The precursor solutions were stirred for at least 1 hour at room temperature. Subsequently, the precursor was fed at 6 mL min -1 and dispersed using 3 L min -1 O2 (> 99.5%, Linde AGA Gas AB, Sweden) at constant pressure (1.6 bar). The flame was ignited by a premixed supporting flame of CH4 and O2 (> 99.5%, Linde AGA Gas AB) at flow rates of 1.5 L min -1 and 3.2 L min -1 , respectively. A 5 L min -1 O2 sheath gas was fed through the outermost sinter metal plate of the FSP burner. Gas flow rates were controlled with calibrated mass flow controllers (Bronkhorst, the Netherlands). The particles were collected on a glass fiber filter (Albert LabScience, Germany) with the aid of a Mink MM 1144 BV vacuum pump (Busch, Sweden).