Polymer Microfiltration and Ultrafiltration Membranes Containing Inorganic Modifiers: Functional Properties and Performance-Review.

Modifying MF and UF polymer membranes with hydrophilic compounds is one of the well-known antifouling strategies, which also allows one to achieve a compromise between fluid permeability and the retention of one or another species. Hydrophilizing inorganic substances are widely used for modifying due to their enhanced chemical stability and multifunctionality. In this review, the inorganic modifiers are categorized according to their effect on organic contaminants and bacteria: (i) non-destructive (natural and synthetic aluminosilicates, phosphates and oxides of multivalent elements, particularly magnetic nanoparticles), (ii) bacteria-destructing (silver nanoparticles, advanced carbon nanomaterials, MXenes), and (iii) strongly destructive, which disrupt both bacteria and organic substances (photocatalysts). The mechanism of antibacterial activity of different modifiers is considered. The main approaches to modifying are stressed: blending polymers with preliminarily formed nanoparticles followed by membrane formation, synthesis of them inside the pores of membranes or on their surface, embedding pre-formed particles into pores, or modifying the surface with them. A comparative analysis of the functional properties and performance of pure polymer membranes and materials containing inorganic modifiers has been conducted. The attention is focused on the ability of modified membranes based on various polymers to retain both macromolecular and low-molecular-weight substances together with high fluid permeability and stability against organic contaminants and biofouling. The limitations of materials containing various types of inorganic modifiers are analyzed. Among the possible directions of further investigations, the development of a universal theoretical approach to modifying is noted; moreover, the testing of the materials has to involve the treatment of real solutions.