Magnetic materials based on layered double hydroxideschemical design, processing and electrochemical applications

Resumen

This thesis addresses the field of layered double hydroxides from three different perspectives. First of all, the study and comprehension of distinct factors that affect the magnetic nature of LDHs. The necessity of a meticulous synthesis in order to avoid impurities that can mislead in the magnetic response, the influence of the distortion on the internal magnetic disorder of the material or the effect of the interlayer distance on the dipolar interactions are studied from the fundamental basis. These studies help in unveiling the fundaments that relies beneath the magnetic behaviour of these systems. Afterwards, a new non-aqueous route was approached in the synthesis of magnetic LDHs, giving rise to nanometric alkoxide-intercalated materials that undergo complete hydrolysis and therefore exfoliation in water. These samples exhibited superparamagnetic behaviour, electrochemical properties and improved possibilities regarding exfoliation procedures, overcoming processability problems related to the most common delaminating reagents. Furthermore, unpublished studies on covalent functionalization and ultrasonic tip exfoliation were also carried out. Finally, the catalytic applications of LDHs towards the synthesis of carbon nanoforms were tested on bulk and ultrathin film samples, highlighting a great variety of possibilities according to the temperature and the arrangement of the samples, that range from the controllable synthesis of bamboo-like carbon nanotubes or carbon spheres to a mixture of different carbon nanoforms. In summary, and thanks to the study of distinct magnetic LDH compositions (CoAl-, CoFe- and NiFe-, highlighting the -Fe3+ LDHs for its difficult synthesis), this thesis depicts an overall and in-depth vision of features linked to these materials such as magnetism, exfoliation, functionalization and applications. The final purpose is to extend the boundaries on the LDH field by contributing with new results that lead to a greater knowledge for these promising materials.