期刊
SEPARATION AND PURIFICATION TECHNOLOGY
卷 282, 期 -, 页码 -出版社
ELSEVIER
DOI: 10.1016/j.seppur.2021.120028
关键词
OSN; pH effect; COFs; ReaxFF
资金
- U.S. Department of Energy, Office of Basic Energy Sciences-BES [DE-SC0020100]
- University of Wyoming's School of Energy Resources Carbon Engineering Initiative
- University of Wyoming Office of Water Programs
- Multi-Scale Fluid-Solid In-teractions in Architected and Natural Materials (MUSE) , an Energy Frontier Research Center - U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy under the Basic En-ergy Sciences Program [DE-SC0019285]
- Center for Produced Water Management
- U.S. Department of Energy (DOE) [DE-SC0020100] Funding Source: U.S. Department of Energy (DOE)
The study investigates the effect of pH on organic solvent nanofiltration using a carboxylated COF membrane. pH changes were found to dramatically affect solvent permeance, solute rejection, solute solvation layer thicknesses, and C-COF pore charges, leading to significant changes in selectivity. This suggests that feed solution pH can be controlled to modify solvated solute radii and surface charge, thereby influencing the selectivity of COF membranes in OSN processes.
Covalent organic framework (COF) membranes for organic solvent nanofiltration (OSN) have attracted growing interest due to their high stability, well-defined pore size, and controllable pore functionality. In aqueous nanofiltration processes, solution pH has a significant effect on membrane permeability, selectivity, and fouling. However, our understanding of pH effects on OSN processes is still limited. Here, we present experimental and reactive force field molecular dynamics (ReaxFF MD) simulation results on the effect of pH on OSN using a well-characterized carboxylated COF (C-COF) membrane. Filtration experimental and modeling results both demonstrate that pH changes can affect solvent permeance and solute rejection dramatically. Specifically, methanol permeance decreases with the increase of NaOH and HCl concentration, respectively. When Alcian Blue dye was used as the solute in methanol, the selectivity increased from 23% to 98% when changing the feed pH from 2.2 to 10.1, respectively. While ReaxFF MD results show that C-COF solvated pore size is only marginally affected by the pH of solution, methanol diffusion is affected by the size of methanol-solvated Na+ and Cl- ions, which increase with increasing Na+ and Cl- concentrations. Solution pH change also affected solute solvation layer thicknesses and C-COF pore charges, contributing to the significant AB dye selectivity increase with pH increase. To summarize, we have shown that dramatic changes in C-COF selectivity are not anomalous in OSN, but are instead controllable by varying feed solution pH to modify solvated solute radii and surface charge.
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