Document Type
Thesis - Open Access
Award Date
2026
Degree Name
Master of Science (MS)
Department / School
Civil and Environmental Engineering
First Advisor
Guanghui Hua
Abstract
he increasing concentration of atmospheric carbon dioxide has intensified the demand for efficient, scalable, and energy-efficient separation technologies capable of supporting carbon capture and environmental remediation. Membrane-based gas separation has emerged as a promising alternative to conventional absorption and adsorption processes due to its low energy consumption, modularity, and operational simplicity. However, conventional polymeric membranes are inherently constrained by the permeability– selectivity trade-off, limiting their practical performance. This thesis addresses these challenges through the development of multifunctional mixed-matrix membranes (MMMs) based on Pebax® 1657 incorporated with amino-functionalized metal–organic cages (MOC–NH₂), designed to enhance facilitated CO₂ transport while enabling colorimetric sensing functionality. A systematic series of Pebax–MOC membranes containing 2–10 wt% MOC–NH₂ was fabricated via solution casting and thoroughly characterized to establish structure– property–performance relationships. Structural and chemical analyses using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed the successful synthesis of MOC–NH₂ and its stable incorporation into the Pebax matrix without disruption of the polymer backbone or cage framework. Scanning electron microscopy revealed uniform dispersion of MOC fillers at low to moderate loadings, while higher concentrations led to partial aggregation, influencing gas-transport behavior. Thermal analysis demonstrated that the incorporation of MOC–NH₂ improved membrane stability and resistance to CO₂-induced plasticization. Gas permeation experiments were conducted using single-gas and mixed-gas CO₂/N₂ systems under varying pressure and temperature conditions. The results show that membranes containing low MOC loadings exhibited significant enhancements in CO₂ permeability and CO₂/N₂ selectivity compared to neat Pebax membranes. An optimal membrane composition achieved CO₂ permeability approaching 200 Barrer with CO₂/N₂ selectivity exceeding 85 at 25 °C and moderate pressures, surpassing the 2019 Robeson upper bound. Variable-pressure and variable-temperature analyses indicated that facilitated transport dominates under moderate operating conditions, driven by reversible interactions between CO₂ molecules and amine-functionalized cage sites. Time-lag diffusion analysis further confirmed increased CO₂ diffusivity and solubility, validating the proposed hybrid transport mechanism. Beyond gas separation, the multifunctional potential of MOC–NH₂ was demonstrated through colorimetric CO₂ sensing experiments. Reversible optical responses were observed during cyclic exposure to low concentrations of CO₂, attributed to acid–base interactions between CO₂, the amine-functionalized cage, and the indicator system. Importantly, structural characterization before and after gas exposure confirmed the chemical and structural stability of the MOC framework during sensing cycles. Overall, this work demonstrates that Pebax–MOC membranes effectively overcome traditional performance limitations while introducing integrated sensing capabilities. The findings highlight the promise of metal–organic cages as versatile fillers for next generation multifunctional membranes, offering significant potential for sustainable carbon capture, environmental monitoring, and advanced separation technologies.
Publisher
South Dakota State University
Recommended Citation
Hassan, Shabi Ul, "Facilitated Transport And Multifunctional Separation In Pebax–MOC Membranes For Sustainable Carbon Capture" (2026). Electronic Theses and Dissertations. 2047.
https://openprairie.sdstate.edu/etd2/2047
Rights Statement
