New technology to improve high permselectivity and anti-biofouling properties of RO membranes

Reverse Osmosis (RO) has attracted wide attention for its wide applicability in the desalination of brackish water and seawater. Polyamide (PA) Thin Film Composite (TFC) Reverse Osmosis Membranes consisting of a dense separation layer and a porous support layer have been the flagship products of this field. However, the relatively low permeability-selectivity of the PA RO membrane and the fouling of the TFC RO membrane limit the widespread applicability of TFC PA RO membranes.

The synthesis of nanocomposite membranes has proven to be an excellent technology to combine the advantages of polymers and inorganic nanomaterials. The native performance of the RO membrane could be improved by refining the composition and structure. For example, hydrotalcite (HT) has been dispersed in an aqueous solution and incorporated into the PA matrix in the interfacial polymerization step to build transport channels for water.

The resulting membrane exhibited high perm-selectivity with increased water flux without sacrificing salt rejection. Additionally, membrane modification (including nanoparticle incorporation, surface coating, and grafting) has proven to be an effective approach to prevent biofouling. Among them, the grafting of anti-biofouling agents onto nanoparticles embedded in the PA matrix could be an excellent strategy to endow RO membranes with anti-biofouling properties without damaging the PA matrix.

HT nanoparticles contain abundant hydroxyls, which can react with the siloxy of silane coupling agents, allowing anti-biofouling grafting. Therefore, new TFC RO membranes with high perm selectivity and anti-biofouling property can be obtained by using HT nanoparticles as dopants in PA layers and by grafting silane coupling agents containing anti-biofouling functional groups onto the surface. of the diaphragm.

Inspired by the properties of HT nanoparticles and silane coupling agents containing quaternary ammonium, Professor Jian Wang from the Institute of Seawater Desalination and Multipurpose Use, Professor Zhun Ma from the University of Science and Technology of Shangdong, Dr. Xinxia Tian of The Institute of Seawater Desalination and Multipurpose Utilization and their team members worked together and developed new RO membranes with prolonged and stable high performance simultaneously improving permanent selectivity and anti-biofouling property.

Their work significantly improves the performance of TFC PA RO membranes, providing valuable technical guidance for desalination in the future. This study is published in Frontiers of environmental science and engineering.

In this study, Mg-Al-CO₃ HT nanoparticles were incorporated into PA layers during interfacial dispersion polymerization in organic solutions. The HT incorporation was performed with a dual role, enhancing water flow and acting as grafting sites. The incorporation of HT increased water flux without sacrificing salt rejection, compensating for the loss caused by the subsequent grafting reaction. The exposed surface of HT acted as graft sites for the anti-biofouling agent dimethyloctadecyl[3-(trimethoxysilyl)propyl] ammonium chloride (DMOT-PAC).

The combination of HT incorporation and DMOTPAC grafting has endowed reverse osmosis membranes with high perm selectivity and anti-biofouling properties. The water flow of PA-HT-0.06 was 49.8 L/m²•h, 16.4% higher than that of the virgin membrane. The salt rejection of PA-HT-0.06 was 99.1%, which was comparable to that of the virgin membrane. With respect to negatively charged lysozyme fouling, the water flux recovery of the modified membrane was higher than that of the virgin membrane (e.g., 86.8% PA-HT-0.06 versus 78. 2% PA-pristin). The sterilization rate of PA-HT-0.06 for E. coli and B. subtilis was 97.3% and 98.7%.

This study is the first to report the formation of covalent bonds between DMOTPAC and HT nanoparticles incorporated into the PA matrix to obtain RO membranes with both high perm selectivity and anti-biofouling properties. The incorporation of integrating nanoparticles and the grafting of functional groups promise the development of RO membranes with high permselectivity and anti-biofouling properties.

Provided by Higher Education Press