Upgrading polytetrafluoroethylene hollow-fiber membranes by CFD-optimized atomic layer deposition

Superfast water transport mixed matrix membranes with asymmetrical micro-nanostructures reinforced by metal-organic frameworks

Metal-organic framework (MOF) based nanofiltration (NF) membrane have emerged as the promising option in the field of efficient water purification. However, challenges associated with limited water transport ability of MOF-based NF membranes with conventional structures over separation process hinder the widespread application. This work, we proposed a nano-confined interfacial polymerization to prepare ultrahigh-flux supported MOF mixed matrix membranes (ZIF/PA membranes) with asymmetrical micro-nanostructures composed of two-dimensional zeolitic imidazolate framework (ZIF-L) and polyamide (PA) under suction force. In the membrane structure, the microscale asymmetric orientation distribution of ZIF-L nanosheets result in the most utilization of MOFs to forming the more regular and shorter diffusion paths; the nanoscale asymmetric hydrophilic interfacial channels between the PA and ZIF-L interfaces enhance the nanofluid transport of water molecules. Thus, the ZIF/PA membranes not only possess high rejection rate for versatile dye molecules (e.g., 99.99 % for Congo red, 99.84 % for Methyl green, 99.99 % for Methylene blue, 99.95 % for Methyl orange, 98.99 % for Reactive black 5, and 99.97 % for Reactive blue 194), but also the corresponding water permeance exceed the most membrane materials reported so far. And the prepared membrane also shows good performance in the real printing and dyeing wastewater treatment, further manifesting advantages for practical applications. Both experimental observations and molecular dynamics (MD) simulations substantiate that the water is transported through ultra-fast nanofluidic flow as a result of asymmetric and continuous interfacial nanochannels.

Membrane Fabrication and Modification by Atomic Layer Deposition: Processes and Applications in Water Treatment and Gas Separation

Membrane-based separation processes are part of most water purification plants worldwide. Industrial separation applications, primarily water purification and gas separation, can be improved with novel membranes or modification to existing ones. Atomic layer deposition (ALD) is an emerging technique that is proposed to upgrade certain kinds of membranes independent of their chemistry and morphology. ALD deposits thin, defect-free, angstrom-scale, and uniform coating layers on a substrate's surface by reacting with gaseous precursors. The surface-modifying effects of ALD are described in the present review, followed by a description of various types of inorganic and organic barrier films and how these can be used in combination with ALD. The role of ALD in membrane fabrication and modification is categorized into different membrane-based groups according to the treated medium, i.e., water or gas. In all membrane types, the ALD-based direct deposition of inorganic materials, mainly metal oxides, on the membrane surface can improve antifouling, selectivity, permeability, and hydrophilicity. Therefore, the ALD technique can broaden the applications of membranes to the treatment of emerging contaminants in water and air. Finally, the advancement, limitations, and challenges of ALD-based membrane fabrication and modification are compared to provide a comprehensive guideline for developing next-generation membranes with improved filtration and separation performance.