Iron oxides and hydroxides (Fe-OH) extracted from natural sources have garnered significant attention for their diverse catalytic applications. This article provides a comprehensive overview of the catalytic potential of naturally occurring Fe-OH, focusing on the influence of natural sources and preparation methods on their morphological characteristics and application in heterogeneous catalysis. The unique physicochemical properties of these catalysts, including their high surface area, redox activity, and tunable surface chemistry, make them promising candidates for various catalytic processes. The review discusses key catalytic reactions facilitated by natural Fe-OH, such as advanced oxidation processes (AOPs), electrochemical applications, catalytic cracking, and biodiesel production. Furthermore, it highlights recent advancements and challenges in utilizing these materials as heterogeneous catalysts. By presenting an analysis of the catalytic potential of natural iron oxides, this review aims to stimulate further research about the use of these materials, which are widely distributed in the Earth’s crust.

Heterogeneous Advanced Oxidation Processes (H-AOPs) are considered a new process for removing emerging pollutants. In this case, the high reactivity of hydroxyl radicals is used to degrade persistent organic pollutants. This review explores the state-of-the-art catalyst for hydroxyl radical generation in AOPs. As a parasite reaction, chloride ions appear in alkaline conditions and compete with the active sites. The theoretical foundation of catalyst performance is explored, focusing on the fundamental principles that govern the efficiency and mechanism of hydroxyl or chloride radical production. The synthesis and electronic modification sections explore the modifications of catalysts. It discusses key methodologies for catalyst preparation, with a particular emphasis on electronic modification that enhances both activity and stability. Finally, laboratory and pilot applications highlight the effectiveness of novel or modified catalysts in different scenarios. These last findings provide insights into the future directions for research and application, aiming to draw attention to the gap between laboratory studies and real-world implementations.

Employing magnetophoresis, we investigate the demulsification of oil-in-water emulsions using SDBS-functionalized magnetic nanoparticles (MNP@SDBS) prepared by two routes: coprecipitation from commercial iron salts (SMNPs) and an alternative sand-derived route using Fe-rich natural sand as the iron source (NMNPs). Demulsification performance was evaluated for pristine MNP@SDBS and for thermally recovered nanoparticles after one demulsification cycle (MNP@SDBS-R). Upon applying a magnetic-field gradient to the MNP@SDBS–oil-in-water mixture (\(27^\circ \) API, 5% v/v), SMNP@SDBS and NMNP@SDBS achieve 98% hydrocarbon removal at 2500 ppm, both within 1 min. These results demonstrate that magnetic demulsifiers prepared from Fe-rich sands have separation efficiencies comparable to those synthesized from commercial iron salts, supporting a magnetophoretically assisted process involving droplet coalescence and nanoparticle precipitation. The recovered MNP@SDBS-R materials retained high demulsification efficiency with only modest performance losses. In contrast, control tests performed in the absence of both nanoparticles and an external magnetic field exhibit neither precipitation nor demulsification even after 10 days. Comprehensive structural, magnetic, microstructural, optical, and elemental characterizations were performed at all stages (as-prepared MNPs, functionalized MNP@SDBS, and recovered MNP@SDBS-R) to guide optimization of MNP use and recovery. In all cases, the analyses confirm inverse-spinel iron oxides. Sand-derived materials were predominantly magnetite (\({\text {Fe}}_{3}{\text {O}}_4\)) and salt-derived materials were predominantly maghemite (\(\gamma -{\text {Fe}}_2{\text {O}}_3\)). All samples exhibited room-temperature superparamagnetic-like behavior. These results support the above-proposed mechanism in which interfacial adsorption of MNP@SDBS and field-gradient-driven magnetophoretic collection promote droplet bridging and coalescence, while also enabling rapid magnetic recovery and reuse of the demulsifier.