146 research outputs found

    Switching ionic diode states with proton binding into intrinsically microporous polyamine films (PIM-EA-TB) immersed in ethanol

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    Intrinsically microporous polyamines (PIM-EA-TB) provide tertiary amine binding sites for protons and in this way allow switching/gating from a low ionic conductivity state to semipermeable anion conductivity through micropores. In ethanolic NaClO4 media ionic conductivity in PIM-EA-TB films (approx. 10 μm thick; deposited asymmetrically onto a 10 μm diameter microhole in 5 μm thick Teflon) is lowered by ion exclusion compared to conductivity observed in aqueous environments. However, in the presence of protons in ethanol PIM-EA-TB films are shown to switch from essentially insulating to anionic diode behaviour. Similar observations are reported for Cu2+ but not for other types of cations such as Na+, K+, Mg2+ (all as perchlorate salts). Binding constants are evaluated, and protonation is identified to cause gating for both H+ and Cu2+. Both chemical and electrochemical gating/switching is demonstrated by placing a platinum electrode close to the PIM-EA-TB film and applying positive or negative bias to locally generate acid/base

    Hydrogen-Mediated Photoelectrocatalysis with Nickel-Modified Poly(Heptazine Imides)

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    Polymeric carbon nitrides (C3N4) are photochemically active organic semiconductors that can be produced in a wide range of structural types. Here, a poly-(heptazine imide) containing nickel single atoms (Ni-PHI) is employed for photochemical hydrogen production and is compared to the non-nickel-doped semiconductor. Film deposits are formed on a platinum disk electrode (to detect hydrogen) and a coating of the molecularly rigid polymer of intrinsic microporosity PIM-1 is applied to (i) mechanically stabilize the photo-catalyst film without impeding photocatalysis and (ii) assist in the interfacial hydrogen capture/oxygen suppression process. In the presence of hole quenchers such as methanol or ethanol, anodic photocurrents linked to hydrogen production/oxidation are observed. A comparison with an experiment on glassy carbon confirms the formation of interfacial hydrogen as a mediator. The effects of hole quencher concentration are evaluated. The system Pt/Ni-PHI/PIM-1 is employed in a single-compartment photo-fuel cell

    Ultrasonic-assisted removal of cationic and anionic dyes residues from wastewater using functionalized triptycene-based polymers of intrinsic microporosity (PIMs)

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    In this work, a series of hypercrosslinked polymers of intrinsic microporosity (HCP-PIMs), namely nitro-triptycene (TRIP-NO2), amino-triptycene (TRIP-NH2), sulfonated-triptycene (TRIP-SO3H) and hydrocarbon-triptycene (TRIP-HC), are employed for the adsorption of organic dyes from wastewater. The materials show the efficient removal of cationic (malachite green, MG) and anionic (methyl orange, MO) dyes. The adsorption parameters herein investigated include the initial pH, the adsorbate concentration and the contact time, with the aim to elucidate their effect on the adsorption process. Furthermore, the adsorption kinetic and isotherms are studied, and the findings suggest the results fit well with pseudo-second-order kinetics and Langmuir model. The reported maximum adsorption capacity is competitive for all the tested polymers. More specifically, TRIP-SO3H and TRIP-HC exhibit adsorptions of ~ 303 and ~ 270 mg g−1 for MG and MO, respectively. The selectivity toward cationic and anionic dyes is assessed by mixing the two dyes, and showing that TRIP-HC completely removes both species, whereas TRIP-NO2, TRIP-NH2 and TRIP-SO3H show an enhanced selectivity toward the cationic MG, compared to the anionic MO. The effect of the type of water is assessed by performing ultrasonic-assisted adsorption experiments, using TRIP-SO3H and TRIP-HC in the presence of either tap or seawater. The presence of competing ions and their concentrations is evaluated by ICP-MS. Our study shows that tap water does not have a detrimental effect on the adsorption of both polymers, whereas, in the presence of seawater, the performance of TRIP-HC toward MO proved to be more stable than MG with TRIP-SO3H, which is probably due to a larger concentration of competing ions. Comparison between ultrasonic-assisted and magnetic stirring adsorption demonstrates that the former exhibits a greater efficiency. This seems due to a more rapid mass transfer, driven by the formation of high velocity micro-jets, acoustic microstreaming and shock waves, at the polymer surface. Reusability studies show a good stability up to five adsorption–desorption cycles

    Novel monomers for polymers of intrinsic microporosity (PIMs)

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    The research described in this thesis is directed towards the synthesis of novel monomers for preparing Polymers of Intrinsic Microporosity (PIMs). Each new monomer contains two catechol units fused via a spiro-centre, which adds a necessary site of contortion, and all are compatible with an efficient polymerisation reaction with 2,3,5,6-tetrafluoroterephthalonitrile. It was anticipated that the resulting PIMs would possess enhanced properties (e.g. microporosity, solubility gas permeability etc.) due to the polar and polarisable substituents that these novel monomers contribute to the polymer structure. This first part of this work describes the synthesis of two families of monomers. The first is based on the spiro-bisindane structural unit in which the spiro centre is shared by two fused five-membered rings, similar to the commercially available 4,4',5,5'-tetrahydroxy-3,3,3',3'-tetramethyl-l,r-spirobisindane, which was found to provide highly microporous polymers in previous work. Various groups (e.g. ketone, phenyl, fluorene) were introduced in place of the four methyl substituents. The second family of monomers is based upon l,l'-spiro-bis(1,2,4,5-tetrahydro-6,7-dihydroxynaphthalene) in which the spiro-centre fuses two six-membered rings. Similar substituents were introduced in order to make a direct comparison of properties to those of the polymers derived from the spirobisindane family. Additionally, the concept of adding 'sacrificial' thioketal groups to the 4,4',5,5'-tetrahydroxy-3,3'-keto-1,1'-spirobisindane monomer was investigated, with the aim of temporarily increasing the solubility and processability of the poorly soluble ketone-containing PIM. The last part of the work is concerned with the results of the polymerisation reactions of these novel monomers with 2,3,5,6-tetrafluoroterephthalonitrile, followed by the characterization of the resulting polymers. In particular, the important physical properties of the polymers were assessed such as solubility, molecular mass (by Gel Permeation Chromatography - GPC), microporosity (using nitrogen adsorption), and thermal stability (by Thermo-Gravimetric Analysis - TGA)

    Sintesi di PNA: una strategia semplice ed efficiente

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    Nell’ambito del nostro gruppo di ricerca è stato sviluppato un processo di sintesi dei singoli monomeri PNA, utilizzando metodologie efficienti e riproducibili, che non comportano purificazioni cromatografiche degli intermedi e che permettono di ottenere i monomeri su larga scala. Si è cercato di ottenere monomeri in cui fosse rispettata l’ortogonalità tra i vari gruppi protettori (Pg1, Pg2, Pg3) sia dello scheletro che delle nucleobasi

    Spirobifluorene-based polymers of intrinsic microporosity for the adsorption of methylene blue from wastewater: effect of surfactants

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    Owing to their high surface area and superior adsorption properties, spirobifluorene polymers of intrinsic microporosity (PIMs), namely PIM-SBF-Me (methyl) and PIM-SBF-tBu (tert-butyl), were used for the first time, to our knowledge, for the removal of methylene blue (MB) dye from wastewater. Spirobifluorene PIMs are known to have large surface area (can be up to 1100 m2 g−1) and have been previously used mainly for gas storage applications. Dispersion of the polymers in aqueous solution was challenging owing to their extreme hydrophobic nature leading to poor adsorption efficiency of MB. For this reason, cationic (cetyl-pyridinium chloride), anionic (sodium dodecyl sulfate; SDS) and non-ionic (Brij-35) surfactants were used and tested with the aim of enhancing the dispersion of the hydrophobic polymers in water and hence improving the adsorption efficiencies of the polymers. The effect of surfactant type and concentration were investigated. All surfactants offered a homogeneous dispersion of the polymers in the aqueous dye solution; however, the highest adsorption efficiency was obtained using an anionic surfactant (SDS) and this seems owing to the predominance of electrostatic interaction between its molecules and the positively charges dye molecules. Furthermore, the effect of polymer dosage and initial dye concentration on MB adsorption were also considered. The kinetic data for both polymers were well described by a pseudo-second-order model, while the Langmuir model better simulated the adsorption process of MB dye on PIM-SBF-Me and the Freundlich model was more suitable for PIM-SBF-tBu. Moreover, the maximum adsorption capacities recorded were 84.0 and 101.0 mg g−1 for PIM-SBF-Me and PIM-SBF-tBu, respectively. Reusability of both polymers was tested by performing three adsorption cycles and the results substantiate that both polymers can be effectively re-used with insignificant loss of their adsorption efficiency (®). These preliminary results suggested that incorporation of a surfactant to enhance the dispersion of hydrophobic polymers and adsorption of organic contaminants from wastewater is a simple and cost-effective approach that can be adapted for many other environmental applications
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