Polymer-matrix nanocomposite membranes for water treatment

• Summarize recent scientific and technological advances in the nanocomposite membrane development.
• Classify nanocomposites based on membrane structure and nanomaterial location.
• Discuss challenges and future research directions in developing nanocomposite membranes.

One of the grand challenges to sustain the modern society is to secure adequate water resources of desirable quality for various designated uses. To address this challenge, membrane water treatment is expected to play an increasingly important role in areas such as drinking water treatment, brackish and seawater desalination, and wastewater treatment and reuse. Existing membranes for water treatment, typically polymeric in nature, are still restricted by several challenges including the trade-off relationship between permeability and selectivity (also called Robeson upper boundary in membrane gas separation), and low resistance to fouling. Nanocomposite membranes, a new class of membranes fabricated by combining polymeric materials with nanomaterials, are emerging as a promising solution to these challenges. The advanced nanocomposite membranes could be designed to meet specific water treatment applications by tuning their structure and physicochemical properties (e.g. hydrophilicity, porosity, charge density, and thermal and mechanical stability) and introducing unique functionalities (e.g. antibacterial, photocatalytic or adsorptive capabilities). This review is to summarize the recent scientific and technological advances in the development of nanocomposite membranes for water treatment. The nanocomposite membranes were classified into (1) conventional nanocomposite, (2) thin-film nanocomposite (TFN), (3) thin-film composite (TFC) with nanocomposite substrate, and (4) surface located nanocomposite, based on the membrane structure and location of nanomaterial. Challenges and future research directions in developing high performance nanocomposite membranes were also discussed.