Amine functionalization of outer SP surfaces was carried out by dispersing 8.0 g supraparticles in 50 mL ethyl acetate under ultrasonication for 5 min. A solution of 50.2 mg 4-aminobutylphosphonic acid in a mixture of 50 mL ethanol and 50 mL water was added to the colloidal suspension and sonicated for 10 min at 30 % amplitude. The amount of amine-ligand was calculated according to 5 surface equivalents considering the total SP surface as obtained from its size distribution shown in Fig. and a ligand anchoring surface of 0.24 nm 2 for phosphates. The colloidal supraparticles were washed afterwards 3 times with 96 %ethanol and dried under vacuum. Ligand crosslinking was carried out by casting the powdered supraparticles into a crucible followed by annealing under N 2 (g) with a dwell time of 18 min, and 1 °C/min heating and cooling ramps up to 325 °C in a tube furnace.