Tailoring the internal void structure of polyamide films to achieve highly permeable reverse osmosis membranes for water desalination

Abstract

The considerable permeability of fully-aromatic polyamide reverse osmosis (RO) membranes is believed to be strongly dependent on the presence of a mount of internal voids within the polyamide separation layer, which provides additional permeation channels in addition to diffusion through the polyamide matrix. Based on this understanding, herein, we reported a novel strategy of developing highly permeable RO membranes via introducing a void-tailoring agent, (3,3,3-trifluoropropyl)trichlorosilane (TFPTCS) into the traditional interfacial polymerization (IP) system composed of m-phenylenediamine and trimesoyl chloride. During IP process, the fast and violent hydrolysis and aminolysis of TFPTCS caused a significantly increasing pore size and porosity of the incipient polyamide film, which resulted in the formation of double- or multi-layer void structures with higher void fraction in the polyamide film. As a result, the TFPTCS added membrane showed a dramatic enhancement in water permeability, and the optimum condition was observed at the 0.03 wt% of TFPTCS concentration with 3.74 L m−2 h−1 bar−1, which was 2.8 times higher than that of the pristine membrane, while the salt rejection was almost unchanged (around 97.0%). These findings demonstrate the feasibility of void-tailoring inside the polyamide film, and encourage further exploration of new alternative void-tailoring agents to prepare highly permeable polyamide RO membranes for water desalination, which were seldom studied previously.