Highly selective thin-film composite membranes for hot hydrogen sieving are prepared via the pyrolysis of thin cyclomatric polyphenoxy phosphazene films that are prepared via a non-conventional interfacial polymerization of hexachlorocyclotriphosphazene with 1,3,5-trihydroxybenzene or m-dihydroxybenzene. The presence of the cyclic phosphazene ring within the weakly branched polymer films gives rise to a distinct thermal degradation evolution, with an onset temperature of around 200 °C. For the trihydroxybenzene derived material, the hydrogen permselectivity of the films shows a maximum pyrolysis temperature of around 450 °C. At this temperature a compact atomic structure is obtained that comprises mostly disordered carbon and accommodates P–O–C and P–O–P bonds. During thermal treatment, these films reveal molecular sieving with permselectivities exceeding 100 for H₂/N₂, H₂/CH₄, and H₂/CO₂, and a hydrogen permeance of 2 × 10⁻¹⁰ to 1.5 × 10⁻⁸ mol/m²/s/Pa (0.6-44.8GPU), at 200 °C. At ambient temperatures, thin films are very effective barriers for small gas molecules. Because of the inexpensive facile synthesis and low- temperature pyrolysis, the polyphosphazene films have the potential for use in high-temperature industrial gas separations, as well as for use as barriers such as liners in high- pressure hydrogen storage vessels at ambient temperature.

A series of cyclomatrix polyphosphazene films have been prepared by nonaqueous interfacial polymerization (IP) of small aromatic hydroxyl compounds in a potassium hydroxide dimethylsulfoxide solution and hexachlorocyclotriphosphazene in cyclohexane on top of ceramic supports. Via the amount of dissolved potassium hydroxide, the extent of deprotonation of the aromatic hydroxyl compounds can be changed, in turn affecting the molecular structure and permselective properties of the thin polymer networks ranging from hydrogen/oxygen barriers to membranes with persisting hydrogen permselectivities at high temperatures. Barrier films are obtained with a high potassium hydroxide concentration, revealing permeabilities as low as 9.4 × 10^-17 cm³ cm cm^-2 s^-1 Pa^-1 for hydrogen and 1.1 × 10^-16 cm³ cm cm^-2 s^-1 Pa^-1 for oxygen. For films obtained with a lower concentration of potassium hydroxide, single gas permeation experiments reveal a molecular sieving behavior, with a hydrogen permeance of around 10^-8 mol m^-2 s^-1 Pa^-1 and permselectivities of H₂/N₂ (52.8), H₂/CH₄ (100), and H₂/CO₂ (10.1) at 200 °C.

An interfacial polymerization process is introduced for the fabrication of thermally stable cyclomatrix poly(phenoxy)phosphazenes thin-film composite membranes that can sieve hydrogen from hot gas mixtures. By replacing the conventionally used aqueous phase with dimethyl sulfoxide/potassium hydroxide, a variety of biphenol molecules are deprotonated to aryloxide anions that react with hexachlorocyclotriphosphazene dissolved in cyclohexane to form a thin film of a highly cross-linked polymer film. The film membranes have persistent permselectivities for hydrogen over nitrogen (16–27) and methane (14–30) while maintaining hydrogen permeances in the order of (10⁻⁸–10⁻⁷ mol m⁻²s⁻¹Pa⁻¹) at temperatures as high as 260 °C and do not lose their performance after exposure to 450 °C. The unprecedented thermal stability of these polymer membranes opens the potential for industrial membrane gas separations at elevated temperatures.

Recovery of ammonia (NH₃) from residual waters offers various reuse opportunities, such as the production of fertilisers and the generation of electricity and heat. However, simultaneous evaporation of water (H₂O) during NH₃ stripping under vacuum results in diluted recovered NH₃ gas with high H₂O contents. Whereas porous gas-permeable membranes are already used for vacuum NH₃ stripping, the use of non-porous silica-based pervaporation (PV) membranes showed promising results in recent literature, with respect to more selective transfer of NH₃ compared to H₂O. In this study, we assessed the selectivity of NH₃ over H₂O transfer (S_NH3/H2O) for different types of membranes, under various hydraulic conditions and feed water compositions. The three following membranes were tested: a porous gas-permeable polytetrafluoroethylene (PTFE) membrane, a hydrophilic (Hybrid Silica PV) membrane and a hydrophobic polydimethylsiloxane PV (PDMS PV) membrane. For the PTFE and the Hybrid Silica PV membrane, S_NH3/H2O ranged between 0.1 and 0.4, indicating that the transfer of NH₃ was consistently less preferred compared to the transfer of H₂O. The preference for H₂O over NH₃ transfer through the membranes at various hydraulic conditions and feed water compositions can be assigned to the similarity in polarity and kinetic diameter of NH₃ and H₂O and the low relative concentration of NH₃ in the used feed waters (approximately 0.1–1.0 wt%). The PDMS PV membrane showed negligible NH₃ transfer and deteriorated rapidly during the NH₃ stripping experiments. The S_NH3/H2O of both gas-permeable and PV membranes was higher for unsteady than for steady hydraulic conditions. Furthermore, the S_NH3/H2O of the both PTFE and the Hybrid Silica decreased when the ionic strength of the feed water increased from 0.0 to 0.8 mol∙L⁻¹ and when the NH₃ feed water concentration increased from 1 to 10 g∙L⁻¹. According to the results, the used PV membranes did not show selectivity of NH₃ over H₂O transfer. In fact, the used PV membranes consistently had a lower S_NH3/H2O than the PTFE membrane. Hence, the dense silica-based PV membranes did not allow for the recovery of gaseous NH₃ from water, with lower H₂O content in the recovered gas, compared to porous PTFE membranes.

We investigated in detail the permeation selectivity in the electro-dialysis of Na⁺, K⁺, Mg²⁺ and Ca²⁺ in both binary and quaternary mixtures using a supported liquid membrane (SLM). The SLM consisted of the organic liquid 2-nitrophenyl octyl ether (NPOE) containing a lipophilic anion, i.e. tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, as the cation-exchanging site, which was used to fill the pores of the supporting membrane Accurel^R. We first determined the electro-phoretic mobilities of the migrating cations in single salt solutions, yielding: Na⁺ > K⁺ > Mg²⁺ > Ca²⁺. This order reflects the different size of the migrating cations. The monovalent cations Na⁺ and K⁺ migrate in the dehydrated state and the divalent cations Ca²⁺ and Mg²⁺ migrate in a (partly) hydrated state, a conclusion was supported by Karl Fisher titrations. Both binary and quaternary salt experiments showed a permeation selectivity in the following order: K⁺ > Na⁺ > Ca²⁺ > Mg²⁺. Since this order does not correlate with the order of electro-phoretic mobilities, we have determined the ion-exchange selectivity constant (K_ex) and found: K⁺ > Ca²⁺ > Mg²⁺ ≈ Na⁺. We conclude that the overall permeation selectivity is determined by the combination of ion-exchange selectivity and electro-phoretic mobility of the cations present in the membrane.

Chemical loss such as surfactants and alkalis by adsorption to reservoir rock surface is an important issue in enhanced oil recovery (EOR). Here, we investigated the adsorption behaviors of anionic surfactants and alkalis on silica for the first time as a function of temperature using quartz crystal microbalance with dissipation (QCM-D). The results demonstrated that the temperature dependent critical micelle concentration of alcohol alkoxy sulfate (AAS) surfactant can be quantitatively described by the thermodynamics parameters of micellization, showing a mainly entropy-driven process. AAS adsorption was mediated under varying temperature conditions, by divalent cations for bridging effect, monovalent cations competitive for adsorption sites but not giving cation bridging, pH regulation of deprotonated sites of silica, presence of alkoxy groups in the surfactants, and synergistic effect of surfactant co-injection. The addition of organic alkalis can enhance the overall adsorption of the species with AAS, whereas inorganic alkali of Na₂CO₃ had capability of the sequestration of the divalent ions, whose addition would reduce AAS adsorption. The typical AAS adsorption indicated a non-rigid multilayer, estimated to have between 2 and 5 layers, with a likely compact bilayer followed by disorganized and unstable further layering. The new fundamental understanding about temperature effect on surfactants and alkalis adsorption contributes to optimizing the flooding conditions of chemicals and developing more efficient mitigation strategies.

High Na⁺ levels are detrimental for most crops. Selective membranes provide the possibility for the selective removal of Na⁺ while preserving beneficial ion species. The challenge is to separate two ion species of the same charge. This study evaluates the implementation of an electrodialysis (ED) system equipped with a supported liquid membrane (SLM) and a commercially available monovalent cation-selective membrane (CIMS) in the treatment of greenhouse drainage water. The SLM shows a (minimum) K⁺ over Na⁺, Ca²⁺ and Mg²⁺ permselectivity of 9, 15 and 30, respectively. Whereas the CIMS holds a high K⁺ over Ca²⁺ and Mg²⁺ permselectivity of 10 and 16, respectively, the K⁺ over Na⁺ permselectivity is just 1.3. With the experimentally obtained membrane characteristics at hand, the treatment of drainage water was simulated by a two-steps process with the two membrane types operating in series. Using real-life operational parameters, analysis revealed the optimal configuration and the ability to recover 96% of the K⁺ and approximately 80% of the water, Ca²⁺ and Mg²⁺. Summarized, this study not only shows the efficient separation of two ion species of the same valance but also the implementation of this technology in a real-life application.

With the increasing demand for efficient extraction of residual oil, enhanced oil recovery (EOR) offers prospects for producing more reservoirs’ original oil in place. As one of the most promising methods, chemical EOR (cEOR) is the process of injecting chemicals (polymers, alkalis, and surfactants) into reservoirs. However, the main issue that influences the recovery efficiency in surfactant flooding of cEOR is surfactant losses through adsorption to the reservoir rocks. This review focuses on the key issue of surfactant adsorption in cEOR and addresses major concerns regarding surfactant adsorption processes. We first describe the adsorption behavior of surfactants with particular emphasis on adsorption mechanisms, isotherms, kinetics, thermodynamics, and adsorption structures. Factors that affect surfactant adsorption such as surfactant characteristics, solution chemistry, rock mineralogy, and temperature were discussed systematically. To minimize surfactant adsorption, the chemical additives of alkalis, polymers, nanoparticles, co-solvents, and ionic liquids are highlighted as well as implementing with salinity gradient and low salinity water flooding strategies. Finally, current trends and future challenges related to the harsh conditions in surfactant based EOR are outlined. It is expected to provide solid knowledge to understand surfactant adsorption involved in cEOR and contribute to improved flooding strategies with reduced surfactant loss.

Organic solvent nanofiltration (OSN) is gradually expanding from academic research to industrial implementation. The need for membranes with low and sharp molecular weight cutoffs that are able to operate under aggressive OSN conditions is increasing. However, the lack of comparable and uniform performance data frustrates the screening and membrane selection for processes. Here, a collaboration is presented between several academic and industrial partners analyzing the separation performance of 10 different membranes using three model process mixtures. Membrane materials range from classic polymeric and thin film composites (TFCs) to hybrid ceramic types. The model solutions were chosen to mimic cases relevant to today's industrial use: relatively low molar mass solutes (330–550 Da) in n-heptane, toluene, and anisole.

In view of enhanced oil recovery, the adsorption behavior of surfactants is usually monitored on smooth model rock surfaces using quartz crystal microbalance with dissipation (QCM-D). However, this is an impractical situation as the effect of the surface roughness of reservoir rocks and its role in surfactant adsorption processes are not yet completely understood. The coupling of electrochemical techniques and QCM-D in one analysis setup (EQCM-D) provides a new methodology to explore complex surfactant adsorption processes. In this work, a uniform, rough, and well-covered model CaCO3 surface was obtained on gold and platinum sensors to model carbonate rocks. This was achieved by the electrochemically formed hydroxide ions in the presence of bicarbonate and calcium ions, by which the controlled deposition of CaCO3 resulted in sensor surface coverages in the range 35-40%. Before using the deposited CaCO3 surfaces, the adsorption of anionic surfactant alcohol alkoxy sulfate (AAS) on a smooth commercially available CaCO3 surface was studied with varying CaCl2 concentrations. For the first time, the structure and characteristics of the formed AAS layer were quantitatively described, indicating the formation of an incomplete bilayer. Compared to the smooth CaCO3 surface, an increase in the frequency shift from 5 to 15 times was observed in sensors covered with rough CaCO3 deposit. This observation was primarily attributed to the rougher surfaces that possess more adsorption sites for AAS binding and also to the effect of liquid trapping, inducing additional frequency shifts. The obtained results show that surfactant adsorption on rough surfaces was vastly different from that on smooth surfaces, and they provide a better understanding of the adsorption behavior of surfactants to mineral surfaces.

Surfactant losses by adsorption to rock surfaces make surfactant-based enhanced oil recovery economically less feasible. We investigated polyacrylate (PA) as a sacrificial agent in the reduction of anionic surfactant adsorption with focus on calcite surfaces by using quartz crystal microbalance with dissipation monitoring. It was found that the adsorption of the anionic surfactant alcohol alkoxy sulfate (AAS) followed a Langmuir adsorption isotherm, and the adsorbed amount reached saturation above its critical micellar concentration. Adsorption of PA was a much slower process compared to AAS adsorption. Increasing the calcium ion concentration also increased the amount of AAS adsorbed as well as the mass increase rate of PA adsorption. Experimental results combined with density functional theory calculations indicated that calcium cation bridging was important for anionic surfactant AAS and PA adsorption to calcite surfaces. To effectively reduce the amount of surfactant adsorption, it was needed to preflush with PA, rather than by a simultaneous injection. Preflushing with 30 ppm of PA gave a reduction of AAS adsorption of 30% under high salinity (HS, 31,800 ppm) conditions, compared to 8% reduction under low salinity (LS, 3180 ppm) conditions. In the absence of PA, the amount of adsorbed AAS was reduced by already 50% upon changing from HS to LS conditions. Lower calcium ion concentrations, as under LS conditions, contributed to this observation. On different mineral surfaces, PA reduced the AAS adsorption in the order of alumina > calcite > silica. These results offer important insights into mitigating surfactant adsorption using PA polyelectrolyte as sacrificial agent and contribute to improved flooding strategies with reduced surfactant loss.

Calcium carbonate (CaCO₃) deposition plays a significant role in processes such as scale formation in power plants and in oil or gas production wells. The development of appropriate methods based on well suitable in situ sensors is important to evaluate and predict the deposition process. In this study, a combination of electrochemical techniques and quartz crystal microbalance with dissipation monitoring (QCM-D) in one analysis setup (EQCM-D) was used for the first time to monitor the CaCO₃ deposition in real time and provide kinetic details of the CaCO₃ deposition process. Through recording the frequency change of quartz crystal sensors, it allows us to perform a quantitative analysis of the morphology, coverage, deposition rate, and mass changes with nanogram sensitivity. By varying the applied voltage, it was found that a lower applied voltage resulted in more deposition of CaCO₃ mass and increase of the thickness of the deposited layer. Under the absence of flow, the CaCO₃ growth rate switched from accelerating to decelerating and this point is characterized by an inflection point (IP). A lower applied voltage resulted in a lower IP. Increasing Ca²⁺ and HCO₃⁻ concentrations, both the deposited amount of CaCO₃ mass and coating thickness increased correspondingly. With the addition of 50 mM Mg²⁺, a reduction in the deposition rate of CaCO₃ as high as 73% was achieved. The higher the Mg²⁺ concentration, the larger the deposition rate reduction, which was attributed to the incorporation of Mg²⁺ into the growing CaCO₃ mineral, resulting in the reduction of growth sites (inhibiting effect). The obtained results contribute to a better understanding of electrochemically induced CaCO₃ deposition and provide valuable insights into the determination of optimal precipitation parameters, with the aim to optimize industry scaling and anti-scaling processes.

This work describes a facile approach allowing Dibenzoyl-L-Cystine (DBC) based hydrogel controlled deposition and controlled detachments over a conducting support. The method itself is an electrochemically assisted approach, where the water oxidation at the electrode surface results in a local pH drop inducing DBC gelation and hydrogel formation. We have comprehensively described the possibility of the hydrogel shaping by alternating the anodic deposition potential, DBC concentration and finally the working electrode geometry. The latter includes macro-electrodes in a form of platinum discs having diameter equal to 200 and 500 μm; hexagonal arrays of circular platinum microelectrodes with a diameter of a single electrode equal to 5 or 10 μm and custom made platinum microelectrodes, having the shape of circles, triangles and squares, that are used to shape the microgels. Over the course of our work we were able to define the conditions to form a number of different hydrogel shapes such as: (i) flat and planar deposits; (ii) hemispherical deposits with an oxygen bubble pocket; (iii) spongy hydrogel structures or (iv) hemispherical micro-cups build from radially oriented DBC fibres directionally growing from the support. Furthermore, we were also able to remotely form and then detach the hydrogel deposit in the initial formulation solution using only an electrochemical trigger. Our work represents a solid proof of concept and opens a number of new avenues for the electrochemically assisted soft matter fabrication down to micrometre scale.

In this work, we have simultaneously examined, electrochemically driven deposition of three proteins (haemoglobin, acid phosphatase, and α-amylase) and silica films at a polarized liquid–liquid interface. The interfacial adsorption of the proteins occurs efficiently within the acidic pH range (pH = 2–4). The interfacial charge transfer reactions recorded in the presence of fully positivity charged macromolecules were followed with cyclic voltammetry on the positive side of the potential window. Faradaic currents attributed to the presence of proteins in the aqueous phase appeared for concentrations equal to ca. 0.1 µM for haemoglobin and acid phosphatase and ca. 1 µM for the α-amylase. Concomitant deposition of silica films was achieved via the addition of tetraethoxysilane molecules to the organic phase (1,2-dichloroethane). The hydrolysis and condensation reactions of tetraethoxysilane were controlled via the interfacial transfer of H⁺ coinciding with the potential for protein adsorption. The effect of tetraethoxysilane concentration – up to 50% by volume – revealed significant shrinkage of the potential window (the region where capacitive currents are recorded). The optimized platform was then used to prepare silica-proteins co-deposits. These could be easily collected from the interface and further analyzed with infrared spectroscopy and transmission electron microscopy.

Adsorption behavior of surfactants to rock surfaces is an important issue in oil recovery, especially in the process of surfactant flooding. The surfactant loss through adsorption to rock surfaces makes such process economically less feasible. Here, we investigated the adsorption behavior of anionic surfactants (alcohol alkoxy sulfate, AAS) onto silica with quartz crystal microbalance with dissipation monitoring. The results demonstrated that the surfactant adsorption followed the Langmuir adsorption isotherm. Up to solution pH 10, surfactant adsorption slightly increased with increasing pH. The higher pH leads to more anionic surface sites for binding with an anionic surfactant with the help of a calcium cation bridging. The amount of anionic surfactant binding also increases with increasing calcium ion concentration up to 50 mM. It was found that sodium ions were able to exchange calcium ions near the silica surface, which would reduce the affinity for surfactant adsorption. The effect of the polyanion polystyrene sulfonate (PSS) on the anionic AAS adsorption was investigated to learn the possible competitive adsorptions. Indeed, this was found. Upon addition of 50 ppm PSS to a 0.05 wt% AAS containing solution, the adsorption of AAS was reduced by about 85 %. The obtained results show the interplay of different interacting species affecting the overall degree of anionic surfactant adsorption to silica surfaces. Optimal tuning of the process conditions according to these results will contribute to a more efficient use of anionic surfactants in enhanced oil recovery.

We have investigated the conditions of colloidal stability of silica nanoparticles smaller than 100 nm for their applications in enhanced oil recovery (EOR), especially pertaining to chemical flooding processes. Using zeta sizer and dynamic light scattering techniques, the stability of silica nanoparticle (SNP) dispersions has been investigated by variation of the pH, composition of salt solutions, addition of surfactants and polyelectrolytes. Such conditions can be encountered in oil reservoirs. It was found that changing pH from 5 to 10 had a negligible effect on the size of SNPs, whereas its zeta potential increased with increasing pH. Aggregation of SNPs is a partially reversible process for low degrees of aggregation in 500 mM NaCl, whereas observed strong aggregation in 1000 mM NaCl was irreversible. A critical aggregation concentration (CAC) was defined for the different salts investigated, above which the SNP dispersion became unstable at a fixed pH of 9.5. The CAC for NaCl was approximately 200 times higher than for CaCl₂ and MgCl₂. Our observations could not be explained completely by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Therefore, we have included non-DLVO interactions such as cation bridging, hydration forces, and steric effects. The additional presence of anionic alcohol alkoxy sulfate (AAS) surfactant slightly destabilized the SNP solution, but by the addition of polyacrylate (PA) was effectively stabilized. With increasing PA concentration, the CAC for both CaCl₂ and MgCl₂ increased. Upon addition of 100 ppm PA, the CAC increased by a factor of five compared to the situation in the absence of PA. Reducing the solution pH below 8.5, SNP can be stabilized in higher salinity in the presence of PA. The obtained results contribute to a better fundamental understanding of the SNP stability mechanism and a guide to optimize the SNP injection process with EOR chemicals.

A novel ion separation methodology using a cation-exchange membrane modified with iron oxide nanoparticles (Fe3O4 NPs) coated with polyhexamethylene guanidine (PHMG) is proposed. The separation is performed in an electrodialysis cell, where firstly phosphate is electro-adsorbed to the PHMG@Fe3O4 NP coating, followed by a desorption step by applying an electric current.

This study demonstrates the effective separation of alkali metal cations using a Supported Liquid Membrane (SLM) containing lipophilic, negatively charged borate moieties, operating under electro dialysis conditions. The selectivity of the membrane is essentially based on differences in dehydration energy and mobility between ion species. The system favors the ion species with the largest crystal radius, despite its lower mobility. In mixtures of K⁺ and Na⁺, the SLM separates K⁺ from Na⁺ with a separation efficiency ranging from ~20% to 90%, depending on the feed solution composition. With solutions containing either K⁺ or Na⁺ and Li⁺, the K⁺/Na⁺ over Li⁺ separation efficiency is nearly 100%. Addition of 15-crown-5 derivative does not improve SLM behavior, but slows down the K⁺ current by approximately 30% whereas the Na⁺ current remains unaffected. As supported by simulations, the free K⁺ and Na⁺ ratio in the membrane (and with that the current ratio) is entirely defined by partitioning and the feed concentration ratio, regardless the presence of 15-crown-5. As a result, the current ratio of two ion species can be described exclusively in terms of their feed concentrations and crystal radii because the latter parameter defines both partitioning and mobility.

Developing multifunctional polymeric binders is key to the design of energy storage technologies with value-added features. We report that a multigram-scale synthesis of perylene diimide polymer (PPDI), from a single batch via polymer analogous reaction route, yields high molecular weight polymers with suitable thermal stability and minimized solubility in electrolytes, potentially leading to improved binding affinity toward electrode particles. Further, it develops strategies for designing copolymers with virtually any desired composition via a subsequent grafting, leading to purpose-built binders. PPDI dye as both binder and electroactive additive in lithium half-cells using lithium iron phosphate exhibits good electrochemical performance.

In this work, the electrified liquid–liquid interface (LLI) was supported with the bare and polyelectrolyte modified fiberglass membranes. The permeability of these supports was then investigated with ion transfer voltammetry (ITV). This work descends from three mutually interconnected experimental tasks. (i) The study of an interfacial behavior of three polyelectrolytes, poly(ethyleneimine) (PEI), polystyrene sulfonate (PSS), and polyhexamethylene guanidine (PHMG) at the polarized LLI. (ii) Electrochemical characterization of the LLI supported by the unmodified fiberglass membrane. (iii) Polyelectrolyte multilayer placement, using layer-by-layer processing, at the surface of the fiberglass membrane and its further utilization as the support for the electrified LLI. Bare and modified membranes were characterized using ITV in the presence of a family of quaternary ammonium cations: tetramethylammonium (TMA⁺), tetraethylammonium (TEA⁺), tetrapropylammonium (TPrA⁺) and tetrabutylammonium (TBA⁺) initially dissolved in the aqueous phase as the chloride salts. The ionic currents related to their transmembrane transfer were affected already after the first polyelectrolyte layer placement. In addition to electrochemistry, the modification process was followed using several complementary techniques, including optical microscopy (OM), atomic force microscopy (AFM), infra-red (IR) spectroscopy, and scanning electron microscopy (SEM). The proposed methodology offers very simple, fast, and versatile (having in mind the available selection of functional polyelectrolytes) protocol for a membrane preparation having size sieving properties. In turn, the electrochemistry at the LLI can be used as an insightful tool to study the ionic transmembrane currents.