## 4 Discussion  
The present study has a dual aim for supporting magnetic nanoparticles over the nanolayers of layered double hydroxides and designing magnetic nano-nets of cobalt ferrite, which is not yet published in the literature. The first aim was achieved through precipitating nanoparticles of cobalt ferrite during construction of the nanolayered structures of the LDH. According to the reaction mechanism of urea hydrolysis [29], it decomposes through two steps to produce cyanate and/or carbonate anions in addition to ammonium cation as shown in the following reactions:  
\[\rm{Urea+H_{2}O\to NH_{4}^{+}+OH^{-}+CNO^{-}+H^{+}} \tag{3}\]  
\[\rm{CNO^{-}+2H_{2}O\to NH_{4}^{+}+CO_{3}^{2-}} \tag{4}\]  
The acidic medium of the solution gradually changes to become alkaline. At these conditions, the layered structures of Co-Fe LDH starts to grow. During the hydrolysis of urea, the iron cations Fe  
Figure 10: Magnetization M–H curves of: (a) the CoFe\({}_{2}\)O\({}_{4}\)-supported LDH and (b) the CoFe\({}_{2}\)O\({}_{4}\) nano-nets. react with OH\({}^{-}\) ions generating goethite Fe(OOH). In addition, cobalt hydroxide is formed by reacting the cobalt cations Co\({}^{2+}\) with OH\({}^{-}\) ions [40]. \[2\text{Fe(OOH)}+\text{Co(OH)}_{2}\rightarrow\text{CoFe}_{2}\text{O}_{4}+2\text{ H}_{2}\text{O} \tag{5}\]  
According to Equation (5), nanoparticles of cobalt ferrite can be synthesized during the building of LDH. Agreeing with XRD results, 13.2% nanoparticles of cobalt ferrite has been prepared and supported by the nanolayered structures of Co-Fe LDH. The second aim was accomplished by treating the supported LDH at critical pressure and temperature. By critical conditions of temperature and pressure, the supported LDH was transformed into nano-nets of cobalt ferrite. These nano-nets consist of nanoparticles and short nanowires. TEM images revealed that the nano-nets have nano-pores with diameters of 5-10 nm. Formation of the cobalt ferrite nano-nets could be explained through the catalytic effect of the cobalt ferrite nanoparticles that was supported over LDH structures. At the critical conditions of the temperature and the pressure, the nanoparticles of cobalt ferrite acted as catalysts for driving and accelerating the decomposition reactions of methanol molecules producing large amount of gases inside the LDH structures and increasing the internal pressure among the nanolayers. To release all these gases from the rigid nanolayers of LDH, holes and vacancies were formed during the transformation of Co-Fe LDH to cobalt ferrite through the dehydroxylation process of the nanolayers. At the same time, the internal pressure of these gases inside the nanolayered structures directed the hexagonal plates of LDH to produce nano-net morphology. The magnetic behavior of the cobalt ferrite nano-nets and the cobalt ferrite-supported LDH were measured and compared with the nanoparticles through vibrating sample magnetometer technique. The magnetic parameters indicated that the prepared nano-nets have ferromagnetic behavior and high coercivity. However, the prepared nanoparticles revealed superparamagnetic state and low coercivity. These results concluded that the incorporation of nanoparticles with nanowires into nano-net structures has been found to be an efficient way to improve their magnetic properties and prevent their agglomerations. Finally, layered double hydroxides are an important source for constructing magnetic nanolayered structures and nano-nets. [PERSON] is the corresponding author and has participated for preparation and characterization of the materials. [PERSON] participated for analyzing the experimental results. [PERSON] has prepared the materials and participated for measuring the physical properties. [PERSON] measured the magnetic properties of the prepared materials. This research was funded by the Deanship of Scientific Research in King Faisal University (Saudi Arabia), grant number 17122002 and The APC was funded by the same grant number 17122002.