Non-electrostatic Interactions Research Articles

Non-electrostatic interactions associated with aggregate formation between polyallylamine and Escherichia coli

Bacterial aggregation by mixing with polymers is applied as pretreatment to identify pathogens in patients with infectious diseases. However, the detailed interaction between polymers and bacteria has yet to be fully understood. Here, we investigate the interaction between polyallylamine and Escherichia coli by isothermal titration calorimetry. Aggregation was observed at pH 10 and the binding was driven by favorable enthalpic gain such as the electrostatic interaction. Neither aggregation nor the apparent heat of binding was observed at pH 4.0, despite the strong positive charge of polyallylamine. These results suggest that intermolecular repulsive forces of the abundant positive charge of polyallylamine cause an increased loss of conformational entropy by binding. Non-electrostatic interaction plays a critical role for aggregation.

Highly adsorptive removal of molecular diclofenac and bacteria using polycation modified ZnO/SiO2 nanocomposites

The present study investigated the adsorptive removal of non-steroidal medication diclofenac (DCF) using polycation, PVBTAC modified zinc oxide/silica nanocomposite (ZnO/SiO2). The ZnO/SiO2 which was fabricated based on nanosilica rice, was examined by XRD, FT-IR, TEM, EDX, and zeta potential measurements. Surface of ZnO/SiO2 was modified by PVBTAC adsorption at pH 9 and 100 mM KCl to reverse the high charge of material. The optimum parameters for DCF removal using PVBTAC-modified ZnO/SiO2 were contact time 90 min, pH 8 and adsorbent dosage 10 mg/mL. The maximum adsorption capacity and the removal efficiency of DCF were found to be 66 mg/g and 91.8%, respectively, while the bacteria Escherichiacoli(E.coli) removal reached greater than 88 %. Adsorption of DCF on PVBTAC-modified ZnO/SiO2 was mainly controlled by electrostatic attraction between anionic DCF molecules and positively charged PVBTAC-modified ZnO/SiO2 surface whereas the E.coli removal was controlled by both electrostatic and non-electrostatic interactions. Adsorption isotherms of DCF on PVBTAC-modified ZnO/SiO2 at different ionic strengths were reasonably represented by a two-step model while adsorption kinetics fitted well with the pseudo-second-order model. After four regenerations of PVBTAC modified ZnO/SiO2, the DCF removal still exceeded 84%. Our materialis agreat performance adsorbent to remove pharmaceutical and bacteria.

Highly adsorptive removal of oxytetracycline in water environment using polyanion modified alumina nanoparticles

In this study, adsorptive removal of an antibiotic oxytetracycline (OTC) using polyanion poly(2-acrylamide-2-methylpropane sulfonic acid), PAMPs modified α-Al2O3 nanoparticles (PAMNA) was investigated. Surface modification of α-Al2O3 nanoparticles by PAMPs enhanced the removal efficiency of OTC significantly from 35.5 to 90.7 %. The optimum conditions for adsorptive removal of OTC using PAMNA were found to be pH 4, contact time 120 min and adsorbent dosage 20 mg/mL. Under selected conditions, the removal efficiency of OTC using PAMNA was greater than 90 % while the maximum adsorption capacity reached 140.2 mg/g. After three regenerations, the removal efficiencies of OTC were still higher than 75 %. The results of adsorption isotherms of OTC on PAMNA and the surface charge change of PAMNA indicate that both electrostatic and non-electrostatic interactions control OTC adsorption on PAMNA.

Ion-Specific Nanoconfinement Effect in Multilayered Graphene Membranes: A Combined Nuclear Magnetic Resonance and Computational Study.

Ion adsorption within nanopores is involved in numerous applications. However, a comprehensive understanding of the fundamental relationship between in-pore ion concentration and pore size, particularly in the sub-2 nm range, is scarce. This study investigates the ion-species-dependent concentration in multilayered graphene membranes (MGMs) with tunable nanoslit sizes (0.5-1.6 nm) using nuclear magnetic resonance and computational simulations. For Na+-based electrolytes in MGMs, the concentration of anions in graphene nanoslits increases in correlation with their chaotropic properties. As the nanoslit size decreases, the concentration of chaotropic ion (BF4-) increases, whereas the concentration of kosmotropic ions (Cit3-, PO43-) and other ions (Ac-, F-) decreases or changes slightly. Notably, anions remain more concentrated than counter Na+ ions, leading to electroneutrality breakdown and unipolar anion packing in MGMs. A continuum modeling approach, integrating molecular dynamic simulation with the Poisson-Boltzmann model, elucidates these observations by considering water-mediated ion-graphene non-electrostatic interactions and charge screening from graphene walls.

High-performance functional cellulose foam fabricated with theoretically optimized imidazolium salts for the efficient removal of ciprofloxacin

With the increasing requirements for sustainable development and environmental protection, the design and development of bio-adsorbent based on the widely sourced cellulose have attracted widespread attention. In this study, a polymeric imidazolium satls (PIMS) functionalized cellulose foam (CF@PIMS) was conveniently fabricated. It was then employed to efficiently remove ciprofloxacin (CIP). Three imidazolium salts containing phenyl groups that can lead to multiple interactions with CIP were elaborately designed and then screened through a combination of molecular simulation and removal experiments to acquire the most significant binding ability of CF@PIMS. Besides, the CF@PIMS retained the well-defined 3D network structure as well as high porosity (90.3 %) and total intrusion volume (6.05 mL g−1) as the original cellulose foam (CF). Therefore, the adsorption capacity of CF@PIMS reached an astonishing value of 736.9 mg g−1, nearly 10 times that of the CF. Furthermore, the pH-affected and ionic strength-affected adsorption experiments confirmed that the non-electrostatic interaction took on a critical significance in the adsorption. The reusability experiments showed that the recovery efficiency of CF@PIMS was higher than 75 % after 10 adsorption cycles. Thus, a high-potential method was proposed in terms of the design and preparation of functionalized bio-adsorbent to remove waste matters from samples of the environment.

The Electrostatic and Non-Electrostatic Interaction Affect on Acidity Constants of Bromocresol Purple in Aqueous Ethanolic Media

The Electrostatic and Non-Electrostatic Interaction Affect on Acidity Constants of Bromocresol Purple in Aqueous Ethanolic Media

Enhanced adsorption of short-chain perfluorobutanoic acid by functionalized periodic mesoporous organosilica: Performance and mechanisms

Removal of short-chain per- and polyfluoroalkyl substances (PFAS) represents a unique challenge in comparison to the long-chain homologs. In this study, a series of functionalized periodic mesoporous organosilica (PMO) materials with tunable molar ratio of fluoroalkyl to amine functional groups were developed and used as platform adsorbents to investigate the adsorption behavior of short-chain PFAS, with a focus on perfluorobutanoic acid (PFBA). Modification with fluoroalkyl group substantially enhanced the adsorption affinity of PFBA with the functionalized PMO materials. Adsorption free energy analysis suggested that although electrostatic interactions were more predominant in PFBA adsorption, modification of PMOs with increased fluoroalkyl group loadings increased the non-electrostatic interactions with PFBA, resulting in more favorable PFBA adsorption. The optimal functionalized PMO showed fast PFBA adsorption kinetics, excellent PFBA removal efficiency in various water chemistry conditions, and can be regenerated and reused for numerous cycles with methanol/water mixture containing 500-mM NH3·H2O as regenerant. Furthermore, the optimal functionalized PMO showed robust performance for the removal of PFAS mixtures under complex natural water matrix. Results of this study suggested the important role of non-electrostatic interactions in enhancing the removal of short-chain PFAS and can provide mechanistic insights into guiding the design of improved adsorbents for PFAS removal.

Theoretical treatment of complex coacervate core micelles: structure and pH-induced disassembly.

Complex coacervate core micelles (C3Ms) are supramolecular soft nanostructures formed by the assembly of a block copolymer and an oppositely charged homopolymer. The coacervation of the charged segments in both macromolecules drives the formation of the core of the C3M, while the neutral block of the copolymer forms the corona. This work introduces a molecular theory (MOLT) that predicts the internal structure and stimuli-responsive properties of C3Ms and explicitly considers the chemical architecture of the polyelectrolytes, their acid-based equilibria and electrostatic and non-electrostatic interactions. In order to accurately predict complex coacervation, the correlations between charged species are incorporated into MOLT as ion-pairing processes, which are modeled using a coupled chemical equilibrium formalism. Very good agreement was observed between the experimental results in the literature and MOLT predictions for the scaling relationships that relate the dimensions of the micelle (aggregation number and sizes of the micelle and the core) to the lengths of the different blocks. MOLT was used to study the disassembly of the micelles when the solution pH is driven away from the value that guarantees the charge stoichiometry of the core. This study reveals that very sharp disassembly transitions can be obtained by tuning the length or architecture of the copolymer component, thereby suggesting potential routes to design C3Ms capable of releasing their components at very precise pH values.

Protein network centralities as descriptor for QM region construction in QM/MM simulations of enzymes.

The construction of a suitable QM region is the most crucial step in setting up hybrid quantum mechanics/molecular mechanics (QM/MM) simulations for enzymatic reactions. The QM region should ideally include all important amino acids residues, while being as small as possible to save computational effort. Most available methods for systematic QM region construction are based either on the distance of single amino acids to the active site or on their electrostatic effect. Such approaches might miss non-electrostatic and long-range allosteric interactions. Here, we present a proof of concept study for the application of protein network analysis to tackle this problem. Specifically, we explore the use of the protein network centralities as descriptor for QM region construction. We find that protein network centralities, in particular the betweenness centrality, can be a useful descriptor for systematic QM region construction. We show that in combination with our previously developed point charge variation analysis, they can be used to identify important residues that are missed in purely electrostatic approaches.

QENS study on local segmental dynamics of polyelectrolytes in complex coacervates

The segmental dynamics of complex coacervates were investigated as a function of salt concentration and a charge type using quasi-elastic neutron scattering (QENS). The coacervates were prepared by mixing two oppositely charged polyether-based polyelectrolyte solutions functionalized for cationic ammonium and guanidinium groups or anionic sulfonate groups. For the QENS time scale, the intrinsic ion pairs were considered effective cross-links, and therefore the dynamics of chain segments between the intrinsic junctions were probed. We observed that as salt concentration increases, both the number of mobile chain segments and their segmental dynamics increase for ammonium-based coacervates where the electrostatic interaction primarily governs the phase behavior. However, the guanidinium-based coacervates show slow and nearly identical segmental relaxation independent of the salt concentration, which is potentially attributed to the non-electrostatic interactions. The combination of the chemical structure of ionic moieties, salt concentration, and temperature plays a significant role to determine polymer chain dynamics mainly affected by the strength of ionic bonding.

Evaluation of the mechanisms of adsorption of microcystins and nodularin-R onto rice husk-based biochar

• Non-electrostatic and electrostatic interactions govern cyanotoxin adsorption onto RH. • Charge-neutral MC-RR displays high adsorption onto RH at different concentrations. • MC-LR and NOD-R at low concentrations experience attractive interactions with RH surface. • MCs with net negative charge and NOD-R show less adsorption onto RH than MC-RR. • Lateral electrostatic repulsions are more pronounced for MC-LA than for MC-LW and MC-LF. Adsorption mechanisms of individual and collective sorption of microcystins (MCs) and nodularin-R (NOD-R) onto heat-treated rice husk (RH) at neutral pH were evaluated. The functional groups on cyanotoxin standards and RH surface as well as their charge indicate that non-electrostatic and electrostatic interactions are present. Surface area and porosity of RH were determined indicating that MCs and NOD-R can be adsorbed in secondary micropores and mesopores of RH. Positively charged guanidinium ion in arginine-containing MCs and NOD-R created attractive electrostatic forces with the negatively charged RH surface (pH PZC ∼3.3). MCs and NOD-R experience electrostatic repulsion with the surface due to the presence of negatively charged carboxylate groups. MC-RR, even at significantly high toxin concentrations, could be removed by RH as it had a strong attraction to the surface due to two arginines and its neutral charge. Other congeners adsorbed on RH experienced lateral intermolecular repulsion and repulsion with molecules in solution. At low sorbate concentrations, MC-LR and NOD-R had electrostatic attraction to the RH surface and MC-LA, MC-LW, and MC-LF experienced electrostatic repulsion with the surface at all concentrations. Non-electrostatic forces govern the adsorption process of MC-LA, MC-LW, and MC-LF, and electrostatic forces are significant for the adsorption of MC-LR, MC-RR and NOD-R at low concentrations (1-100 ng/mL) as well as the adsorption of MC-RR at high concentrations (1000 ng/mL). The presence of 0.3 M NaCl increases the adsorption of MC-LA and MC-LF proving that those molecules undergo repulsive interactions with RH. The adsorption of MCs and NOD-R onto RH is pH dependent, and it appears to be improved at pH values < pH PZC . Overall, the adsorption of MCs and NOD-R onto RH biochar depends on congener concentration, structure, and charge, and can be modified through optimization of structural properties of RH sorbent and sorption conditions, such as ionic strength and pH.

Biomolecular Complexation on the "Wrong Side": A Case Study of the Influence of Salts and Sugars on the Interactions between Bovine Serum Albumin and Sodium Polystyrene Sulfonate.

In the protein purification, drug delivery, food industry, and biotechnological applications involving protein–polyelectrolyte complexation, proper selection of co-solutes and solution conditions plays a crucial role. The onset of (bio)macromolecular complexation occurs even on the so-called “wrong side” of the protein isoionic point where both the protein and the polyelectrolyte are net like-charged. To gain mechanistic insights into the modulatory role of salts (NaCl, NaBr, and NaI) and sugars (sucrose and sucralose) in protein–polyelectrolyte complexation under such conditions, interaction between bovine serum albumin (BSA) and sodium polystyrene sulfonate (NaPSS) at pH = 8.0 was studied by a combination of isothermal titration calorimetry, fluorescence spectroscopy, circular dichroism, and thermodynamic modeling. The BSA–NaPSS complexation proceeds by two binding processes (first, formation of intrapolymer complexes and then formation of interpolymer complexes), both driven by favorable electrostatic interactions between the negatively charged sulfonic groups (−SO3–) of NaPSS and positively charged patches on the BSA surface. Two such positive patches were identified, each responsible for one of the two binding processes. The presence of salts screened both short-range attractive and long-range repulsive electrostatic interactions between both macromolecules, resulting in a nonmonotonic dependence of the binding affinity on the total ionic strength for both binding processes. In addition, distinct anion-specific effects were observed (NaCl < NaBr < NaI). The effect of sugars was less pronounced: sucrose had no effect on the complexation, but its chlorinated analogue, sucralose, promoted it slightly due to the screening of long-range repulsive electrostatic interactions between BSA and NaPSS. Although short-range non-electrostatic interactions are frequently mentioned in the literature in relation to BSA or NaPSS, we found that the main driving force of complexation on the “wrong side” are electrostatic interactions.

Effects of surface rigidity and metallicity on dielectric properties and ion interactions at aqueous hydrophobic interfaces.

Using classical molecular dynamics simulations, we investigate the dielectric properties at interfaces of water with graphene, graphite, hexane, and water vapor. For graphite, we compare metallic and nonmetallic versions. At the vapor-liquid water and hexane-water interfaces, the laterally averaged dielectric profiles are significantly broadened due to interfacial roughness and only slightly anisotropic. In contrast, at the rigid graphene surface, the dielectric profiles are strongly anisotropic and the perpendicular dielectric profile exhibits pronounced oscillations and signchanges. The interfacial dielectric excess, characterized by the shift of the dielectric dividing surface with respect to the Gibbs dividing surface, is positive for all surfaces, showing that water has an enhanced dielectric response at hydrophobic surfaces. The dielectric dividing surface positions vary significantly among the different surfaces, which points to pronounced surface-specific dielectric behavior. The interfacial repulsion of a chloride ion is shown to be dominated by electrostatic interactions for the soft fluid-fluid interfaces and by non-electrostatic Lennard-Jones interactions for the rigid graphene-water interface. A linear tensorial dielectric model for the ion-interface interaction with sharp dielectric interfaces located on the dielectric dividing surface positions works well for graphene but fails for vapor and hexane, because these interfaces are smeared out. The repulsion of chloride from the metallic and nonmetallic graphite versions differs very little, which reflects the almost identical interfacial water structure and can be understood based on linear continuum dielectric theory. Interface flexibility shows up mostly in the nonlinear Coulomb part of the ion-interface interaction, which changes significantly close to the interfaces and signals the breakdown of linear dielectric continuum theory.

Highly adsorptive protein inorganic nanohybrid of Moringa seeds protein and rice husk nanosilica for effective adsorption of pharmaceutical contaminants

The present study aims to investigate adsorption characteristics and mechanisms of Moringa (MO) seeds protein on nanosilica rice husk and their applications in removal of pharmaceutical residues including the fluoroquinolone antibiotic levofloxacin (LFX) and the nonsteroidal anti-inflammatory drug diclofenac (DCF) in aquatic environment. Molecular weight of MO protein was determined by gel-permeation chromatography (GPC) method while its amino acids were quantified by high performance liquid chromatography (HPLC). The number-(Mn) and weight-average molecular weights (Mw) of MO protein were 1.53 × 104 and 1.61 × 104 g/mol, respectively. Different effective conditions on adsorption protein on nanosilica including contact time, pH, adsorbent dosage, and ionic strength were systematically optimized and found to be 180 min, 10, 10 mg/mL and 1 mM KCl, respectively. The surface charge change by zeta potential, surface modification by Fourier-transform infrared spectroscopy (FT-IR) and adsorption isotherms demonstrated that protein adsorption on nanosilica was governed by both electrostatic and non-electrostatic interactions. Application of protein functionalized nanosilica (ProFNS) in LFX and DCF removal were also thoroughly studied. The selected conditions for LFX and DCF removal using ProFNS were 1 mM KCl for both LFX and DCF; pH 8 and pH 6; contact time 90 and 120 min, and adsorption dosage 10 and 5 mg/ml for LFX and DCF, respectively. Adsorption isotherms of protein on nanosilica as well as LFX and DCF onto ProFNS at different ionic strengths were reasonably fitted by the two-step model while a pseudo-second-order model could fit adsorption kinetic well. The removal of LFX and DCF using ProFNS significantly increased from 51.51% to 87.35%, and 7.97%–50.02%, respectively. High adsorption capacities of 75.75 mg/g for LFX and 59.52 mg/g for DCF, indicate that ProFNS is a great performance for pharmaceutical residues removal in water environment.

Efficient adsorption of acetaminophen from the aqueous phase using low-cost and renewable adsorbent derived from orange peels

Pharmaceutically active compounds (PhACs) are frequently detected emerging pollutants in water resources worldwide that provoke pernicious influences on human health and the ecosystem. Developing effective carbonaceous adsorbents from biomass for the efficient removal of PhACs has lately drawn significant research attention. Herein, an efficient and cost-effective activated carbon was produced via ZnCl2-activation, employing orange peels as a precursor (named hereafter as OPAC). OPAC was well-characterized and applied in the sequestration of acetaminophen (N-acetyl-para-aminophenol, APAP), a broadly used non-steroidal anti-inflammatory drug, from water media using the batch technique. OPAC exhibited excellent performance, and more than 95.5% APAP was removed after 90 min, in the pH range of 2.0–8.0, using 1 g/l adsorbent at 25 °C. Additionally, the equilibrium and the kinetic studies outcomes unveiled the suitability of the Langmuir and the pseudo-second-order kinetic models, respectively, to describe the adsorption process. Based on the pH-adsorption dependence and OPAC properties, the presumable mechanism was mainly dominated by non-electrostatic interactions, including hydrogen bonding, π-π interactions, and pore diffusion. Thermodynamically, the process was found to be spontaneous and endothermic. Ultimately, OPAC manifested outstanding recyclability, with at least 95% of the initial efficiency being preserved after five cycles, making it more attractive from the environmental and economic perspectives.

Preparation of a novel acrylic fiber-based hydrogel and its utilization for the removal of aqueous lead ion

The pollutant binding capacity of amino functional groups has been widely documented. In this study, abundant amino groups were added onto acrylic fibre via functionalization with 1,2-diaminoethane to yield acrylic fibre-based hydrogel (Ac-EDA). The Ac-EDA was further applied for the adsorptive uptake of lead ions. The successful attachment of amino groups on the fibre was verified from the fourier transform infrared spectroscopy and scanning electron microscopy-energy dispersive x-ray, SEM-EDX results. The study on the effect of process variables highlighted a pH non-responsive sorption, due to the non-electrostatic interaction between the basic nitrogen atom of the amino groups and the lead ion. The Langmuir maximum adsorption capacity of 371.26 mg/g was recorded at optimum process conditions. The adsorption modelling emphasized the predominance of internal diffusion as the rate-limiting step. This study showed the effectiveness of the Ac-EDA for the uptake of aqueous lead ions.

Adsorption Equilibria, Kinetics, and Column Dynamics of L-Tryptophan on Mixed-Mode Resin HD-1.

The adsorption amount and selectivity of L-tryptophan (l-Trp) on the hydrophobic interaction and ion exchange mixed-mode chromatography medium HD-1 were studied as well as the salt resistance of the resin via adsorption equilibrium experiments. The adsorption mechanisms of l-Trp were illuminated by combining adsorption equilibria and a kinetics analysis. The separation effect was studied by dynamic separation experiments in a fixed-bed. The results indicate that an increase of the concentration proportion of l-Trp zwitterion benefits the adsorption of l-Trp. The resin shows a high adsorption selectivity for l-Trp at different pH values. The adsorption amount of l-Trp is not affected significantly by NaCl. Various groups play a role in the adsorption of l-Trp. An adsorption energy lower than 8 kJ/mol indicates that the adsorption of l-Trp is mainly based on non-electrostatic interactions, with an electrostatic interaction as a supplement. The adsorption equilibrium model considering the dissociation equilibrium of the resin and l-Trp proposed in this work can simulate the adsorption equilibrium data of l-Trp at different pH values as well. The mass transfer rate of l-Trp is controlled by intraparticle and liquid film diffusion simultaneously. The fixed-bed packed with resin HD-1 can separate l-Trp with the purity of l-Trp higher than 99%, recovery rate higher than 95%, and concentration of 4.69 × 10–3 mol/L.

Single Molecular Chelation Dynamics Reveals That DNA Has a Stronger Affinity toward Lead(II) than Cadmium(II)

Lead ions can bind to DNA via nonelectrostatic interactions and hence alter its structure, which may be related to their adverse effects. The dynamics of Pb2+-DNA interaction has not been well understood. In this study, we report the monomolecular dynamics of the Pb2+-DNA interaction using a magnetic tweezers (MT) setup. We found that lead cations could induce DNA compaction at ionic strengths above 1 μM, which was also confirmed by morphology characterization. The chelation behavior of the Pb2+-DNA and the Cd2+-DNA complex solutions after adding EDTA were compared. The results showed that EDTA chelated with the bound metal ions on DNA and consequently led to restoring the DNA to its original length but with different restoration speeds for the two solutions. The fast binding dynamics and the slower chelation dynamics of the Pb2+ scenario compared to that of Cd2+ suggested that Pb2+ was more capable to induce DNA conformational change and that the Pb2+-DNA complex was more stable than the Cd2+-DNA complex. The stronger affinities for DNA bases and the inner binding of lead cations were two possible causes of the dynamics differences. Three agents, including EDTA, sodium gluconate, and SDBS, were used to remove the bound lead ions on DNA. It was shown that EDTA was the most efficient, and sodium gluconate could not fully restore DNA from its compact state. We concluded that both EDTA and SDBS were good candidates to restore the Pb2+-bound DNA to its original state.

Versatile Diblock Polyampholytes Can Form Two Types of Charged and Internally Structured Core-Shell Particles by Complexation with Cationic or Anionic Surfactants.

We used diblock poly(acrylic acid)-b-poly(2-dimethylamino ethyl methacrylate) (PAA-b-PDMAEMA) polyampholytes to prepare core-shell complexes with ionic surfactants. The dispersions have been characterized by means of small-angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (Cryo-TEM), dynamic light-scattering, and zeta potential methods. Using cationic or anionic surfactants it is possible to produce particles with either positively or negatively charged shells, both having an internal liquid-crystalline core structure. For the different systems, different preparation protocols were found to be successful to produce stable and reproducible particles. The particle morphologies depend on the surfactant used. Complexes with the cationic surfactant hexadecyltrimethylammonium (CTA+) form oblate particles, while complexes with dodecyl sulfate (DS-) form cylindrical rods. In both complexes, the smallest dimension of the core does not exceed twice the block length of the core-forming polymer block. For the particles with CTA+, nonelectrostatic attractive interactions among the PDMAEMA chains in the shells seem to be present, affecting the particle shape. In both types of particles, the surfactant in the core forms rod-like aggregates, arranged in a two-dimensional hexagonal structure with the surfactant rods aligned with the axis of rotational symmetry in the particle. With charged polymer chains in the shell, the aggregates present a striking stability over time, displaying no change in particle size over the time scale investigated (10 months). Nevertheless, the aggregates are highly dynamic in nature, and their shapes and structures can be changed dramatically in dispersion, without intermediate precipitation, by changes in the composition of the medium. Specifically, a transition from aggregates with cationic surfactant to aggregates with anionic surfactant can be achieved.

Revealing the mechanisms of irreversible fouling during microfiltration – The role of feedwater composition

While microfiltration has seen wide acceptance in water treatment, the irreversible fouling of microfilters remains as the biggest impediment to their long-term performance. Thus, developing a better understanding of the mechanisms of irreversible fouling is crucial. To this end, we investigated the mechanism of effluent organic matter (EfOM)-membrane interactions responsible for irreversible fouling of polyvinylidene fluoride (PVDF) microfiltration membranes during wastewater effluent filtration by evaluating the backwash efficacy of different backwashing solutions (ultrapure water, NaCl, CaCl2, HCl, NaOH, and NaClO). The backwash efficiency followed the order HCl < salt solution ≈ Ultrapure water < NaOH < NaClO. A combined analysis of these results suggests that electrostatic interactions (divalent cation influenced EfOM-membrane bridging) play a minimal role in effecting irreversible fouling and non-electrostatic direct EfOM-membrane interactions like hydrophobic interactions dominantly influence irreversible fouling. Since model organic matter species (bovine serum albumin, alginate, and humic acid) are regularly used to simulate wastewater effluent, we also evaluated the mechanism of irreversible fouling during filtration of model organic matter solution using salt solution backwashing. The efficiency followed the order – CaCl2 < Ultrapure water < NaCl, indicating electrostatic interactions as the dominant fouling mechanism. Thus, results from lab-scale studies employing model organic matter species should be interpreted cautiously and conservatively.