金属酸化物ナノシート膜の開発：水および有機溶剤中における分離性能

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(1)２Ｂ０１［Invited lecture］ Development of metal oxide nanosheet membranes: separation performance in water and organic solvent （Kobe University）○ Keizo NAKAGAWA 1. Introduction Membrane separation is an advanced technology for. water and organic solvents were investigated. The niobate. solving environmental and energy issues. Nanomaterials. to improve the membrane performances.. nanosheet-GO composite membranes were also fabricated. for membranes have been extensively studied to overcome the limitations of conventional polymeric or inorganic. 2. Laminar niobate nanosheet membrane. membrane materials. Two dimensional (2D) nanosheet. Niobate nanosheets were prepared by a bottom-up. membranes have opened up a new avenue for fabricating. approach. size-selective molecular separation membranes, benefiting. triethanolamine (TEOA) (Fig.2a) , and then, laminar. from their unique atomic thickness with micrometer. niobate nanosheet (NbO) membranes were assembled on. lateral dimensions. Laminar nanosheet membranes are. a cellulose nitrate (CN) support modified with. formed by assembling single molecular sheets into thin. 3-aminopropyl-triethoxysilane (APTES) by a simple. membranes, and contain 2D nanochannels between the. vacuum filtration (Fig.2b)3,4). The structural differences. stacked sheets that allow water to pass through whilst. between dry and wet conditions were investigated using. using. hydrothermal. synthesis. with. 2). rejecting unwanted solutes (Fig.1) . However, only a. XRD. Only a slight increase of the interlayer distance was. narrow range of nanosheet materials, such as graphene. observed in wet condition (Fig.2c). Thus the laminar NbO. oxide (GO) and transition metal dichalcogenides, have. membranes had a dense structure and were highly stable. been studied. Metal oxide nanosheets offer attractive. during separation tests. This is because TEOA molecule. surface and catalytic properties. Therefore, they represent. reacted with acid sites of niobate nanosheet5,6), resulting in. promising materials for potentially high-functional. the strong interactions between nanosheets. The simple. membranes for liquid separation.. method allowed the creation of nanochannels in the. 1). stacked NbO membranes, which were found to act as nanofiltration (NF) membranes with good rejection against organic dyes and salts3,4). Negative charges on niobate nanosheet affected the rejection performances. A water pathway model based on the void structure is. Water Solute. (b). (a). Surface of laminar nanosheet membrane. Nanosheet. (d). (c). Electrostatic interactions. Intensity/a.u.. Size exclusion. Ion adsorption. Fig. 1 Schematic image of water permeation and separation of solutes for laminar nanosheet membrane. nanosheet. membranes. using. 100 nm. Size‐selective nanochannel. Donnan exclusion Niobate Nanosheet. Dry: d = 1.0 nm. 2. 4. 6. 8 10 12 14 16 18 20 2θ/degree. Cl‐, SO42‐. (Negative charge). Support. Fig. 2 (a) STEM image of niobate nanosheets, inset: picture of niobate sheet colloidal suspension, (b) cross–section SEM image of NbO membrane, (c) XRD patterns of NbO membranes in dry and wet conditions, (d) Schematic image of water permeation and nanochannels in NbO membranes.. In this study, we fabricated laminar metal oxide-based. Wet: d = 1.1 nm. Polymer Support. niobate. nanosheets. The membrane structure and performances in. -36-.

(2) presented to explain the membrane performances (Fig.2d).. and organic solvents such as methanol, ethanol and hexane. These results suggest that the laminar NbO membrane was stable against such organic solvents. 3. Niobate nanosheet-based composite membranes Intercalation of nanomaterials between nanosheets is. without swelling. Furthermore, the NbO membranes. a promising strategy to control the channel structure in the. demonstrated relatively high rejection performances such. laminar membrane. NbO-GO nanosheet composite. as 85% rejection for Evans blue (EB, Mw: 960.8) in. membranes were fabricated using NbO and GO colloidal. methanol.. nanosheets by same vacuum filtration. The effects of the. membranes in organic solvents will be discussed.. The. separation. mechanism. for. NbO. composite ratio of NbO/GO and composite methods on their membrane performances were investigated. The water permeability of the NbO/GO composite membranes. 5. Conclusion In summary,. was drastically changed by the composite ratio. A. oxide-based nanosheet membranes by simple vacuum. composite membrane with weight ratio of NbO:GO =. filtration. The membranes retained structural stability in. 55:45 (NbO55/GO45) showed higher water permeability. water and organic solvents, and demonstrated superior. as compared with NbO membranes and GO membranes. rejection of organic dyes and salts, thus fulfilling. with similar rejection against salts . Thus the water. important criteria for water purification and organic. permeability of NbO membrane was apparently improved. solvent filtration. This approach is expected to be. by the addition of GO. The changes of nanochannel size. expandable to other transition metal oxide nanosheet. and surface charge affected their membrane performances.. membranes, which may open valuable perspectives for. 7). 20. Rej. of Na2SO4 2 4. fabricated. laminar. metal. wide applications of functional membranes such as. 100. Permeability. catalytic membrane reactor.. 80. 15. 60. 10. 40. 5. 20. 0. 0. Rejection [%]. Permeability [L m-2 h-1 bar-1]. 25. we. References 1) Liu, G., Jin, W., Xu, N., Chem. Soc. Rev., 44, (15), 5016 (2015). 2) Nakagawa, K., Jia, T., Zheng, W., Fairclough, S. M., Katoh, M., Sugiyama, S., Tsang, S. C. E., Chem. Commun., 50, (89), 13702 (2014). 3) Nakagawa, K., Yamashita, H., Saeki, D., Yoshioka, T., Shintani, T., Kamio, E., Kreissl, H. T., Tsang, S. C. E., Sugiyama, S., Matsuyama, H., Chem. Commun.,. Fig. 3 Water permeability and .rejection of Na2SO4 for the NbO-GO composite membranes.. 53, (56), 7929 (2017). 4) Nakagawa, K., Sera, T., Kunimatsu, M., Yamashita, H., Yoshioka, T., Shintani, T., Kamio, E., Tsang, S. C. E., Matsuyama, H., Sep. Purif. Technol. 219, 222. 4. Separation performance in organic solvents. (2019).. Solvent-related separations, such as purification of. 5) Kreissl, H. T., Nakagawa, K., Peng, Y.-K., Koito, Y.,. products from impurities, concentration of products and. Zheng, J., Tsang, S. C. E., J. Catal., 338, 329 (2016).. solvent recovery are critical issues in view point of. 6) Kreissl, H. T., Li, M. M. J., Peng, Y.-K., Nakagawa,. economic, operational and environmental considerations. Therefore,. membrane. structure. and. K., Hooper, T. J. N., Hanna, J. V., Shepherd, A., Wu,. separation. T.-S., Soo, Y.-L., Tsang, S. C. E., J. Am. Chem. Soc.,. performances in organic solvents have also been. 139, (36), 12670 (2017).. investigated. For NbO membrane, anodic aluminum oxide. 7) Kunimatsu, M., Nakagawa, K., Yoshioka, T., Shintani,. was used as a support. There was little difference in the. T., Yasui, T., Kamio, E., Tsang, S. C. E., Li, J.,. interlayer spacing of the laminar structure between water. Matsuyama, H., submitted.. -37-.

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