Developing a novel nitrogen-doped hollow porous carbon sphere (N-HPCS) blended nanofiltration membrane with superior water permeance characteristic for high saline and colored wastewaters treatment

This study developed a novel mixed matrix polyethersulfone (PES) nanofiltration membrane by blending nitrogen-doped hollow carbon sphere with a mesoporous shell (N-HPCS). By loading only 0.25 wt% of N-HPCS into membrane matrix (M2), hydrophilicity (28.9°), pure water flux (105.6 L/m2h), mean pore diameter (1.59 nm), and fouling resistance extensively increased. Compared to the unmodified membrane (M0), the rejection of four studied salts at 3 bar enhanced averagely by 2.4-times using the M2 membrane. M2 showed 97.0%, 98.7%, and 99.2% of dye retention for methylene blue, rhodamine B, and reactive red 195, respectively. In addition, its removal percentage for Pb(II) and Cd(II) was above 98%. The results showed that the Na2SO4 concentration adversely affected its rejection due to the reduction in Debye length at higher ionic strength. While the reactive red 195 retention and Pb(II) removal almost remained constant by increasing their concentration. For studying the potential ability of M2 for high saline textile wastewater treatment, reactive red 195 retention was studied as a function of Na2SO4 concentrations from 100 to 5000 mg/L. At the highest salt concentration of 5000 mg/L, outstanding dye retention of > 97.9% with water permeate > 104.1 L/m2 was observed. Furthermore, 58 h successful continuous filtration of high concentration of Na2SO, reactive red 195, and Pb(II) demonstrated long-term stability of M2. Overall, our study provides a promising new approach for fabricating a high-performance modified membrane by N-HPCS for application in the practical context of wastewater treatment, especially in dye and textile industries.