Plasma activation of porous polytetrafluoroethylene membranes for superior hydrophilicity and separation performances via atomic layer deposition of TiO2

• Conformal layers of TiO2 were atomic layer deposited on activated PTFE membranes.
• Strong adhesion between TiO2 and PTFE was evidenced by a harsh ultrasonication.
• The surface approached to superior hydrophilicity at moderate ALD cycle numbers.
• The flux and retention of PTFE membranes were simultaneously upgraded.

Conformal and smooth TiO2 thin layers were coated on the surface of porous PTFE membranes subjected to a plasma activation process by atomic layer deposition (ALD). In contrast, TiO2 was deposited on the PTFE surface as globular particulates without plasma activation due to the inert chemical nature of PTFE surface. X-ray photoelectron spectrometry confirmed the formation of functional groups on the plasma-activated PTFE surface which served as active sites for the homogeneous adsorption and reaction of ALD precursors. Scanning and transmission electron microscopy revealed the uniformity of the deposited layer and the precise control of its thickness by changing ALD cycle numbers. The water contact angle measurement showed that the hydrophobic surface gradually turned to be near superhydrophilic with the increment of ALD numbers. Also, the membrane mean pore size was progressively reduced by simply altering the ALD numbers. At proper deposition conditions, the modified membranes gained an increase of pure water flux of more than 150% and simultaneously a doubled retention compared to the original unmodified membrane. This research provides an efficient approach devoid of any harsh treatments to modifying PTFE membranes for achieving specific functions, which also can be applied to other organic materials especially with chemical inert surface.