Adsorption and kinetic studies of cationic and anionic dyes on pyrophyllite from aqueous solutions

The adsorption of cationic Methylene Blue (MB) and anionic Procion Crimson H-EXL (PC) dyes from aqueous medium on pyrophyllite was studied. Changes in the electrokinetics of pyrophyllite as a function of pH were investigated in the absence and presence of multivalent cations. The results show that pyrophyllite in water exhibits a negative surface charge within the range pH 2-12. Pyrophyllite is found to be a novel adsorbent for versatile removal of cationic and anionic dyes. The negative hydrophilic surface sites of pyrophyllite are responsible for the adsorption of cationic MB molecules. The adsorption of anionic PC dye is possible after a charge reversal by the addition of trivalent cation of Al. Nearly 2 min of contact time are found to be sufficient for the adsorption of both dyes to reach equilibrium. The experimental data follow a Langmuir isotherm with adsorption capacities of 70.42 and 71.43 mg dye per gram of pyrophyllite for MB and PC, respectively. For the adsorption of both MB and PC dyes, the pseudo-second-order chemical reaction kinetics provides the best correlation of the experimental data.     

Bifunctional Cage‐Type Cubic Mesoporous Silica SBA‐1 Nanoparticles for Selective Adsorption of Dyes

Bifunctional SBA‐1 mesoporous silica nanoparticles (MSNs) with carboxylic acid and amino groups (denoted as CNS‐10‐10) have been successfully synthesized, characterized, and employed as adsorbents for dye removal. Adsorbent CNS‐10‐10 shows high affinity towards cationic and anionic dyes in a wide pH range, and exhibits selective dye removal of a two‐dye mixture system of cationic methylene blue and anionic eosin Y. By changing the pH of the medium, the selectivity of the adsorption behavior can be easily modulated. For comparison purposes, the counterparts, that is, pure silica SBA‐1 MSNs (CS‐0) and those with either carboxylic acid or amino functional groups (denoted as CS‐10 and NS‐10, respectively) were also prepared to evaluate their dye‐adsorption behaviors. As revealed by the zeta‐potential measurements, the electrostatic interaction between the adsorbent surface and the dye molecule plays an important role in the adsorption mechanism. Adsorbent CNS‐10‐10 can be easily regenerated and reused, and maintains its adsorption efficiency up to 80 % after four cycles.     

Adsorption of a cationic dye molecule on polystyrene microspheres in colloids: effect of surface charge and composition probed by second harmonic generation

Nonlinear optical probe, second harmonic generation (SHG), of the adsorption of the dye molecule malachite green (MG), in cationic form at pH < or = 5, on polystyrene microspheres in aqueous solution is used to study the effect of surface charge and composition on molecular adsorption. Three types of polystyrene microspheres with different surface composition are investigated: (1) a sulfate terminated, anionic surface, (2) a neutral surface without any functional group termination, and (3) an amine terminated, cationic surface. The cationic dye was found to adsorb at all three surfaces, regardless of surface charge. The adsorption free energies, DeltaG's, measured for the three surfaces are -12.67, -12.39, and -10.46 kcal/mol, respectively, with the trend as expected from the charge interactions. The adsorption density on the anionic surface, where attractive charge-charge interaction dominates, is determined by the surface negative charge density. The adsorption densities on the neutral and cationic surfaces are on the other hand higher, perhaps as a result of a balance between minimizing repulsive charge interaction and maximizing attractive molecule-substrate and intermolecular interactions. The relative strength of the SH intensity per molecule, in combination of a model calculation, reveals that the C(2) axis of the MG molecule is nearly perpendicular to the surface on the anionic surface and tilts away from the surface norm when the surface is neutral and further away when cationic. Changing the pH of the solution may alter the surface charge and subsequently affect the adsorption configuration and SH intensity.     

Orientational behavior of thermotropic liquid crystals on surfaces presenting electrostatically bound vesicular stomatitis virus

We report the orientational behavior of nematic phases of 4-cyano-4'-pentylbiphenyl (5CB) on cationic, anionic, and nonionic surfaces before and after contact of these surfaces with solutions containing the negatively charged vesicular stomatitis virus (VSV). The surfaces were prepared on evaporated films of gold by either adsorption of poly-L-lysine (cationic) or formation of self-assembled monolayers (SAMs) from HS(CH2)2SO3- (anionic) or HS(CH2)11(OCH2CH2)4OH (nonionic). Prior to treatment with virus, we measured the initial orientation of 5CB (delta epsilon = epsilon(parallel) - epsilon(perpendicular) > 0) to be parallel to the cationic surfaces (planar anchoring) but perpendicular (homeotropic) after equilibration for 5 days. A similar transition from planar to homeotropic orientation of 5CB was observed on the anionic surfaces. Only planar orientations of 5CB were observed on the nonionic surfaces. Because N-(4-methoxybenzylidene)-4-butylaniline (MBBA, delta epsilon = epsilon(parallel) - epsilon(perpendicular) < 0) exhibited planar alignment on all surfaces, the time-dependent alignment of 5CB on the ionic surfaces is consistent with a dipolar coupling between the 5CB and electrical double layers formed at the ionic interfaces. Treatment ofpoly-L-lysine-coated gold films (cationic) with purified solutions of VSV containing 10(8)-10(10) plaque-forming units per milliliter (pfu/mL) led to the homeotropic alignment of 5CB immediately after contact of 5CB with the surface. In contrast, treatment of anionic surfaces and nonionic surfaces with solutions of VSV containing approximately 10(10) pfu/mL did not cause immediate homeotropic alignment of 5CB. These results and others suggest that homeotropic alignment of 5CB on cationic surfaces treated with VSV of titer > or = 10(8) pfu/mL reflects the presence of virus electrostatically bound to these surfaces.     

Structural and electron-transfer characteristics of carbon-tethered porphyrin monolayers on Si(100)

Structural and electron-transfer characteristics are reported for two classes of zinc porphyrin monolayers attached to Si(100) surfaces via Si-C bonds. One class, designated ZnP(CH(2))(n)- (n = 2-4), contains an alkyl linker appended to the meso-position of the porphyrin, with the nonlinking substituents being p-tolyl groups. The other, designated ZnPPh(CH(2))(n)- (n = 0-3), contains a phenyl or phenylalkyl linker appended to the meso-position of the porphyrin, with the nonlinking substituents being mesityl groups. Both classes of zinc porphyrin monolayers on Si(100) were examined using Fourier transform infrared spectroscopy and various electrochemical methods. The studies reveal the following: (1) The structural and electron-transfer characteristics of the ZnP(CH(2))(n)- and ZnPPh(CH(2))(n)- monolayers are generally similar to those of monolayers formed from porphyrins with analogous linkers, but anchored with an O, a S, or a Se atom. (2) The ZnP(CH(2))(n)-, ZnPPh-, and ZnPPhCH(2)- monolayers exhibit lower saturation coverages and have their porphyrin ring more tilted with respect to the surface normal than the ZnPPh(CH(2))(2)- and ZnPPh(CH(2))(3)- monolayers. (3) The electron-transfer rates for both the ZnP(CH(2))(n)- and ZnPPh(CH(2))(n)- classes of monolayers monotonically decrease as the length of the linker increases. (4) For all the ZnP(CH(2))(n)- and ZnPPh(CH(2))(n)- monolayers, both electron-transfer rates and charge-dissipation rates decrease monotonically as the surface coverage increases. Collectively, the studies reported herein provide a detailed picture of how the linker type influences the structural and electron-transfer characteristics of these general classes of monolayers.     

Incorporation of Triarylmethane Dyes into Sol–Gel Matrices Deposited on Textiles

The incorporation of triarylmethane dyes into sol–gel layers formed by modified silica was used for coating of textile materials. The coatings were performed with three triarylmethane dyes differ in electrical net charge and structure: The cationic dye Malachite Green, the anionic Guinea Green and the non-polar Reflex Blue 61. All coating procedures were performed using an acidic sol–gel process starting from a solution of tetraethoxysilane (TEOS) and the dye in a mixture of water and ethanol. Depositions were performed on polyester, polyamide and cotton textiles. Investigation of leaching and photobleaching fastness showed that the stability of the dyes was enhanced by incorporation into the silica layer. Sufficient leaching fastness was only achieved with the cationic dye due to direct attractive electrostatic interaction with the negatively charged silica matrix. Also the addition of a small amount of epoxysilane to the silica sols lead to an enhancement of leaching and bleaching fastness.     

Mechanism of TiO2-assisted photocatalytic degradation of dyes under visible irradiation: photoelectrocatalytic study by TiO2-film electrodes

Photoelectrocatalytic degradation of various dyes under visible light irradiation with a TiO(2) nanoparticles electrode has been investigated to reveal the mechanism for TiO(2)-assisted photocatalytic degradation of dyes. The degradation of both cationic and anionic dyes at different biases, including the change in the degradation rate of the dyes and the photocurrent change with the bias potential, the degraded intermediates, the voltage-induced adsorption of dyes, the accumulation of electrons in the TiO(2) electrode, the effect of various additives such as benzoquinone (BQ) and N,N-dimethyl aniline (DMA), and the formation of active oxygen species such as O(2)(*-) and H(2)O(2) were examined by UV-visible spectroscopy, HPLC, TOC, and spin-trap ESR spectrometry. It was found that the dyes could controllably interact with the TiO(2) surface by external bias changes and charging of dyes. The cationic dyes such as RhB and MG underwent efficient mineralization at negative bias, but the N-dealkylation process predominated at positive bias under visible light irradiation. The discolorations of the anionic dyes SRB and AR could not be accelerated significantly at either negative or positive bias. At a negative bias of -0.6 V vs SCE, O(2)(*-) and dye(*+) were formed simultaneously at the electrode/electrolyte interface during degradation of cationic RhB. In the case of anionic dyes, however, it is impossible for the O(2)(*-) and dye cationic radical to coexist at the electrode/electrolyte surface. Experimental results imply both the superoxide anionic radical and the dye cationic radical are essential to the mineralization of the dyes under visible light-induced photocatalytic conditions.     

Study on the supramolecular system of TAPP with cyclodextrins by polarography

The interaction of cyclodextrins with meso- Tetrakis (4-N-trimethylaminobenzyl) porphyrin (TAPP) in 0.1 mol l(-1) phosphate buffer (pH 7.0, 20 degrees C) has been studied by polarography. The TAPP can form the 1:1 inclusion complex with Sulfobutylether-beta-cyclodextrin (SBE-beta-CD) and1:2 inclusion complexes with other four cyclodextrins. A new expression, which is used to calculate the inclusion constant for1:2 inclusion complex by polarography, has been educed and testified firstly in this paper. Furthermore, the inclusion abilities of different kinds of cyclodextrins are compared. The result shows the inclusion ability of anionic cyclodextrin SBE-beta-CD with cationic porphyrin TAPP is very strong. It suggests that the charge attraction between CDs and TAPP plays an important role in the inclusion procedure except for the hydrophobic effect. The inclusion formation of anionic cyclodextrins with drugs can increase released rate of drugs at high pH; therefore, the suparmolecular data for the controlled release of the drugs that owned the similar properties as hematoporphyrin have been offered by polarography in this paper.     

Thorium(IV) molecular clusters with a hexanuclear Th core

Three polynuclear thorium(IV) molecular complexes have been synthesized under ambient conditions from reactions of an amorphous Th precipitate, obtained via hydrolysis, with carboxylate functionalized ligands. The structures of Th(6)(OH)(4)O(4)(H(2)O)(6)(HCO(2))(12)·nH(2)O (1), Th(6)(OH)(4)O(4)(H(2)O)(6)(CH(3)CO(2))(12)·nH(2)O (2), Th(6)(OH)(4)O(4)(H(2)O)(6)(ClCH(2)CO(2))(12)·4H(2)O (3) each consist of a hexanuclear Th core wherein six 9-coordinate Th(IV) cations are bridged by four μ(3)-hydroxo and four μ(3)-oxo groups. Each Th(IV) center is additionally coordinated to one bound "apical" water molecule and four oxygen atoms from bridging carboxylate functionalized organic acid units. "Decoration" of the cationic [Th(6)(μ(3)-O)(4)(μ(3)-OH)(4)](12+) cores by anionic shells of R-COO(-) ligands (R = H, CH(3), or CH(2)Cl) terminates the oligomers and results in the formation of discrete, neutral molecular clusters. Electronic structure calculations at the density functional theory level predicted that the most energetically favorable positions for the protons on the hexanuclear core result in the cluster with the highest symmetry with the protons separated as much as possible. The synthesis, structure, and characterization of the materials are reported.     

Charge‐selective separation and recovery of organic ions by polymeric micelles

Charge‐selective separation and recovery of organic ionic dyes by polymeric micelles (PMs) are reported. Branched polyethylenimine (PEI) functionalized with 4‐cetyloxybenzaldehyde (CBA) via Schiff‐base bonds (PEI@CBA) can extract an anionic dye from cationic contaminants, and transfer it from an aqueous phase into an apolar oil phase, and thus leading to separation. While a physical micelle of PAA@PS, with polyacrylic acid (PAA) as core and polystyrene (PS) as shell, can selectively extract a cationic dye from anionic contaminants. When polar, yet nonionic groups are eliminated from the core of a PM, charge selectivity can be significantly enhanced. Although many anionic–cationic dyes can form a poorly water‐soluble complex or precipitate, separation is still feasible with a reasonably designed PM. Finally, entrapment of a guest by a PM is found easy but release may be difficult; in this case, PEI@CBA with an acid‐sheddable shell, can recover the entrapped guest. It is also found the encapsulation of a dye is usually accompanied with dye stacking, resulting in a changed UV/vis spectrum. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 872–881     

pH响应的介孔二氧化硅纳米颗粒的制备及可控释放

选择带负电荷且溶解度和分子结构对pH值非常敏感的聚丙烯酸作为封堵分子, 采用静电吸附的修饰方法, 制备了pH响应的MCM-41型介孔二氧化硅纳米颗粒. 利用高倍透射电子显微镜(TEM)、 X射线衍射(XRD)、 傅里叶变换红外光谱(FTIR)及比表面积分析等手段表征了介孔二氧化硅纳米颗粒的物理化学性质. 以联钌吡啶染料分子作为模式客体分子, 研究了pH调控下的模式客体分子在介孔二氧化硅纳米颗粒中的包裹及释放行为. 结果表明, 该介孔二氧化硅纳米颗粒对pH具有很好的响应性; 在近中性条件下, 带正电的二氧化硅纳米颗粒通过静电吸附作用吸附带负电的聚丙烯酸, 导致介孔封堵, 使包载的染料分子几乎无释放; 客体分子的释放率随着pH值的降低而升高, 当pH≤5时, 染料分子显著释放, pH=1时客体分子的释放率高达98％, 可以实现对包载客体分子的控制释放. 该pH响应的介孔二氧化硅纳米颗粒载体具有制备简便、 价格低廉和包载量大等优点, 有望应用于药物的控制释放.     

SIMILARITIES IN THE INDUCTION OF SYNTHESIS OF A CELL-SURFACE POLYPEPTIDE IN Arthrobacter sp. BY NEAR-UV IRRADIATION and PHOTODYNAMIC CONDITIONS

Irradiation of aerobic suspensions of Arthrobacter sp. with near-UV light (310-400 nm) induced synthesis of a 21 000 dalton, cell-surface polypeptide. Synthesis of this polypeptide also was induced by visible light in the presence of photodynamic dyes, as shown previously (Hoober, 1978). Induction of the polypeptide in near-UV light and with visible light plus dyes was inhibited by histidine. Hemin inhibited induction in near-UV light and in visible light with methylene blue, neutral red and acrifiavin, which are cationic dyes, but failed to inhibit induction in visible light with rose bengal, an anionic dye. These results suggested that inhibition by hemin required electrostatically favored interaction between the anionic porphyrin and the sensitizer, and that the near-UV light effect was mediated by a cationic or neutral endogenous sensitizer. The similarities in the responses of the cells to near-UV irradiation and visible light plus dyes suggested that the mechanism of induction under the two conditions was the same.     

Synthesis and Electrochemistry of Tetraphenylporphyrins Containing an Antimony-Carbon sigma-Bond

The following five antimony(V) tetraphenylporphyrins with sigma-bonded antimony-carbon bonds were synthesized: [(TPP)Sb(CH(3))(2)](+)PF(6)(-), [(TPP)Sb(OCH(3))(OH)](+)PF(6)(-), [(TPP)Sb(CH(3))(OH)](+)ClO(4)(-), [(TPP)Sb(CH(3))(OCH(3))](+)ClO(4)(-), and [(TPP)Sb(CH(3))(F)](+)PF(6)(-). Each compound is stable toward air and moisture and has a high melting point (>250 degrees C). The electrochemistry and spectroelectrochemistry of these sigma-bonded porphyrins were examined in benzonitrile or dichloromethane containing 0.1 M tetrabutylammonium perchlorate as supporting electrolyte and the data compared to those for three previously synthesized OEP derivatives containing similar sigma-bonded and/or anionic axial ligands. Each porphyrin shows two reversible reductions and up to a maximun of one oxidation within the potential window of the solvent. Spectroelectrochemical data indicate formation of a porphyrin pi anion radical upon the first reduction as do ESR spectra of the singly reduced species. However, a small amount of the Sb(III) porphyrin products may be generated via a chemical reaction following electron tranfer. An X-ray crystallographic analysis of [(TPP)Sb(CH(3))(F)](+)PF(6)(-) is also presented: monoclinic, space group C2/c, Z = 8, a = 24.068(5) ?, b = 19.456(4) ?, c = 18.745(3) ?, beta = 94.69(2) degrees, R = 0.056.     

The Adsorption of Gemini and Conventional Surfactants onto Some Soil Solids and the Removal of 2-Naphthol by the Soil Surfaces

The adsorption of two cationic gemini surfactants, [C(n)H(2n+1) N(+)(CH(3))(2)-CH(2)CH(2)](2).2Br(-), where n=12 and 14, on limestone, sand, and clay (Na-montmorillonite) from their aqueous solution in double-distilled water and the effect of this adsorption on the removal of 2-naphthol have been studied. Compared to those of conventional cationic surfactants with similar single hydrophilic and hydrophobic groups (C(n)H(2n+1)N(+)(CH(3))(3).Br(-), where n=12 and 14), the molar adsorptions of the gemini and the conventional surfactants on Na-montmorillonite are almost identical and very close to their cation exchange capacities. On sand and limestone, the molar adsorption of the cationic gemini surfactants is much larger than that of their corresponding conventional surfactants. Adsorption studies of the pollutants onto the three kinds of solids treated by either the gemini or the conventional surfactants show that the former are both more efficient and more effective at removing 2-naphthol from the aqueous phase. On all three soil solids, the addition of KBr increases the efficiency of the adsorption of both types of cationics and for most cases increases also the maximum amount adsorbed, but decreases slightly the efficiency of removal of 2-naphthol. On limestone, the anionic gemini adsorbs with one hydrophilic group oriented toward the Ca(2+) sites on the surface and its second hydrophilic group oriented toward the aqueous phase. The conventional anionic surfactant forms a double layer. The gemini anionic is more efficient and more effective than the conventional anionic in the removal of 2-naphathol from the aqueous phase. Both anionic conventional and gemini surfactants have no adsorption on sand. The adsorption mechanisms for all the surfactants on the three soil solid surfaces are discussed. Copyright 2001 Academic Press.     

The infrared spectrum of solid L-alanine: influence of pH-induced structural changes

The influence of the pH on the infrared spectrum of L-alanine has been analyzed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The amino acid was precipitated from aqueous solutions and dried at 36.5 degrees C, in order to stabilize cationic L-alanine or alaninium [CH3CH(NH3(+))COOH] at pH 1, the zwitterionic form [CH3CH(NH3(+))COO(-)] at pH 6, and anionic L-alanine or alaninate [CH3CH(NH2)COO(-)] at pH 13. New insight on the specific inter and intramolecular interactions in the different forms of L-alanine was reached by a novel methodological approach: an infrared technique not used before to analyze solid amino acid samples (DRIFTS), in combination with a detailed analysis based on spectral deconvolution. The frequency ranges of interest include the carbonyl/carboxyl stretching and amine deformation modes and the OH/NH stretching modes. It was shown that intermolecular hydrogen bonds between the NH3(+) and COO(-) groups are predominant in the zwitterionic form, whereas in cationic L-alanine, H bonds between the COOH groups are responsible for the formation of dimers. In anionic L-alanine, only strong electrostatic interactions between the COO(-) groups and Na(+) ions are proposed, evidencing the relevant role of the counterion.     

Release and molecular transport of cationic and anionic fluorescent molecules in mesoporous silica spheres

We describe here a method for study of bulk release and local molecular transport within mesoporous silica spheres. We have analyzed the loading and release of charged fluorescent dyes from monodisperse mesoporous silica (MMS) spheres with an average pore size of 2.7 nm. Two different fluorescent dyes, one cationic and one anionic, have been loaded into the negatively charged porous material and both the bulk release and the local molecular transport within the MMS spheres have been quantified by confocal laser scanning microscopy. Analysis of the time-dependent release and the concentration profiles of the anionic dye within the spheres show that the spheres are homogeneous and that the release of this nonadsorbing dye follows a simple diffusion-driven process. The concentration of the cationic dye varies radially within the MMS spheres after loading; there is a significantly higher concentration of the dye close to the surface of the spheres (forming a "skin") compared to that at the core. The release of the cationic dye is controlled by diffusion after an initial period of rapid release. The transport of the cationic dye within the MMS spheres of the dye from the core to near the surface is significantly faster compared to the transport within the surface "skin". A significant fraction of the cationic dye remains permanently attached to the negatively charged walls of the MMS spheres, preferentially near the surface of the spheres. Relating bulk release to the local molecular transport within the porous materials provides an important step toward the design of new concepts in controlled drug delivery and chromatography.     

Methylammonium groups at the solid walls of nanometer-sized, water-filled monolayer gaps as binding sites for a tetraanionic porphyrin

Long-chain hydrosulfides containing two secondary amide functions and either electron-poor or electron-rich carbon-carbon double bonds were self-assembled on gold surfaces around a flat-lying, octaanionic porphyrin. Rigid and reactive surface monolayers with 2 nm-wide, porphyrin-based gaps were thus obtained. The gold electrodes were then immersed in water, and the double bonds on the gaps' surfaces reacted with methylamine. It was added to the double bonds either by Michael addition or by bromination with hypobromite followed by methylamine substitution. Only the double bonds at the border of the gaps were accessible to methylamine dissolved in the bulk water volume and could react. The walls of the rigid membrane gaps now contained methylammonium groups at the sites of the double bonds in defined heights. A tetracationic copper(II) porphyrinate could not diffuse any more into the gap and did not quench the fluorescence of the octaanionic porphyrin on the bottom of the gap. A tetraanionic porphyrin, on the other hand, was fixated by the ring of ammonium groups. The bound porphyrin then acted as molecular cover for the gap with respect to ferricyanide transport from bulk water to the electrode. It was removed by raising the pH to a value of 12, where the methylammonium groups were neutralized to amines. Lowering the pH to 7 again and addition of more of the anionic porphyrin reclosed the gap.The porphyrin "cover" should be localized at distances of 8-10 and 20 A from the bottom porphyrin by multiple charge interactions. The 8-10 A distance is ideal for studies of photoinduced electron transfer between two porphyrin monomers of different redox potential. Furthermore it was found, that redox-active tyrosine could be trapped in the water volume above the porphyrin on gold.     

Cationic Zr-based metal-organic framework via post-synthetic alkylation for selective adsorption and separation of anionic dyes

Adsorption and separation of toxic organic dyes are of great importance in wastewater treatment and dye recycling. In this work, cationic metal-organic framework MIL-140C–2NMe⁺ with triangular hydrophobic channels was prepared in which methyl groups were added to the pyridyl sites of the ligand [2,2'-bipyridine]-5,5'-dicarboxylic acid (H₂bpydc) via post-synthetic alkylation reaction. MIL-140C–2NMe⁺ can be used as an efficient adsorbent for the selective adsorption and separation of anionic dyes in the aqueous mixture of cationic/anionic dyes. Specifically, the adsorption capacities of MIL-140C–2NMe⁺ for anionic methyl orange can reach 310 mg/g in 10 min. With a facile doctor-blading process, we have also polymerized the MIL-140C–2NMe⁺ nanocrystals and polyvinylidene fluoride (PVDF) polymer to fabricate a flexible and self-supporting mixed matrix membrane (MMM), which can selectively capture and separate the anionic organic dyes from the binary dye mixtures.     

Effect of polyelectrolytes and polyelectrolyte mixtures on the electrokinetic potential of dispersed particles. 2. Electrokinetic potential of silica particles in electrolyte, polyelectrolyte and polyelectrolyte mixtures solutions

The effect pH, ionic strength (KCl concentration), weakly and medium charged anionic and cationic polyelectrolytes (PEs) as well as their binary mixtures on the electrokinetic potential of silica particles as a function of the polyelectrolyte/mixture dose, its composition, charge density (CD) of the PE, and way of adding the polymers to the suspension has been studied. It has been shown that addition of increasing amount of anionic PEs increases the absolute value of the negative zeta-potential of particles at pH > pH isoelectric point (IEP = 2.5); this increase is stronger the charge density of the polyelectrolyte is higher. Adsorption of cationic polyelectrolytes at these pH values gives a significant decrease in the negative ζ-potential and overcharging the particles; changes in the ζ-potential are more pronounced for PE samples with higher CD. In mixtures of cationic and anionic PE at pH > pHIEP, the ζ-potential of particles is determined by the adsorbed amount of the anionic polymer independently of the CD of PEs, the mixture composition and the sequence of addition of the mixture components. Unexpectedly, the ζ-potential of silica at pH = 2.1, i.e. < pHIEP, turned out to be positive in the presence of both anionic PE and cationic + anionic PE mixtures. This is explained by formation (and adsorption onto positively charged silica surface) of pseudo-cationic PEs from anionic ones due to transfer of protons from the solution to the amino-group of the anionic polymer. Considerations about the role of coulombic and non-coulombic forces in the mechanism of PE adsorption are presented.     

Charge selective encapsulation by polymeric micelles with cationic,anionic, or zwitterionic cores

Polymeric micelles showing charge selective and pH‐reversible encapsulation are reported. It is found that for a guest mixture of organic cationic–anionic dyes, a unimolecular micelle (PEI@PS) with a polystyrene (PS) as shell and a hyperbranched polyethylenimine (PEI) as core can exclusively entrap the anionic one; and a physical micelle consisting of brush‐like macromolecule (mPS‐PAA) with multi PS‐b‐polyacrylic acid (PAA) as grafts can exclusively entrap the cationic one. A covalent micelle (PEI‐COOH@PS) bearing a zwitterionic core, that is, PEI covalently derived with dense carboxylic acids, can undergo highly pH‐switchable charge selective and pH‐reversible encapsulation. Both PEI@PS and mPS‐PAA can be used for highly charge‐selective separation of ionic dyes but the pH‐reversibility of the encapsulation is relatively limited. In contrast, PEI‐COOH@PS is less effective to differentiate the anionic–cationic dyes but is well recyclable. A physical micelle obtained from the self‐assembly of PEI and mPS‐PAA shows similar property to PEI‐COOH@PS. The combination of these micelles in mixture separation can enhance the recyclability of the micelle and widen the spectrum of mixtures that can be well separated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012