Search Results (38)

Cationic surfactants from quaternary ammonium compounds (QACs) are increasingly recognized as relevant micropollutants particularly following their widespread use during and after the COVID-19 pandemic. The new EU Urban Wastewater Treatment Directive (2024/3019) highlights micropollutant removal as a regulatory priority, mandating advanced treatment for their elimination. In this context, this study examined benzalkonium chloride (BAC) retention and membrane response during nanofiltration (NF) and reverse osmosis (RO), across concentrations ranging from monomeric to micellar. RO membranes achieved >97% rejection, whereas NF showed 65–96% removal strongly affected by micelle formation. Flux decline was most pronounced in RO, with relative permeability (J/J₀) decreasing to ~0.12 at 1.0 CMC, while NF membranes exhibited better hydraulic stability. Membrane active layer zeta potential measurements confirmed adsorption and charge neutralization, with shifts toward less negative values after BAC exposure. Hermia model analysis revealed that fouling was governed by cake layer formation or pore blocking, depending on membrane type and feed concentration. Full article

Tight oil reservoirs are widely recognized as a critical successor in global unconventional energy development and are generally characterized by distinct geological features, including fine pore throats, pronounced heterogeneity, and a high concentration of clay minerals (e.g., montmorillonite and mixed-layer illite/smectite). Severe hydration, swelling, and fines migration are readily induced during water injection or conventional water-based fluid operations, thereby resulting in irreversible impairment of reservoir permeability. Despite the excellent injectivity and capacity for viscosity reduction associated with CO₂ flooding, sweep efficiency is severely compromised by viscous fingering and gas channeling, which are induced by the inherent low viscosity of the gas. While CO₂ foam technology is widely acknowledged as a pivotal solution for addressing mobility control challenges, its implementation is hindered by a primary technical bottleneck: the incompatibility between traditional water-based foam systems and strongly water-sensitive reservoirs. A dual challenge comprising water injectivity constraints and gas channeling is presented by strongly water-sensitive tight oil reservoirs. To address these impediments, three emerging low-damage CO₂ foam systems are critically evaluated in this review. First, the synergistic mechanisms of novel quaternary ammonium salts and polymers in inhibiting clay hydration and enhancing foam stability within modified water-based systems are elucidated. Next, the physical isolation strategy of substituting the water phase with a non-aqueous phase (oil/organic solvent) in organic emulsion systems is analyzed, highlighting advantages in wettability alteration and the mitigation of water blocking. Finally, the prospect of waterless operations using CO₂-soluble foam systems—wherein supercritical CO₂ is utilized as a surfactant carrier to generate foam or viscosify fluids via in situ formation water—is discussed. It is revealed by comparative analysis that: (1) Modified water-based systems are identified as the most economically viable option for reservoirs with moderate water sensitivity, wherein cationic stabilizers are utilized to inhibit hydration; (2) Superior wettability alteration and the elimination of aqueous phase damage are provided by organic emulsion systems, rendering them ideal for ultra-sensitive, high-value reservoirs, despite higher solvent costs; (3) CO₂-soluble systems are recognized as the future direction for “waterless” flooding, specifically tailored for ultra-tight formations (<0.1 mD) where injectivity is critical. Current challenges, such as surfactant solubility, high-temperature stability, and cost control, are identified through a comparative analysis of these three systems with respect to structure-activity relationships, rheological properties, damage control capabilities, and economic feasibility. What is more, an outlook is provided on the molecular design of future environmentally sustainable, cost-effective CO₂-philic materials and smart injection strategies. Consequently, theoretical foundations and technical support are established for the efficient exploitation of strongly water-sensitive tight oil reservoirs. By bridging the gap between reservoir damage control and mobility enhancement, this study identifies viable strategies for enhanced oil recovery. Crucially, it supports carbon neutrality and sustainable energy targets via CCUS integration. Full article

Cationic surfactants from the group of quaternary ammonium compounds (QACs) are widely used in disinfectants, cosmetics, and household and industrial products. Their strong antimicrobial activity and chemical stability make them valuable in applications but also highly persistent and toxic when released into aquatic environments. This problem has become increasingly relevant during and after the COVID-19 pandemic, when global use of QAC-based disinfectants increased drastically, resulting in their frequent detection in municipal, hospital, and industrial effluents. The concentrations of QACs reported in wastewater range from trace levels to several mg/L, often reaching inhibitory thresholds for biological treatment processes. Although surfactants are not listed in any current European directive, the revised Directive (EU) 2024/1440 classifies micropollutants as a priority group, imposing stricter environmental quality standards and mandatory monitoring requirements. Within this regulatory framework, QACs are recognized as compounds of emerging concern, and their effective removal from wastewater has become a critical challenge. This review summarizes the current knowledge on conventional treatment technologies (coagulation, adsorption, ion exchange, advanced oxidation, and biological processes) and membrane-based methods (ultrafiltration, nanofiltration, reverse osmosis, forward osmosis, and hybrid systems) for the removal of cationic surfactants from water and wastewater. Mechanisms of separation, performance, and operational limitations are discussed. Full article

The effects of polymer concentration on rheology, surface tension, and electrical conductivity of polymer–surfactant mixtures are investigated experimentally. The polymer studied is a cationic quaternary ammonium salt of hydroxyethyl cellulose, and the surfactant used is anionic sodium lauryl sulfate. The polymer concentration is varied from 1000 to 4000 ppm, and the surfactant concentration varied from 0 to 500 ppm. Polymer concentration affects the properties of the mixtures substantially. At a given surfactant concentration, the consistency of the polymer–surfactant mixture rises sharply with the increase in polymer concentration. The mixture also becomes more shear-thinning with the increase in polymer concentration. The surface tension decreases substantially, and the electrical conductivity increases with the increase in polymer concentration at a fixed surfactant concentration. At a given polymer concentration, the consistency index generally exhibits a maximum and the surface tension exhibits a minimum at some intermediate surfactant concentration. With the increase in polymer concentration, the maximum in the consistency index and the minimum in surface tension shift to higher surfactant concentrations. Although the exact mechanisms are not clear at present, a possible explanation for the observed initial changes in rheological and surface-active properties of polymer–surfactant mixtures with the addition of surfactant is charge neutralization and entanglement of polymer chains. At high surfactant concentrations, recharging and disentanglement of polymer chains probably take place. Full article

Due to the growing emergence of bacterial and fungal resistance, there is an urgent need for novel antimicrobial compounds. Cationic surfactants are effective antimicrobial agents; however, traditional quaternary ammonium compounds (QACs) are increasingly scrutinized due to their cytotoxicity, poor biodegradability, and harmful effects on aquatic ecosystems. While the antimicrobial efficacy of many new biocides, including QACs, has been extensively studied, comprehensive experimental strategies that simultaneously assess antimicrobial activity, mammalian cell toxicity, and ecotoxicity remain limited. Recent studies have reported that amino-acid-based surfactants containing arginine-phenylalanine and arginine-tryptophan exhibit excellent antibacterial activity and are biodegradable. This work extends their biological characterization to evaluate their potential applications. Specifically, we examined how variations in the head group architecture and hydrophobic moiety influence antifungal and antibiofilm activity. We also assessed how these structural parameters impact cytotoxicity and ecotoxicity. These compounds demonstrated strong activity against a wide range of Candida strains. Their hydrophobic character primarily influenced both antifungal efficacy and cytotoxicity. Importantly, these surfactants exhibited potent antimicrobial and antibiofilm effects at non-cytotoxic concentrations. Notably, their aquatic toxicity was significantly lower than that of conventional QACs. Full article

The modification of the layered silicate with a structural type 2:1 montmorillonite by the cationic surfactant hexadecyltrimethylammonium bromide was carried out. The obtained organomontmorillonite was milled for 2–25 min in a high-energy planetary ball mill. The structural and physicochemical characteristics of the modified montmorillonite and the mechanochemically activated montmorillonite were investigated using various methods such as X-ray diffraction, thermal analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and determination of the specific surface area as well as the parameters of the porous structure by the low-temperature adsorption–desorption of nitrogen. The modification of montmorillonite with the quaternary ammonium salt led to a slowdown of deformation and subsequent amorphization of the montmorillonite structure during the high-energy milling. Mechanochemical activation of the modified montmorillonite increased its sorption capacity nine times, with the maximum uranium sorption achieved after mechanochemical treatment for 10 min. Full article

The efficiency of integrated treatment systems for wastewater generated during the washing of disinfectant production lines was investigated. The high organic load (COD 2000 mg/L, TOC 850 mg/L) and 300 mg/L of toxic benzalkonium chloride (BAC) make wastewater an environmental hazard that requires advanced treatment. Initial tests on model BAC solutions (in concentrations corresponding to those found in wastewater), using nanofiltration and ultrafiltration membranes, resulted in up to 70% retention of BAC. To enhance purification, ion exchange and adsorption were introduced as post-membrane treatment steps. In the second part of the investigation, membrane modules characterized by the best separation properties were integrated together with macroporous cation-exchange resin and activated carbon into the purification system to treat wastewater. The research carried out showed that the purification of multicomponent wastewater is a complex task. Significantly lower BAC removal (30%) was achieved in membrane processes compared to the model solutions treatment. In integrated systems, the BAC concentration was reduced to 100 mg/L, TOC to 200 mg/L, and COD to 120 mg/L. Full article

Density functional theory (DFT) and molecular dynamics (MD) simulations were employed to investigate the inhibition mechanism of cationic quaternary ammonium surfactant corrosion inhibitors (CIs) with varying chain lengths in 1.0 M HCl and 500 ppm acetic acid on Fe (110) surfaces. DFT calculations demonstrated that all surfactant CI molecules possess favorable inhibition properties, with the cationic quaternary ammonium groups (N⁺) and alpha carbon serving as electron-donating reactive centers, characterized by a low band-gap energy of 1.26 eV. MD simulations highlighted C12, with a 12-alkyl chain length, as the most promising CI molecule, exhibiting high adsorption and binding energies, a low diffusion coefficient, and a random distribution at low concentrations, thereby facilitating optimal adsorption onto the Fe (110) metal surface. The insights gained from computational modeling regarding the influence of alkyl chain length on inhibition efficiency, coupled with the comprehensive theoretical understanding of cationic quaternary ammonium surfactant CI molecules in acidic corrosion systems, can serve as a foundation for the future development of innovative surfactant CI molecules incorporating ammonium-based functional groups. Full article

Cationic gemini surfactants are used due to their broad spectrum of activity, especially surface, anticorrosive and antimicrobial properties. Mixtures of cationic and anionic surfactants are also increasingly described. In order to investigate the effect of anionic additive on antimicrobial activity, experimental studies were carried out to obtain MIC (minimal inhibitory concentration) against E. coli and S. aureus bacteria. Two gemini surfactants (12-6-12 and 12-O-12) and two single quaternary ammonium salts (DTAB and DDAC) were analyzed. The most commonly used commercial compounds of this class, i.e., SDS and SL, were used as anionic additives. In addition, computer quantum mechanical studies were also carried out to confirm the relationship between the structure of the mixture and the activity. The obtained results of microbiological tests and quantum mechanical calculations are in agreement with each other and show the lack of synergism in catanionic mixtures in the case of antibacterial activity. Full article

Three types of coatings (contact-based, release-based, and combined coatings with both contact-based and release-based actions) were prepared and tested for the ability to inactivate SARS-CoV-2. In these coatings, quaternary ammonium surfactants were used as active agents since quaternary ammonium compounds are some of the most commonly used disinfectants. To provide contact-based action, the glass and silicon surfaces with covalently attached quaternary ammonium cationic surfactant were prepared using a dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride modifier. Surface modification was confirmed by attenuated total reflection infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and contact angle measurements. The grafting density of the modifier was estimated by XPS and elemental analysis. To provide release-based action, the widely used quaternary ammonium cationic disinfectant, benzalkonium chloride (BAC), and a newly synthesized cationic gemini surfactant, C18-4-C18, were bound non-covalently to the surface either through hydrophobic or electrostatic interactions. Virus titration revealed that the surfaces with combined contact-based and release-based action and the surfaces with only release-based action completely inactivate SARS-CoV-2. Coatings containing only covalently bound disinfectant are much less effective; they only provide up to 1.25 log10 reduction in the virus titer, probably because of the low disinfectant content in the surface monolayer. No pronounced differences in the activity between the flat and structured surfaces were observed for any of the coatings under study. Comparative studies of free and electrostatically bound disinfectants show that binding to the surface of nanoparticles diminishes the activity. These data indicate that SARS-CoV-2 is more sensitive to the free disinfectants. Full article

The network formed by wax precipitation at low temperature and colloid asphaltene at high temperature leads to poor fluidity of heavy oil, and the gelling characteristics of crude oil lead to pipeline blockage, which affects the exploitation, transportation and refining of crude oil. This work prepares a series of cationic surfactant-modified nano hydrotalcite (CSNH) to weaken the network structure and enhance the fluidity of the crude oil by the interaction of organic and inorganic functional groups on the CSNH surface and the components of the crude oil. The results show that CSNHs can all reduce the viscosity of crude oil from different oilfields, among which BTNH can reduce the viscosity of Yanglou (YL) crude oil by 98.8% (31 °C) and depress the pour point by 16.0 °C at most. In the investigation of the universality of crude oil, the modified hydrotalcite was applied to the mixed crude oil (CQH) of Changqing Oilfield, the crude oil (J76) of Jidong Oilfield, the high pour point oil (GN) of Huabei Oilfield, and the crude oil (HQ) of Tuha Oilfield. The viscosity reduction rates were 53.2%, 86.2%, 42.7%, and 63.8%, respectively. The characterization of this nano material confirms the modification of quaternary ammonium cationic surfactant on the surface, resulting in a smaller particle size, and the nano particles are stable under conventional conditions. The mechanism of viscosity and pour point reduction in crude oil by BTNH was discussed by DSC and optical microscopy analysis. The OH- and long-chain alkyl groups on the BTNH surface may interact with the resins, asphaltene and wax through hydrogen bonding and co-crystal, weakening or dispersing their aggregates, thereby improving the fluidity of crude oil. Finally, a cost evaluation was conducted on BTNH, providing useful support for subsequent promotion and application. Full article

Esterquats constitute a unique group of quaternary ammonium salts (QASs) that contain an ester bond in the structure of the cation. Despite the numerous advantages of this class of compounds, only two mini-reviews discuss the subject of esterquats: the first one (2007) briefly summarizes their types, synthesis, and structural elements required for a beneficial environmental profile and only briefly covers their applications whereas the second one only reviews the stability of selected betaine-type esterquats in aqueous solutions. The rationale for writing this review is to critically reevaluate the relevant literature and provide others with a “state-of-the-art” snapshot of choline-type esterquats and betaine-type esterquats. Hence, the first part of this survey thoroughly summarizes the most important scientific reports demonstrating effective synthesis routes leading to the formation of both types of esterquats. In the second section, the susceptibility of esterquats to hydrolysis is explained, and the influence of various factors, such as the pH, the degree of salinity, or the temperature of the solution, was subjected to thorough analysis that includes quantitative components. The next two sections refer to various aspects associated with the ecotoxicity of esterquats. Consequently, their biodegradation and toxic effects on microorganisms are extensively analyzed as crucial factors that can affect their commercialization. Then, the reported applications of esterquats are briefly discussed, including the functionalization of macromolecules, such as cotton fabric as well as their successful utilization on a commercial scale. The last section demonstrates the most essential conclusions and reported drawbacks that allow us to elucidate future recommendations regarding the development of these promising chemicals. Full article

Using surfactants in the galvanic replacement reaction (GRR) offers a versatile approach to modulating hollow metal nanocrystal (NC) morphology and composition. Among the various surfactants available, quaternary ammonium cationic surfactants are commonly utilised. However, understanding how they precisely influence morphological features, such as the size and void distribution, is still limited. In this study, we aim to uncover how adding different surfactants—CTAB, CTAC, CTApTS, and PVP—can fine-tune the morphological characteristics of AuAg hollow NCs synthesised via GRR at room temperature. Our findings reveal that the halide counterion in the surfactant significantly controls void formation within the hollow structure. When halogenated surfactants, such as CTAB or CTAC, are employed, multichambered opened nanoboxes are formed. In contrast, with non-halogenated CTApTS, single-walled closed nanoboxes with irregularly thick walls form. Furthermore, when PVP, a polymer surfactant, is utilised, changes in concentration lead to the production of well-defined single-walled closed nanoboxes. These observations highlight the role of surfactants in tailoring the morphology of hollow NCs synthesised through GRR. Full article

In this paper, a novel hydroxyl-containing quaternary ammonium surfactant N-(2-Hydroxyethyl)-N, N-dimethyl-3-[(1-oxododecyl)amino]-1-propanaminium (LPDC) was synthesized and introduced as a collector for the reverse cationic flotation separation of apatite from quartz; the adsorption mechanisms between LPDC and two mineral surfaces were investigated by Fourier transform infrared spectrometer (FTIR), zeta potential measurements and X-ray photoelectron spectroscopy (XPS) analysis. The micro-flotation tests showed that LPDC exhibited excellent flotation performance. When the pulp was at natural pH and LPDC concentration was 25 mg/L, the apatite concentrate with a P₂O₅ recovery of 95.45% and P₂O₅ grade of 38.94% could be obtained from artificially mixed minerals. FTIR, zeta potential, and XPS analysis indicated that the adsorption of LPDC onto quartz surface is stronger than that onto apatite surface; meanwhile, the adsorption of LPDC onto quartz surface is mainly provided by electrostatic force and hydrogen bonding. Full article

Ibuprofen (Ibf) is a biologically active drug (BADs) and an emerging contaminant of concern (CECs) in aqueous streams. Due to its adverse effects upon aquatic organisms and humans, the removal and recovery of Ibf are essential. Usually, conventional solvents are employed for the separation and recovery of ibuprofen. Due to environmental limitations, alternative green extracting agents need to be explored. Ionic liquids (ILs), emerging and greener alternatives, can also serve this purpose. It is essential to explore ILs that are effective for recovering ibuprofen, among millions of ILs. The conductor-like screening model for real solvents (COSMO-RS) is an efficient tool that can be used to screen ILs specifically for ibuprofen extraction. The main objective of this work was to identify the best IL for the extraction of ibuprofen. A total of 152 different cation–anion combinations consisting of eight aromatic and non-aromatic cations and nineteen anions were screened. The evaluation was based upon activity coefficients, capacity, and selectivity values. Furthermore, the effect of alkyl chain length was studied. The results suggest that quaternary ammonium (cation) and sulfate (anion) have better extraction ability for ibuprofen than the other combinations tested. An ionic liquid-based green emulsion liquid membrane (ILGELM) was developed using the selected ionic liquid as the extractant, sunflower oil as the diluent, Span 80 as the surfactant, and NaOH as the stripping agent. Experimental verification was carried out using the ILGELM. The experimental results indicated that the predicted COSMO-RS and the experimental results were in good agreement. The proposed IL-based GELM is highly effective for the removal and recovery of ibuprofen. Full article