Abstract
Enhancing the water flux while maintaining the high salt rejection of existing reverse osmosis membranes remains a considerable challenge. Herein, we report the use of a porous carbon nitride (C3N4) nanoparticle to potentially improve both the water flux and salt rejection of the state-of-the-art polyamide (PA) thin film composite (TFC) membranes. The organic–organic covalent bonds endowed C3N4 with great compatibility with the PA layer, which positively influenced the customization of interfacial polymerization (IP). Benefitting from the positive effects of C3N4, a more hydrophilic, more crumpled thin film nanocomposite (TFN) membrane with a larger surface area, and an increased cross-linking degree of PA layer was achieved. Moreover, the uniform porous structure of the C3N4 embedded in the ”ridge” sections of the PA layer potentially provided additional water channels. All these factors combined provided unprecedented performance for seawater desalination among all the PA-TFC membranes reported thus far. The water permeance of the optimized TFN membrane is 2.1-folds higher than that of the pristine PA-TFC membrane, while the NaCl rejection increased to 99.5% from 98.0%. Our method provided a promising way to improve the performance of the state-of-art PA-TFC membranes in seawater desalination.
Highlights
Water scarcity is a global issue currently affecting about two-thirds of the world’s population [1].Over the last half century, reverse osmosis (RO) has been demonstrated as an affordable approach to producing drinking water from seawater [2]
This is mainly owing to the successful development of the start-of-the-art RO membrane: a polyamide thin-film composite (PA-thin film composite (TFC)) membrane consisting of a thin and highly cross-linked PA selective layer atop a strong and porous support layer [3,4,5,6,7,8]
Several other publications have reported the use of a sublayer made of cellulose nanofibers [28], tannic acid/Fe3+ nanoscaffold [29], or carbon nanotubes [22,30] to optimize the process of interfacial polymerization (IP)
Summary
Water scarcity is a global issue currently affecting about two-thirds of the world’s population [1]. Several other publications have reported the use of a sublayer made of cellulose nanofibers [28], tannic acid/Fe3+ nanoscaffold [29], or carbon nanotubes [22,30] to optimize the process of IP These membranes demonstrate an improved water flux, their NaCl rejection values are generally low. It was determined that embedding the C3 N4 nanoparticles into the PA layer during the IP process could significantly enlarge the ridge-and-valley surface structure This effect, as well as the additional transport pathway for water, substantially improved the water permeance of the membrane to 3.2 ± 0.2 Lm−2 ·h−1 /bar (LMH/bar) and endowed it with an excellent NaCl rejection of 99.5%, which surpassed the performances of most.
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