Influence of hydrophilic carbon dots on polyamide thin film nanocomposite reverse osmosis membranes

There is critical to fabricate reverse osmosis (RO) membranes with high water-solute selectivity, thereby decreasing the energy input required in desalination processes. To achieve this, a super hydrophilic nano Carbon Dots (CDs) with quantum size of 6.8 nm was self-synthesized and successfully incorporated into the selective layer of polyamide (PA) thin-film nanocomposite (TFN) RO membrane. The novel CDs-TFN RO membrane was fabricated by dispersing the CDs nanoparticles at varying quantities into aqueous solution through interfacial polymerization (IP) of monomers of m-phenylenediamine (MPD) and trimesoyl chloride (TMC). Using Excitation and emission matrix (EEM) to explore the incorporation of CDs into the membrane skin layer, we observe that the fluorescence properties of CDs-TFN membrane decreased in order of increasing CDs concentration in relation to the unmodified TFC RO membrane which has the highest fluorescence count. The surface morphology of all TFN membranes transform from a leaf-like structure into ridge-and-valley structure with increased roughness, which has an important implication for flux enhancement. The TFN membrane with 0.02 wt% CDs incorporation exhibited promising desalination performance with water flux of 87.1 L/m(2)/h and salt rejection of 98.8% than the control thin film composite (TFC) membrane (2000 ppm NaCl solution, 25 degrees C, 1.55 MPa). The improved performances of CDs-TFN membrane were attributed to the enhanced hydrophilicity, decreased thickness as well as the increased density of the selective layer due to the incorporation of small amounts of CDs nanoparticles. By extending the deposition time of CDs on the polysulfone substrate, the membrane performance was further improved with water flux of 88.7 L/m(2)/h and salt rejection of 99.0%.