Controlled synthesis of stable poly(vinyl formamide-co-vinyl amine)/silica hybrid particles by interfacial post-cross-linking reactions

 The chemical synthesis and the physicochemical properties of stable poly(vinyl formamide-co-vinyl amine)/silica hybrid particles are presented. Copolymers of poly(vinyl formamide) (PVFA) and poly(vinyl amine) (PVAm) and their protonated forms were adsorbed onto silica from aqueous solutions. The influences of the pH strength and the ion concentration of the aqueous solution as well as the copolymer composition (degree of hydrolyzation of PVFA), and the molecular mass on the adsorption process were investigated by electrokinetic measurements, potentiometric titration, and quantitative elemental analyses. Silica surface-charge neutralization is achieved at a pH strength above 10 for highly hydrolyzed (95%) PVFA polymers. Decreasing the amino content in the PVAm chain shifts successively both the point of zero charge and the isoelectric point to lower pH values. PVFA-co-PVAm layers onto silica are adsorbed weakly. To fix these layers irreversibly, cross-linking reactions with (4,4′-diisocyanate)diphenyl methane were carried out on the surface of solid PVFA-co-PVAm/silica hybrid particles suspended in acetone. The cross-linking reaction, which is connected with the conversion of amino groups, is also a tool to control the surface charge of the PVFA-co-PVAm/silica hybrids. X-ray photoelectron spectroscopy and solid-state ¹³C cross-polarization magic-angle spinning NMR spectroscopy were used to obtain information on the number of and the structure of the functionalized polyelectrolyte layers on silica. The success of cross-linking was also shown by the results of these spectroscopic methods. Received: 28 June 1999 /Accepted: 27 August 1999     

Flame atomic absorption spectrometric determination of zinc after colloid precipitate flotation with hydrated iron(III) oxide and iron(III) tetramethylenedithiocarbamate as collectors

Colloid flotation of zinc from fresh water with a combination of two collectors, hydrated iron(III) oxide (Fe(2)O(3).xH(2)O) and iron(III) tetramethylenedithiocarbamate (Fe(TMDTC)(3)), permits rapid separation of the precipitate before its atomic absorption spectrometric (AAS) analysis. All important parameters necessary for the successful flotation like optimal mass of collectors, pH of the medium, electrokinetic potential of the collector particle surfaces, type of tenside, induction time etc., were checked. At the optimal pH value of medium (5.5) establishing by recommended procedure, zinc was separated quantitatively (97.4-98.8%) with 5 mg Fe(III) as constitutive element of the two collectors used. The content of zinc was determined by flame atomic absorption spectrometry (FAAS). These results were compared with the results obtained by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The FAAS detection limit for zinc is 9.4 mug 1(-1). The proposed method is simple, rapid and applicable to the zinc separation at mug 1(-1) levels from a large volume of water.     

Interaction between poly(styrene-acrylic acid) latex nanoparticles and zinc oxide surfaces

Latex particles with an average diameter of 70 nm, functionalized at the surface with carboxylic groups, are chemically coated by layer-by-layer deposition onto a spherical probe attached on an atomic force microscope cantilever. The forces between poly(styrene-acrylic acid) latex nanoparticles and differently terminated zinc oxide surfaces are studied by a homemade atomic force microscope based apparatus. The results confirmed a preferred adhesion of the latex particles to zinc-terminated ZnO faces, 0001, compared to oxygen-terminated and apolar faces. The method proposed allows the measurement of the interaction between nanometric particles and planar surfaces, which may be of interest for different applications in surface and colloid sciences.     

ATR-IR spectroscopic study of antimonate adsorption to iron oxide

Antimonate ions adsorb to iron oxides in mining contexts, but the nature of the adsorbed antimonate species has not frequently been investigated. In this study, ATR-IR spectroscopy was used to reveal that the adsorption of Sb(OH)6- ion from aqueous solutions onto an amorphous iron oxide particle film is accompanied by changes in the Sb(OH)6- spectrum and the loss of OH stretching absorptions from iron oxide surface hydroxyl groups. These spectral changes upon adsorption imply an inner-sphere surface interaction with the formation of Sb-O-Fe bonds as well as some outer-sphere adsorption. The corresponding results from solutions of antimonate in D2O confirm that chemisorption occurs. The dependence of antimonate adsorption on pH in the range from 8 to 3 follows that expected for anions on iron oxide considering its pH-dependent surface charge, with the greatest amount of adsorbed antimonate at pH 3. The study of adsorption/desorption kinetics showed a more rapid desorption of adsorbed antimonate under alkaline conditions. This trend is expected from the pH dependence of the antimonate charge and iron oxide surface charge, but it might be partly due to the fact that high pH favors hydrolysis of antimonate oligomers formed on the iron oxide surface from adsorption under acidic conditions.     

Ni(II) complexation to amorphous hydrous ferric oxide: an X-ray absorption spectroscopy study

Ni(II) sorption onto iron oxides and in particular hydrous ferric oxide (HFO) is among the important processes impacting its distribution, mobility, and bioavailability in environment. To develop mechanistic models for Ni, extended X-ray absorption fine structure (EXAFS) analysis has been conducted on Ni(II) sorbed to HFO. Coprecipitation revealed the formation of the metastable alpha-Ni(OH)(2) at a Ni(II) loading of 3.5 x 10(-3) molg(-1). On the other hand, Ni(II) formed inner-sphere mononuclear bidentate complexes along edges of FeO(6) octahedra when sorbed to HFO surfaces with Ni-O distances of 2.05-2.07 A and Ni-Fe distances of 3.07-3.11 A. This surface complex was observed by EXAFS study over 2.8 x 10(-3) to 10(-1) ionic strength, pH from 6 to 7, a Ni(II) loading of 8 x 10(-4) to 8.1 x 10(-3) molg(-1) HFO, and reaction times from 4 hours to 8 months. The short- and long-range structure analyses suggest that the presence of Ni(II) inhibited transformation of the amorphous iron oxide into a more crystalline form. However, Ni(2+) was not observed to substitute for Fe(3+) in the oxide structure. This study systematically addresses Ni(II) adsorption mechanisms to amorphous iron oxide. The experimentally defined surface complexes can be used to constrain surface complexation modeling for improved prediction of metal distribution at the iron oxide/aqueous interface.     

Synthesis, characterization, and intracellular uptake of carboxyl-terminated poly(amidoamine) dendrimer-stabilized iron oxide nanoparticles

We report the synthesis and characterization of a group of carboxyl-functionalized poly(amidoamine) (PAMAM) dendrimers of generation 3 (G3) that were used for the stabilization of superparamagnetic iron oxide (Fe(3)O(4)) nanoparticles (NPs). Folic acid (FA) molecules were conjugated onto the dendrimer surfaces in an attempt to achieve specific targeted imaging of tumor cells that overexpress FA receptors using dendrimer-stabilized Fe(3)O(4) NPs. Fe(3)O(4) NPs were synthesized using controlled co-precipitation of Fe(ii) and Fe(iii) ions and the formed dendrimer-stabilized Fe(3)O(4) NPs were characterized using transmission electron microscopy (TEM) and polyacrylamide gel electrophoresis (PAGE). The intracellular uptake of dendrimer-stabilized Fe(3)O(4) NPs was tested in vitro using KB cells (a human epithelial carcinoma cell line) that overexpress FA receptors. It appears that carboxyl-terminated PAMAM dendrimer-stabilized Fe(3)O(4) NPs can be uptaken by KB cells regardless of the repelling force between the negatively charged cells and the negatively charged particles. In the presence of a large amount of carboxyl terminal groups on the dendrimer surface, the receptor-mediated endocytosis of Fe(3)O(4) NPs stabilized by FA-modified dendrimers was not facilitated. It implies that the surface charge of dendrimer-stabilized magnetic iron oxide NPs in biological medium is an important factor influencing their biological performance.     

Chicken and duck eggshell beads modified with iron (III) oxide-hydroxide and zinc oxide for reactive blue 4 dye removal

Releasing contaminated dyes into water bodies might create environmental problems for water quality and toxic aquatic organisms. The toxicity of dyes might affect human health throughout the food chain, so it is necessary to treat contaminated dye in wastewater before discharging it into the water body. Chicken eggshell beads (CB), duck eggshell beads (DB), chicken eggshell beads mixed iron (III) oxide-hydroxide (CBF), duck eggshell beads mixed iron (III) oxide-hydroxide (DBF), chicken eggshell beads mixed zinc oxide (CBZ), and duck eggshell beads mixed zinc oxide (DBZ) were synthesized, and several characterized techniques of XRD, FESEM-FIB, EDX, and FTIR were used to identify the crystalline structure, surface morphology, and chemical composition and functional groups. Reactive blue 4 (RB4) dye removal efficiencies on dye adsorbent materials were investigated through batch experiments with varying doses, contact time, temperature, pH, and concentration. Their adsorption patterns and mechanisms also were studied by adsorption isotherm and kinetics. All dye adsorbent materials demonstrated semi-crystalline structures, and their surface morphologies had a spherical shape with coarse surfaces. Oxygen, carbon, calcium, chlorine, and sodium and four main function groups of OH, NH, CO, and COC were detected in all dye adsorbent materials. For batch tests, they could remove RB4 dye by more than 56%, and CBF represented the highest RB4 dye removal efficiency at 84.44%. Moreover, the addition of iron (III) oxide-hydroxide and zinc oxide helped to improve RB4 dye adsorbent efficiencies which an iron (III) oxide-hydroxide increased RB4 removal efficiency of chicken and duck eggshell beads more than zinc oxide. Their adsorption patterns and mechanisms were well explained by Freundlich and pseudo-second-order kinetic models. Therefore, all dye adsorbent materials especially CBF are potential dye adsorbent materials for further industrial applications.     

Patterned langmuir-blodgett films of monodisperse nanoparticles of iron oxide using soft lithography

Langmuir-Blodgett (LB) films of monodisperse iron oxide nanoparticles have been successfully deposited onto patterned poly(dimethylsiloxane) surfaces. These patterned LB films of iron oxide nanoparticles were transferred onto solid substrates using micro contact printing.     

Immobilization of anionic iron(III) porphyrins onto in situ obtained zinc oxide

A family of anionic iron(III) porphyrins (FePor) was immobilized onto zinc oxide (ZnO) obtained by the in situ hydrothermal decomposition of zinc hydroxide nitrate, a layered hydroxide salt. The immobilization probably occurred via the interaction between the anionic charges on the porphyrins and the positively charged surface of the ZnO, in slightly acidic to neutral pH. The resulting solids were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRDP), Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR), and ultraviolet-visible spectroscopy (UV-Vis) (solid samples), which confirmed the formation of ZnO and the immobilization of the FePor. The prepared materials were employed as catalysts for the heterogeneous catalytic oxidation of cyclooctene, cyclohexane, and n-heptane, using iodosylbenzene as the oxygen donor. Good catalytic results were achieved for all the substrates, and selectivity for the alcohol was verified during the oxidation of alkanes. The reuse capacity of the solid catalyst was also investigated.     

Zerovalent metal polymer composites. III. Metallization of metal oxide surfaces with the aid of metallized functional polymer microdispersions

The adsorption of poly[N-(m- and p-vinylbenzyl)-N,N,N-trimethylammonium tetrachloropal-ladate] complex on inorganic oxide surfaces followed by reduction of the palladium salt to form a catalytically active zerovalent metal polymer composite dispersed on the oxide surface and further deposition of transition metals, e.g., nickel, cobalt, and copper, by “additive” or “subtractive” deposition from electroless plating solutions is described. γ-Ferric oxide was used as a template for such intermetallic replacement reactions, providing materials with controlled amounts of metal. Multimetallic catalysts based on aluminum oxide, zinc oxide, lanthanum oxide, magnesium oxide, and silica were prepared. Iron oxide modified by subtractive deposition of rhodium and iridium on nickel-clad iron oxide were evaluated in Fischer–Tropsch carbonylation reactions leading from synthesis gas to alkanols.     

Preconcentration of some phosphorus-containing anions by adsorption on hydrated iron(III) oxide

The adsorption behaviour of orthophosphate, triphosphate, pyrophosphate, monomethylphosphate, phosphite, α- and β-glycerophosphates, dimethylphosphate, and hypophosphite on hydrated iron(III) oxide precipitate is studied as a function of pH. Orthophosphate is adsorbed quantitatively at pH 4.0–8.0, triphosphate and pyrophosphate at pH 4–9.3 and the next three compounds at pH 4–6.8. The last two ions were only slightly adsorbed at any pH examined.     

Adsorption properties of poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) at a hydrophobic interface: influence of tribological stress, pH, salt concentration, and polymer molecular weight

The adsorption properties of a graft copolymer of poly(ethylene glycol) (PEG) with a polycationic backbone, namely, poly( l-lysine)- graft-poly(ethylene glycol) (PLL- g-PEG), onto nonpolar, hydrophobic PDMS surfaces from aqueous solution and the lubrication properties of the self-mated sliding contacts of PDMS surfaces modified with PLL- g-PEG have been investigated. Whereas PLL- g-PEG is spontaneously attracted to negatively charged surfaces as a result of the polycationic PLL backbone, the collective interaction of (CH 2) 4 hydrocarbon moieties on the lysine units in the PLL backbone with nonpolar, hydrophobic surfaces also enables the adsorption of PLL- g-PEG onto hydrophobic surfaces such as PDMS. The adsorption and lubrication properties of PLL- g-PEG have been investigated by varying the aqueous solution parameters, such as pH (2, 7, and 12) and KCl concentration (0, 0.01, 0.1, and 1 M) as well as the length of the PLL backbone of the copolymer (20 vs 375 kDa). In the absence of tribological stress, the adsorption of PLL- g-PEG onto PDMS surfaces was mainly governed by the KCl concentration, whereas the role of pH or the molecular weight of the copolymer was of relatively minor importance; for all pH values, the adsorbed mass decreased with increasing KCl concentration. Under tribological stress, however, a clear dependence of the lubrication properties of PLL- g-PEG on all of the studied parameters, including pH, KCl concentration, and backbone molecular weight, was observed. The adsorption strength of PLL- g-PEG on PDMS surfaces, rather than the adsorbed mass itself, appeared to be the most critical parameter in determining the lubrication properties.     

Adsorption of microcystin-Lr onto iron oxide nanoparticles

In this study, the adsorption of microcystin-LR onto iron oxide (maghemite) nanoparticles from water was examined. Factors influencing the sorption behavior included microcystin and maghemite concentration, pH, ionic strength, and the presence of natural organic matter. Adsorption of microcystin-LR was strongly affected by pH. The adsorption increased with decreasing pH, with a maximum adsorption around pH 3. Adsorption of microcystin-LR on maghemite was primarily attributed to electrostatic interactions, although hydrophobic interactions may also play a role. The extent of microcystin-LR adsorption onto maghemite increased with increasing ionic strength at pH 6.4, since salt ions screened the electrostatic repulsion between adsorbed microcystin molecules. Adsorption of microcystin-LR was not significantly affected by the presence of Suwannee River Fulvic acid (SRFA) below 2.5 mg/L. However, adsorption decreased at higher SRFA concentrations (2.5–25 mg/L) due to competitive adsorption between SRFA and microcystin-LR for limited sorption sites.     

Effect of iron oxide coatings on zinc sorption mechanisms at the clay-mineral/water interface

Oxide surface coatings are ubiquitous in the environment, but their effect on the intrinsic metal uptake mechanism by the underlying mineral surface is poorly understood. In this study, the zinc (Zn) sorption complexes formed at the kaolinite, goethite, and goethite-coated kaolinite surfaces, were systematically studied as a function of pH, aging time, surface loading, and the extent of goethite coating, using extended X-ray absorption fine structure (EXAFS) spectroscopy. At pH 5.0, Zn partitioned to all sorbents by specific chemical binding to hydroxyl surface sites. At pH 7.0, the dominant sorption mechanism changed with reaction time. At the kaolinite surface, Zn was incorporated into a mixed metal Zn-Al layered double hydroxide (LDH). At the goethite surface, Zn initially formed a monodentate inner-sphere adsorption complex, with typical Zn-Fe distances of 3.18 A. However, with increasing reaction time, the major Zn sorption mechanism shifted to the formation of a zinc hydroxide surface precipitate, with characteristic Zn-Zn bond distances of 3.07 A. At the goethite-coated kaolinite surface, Zn initially bonded to FeOH groups of the goethite coating. With increasing aging time however, the inclusion of Zn into a mixed Zn-Al LDH took over as the dominant sorption mechanism. These results suggest that the formation of a precipitate phase at the kaolinite surface is thermodynamically favored over adsorption to the goethite coating. These findings show that the formation of Zn precipitates, similar in structure to brucite, at the pristine kaolinite, goethite, and goethite-coated kaolinite surfaces at near neutral pH and over extended reaction times is an important attenuation mechanism of metal contaminants in the environment.     

Click-chemistry for surface modification of monodisperse-macroporous particles

In this study, click chemistry was proposed as a tool for tuning the surface hydrophilicity of monodisperse-macroporous particles in micron-size range. The monodisperse-porous particles carrying hydrophobic or hydrophilic molecular brushes on their surfaces were obtained by the proposed modification. Hydrophilic poly(glycidyl methacrylate-co-ethylene dimethacrylate), poly(GMA-co-EDM) particles were hydrophobized by the covalent attachment of poly(octadecyl acrylate-co-propargyl acrylate), poly(ODA-co-PA) copolymer onto the particle surface via triazole formation by click chemistry. In the second part, Hydrophobic poly(4-chloromethylstyrene-co-divinylbenzene), poly(CMS-co-DVB) particles were hydrophilized by the covalent attachment of poly(vinyl alcohol), PVA onto their surface also via triazole formation by click chemistry. The presence of PVA and poly(ODA-co-PA) copolymer on the corresponding particles was shown by FTIR-DRS. After click-coupling reactions applied for both hydrophobic poly(CMS-co-DVB) and hydrophilic poly(GMA-co-EDM) particles, the marked changes in surface polarity were shown by contact angle measurements. Protein adsorption characteristics of plain and modified particles were investigated for both materials. In the isoelectric point of albumin, the non-specific albumin adsorption decreased from 225 to 80 mg/g by grafting PVA onto the poly(CMS-co-DVB) beads. On the other hand, the non-specific albumin adsorption onto the plain poly(GMA-co-EDM) beads increased from 50 to 400 mg/g by the covalent attachment of poly(ODA-co-PA) copolymer onto the bead-surface via click chemistry. The protein adsorption behavior was efficiently regulated by the covalent attachment of appropriate molecular brushes onto the surfaces of selected particles. The results indicated that "click chemistry" was an efficient tool for controlling the polarity of monodisperse-macroporous particles.     

Antibiofouling polymer-coated superparamagnetic iron oxide nanoparticles as potential magnetic resonance contrast agents for in vivo cancer imaging

We report the fabrication and characterization of antifouling polymer-coated magnetic nanoparticles as nanoprobes for magnetic resonance (MR) contrast agents. Magnetite superparamagnetic iron oxide nanoparticles (SPION) were coated with the protein- or cell-resistant polymer, poly(TMSMA-r-PEGMA), to generate stable, protein-resistant MR probes. Coated magnetic nanoparticles synthesized using two different preparation methods (in situ and stepwise, respectively) were both well dispersed in PBS buffer at a variety of pH conditions (pH 1-10). In addition, dynamic light scattering data revealed that their sizes were not altered even after 24 h of incubation in 10% serum containing cell culture medium, indicative of a lack of protein adsorption on their surfaces. When the antibiofouling polymer-coated SPION were incubated with macrophage cells, uptake was significantly lower in comparison to that of the popular contrast agent, Feridex I.V., suggesting that the polymer-coated SPION can be long-circulated in plasma by escaping from uptake by the reticular endothelial system (RES) such as macrophages. Indeed, when the coated SPION were administered to tumor xenograft mice by intravenous injection, the tumor could be detected in T2-weighted MR images within 1 h as a result of the accumulation of the nanomagnets within the tumor site. Although the poly(TMSMA-r-PEGMA)-coated SPION do not have any targeting ligands on their surface, they are potentially useful for cancer diagnosis in vivo.     

Poly(methyl methacrylate) composites prepared by in situ polymerization using organophillic nano-to-submicrometer zinc oxide particles

Nano- and submicrometer zinc(II) oxide particles were synthesized by the polyol method and were used for the preparation of ZnO/poly(methyl methacrylate) (ZnO/PMMA) composite materials by the chain polymerization of methyl methacrylate (MMA) in bulk. ZnO particles with an organophilic surface layer were homogeneously dispersed in the PMMA matrix. Very low concentrations (0.1 wt.%) of nano zinc oxide absorbed over 98% of UV light as determined by UV-vis spectroscopy. Nano zinc oxide (75 nm) increased the initial decomposition temperature of the PMMA matrix by 30-40 °C at concentrations of 0.1% and above. This was explained by the changes in the termination mechanism of MMA polymerization resulting in a reduced concentration of vinylidene chain ends. Nano ZnO also increased the MMA polymerization reaction rate and reduced the activation energy. Submicrometer ZnO showed lower UV absorption, thermal stabilization and no influence on the reaction kinetics indicating that average particle size is of vital importance for the properties of PMMA nanocomposites and for MMA polymerization.     

Adsorption of barium and calcium chloride onto negatively charged alpha-Fe(2)O(3) particles

Adsorption of cations (Na(+), Ca(2+), Ba(2+)) onto negatively charged (pH 10.4) hematite (alpha-Fe(2)O(3)) particles has been studied. The oxide material was carefully prepared in order to obtain monodisperse suspensions of well-crystallized, quasi-spherical particles (50 nm in diameter). The isoelectric point (IEP) is located at pH 8.5. Adsorption of barium ions onto oxide particles was carried out and the electrophoretic mobility was measured throughout the adsorption experiment. Comparison with calcium adsorption at full coverage reveals a higher uptake of Ba(2+). In both cases it shows also that chloride ions coadsorb with M(2) ions. Simultaneous uptake of the positive and negative ions explains why the electrophoretic mobility does not reverse to cationic migration. A theoretical study of the surface speciation has been carried out, using the MuSiC model. It reveals the presence of negative as well as positive sites on both sides of the point of zero charge (PZC) of the hematite particles, which may explain the coadsorption of Ba(2+) and Cl(-) at pH 10.4. The effective charge of the oxide particles, calculated from the electrophoretic mobility, is in very good agreement with the results found with the MuSiC modelization and the chloride/barium adsorption ratio. It also verifies the theory of ionic condensation. Calorimetric measurements gave a negative heat for the overall reaction occurring when Ba(2+)/Cl(-) ions adsorb onto hematite. Despite the fact that anions (Cl(-) and OH(-)) adsorption onto mineral oxides is an exothermic phenomenon, it is likely that barium and calcium adsorption is endothermic, denoting the formation of an inner-sphere complex as reported in the literature.     

Equilibrium and kinetic aspects of the uptake of poly(ethylene oxide) by copolymer microgel particles of N-isopropylacrylamide and acrylic acid

The use of microgels for controlled uptake and release has been an area of active research for many years. In this work copolymer microgels of N-isopropylacrylamide (NIPAM) and acrylic acid (AAc), containing different concentrations of AAc and also cross-linking monomer, have been prepared and characterized. These microgels are responsive to pH and temperature. As well as monitoring the equilibrium response to changes in these variables, the rates of swelling/de-swelling of the microgel particles, on changing either the pH or the temperature, have also been investigated. It is shown that the rate of de-swelling of the microgel particles containing AAc is much faster than the rate of swelling, on changing the pH appropriately. This is explained in terms of the relative mobilities of the H(+) and Na(+) ions, in and out of the particles. It was observed that the microgels containing AAc, at pH 8, de-swelled relatively slowly on heating to 50 degrees C from 20 degrees C. This is attributed to the resistance to collapse associated with the large increase in counterion concentration inside the microgel particles. The swelling and de-swelling properties of these copolymer microgels have also been investigated in aqueous poly(ethylene oxide) (PEO) solutions, of different MW (2000-300 000). The corresponding absorbed amounts of PEO from solution onto the microgels have also been determined using a depletion method. The results, as a function of AAc content, cross-linker concentration, PEO MW, pH, and temperature, have been rationalized in terms of the ease and depth of penetration of the PEO chains into the various microgel particles and also the H-bonding associations between PEO and either the -COOH of the AAc moeities and/or the H of the amide groups (much weaker). Finally, the adsorption and desorption of the PEO molecules in to and out of the microgel particles have been shown to be extremely slow compared to normal diffusion time scales for polymer adsorption onto rigid surfaces.