Desalination has taken off in the 1970s, and three hundred million people now get their fresh water from the seawater. The first and most common desalination method is distillation that needs a lot of energy consumption. Therefore, there have been many industrial and academic attempts to develop alternative desalination methods that require less energy consumption such as reverse osmosis, forward osmosis, or pumping with biomimetic membranes. Among them, forward osmosis has drawn a great attention because of its lower energy costs and reduced membrane fouling. Forward osmosis method extracts fresh water from salt water through the membrane into a solution that contains draw solute (inorganic salts, organic ionic salts, or polyelectrolytes), and the draw solute is designed to be easily removable. In contrast to normal osmosis where water molecules pass through a semipermeable membrane into a solution with higher concentration (Figure 1 A), draw molecules are added to the feed water and induce higher salt concentration for desalination of sea water. Therefore, water molecules migrate by natural osmosis, without energy input, into an even more concentrated draw solution from seawater (Figure 1 (B)). However, the atomistic detail of forward osmosis is not known, and this has proven to be a hindrance in understanding how desalination is obtained and in designing new draw solute molecules. In this study, we performed molecular dynamics simulations of the desalination by forward osmosis. We model the draw molecules and membranes at the atomistic level, and examine their role of desalination. We simulated the forward osmosis system composed of NH<sub>3</sub>/CO<sub>2</sub> gas (draw molecules) and graphene sheet or boron nitride sheet membrane. We measured the flux of water by varying the environmental parameters such as concentration of the draw molecule and the radius of the hole of membrane.

Computer simulations of forward osmosis for desalination

249th National Meeting (2015)

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