Increasing hydrophobicity of ceramic membranes by post-deposition nitrogen annealing of molecular layer deposition grown hybrid layers

• MLD of alucones from trimethyl-aluminum (TMA) with aliphatic or aromatic alcohols. • Functionalization of ceramic membranes with hydroxylated surfaces. • Aromatic alcohols exhibiting higher physical/chemical affinity towards TMA. • Using post-deposition nitrogen annealing to increase hydrophobicity. Molecular layer deposition is increasingly used to functionalize the surface of planar and 3D porous substrates. This study explores functionalized ‘alucone’ hybrid layers grown on ceramic substrates to enhance their surface hydrophobicity. The layers were made from trimethyl-aluminum as a precursor with five different alcohols as a co-reactant: aliphatic (ethane-1,2-diol, 2,2-oxydiethanol, 1,6-hexanediol), and aromatic (4-aminophenol, benzene-1,4-diol). After post-deposition annealing in N 2 atmosphere at 250 and 350 °C, the changes in the physical properties and the chemical affinity of the layers were studied and compared to those of the as-deposited hybrid layers. Differential thermal analysis of the hybrid layers showed higher decomposition temperatures for the layers grown from aromatic alcohols than for those grown from aliphatic alcohols. Additionally, Fourier-transform infrared and X-ray photoelectron spectroscopy showed that an increase in annealing temperature decreased the concentrations of surface hydroxyl-groups and caused changes in the carbon-related groups. These results could be correlated to the hydrophobicity of the layers: higher water contact angles (>90°) were measured for annealed samples, compared to those (<90°) of the as-deposited samples grown at 150 °C. These findings confirm that the proposed method of MLD functionalization and post-deposition annealing can be used to tune the surface hydrophobicity of ceramic membranes.