▎ 摘　　要

NOVELTY - Composite film comprises supporting layer (2) and a functional layer located on the surface of the supporting layer. The functional layer comprises a seed layer and a metal-organic framework layer (1) located on the surface of the seed layer. The seed layer is directly contact with the support layer. The seed layer comprises a graphene oxide layer structure and the metal-organic framework of material in-situ growing in the graphene oxide layer structure. USE - The composite film is used for selectively separating cation in water environment (claimed). ADVANTAGE - The composite film effectively applied to the separation and recovery process of the resource in the salt lake and lithium water body. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for preparing composite film. DESCRIPTION OF DRAWING(S) - The drawing shows a top view of composite film for selectively separating cation in water environment. 1Metal-organic framework layer 2Supporting layer