Iron based nanostructures: synthesis, characterization and environmental applications
Authors:   , Cervera Gabalda Laura María 
Published: June 2022

Environmental pollution has become a topic of public concern in recent years. Due to different activities, organic and inorganic compounds end up in the environment mainly affecting water sources and air quality. There are numerous methods employed for pollutant removal. Among them, adsorption method stands out due to its simplicity, low-cost and high efficiency. The stability, porosity, high surface area, electron transfer ability, among other properties, make nanomaterials widely used as pollutant removal. Particularly, magnetic nanostructures are extensively employed as promising adsorbents due to the possibility to separate them from the environment in which they are immersed employing an external magnetic field. This feature also enhances the possibility of recycling and reusing these nanomaterials to reduce process costs. Specifically, iron carbon based nanomaterials are proposed as highly efficient adsorbents due to the high adsorption capacity of carbon. Moreover, the natural abundance of iron, low cost, magnetic and chemical properties, and low toxicity makes these nanomaterials very interesting for their application in the environmental remediation field. Furthermore, photocatalysts have also interest for their applications as pollutant removal. In this context, again, magnetic nanoparticles have gained attention due to their physicochemical properties. Particularly, spinel ferrites with different cations are employed for their use as photocatalysts due to the possibility to design ferrites with narrow band-gaps and optimum magnetic and photocatalytic properties. Specifically, in this thesis Co-Zn ferrites have been analyzed as visible light photocatalytic materials. Firstly, Fe-C based nanostructures have been synthesized employing three different procedures having as common research strategy the use of sugar (glucose, fructose or sucrose) as carbon source. The first process consists of mixing iron salts (Fe3+) with different sugars as carbon source in an aqueous solution. Then the solution is dried and annealed at different temperatures. The second synthesis process to obtain Fe-C nanostructures is based on the reduction of Fe3O4 nanoparticles employing the thermal decomposition of fructose. Finally, Magnetic Induction Heating (MIH) has been explored as a novel method to carbon coat Fe3O4 magnetic nanoparticles. The obtained nanostructures from each method have been structurally characterized employing different techniques such as Thermal Gravimetric Analysis (TGA), Fourier-Transform Infrared Spectroscopy (FTIR), X-ray diffraction, Electron Microscopy (TEM/STEM), or Raman spectroscopy. Magnetic characterization of the samples has been carried out by SQUID magnetrometry. The combination of the structural and magnetic characterization has allowed to comparatively anayze the different employed synthesis methods to obtain Fe-C nanostructures. Once the Fe-C nanostructures have been widely characterized, the adsorption capacities of some selected samples obtained by each method have been evaluated as well as their reusability. For that purpose, Cr (VI) and phenol have been chosen as inorganic and organic pollutant models, respectively. Additionally, MIH has been studied as an alternative phenol desorption method and compared to a conventional heat treatment. Finally, CoxZn1-xFe3O4 nanoparticles have been synthesized employing the co-precipitation method. They have been structurally (X-Ray diffraction, X-Ray fluorescence spectroscopy, and Scanning Transmission Electron Microscopy), optically (UV-Vis diffuse reflectance spectroscopy and Photoluminescence spectroscopy), and magnetically (SQUID magnetometry) characterized. Additionally, Inductively Coupled Plasma Optical Emission spectroscopy, specific surface area, and Zeta Potential measurements have been carried out to complete the characterization of the nanoparticles. The photocatalytic activity of the Co-Zn ferrites has been evaluated employing phenol and toluene as water and air pollutant models, respectively.