Studying and developing the thin film membranes for reverse osmosis application
Authors:   , Kadhom Mohammed 
Published: April 2021

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Desalination by semi-permeable membranes is the most applicable method of water-salt separation, where reverse osmosis (RO) account for the major portion of the overall water production. The membrane is the most important part in the RO process, which controls the amount of produced water and rejected salt. This work aimed to study and develop the state of the art membrane for this operation, the thin film composite (TFC) membrane. In the beginning, we introduced 2,2,4-trimethylpentane (isooctane) as a TMC solvent and used it through all our projects. Isooctane was introduced because of its appropriate properties as the organic phase solvent and relatively low volatility. Porous MCM-41 silica NPs were filled inside the membrane by dispersing those in MPD aqueous solution or in TMC organic solution. The thin film nanocomposite (TFN) membranes made via loading the silica NPs in the MPD solution had a slightly better performance than the filling in the TMC solution. By optimizing conditions of membrane synthesis, we developed high performance TFC membranes with the best performance results comparable or better than what were reported in the literature. We studied the effect of MPD and TMC contact times, PSU support sheet preparation methods and thickness, and curing temperature. The study showed that at 25 s MPD contact time and short reaction time, around 5 s, the membrane performance was the best. PSU support layer, however, affected the TFC membrane filtration efficiency. Reports were limited on the impact of support sheet to the TFC performance for desalination; we therefore evaluated the effects of PSU sheets preparation methods and thickness. The effect of curing temperature was also examined, showing that if the membrane was dried at 110 [degrees]C, it gave better results than at 80 [degrees]C. Bentonite NPs were examined as fillers as well since the material has good thermal and mechanical properties and is abundant in nature, easily available from synthesis in the laboratory with low cost, and environmentally green. Loading this material into TFN membrane improved its properties and performance. The thickness of these particles (~1 nm) helped fitting them tightly inside the membrane structure. To understand how the impact occurred, we investigated the reaction solvents adsorption in the meso and microporous cavities inside the particles. Water uptake phenomenon in clays was comprehended as a part of water transfer process inside the membrane, its impact on the membrane structure was considered. Finally, we investigated the filling of metal-organic frameworks (MOFs) in the TFN membrane. MOFs are a class of materials that combine organic and inorganic materials in one structure with many unique properties. Among over 20000 types of MOFs, we selected UiO-66 and MIL-125 to investigate because of their hydrophilic nature, water and chemical stability, large surface area and pore size, and low cost when comparing with other MOFs. We found that filling MIL-125 in the membrane improved water flux more than the UiO-66 did, while in both cases the salt rejection was maintained or increased at some loadings when comparing with the pristine membrane.