Ammonium ferrous sulfate

The PVDF membrane (Pore size 0.1 μm, Jiangsu Dafu Co. Ltd.) was washed by pure water and then immersed into a glass tube which contains 5% wt of HEA (>99% wt, Sinopharm Chemical Reagent Co., Lt D, China) solution with 0.7% wt of ammonium ferrous sulfate (>99% wt, Sinopharm Chemical Reagent Co., Lt D, China) as the polymerization inhibitor. For grafting modification, studies have reported that the initiator concentration of 4–5% (w/v) was the optimum concentration to obtain better results^{11 (link), 36 (link)}. 5% HEA was adopted in this study for this reason. The glass tube was purged with nitrogen, and then irradiated with γ-rays from a Co⁶⁰ source (Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, 201800, China) with a irradiation dose rate of 1.0 kGy/h at room temperature (25 ± 1 °C) for 20 hours. The grafting rate was calculated by the method reported in a previous study^{37 (link)}. The grafted membrane was washed thoroughly and kept in pure water for testing. The schematic illustration of grafting process is shown in Fig. 1.Figure 1

The schematic illustration of the grafting process.