Atmospheric pressure atomic layer deposition for tight ceramic nanofiltration membranes: Synthesis and application in water purification

Tight ceramic nanofiltration (NF) membranes allow efficient separation of organic matter and ions for advanced water treatment. These membranes are typically produced by the sol-gel method. Recently, atomic layer deposition (ALD), a self-limiting gas phase coating technique, has been explored for membrane fabrication and modification. In this work, the synthesis of tight ceramic NF membranes is demonstrated using atmospheric pressure ALD (APALD), which is operated without a vacuum-generation system compared to the commonly reported vacuum-based ALD method. Titanium dioxide was coated on nano-porous membrane substrates using merely one to three cycles of APALD. The average size of active pores was effectively narrowed by 0.2nm, from 0.7 to 0.5nm. In addition, the size distribution of the active pores became more uniform after the APALD modification. The fabricated tight ceramic NF membranes had a molecular weight cut-off (MWCO) ranging from 260 to 380Da while maintaining high water permeability at 11–16Lm−2h−1bar−1, which is notably higher than the commercial tight polymeric NF and sol-gel-made tight ceramic NF membranes. It was observed that conformal TiO2 thin films can be deposited on planar surfaces under the APALD with a growth rate of 0.39nm per cycle, while the deposition in the membrane micropores was at a lower rate, estimated as 0.05nm per cycle.