Engineering loose nanofiltration membranes through amion-functionalized nanodiamonds for efficient dye/salt separation

It is extremely important to realize the separation of dyes and salts in textile wastewater. The nanofiltration membranes with high hydrophilic surface and loose structure are the best choice for efficient dye/salt separation. Herein, the ultrafiltration substrate membrane is firstly prepared employing polyimides as raw material and nanodiamonds grafted by polyethyleneimine as additive. Then tannic acid and Fe³⁺ are introduced to assemble into metal-polyphenol networks, finally achieving the construction of loose nanofiltration membrane. The experimental results show that as-obtained nanofiltration membrane possesses excellent mechanical properties and delivers a pure water flux of 42.57 L m^-2 h^-1, which is twice that of nanofiltration membrane without nanodiamonds. The as-obtained nanofiltration membrane also showed effective dye/salt separation with high dye rejection (CR, 99.03 %) and low inorganic salt rejection (NaCl, 4.13 %). The flux recovery rate of the membrane to humic acid is as high as 96.50 %, and it has considerable antifouling performance.