); [EMAIL_ADDRESS] (J.C.M.-C.); [EMAIL_ADDRESS] (N.C.A.-H)  
[PERSON]  
1 National Institute of Astrophysics, Optics and Electronics (INAOE), Electronics, Tonantzintla, Puebla 72840, Mexico; [PERSON]ADDRESS] (C.Z.I. ); [PERSON]ADDRESS] (M.M. ); [EMAIL_ADDRESS] (W.C.A. ); [EMAIL_ADDRESS] (J.C.M.-C.); [EMAIL_ADDRESS] (N.C.A.-C.); [EMAIL_ADDRESS] (C.R.A.-H)  
[PERSON]  
1 National Institute of Astrophysics, Optics and Electronics (INAOE), Electronics, Tonantzintla, Puebla 72840, Mexico; [EMAIL_ADDRESS] (C.Z.I. ); [EMAIL_ADDRESS] (M.M. ); [EMAIL_ADDRESS] (W.C.A. ); [EMAIL_ADDRESS] (J.C.M.-C.); [EMAIL_ADDRESS] (N.C.A.-H)  
[PERSON]  
1 National Institute of Astrophysics, Optics and Electronics (INAOE), Electronics, Tonantzintla, Puebla 72840, Mexico; [EMAIL_ADDRESS] (C.Z.I. ); [EMAIL_ADDRESS] (M.M. ); [EMAIL_ADDRESS] (W.C.A. ); [EMAIL_ADDRESS] (J.C.M.-C.  
demonstrated that because of the nanometer size of TiO\({}_{2}\) nanosheets, this material has a better contact with molecules for highly efficient catalysts [5]. In this same sense, nanobowls--nanostructures with shapes like cups--have been studied for catalytic applications, solar cells, and light trapping [6; 7; 8]. For instance, [PERSON] et al. reported that TiO\({}_{2}\) nanobowls used in colored perovskite solar cells showed an improved efficiency owing to their special shape with preferential orientation, which improved crystallinity and decreased grain size [7]. Whereas [PERSON] et al. demonstrated that these nanostructures considerably enhance the catalytic activity for direct methanol fuel cells due to the electronic effects of nanobowls [8]. In the last few years, TiO\({}_{2}\) nanotubes have also been studied widely for diverse applications, such as catalysts, solar cells, femur prostheses, plasmonic effects; and chemical, biological, and gas sensors [1; 9]. Several papers about nanotubes applications have been published recently due to their tubular shape and excellent electrical, chemical, mechanical and optical properties [1; 9; 10; 11; 12]. Besides, it is worth mentioning that electrochemical anodization is the most used technique for their fabrication [9; 10; 11; 12; 13]. For instance, [PERSON] et al. fabricated a field-effect transistor based on TiO\({}_{2}\) nanotubes for humidity sensing and, at the same time, reported that a single nanotube had a high sensibility because it had a larger surface area than a TiO\({}_{2}\) nanotubes film [10]. Also, the open channel TiO\({}_{2}\) nanotubes were reported by [PERSON] et al. [11]. These had better photocatalytic activity than nanotubes with nanograss and other nanostructures. Concerning the improvement of the catalytic activity, many scientists have studied the shape and size of nanostructures, likewise their defect states [12]. In this regard, [PERSON] et al. reported that the high crystallinity of the anatase phase of TiO\({}_{2}\) increases the photocatalytic activity by decreasing defect states of TiO\({}_{2}\)[14]. On the contrary, [PERSON] et al. showed that the enhancement in catalytic activity occurred once the oxygen vacancies in the TiO\({}_{2}\) film increased, due to the narrowing of the band gap [15]. In this work, TiO\({}_{2}\) nanotubes (TiO\({}_{2}\)-nt), TiO\({}_{2}\) nanocavities (TiO\({}_{2}\)-nc), TiO\({}_{2}\) nanosheets assembled on TiO\({}_{2}\) nanocavities (TiO\({}_{2}\)-ns/TiO\({}_{2}\)-nc) and TiO\({}_{2}\) nanobowls assembled on TiO\({}_{2}\) nanocavities (TiO\({}_{2}\)-nb/TiO\({}_{2}\)-nc) were studied for catalytic applications. The nanostructures were prepared by two-step electrochemical anodization for TiO\({}_{2}\)-ns/TiO\({}_{2}\)-nc, TiO\({}_{2}\)-nb/TiO\({}_{2}\)-nc and TiO\({}_{2}\)-nc; and three-step for TiO\({}_{2}\)-nt. The relationships of the defect states, crystallinity, shape, size, and band gap of these complex nanostructures with catalytic activity are discussed.