A new class of hydrophobic CuO nanosheets is introduced by functionalization of the cupric oxide surface with p-xylene, toluene, hexane, methylcyclohexane, and chlorobenzene. The resulting nanosheets exhibit a wide range of contact angles from 146 degrees (p-xylene) to 27 degrees (chlorobenzene) due to significant changes in surface composition induced by functionalization, as revealed by XPS and ATR-FTIR spectroscopies and computational modeling. Aromatic adsorbates are stable even up to 250-350 degrees C since they covalently bind to the surface as alkoxides, upon reaction with the surface as shown by DFT calculations and FTIR and H-1 NMR spectroscopy. The resulting hydrophobicity correlates with H-2 temperature-programmed reduction (H-2-TPR) stability, which therefore provides a practical gauge of hydrophobicity.