Anna Donnadio

Survey on the phase transitions and their effect on the ion-exchange and on the proton-conduction properties of a flexible and robust Zr phosphonate coordination polymer.

The flexible zirconium tetraphosphonate coordination polymer with formula Zr(O(3)PCH(2))(2)N-C(6)H(10)-N(O(3)CH(2)P)(2)X(2-x)H(2+x)·nH(2)O (X = H, Li, Na, K, 0 < x < 1, 4 < n < 7.5) (1) possesses an open framework structure with 1D cavities decorated with polar and acids P═O and P-OH groups. 1 has been fully protonated by adding HCl and then subjected to several acid-base ion-exchange reactions with alkaline metals hydroxides. 1 is a very robust coordination polymer because it can be regenerated in H- form using strong acid solutions and ri-exchanged several times without hydrolysis and loss of crystallinity. The flexibility of 1 has been also studied by means of TDXD (temperature dependent X-ray diffraction) evidencing remarkable phase transformations that lead to a different disposition of the water molecules. These transformations also influence the accessibility of the cations on the P-OH groups placed inside the channels and thus the ion-exchange properties. The dependence of the proton conductivity properties on these phase transitions has been also investigated and discussed.

Ag/AgCl nanoparticle decorated layered double hydroxides: synthesis, characterization and antimicrobial properties

A layered double hydroxide (LDH) surface was employed as a substrate for growing silver nanoparticles (NPs). An efficient method to produce stable silver/silver chloride nanoparticles supported on the ZnAl-LDH surface was developed. NPs of AgCl were grown on the ZnAl-LDH surface by using AgNO3 as the silver source. The ZnAl-LDH in chloride form acts as a nucleating agent, and depending on the pH of the LDH dispersion, AgClNPs with different dimensions were obtained. In particular AgClNPs with a diameter of 60 nm were formed at pH 5. The AgClNPs supported on LDH sheets were partially reduced by different reducing agents (NaBH4 and formaldehyde) resulting in a Ag/AgCl-LDH nanocomposite. The silver chloride and silver NP dimensions were evaluated by X-ray powder diffraction, field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). UV-Vis spectra of the samples upon reduction showed a band centred at 415 nm due to the surface plasmon resonance of silver nanoparticles with a diameter of about 10 nm, in agreement with the TEM analysis. The AgCl-LDH and Ag/AgCl-LDH nanocomposites, subjected to antimicrobial tests, exhibited good antimicrobial activity against both Gram-negative (Pseudomonas aeruginosa) and Gram-positive (Staphylococcus epidermidis and S. aureus) bacteria and yeast (Candida albicans). The nanocomposites were also studied for their ability to release silver by obtaining release curves, under conditions of antibacterial assays. Finally, the nanocomposites antibacterial behavior, as a function of time, was investigated by performing time-kill experiments using S. aureus and Candida albicans.

Water-mediated proton conduction in a robust triazolyl phosphonate metal-organic framework with hydrophilic nanochannels.

The development of water-mediated proton-conducting materials operating above 100 °C remains challenging because the extended structures of existing materials usually deteriorate at high temperatures. A new triazolyl phosphonate metal-organic framework (MOF) [La3L4(H2O)6]Cl⋅x H2O (1, L(2-) = 4-(4H-1,2,4-triazol-4-yl)phenyl phosphonate) with highly hydrophilic 1D channels was synthesized hydrothermally. Compound 1 is an example of a phosphonate MOF with large regular pores with 1.9 nm in diameter. It forms a water-stable, porous structure that can be reversibly hydrated and dehydrated. The proton-conducting properties of 1 were investigated by impedance spectroscopy. Magic-angle spinning (MAS) and pulse field gradient (PFG) NMR spectroscopies confirm the dynamic nature of the incorporated water molecules. The diffusivities, determined by PFG NMR and IR microscopy, were found to be close to that of liquid water. This porous framework accomplishes the challenges of water stability and proton conduction even at 110 °C. The conductivity in 1 is proposed to occur by the vehicle mechanism.

Gels of zirconium phosphate in organic solvents and their use for the preparation of polymeric nanocomposites

Gels of α-zirconium phosphate (α-ZrP) in water have been prepared by exfoliation of crystalline α-ZrP induced by intercalation–deintercalation of propylamine. Although these gels are X-ray amorphous, their Raman spectra indicate that the α-type layers of the starting material remain essentially unaltered. Replacement of gel water with water miscible organic solvents has allowed the formation of α-ZrP gels in a great variety of solvents, such as alkanols, N,N-dimethylformamide (DMF), 1-methyl-2-pyrrolidone (NMP), acetone, tetrahydrofuran (THF) and even chloroform. Particular attention has been devoted to α-ZrP gels in DMF. On the basis of the surface area of the dry gels, the average thickness of the particles of exfoliated α-ZrP has been estimated between 25 and 80 nm for α-ZrP percentages in the starting gels between 2.5 and 10 wt%, respectively, in agreement with SEM images. α-ZrP gels in THF have been used for the preparation of polystyrene/α-ZrP nanocomposites with filler loadings up to 8 wt%. The presence of exfoliated α-ZrP delays the beginning of thermal decomposition of the polymer by a maximum of 45 °C for 4 wt% filler loading. The state of filler exfoliation has been confirmed by transmission electron microscopy.

Chitosan films containing mesoporous SBA-15 supported silver nanoparticles for wound dressing

Chitosan films containing mesoporous SBA-15 supported silver nanoparticles (AgNPs) were prepared to be applied as a potential wound dressing material. First SBA-15-silver nanoparticle (SBA-15-Ag) composite materials were prepared by a controlled annealing process without the use of organic solvents and reagents. The SBA-15-AgNPs were characterized in detail by X-ray powder diffraction, field emission scanning electron microscopy and transmission electron microscopy which evidenced the presence of uniformly distributed silver nanostructures inside the silicate pores. UV-vis spectra of the sample showed a band at 430 nm characteristic of the surface plasmon resonance of silver nanoparticles with a diameter below 10 nm and X-ray photoemission spectra confirmed the formation of metal-nanoparticles on the silicate template. Then SBA-15-Ag was used to prepare chitosan films which were characterized in detail. In particular, they showed good hydration properties, water vapor transmission rate and mechanical properties. After hydration films exhibited good antimicrobial activity against both Gram-negative (Pseudomonas aeruginosa) and Gram-positive (Staphylococcus epidermidis and S. aureus) bacteria.

Advances in the Chemistry of Nanosized Zirconium Phosphates: A New Mild and Quick Route to the Synthesis of Nanocrystals

Simple addition of zirconyl propionate to phosphoric acid in alcoholic media surprisingly led to the formation, in few minutes, of transparent gels containing solvent intercalated zirconium phosphate (ZrP) nanoparticles with hexagonal shape and a planar size of about 40 nm. With the help of elemental analysis, inductively coupled plasma-optical emission spectrometry (ICP-OES), and (31)P magic angle spinning (MAS) NMR, the nanoparticle composition was formulated as Zr(R)(w)(HPO(4))(x)(H(2)PO(4))(y), in which R can be an hydroxyl or a propionate group. The stoichiometric coefficients for propanol intercalated ZrP are x = 1.43, y = 0.83, and w = 0.32. Solvent elimination at 60 °C gave rise to an increase in the x value and a decrease in the y and w values. X-ray powder diffraction analysis and transmission electron microscopy (TEM) observations showed a concomitant increase in the particle size: planar size and thickness ranged from 90 to 200 nm and from 20 to 85 nm, respectively, depending on the nature of the solvent. A possible mechanism explaining the change in the x, y, and w values, the growth of nanoparticles, and the role of the solvent is proposed. Finally, the possibility of using these gels to disperse the ZrP nanoparticles within the polymer matrix of Nafion117 is shown.

Organically Modified Zirconium Phosphate by Reaction with 1,2-Epoxydodecane as Host Material for Polymer Intercalation: Synthesis and Physicochemical Characterization

Organically modified alpha-layered zirconium phosphate samples (ZrP(C(12))(x)) containing dodecyl groups bonded to the alpha-layers through P-O-C bonds have been prepared by reaction of 1,2-epoxydodecane solutions in tetrahydrofuran (THF) with gels of partially exfoliated zirconium phosphate in THF. Two dimensional correlation solid state NMR experiments for (1)H-(13)C and (1)H-(31)P nuclei have been used to prove the formation of P-O-C bonds arising from nucleophilic attack of POH mainly to carbon 1 and, to a lesser extent, to carbon 2 of epoxydodecane. ZrP(C(12))(x) samples with x in the range from approximately 0.5 to approximately 2.0 are thermally stable up to at least 200 degrees C, and their interlayer distance increases continuously with x from approximately 20 to approximately 35 A. On the basis of structural considerations, it has been suggested that samples with low x values could intercalate aliphatic polymers. Accordingly, preliminary results have shown that molten polyethylene is intercalated in ZrP(C(12))(0.49) and ZrP(C(12))(0.73). These materials can therefore be regarded as filler candidates for polymer matrixes.

A Layered Mixed Zirconium Phosphate/Phosphonate with Exposed Carboxylic and Phosphonic Groups: X-ray Powder Structure and Proton Conductivity Properties

A novel mixed zirconium phosphate/phosphonate based on glyphosine, of formula Zr2(PO4)H5(L)2·H2O [L = (O3PCH2)2NCH2COO], was synthesized in mild conditions. The compound has a layered structure that was solved ab initio from laboratory PXRD data. It crystallizes in the monoclinic C2/c space group with the following cell parameters: a = 29.925(3), b = 8.4225(5), c = 9.0985(4) Å, and β = 98.474(6)°. Phosphate groups are placed inside the sheets and connect the zirconium atoms in a tetradentate fashion, while uncoordinated carboxylate and P-OH phosphonate groups are exposed on the layer surface. Due to the presence of these acidic groups, the compound showed remarkable proton conductivity properties, which were studied in a wide range of temperature and relative humidity (RH). The conductivity is strongly dependent on RH and reaches 1 × 10(-3) S cm(-1) at 140 °C and 95% RH. At this RH, the activation energy of conduction is 0.15 eV in the temperature range 80-140 °C. The similarities of this structure with related structures already reported in the literature were also discussed.

Synthesis, Crystal Structure, and Proton Conductivity of One-Dimensional, Two-Dimensional, and Three-Dimensional Zirconium Phosphonates Based on Glyphosate and Glyphosine

The reaction of two small phosphono-amino acids based on glycine (glyphosine and glyphosate) with zirconium under mild conditions led to the attainment of three related zirconium derivatives with 1D, 2D, and 3D structures of formulas ZrF[H3(O3PCH2NHCH2COO)2] (1), Zr3H8[(O3PCH2)2NCH2COO]4·2H2O (2), and Zr[(O3PCH2)(HO3PCH2)NHCH2COOH]2·2H2O (3), respectively, whose structures were solved by X-ray powder and single-crystal diffraction data. The glyphosate derivative has 1D ribbon-type structure whereas the dimensionality of the glyphosine-derived materials (2D and 3D) can be tuned by changing the synthesis conditions. The low-dimensional compounds (1 and 2) can be directly produced in the form of nanoparticles with different size and morphology whereas the 3D compound (3) has a higher crystallinity and can be obtained as single crystals with a prismatic shape. The different structural dimensionality reflects the shape and size of the crystals and also differently affects the proton conductivity properties, measured over a wide range of temperature at 95% relative humidity. Their high thermal and chemical stability together with the small size may promote their use as fillers for polymeric electrolyte membranes for fuel cells applications.

Innovative multifunctional silk fibroin and hydrotalcite nanocomposites: a synergic effect of the components.

Novel hybrid functional materials are formed by combining hydrotalcite-like compounds and silk fibroin (SF-HTlc) via an environmental friendly aqueous process. The nanocomposites can be prepared with different weight ratio of the constituting components and preserve the conformational properties of the silk protein and the lamellar structure of hydrotalcites. Optical microscopy, scanning electron microscopy, and atomic force microscopy analyses show a good dispersion degree of the inorganic nanoparticles into the organic silk matrix. A mutual benefit on the stability of both organic and inorganic components was observed in the nanocomposites. SF-HTlc displayed limited dissolution of hydrotalcite in acidic medium, enhanced mechanical properties, and higher protease resistance of silk protein. The transparency, flexibility, and acidic environment resistance of silk fibroin combined to the protective and reinforcing properties of hydrotalcites generate a hybrid material, which is very attractive for applications in recently reported silk based opto-electronic and photonics technologies.