A new synthetic method for TiO2 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 oil 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.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)