Synthesis and incorporation of thin 2D sheets of graphitic carbon nitride in polyamide thin film nanocomposite membranes for enhanced desalination and anti-biofouling properties

Among the various desalination technologies developed so far, membrane-based desalination is rapidly growing; however, desalination membranes suffer from challenges such as the typical trade-off between permeate flux and solute selectivity, as well as membrane fouling. Hence, the current work was designed to synthesize extremely thin 2D sheets of graphitic carbon nitride (G-CN) with a thickness of approximately 1.413 nm using a simple approach based on thermal exfoliation for incorporation into the membrane structure, thereby enhancing desalination. Upon confirming the 2D structure of G-CN by FE-TEM, these 2D sheets were incorporated into the active layer of the nanofiltration membranes by interfacial polymerization (IP). The resultant thin film nanocomposite (TFN) G-CN-PIP/TMC membrane exhibited a significant improvement in permeate flux, accompanied by reasonable salt rejection. At a transmembrane pressure of 12 bar, the permeate flux was recorded to be 69.4 and 154.8 L m⁻² h⁻¹ for PIP/TMC control and G-CN-PIP/TMC TFN membrane. The salt rejection studies revealed that the G-CN-PIP/TMC membrane rejected 97 % of Na₂SO_4, and the PIP/TMC membrane rejected 95 % of the MgSO₄. Similarly, the stability analysis of the membrane showed that the permeate flux and salt rejection remained nearly constant for the membranes with only slight variations over 450 min using Na₂SO₄ feed (2000 ppm). The antifouling studies using bovine serum albumin (BSA) demonstrated that the membranes have excellent potential for reuse, with a flux recovery ratio (FRR) of 91.8 % for G-CN-PIP/TMC, following a decline of 45.0 % in normalized flux. The determination of the bacteriostatic rate for the PIP/TMC and G-CN-PIP/TMC membranes showed 69.6 % and 82.9 % inhibition of E. coli ATCC 25922 and S. aureus ATCC 25923, respectively.