Gel structure and water desalination properties of divinylpyrazine-bridged polysilsesquioxanes

A divinylpyrazine-bridged trialkoxysilane, 2,5-bis[2-(triethoxysilyl)vinyl]pyrazine (BTES-VPz), was synthesized for use as a reverse osmosis membrane. The gel structure and water desalination properties of BTES-VPz were compared with those of previously reported 1,4-bis[2-(triethoxysilyl)vinyl]benzene (BTES-VB) and 2,5-bis[2-(triethoxysilyl)vinyl]pyridine (BTES-VP). The water contact angles of the film surface were in the order BTES-VP < BTES-VPz < BTES-VB, which indicates that the surface hydrophilicity of the films is related to the order of dipole moment of the monomer. The BTES-VPz membrane showed water permeation of 2.1 × 10 –13 m 3 /(m 2 ·Pa·s) with sodium chloride rejection of 97%. The water permeance of the membrane was in the order BTES-VPz > BTES-VP > BTES-VB. The superior water desalination performance of the BTES-VPz membrane was attributed to the water affinity of the nitrogen atoms, which was supported by the result of water solvation energy calculated by density functional theory. Graphical Abstract We synthesized a new bridged trialkoxysilanes, 2,5-bis[2-(triethoxysilyl)vinyl]pyrazine (BTES-VPz) for reverse osmosis membrane. The prepared membrane showed improved water permeance compared with benzene- and pyridine-bridged polysilsesquioxane and a high NaCl rejection of 97%. The superior water desalination performance of BTES-VPz is attributed to the effect of hydrophilicity of the two nitrogen atoms in benzene rings.