The present invention provides a semipermeable membrane having enhanced alkaline stability and a method of forming a semipermeable membrane having enhanced alkaline stability, comprising steps of: providing an ultrafiltration (UF) base membrane, immersing said UF membrane in a solution comprising at least one substance selected from the group consisting of a polymer preferably polyethylenimine (PEI), a condensate solution and a mixture thereof, thereby forming reactive moieties upon said UF membrane, and forming at least one first layer upon at least portion of said UF base support membrane by immersing said UF base support membrane of step (b) in a solution comprising at least one ingredient selected from the group consisting of polymer preferably polyethylenimine (PEI), condensate solution and a mixture thereof thereby forming a cross-linked skin on the surface of said base membrane.

The present invention provides a separation functional layer that exhibits suppressed leakage of an ionic liquid and has an enhanced strength. A separation functional layer of the present invention includes: an ionic liquid; a polymer A that forms a crystal structure in the ionic liquid; and a polymer B different from the polymer A. A separation membrane of the present invention includes: the separation functional layer; and a porous support member supporting the separation functional layer.

An object is to realize a novel reverse osmosis membrane (more specifically, reverse osmosis composite membrane) that is capable of suppressing biofouling. The object is attained with use of a reverse osmosis composite membrane which is obtained by chemically modifying a surface thereof with a compound that has an amino group and that is obtained by modifying the amino group with two molecules of -picolyl group and has a dipicolylamine structure.