Magnetically recoverable photocatalytic nanocomposite particles for water treatment

Magnetically recoverable, photocatalytic, nanocomposite particles were prepared by the simple heteroagglomeration of previously synthesized anatase nanoparticles and superparamagnetic maghemite nanoparticles in an aqueous suspension by applying attractive electrostatic forces between the nanoparticles with an opposite electric surface charge. The anatase nanoparticles, with sizes between 3 and 5 nm, were synthesized using a simple hydrolysis of aqueous TiOSO4, and the maghemite nanoparticles, with size approximately 13 nm, were synthesized with a simple co-precipitation from an aqueous solution of Fe2+/Fe3+ using ammonia. The surface charge of the maghemite nanoparticles was modified by grafting aminopropyl triethoxy silane (APS) onto their surfaces. The nanocomposite particles formed in the suspension at neutral pH, where the as-synthesized anatase nanoparticles display a negative charge and the APS-grafted maghemite nanoparticles display a positive charge, and consequently the two types of nanoparticles heteroagglomerate. Testing the nanocomposite particles for magnetic separation using a laboratory separator showed that they can be effectively separated from a water suspension, even when they contain only a small amount, i.e., 10% of magnetic phase. Their photocatalytic activity was tested in the decomposition of formic acid as a model compound. It appeared that the activity of the anatase nanoparticles increased when they were combined with the maghemite nanoparticles in the nanocomposite, providing the content of maghemite was below ∼50%.