Cation-Intercalated Clay-Based Two-Dimensional Membranes for Effective Desalination and Molecule Sieving

Montmorillonite (MMT) is known as an ion-exchangeable material, and cations between MMT nanosheets are easily exchanged by other cations. In this work, Ca²⁺, Fe³⁺, and Al³⁺ intercalated two-dimensional MMT membranes were developed by ion exchange of pristine MMT membranes (Na⁺-MMT), and their ion and dye removal abilities were investigated. The d-spacings of hydrated Fe³⁺ intercalated MMT membrane (Fe³⁺-MMT) and Al³⁺ intercalated MMT membrane (Al³⁺-MMT) were decreased compared with hydrated Na⁺-MMT membrane due to the stronger electrostatic attraction between Fe³⁺/Al³⁺ and negatively charged MMT nanosheets. Ion and dye sieving performances were improved significantly after the intercalation of Ca²⁺, Fe³⁺, and Al³⁺ into MMT membranes. Al³⁺-MMT membrane with a thickness of 1.17 μm could exclude 94% of Na⁺, and its ion sieving performance remained stable during a 120-h ion sieving experiment. Moreover, the rejection rate for rhodamine B (RB) reached 94% using an Al³⁺-MMT membrane with a thickness of 500 nm, and a water permeance of 73 L m^-2 h^-1 bar^-1 was achieved. The excellent ion and dye sieving performances make it promising in the application of desalination and nanofiltration.