Reverse osmosis (RO) technology has attracted a lot of attention due to its wide applicability for brackish and sea water desalination. Thin film composite (TFC) polyamide (PA) reverse osmosis membranes, consisting of a dense separation layer and a porous support layer, have been the leading products in this field. However, the low permeability of PA RO membranes and fouling of TFC reverse osmosis membranes limit the widespread use of PA RO TFC membranes. googletag.cmd.push(function() { googletag.display(‘div-gpt-ad-1449240174198-2′); });
The synthesis of nanocomposite membranes has proven to be an excellent method for combining the advantages of polymeric and inorganic nanomaterials. The natural characteristics of reverse osmosis membranes can be improved by fine tuning the composition and structure. For example, hydrotalcite (HT) was dispersed in an aqueous solution and included in the PA matrix at the stage of interfacial polymerization to create water transport channels.
The resulting membranes exhibit high permeability selectivity and increased water flow without sacrificing salt repellency. In addition, membrane modification, including nanoparticle incorporation, surface coating, and grafting, has been shown to be an effective approach to prevent biofouling. Among them, grafting anti-fouling agents onto nanoparticles embedded in the PA matrix is an excellent strategy to impart anti-fouling properties to reverse osmosis membranes without damaging the PA matrix.
The HT nanoparticles are rich in hydroxyl groups, which can react with the siloxy groups of silane coupling agents to achieve antifouling grafting. Therefore, a novel TFC reverse osmosis membrane with high selectivity and anti-fouling properties can be obtained by using HT nanoparticles as dopants in the PA layer and grafting anti-fouling functional group-containing silane coupling agents onto the membrane surface.
Prof. Wang Jian from the Institute of Desalination and Integrated Seawater Utilization, Prof. Ma Zhong from Shandong University of Science and Technology, Dr. Tian Xinxia from the Chinese Academy of Sciences, inspired by the characteristics of HT nanoparticles and silane coupling agents containing quaternary ammonium salts. , and members of their team together. Efforts have been made to develop a new type of reverse osmosis membrane with long-term stable high performance by simultaneously improving the original permeability selectivity and anti-fouling.
Their work significantly improved the performance of TFC PA reverse osmosis membranes and provided valuable technical advice for the future of seawater desalination. The study was published in the journal Frontiers of Environmental Science & Engineering.
In this study, Mg-Al-CO3 HT nanoparticles were incorporated into a PA layer by dispersion in an organic solution during interfacial polymerization. The inclusion of HT plays a dual role, enhancing water flow and serving as a grafting site. The inclusion of HT increased the water flow without sacrificing salt rejection, compensating for the losses caused by the subsequent grafting reaction. The exposed surface of the HT serves as a grafting site for the antifouling agent dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOT-PAC).
The combination of HT incorporation and DMOTPAC grafting endows reverse osmosis membranes with high permeability selectivity and anti-fouling properties. The water flow of PA-NT-0.06 was 49.8 l/m2·h, which is 16.4% higher than that of the original membrane. The degree of rejection of the PA-HT-0.06 salt was 99.1%, which is comparable to that of the original membrane. With respect to negatively charged lysozyme contamination, the aqueous flux recovery of the modified membrane was higher than that of the original membrane (eg, 86.8% for PA-HT-0.06 versus 78.2% for PA-original). The degree of bactericidal activity of PA-HT-0.06 against Escherichia coli and Bacillus subtilis was 97.3% and 98.7%, respectively.
This study is the first to report the formation of covalent bonds between DMOTPAC and HT nanoparticles embedded in PA matrices to produce reverse osmosis membranes with high permeability selectivity and anti-fouling properties. The incorporation of integrated nanoparticles and functional group grafting enable the development of reverse osmosis membranes with high permeability selectivity and anti-fouling properties.
Further information: Xinxia Tian et al., Preparation of a reverse osmosis membrane with high selectivity and anti-fouling properties for seawater desalination, Frontiers in Environmental Science and Engineering (2021). DOI: 10.1007/s11783-021-1497-0
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Post time: Jan-04-2023