Reverse osmosis (RO) has attracted a great deal of attention for its wide applicability in desalination of brackish water and seawater. Thin film composite (TFC) polyamide (PA) RO membranes consisting of a dense separation layer and a porous support layer have been the leading products in 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 adjusting the composition and structure. For example, hydrotalcite (HT) was dispersed in an aqueous solution and incorporated into the PA matrix in the interfacial polymerization step to build transport channels for water.
The obtained membrane exhibited high permeability selectivity with higher water flux without sacrificing salt rejection. In addition, membrane modification (including nanoparticle incorporation, surface coating, and grafting) has been shown to be an effective method of preventing biofouling. Among them, the grafting of antifouling agents onto nanoparticles embedded in the PA matrix could be an excellent strategy to provide reverse osmosis membranes with antifouling properties without damaging the PA matrix.
HT nanoparticles contain abundant hydroxyls, which can react with the siloxy of silane coupling agents, allowing antifouling grafting. Consequently, novel TFC RO membranes with high permeability selectivity and biological antifouling property can be obtained by employing HT nanoparticles as dopants in the PA layers and grafting silane coupling agents containing antifouling functional groups on the membrane surface.
Inspired by the properties of HT nanoparticles and quaternary ammonium-containing silane coupling agents, Prof. Jian Wang of the Institute of Seawater Desalination and Multipurpose Utilization, Prof. Zhun Ma of the University of Science and Technology of Shangdong, Dr. Xinxia Tian of the Institute of Seawater Multipurpose Utilization and Desalination and his team members have worked together and developed new reverse osmosis membranes with long and stable high performance by improving the original property of permeability and biological antifouling simultaneously.
Their work greatly 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, the Mg-Al-CO3 HT nanoparticles were incorporated into PA layers during interfacial polymerization by dispersing in organic solutions. The incorporation of HT was carried out with a double role, enhancing the flow of water and acting as graft sites. The incorporation of HT increased the water flux without sacrificing salt rejection, compensating for the loss caused by the following grafting reaction. The exposed surface of HT acted as a grafting site for the antifouling agent dimethyloctadecyl.[3-(trimethoxysilyl)propyl] ammonium chloride (DMOT-PAC).
The combination of HT incorporation and DMOTPAC grafting provided reverse osmosis membranes with high permeability and antifouling properties. The water flow of PA-HT-0.06 was 49.8 L/mtwo•h, which was 16.4% higher than that of the pristine membrane. The salt rejection of PA-HT-0.06 was 99.1%, comparable to that of the pristine membrane. Regarding the fouling of negatively charged lysozyme, the water flux recovery of the modified membrane was higher than that of the pristine membrane (e.g., 86.8% PA-HT-0.06 compared to 78). .2% PA-pristine). 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 embedded in a PA matrix to obtain reverse osmosis membranes with high permeability selectivity and antibiofouling properties. The incorporation of integrating nanoparticles and the grafting of functional groups promise the development of reverse osmosis membranes with high permeability and antifouling properties.
Scientists cut their teeth with new separation technology
Xinxia Tian et al, Preparation of reverse osmosis membrane with high permselectivity and antifouling properties for desalination, Frontiers of environmental science and engineering (2021). DOI: 10.1007/s11783-021-1497-0
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Citation: New Technology to Enhance High Permselectivity and Antifouling Properties of Reverse Osmosis Membranes (Aug 31, 2022) Accessed Aug 31, 2022 at https://phys.org/news/2022-08-technology-high -permselectivity-anti-biofouling -properties.html
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