Stabilization of mesoporous nanocrystalline zirconia with Laponite

Abstract

The mesoporous nanocrystalline zircoina was synthesized via solid state reaction--structure directing method in the presence of Laponite. The introduction of Laponite renders the higher thermal stability and lamellar track to the zirconia. Laponite acts as inhibitor for crystal growth and also hard template for the mesostructure. The role of Laponite is attributed to the interaction between the zirconia precursors and the nano-platelets of Laponite via the bridge of hydrophilic segments of surfactant. It results in the formation of Zr-O-Mg-O-Si frameworks in the direction of Laponite layer with the condensation of frameworks during the calcination process, which contributes the higher stability and lamellar structure to the nano-sized zirconia samples.Keywords: mesoporous nanocrystalline zirconia, Laponite, stabilization mechanism. DOI: 10.1360/982004-83ZrO 2 has attracted much attention because of its high performance as structural materials, electrode materials, electronics and oxygen sensors, supports and catalysts [1][2][3][4][5][6] . However, a major problem of this nonsiliceous oxide is its thermal stability. The surfactant removal by calcination, as used for porous silicates, leads to structure collapse because of phase transformation, hydrolysis and redox reaction occurring at elevated temperature, which results in the loss of surface area and porosity. In addition, nano-sized particles prefer to aggregate to resist its higher surface energy. It means that for mesostructured or nanocrystalline zirconia, thermal stability is always a challenging area.Recently, many synthesis routes have been proposed for the synthesis of thermally stable zirconia. The major approaches are to tune its electronic property or to enlarge the pore wall [7][8][9][10][11] . For example, the inorganic framework is either phosphate or sulfate groups as stabilizers [12][13][14] . These anions can inhibit the crystallization of precursor species during the calcination. The introduction of phosphate or sulfate groups can be achieved by the self-assembly process of organic and inorganic species using the surfactant with phosphate or sulfate hydrophilic head or by post treatment with these anions after the materials are obtained. Also, aliovalent and tetravalent dopants, such as Na + , Ca 2+ , Y 3+ , Si 4+ , Ce 4 , Th 4+ , etc. have been used to reinforce the nanocrystalline structures [15][16][17][18][19] . The stabilization was believed to be achieved by strong surface interaction between dopants ions and zirconia or by higher coordination number via addition of large size dopants.The zirconia prepared via solid-state reaction--structure directing method--bear large surface area and optimum pore structure [20] . Its phase can be tailored among amorphous, tetragonal and monoclinic phase by controlling the synthesis parameters. In order to improve the thermal stability of the zirconia with MSU structure, Laponite was introduced into the inorganic framework. This study demonstrates that electronic and structural effects of Lapo...