Syntheses and pilarization of layered silicic acids

Author(s)

Cléo Thomás Gabriel Vilela Menegaz Teixeira Pires

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2010-03-08

Examining board members

Claudio Airoldi; João Barros Valim; Herenilton Paulino Oliveira; Teresa Dib Zambon Atvars; Celso Aparecido Bertran

• Advisor: Claudio Airoldi

Abstract

Recently, the interest to obtain modified layered materials is increasing, due to their properties and possible scientific and technological applications. Silicic acids such as magadiite, kenyaite and ilerite are extremely versatile compounds, allowing to vary the basal spacing by intercalation with carbonic long chains groups or ionic exchange process. Other possible modifications are isomorphic substitution by aluminum, titanium or iron atoms, with changeing the lamella chemical properties. In this investigation layered silicic acids magadiite, ilerite and kenyaite, containing also Al and Ti atoms inserted into the lamellar structure, were synthesized by hydrothermal method. For all cases was observed that with the increase of metal amount added or the hydrothermal treatment time there are phase transitions, following the order: from amorphous, to layered phase to crystobalite and tridimite, as mixtures of them at intermediate situations. Different pilarization methods with TiO2 were exhaustedly tested by varying many parameters. The most efficient methods used CTAB and TBAOH as swelling agents under reflux at 353 K, followed by direct alcoxide addition on the dry material, then refluxed at 363 K with dry nitrogen atmosphere. These materials have mesopores with 4.8 nm average diameter, nevertheless just 270 m g surface area. Some pillared materials were used to immobilize the photocatalyst pyrylium (TPP) and thiopyrylium (TPTP) and then test in the photocatalytic degradation of methidathion pesticide. The hybrid materials showed a better activity than that of pure organic, what means a great initial point to optimize this process. The photophysic behavior of impregnated dyes on pillared materials was also studied (AU)