High-performance robust graphitic carbon nitride nanosheets embedded membranes for desalination through direct contact membrane distillation

Abstract

Two-dimensional (2D) graphitic carbon nitride (g-C3N4)-based membranes have recently received widespread attention due to their fantastic separation performance. In the present investigation, for the first time, we assessed the desalination performance of membranes incorporated with g-C3N4 nanosheets through the membrane distillation (MD) process. For this purpose, different concentrations (0–0.06 wt.%) of synthesized nanosheets were embedded within the hydrophobic PVDF matrix by simple phase inversion method. Upon loading 0.03 wt.% g-C3N4, the water contact angle and LEP augmented from 80.5° and 6 bar for the pure PVDF membrane to 95.2° and 8 bar, respectively. Adding the g-C3N4 nanosheets also improved both the tensile strength and the elongation at break by 21.32% and 36.46% than the pristine membrane, respectively. The mixed matrix membranes favorably improved MD performance; so that, 0.03 wt.% g-C3N4 embedded membrane exhibited a flux of 27.63 kg/m2h with an enhancement of 70% relative to its pure counterpart. Continuous testing for up to 24 h filtration of a 3.5 wt.% NaCl solution still showed a stable flux and almost complete salt rejection for the mentioned mixed matrix membrane. The anti-fouling properties of the membranes were also improved by incorporation of the g-C3N4 nanosheets. The 0.03 wt.% gCN embedded membrane recovered about 90% of the original permeation flux after 20 h desalination operations using real seawater as a feed solution. This work holds promise for developing next-generation MD membranes with superior desalination performance in terms of water vapor permeability and salt rejection.