The present disclosure relates to a filtration membrane and a process for its preparation. The filtration membrane comprises at least one exfoliated clay intercalated with at least one external cation. The exfoliated clay is in the form of nano-sheets. The filtration membrane can be used for the purification of water contaminated with dye. The filtration membrane of the present disclosure demonstrated high water flux, and high dye/salt rejection. The process for the preparation of the filtration membrane of the present disclosure is cost-effective, easily scalable and simple.