A review on two-dimensional metal oxide and metal hydroxide nanosheets for modification of polymeric membranes

Recently, ultrathin two-dimensional (2D) materials, known as nanosheets, have attracted great interest owning to their ultimate structural and desirable physical, chemical, thermal, electrical, and optical characteristics. Various potential applications of 2D nanomaterials have been reported in electronics/optoelectronics, electrocatalysis, batteries, supercapacitors, solar cells, sensors, photocatalysis, and other environmental processes. Modification of polymeric membranes using nanosheets is increasingly reported in the literature. The incorporation of inorganic nanostructured additives, such as metal oxide and metal hydroxide nanosheets, can impart desired characteristics to the surface and matrix of the membrane and improves its filtration performance. This review summarizes the preparation methods of the metal oxide and metal hydroxide nanosheets, with a special emphasis on the recent advances in this field. The structural and physicochemical properties of the 2D nanosheets have been discussed, and after that, the applications of these nanosheets for modification of polymeric membranes are presented with a focus on the membranes used for environmental applications. Finally, the existing challenges and future perspectives for synthesis and membrane-related applications of 2D metal oxide and metal hydroxide nanosheets are discussed.