Expanded graphite-based membrane for water desalination

For the first time, the expanded graphite (EG) was used as membrane-based for the desalination application. The EG is fabricated at room temperature using the optimizing weight ratio between ammonium persulfate and sulfuric acid. The highest expansion grade is 241 mL g–1 which is corresponded to the graphite with 305 μm of size, and the ratio between salt (NH4)2S2O8 and acid H2SO4 is 5:4. The conductivity of the filtered salt solution is 0.35 mS cm–1, demonstrating two conductivity orders inferior to the initial salt solution 0.5 M (17.7 mS cm–1). Besides, the filtered salt solution conductivity is located in the standard range of tap water. The salt removal capacity of EG is 9.32 mg g–1 (after filtering 500 mL of NaCl 0.5 M). This desalination capacity is lower than that of the 3D graphene-based membrane reported in the literature, 71.4 mg g–1[1]. However, it is necessary to point out the preparation cost of EG is negligible compared with the cost preparation of 3D graphene membrane. Still, it is relatively higher than other desalination-based membranes reported in the literature, such as activated carbon, 2–5 mg g–1[2]. The desalination result can be explained by the 2-dimensional structure of EG, which can provide an excellent molecular and ionic sieving effect. However, the EG exhibits low desalination stability due to the swell effect when it is contacted to an aqueous solution.