Particles morphology was evaluated by scanning electron microscopy (SEM). The sample was diluted 1:10 in ultrapure water (Purelab Flex, ELGA-Veolia LabWater, Zoppola, Italy) and 20 µL were deposed on an aluminium stub and left to dry. The sample was then observed without further metallization using an Ultra High Resolution Field Emission SEM (SUPRA 40, CarlZeiss, Oberkochen, Germany) operated at an operating voltage of 1.00 kV.