A critical review on thin-film nanocomposite membranes enabled by nanomaterials incorporated in different positions and with diverse dimensions: Performance comparison and mechanisms

Nanomaterials with diverse dimensions have been incorporated in different positions during the development of novel thin-film nanocomposite (TFN) membranes for water and wastewater treatment. However, a comprehensive comparison and rational selection are yet to be attained. According to the incorporation positions of nanomaterials, i.e., in the active layer, in the support layer and at the interface between the two, the membranes can be classified into TFNa, TFNs, and TFNi membranes, respectively. In this study, the roles of incorporation positions and dimensions of nanomaterials in TFN membrane construction are critically summarized, covering 187 pairs of optimal TFN membranes and corresponding control membranes reported in the literature. The water permeance, water/salt selectivity and characterization parameters of these membranes were mainly analyzed to compare the efficacy of nanomaterial incorporation in tailoring membrane properties and separation performance. Some instructive results demonstrated, for example, that TFNa membranes for reverse/forward osmosis and TFNi membranes for nanofiltration were superior in terms of overcoming the trade-off between water permeance and selectivity. In preparation of TFNi and TFNs membranes, utilization of 1D or 2D nanomaterials was more conducive to achieving an excellent water/salt selectivity than nanoparticles. This review can provide guidance for the targeted construction of high-performance TFN membranes. • The quantitative comparison on the three types of TFN membranes is conducted. • The role of nanomaterial dimensions in affecting membrane performance is summarized. • Conclusions on the rational selection of nanomaterials and incorporation methods are provided. • Future research gaps and outlooks in TFN membrane development are discussed.