Rapid, efficient, and thermal degradation of chlorophenols using polymer-coated or metal-doped magnetic nanoparticles, with and without the application of AMF

Chlorophenols (CPs) are hazardous persistent organic pollutants widely used in many industries, yet they pose serious risks on the environment and human health. Thus, there is a great demand for innovative, effective, and rapid CPs remediation to safer harmless products. Herein, we prepared different panels of tailor-made iron oxide magnetic nanoparticles (MNPs), either coated with polymers (i.e. PVP, Chitosan, Starch) or doped with transition metals (i.e. M2+ = Co2+, Ni2+, Zn2+) and explored how the identity of the coated polymer or doped metal influences the catalytic performance towards removal of two common organic CP contaminants: 4-Chlorophenol (4-CP) and 2-Chlorophenol (2-CP). All MNPs were thoroughly characterized using TEM, XRD, FTIR, SEM-EDX, and VSM, confirming nanosized particles (~ 8–15 nm), highly crystalline spinel structures (pure Fe3O4 and MFe2O4 phases), and superparamagnetic behavior (Ms = ~ 40–70 emu/g). Experimental degradation studies showed that both polymer-coated MNPs (PMNPs) and metal-doped MNPs (MMNPs) were highly effective at eliminating CPs, albeit at different efficiencies. While polymer coatings provide structural stability, they tend to reduce degradation rates by limiting active site exposure. Interestingly, MMNPs, particularly CoFe2O4, exhibited outstanding performance, achieving complete degradation of 4-CP and 2-CP (50 ppm, neutral pH) within only few seconds with an exceptionally high-rate constant (kr = 5.743 min−1) and an extremely short half-life of 0.12 min, indicating one of the fastest reported nanocatalysts. In contrast, both NiFe2O4 (kr = 0.172 min−1, t½ = 4.03 min) and ZnFe2O4 (kr = 0.342 min−1, t½ = 2.03 min) demonstrated slightly lower but excellent activities. Degradation data well fitted the pseudo-first-order kinetics model. All these variations highlight the critical role of dopant metal type or surface modification in tuning catalytic properties. Additional factors including a wide pH range (3–10), catalyst dosage (2–10 mg/mL), pollutant concentration (10–70 ppm), H₂O₂ levels, and temperature (25–55 °C) were also tested and were found to influence degradation. Reusability studies demonstrated that the different MNPs could be reused for six consecutive cycles with high removal efficiencies (~ 80–100%), without the use of any desorption agents. Interestingly, thermal degradation driven by the application of an alternating magnetic field (AMF) inducing heat dissipation from MNPs, markedly accelerated the degradation process. According to our knowledge, these results utilizing AMF to thermally degrade CPs are presented for the first time. This underscores the promise of such MMNPs/PMNPs as fast, efficient, and reusable nanocatalysts for potential industrial wastewater treatment.