BARRADO, C. M.

CAMARGO, E. R.

LEITE, E. R.

LONGO, E.

RIBEIRO, C.

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Page 1 of 1Abstract Number: S9.1 Day I Time: Wednesday, Dec. 3, 8:00 PM - 11:00 PMPhase Transformation in Titania Nanocrystals by the Oriented AUachmentMechanism: The Role of pH Medium.C.Ribeiro 1; C.M.Barrado 2; E.R.Camargo 2; E.Longo 3; E.R.Leite 2. 1. Embrapa Instrumenta ç ao~Agropecu a ria, Sao Carlos, SP, Brazil; 2. Chemistry, Universidade Federal de Sao Carlos, Sao Carlos,Sao Paulo, Brazil; 3. Chemistry, Universidade Estadual Paulista, Araraquara, Sao Paulo, Brazil.Nanoparticle growth mechanisms have received much attention in recent years, especially in view ofthe importance of controling nanostructural sizes and morphologies. In-depth investigations intoclassical nanoparticle coarsening processes (Ostwald ripening, OR) have demonstrated the importanceof proper control in this stage of the synthesis 50 that the desired nanostructures can be obtained.However, the Oriented Attachment (OA) mechanism has been highlighted as a common step innanocrystal growth, even in systemswith high solubility (when OR is expected). The influence of thismechanism on the anisotropy of oxide nanocrystals has been investigated, and a wide range of distinctnanostructures are reportedly formed through this mechanism. However, although the role of thismechanism in nanoparticle morphology is well understood, investigations into other implications arestill incipient. One of these aspects is the mechanism's influence in phase control, an importantvariable, particularly in systems with many polymorphs, and one that is frequently disregarded. The roleof the growth mechanism in phase control can be understood in terms of its influence on the totaldistribution of the facets, which can be attained by tailoring anisotropic structures (since the OAmechanism is related to this aspect). Its influence is interpreted as the modification of the AreaNolumerelation in the formed particles, favoring phase transformation or not according to the crystallographicplanes exposed after the event. However, the surface energy of each plane is strongly influenced by thepresence of counterions in the medium. As an example, in the synthesis of Ti02 nanoparticles, it hasbeen shown that the presence of common ions in the synthesis environment, such as CI- or organicchains from the precursors, can alter phase stability. In order to obtain a representative system for Ti02with minimal interferences, we have developed a clean synthesis using metallic Ti and hydrogenperoxide as precursors, crystallized in a conventional hydrothermal apparatus. This system can offersome insights concerning the influence of surface energy in the OA mechanism and its importance foradequate phase control of nanoparticles during synthesis. The results revealed the evolution of thecrystal morphology dictated by the conditions of pH, which shows a strong dependence on the surfaceconditions, i.e., surface energy. The occurrence of the OA mechanism as an important way to modifythe morphology and, hence, the distribution of surface energy, confirmed that the mechanism canaccelerate some phase transitions, albeit with interference of the pH medium in terms of how themechanism affects the final particle morphology and direction of crystalline growth. Finally, theimportance of the mechanism was also apparent in an extremely basic condition, indicating a possiblecorrelation with the formation of hydrogen titanate nanostructures.Citation: C.Ribeiro, C.M.Barrado, E.R.Camargo, E.Longo, E.R.Leite. Phase Transformation in TitaniaNanocrystals by the Oriented Attachment Mechanism: The Role of pH Medium.. Abstract No. S9.1.2008 Abstract Viewer. Boston, MA: Materiais Research SocietyApplication Design and Programming Copyright ScholarOne, Inc. Ali Rights Reserved. PatentPending.Abstract Viewer

Phase transformation in titania nanocrystals by the oriented attachment mechanism: the role of pH medium.

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