Porous nano-hydroxyapatites doped into substrate for thin film composite forward osmosis membrane to show high performan
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pISSN: 0256-1115 eISSN: 1975-7220
INVITED REVIEW PAPER
INVITED REVIEW PAPER
Porous nano-hydroxyapatites doped into substrate for thin film composite forward osmosis membrane to show high performance Weiwen Wang, Yue Guo, Miyu Liu, Xiaokun Song, and Jihai Duan† State Key Laboratory of Ecochemical Industry, School of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042 (Received 24 December 2019 • Resived 31 March 2020 • Accepted 4 April 2020) AbstractThe incorporation of inorganic nanoparticles into thin film composite forward osmosis (TFC FO) membranes is an effective method to alleviate internal concentration polarization (ICP) and enhance the flux performance of the FO membrane. In this paper, synthetic hydrophilic rod-like porous nano-hydroxyapatites (PNHAs) were doped into polysulfone (PSf) casting solution to form support layer by phase inversion; further interfacial polymerization was carried out to prepare a high performance TFC FO membrane. The results showed that the incorporation of PNHAs not only improved the thickness, porosity, hydrophilicity, and connectivity of the support layer, but also enhanced the roughness of the active layer. The measured mass transfer parameters prove that these improvements were beneficial. Further FO experiments showed that when using deionized water as the feed solution and 1 mol/L NaCl as the draw solution, TFN 0.75 showed higher water flux than TFC FO membrane in both AL-FS (18.5 vs 7.16 L/m2 ·h) and AL-DS (33.26 vs 9.93 L/m2 ·h) modes. Reverse salt flux had not increased significantly. At the same time, TFN 0.75 (697 m vs 1,960 m) showed the smallest structural parameter. This study shows that PNHA is a suitable nanomaterial for mitigating the ICP effect of FO membranes. Keywords: Forward Osmosis, Nano-hydroxyapatites, Thin Film Nanocomposite Membrane, Desalination, Internal Concentration Polarization
separation of FS with high fouling potential and high salinity [8-10]. However, before practical application in water treatment, the further development and commercialization of FO technology is hampered by the lack of efficient and stable FO membranes. The common FO membrane is thin film composite (TFC) FO membrane composed of a supporting layer (otherwise known as the substrate) and an active layer (AL) [11]. In this paper we decided to optimize the substrate. The ideal TFC FO membrane substrate has the following characteristics: (1) thin, porous, and low pore tortuosity [12]. Internal concentration polarization (ICP), which occurs inside the substrate, is caused by the change of solute concentration in the boundary layer in the substrate. ICP is the key factor limiting the flux of FO membrane, making the water flux much lower than the theoretical value [13]. The structural parameter (S) is used to measure ICP (equivalent to thickness×tortuosity/porosity). The thinner the substrate, the lower the tortuosity; the higher the porosity, the smaller the ICP effect is [14]. (2) Hydrophilicity. The hydrophilicity of the substrate is strongly
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