Abstract Core–shell SiO2-coated iron nanoparticles were synthesized using a one-step Stöber method in the presence and absence of PEG400. The 2,4-dichlorophenol degradation and antioxidation abilities of the nanoparticles were investigated. The effects of isopropanol/H2O ratio, NaOH dosage, tetraethyl orthosilicate (TEOS) dosage, and reaction time used in the synthesis were investigated. The SiO2-coated iron nanoparticles were characterized using transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. The results showed that N2 protection during filtration and drying were unnecessary, and the iron particle preparation was simple. The nanoparticles were stable in the presence of PEG400. The effects of isopropanol/H2O ratio and TEOS dosage on 2,4-dichlorophenol degradation and antioxidation abilities were significant, although the effects of NaOH dosage and reaction time were small. The isopropanol/H2O ratio changed the nanoparticle nucleation process, whereas NaOH dosage, TEOS dosage, and reaction time changed the mesoporous coating structure. A comparison of the removal rates of 2,4-dichlorophenol using pure iron nanoparticles and using SiO2-coated iron nanoparticles showed an improvement of about 30% using SiO2-coated iron nanoparticles, suggesting that SiO2-coated iron nanoparticles improve the antioxidation abilities and reducing capacity of iron nanoparticles; such nanoparticles could have wide applications in chlorophenol degradation.