Efficient removal of high-concentration copper ions from wastewater via 2D g-C3N4 photocatalytic membrane filtration

Abstract Removal of high-concentration metal ions from wastewater still faces challenges. Since membrane-based technologies have sufficiently proven their effectiveness in removing heavy metals from water, research into the development and application of even more effective membranes is being carried out by researchers around the world. Here, graphitic carbon nitride, g-C3N4, due to its multiple properties, among other things its large specific surface area, its good hydrophilicity, its functional group and above all its photocatalytic capacities made it possible to generate a photocatalytic membrane for the removal of copper ions in water by membrane filtration method. When using the g-C3N4 membrane with thickness of about 310 nm for copper ion wastewater filtration, the efficiency of the light-treated g-C3N4 membrane after 15 h of filtration revealed an average water permeance of 47.82 L m−2 h−1 bar−1 as well as an average rejection rate of 98.03% for the copper ion concentration of 2500 mg/L, which is superior to that of commercial membranes. The g-C3N4 membrane exhibited similar trends in the removal of other heavy metal ions. Three effect have been identified as responsible of high rejection rate of heavy metal ions namely, adsorption due to the functional amino groups of g-C3N4, the effect of electrostatic repulsion and the steric effect. Exposing the membrane to light removed all copper ions present in the water, reducing them to their elemental form. Furthermore, an adsorption-photo reduction-filtration mechanism was proposed for the 2D g-C3N4 membrane to remove copper ions. It therefore opens the way for the use of 2D g-C3N4-based nanomaterials in the field of membrane filtration as photocatalytic membranes for the elimination of heavy metals in wastewater.