Research on Reverse Osmosis (RO)/Nanofiltration (NF) Membranes Based on Thin Film Composite (TFC) Structures: Mechanism, Recent Progress and Application

Abstract

The global shortage of clean water is a major problem, even in water-rich regions. To solve this problem, low-cost and energy-efficient water treatment methods are needed. Membrane separation technology (MST), as a separation method with low energy consumption, low cost, and good separation effect, has been widely used to deal with seawater desalination, resource recovery, industrial wastewater treatment, and other fields. With the continuous progress of scientific and technological innovation and the increasing demand for use, NF/RO membranes based on the TFC structure are constantly being upgraded. This paper presents the recent research progress of NF and RO membranes based on TFC structures and their applications in different fields, especially the formation mechanism and regulation of selective layer structures and the modification methods of selective layers. Our summary provides fundamental insights into the understanding of NF and RO membrane processes and hopefully triggers further thinking on the development of membrane filtration process optimization.

Keywords: interfacial polymerization; membranes; modification methods; thin film composites.

Figure 1

(a) Three-layer structure of TFC membrane [13]; (b) Selective layer morphology of NF and RO membranes [14,15]; (c) Schematic diagram of the interfacial polymerization process.

Figure 2

(a) Escape of dissolved gases during the IP reaction; (b) Effect of solvent vaporization on the structure; (c) Effect of gases on the membrane structure; (d) Effect of the number of reacting monomers on the PA structure; (e) Structures of the five PA layers; (f) Small-angle diffraction technique used to analyze the generation of the PA structure.

Figure 3

(a) Co-solvent-formed ridge and valley structure with roof-like shape; (b) low magnification SEM of membrane cross-section; (c) high magnification SEM of membrane cross-section: (d) low magnification SEM of membrane surface: (e) high magnification SEM of membrane surface [67].

Figure 4

(a) Schematic diagram of rolled membrane module [117]; (b) schematic diagram of hollow fiber curtain membrane module [118]; (c) schematic diagram of flat membrane module [119]; (d,e) schematic diagram of hollow fiber-shell membrane module [120,121]; (f) 3D Printing Spacer Types [122].

Figure 5

Summary diagram of modification and application (Actual application pictures can be referred to [112,154,157,158]).