Carbon membranes (CMs) are newly developed inorganic membrane materials for fluid mixture separation. In addition to excellent separation performance, CMs have the advantages of outstanding thermal stability and chemical inertness . Owing to these comprehensively outstanding properties, CMs have become increasingly attractive for a large variety of fields, including chemical engineering, pharmaceutics, biologies, environmental protection, transportation and so on [2,3].
In general, the membrane surface of CMs is dominated by hydropho- bicity that is more beneficial for separation of non-polar gases than polar liquid mixtures, e.g., water. The rapid development of organic polymeric membranes for gas separation is the current mainstream. Therefore, most researchers concentrate on gas separation of CMs. Before the beginning of this century, prior to the discovery of novel carbons such as fullerene, carbon nanotubes, grapheme, graphyle, carbon dots and so on, the in-depth nature of carbon materials was not well understood . As a matter of fact, the edges or defects in carbon materials have a large number of active chemical groups . This finding provides more opportunities for a large variety of designs and applications based on the structure and properties of CMs .
All membrane materials are subject to a trade-off relationship between permeability and selectivity . Consequently, people are keen to develop novel membrane materials by combining the easily tunable porous structure and the excellent separation efficiency of membranes such as carbon nanotube membranes and ordered porous membranes [8, 9]. However, the sub-nanoscale pore dimension of these membranes is too large for selective separation of gases, despite their use in removing large molecules, such as organic pollutants, from water. Although the effectiveness of this route for improving the separation property of CMs in comparison to traditional polymeric membranes has been demonstrated, the membranes should be called "carbon-doped polymeric membranes" rather than "carbon membranes" because the membrane matrix is mainly composed of polymer. Nevertheless, researchers have been inspired to explore functional carbon membranes with mesopores and macropores via hybridization or imitating ceramic membranes, or tailoring the surface properties, for the application of microfiltration, ultrafiltration and nanofiltration . Undoubtedly, this exploration has broadened the horizon for the research and development of CMs.
Consequently, this chapter will focus on research into CMs for microfiltration, ultrafiltration and nanofiltration. There are many reports in the literature on the use of carbon nanotubes, activated carbon, graphene and carbon quantum dots as dopants into a continuous polymer matrix for liquid mixture separations such as microfiltration, ultrafiltration and nanofiltration. Researchers can find some well-documented reviews of those aspects [5,11]. Here, only membranes composed from continuous carbon materials are summarized and reviewed in terms of preparation, modification and application.