Molecular layer deposited metalcone hybrid layers for solvent-resistant nanofiltration membranes: surface wetting and permeation

• Optimizing solvent-resistant nanofiltration membranes via atmospheric-pressure MLD. • Post-deposition air and N 2 annealing creating membranes with sub-2 nm pore sizes. • Metalcone hybrid layers with controlled physicochemical properties and performance. • Hybrid layers with high chemical stability in solvents and water-solvent mixtures. • Increasing hydrophobicity by surface-silanization using methyltrimethoxysilane. Solvent-resistant nanofiltration (SRNF) has emerged as a promising alternative to conventional distillation for removing impurities, recovering solutes, and regenerating solvents from diluted process streams. For most industries, such as the pharmaceutical and (petro)chemical industry, the key important factor here is energy-efficiency gain. This study investigates the physicochemical properties of metalcone hybrid layers, such as layer thickness, composition, and layer-solvent interactions. It also utilizes surface-silanization to increase the hydrophobicity of these layers, grown on both planar silicon and 3D-porous ceramic substrates. Using the molecular layer deposition (MLD) technique, vapor-phase titanium tetra-chloride and trimethyl-aluminum are employed as precursors, with ethylene glycol as a co-reactant for nanopore fabrication and methyltrimethoxysilane for surface-silanization. MLD layers were deposited at 125°C and 150°C, followed by annealing in air and nitrogen (N 2 ) at 250°C and 350°C. The resulting SRNF membranes demonstrated high chemical stability in polar and non-polar solvents, as well as in water-solvent mixtures, maintaining permeation rates after 48 hours of continuous exposure. Furthermore, after surface-silanization and enhanced hydrophobicity, the n-hexane permeance was tripled for surface-silanized titanicone and doubled for alucone hybrid layers compared to the unsilanized hybrid layers. Conversely, demineralized water permeance decreased. The SRNF membranes, with pore diameters of <2 nm, show a >90% rejection for polyethylene glycol molecular sizes >390 Dalton. The final n-hexane permeance of surface-silanized, air- and N 2 -annealed metalcone hybrid layer membranes was >10 L·m⁻ 2 ·hr⁻ 1 ·bar⁻ 1 . These results demonstrate the versatility of MLD as a technology ready for further developing membranes towards large-scale industrial applications.