論 文
題 目の要

旨Development of Highly Water Permeable Robust PSQ-RO Membranes for Water Separation（高透水性有機シリカ逆浸透水分離膜の開発）
氏 名張 典The development of high-efficiency, low-cost seawater desalination technology is highly desired toresolve the problem of water scarcity. Water desalination by reverse osmosis (RO) membranes has been
extensively studied and many types of membranes have been reported so far, including conventional
polyamide membranes. Polyamide-based RO membranes are widely used in industry because of their
excellent water permeability and high salt rejection. However, polyamide-RO membranes still have someproblems including low resistance to chlorine and to high-temperature operation.
Organically bridged polysilsesquioxanes (PSQs) that can be easily prepared via thehydrolysis/condensation reaction (sol-gel (SG) process) of bridged alkoxysilanes have attracted muchattention as robust organic-inorganic hybrid materials due to their three-dimensional thermally stable but
flexible siloxane (Si-O-Si)-based frameworks. Organically bridged PSQs can be used as RO membranematerials with high stability to heat and chlorine treatment. In the previous work, it was demonstrated
that organically bridged PSQ-RO membranes derived from the SG process using precursors such asbis(triethoxysilyl)ethane (BTESE) and bis(triethoxysilylpropyl)amine (BTESPA) exhibited excellent salt
rejection, favorable thermal stability, and high chlorine resistance. However, these membranes present
insufficient water permeability on the order of 10-13 m3/m2sPa, which is more than 10 times lower thanthat of commercial polyamide-based RO membranes. Therefore, it is necessary to develop strategies toimprove the water permeability of PSQ-RO membranes. In this work, four new strategies to improve thewater permeability of PSQ-RO membranes were studied.
In Chapter 1, the author optimized the bridging structures of alkoxysilane monomers in themembranes. According to the previous work in the literature, rigid and polar organic bridging structures
tend to increase water permeability. For example, membranes derived from bis(triethoxysilyl)ethene(BTESE2) and bis(triethoxysilyl)ethyne (BTESE3) exhibit higher water permeability than BTESE-basedmembranes.

Inthepresentwork

precursors

withthreereactiveethoxysilyl

units:

tris[(triethoxysilyl)propyl]amine (TTESPA), tris[(diethoxymethylsilyl)propyl]amine (TDEMSPA), andtris[(triethoxysilyl)methyl]amine (TTESMA) were prepared, as shown in Figure 1. It was anticipatedthat these precursors with three reactive ethoxysilyl
units would form dense RO membranes, thereby
improving RO performance. In addition, the author
preparedtris[(triethoxysilyl)propenyl]amine(TTESP2A) and tris[3-triethoxysilyl)prop-2-ynyl]amine (TTESP3A) as the precursors, in which rigid
and polar ethenylene and ethynylene linkages wereFigure 1. Organically bridged precursors for RO membrane preparation.

expected to improve RO performance of theresultant membranes.
In Chapter 2, hydroxyl groups were successfully introduced into PSQ-RO membranes bycopolymerizing BTESPA with triethoxy(3-glycidyloxypropyl)silane (TEGPS). It was demonstrated thatepoxy groups in TEGPS underwent a ring-opening reaction by the nucleophilic attack of the amine unitof BTESPA to form hydroxy (C-OH) groups, which significantly improved the water permeability. The
RO experiments by using a 2000 ppm NaCl aqueous solution clearly indicated that the use of epoxycontaining monomer TEGPS
significantlyimproved

ROperformance, yielding waterpermeability of 1 × 10-12m3/m2sPa and salt rejection of98 %, approximately.
In Chapter 3, the author copolymerized BTESPA with N-(2OHhydroxyethyl)-N′-[3-(triethoxysilyl)propyl]urea (HETESPU). TheOHHNHNO

HN

RO experiments of the copolymer membranes indicated that thewater permeability was extremely improved approximately 19 times
comparing to BTESPA homopolymer based membrane (1.86 × 10-12AFM100 nmOOHNSiOOOSiOOFigure 3. AFM image and the hydrophilic water
channels formed by the aggregation throughhydrogen bonding.

m3/m2sPa), with salt rejection remaining nearly unchanged (96%).
This is the highest water permeability so far obtained for PSQ membranes that show salt rejection higher
than 90%. The extreme improvement of water permeability is likely due to the aggregation ofhydroxyethylurea units through hydrogen bonding in the PSQ layer to form hydrophilic water channels.

In Chapter 4, mixed matrix membranes (MMMs) were prepared by the introduction of SiO2
nanoparticles into the PSQ membranes. It was exhibited that the introduction of SiO2 nanoparticles
provided increased surface area and micropores in the PSQ membranes by the filler effects, thus
enhancing the porosity andwater permeability. It wasalso demonstrated that thethermalstability

andchlorine resistance of SiO2

Figure 4. Preparation of PSQ-RO membranes modified by SiO2 nanoparticles

nanoparticle-composite
membranes were also improved, which was probably due to the robust and rigid inorganic SiO2
nanoparticles that stabilized the organically bridged PSQ structure by immobilization.