An explanation of silicate exfoliation in polyacrylonitrile/silicate nanocomposites prepared by in situ polymerization using an initiator adsorbed on silicate

Sodium montmorillonite (Na-MMT) absorbed a radical initiator, potassium persulfate (KPS), by way of hydrogen bonding between hydroxyl groups in the Na-MMT lattice and the sulfonic anions of KPS. FT-IR absorbance bands of hydroxyl groups in the Na-MMT lattice and the sulfonic anions of KPS shifted to lower wavenumber regions, compared with the free silicate and the initiator. The amounts of initiator adsorbed on the silicate were determined by using thermogravimetric analysis. The initiator adsorbed on silicate (IAS) commenced the polymerization of acrylonitrile (AN), delaminating silicate layers in polyacrylonitrile (PAN)/silicate nanocomposites. Molecular weights of PANs extracted from the nanocomposites decreased as the amount of initiator in IAS increased. Heterogeneous nucleation, polymerization in the basal spacing of the silicate layers, was analyzed by high performance liquid chromatograph. Storage moduli, E′, of the nanocomposites were enhanced with the molecular weights of PAN matrixes. Glass temperatures, T_g, of the nanocomposites were dependent on the molecular weights of the PAN matrixes and the contents of the 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) charged.     

Synthesis and characterization of poly(acrylonitrile)/montmorillonite nanocomposites from surface‐initiated redox polymerization

We have developed a facile method to prepare polyacrylonitrile/montmorillonite (PAN/MMT) nanocomposites using the surface‐initiated redox polymerization of acrylonitrile (AN) in the aqueous phase. The MMT silicate surfaces were first treated with diethanolamine, and the modified MMT (DEA‐MMT) was subsequently used together with the Ce(IV) salt to serve as a redox system. The PAN chains growing on a surface‐tethered DEA expand the interlayer space, and thus lead to intercalated/exfoliated nanocomposites. The nano‐morphology of the prepared nanocomposites depends on the AN/OH molar ratio in feed. An exfoliated PAN/MMT nanocomposite was obtained when the feeding AN/OH molar ratio = 300 was used. The molecular weight of PAN in the nanocomposites prepared by the present method is also dependent on the AN/OH molar ratio in feed and can be up to ca. 160,000 g/mol. The differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) analyses show that the increasing fraction of exfoliated silicate structures should enhance the contact interface between the silicate and polymer, resulting in the higher glass transition temperature and thermal stability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Characterization and catalytic investigation of Fe-ZSM5 for urea-SCR

Fe-ZSM5 was prepared with high iron content by solid-state ion exchange and characterized by ICP-AES, BET surface measurements, TEM, UV–vis, EPR and DRIFT spectroscopy as well as supplementing catalytic tests in order to clear up its functionality in urea-SCR. Due to the over-exchange with iron small Fe₂O₃ particles were formed, identified by UV–vis, EPR and TEM measurements, which were proved to be not active for the SCR reaction. However, the oxidation of NO to NO₂ over Fe³⁺ ions in the catalyst was realized to be a pre-requisite for the SCR reaction and the rate-determining step. DRIFT investigations under SCR conditions showed adsorbates on Fe²⁺ up to 300 °C. The high SCR activity above 300 °C can be explained by the faster reoxidation of Fe²⁺ to Fe³⁺ sites at high temperatures. The observed inhibition of the SCR reaction by excess ammonia at low and intermediate temperatures can be explained in this context by the reducing properties of ammonia converting Fe³⁺ to Fe²⁺ or by preventing the reoxidation of Fe²⁺.     

Fe/Fe cycling promoted by Ta3N5 under visible irradiation in Fenton degradation of organic pollutants

Ta₃N₅ was synthesized by nitridation of Ta₂O₅ under NH₃ flow at 700 °C. The catalyst was pure Ta₃N₅ according to X-ray diffraction (XRD), and was about 5 nm in size with a BET specific surface area 52.8 m²/g. When Ta₃N₅ was added to Fe³⁺/H₂O₂ solution (known as Fenton-like system), most Fe³⁺ were adsorbed on the Ta₃N₅ surface and could not react with H₂O₂ in the dark, which is different from the general Fenton reaction. Under visible light irradiation, adsorbed Fe³⁺ ions were reduced to Fe²⁺ rapidly and Fe²⁺ were reoxidized by H₂O₂ on the Ta₃N₅ surface, thus a fast Fe³⁺/Fe²⁺ cycling was established. Kinetics and ESR measurements supported this mechanism. The Ta₃N₅/Fe³⁺/H₂O₂ system could efficiently decompose H₂O₂ to generate hydroxyl radicals driven by visible light, which could accelerate significantly the degradation of organic molecules such as N,N-dimethylaniline (DMA), and 2,4-dichlorophenol (DCP). A mechanism was proposed for iron cycling on the basis of experimental results.     

Partial oxidation of propane on Nafion supported catalytic membranes

Nafion supported catalytic membranes were found to be effective in the partial oxidation of propane to oxygenates with H₂O₂ in the presence of Fe²⁺ under mild conditions. The influence of [Fe²⁺] and [H₂O₂] on the reaction rate and product distribution in the temperature range 80–110°C has been ascertained. A reaction pathway involving the electrophilic activation of propane on superacid sites and subsequent reaction of the activated propane molecules with OH radicals generated by Fe²⁺/H₂O₂ Fenton system is discussed.     

Novel route of synthesis of Mn---Mg---ferrites using stabilised MnO

Stoichiometric polycrystalline samples of Mn_xMg_1−xFe₂O₄ (0·5 ≤ x ≤ 0·66) have been synthesized by following a novel route using stabilized MnO and Fe₂O₃ at high temperatures. This route precludes the formation of large amounts of Mn³⁺ and Fe²⁺ and precipitation of MgO and -Fe₂O₃ which are generally observed during the usual route of preparation by conventional ceramic techniques. These samples have been characterized for their structural and magnetic properties using X-ray diffraction, Fe⁵⁷ Mössbauer spectroscopy and bulk magnetic properties such as initial permeability, loss factor, ferromagnetic transition temperature, remanance and coercivity. For X = 0·62, these ferrites exhibit the highest remanance ratio 0·96, suitable for square loop applications.     

Kinetics and mass transfer effects in the oxidation of ferrous sulfate over doped active carbon catalysts

Ferric sulfate is used in water purification. The oxidation of ferrous sulfate, FeSO₄, to ferric sulfate in acidic aqueous solutions of H₂SO₄ over finely dispersed active carbon particles was studied in a vigorously stirred batch reactor. Molecular oxygen was used as the oxidation agent and two kinds of catalysts were utilized: active carbon, doped active carbon. Both active carbon and doped active carbon catalysts enhanced the oxidation rate considerably.

Systematic kinetic experiments were carried out at the temperature and pressure ranges of 60–100°C and 4–10 bar, respectively. The results revealed that both non-catalytic and catalytic oxidation of Fe²⁺ take place simultaneously. The experimental data were fitted to rate equations, which were based on a plausible reaction mechanism: adsorption of dissolved oxygen on active carbon, electron transfer from Fe²⁺ ions to adsorbed oxygen and formation of surface hydroxyls. A comparison of the Fe²⁺ concentrations predicted by the kinetic model with the experimentally observed concentrations indicated that the mechanistic rate equations were able to describe the intrinsic oxidation kinetics of Fe²⁺ over pure active carbon and doped active carbon catalysts.     

Influence of isovalent and aliovalent substitutions at Ti site on bismuth sodium titanate-based compositions on piezoelectric properties

The effect of isovalent and aliovalent substitutions in Bi_0.5Na_0.485La_0.005TiO₃ (BNLT) compounds were studied within the additive ranges of 0–2.5 at%. The Zr⁴⁺, Nb⁵⁺ and Fe³⁺ ions were selected as the substituents. The modified BNLT compounds were prepared by conventionally mixed-oxide method. The calcination and sintering were performed at the temperatures of 750–850 °C and 1050–1150 °C, respectively. An increase in the substituents contents affected the physical and piezoelectric properties. The BNLT compositions with the addition of 1 at% Zr⁴⁺, Nb⁵⁺ and Fe³⁺ ions exhibited high relative permittivities (_r) at 730, 735 and 660, respectively. The modified-BNLT with an addition of 1.0 at% Fe provided a piezoelectric coefficient (d₃₃) of 155 pC/N, Curie temperature (T_c) of 320 °C and electromechanical coupling factors in planar (k_p) and thickness (k_t) modes of 15 and 45%, respectively.     

Mineralization of paracetamol by ozonation catalyzed with Fe, Cu and UVA light

Acid solutions containing up to 1 g l⁻¹ of the drug paracetamol have been treated with ozone alone and ozonation catalyzed with Fe²⁺, Cu²⁺ and/or UVA light at 25.0 °C. Direct ozonation yields poor degradation due to the high stability of final carboxylic acids formed, whereas more than 83% of mineralization is attained with the catalyzed methods. Under UVA irradiation, organics can be efficiently destroyed by the combined action of generated H₂O₂ and UVA light. In the presence of Fe²⁺ and UVA light, the process is accelerated due to the production of oxidant hydroxyl radical (OH) and the photodecomposition of Fe³⁺ complexes. The highest oxidizing power is achieved by combining Fe²⁺, Cu²⁺ and UVA light, because complexes of final acids with Cu²⁺ are more quickly degraded than those competitively formed with Fe³⁺. For all catalyzed methods, the initial mineralization rate is enhanced and the percent of degradation generally drops with increasing drug concentration. The paracetamol decay always follows a pseudo-first-order reaction with slightly higher rate constant for catalyzed systems than direct ozonation. Aromatic products such as hydroquinone, p-benzoquinone and 2-hydroxy-4-(N-acetyl)aminophenol are identified by gas chromatography–mass spectrometry (GC–MS) and reversed-phase chromatography. Acetamide is generated when hydroquinone is produced. These products are degraded to oxalic and oxamic acids as ultimate carboxylic acids, as detected by GC–MS and ion-exclusion chromatography. Oxalic acid is generated via glycolic, glyoxylic, tartronic, ketomalonic and maleic acids. While Fe³⁺-oxalato complexes are photolyzed by UVA light, Cu²⁺-oxalato, Fe³⁺-oxamato and Cu²⁺-oxamato complexes are oxidized with OH. NH₄⁺ and NO₃⁻ ions are produced during mineralization.     

Nanocomposites based on layered silicate and miscible PVDF/PMMA blends: melt preparation, nanophase morphology and rheological behaviour

Polyvinylidene fluoride (PVDF)–organoclay nanocomposites were prepared by melt-extrusion using polymethylmethacrylate (PMMA) as an interfacial agent. These nanocomposite materials were analysed with respect to their morphological and rheological properties. The nanophase morphology development and nanophase dispersion were studied using TEM. A fine dispersion of partially to nearly fully exfoliated silicate layers in miscible PVDF/PMMA blend matrices was observed when organophilic montmorillonite was used. Increasing the amount of PMMA in the PVDF/PMMA blend leads to high degree of exfoliation.

The rheological behaviour of intercalated/exfoliated PVDF/PMMA nanocomposites containing various concentrations of organophilic silicate was also investigated. At low frequencies, the storage modulus is increasing with increasing PMMA content and the frequency dependence of the storage modulus gradually changes from liquid-like to solid-like for nanocomposites when 10 wt% of PMMA is added, indicating formation of a network structure.

Dynamic mechanical investigations show a dramatic increase of the storage modulus in the rubbery plateau compared to conventional mineral fillers, as a result of the network structure. Due to the ‘nano’-sized dispersion, property efficiency is already realized at low loading levels (3–5 wt%).     

Ferroelectric Pb5-xBix (Ge.Si)3-xBxO11 single crystals as a material for IR radiation detectors

The coupled substitution of Bi³⁺ for Pb₂₊ and B³⁺ for Ge⁴⁺ was successfully achieved in ferroelectric Pb₅Ge₃O₁₁. Large single crystals of optical quality were grown from the melt. Deterioration of the crystal quality could not be observed within a period of two years under ambient conditions. The dielectric permittivity ε_r, electric conductivity p and pyroelectric coefficient γ are investigated as a function of temperature. The room temperature data (εr = 43, γ = 2.4·10^-4Cm^-2 K^-1, p = 7·10⁷ Ω, volume specific heat s = 2·10⁶ Jm^-3K^-1) show the usefulness of Pb_5-xBi_xGe_3-xB_xO₁₁ around x = 0.1 as a material for pyroelectric thermal detectors operating at room temperature. Also the difficulty of producing lead germanate silicate mixed crystals in the size and quality needed for vidicon applications is overcome by additional replacement of some Pb and Ge by Bi and B.     

EPR study of Fe3 in KTiOPO4 single crystals

EPR measurement of Fe³⁺ in as-grown KTiOPO₄ single crystals has been carried out at room temperature by employing a Bruker Q-band spectrometer. In addition to the centers ST2 and ST4 reported by Gaite et al, we have identified two extra Fe³⁺ centers having a mirror symmetry of ST2 and ST4, respectively. For all Fe³⁺ centers, parameters of the general spin Hamiltonian are calculated: the diagonal values of the second-order tensors and orientations of the principal axes are determined. The possible origin of the additional centers is discussed in terms of the local site symmetry at Fe³⁺ in KTiOPO₄.     

Removal of Fe(III) ion from aqueous solution by adsorption on raw and treated clinoptilolite samples

Iron (III) adsorption from aqueous solutions onto raw and pretreated clinoptilolite was investigated here. Various parameters for iron removal; initial solution pH, contact time and metal ion concentration were optimized. The equilibrium data were modeled by both the Langmuir and Freundlich adsorption isotherms at optimal conditions. Adsorption capacities of raw samples and those pretreated with Na₂S₂O₈ at 20 °C , 70 °C and with HNO₃ at 20 °C were all similar but samples pretreated with HNO₃ at 70 °C were significantly different; iron (III) removal from samples pretreated with HNO₃ decreased with increasing pretreatment temperature. Tests with Fe⁺³ solutions containing phenol, CsCl or KCl, indicated the continued presence of these ions in zeolite which either promoted or retarded the adsorption of iron. The Fe⁺³ adsorption capacity of clinoptilolite pretreated with HNO₃ at 70 °C was about two times greater with, than without, CsCl and KCl. The kinetics of iron adsorption from aqueous solution were also investigated using the first-order Lagergren equation and a pseudo-second-order model.     

Catalytic wet oxidation of H2S to sulfur on Fe/MgO catalyst

The room temperature wet catalytic oxidation was conducted in a batch reactor with Fe/MgO catalyst. Fe/MgO catalyst was prepared by the dissolution–precipitation method. XRD and temperature-programmed reductions (TPR) indicate that Fe oxide in the Fe/MgO is finely dispersed in the MgO support. The high H₂S removal capacities of Fe/MgO can be explained by the finely dispersed iron oxide MgO. The H₂S removal capacities of Fe/MgO are dependent on oxygen partial pressure (1.0 g H₂S/g_cat in air and 2.6 g H₂S/g_cat in oxygen). The valence state analysis of Fe/MgO catalyst suggests that the H₂S oxidation on Fe/MgO can occur by a redox couple reaction, reducing Fe³⁺ into Fe²⁺ by H₂S and oxidizing Fe²⁺ to Fe³⁺ by O₂.     

The effects of intragallery polymerization on the structure of PMMA-clay nanocomposites

In situ bulk polymerization of polymethylmethacrylate (PMMA)-clay nanocomposites was initiated with a benzoyl peroxide/amine redox couple at room temperature. This was accomplished with a newly synthesized cationic molecule—containing an aliphatic chain and an aromatic tertiary amine—that was ion exchanged onto the clay surface in order to control the rate of intragallery polymerization relative to that of extragallery polymerization. The rate and location of initiation significantly affected the degree of dispersion of the silicate layers. Accelerating intragallery polymerization of clay with low cation exchange capacity was found to produce the maximum interlayer distance as evident from transmission electron microscope images.     

Synthesis and characterization of exfoliated poly(styrene-co-methyl methacrylate)/clay nanocomposites via emulsion polymerization with AMPS

A method was described for synthesis of exfoliated poly(styrene-co-methyl methacrylate)/clay nanocomposites through an emulsion polymerization with reactive surfactant, 2-acrylamido-2-methyl-1-propane sulfonic (AMPS) which made the polymer end-tethered on pristine Na-MMT.AMPS widened the gap between clay layers and facilitates comonomers penetrate into clay. Silicate layers affect the composition of comonomers, for example A0.3M10S10T5 showed the elevated composition of MMA end tethered on silicate when compared to the feed ratio and polar methyl methacrylate (MMA) was considered to have the stronger interaction with clay layers than styrene.The exfoliated structure of extracted nanocomposite was confirmed by XRD and transmission electron microscopy. The onset of thermal decomposition for nanocomposites shifted to a higher temperature than that for neat copolymer. The dynamic moduli of nanocomposites increase with clay content. Dynamic storage modulus and complex viscosity increased as the clay content increased. In low frequency region all prepared nanocomposites exhibited apparent low-frequency plateaus in the linear storage modulus. Complex viscosity showed shear-thinning behavior as the clay content increases.     

Thermal properties and flammability of acrylic nanocomposites based upon organophilic layered silicates

Summary Thermal and mechanical properties of poly(methylmethacrylate-co-dodecylmethacrylate) nanocomposites based upon exfoliated organophilic layered silicates, were investigated as a function of the silicate and comonomer content. Layered silicates such as sodium bentonite were rendered organophilic by means of ion-exchanging sodium cations for N,N,N,N-dioctadecyl-dimethyl-ammonium cations. Silicate exfoliation was enhanced by means of 5 and 10 wt.-% dodecyl-methacrylate (LMA) addition to afford translucent reinforced acrylic nanocomposites. In contrast to conventional filled acrylic polymers, only 10 wt.-% organophilic silicate was sufficient to increase Young's modulus from 2200 to 4030 MPa, glass temperature from 72 to 80 °C and degradation temperature from 220 to 256 °C with respect to the neat MMA/LMA (90 wt.-%/10 wt.-%) copolymer. Flammability studies, performed on a cone calorimeter, revealed that the maximum heat release rate of MMA/LMA copolymer nanocomposite decreased from 837 kW/m² to 566 kW/m². The nanocomposite morphology was examined by means of transmission electron microscopy (TEM). Received: 28 May 1999/Revised version: 24 September 1999/Accepted: 24 September 1999     

Catalytic behavior of the Fe/Fe system in the electro-Fenton degradation of the antimicrobial chlorophene

The catalytic behavior of the Fe³⁺/Fe²⁺ system in the electro-Fenton degradation of the antimicrobial drug chlorophene has been studied considering four undivided electrolytic cells, where a Pt or boron-doped diamond (BDD) anode and a carbon felt or O₂-diffusion cathode have been used. Chlorophene electrolyses have been carried out at pH 3.0 under current control, with 0.05 M Na₂SO₄ as supporting electrolyte and Fe³⁺ as catalyst. In these processes the drug is oxidized with hydroxyl radical (OH) formed both at the anode from water oxidation and in the medium from electrochemically generated Fenton's reagent (Fe²⁺ + H₂O₂, both of them generated at the cathode). The catalytic behavior of the Fe³⁺/Fe²⁺ system mainly depends on the cathode tested. In the cells with an O₂-diffusion cathode, H₂O₂ is largely accumulated and the Fe³⁺ content remains practically unchanged. Under these conditions, the chlorophene decay is enhanced by increasing the initial Fe³⁺ concentration, because this leads to a higher quantity of Fe²⁺ regenerated at the cathode and, subsequently, to a greater OH production from Fenton's reaction. In contrast, when the carbon felt cathode is used, H₂O₂ is electrogenerated in small extent, whereas Fe²⁺ is largely accumulated because the regeneration of this ion from Fe³⁺ reduction at the cathode is much faster than its oxidation to Fe³⁺ at the anode. In this case, an Fe³⁺ concentration as low as 0.2 mM is required to obtain the maximum OH generation rate, yielding the quickest chlorophene removal. Chlorophene is poorly mineralized in the Pt/O₂ diffusion cell because the final Fe³⁺–oxalate complexes are difficult to oxidize with OH. These complexes are completely destroyed using a BDD anode at high current thanks to the great amount of OH generated on its surface. Total mineralization is also achieved in the Pt/carbon felt and BDD/carbon felt cells with 0.2 mM Fe³⁺, because oxalic acid and its Fe²⁺ complexes are directly oxidized with OH in the medium. Comparing the four cells, the highest oxidizing power regarding total mineralization is attained for the BDD/carbon felt cell at high current due to the simultaneous destruction of oxalic acid at the BDD surface and in the bulk solution.     

Ultrafiltration recovery of alginate: Membrane fouling mitigation by multivalent metal ions and properties of recycled materials

Recovery of alginate extracted from aerobic granular sludge (AGS) has given rise to a novel research direction. However, these extracted alginate solutions have a water content of nearly 100%. Alternately, ultrafiltration (UF) is generally used for concentration of polymers. Furthermore, the introduction of multivalent metal ions into alginate may provide a promising method for the development of novel nanomaterials. In this study, membrane fouling mitigation by multivalent metal ions, both individually and in combination, and properties of recycled materials were investigated for UF recovery of sodium alginate (SA). The filtration resistance showed a significantly negative correlation with the concentration of metal ions, arranged in the order of Mg²⁺ < Ca²⁺ < Fe³⁺ < Al³⁺ (filtration resistance mitigation), and the moisture content of recycled filter cake showed a marked decrease. For Ca²⁺, Mg²⁺, Fe³⁺, and Ca²⁺+Fe³⁺, the filtration resistances were almost the same when the total charge concentration was less than 5 mmol·L^-1. However, when the total charge concentration was greater than 5 mmol·L^-1, membrane fouling mitigation increased significantly in the presence of Ca²⁺ or Fe³⁺ and remained constant for Mg²⁺ with the increase of total charge concentration. The filtration resistance mitigation was arranged in the order of Fe³⁺ > Fe³⁺ + Ca²⁺ > Ca²⁺ > Mg²⁺. Three mechanisms were proposed in the presence of Fe³⁺, such as the decrease of SA concentration, change in pH, and production of hydroxide iron colloids from hydrolysis. The properties of recycled materials (filter cake) were investigated via optical microscope observation, dynamic light scattering, Fourier transform infrared, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. The results provide further insight into UF recoveries of alginate extracted from AGS.     

Synthesis and characteristics of poly(methyl methacrylate)/expanded graphite nanocomposites

In this work, we synthesized poly(methyl methacrylate) (PMMA)/expanded graphite (EG) nanocomposites by a new polymerization method. The volume electrical conductivity of the nanocomposite prepared by this way is very high (when the content of EG is about 8 wt %, the conductivity could reach 60 S/cm). The structure of the nanocomposite was investigated by SEM, TEM, IR, and XRD. And we found temperature and voltage were important parameters of governing the electrical conductivity of PMMA/EG nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1427–1431, 2006