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Global energy supply is currently dominated by fossil fuel combustion. One of the emerging technologies that aims to minimize the overall emissions is Pressure Retarded Osmosis (PRO), which consists of harvesting the Gibbs energy resulting from mixing fresh and salt water and converting it into power. A membrane that is able to deliver high water permeability and good salt rejection, as well as to operate in the saturated salt gradient - which leads to 200 bars of pressure-, is required. The commercially available RO membranes that have a potential utility in a PRO system exhibit high salt rejection rate but low water permeability and mechanical stability. Since commercial Reverse Osmosis (RO) membranes available in the market can only handle a maximum of 100 bars, membrane modification is a promising option for enhancing the resistance to pressure of such PRO membranes. Membrane modification with hydrophilic materials (e.g. polydopamine – PDA) and mesoporous materials (e.g. zeolites) can increase the filtration performance of the membranes and the additional modification, which increases the thickness of the membrane can be beneficial in reinforcing the membrane. PDA is one of the most popular membrane modifiers that does not only provide increased hydrophilicity but also facilitates the binding of other compounds to its surface. Zeolites, composed of microporous, crystalline aluminosilicate particles, are also promising materials for this purpose. They consist of high porosity and hydrophilic 3D structures, which confer an extremely high mechanical stability. Graphene Oxide (GO) made of carbon, oxygen and hydrogen, also possesses increased hydrophilicity, excellent high surface-area-to-volume ratio and unprecedented elevated mechanical stability.

In this work, we carried out the modification of commercial thin film composite (TFC) RO membranes with different modifiers. The mechanical stability of the membranes was tested in terms of tensile strength and elongation. Here, we modified the commercial RO membrane with PDA and zeolites (ZSM-5) and observed improved filtration performance of the membrane (increased water permeability and maintained salt permeability). The tensile tests showed enhanced reinforcement of the modified membranes. Interestingly, a lower concentration of PDA and zeolites gave a higher mechanical strength of the modified membranes. Such results were likely due to a more homogenous coating layer when a low modifier concentration was applied. The thin and uniform layer can better absorb energy when the membranes were under high pressure. To our knowledge, this is the first time that zeolites are used for the PRO application.

On the other hand, PRO membrane system was carried out where we combined physical adsorption of polyelectrolyte (PE) and graphene oxide (GO) layer-by-layer (LbL) assembly system. The hybrid LbL structure is proposed as a strategy to simultaneously increase hydrophilicity and power density in PRO approach. Tailoring membrane surface chemistry allowed to increase PRO membrane performance without compromising its mechanical properties.

It was observed, that after selected modifications, water permeability increased and salt rejection did not change in comparison to the pristine membrane. In addition, the membranes gained high level of mechanical stability even at low concentration of modifiers.