Preparation of Zirconium Phosphate Nanomaterials and Their Applications as Inorganic Supports for the Oxygen Evolution Reaction

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.

Elucidating structure and dynamics of crystalline α-zirconium phosphates intercalated with water and methanol by multinuclear solid-state MAS NMR: A comprehensive NMR approach

Solid-state NMR experiments on ² H, ³¹ P, ¹³ C, and ¹ H nuclei, including ³¹ P T₁ , ¹ H T₁ , and ¹ H T_1ρ measurements, as well as on the kinetics of proton-phosphorus cross-polarization have been performed to characterize the crystalline and amorphous α-zirconium phosphates, which were intercalated with D₂ O and/or CD₃ OD. The ¹³ C{¹ H} CP MAS NMR experiment performed for compound 1-CD₃ OD (Zr (HPO₄ )₂^. 0.2CD₃ OD) with carbon cross-polarization via protons of phosphate groups has provided a prove that the methanol was intercalated into the interlayer spaces of this compound. The variable-temperature ² H solid-echo MAS NMR spectra of intercalated compounds demonstrated that the methanol molecules, in contrast to the mobile water, were immobile, keeping, however, free CD₃ rotations around the C₃ -axis. It has been demonstrated that the intercalated species, D₂ O and CD₃ OD, do not affect the high-frequency motions of the phosphate groups. By utilizing local structural models that satisfy the constraints of the experimental data, it has been suggested that the immobile methanol molecules are located in the cavity between two neighboring layers of the zirconium phosphates. Thus, the present work illustrates the reliable criteria in a comprehensive NMR approach to structural and dynamic studies of such systems.

One-step preparation of bioactive enzyme/inorganic materials

Simultaneous exfoliation of crystalline α-zirconium phosphate (α-ZrP) nanosheets and enzyme binding, induced by shearing, without the addition of any toxic additives is reported here for the first time. These materials were thoroughly characterized and used for applications. The bulk α-ZrP material (20 mg mL^-1) was exfoliated with low concentrations of a protein such as bovine serum albumin (BSA, 3 mg mL^-1) in a shear reactor at 10k rpm for <80 minutes. Exfoliation was monitored by powder X-ray diffraction with samples displaying a gradual but complete loss of the 7.6 Å (002) peak, which is characteristic of bulk α-ZrP. The fully exfoliated sample loaded with the protein was characterized by transmission and scanning electron microscopy in addition to other biophysical methods. Lysozyme, glucose oxidase, met-hemoglobin, and ovalbumin also induced exfoliation and directly produced enzyme/ZrP biocatalysts. Thus, exfoliation, biophilization and enzyme binding are accomplished in a single step. Several factors contributed to the exfoliation kinetics, and the rate increased with α-ZrP and BSA concentrations and decreased with pH. However, the exfoliation efficiency inversely depended on the isoelectric point of the protein with ovalbumin (pI = 4.5) being the best and lysozyme (pI = 11.1) being the worst. A strong correlation between the protein size and exfoliation efficiency was noted, and the latter suggests the role of hydrodynamic factors in the process. Exfoliation was also achieved by simple stirring using a magnetic stirrer, under low volumes, and model enzymes, indicating 60-90% retention of bound enzymatic activities. The addition of BSA to enzymes as the diluent and stabilizing agent also prevents enzymes from the denaturing effect caused by stirring. This new method requires no pre-treatment of α-ZrP with toxic exfoliating agents such as tetrabutyl ammonium hydroxide and provides bioactive enzyme/inorganic materials in a single step. These protein-loaded biocompatible nanosheets may be useful for biocatalysis and biomedical applications.