A team of researchers from the Institute of Seawater Desalination and Multipurpose Utilization and the Shangdong University of Science and Technology have worked together to develop novel reverse osmosis (RO) membranes with improved perm-selectivity and anti-biofouling properties. These improvements have greatly enhanced the membrane’s performance and stability.
RO has attracted wide attention for its applicability in brackish water and seawater desalination. The leading type of membranes in this field are thin-film composite (TFC) polyamide (PA) RO membranes, which consist of a dense separating layer and a porous support layer. However, the relatively low permeability-selectivity of the PA membrane, paired with the membrane fouling of the TFC membrane, limit the applicability of this type of the TFC-PA RO membrane.
The team noticed that nanocomposite membranes can combine the advantages of polymers and inorganic nanomaterials — and, by fine-tuning the composition and structure, could improve the native performance of RO membranes.
The team tried dispersing hydrotalcite (HT) in an aqueous solution and incorporating it into a PA matrix. The obtained membrane showed high perm-selectivity with an increased water flux — and without sacrificing salt rejection. In addition, HT nanoparticles contain abundant hydroxyls, which can react with silane coupling agents. Because of this, the team were also able to graft anti-biofouling groups onto the membrane’s surface.
This study entitled “Preparation of reverse osmosis membrane with high permselectivity and anti-biofouling properties for desalination” is published online in Frontiers of Environmental Science & Engineering.
Specifically, in the study, the Mg-Al-CO3 HT nanoparticles were incorporated in PA layers during interfacial polymerization by dispersing in organic solutions. HT incorporation was performed with a dual role, enhancing water flux and acting as grafting sites. The HT incorporation increased the water flux without sacrificing the salt rejection, compensating for the loss caused by the following grafting reaction: The exposed surface of HT acted as grafting sites for anti-biofouling agent dimethyloctadecyl[3-(trimethoxysilyl)propyl] ammonium chloride (DMOT-PAC). The combination of HT incorporation and DMOTPAC grafting endowed RO membranes with high perm-selectivity and anti-biofouling properties.
The water flux was 16.4% higher than that of the pristine membrane. The salt rejection was 99.1%, which was comparable to that of the pristine membrane. As to 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% of PA-HT-0.06 compared to 78.2% of PA-pristine). The sterilization rate of PA-HT-0.06 for E. coli and B. subtilis were 97.3% and 98.7%.
The study is the first to report the formation of covalent bonds between DMOTPAC and HT nanoparticles embedded in a PA matrix to obtain RO membranes with both high perm-selectivity and anti-biofouling properties.
