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Advancement of carbon nanomembranes for filtration of aqueous solutions : doctoral dissertation
Ambrož, Ana, kemija
Membrane-based separation technologies play a critical role in water treatment, yet they remain constrained by fundamental trade-offs between permeability and selectivity, as well as performance ...losses during prolonged operation. To address these limitations, this dissertation investigates the potential of carbon nanomembranes (CNMs), ultrathin, two-dimensional carbon sheets with nanometer-scale thickness, as selective barriers with high water flux and controlled solute rejection. Two types of CNM-composite membranes are fabricated and examined: (i) transferred CNMs, where CNM layer is first fabricated on the initial substrate and then transferred onto ceramic or track-etched polyethylene terephthalate (TE-PET) supports, and (ii) transfer-free CNMs, where the selective CNM layer is directly fabricated on ion-irradiated PET, avoiding transfer-related defects and scalability limitations. The fabricated membranes are characterized for their surface morphology, stability, and filtration performance. Transferred CNMs reveal major adhesion challenges, particularly on rough ceramic supports, leading to delamination and ruptures that compromise membrane integrity. TE-PET provides a more compatible surface due to its smoother topography, yet stability during forward osmosis (FO) filtration remains problematic. Transfer-free CNMs, by contrast, exhibit better structural robustness and scalability, enabling systematic testing in both FO and low-pressure reverse osmosis (LPRO). Performance evaluation highlights the potential of CNMs as high-efficiency membranes. In FO, transfer-free CNM with low defect densities achieves water fluxes of 28 L/m2h, nearly double those of a commercial FO membrane, while maintaining minimal solute reverse flux (0.02 g/L). In LPRO, CNMs demonstrate stable nanofiltration-like rejection of ~50% of NaCl across multiple filtration cycles, comparable to commercial benchmarks. These findings confirm that molecularly thin CNMs can be tailored for high permeability and selectivity, addressing key limitations of conventional membranes. However, challenges remain with TE-PET supports. A gradual water flux decline is observed during extended aqueous filtration, primarily due to polymer swelling within pore walls. To mitigate swelling, surface functionalization with trimethylchlorosilane is explored, reducing hydrophilicity and improving flux stability. By demonstrating that ultrathin CNMs can achieve water permeabilities and selectivities comparable to or exceeding state-of-the-art membranes, while diagnosing and addressing critical fabrication and support-related challenges, this work advances CNMs one step closer toward practical application. With further optimization of support materials, fabrication methods, and surface modifications, CNM-composite membranes hold strong potential as next-generation solutions for water treatment and related separation technologies.
Type of material - dissertation
; adult, serious
Publication and manufacture - Maribor : [A. Ambrož], 2025
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