Abstract: According to some aspects, a semi-permeable membrane is provided for performing separation processes as well as its method of manufacture. In some instances, a membrane may include a porous substrate, and an active layer disposed upon the substrate. The active layer may include at least one atomically thin layer having a plurality of open pores that allow transport of some species through the membrane while restricting transport of other species through the membrane. The open pores may have a mean pore size between 0.5 nm and 10 nm and a number density between 109 cm?2 and 1014 cm?2.