BACKGROUND: Magnetite (Fe3O4) is an efficient Fenton-like heterogeneous catalyst for degradation of environmental pollutants. However, Fe3O4 is easy to aggregate and has bad dispersion stability because of its magnetism. This is the reason why the catalytic efficiency of Fe3O4 is not positive. In order to accelerate the dispersibility and improve the catalytic efficiency, the surface of Fe3O4 was modified with saponin, a natural plant-biosurfactants. It is anticipated that saponin-modified Fe3O4 nanoparticles (S-Fe3O4) can expose more catalytic sites and has better dispersion stability to improve catalytic efficiency for activating H2O2. RESULTS: The S-Fe3O4 was prepared through oxidative polymerization. It has a pattern of regular hexagon with a diameter of 70-80 nm and it is superparamagnetic. The sedimentation experiment shows that S-Fe3O4 was able to maintain notable dispersibility for 18 days. During a 90 min reaction, 100% of p-nitrophenol (IUPAC name 4-Nitrophenol, PNP) can be removed using 2.0 g L(-1)catalyst at initial pH 3.0 +/- 0.3, initial PNP concentration 250 mgL(-1), H2O2 20 mmol L-1, and temperature 30 degrees C. CONCLUSION: Saponin-modified Fe3O4 nanoparticles (S-Fe3O4) accelerate the efficiency of degradation of PNP by enhancing the dispersibility of Fe3O4. It is anticipated that this provides a new catalyst for remediation of wastewater. (C) 2016 Society of Chemical Industry