Atomic layer deposition (ALD) is a widely used vapor-phase deposition technique that allows ultra-thin coating of a surface with target substances. Its capability to control the coating thickness at an atomistic scale is instrumental to modify the surface of porous polymeric membranes by chemically-resistant, hydrophilic inorganic substances such as metal oxides. We here examined the ALD of TiO2 onto polyamide thin film composite membranes of which pore sizes are of a similar size scale as the ALD precursor chemicals, tetrakis-dimethylamido titanium (TDMAT) and water. Our results suggest that the optimal ALD conditions, the film growth kinetics, and the depth of deposition differed between nanofiltration (NF) and reverse osmosis (RO) membranes due to differential diffusive transport of TDMAT through the membrane pores. The TiO2 coating was confined to the surface of RO membrane; in contrast, TiO2 deposition extended to the depth of the NF membrane. The ALD coating deteriorated membrane water permeability and salt rejection beyond 10 cycles of ALD coating (i.e., one cycle consisting of consecutive exposure of TDMAT and H2O), the condition commonly employed in the literature. With less than 10 cycles, the TiO2 coating of RO membrane increased the membrane surface charge without negatively affecting water permeability and salt rejection. The deposition of TiO2 inside the pores in the NF membrane led to the tuning of pore size and increased rejection of select solutes.

Controlled TiO2 growth on thin film composite membranes by atomic layer deposition: Mechanisms and potential applications

256th National Meeting (2018)

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