Looking for New Hybrid Polymer Fillers: Synthesis of Nanosized α-Type Zr(IV) Organophosphonates through an Unconventional Topotactic Anion Exchange Reaction

Immobilization of Alendronate on Zirconium Phosphate Nanoplatelets

Different amounts of sodium-alendronate (ALN) were loaded into layered zirconium phosphates of alpha and gamma type (αZP and γZP) by means of topotactic exchange reactions of phosphate with ALN. In order to extend the exchange process to the less accessible interlayer regions, ALN solutions were contacted with colloidal dispersions of the layered solids previously exfoliated in single sheets by means of intercalation reaction of propylamine (for αZP) or acetone (for γZP). The ALN loading degree was determined by liquid P-nuclear magnetic resonance (NMR) and inductively coupled plasma (ICP), and it was reported as ALN/Zr molar ratios (Rs). The maximum R obtained for γZP was 0.34, while αZP was able to load a higher amount of ALN, reaching Rs equal to 1. The synthesized compounds were characterized by X-ray powder diffractometry, scanning electron microscopy (SEM), solid-state NMR, and infrared spectroscopy. The way the grafted organo-phosphonate groups were bonded to the layers of the host structure was suggested. The effect of ZP derivatives was assessed on cell proliferation, and the results showed that after 7 days of incubation, none of the samples showed a decrease in cell proliferation.

Mixed Zirconium Phosphate Bis-Phosphonomethyl Glycine from Nanocrystalline α-Zirconium Phosphate: A Tailored Suite for Gold Nanoparticles

A novel synthetic approach was investigated for the preparation of nanoplatelets of mixed zirconium phosphate bis-phosphonomethyl glycine, ZPGly, by the reaction of a gel of nanocrystalline α-type zirconium phosphate with N,N-bis-phosphonomethyl glycine, H₃Gly. The syntheses were carried out in the absence of hydrofluoric acid by changing both the reagent relative amounts and temperature. An H₃Gly/Zr molar ratio >2 did not significantly improve the degree of crystallinity of the materials, while an increase of temperature from 80 °C to 120 °C improved the crystallinity; the best result was obtained with H₃Gly/Zr molar ratio = 2 and with a temperature reaction of 120 °C. The sample consisted of nanoplatelets with the size in the range 20-40 nm, and it was successfully exfoliated by treatment with a solution of methylamine. By treatment of the ZPGly colloidal dispersions with HAuCl₄, a color change from white to red-violet was observed, indicating the formation of gold nanoparticles. The size and morphology of the gold particles were affected by the degree of crystallinity and, in turn, by the composition of the ZPGly support. As a matter of fact, large micrometric Au particles with a cubo-octahedral morphology were obtained by using the less crystalline ZPGly_R2-80 sample, while interconnected Au particles, with a size of about 16 nm, were obtained by using ZPGly_R2-120. The samples exhibited an absorption maximum in the visible region due to the surface plasmon resonance of gold nanoparticles.

Solvent-Free Synthesis of Nano Zirconium Phenylphosphonates with Molten Phenylphosphonic Acid

Nanosized α-zirconium phenylphosphonate particles were successfully prepared by the reaction between different zirconium sources and molten phenylphosphonic acid in the absence of solvent. The resultant nanoplates exhibit particle sizes in the range of 15 to 30 nm. The use of a topotactic anion exchange method starting from α-zirconium phosphate instead resulted in the generation of 15 to 180 nm plates, while also resulting in nanoparticles with a higher degree of crystallinity. The topotactic anion exchange of the phosphate groups by phenylphosphonate groups could be performed to completion when performed in molten phenylphosphonic acid. Characterization of both the final products as well as the individual steps in the anion exchange were performed by powder XRD, fast neutron activation analysis, TGA, FTIR spectroscopy, TEM, solid-state NMR and XPS.

A new challenge for nanocrystalline α-zirconium phosphate: reaction with a diepoxyalkane

New organic derivatives of α-zirconium phosphate (ZrP) were prepared by reaction of a gel of nanocrystalline ZrP with 1,2,7,8-diepoxyoctane (diepoxide), leading to the formation of P-O-C bonds. A series of compounds having composition Zr(O₃POH)_2-2x(O₃POCH₂CH(OH)(CH₂)₄CH(OH)CH₂OPO₃)_x (hereafter indicated as ZrP(dep)_x) were obtained by varying the diepoxide/Zr molar ratio in the range 0.25-1. The samples were characterized by elemental, thermal and X-ray powder diffraction analysis. The reaction turned out to be nearly quantitative, the x values of ZrP(dep)_x being in the range 0.16 to 1.0. The interlayer distance slightly increased with increasing x, going from 12.7 to 13.2 Å. Interestingly, the materials easily intercalated alkanols at room temperature, both from liquid and vapor phases; it is noteworthy that ZrP(dep)_0.30 was able to reversibly take up 42 wt% ethanol from the vapor phase, in agreement with the presence of available free space both in the interlayer and in the intercrystal region. Geometrical structural models in which the α-ZrP layers are connected by the dep chains were proposed to support the obtained results.

Formation of Layered Proton-Conducting Zirconium and Titanium Organophosphonates by Topotactic Reaction: Physicochemical Properties, Proton Dynamics, and Atomic-Resolution Structure

A series of new zirconium and titanium phosphates-organophosphonates, in which the organophosphonate moiety is functionalized with a sulfo group, was prepared by a topotactic reaction involving the gamma modification of zirconium or titanium hydrogen phosphate with 2-bis(phosphonomethyl)amino-ethan-1-sulfonic acid (H₄TDP). H₄TDP represents a new type of functionalizing agent, which can be easily prepared by a Moedritzer-Irani reaction from taurine (2-aminoethanesulfonic acid). The gamma modification of zirconium hydrogen phosphate (γ-ZrP) with H₄TDP provides mixed phosphate-organophosphonate compounds with the formula Zr(PO₄)(H₂PO₄)_1-2x(H₂TDP)_x·yH₂O, where x = 0.15, 0.34, 0.45, and is controlled by the γ-ZrP/H₄TDP ratio in the starting mixture. On the contrary, by the topotactic gamma modification of titanium hydrogen phosphate (γ-TiP) with H₄TDP, only one product with the formula Ti(PO₄)(H₂PO₄)_1-2z(H₂TDP)_z·yH₂O, where z = 0.41 ± 0.01, was obtained regardless of the composition of the starting mixture. The synthesized compounds were characterized by elemental analysis, thermogravimetric analysis, energy-dispersive X-ray analysis, and infrared spectroscopy. The way the topotactic reaction proceeds and how the grafted organophosphonate groups are bonded to the layers of the host structure were suggested on the basis of the solid-state NMR data. It was found that the grafted moieties are spread evenly in the host layers among the hydrogen phosphate groups. The obtained solids are able to intercalate basic molecules, as was proved by the intercalation reactions of the zirconium series with butylamine. The amount of intercalated butylamine increases with increasing x. It is known that both host compounds, γ-ZrP and γ-TiP, are protonic conductors. It was found that the incorporation of H₂TDP increases conductivity of the zirconium compound when x = 0.15, but further incorporation of H₂TDP into the γ-ZrP host structure leads to a decrease of conductivity. This behavior is explained on the basis of the ¹H MAS and the ¹H-¹H EXSY NMR data.

Improving the mechanical stability of proton conducting SPEEK membranes by in situ precipitation of zirconium phosphate phenylphosphonates

Zirconium phosphate phenylphosphonate nanoparticles improve mechanical properties and the stability of the proton conductivity of composite SPEEK membranes.

A combined strategy for the synthesis of double functionalized α-zirconium phosphate organic derivatives

Zirconium ethylphosphonate organophosphates are easily synthesized by the reaction of zirconium phosphate ethylphosphonates with an alkyl epoxide, thus forming P–O–C bonds.

Surface functionalization of zirconium phosphate nanoplatelets for the design of polymer fillers

Inorganic-organic hybrid materials were synthesized by covalent attachment of epoxides to the surface of zirconium phosphate (ZrP) nanoplatelets. X-ray powder diffraction, FTIR, and TGA were utilized to confirm the presence of the modifiers and exclusive functionalization of the ZrP surface. NMR experiments were conducted to confirm the formation of P-O-C bonds between surface phosphate groups and epoxide rings. The applicability of the organically modified products was demonstrated by their use as fillers in a polymer matrix. Subsequently, a two step intercalation and surface modification procedure was utilized to prepare polymer nanocomposites that were imparted with functionality through the encapsulation of molecules within the interlayer of surface modified ZrP.

Surface modification of layered zirconium phosphates: a novel pathway to multifunctional materials

The combination of surface modification and intercalation chemistry of inorganic layered materials allows for the design of nanoparticles for specific applications.