A novel ex-situ method to fabricate pH-responsive material based on core-shell Fe3O4@SiO2 nanoparticles for multi-functional oil-water separation and efficient recycling

The ex-situ method is suitable for the preparation and practical engineering application of large-sized adsorption materials like sponges. pH-responsiveness can solve the post-treatment problem of oil-absorbing sponges. Here, a facile ex-situ method is proposed to construct large-sized multi-functional oil-water separation materials by adsorbing pH-responsive magnetic core-shell structured nanoparticles (MNP) onto different substrates including sponge, metal mesh, and sandpaper. The MNPs are prepared by chemical coating and surface modification. The sponge can achieve in-situ renewable oil-water separation through the "oil absorption - oil desorption" process under different pH values, and the oil droplets exhibit a segmented wiredrawing desorption process. The generated secondary oily wastewater can be further separated through modified metal mesh, which can treat oily wastewater with more complex situations such as oil-water-oil three-phase mixtures. The detached nanoparticles (NP) can be easily recycled and reused through magnets. This method can achieve a large-scale in-situ treatment renewable oil-water separation process that integrates wastewater purification, oil collection, and material regeneration, which is environmentally friendly, energy-saving, and suitable for engineering applications.