) in the municipal organic waste should be concerned during the waste disposal via anaerobic digestion process.

Potentially self-dopable poly(3-hexylthiophene) block copolymers/carbon nanotube nanocomposites for enhanced processibility and electrical properties

Development of new hole-transport layer (HTL) materials for organic photovoltaic (OPV) applications is one crucial issue to mitigate such limitations of low power efficiency, processibility, and stability derived from poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a common HTL material. To this end, poly(3-hexylthiophene) (P3HT)-based diblock copolymers including the different ratios between polystyrene (PSty) or/and poly(neopentyl styrene sulfonate) (PNSS) as a second block segment were designed and then used for incorporating with single wall carbon nanotubes (SWCNTs) to form potentially self-dopable nanocomposites. The structure of fabricated P3HT-based diblock copolymer/SWCNT nanocomposites was examined by microscopic and spectroscopic characterizations, exhibiting a charge transfer behavior between P3HT and SWCNT, and growth of the P3HT crystalline phase along the SWCNT surface with a form of the conducting path. The acquired SWCNT nanocomposites exhibited good solubility and dispersion in various organic solvents including toluene, chlorobenzene, THF, chloroform, and DMF, which are good solvents for the PSty or/and PNSS neutral second block. The concept for the neutralized second block by protecting groups can prevent the poisoning ITO substrate by water contamination as shown in the conventional aqueous PEDOT-PSS solution. Notably, the PNSS constituent in the nanocomposite was merely acidified to give in-situ sulfonic acid groups in PSty by simple thermolysis process at 160 °C for 30 min after a solution process for fabrication of a thin film. The thermolysis step provided efficient doping of P3HT by PSS, in which the thiophene groups worked as Brønsted base are protonated by taking protons from sulfonic acid groups and then lead to a form of ionic bonds between cationic thiophene and anionic sulfonate groups. In addition, the formed ionic bonds in the nanocomposites led to an insoluble thin film, which has a good advantage for the further solvent process without substantial damages. The beneficial features of the conducting path along SWCNT and the efficient doping of P3HT by PSS in the acquired nanocomposites led to ca. 5-fold higher electrical conductivity (3.16 S cm−1) and similar work function (5.1 eV) in comparison to water contained commercial PEDOT:PSS (0.6 S cm−1 and 5.0 eV, respectively). As such, the rationally designed potentially self-dopable SWCNT nanocomposites can be one of the promising alternatives beyond the commercial PEDOT: PSS HTL material.

Effect of Amino Acids on Micellization and Micellar Parameters of Anionic Surfactant Alpha Olefin Sulfonate C14–C16 in Aqueous Solutions: Surface Tension, Conductometric, Volumetric, and Fluorescence Studies

The effect of l-glycine, l-alanine, and l-leucine on micellization, surface activity, and colloidal parameters of an anionic surfactant sodium alpha olefin sulfonate C14–C16 in aqueous solutions at different temperatures was studied. It was shown that the hydrophobicity of the studied amino acids had great influence on behavior of physicochemical parameters. In studied systems, the electrostatic interactions between zwitterionic groups of amino acids and ions of sodium alpha olefin sulfonate C14–C16 were also important.

Development of Hierarchically Porous Ionomer Membranes for Versatile and Fast Metal Ion Conduction.

Innovative design concepts can play a key role in the realization of high-performance ionomer membranes that are capable of exclusive metal ion conduction and potentially applicable in electrochemical devices including sensors, fuel cells, and high-energy batteries. Herein, we report on the development of new ionomers, based on sulfonated poly(ether ether ketone) (SPEEK), engineered to conduct a variety of ions, namely, Li+, Na+, K+, Zn2+, and Mg2+, when soaked with nonaqueous solvents. Application of a facile phase-inversion method results in M-SPEEK (M = Li/Na/K/Zn/Mg) membranes with a hierarchical porous network, facilitating organic solvent infusion that is necessary to promote dissociation and rapid transport of cations between anionic sulfonate groups on the polymer chains. This strategy leads to membranes with alkali ion conductivities approaching 10–4 S cm–1 at room temperature, and near unity cation transference numbers (tM+ ≥ 0.9). Furthermore, an exceptionally high Zn-ion conductivity of 10–2 S cm–1 is obtained for the water-infused Zn-SPEEK membrane. In comparison, the dense membranes demonstrate 2–3 orders of magnitude lower conductivities because of insufficient solvent infusion. Preliminary electrochemical studies with solvent-infused ionomer membranes as the electrolyte look promising.

Preparation of PSSS‐grafted polysulfone microfiltration membrane and its rejection and removal properties towards heavy metal ions

3‐Hydroxy‐N,N‐diethylaniline (HDEA) as a tertiary aromatic amine was introduced onto the surface of chloromethylated polysulfone (CMPSF) microfiltration membrane through modification reaction, resulting in the modified membrane PSF‐DEA. A redox surface‐initiating system (DEA/APS) was constituted by the bonded tertiary aromatic amine group DEA and ammonium persulfate (APS) in aqueous solution, and so, the free radicals formed on the membrane initiated sodium p‐styrenesulfonate (SSS) as an anionic monomer to produce graft polymerization, getting the grafting‐type composite microfiltration membrane, PSF‐g‐PSSS membrane. Subsequently, the adsorption property of PSF‐g‐PSSS membrane for three heavy metal ions, Pb2+, Zn2+, and Hg2+ ions, was fully examined, and the rejection performance of PSF‐g‐PSSS membrane towards the three heavy metal ions was emphatically evaluated via permeation experiments. The experimental results show that by the initiating of the surface‐initiating system of DEA/APS, the graft polymerization can smoothly be carried out under mild conditions. PSF‐g‐PSSS membrane as a functional microfiltration membrane has strong adsorption ability for heavy metal ions by right of strong electrostatic interaction (or ion exchange action) between the anionic sulfonate ions on the membrane and heavy metal ions. The order of adsorption capacity is Pb2+ &gt; Zn2+ &gt; Hg2+, and the adsorption capacity of Pb2+ ion gets up to 2.18 μmol/cm2. As the volume of permeation solutions, in which the concentrations of the three metal ions are 0.2 mmol/L, are in a range of 50 to 70 mL, the rejection rate of PSF‐g‐PSSS membrane for the three heavy metal ions can reach a level of 95%, displaying a fine rejection and removing performance towards heavy metal ions.

Development of novel surfactant functionalized porous graphitic carbon as an efficient adsorbent for the removal of methylene blue dye from aqueous solutions

In this work, an environmentally friendly and economically effective surfactant modified porous graphitic carbon (S-PGC) obtained from alginate biomass was successfully fabricated by functionalizing with anionic surfactants (sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS)) and used as an adsorbent for the removal of methylene blue cationic dye from aqueous solutions. The structural order and textural properties were examined using XRD, Raman spectroscopy and SEM-EDX. Batch adsorption experiments were conducted, where the influence of operating parameters such as solution pH, contact time, adsorbent dosage, initial MB concentration, and temperature on the sorption capacity were investigated. Compared with pristine PGC, the surfactant modified PGC (S-PGC) exhibited a much higher sorption capacity for MB due to the enhanced electrostatic interaction between the cationic dye and negatively charged S-PGC adsorbent. The adsorption isotherm and kinetics of adsorption were well fitted by the Freundlich isotherm and pseudo-second order model, respectively. The maximum adsorption capacity calculated from Langmuir isotherm was 714 and 769 mg/g for two adsorbents SDBS-PGC-3000 and SDS-PGC-3000, respectively at 25 °C, suggesting SDS-PGC has a comparatively higher sorption capacity. Further investigation confirmed that the adsorption of MB over S-PGC was spontaneous and endothermic in nature. Successful regeneration of the spent adsorbents with methanol along with its high dye adsorption performance strongly confirms the ability of utilizing S-PGC as a promising and reliable adsorbent for cationic dye removal.

Membrane Filtration of Anionic Surfactant Stabilized Emulsions: Effect of Ionic Strength on Fouling and Droplet Adhesion

Membranes hold great potential to be used for the successful treatment of oily waste water, but membrane fouling leads to substantial decreases in performance. Here we study the impact of ionic strength on membrane fouling from an emulsion stabilized by the anionic surfactant sodium dodecyl sulfonate (SDS). For this we use a unique combinatorial approach where droplet adhesion to a cellulose surface in a flow cell is compared to membrane fouling (flux decline) on a cellulose membrane. In the initial membrane fouling stages droplet adhesion dominates. While the flow cell demonstrates a high number of droplets adhering especially at high ionic strengths (100 mM NaCl), the strongest flux decline is observed at intermediate (10 mM NaCl) ionic strength. This suggests that the fouling mechanism must be different, with pore blocking expecting to dominate at intermediate ionic strength. At the later fouling stages the porosity of the cake layer plays a key role in the flux reduction. At low ionic strength, oil droplets repel each other strongly and an open, more permeable, cake layer is formed. However at higher ionic strength, a screening of charge interactions leads to a lower porosity and thereby a lower flux. This leads to a clear trend: with a higher ionic strength a higher flux decline is observed. Flux recovery is high at all ionic strengths, in line with the observation in the flow cell that oil droplets can easily be sheared of a cellulose surface at all ionic strengths. This work thus highlights the critical effect of the ionic strength on membrane fouling by anionically stabilized emulsions. Moreover it shows how the use of an optical flow cell can provide key insights to help explain observations in more standard membrane fouling experiments.