Vapor Phase Infiltration of Metal Oxides for Water Treatment Membranes: Potential and Limitations

Membrane-based water treatment processes are critical for global water security, yet current state-of-the-art polymeric membranes face limitations in mechanical, chemical, and thermal stability. Ceramic membranes, on the other hand, foul less, are easy to clean, and have high modulus values, but they are brittle and less permeable when used as dense membranes. Vapor phase infiltration (VPI) of metal oxides, a derivative of atomic layer deposition (ALD) that transforms organic polymers into organic–inorganic hybrid materials, offers a novel method to modify polymeric membranes and allow them to have the advantages of both polymeric and ceramic membranes. In this review, we combine insights from the use of VPI with polymeric substrates and organic solvent separation membranes to provide our view of the potential and limitations of VPI for enhancing water treatment membranes. We examine how VPI of metal oxides improves the mechanical strength, which is relevant to compaction-resistant reverse osmosis supports, and chemical stability, which could play a role in membrane chlorine and extreme-pH tolerance. We also critically evaluate the associated trade-offs, most notably potential reductions in water permeance arising from the intrinsically lower water permeability of metal oxides. We further identify ion exchange membranes and electrodialysis as especially promising targets, where suppressed water transport is advantageous for ion–ion selectivity. Together, these insights clarify where VPI of metal oxides can most effectively advance emerging membrane-based water treatment technologies.