Inspired by the preparation process of soybean skin, a traditional Chinese food, the SIEPM group of Zhejiang University developed a new method for the preparation of thin layer composite nanofiltration membrane assisted by gas-liquid interface. Its characteristic is that the selective cortex is assembled at the gas-liquid interface driven by interfacial tension, so it is almost not affected by the base membrane, thus greatly improving the controllability of the preparation process of composite nanofiltration membrane. Taking polyphenols/polyamines as an example, they are oxidized and self-polymerized in air to form amphiphilic surfactant like nanoparticles. In order to reduce the overall energy, the nanoparticles spontaneously assemble at the gas-liquid interface to form self-supporting films. The self-supporting film is characterized by an asymmetrical, wetting and dihedral structure (or dihedral structure), that is, hydrophobic to air and hydrophilic to aqueous solution. Based on this structure, a hydrophobic porous supporting membrane is only needed to float on the surface of polyphenols/polyamines solution, and the self-supporting membrane assembled and formed under the hydrophobic force can be synchronously composite to the surface of the supporting membrane, realizing the preparation of thin layer composite nanofiltration membrane in a one-step method without transfer.

Fig. 1 Formation process and morphology of thin layer composite nanofiltration membrane at gas-liquid interface

The gas-liquid interface assisted membrane formation method developed by SIEPM realizes the effective control of parameters such as selective layer thickness, membrane formation time and surface charge of nanofiltration membrane, and also greatly simplifies the preparation process, providing a new way for simple and controllable design and preparation of a new generation of high-performance nanofiltration membrane.

Fig. 2 Lysozyme thin layer composite membrane for organic nanofiltration