HfO 2 nanoparticles HfO 2 NCs were synthesized using a solvothermal method according to Lauria et al. In a nitrogen-filled glovebox, 2.26 g of hafnium(IV) tert-butoxide (4.8 mmol, 1.94 mL) and 40 mL of anhydrous benzyl alcohol were mixed in a Teflon-lined 125 mL Parr bomb, sealed and taken out of the glovebox. The Parr bomb was then placed in a muffle furnace for 96 h at 220 • C. After synthesis, the nanoparticles were collected by addition of 20 mL of diethyl ether and centrifugating for 3 min at 8000 rpm. The supernatant was discarded and the precipitate was washed once more with 20 mL of diethyl ether. For functionalization, the nanoparticles were dispersed in 5 mL of toluene, resulting in a milky turbid liquid, to which 381 uL of 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA, 0.328 g, 1.82 mmol)