Water-Induced Multicyclization of Alcohol Molecules on Copper Visualized by Atomic Force Microscopy

Methanol and ethanol are widely used as solvents, energy storage materials, and feedstocks for manufacturing other chemicals, in which the steam reforming of methanol/ethanol provides an efficient approach for H₂ production. Therefore, the interaction of water and alcohol molecules on solid surfaces attracts much interest, but the atomic-scale characterization of the structures of water-alcohol mixtures is limited. Here, using noncontact atomic force microscopy (nc-AFM) in combination with density functional theory (DFT) calculations and AFM simulations, we directly visualize the atomic structures of water-alcohol hydrogen-bonding complexes on copper substrates, in which the detailed H-bonding network and the methyl/ethyl groups of alcohol molecules are discerned. We find that the methanol clusters and chains would transform into bicyclic and tricyclic H-bonding networks that are composed of pentamers and hexamers when water is involved. These specific methanol rings bridged by water molecules could form on both Cu(111) and Cu(110) surfaces. More interestingly, the water-induced multicyclization phenomenon is also applicable to ethanol and is expected to be general to a wide range of H-bonding systems that contain both hydrophilic and hydrophobic groups.