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Cunha J, da Silva MP, Beira MJ, Corvo MC, Almeida PL, Sebastião PJ, Figueirinhas JL, de Pinho MN. Water Molecular Dynamics in the Porous Structures of Ultrafiltration/Nanofiltration Asymmetric Cellulose Acetate-Silica Membranes. MEMBRANES 2022; 12:1122. [PMID: 36363677 PMCID: PMC9693417 DOI: 10.3390/membranes12111122] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Revised: 10/26/2022] [Accepted: 11/01/2022] [Indexed: 06/16/2023]
Abstract
This study presents the characterization of water dynamics in cellulose acetate-silica asymmetric membranes with very different pore structures that are associated with a wide range of selective transport properties of ultrafiltration (UF) and nanofiltration (NF). By combining 1H NMR spectroscopy, diffusometry and relaxometry and considering that the spin-lattice relaxation rate of the studied systems is mainly determined by translational diffusion, individual rotations and rotations mediated by translational displacements, it was possible to assess the influence of the porous matrix's confinement on the degree of water ordering and dynamics and to correlate this with UF/NF permeation characteristics. In fact, the less permeable membranes, CA/SiO2-22, characterized by smaller pores induce significant orientational order to the water molecules close to/interacting with the membrane matrix's interface. Conversely, the model fitting analysis of the relaxometry results obtained for the more permeable sets of membranes, CA/SiO2-30 and CA/SiO2-34, did not evidence surface-induced orientational order, which might be explained by the reduced surface-to-volume ratio of the pores and consequent loss of sensitivity to the signal of surface-bound water. Comparing the findings with those of previous studies, it is clear that the fraction of more confined water molecules in the CA/SiO2-22-G20, CA/SiO2-30-G20 and CA/SiO2-34-G20 membranes of 0.83, 0.24 and 0.35, respectively, is in agreement with the obtained diffusion coefficients as well as with the pore sizes and hydraulic permeabilities of 3.5, 38 and 81 kg h-1 m-2 bar-1, respectively, reported in the literature. It was also possible to conclude that the post-treatment of the membranes with Triton X-100 surfactants produced no significant structural changes but increased the hydrophobic character of the surface, leading to higher diffusion coefficients, especially for systems associated with average smaller pore dimensions. Altogether, these findings evidence the potential of combining complementary NMR techniques to indirectly study hydrated asymmetric porous media, assess the influence of drying post-treatments on hybrid CA/SiO2 membrane' surface characteristics and discriminate between ultra- and nano-filtration membrane systems.
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Affiliation(s)
- João Cunha
- Center of Physics and Engineering of Advanced Materials (CeFEMA), Laboratory for Physics of Materials and Emerging Technologies (LaPMET), Instituto Superior Técnico (IST), Universidade de Lisboa (ULisboa), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
- Department of Physics (DF), Instituto Superior Técnico (IST), Universidade de Lisboa (ULisboa), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
| | - Miguel P. da Silva
- Center of Physics and Engineering of Advanced Materials (CeFEMA), Laboratory for Physics of Materials and Emerging Technologies (LaPMET), Instituto Superior Técnico (IST), Universidade de Lisboa (ULisboa), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
- Department of Chemical Engineering (DEQ), Instituto Superior Técnico (IST), Universidade de Lisboa (ULisboa), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
| | - Maria J. Beira
- Center of Physics and Engineering of Advanced Materials (CeFEMA), Laboratory for Physics of Materials and Emerging Technologies (LaPMET), Instituto Superior Técnico (IST), Universidade de Lisboa (ULisboa), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
- Department of Physics (DF), Instituto Superior Técnico (IST), Universidade de Lisboa (ULisboa), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
| | - Marta C. Corvo
- Centro de Investigação em Materiais (CENIMAT), Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal
| | - Pedro L. Almeida
- Centro de Investigação em Materiais (CENIMAT), Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal
- Department of Physics, ISEL, R. Conselheiro Emídio Navarro 1, 1959-007 Lisboa, Portugal
| | - Pedro J. Sebastião
- Center of Physics and Engineering of Advanced Materials (CeFEMA), Laboratory for Physics of Materials and Emerging Technologies (LaPMET), Instituto Superior Técnico (IST), Universidade de Lisboa (ULisboa), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
- Department of Physics (DF), Instituto Superior Técnico (IST), Universidade de Lisboa (ULisboa), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
| | - João L. Figueirinhas
- Center of Physics and Engineering of Advanced Materials (CeFEMA), Laboratory for Physics of Materials and Emerging Technologies (LaPMET), Instituto Superior Técnico (IST), Universidade de Lisboa (ULisboa), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
- Department of Physics (DF), Instituto Superior Técnico (IST), Universidade de Lisboa (ULisboa), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
| | - Maria Norberta de Pinho
- Center of Physics and Engineering of Advanced Materials (CeFEMA), Laboratory for Physics of Materials and Emerging Technologies (LaPMET), Instituto Superior Técnico (IST), Universidade de Lisboa (ULisboa), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
- Department of Chemical Engineering (DEQ), Instituto Superior Técnico (IST), Universidade de Lisboa (ULisboa), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
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