Partitioning behavior and stabilization of hydrophobically coated HfO2, ZrO2 and HfxZr1−xO2 nanoparticles with natural organic matter reveal differences dependent on crystal structure

► Intact transition metal oxide nanoparticles may end up in the aquatic environment. ► Characterization of phase transfer was achieved by spectroscopy and microscopy analyses. ► Humic acids play a vital role in the aqueous stabilization of nanocrystals. ► Extent of phase transfer is different for monoclinic and tetragonal nanocrystals. ► Preferential binding of humic acid and water onto monoclinic surfaces.