5g of crashed diatomite powered was resuspended into 250 mL of absolute EtOH and sonicated for 18 h to break large aggregates. The dispersion was sieved through a nylon net filter with pore size of 41 μm, and then filtered with pore size of 0.45 μm (Millipore, Billerica, MA, USA). The diatomite nanopowder was purified to remove the organic and inorganic impurities. First, the sample was centrifuged and the pellet treated with Piranha solution (2 MH2so4, 10% H2O2) for 30 min at 80 C. Then, the NP dispersion was centrifuged for 30 min at 13.500 rpm, washed twice with distilled water, resuspended in 5 M HCl, and incubated overnight at 80 C. DNPs were then centrifuged for 30 min at 13.500 rpm and washed twice with distilled water to eliminate HCl residues. 1The diatomite powder was morphologically characterized before and after the processing by TEM, SEM, and DLS analysis. Before the processing, diatomite resulted as a mixture of fragments with circular, elliptical, elongated, and squared shape, with dimension distribution ranging from few microns up to~ 40 μm, as shown in Fig. S1. 2