The use of nanomaterials is considerably due to the wide field of applications in devices, cosmetics and food . In addition to this applications, the motivation due to unique properties achieved in systems formed by nanomaterials is is getting bigger. Incorporation of nanostructures in order to develop new products has been the motivation of different research groups. Some of these researches are already well established in three pillars; composition, size and shape . The choice of a given material is related to the physical-chemical property achieved in relation to optical, magnetic, electrical, thermal, mechanical and rheological [3, 4]. The application of nanoparticles is well established, generating great interest in the development of new advanced nanostructured materials . Synthesis of new nanostructured materials and the search for new methodologies is a trend today, and promises to play a very important role in future technologies. This, thanks to the properties allowing for versatility and applications .
Hollow nanomaterials, which an empty space in their interior, can be single-shell, multi-shell or rattle-type . These materials are obtained in various sizes, different geometric shapes and compositions. Considered as a special class of nanostructured materials, search for their development has been increasing in recent decades [8, 9]. Caruso , used a hard-template strategy to synthesize submicrometric silicon oxide spheres. Due to their very high surface area and low density, these structures exhibit great potential and a wide field of application in sensing, chemical catalysis, rechargeable batteries, supercapacitors and energy production . Incorporating specific characteristics to the structure of a nanometric shell can be used in a more targeted and specific way . Fang , presented an improvement of a catalytic process applying hollow structures of alumin-silicates in catalysis activity, through the control of pore size.
Due to the confined environment of hollow structures, the search for new alternatives has aroused considerable interest for application in catalysis . Structures of hollow semiconductor octahedrons based on CuInS2, obtained by using the self-template synthesis, were used, aiming at the production of hydrogen through photocatalytic processes. Hollow structures of spherical morphology, composed by iron oxide, can also be observed in works demonstrating the application of these structures in lithium batteries . Iron is one of the most abundant elements on earth  with high biocompatibility and magnetic properties.
For different applications, is necessary to achieve some characteristics such as: monodispersity, shape control, reproducibility, scalability and synthesis complexity. Magnetic resonance imaging (NMR) is a very important technique in medicine, and it is possible to observe biological events such as gene expression, metastasis at cellular and subcellular levels, and use of magnetic particles as contrast agents . Magnetic particles have already been found in lung, liver and spleen, originating from contrast material for NMR imaging . Chaves et al.  reported the accumulation of magnetic particles in mouse lungs for three months, reporting no cytotoxic association with the magnetic material. These particles are metabolized enzymatically at the cellular level, as reported by Robson and Nissim , attributing and highlighting the importance of ferritin and transferritin in the biodegradation process of these iron nanoparticles. The excellent biocompatibility, added to the confined environment (empty space) and the very low density, give the hollow iron oxide structures promising applications in controlled drug release, contrasting agent in NMR imaging, among other biological applications.
Hollow materials formed from magnetic phases have a promising application in hard disk, random memories (RAMs) or in biological applications, with controlled release of drugs and magnetohyperthermia . Some works have already demonstrated the importance of the study and the unique characteristics of magnetic materials on a nanometric scale. Quan-Lin Ye  reported optical properties and magnetic anisotropy of Fe3O4 submicron hollow-sphere systems compared to their dense form, having thin film characteristics due to shell thickness. Streubel, et al. reported the fundamental magnetization states due curved geometries . Magnetic characteristics and properties have already been demonstrated by Revoredo et al., demonstrating magnetic properties in magnetic nanohelmet arrays . Satoru Kobayashi et al.  describe studies on Fe3O4 hollow spheres, showing the presence of vortex-like magnetic states describing first-order magnetization reversal. These phenomena in nanostructured materials with curved morphologies that present a one-domain magnetic have already been demonstrated both experimentally  and in theoretical works .
Using a hard-template route, Yoshikawa and collaborators  synthesize hollow structures of iron and cobalt by direct chemical deposition, using 600 nm polystyrene (PS) particles as a template. The search for sizes smaller than 600 nm is important for magnetic applications [29, 30] and is not possible by the above metodology. Given this, and all the application possibilities involving hollow spherical structures, the present work investigate and develop a new coherent synthesis strategy in order to obtain hollow iron oxide structures with diameters smaller than 200 nm.