Phase Transformation in Titania Nanocrystals by the Oriented Attachment Mechanism: The Role of the pH Value

Abstract

The oriented attachment (OA) mechanism has been investigated as an important process in the formation of anisotropic nanostructures such as depicted. The results showed that the control of a desired phase in this system may be attained by the control of OA mechanism through pH value, obtaining several morphologies.A new synthetic method for TiO(2) nanocrystals starting from metallic Ti and hydrogen peroxide was developed, in order to obtain minimal interferences to evaluate phase transformation in the system. The results revealed that the crystal morphology appeared to be dictated by the pH value, which shows a strong dependence on the surface energy. The involvement of the oriented attachment (OA) mechanism is important to modify the morphology and, hence, the distribution of the surface energy and confirmed that the mechanism can accelerate certain phase transitions, albeit pH dependence in terms of how the mechanism affects the final particle morphology and direction of crystalline growth. The importance of the mechanism was also apparent in extremely basic conditions, which indicates a possible correlation with the formation of hydrogen titanate nanostructures.

CeO2nanoparticles synthesized by a microwave-assisted hydrothermal method: evolution from nanospheres to nanorods

“…Among these methods, hydrothermal treatments appear to be potentially interesting in terms of morphological variations. [25][26][27][28][29][30][31] Guan et al reported a systematic study of ceria materials with different morphologies such as sphere, rods, and prisms via the hydrolysis of solutions containing Ce(NO 3 ) 3 and urea under hydrothermal conditions. 32 According to these authors, different morphologies were obtained by carefully adjusting the synthesis conditions such as salt concentration, temperature and synthesis time.…”

Novel synthesis of nanophase anatase under conventional- and microwave-hydrothermal conditions: DeNOx properties

“…Ribiero et al, [31] recently reported the synthesis of titanium oxide nanocrystals, especially the rutile TiO 2 phase by a method based on peroxotitanium complex decomposition. A new synthetic method for TiO 2 nanocrystals starting from metallic Ti and hydrogen peroxide was developed by Ribiero et al, [32,33]. The results reported here are for nanophase anatase synthesis using a highly simplified one-pot method by conventional-and microwave-hydrothermal methods.…”

Nanoestruturas em fotocatálise: uma revisão sobre estratégias de síntese de fotocatalisadores em escala nanométrica

“…79,80 A concentração do precursor no reator hidrotermal possui um papel importante na fase e morfologia obtida. Isto acontece, pois a concentração é um fator chave em uma determinada cinética reacional, influenciando na mobilidade das partículas suspensas e na proporção de choques efetivos.…”

“…Em condições altamente alcalinas, o material obtido apresenta características tubulares. 80 Estruturas tubulares em nanoescala são interessantes devido à sua alta área superficial específica que é um fator decisivo em fotocatálise. Desde 1991, quando Iijima 86 reportou pela primeira vez a síntese de nanotubos de carbono, têm surgido diversas pesquisas de síntese de nanotubos, inclusive de semicondutores.…”