Probing Facet Specific Interaction of 2-Propanol and CoFe₂O₄ at Near-Ambient Conditions

The interaction between 2-propanol and low-index facets of cobalt ferrite thin films under near-ambient conditions has been studied using surface-sensitive vibrational sum frequency spectroscopy (vSFS) and ab initio molecular dynamics (AIMD) simulations. The experimental and theoretical findings suggest that 2-propanol undergoes molecular and dissociative adsorption on different facets of CoFe₂O₄. Dissociation was found to be more prevalent on the (111) surface than on the (001) surface. Under dry conditions, the active regions on the (111) surface consist of Co²⁺-O₂-propoxide-Fe³⁺ bridges. In contrast, the Co²⁺ surface atoms are inactive on the (001) surface under dry conditions. The Fe³⁺ surface atoms are the preferred adsorption sites. Molecular water plays a detrimental role because it competitively adsorbs onto the active sites with 2-propanol, inhibiting its decomposition. Moreover, OH groups with a lower concentration promote the formation of 2-propoxide. These results contrast with our recent study in which 2-propanol remained molecularly adsorbed on the Co₃O₄ (001) surface. These findings underscore the ambivalent role of hydroxyl groups on surfaces and also highlight the importance of dissociation state and water concentration as critical parameters for 2-propanol activation.