Effluent wastewater containing dyes from textile, paint, and various other industrial wastes have long posed environmental damage. Functional nanomaterials offer new opportunities to treat these ...effluent wastes in an unprecedentedly rapid and efficient fashion due to their large surface area-to-volume ratio. In this work, we explore a new approach of wastewater treatment using macroionic coacervate complexes formed with zwitterionic polyampholytes and anionic inorganic polyoxometalate (POM) nanoclusters to extract methylene blue (MB) dye as well as other cationic industrial dyes from model wastewater. Biphasic organic–inorganic macroion complexes are designed to produce a small volume of coacervate adsorbents of high density and viscoelasticity, in contrast to a large volume of supernatant solution for rapid and efficient dye removal. The efficiency of coacervate extraction is characterized by the adsorption isotherm and maximum MB uptake capacity against the concentrations of polyampholyte, POM, and LiCl salt using UV–vis spectrophotometry to optimize the coacervate formation conditions. Our macroionic coacervate complexes could reach nearly 99% removal efficiency for the model wastewater samples of varied MB concentration in <1 min. The extraction capacity up to ∼400 mg/g far surpasses the dye extraction efficiency of widely used activated carbon adsorbents. We also explore the regeneration of coacervate complexes containing high concentration of extracted MB by a simple Fenton oxidation process to bleach coacervate complexes for repeated POM usage, which shows similar MB extraction efficiency after regeneration. Hence, coacervate extraction based upon spontaneous liquid–liquid separating complexation between polyzwitterions and POMs is demonstrated as a rapid, efficient, and sustainable method for industrial dye wastewater treatment. In perspective, coacervate extraction could advantageously possess dual processing options in separation industry through either membrane fabrication or use directly in mixer-settlers.
Understanding the interaction between functional nanoparticles and cell membranes is critical to use nanomaterials for broad biomedical applications with minimal cytotoxicity. In this work, we have ...investigated the effect of adsorbed semihydrophobic nanoparticles (NPs) on the dynamics and morphology of model cell membranes. We have systematically varied the degree of surface hydrophobicity of carboxyl end-functionalized polystyrene NPs of varied size in buffer solutions with varied ionic strength. It is observed that semihydrophobic NPs can readily adsorb on neutral SLBs and drag lipids from SLBs to NP surfaces. Above a critical NP concentration, the disruption of SLBs is observed, accompanied with the formation and rapid growth of lipid-poor regions on NP-adsorbed SLBs. In the study of the effect of solution ionic strength on NP surface hydrophobic degree and the growth of lipid-poor regions, we have concluded that the hydrophobic interaction enhanced by screened electrostatic interaction underlies the envelopment of NPs by lipids that are attracted from SLBs to the surface of NPs or their aggregates. Hence, the formation and growth of lipid-poor regions, or vaguely referred as “pores” or “holes” in the literature, can be controlled by NP concentration, size, and surface hydrophobicity, which is critical to design functional nanomaterials for effective nanomedicine while minimizing possible cytotoxicity.
The effect of net charge of zwitterionic polymers on the phase behavior and viscoelastic properties of hybrid polyampholyte-polyoxometalate (POM) complexes in salted aqueous solutions is investigated ...with polyampholyte copolymers consisting of both positively and negatively charged monomers. Zwitterionic polyampholytes of varied net charge, abbreviated as PA
x
M
y
, are synthesized by varying the feeding molar ratio of negatively charged 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) to positively charged 3-(methacryloylamino)propyltrimethylammonium chloride (MAPTAC) monomers in aqueous solution. The coacervate formation between PA
x
M
y
and inorganic anionic metatungstate POM ({W
12
}) in LiCl added aqueous solutions can be enhanced by increasing the molar fraction of positively charged MAPTAC monomer and LiCl concentration. The salt-broadened coacervation, clearly distinct from the salt-suppressed one between oppositely charged polyelectrolytes, suggests the account of zwitterion-anion pairing for PA
x
M
y
-{W
12
} coacervate formation due to stronger binding of multivalent {W
12
} giant ions with PA
x
M
y
than simple ions. Importantly, as AMPS or MAPTAC monomer fraction in polyampholytes is varied by merely ±5% from the effective net neutral case, the viscoelasticity of PA
x
M
y
-{W
12
} coacervates can be modified by 4-5 folds, suggesting a new tuning parameter to fine control the macroionic interactions and material properties of biomimetic complex coacervates.
Effect of polyampholyte net charge on the phase diagram and viscoelasticity of polyzwitterion-polyoxometalate coacervates.
Membranes derived from self-assembled block polymers have shown promise as highly selective and highly permeable filters, but the complex synthetic routes and limited pore functionalities of existing ...systems need to be improved if these materials are to serve as a platform for the next generation of nanostructured membranes. Here, the facile synthesis of a polyisoprene-b-polystyrene-b-poly(N,N-dimethylacrylamide) (PI–PS–PDMA) triblock polymer using a controlled reversible addition-fragmentation chain transfer (RAFT) polymerization mechanism is reported. This material is then processed into a membrane using a self-assembly and non-solvent induced phase separation (SNIPS) technique, which creates an asymmetric, porous structure consisting of a selective layer that contains a high density of PDMA-lined pores (9.4×1013poresm−2) with an average diameter of 8.1nm, as determined using solute rejection tests. Solvent flow experiments demonstrate that the PI–PS–PDMA membrane has a pH-independent permeability of 6Lm−2h−1bar−1. The PDMA moiety lining the pore walls is converted, through simple hydrolysis in the solid state, to yield a poly(acrylic acid)-lined (PAA-lined) structure. The permeability of the PI–PS–PAA membrane is pH-dependent, and ranges from 0.6Lm−2h−1bar−1 for solutions with a pH greater than 4 to 16Lm−2h−1bar−1 for a solution at pH 1. Solute rejection tests demonstrated a pore size of 3.4nm for the PI–PS–PAA membrane, which is the smallest pore size reported to date for membranes fabricated from self-assembled block polymers. The facile synthesis of the PI–PS–PDMA material, the scalable SNIPS membrane fabrication protocol, and the simple conversion chemistry of the pore functionality demonstrate that these nanostructured membranes are a strong platform for applications within the range of water purification, pharmaceutical separations, sensors, and drug delivery.
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•UF/NF membranes are fabricated from a self-assembled PI–PS–PDMA triblock polymer.•The PDMA block can be converted to PAA without disrupting the membrane morphology.•The PI–PS–PDMA membranes demonstrates a pH-independent permeability and sharp MWCO.•The PI–PS–PAA membranes demonstrates a pH-dependent permeability; pore radii <2nm.•Ionic liquids enable membrane morphology in the solvated state to be imaged via SEM.
Ionic liquids (ILs) are salts that remain liquid down to low temperatures, and sometimes well below room temperature. ILs have been called "green solvents" because of their extraordinarily low vapor ...pressure and excellent solvation power, but ecotoxicology studies have shown that some ILs exhibit greater toxicity than traditional solvents. A fundamental understanding of the molecular mechanisms responsible for IL toxicity remains elusive. Here we show that one mode of IL toxicity on unicellular organisms is driven by swelling of the cell membrane. Cytotoxicity assays, confocal laser scanning microscopy, and molecular simulations reveal that IL cations nucleate morphological defects in the microbial cell membrane at concentrations near the half maximal effective concentration (EC50) of several microorganisms. Cytotoxicity increases with increasing alkyl chain length of the cation due to the ability of the longer alkyl chain to more easily embed in, and ultimately disrupt, the cell membrane.
The conformational structure of a polyelectrolyte chain in dilute aqueous solution is strongly coupled with its surrounding electrostatic environment. With the introduction of branched topology, the ...distribution of counterions in the vicinity of a polyelectrolyte chain becomes highly inhomogeneous, giving rise to complex structures of branched polyelectrolytes in dilute aqueous solution. To directly probe the local electrostatic conditions near a branched polyelectrolyte in aqueous solutions, star-shaped poly(2-vinylpyridine) (P2VP) polymers with precise labeling of one single fluorophore at different locations, for example, the star center or the terminal group of one arm, were synthesized using reversible addition–fragmentation chain transfer (RAFT) polymerization of vinyl-terminated P2VP macromonomers. Using fluorescence correlation spectroscopy (FCS) combined with photon counting histogram (PCH) analysis, the conformational structures and local electric potential of P2VP star polyelectrolytes were investigated in dilute aqueous solutions of varied pH at a single molecule level. Despite the same hydrodynamic radius of P2VP stars, pH-sensitive fluorophores labeled at different locations sensitively differentiated the higher electric potential at the star center from the lower electric potential at the periphery in dilute aqueous solutions.
A facile and low-cost method is developed to functionalize engineering metal membrane supports, such as stainless steel (SS), with epoxy-containing polymer poly(glycidyl methacrylate) (PGMA) to ...produce a versatile and universal platform for subsequent surface modification. With a PGMA anchoring layer, we have demonstrated that hydrogel particles, such as polyacrylamide-co-poly(acrylic acid) (PAM-co-PAA), can be subsequently grafted to form functional polymer membranes for rapid and efficient oil–water separation. By contact angle and AFM measurement, we have confirmed that PAM-co-PAA hydrogel particle layer grafted on a PGMA-modified SS surface exhibits excellent selectivity as required for liquid–liquid separation, showing high affinity to water but not to oils as an ideal membrane for oil–water separation. To evaluate the separation efficiency, a simple flow-through device is employed to separate free-floating oil from water in the mixture of varied initial oil volume fraction and oil composition. Under substantially high pump flow rate up to 1.3 L/min, PAM-co-PAA hydrogel treated SS mesh can achieve excellent separation efficiency with less than 5% oil or water in the respective filtrate at the flux of as high as 540 m3/(m2·h) and retentate at the flux of 1.95 m3/(m2·h). This separation efficiency is better than, or comparable to, the maximal performance achieved using conventional gravity methods at much lower flow rate. Similar approach could be also adapted to graft superhydrophobic and superoleophilic polymer membranes with PGMA-treated engineering support to separate water from oil.
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We report on studies of lipid transfer rates between different morphology nanoparticles and lipids with different length acyl chains. The lipid transfer rate of dimyristoylphosphatidylcholine ...(di-C14, DMPC) in discoidal “bicelles” (0.156 h–1) is 2 orders of magnitude greater than that of DMPC vesicles (ULVs) (1.1 × 10–3 h–1). For both bicellar and ULV morphologies, increasing the acyl chain length by two carbons going from di-C14 DMPC to di-C16, dipalmitoylphosphatidylcholine (DPPC) causes lipid transfer rates to decrease by more than 2 orders of magnitude. Results from small angle neutron scattering (SANS), differential scanning calorimetry (DSC), and fluorescence correlation spectroscopy (FCS) are in good agreement. The present studies highlight the importance of lipid dynamic processes taking place in different morphology biomimetic membranes.
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