Adsorption Of Sulfonate Research Articles

Adsorption of dibenzothiophene sulfone using Fe3+ and Fe6+-impregnated clay adsorbents

In this study, the adsorption of dibenzothiophene sulfone (DBTO) was investigated using clay minerals as adsorbents. Raw bentonite (BR) and raw activated clay (ACR) were impregnated with Fe3+ and Fe6+, creating bentonite-Fe3+ (BF3), bentonite-Fe6+ (BF6), activated clay-Fe3+ (ACF3), and activated clay-Fe6+ (ACF6). The surface functional groups, surface morphology, and surface area of the raw and modified adsorbents were studied through Fourier transform infrared spectroscopy, a scanning electron microscope, and Brunauer, Emmett, and Teller analysis, respectively. Batch experiments on simulated oil were done to test the effect of adsorption time (0.5–24 h), adsorption dosage (0.3–1.5 g), and adsorption temperature (30–50 °C). The results of the experiments showed the suitability of the pseudo-second order kinetic model on the clay adsorbent and sulfone system. This suggests that chemisorption is the rate-limiting step of the reaction. Equilibrium isotherms indicated the adherence of DBTO onto BR and BF3 to the Freundlich model, implying the heterogeneous adsorption of the sulfones onto the adsorbents. The systems of DBTO with BF6, ACR, ACF3, and ACF6 showed a better fit with the Dubinin-Radushkevich model. This denotes that adsorption happens through the filling of sulfones of the micropores on the adsorbent. Lastly, thermodynamic studies revealed the endothermic and non-spontaneous nature of the clay adsorbents and sulfone systems. The experiments showed that the impregnation of Fe3+ and Fe6+ lowered the desulfurization ability of the adsorbents. This could be due to the iron ions being hard acids and the sulfones being soft bases, thus showing lower compatibility than the raw counterparts of the adsorbents. Comparison with related studies showed that the prepared adsorbents, namely BF3 (5.1 mg g−1) and BF6 (6.4 mg g−1), had a higher adsorption capacity than Ni2+-loaded activated carbon (4.9 mg g−1) and activated clay (4.1 mg g−1). The study shows that BR (7.2 mg g−1) is the best-performing adsorbent, which can be set as the direction for future research. This study is a step toward the commercialization of oxidative desulfurization methods.

Characterization of Polyallylamine/Polystyrene Sulfonate Polyelectrolyte Microcapsules Formed on Solid Cores: Morphology.

Polyelectrolyte microcapsules (PMC) based on polyallylamine and polystyrene sulfonate are utilized in various fields of human activity, including medicine, textiles, and the food industry, among others. However, characteristics such as microcapsule size, shell thickness, and pore size are not sufficiently studied and systematized, even though they determine the possibility of using microcapsules in applied tasks. The aim of this review is to identify general patterns and gaps in the study of the morphology of polyelectrolyte microcapsules obtained by the alternate adsorption of polystyrene sulfonate and polyallylamine on different solid cores. First and foremost, it was found that the morphological change in polyelectrolyte microcapsules formed on different cores exhibits a significant difference in response to varying stimuli. Factors such as ionic strength, the acidity of the medium, and temperature have different effects on the size of the microcapsules, the thickness of their shells, and the number and size of their pores. At present, the morphology of the microcapsules formed on the melamine formaldehyde core has been most studied, while the morphology of microcapsules formed on other types of cores is scarcely studied. In addition, modern methods of nanoscale system analysis will allow for an objective assessment of PMC characteristics and provide a fresh perspective on the subject of research.

Boosting Oxygen Reduction at Pt(111)|Proton Exchange Ionomer Interfaces through Tuning the Microenvironment Water Activity.

A proton exchange ionomer is one of the most important components in membrane electrode assemblies (MEAs) of polymer electrolyte membrane fuel cells (PEMFCs). It acts as both a proton conductor and a binder for nanocatalysts and carbon supports. The structure and the wetting conditions of the MEAs have a great impact on the microenvironment at the three-phase interphases in the MEAs, which can significantly influence the electrode kinetics such as the oxygen reduction reaction (ORR) at the cathode. Herein, by using the Pt(111)|X ionomer interface as a model system (X = Nafion, Aciplex, D72), we find that higher drying temperature lowers the onset potential for sulfonate adsorption and reduces apparent ORR current, while the current wave for OHad formation drops and shifts positively. Surprisingly, the intrinsic ORR activity is higher after properly correcting the blocking effect of Pt active sites by sulfonate adsorption and the poly(tetrafluoroethylene) (PTFE) skeleton. These results are well explained by the reduced water activity at the interfaces induced by the ionomer/PTFE, according to the mixed potential effect. Implications for how to prepare MEAs with improved ORR activity are provided.

Selective perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) adsorption by nanoscale zero-valent iron (nZVI): performance and mechanisms

This study investigated the adsorption of PFOA and PFOS by nanoscale zero-valent iron, revealing the adsorption mechanism and enriching the understanding of environmental remediation.

Enhanced electrochemical properties of nickel-cobalt hydroxide nanosheet by high-gravity liquid phase modification

Nickel-cobalt layered double hydroxide (Ni-Co LDH) nanosheet has a low specific capacity and poor rate capability. This study uses an anionic surfactant to modify Ni-Co LDH by the high-gravity liquid-phase method. The results reveal that the sodium dodecyl benzene sulfonate (SDBS) adsorption and intercalation can increase electrode interface area, enlarge interlayer spacing of Ni-Co LDH, accelerate the diffusion of electrolyte ions, and thus improve its specific capacity and rate capability. Compared with the stirred flow field, the high gravity further intensifies the surface adsorption and substitution intercalation of SDBS, resulting in a bigger interface area and interlayer spacing of Ni-Co LDH, which is more favorable to its specific capacity and rate capability. The specific capacity of Ni-Co LDH after high-gravity modification is 984 C g−1 (2187 F g−1, 2 A g−1), and its capacity retention rate reached 80 % (1–30 A g−1), significantly higher than that of the untreated one. Besides, an electrochemical kinetic study shows that a high gravity modification substantially enhances the ion diffusion rate. The modified materials under a high gravity field are utilized as anode materials and activated carbons (ACs) as cathode materials to construct supercapacitors. The Ni-Co LDHs//AC has a 50 Wh kg−1 energy density with well cycling stability. The paper proposes a high-gravity liquid-phase modification method to explore potential high-performance electrode materials.

Improving gold recovery in carbonaceous gold ores using naphthalene sulphonate as a blanking agent

Naphthalene sulphonate was used as a blanking agent to treat a gold ore with an 87% preg-robbing index with the aim of improving the gold recovery during carbon-in-leach (CIL). The adsorption of naphthalene sulfonate, an anionic surfactant, was significantly higher under acid conditions: 0.51 µmol/g at pH 2.4 and 0.24 µmol/g at pH 11.3. However, conditioning the ore at the expected pH for 30 mins prior to adsorption led to a similar loading of naphthalene sulfonate regardless of the initial solution pH. The gold recovery of the ore was improved from 57% to 80% during CIL, after the ore was treated with 4.48 mM naphthalene sulfonate at pH 11.3 adjusted by 4.36 mM Ca(OH)2. The main factor, that was likely responsible for the improved gold recovery, was the passivation of the adsorption sites on the carbonaceous matter in the ore. The impact of electrostatic repulsion of Au(CN)2- was negligible due to relatively unchanged surface potential before and after naphthalene sulphonate adsorption.

The Influence of Surface Heterogeneity of Fluorite on the Adsorption of Alkyl Sulfonates

Surface heterogeneity of minerals can significantly affect the adsorption of collectors. Petroleum sulfonate is widely used as a fluorite collector, but how the surface heterogeneity of fluorite influences the adsorption of alkyl sulfonates remains unknown. Herein, two kinds of surface heterogeneity situations, i.e., edge and (1 1 1) _vacancy, were modeled, and the adsorption of sodium dodecyl sulfonate on them was simulated. The results show that the stable adsorption configuration of sodium dodecyl sulfonate on the edge was in a bridged mode, and the stable interaction configuration with vacancy was in a tridentate mode. The 2p orbit of fluorine on the surface of the edge and the vacancy could hinder collector adsorption. After adsorption, the 3d orbit of calcium interacted with the collector orbit above Fermi level, and moved towards the lower energy level, benefiting the adsorption process. It was also found that the adsorption intensity/strength of alkyl sulfonate on fluorite was directly proportional to the interaction intensity of the collector with the 3d orbits of calcium ions on the surface and vacancy. Therefore, the rough fluorite surface had a stronger adsorption effect on the collector, and the existence of vacancy could improve the surface adsorption energy, and thus enhance the adsorption of the collector on the fluorite surface. The rough fluorite surface requires high collector concentration to achieve saturated monolayer adsorption, so increasing vacancy was the better choice to improve the adsorption capacity of alkyl sulfonate on the fluorite surface. This study provides novel insights into the flotation mechanism, in the context of surface heterogeneity, and could guide the design of high-performance collectors for fluorite ore flotation.

Surfactant Additives Containing Hydrophobic Fluorocarbon Chains and Hydrophilic Sulfonate Anion for Highly Reversible Zn Anode.

Aqueous zinc-ion batteries (AZIBs) show enormous potential as a large-scale energy storage technique. However, the growth of Zn dendrites and serious side reactions occurring at the Zn anode hinder the practical application of AZIBs. For the first time, we reported a fluorine-containing surfactant, i.e., potassium perfluoro-1-butanesulfonate (PPFBS), as an additive to the 2 M ZnSO4 electrolyte. Benefitting from its hydrophilic sulfonate anion and hydrophobic long fluorocarbon chain, PPFBS can promote the uniform distribution of Zn2+ flux at the anode/electrolyte interface, allowing the Zn/Zn cell to cycle for 2200 h. Furthermore, PPFBS could inhibit side reactions due to the existence of the perfluorobutyl sulfonate (C4F9SO3-) adsorption layer and the presence of C4F9SO3- in the solvation structure of Zn2+. The former can reduce the amount of H2O molecules and SO42- in contact with the Zn anode and C4F9SO3- entering the Zn2+-solvation structure by replacing SO42-. The Zn/Cu cell exhibits a superior average CE of 99.47% over 500 cycles. When coupled with the V2O5 cathode, the full cell shows impressive cycle stability. This work provides a simple, effective, and economical solution to the common issues of the Zn anode.

Alpha olefin sulfonate (AOS) adsorption on calcite and dolomite: Role of active complex formation and electrical double layer capacitance

The surfactant injection process is used in the oil industry for various purposes, such as changing the wettability of the rock surfaces, decreasing the interfacial tension, and consequently increasing the oil production, using it as a de-emulsification agent and base material for foam formation. Usually in surfactant injection processes, one of the important issues is surfactant loss which can affect the economic and operational feasibility of the method. One of the phenomena involved in surfactant loss is its adsorption on the rock. In this study, the effective factors of the surfactant adsorption phenomenon in an electrolyte-mineral solid system were investigated. For this purpose, the mechanisms of surface potential formation, the electrical double layer capacitance and its relationship with the zeta potential, repulsive and attractive forces between suspended particles, and changes in the Gibbs energy of the multi-component system as a result of adsorption were explained. Laboratory measurements of adsorption of an anionic surfactant, alpha olefin sulfonate (AOS), on calcite and dolomite surfaces were performed. For this purpose, ultraviolet and infrared spectroscopy measurements were conducted for each test. Results showed that increasing the salinity, from 0.001 M to 0.1 M, reduced the adsorption of AOS on calcite by about 50%. The presence of the divalent cation of magnesium, and the divalent anion of sulfate, causes the release of the sulfonate anion from the unstable complex of calcium sulfonate and consequently adsorption reduction. The magnesium sulfonate complex is stable and more active than the calcium sulfonate complex. Therefore, the adsorption of sulfonate on dolomite was negligible. Considering that sulfonates are one of the most common surfactants used in enhanced oil recovery processes, the results of this study can be effective in controlling its adsorption phenomenon. Also, the results of this study can be used in the design of wettability alteration processes.

Improved Oxygen Reduction Reaction (ORR) Kinetics Via Interfacial Engineering

Sluggish oxygen reduction reaction (ORR) kinetics, even on the best available catalyst (Pt), is one of the major challenges in widespread commercialization of polymer electrolyte membrane fuel cells (PEMFC).1 Significant advances have been made towards making highly active Pt catalysts through nanostructuring, alloying, size, and shape control to mitigate these kinetic losses.2 An additional strategy for ORR activity enhancement is though the targeted engineering of the electrochemical interface. For example, Ionic liquid (IL) interlayers improve the ORR kinetics on bulk and nanostructured catalysts for both Pt and alloyed-Pt materials.3 Along with the kinetic enhancement, ionic liquid interlayers also mitigate the sulfonate adsorption on Pt and improve the durability of Pt/C thin films.4,5 Despite remarkable improvement in performance at half-cell and MEA-level, the mechanism of this improvement is not completely understood. In this work, we combine single crystal voltammetry with microkinetic modeling to analyze the mechanism of ORR enhancement in presence of ionic liquids. With iterative feedback between single crystal voltammetry and microkinetic model output, we establish the importance of accounting for lateral interactions between adsorbed oxygenated species by using real data informed adsorption isotherms. With our experimentally validated model, we show that the mechanism of impact of ILs on ORR activity is through exclusion of water and reduction in electrochemical interface solvation, yielding lower spectator hydroxyl coverages and a reduced barrier for hydroxyl removal, resulting in higher surface site availability during the ORR. This improved understanding will help design Pt-interfaces to moderate the interaction of the interfacial water network with Pt active sites, providing another strategy for improving ORR kinetics.

An Investigation on Mineral Dissolution and Precipitation in Cement-Stabilized Soils: Thermodynamic Modeling and Experimental Analysis

Thermodynamic modeling helps to reveal insights into the basic chemical kinetics of dissolution and precipitation in cementitious materials, but relevant applications to cement-stabilized soils have seldom been reported. Based on the thermodynamic database of Cemdata18 and the pore solution composition of cement-stabilized soils, this study formulated a specialized thermodynamic model, using essential thermodynamic constants for soil minerals that were calculated to ensure the model’s accuracy. Two commercial admixtures of alkaline activator and polynaphthalene sulfonate were selected for the different modification mechanisms and plain and modified cement-stabilized soils were prepared. Compressive strength was tested to determine the specimens for pore solution analysis and the influences of the admixture type and dose on dissolution and precipitation were investigated by modeling the ionic activity products and saturation indexes. An X-ray diffraction (XRD) analysis was performed to verify and complement the thermodynamic results. The major research findings were that (1) thermodynamic modeling can be reliably applied to cement-stabilized soils by providing the essential thermodynamic data and an appropriate product model, (2) the pozzolanic reaction is accelerated by increasing the OH− concentration in the pore solution, while the cement hydration is highly dependent on the dissolution of Ca(OH)2 and the relevant complexes and (3) the dissolution equilibrium of Ca(OH)2 is directly affected by the alkaline activator dissolution and is indirectly affected by the polynaphthalene sulfonate adsorption of the reactants.

Adsorption of sodium dodecyl benzene sulfonate on zeolitic imidazolate framework-8 synthesized using surfactant-free microemulsion as template

While surfactants created great convenience for the development of society, the abuse use of surfactants also brought about severe challenges, such as contamination to the environment and life, inactivation and degradation of nanomaterials due to the blockage of active sites. To this end, a surfactant-free microemulsion (SFME) was utilized here for the first time to prepare nanoscale zeolitic imidazolate framework-8 (ZIF-8) material for surfactant removal from wastewater. The results demonstrated that SFME can effectively control the crystal size of ZIF-8 nanoparticles, just like surfactant-based microemulsion (SBME) system, with a uniform particle size distribution from 20 to 40 nm, smaller and more integral than that was obtained by conventional solvothermal method. Nano ZIF-8 material can efficiently remove surfactant from the wastewater by adsorption, especially for anionic surfactants (sodium dodecyl benzene sulfonate (SDBS)). The adsorption of SDBS on nano ZIF-8 well fitted the pseudo-second order kinetic model and Langmuir adsorption model, with the highest adsorption capacity of 548 mg/g at 318 K. Compared with ZIF-8 based on SBME, ZIF-8 based on SFME showed higher adsorption capacity to SDBS, because of larger surface area and pore volume. The data of zeta potential, FT-IR, XPS and SEM-EDS revealed that the adsorption of SDBS on ZIF-8 not only involves the electrostatic attraction but also hydrophobic interaction including π-π and dispersion force interactions. The current study provides a simple, energy-efficient, green and sustainable route of synthesizing nano ZIFs, without worrying about the secondary pollution, and the as-synthesized can be used as a high-efficient adsorbent to remove the pollutant from water.

Coupling effects of tide and salting-out on perfluorooctane sulfonate (PFOS) transport and adsorption in a coastal aquifer

The adsorption of perfluorooctane sulfonate (PFOS) on sediments is thought to be enhanced by the ‘salting-out effect’ (SOE), which reduces contaminant solubility as water salinity increases. The process of salting-out has been observed for PFOS in surface estuaries and likely operates in ‘subterranean estuaries’, where tide-induced groundwater circulation creates a dynamic saltwater-freshwater mixing zone in the aquifer adjacent to the ocean. The presence of this dynamic interface between dense seawater and fresh groundwater modifies the flow path of land-derived organic contaminants. However, it is unclear how SOE combined with tidal forcing of salt water, affects the transport and fate of these contaminants in a subterranean estuary. Numerical studies of groundwater dynamics in a coastal aquifer are carried out using a modified version of SUTRA to investigate the behavior of PFOS, as it moves through an aquifer-ocean interface. Three adsorption scenarios are investigated: no adsorption and linear adsorption with a constant coefficient (Kd) and a salinity-dependent Kd (due to SOE). Without adsorption, point-injected PFOS moves and spreads as a plume around the margin of the tide-induced upper saline plume (USP). This is in agreement with previous studies showing that a contaminant plume follows the freshwater discharge path and exits the aquifer around the USP in the intertidal zone. The increase of tidal amplitude enlarges the USP, forcing the discharge points of freshwater and PFOS seaward. In the case of a constant Kd, PFOS concentration decreases in the groundwater as expected with an increase of PFOS residence time in the aquifer. The spatial distribution of the contaminant plume is similar to that of the ‘no adsorption’ case. In the case with the SOE, which enhances the solute adsorption in the saltwater zone, PFOS tends to be intercepted by the USP, concentrated at its center, and subsequently discharged with the tide-induced saltwater circulation. SOE reduces both peak PFOS discharge rate and plume dispersion. In addition, the PFOS flow path moves upward and the PFOS discharges above the USP. The findings highlight the potential importance of investigating the SOE of organic contaminants for benthic organisms when considering their transport and fate in tidally influenced coastal aquifers.

Characterization of a Sulfonated Poly(Ionic Liquid) Block Copolymer as an Ionomer for Proton Exchange Membrane Fuel Cells using Rotating Disk Electrode

Ionic liquid (IL) additives to both traditional and advanced oxygen reduction reaction (ORR) electrocatalysts have yielded remarkable improvements in catalyst performance and durability. However, incorporating ILs or IL-modified catalysts into the electrodes of a proton exchange membrane fuel cell (PEMFC) membrane electrode assembly (MEA) has proven to be challenging. Sulfonated poly(ionic liquid) block copolymers (S-PILBCP) present an opportunity to incorporate IL functionality directly into the ionomer, orthogonal to protonic conductivity. Here, we use a rotating disc electrode (RDE) to characterize the interface between a S-PILBCP and Pt catalyst in comparison to Nafion. Catalyst thin films prepared with S-PILBCP show an 80% improvement in the ORR activity over those containing Nafion. Thin films of S-PILBCP also show a significantly reduced degree of poisoning sulfonate adsorption on a Pt(111) surface in comparison to Nafion. These half-cell results provide useful insights that help to highlight the source of the impact of the S-PILBCP on PEMFC MEA performance.

Ionic Liquid Composite Electrocatalysts for the Oxygen Reduction Reaction in PEM Fuel Cells

The cathode catalyst layer (CCL) of the proton exchange membrane fuel cell (PEMFC) cathode requires a high amount of Pt to compensate for the sluggish oxygen reduction reaction (ORR) kinetics. Reducing the Pt loading in the CCL remains the major challenge in commercializing fuel cell devices. Recent developments enable up to 20-fold improvement in the activity of ORR electrocatalysts and facilitate a lower amount of Pt in the catalyst layer.1 However, these low-Pt-loaded cathodes show significant voltage losses at high current densities (HCD).2 These performance losses are associated with local oxygen transport resistances due to higher particle-particle distance and the interfacial resistance between Pt and PFSA-based ionomers.3 The interfacial resistance observed at the catalyst-ionomer interface is exacerbated with the thickness of the ionomer film on catalyst particles4 and specific adsorption of sulfonate groups.5 These challenges can be potentially addressed by modifying the catalyst-ionomer interface at fuel cell cathode. Protic and hydrophobic Ionic liquids (ILs) are known to enhance the ORR performance of state-of-the-art catalysts in half cell experiments.6 Our research group has previously shown that an ionic liquid interlayer on the Pt surface mitigates the specific adsorption of sulfonate groups. Despite remarkable half-cell performance of ionic liquid modified catalysts (100-150%), ionic liquid incorporated CCLs show only a modest improvement (10-15%).7 Inhomogeneous distribution of ionic liquids in the catalyst layer and potential loss of ionic liquids during fuel cell operation are possible reasons behind this discrepancy. The use of sulfonated polymerized ionic liquid block copolymer (SPILBCP) as an ionomer presents a novel method to incorporate ionic liquids in the catalyst layer. SPILBCP has sulfonated domains to enable proton conduction and ionic liquid domains to facilitate oxygen transport and mitigate sulfonate adsorption. In this work, we implement rotating disk electrode (RDE) techniques to analyze a polymeric ionic liquid block copolymer (SPILBCP) as an ionomer for the PEMFC cathode. We found that Pt/C catalyst films prepared using PILBCP show two-fold improvement over those prepared using Nafion, a state-of-the-art ionomer. We use the CO displacement technique to show that PILBCP thin films exhibit a lower degree of sulfonate adsorption than Nafion on a highly ordered Pt surface. Furthermore, thin films of SPILBCP and Nafion show comparable proton conductivity and oxygen permeability. These results support the recent finding showing up to two-fold improvement in the kinetic activity of PEMFCs using SPILBCP as a catalyst binder. 8 References Shao M, Chang Q, Dodelet JP, Chenitz R. Recent Advances in Electrocatalysts for Oxygen Reduction Reaction. Chem Rev. 2016;116(6):3594-3657. doi:10.1021/acs.chemrev.5b00462 Kongkanand A, Mathias MF. The Priority and Challenge of High-Power Performance of Low-Platinum Proton-Exchange Membrane Fuel Cells. J Phys Chem Lett. 2016;7(7):1127-1137. doi:10.1021/acs.jpclett.6b00216 Weber AZ, Kusoglu A. Unexplained transport resistances for low-loaded fuel-cell catalyst layers. J Mater Chem A. 2014;2(41):17207-17211. doi:10.1039/c4ta02952f Sasikumar G, Ihm JW, Ryu H. Dependence of optimum Nafion content in catalyst layer on platinum loading. J Power Sources. 2004;132(1-2):11-17. doi:10.1016/j.jpowsour.2003.12.060 Garrick TR, Moylan TE, Yarlagadda V, Kongkanand A. Characterizing electrolyte and platinum interface in PEM fuel cells using CO displacement. J Electrochem Soc. 2017;164(2):F60-F64. doi:10.1149/2.0551702jes Snyder J, Fujita T, Chen MW, Erlebacher J. Oxygen reduction in nanoporous metal-ionic liquid composite electrocatalysts. Nat Mater. 2010;9(11):904-907. doi:10.1038/nmat2878 Snyder J, Livi K, Erlebacher J. Oxygen reduction reaction performance of [MTBD][beti]-encapsulated nanoporous NiPt alloy nanoparticles. Adv Funct Mater. 2013;23(44):5494-5501. doi:10.1002/adfm.201301144 Li Y, Cleve T Van, Sun R, et al. Modifying the Electrocatalyst-Ionomer Interface via Sulfonated Poly ( Ionic Liquid ) Block Copolymers to Enable High-Performance Polymer Electrolyte Fuel Cells. 2020. Figure 1

Adsorption of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) emerging contaminants on Y and silver-Y exchanged zeolites using thermal analysis and X-ray diffraction facilities

Adsorption of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) emerging contaminants on Y and silver-Y exchanged zeolites using thermal analysis and X-ray diffraction facilities

Influence of intramolecular charge coupling on intermolecular interactions of polycarboxybetaines in aqueous solution and in polyelectrolyte multilayers

The present paper deals with the correlation between intramolecular and intermolecular interactions of polycarboxybetaines. The degree of coupling between the opposite charges within the polycarboxybetaine molecules was varied by spacers of different length and by the substitution of additional alkyl chains at the quaternary nitrogen atom. In order to check intermolecular interactions between polycarboxybetaines, SANS measurements were carried out at aqueous polycarboxybetaines solutions. For getting information about the interaction with an oppositely charged polyelectrolyte, multilayers were formed by alternating adsorption of polystyrene sulfonate (PSS) and polycarboxybetaines from aqueous solutions. The occurrence of a structure peak in SANS spectra and the ability to form polyelectrolyte multilayers provide an indicator for the polyelectrolyte character of some of the studied polycarboxybetaines. Not only the charge but also the hydrophobicity of the polycarboxybetaines has a pronounced effect on the chain conformation and therefore on the thickness of the polyelectrolyte multilayers. The results show that small differences in molecular architecture lead to pronounced differences in intermolecular interactions.

Adsorption and solid-phase photocatalytic degradation of perfluorooctane sulfonate in water using gallium-doped carbon-modified titanate nanotubes

Perfluorooctane sulfonate (PFOS) has drawn increasing attention due to its omnipresence and adverse health effects. We prepared a new adsorptive photocatalyst, Ga/[email protected], based on activated carbon and TiO2, and tested the adsorption and subsequent solid-phase photodegradation of PFOS. Ga/[email protected] showed faster adsorption kinetics and higher affinity for PFOS than the parent AC, and could degrade 75.0% and mineralize 66.2% of pre-sorbed PFOS within 4-h UV irradiation. The efficient PFOS photodegradation also regenerates Ga/[email protected], allowing for repeated uses without invoking chemical regenerants. The superior photoactivity is attributed to the oxygen vacancies, which not only suppressed recombination of the e−/h+ pairs, but also facilitated O2− generation. Both h+ and O2− played critical roles in the PFOS degradation, which starts with cleavage of the sulfonate group and converts it into PFOA that is then decarboxylated and defluorinated following the stepwise defluorination mechanism. Ga/[email protected] holds the potential for more cost-effective PFOS degradation.

Mechanistic insights into fast adsorption of perfluoroalkyl substances on carbonate-layered double hydroxides

Layered double hydroxide (LDH) with the metal composition of Cu(II)Mg(II)Fe(III) was prepared as an adsorbent for fast adsorption of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA). 84% of PFOS and 48% of PFOA in relation to the equilibrium state were adsorbed in the first minutes of contact with 0.1 g/L of suspended µm-sized LDH particles. The adsorption mechanisms of PFOS and PFOA on the CuMgFe-LDH were interpreted. Hydrophobic interactions were primarily responsible for the adsorption of these compounds in accordance with the different adsorption affinities of long-chain (C8, Kd = 105 L/kg) and short-chain (C4, Kd = 102 L/kg) perfluorinated carboxylic acids. PFOA adsorption on CuMgFe-LDH was strongly suppressed under alkaline conditions while PFOS uptake was only slightly affected in the pH range from 4.3 to 10.7, indicating a significant role of electrostatic interactions for PFOA adsorption. The adsorption of PFOS and PFOA was rather insensitive to competition by monovalent anions. The previously reported ‘memory effect’ of calcined CuMgFe-LDH for sorption of organic anions was not confirmed in the present study. Spent CuMgFe-LDH could be easily regenerated by extraction with 50 vol% methanol in water within 1 h and maintained a high PFOS removal in subsequent usage cycles.

Density functional theory study of perfluorooctane sulfonate adsorption on fluorinated graphene

Density functional theory calculations are carried out to explore the adsorption behaviour of perfluorooctane sulfonate (PFOS) on pristine and fluorinated graphene. Then, the effects of different degrees of fluorination of graphene on the adsorption of PFOS are systematically investigated by analysis of the adsorption energy (E ads), electron transfer and partial density of states. Finally, the unique adsorption behaviour of PFOS on graphene and fluorinated graphene is demonstrated by a companion study of four other organic molecules, namely hepta-fluorobutyric acid, phenanthrene, phenol and perfluorooctanoate.