Magnetic Catalysts for Environmental Remediation and Sustainable Chemical Processing: A Multidisciplinary Review

Abstract

Magnetic catalysts have emerged as multifunctional materials that combine catalytic activity with rapid separation under an external magnetic field. This combination addresses a persistent limitation of conventional homogeneous and nanoscale heterogeneous catalysts: difficult recovery from liquid reaction media. Magnetite, maghemite, spinel ferrites, magnetic biochars, core–shell nanoparticles, magnetic metal–organic frameworks, and noble-metal-decorated magnetic supports have been investigated for wastewater treatment, advanced oxidation, photocatalysis, heavy-metal transformation, organic synthesis, biomass conversion, hydrogenation, carbon–carbon coupling, and biodiesel production. Their magnetic cores permit catalyst recovery without energy-intensive centrifugation or filtration, while surface coatings and catalytic phases provide adsorption, oxidation, reduction, acid–base, or metal-mediated reaction sites. This multidisciplinary review examines the design, preparation, characterization, reaction mechanisms, environmental applications, and sustainable-processing potential of magnetic catalysts. Particular attention is given to heterogeneous Fenton and photo-Fenton reactions, peroxide and persulfate activation, photocatalytic pollutant degradation, reduction of nitroaromatic contaminants, recyclable palladium and nickel catalysts, and magnetic solid acids for renewable-fuel production. The effects of particle size, surface area, oxidation state, porosity, magnetic saturation, active-phase dispersion, and interfacial electron transfer are discussed. Although laboratory studies frequently demonstrate high catalytic activity and repeated magnetic recovery, practical deployment remains restricted by nanoparticle aggregation, metal leaching, surface passivation, loss of magnetization, complex water matrices, mass-transfer limitations, and insufficient life-cycle evaluation. Future research should prioritize non-toxic compositions, waste-derived supports, continuous-flow magnetic separation, standardized recyclability testing, process intensification, techno-economic analysis, and complete environmental-risk assessment. Magnetic catalysts can contribute significantly to circular chemical manufacturing when catalytic performance, recoverability, material safety, and resource efficiency are optimized simultaneously.