Design of Iron Oxide Nanocatalysts for The Magnetic Induction-Assisted Degradation of Emergent Contaminants

The application of nanomaterials in environmental remediation is of utmost importance in addressing the pressing ecological challenges of our time. Nanomaterials offer unique advantages, such as their high surface area and reactivity, which make them exceptionally effective in adsorbing, degrading, and immobilizing various pollutants in air, water, and soil. Within these nanomaterials, iron oxide nanoparticles (IONPs) stand out as great alternatives due to their low price, biodegradability and magnetic properties. Specifically, IONPs when subjected to alternating magnetic fields (AMF), generate localized heat through their physical motion or rotation of their magnetic moments [1]. This controlled heating can be harnessed to accelerate the degradation of various pollutants, including emerging contaminants (<i>e.g. </i>microplastics, antibiotics, cosmetics, etc.). Furthermore, the ability to manipulate the nanoparticles' movement through the application of external magnetic fields enables reduced operational costs for separation processes, while minimizing ecological disruption.<br/>In this study, we developed a catalytic system via the polyol process, designed specifically for the magnetic induction-assisted degradation of organic matter. The resulting nanocatalyst (NC) displayed a multi-core structure measuring 40 nm, comprising small magnetic cores of 12 nm each [2]. These magnetic cores exhibited a well-ordered crystalline aggregation, which contributed to a collective magnetic behavior, enhancing magnetic induction heating and facilitating efficient separation due to the substantial magnetic moment per particle. To assess the industrial applicability of this approach, we successfully scaled up the production of NCs to a gram-level with remarkable reproducibility in terms of both structure and magnetic properties.<br/>The scaled NCs were used for the magnetic induction-assisted degradation of microplastics (MPs). For this purpose, polyethylene MPs were extracted from a commercial facial scrub and we investigated a combined treatment approach for their degradation. Initially, we subjected the MPs to a hydrolysis process at 150 ^oC, breaking them down into monomers. Subsequently, we conducted a Fenton-like reaction, employing the as-prepared NCs in the presence of hydrogen peroxide, to degrade the hydrolyzed molecules via highly oxidative species. To assess the efficacy of this process, we monitored the changes in the Total Organic Carbon (TOC) content of the supernatant before and after each stage, which provided insights into the MPs' degradation. Notably, we observed that the mineralization of TOC was temperature-dependent, increasing from 20 to 65% at room temperature (RT) and 90 ^oC. This yield saw a further boost when employing IONPs as a heat source under the influence of an alternating magnetic field, likely attributable to the creation of hot spots on the surface at temperatures exceeding 80 ^oC.<br/>In general, the use of magnetic nanoparticles in environmental remediation processes brings the advantages of magnetic induction heating, which can significantly reduce energy consumption and enhance the overall catalytic efficiency. As we continue to tackle the challenges of diminishing contamination and advancing sustainable energy solutions, magnetic nanoparticles represent a compelling avenue for achieving environmental remediation, making them a promising technology with the potential to reshape our approach to mitigate climate change.<br/><b>Acknowledgements</b><br/>This research was funded by the Spanish Ministry of Science and Innovation (AEI/FEDER, UE), project reference: TED2021-130191B-C43, PID2020-113480RB-I00 and EU project 101007629-NESTOR-H2020-MSCARISE-2020.<br/><b>References </b><br/>[1] J.G. Ovejero, et al. <i>Nanoletters. </i>21, 17 (2021) 7213–7220<br/>[2] Gallo-Cordova, et al. <i>J. Colloid. Inter. Sci. </i>608, (2022) 1585-1597