Conjugated microporous polymer Janus membrane for dye rejection from water

Abstract

Forward osmosis (FO) is a process that uses the osmotic pressure of a high-concentration draw solution to separate solutes, e.g., ions and molecules, from solvents. We prepared a conjugated microporous polymer (CMP) Janus membrane with very thin hydrophilic and hydrophobic surfaces at both sides, respectively, for FO measurement, in which the asymmetric membrane architecture results in water diode phenomenon, namely, the transport of water in one direction is accelerated while the salt diffusion in the reverse direction is depressed. The asymmetric transport effect of the TTB-CMP Janus membrane on water and salt was thoroughly investigated by using various salt solutions with different hydrated radius as draw solution, e.g., NaCl, KCl, MgCl2, K3[Fe(CN)6], etc. Thanks to the asymmetric transport of water and salts, the Janus membrane shows a high recovered water flux (Jw) of 10.6 L m-2 h-1, with reverse salt flux (Js) as low as 1.39 g m-2 h-1 when 0.1 M NaCl is used as the draw solution. When further used for recovering water from dye solutions, the recovered water flux maintains up to 9.4 L m2 h-1, with molecular weight cut-off (MWCO) of 680 g mol-1, exhibiting obvious molecular sieving effect originated from the pore size of CMP. This study provides fundamental insight and guidance into the potential application of porous Janus membrane for removing dyes from water.