Modification of the Surface Properties of Porous Nanometric Zirconia Particles by Covalent Grafting

Abstract

We here report on the covalent grafting of various phosphated species (phosphoric acid, phenylphosphonic acid, and octyl phosphate) onto the surface of monoclinic zirconia nanoparticles obtained by hydrothermal treatment of zirconium acetate. The initial particles are 60 nm aggregates of nanometric primary grains and present an inner porosity. Small-angle X-ray scattering shows that the high specific area of the colloidal particles (450 m2·g-1) decreases to 150 m2·g-1 upon drying. Therefore, phosphated reactants can access the whole internal surface of the aggregates only before drying. The surface of the particles can be covered with functional groups bound through a variable number of Zr−O−P bonds. Several factors probably enhance the reaction between the particles and the phosphates or phosphonates: the large specific area of the particles, a fully accessible porous network, and a large concentration of surface terminal groups. At the same time, the morphology of the particles is well preserved upon grafting. This is due to the good crystallinity of the primary grains that constitute the particles. In addition, the grafting drastically modifies the surface properties of the colloids. For example, the polarizability of the particles decreases in the sequence −POH > as-prepared ZrO2 > −PC6H5 > −POC8H17. Furthermore, the grafting of octyl phosphate allows exclusion of water from pores of 2 nm radius, up to hydrostatic pressures of 20 MPa.

A Facile Synthetic Route for the Preparation of Superparamagnetic Iron Oxide Nanorods and Nanorices with Tunable Surface Functionality

“…Moreover, if necessary, the alumina coating is readily dissolvable in basic media, providing access to superparamagnetic anisometric nanoparticles with a surface primarily composed of iron oxide. On the other hand, zirconia interacts strongly with phosphate compounds, [9] and in fact has been used as a highly selective adsorbent for compounds containing phosphonic acid. [10] Consequently, it is reasonable to expect high stability and functionality once the zirconia coating has been grafted with phosphate moieties.…”

“…Finally, it is worth noting that electrophoretic mobility measurements indicate that SPNRs coated with alumina are positively charged at physiological pH. In contrast, a simple protocol ([H 3 PO 4 ] ¼ 0.1 M, 4 h at 100 8C) [9] has been used to successfully graft zirconia-coated SPNRs with phosphate moieties. In summary, we have shown that a relatively simple approach can be used to prepare anisometric superparamagnetic iron oxide nanoparticles despite the inherent difficulties associated with shape anisotropy.…”

Superparamagnetic Composites: Magnetism with No Memory

“…We have recently proposed the use of zirconia matrixes because of their high stability at different pHs and high reactivity with phosphate compounds. [110] Zirconia easily reacts with phosphate compounds, [111] and in fact is used as a highly selective adsorbent for compounds containing phosphonic acid. [112] Titania matrixes could also be considered a good replacement to silica, especially because they can impart photocatalytic properties to the SPCs.…”

New Hybrid Bidentate Ligands as Precursors for Smart Catalysts

“…After 12 h of heating detectable traces neither of 5 nor of 5' were found in solutions corresponding to a 20 wt % loading. The CP-MAS 31 P NMR spectrum of 5@ZS 20 C showed two large main peaks at d = 3.5 and 54 ppm, which were ascribed to the phosphonate moiety [17] and to the phosphine, respectively. Interestingly, the second chemical shift (d = 54 ppm) is shifted significantly downfield relative to that recorded for the free ligand (d = À9 ppm).…”