Engineering metal-organic frameworks and their composite materials for separation applications
Open Access
- Author:
- Zha, Jie
- Graduate Program:
- Chemical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 23, 2020
- Committee Members:
- Xueyi Zhang, Dissertation Advisor/Co-Advisor
Xueyi Zhang, Committee Chair/Co-Chair
Andrew Zydney, Committee Member
Michael Anthony Hickner, Outside Member
Darrell Velegol, Committee Member
Phillip E Savage, Program Head/Chair - Keywords:
- separation
metal-organic frameworks
crystallization
gas adsorption
MOF membrane - Abstract:
- Separation processes play significant roles in both industry and daily life. Adsorption and membrane separations are desirable technologies for a variety of separation processes from aspects of moderate capital cost, high energy efficiency, and low environmental impacts. Metal-organic frameworks (MOFs), a type of crystalline porous material, exhibit great advantages in separations due to their tunable pore structure and versatile chemistry. However, because of the lack of understanding the relationship between MOFs’ structures and functions, MOF materials have not been fully utilized as they should. To improve the performance of MOFs in gas adsorption, two-dimensional MOFs with different functionalities were prepared through a simple room-temperature synthesis. According to the gas adsorption test, it was found that the surface functionality of 2D MOFs was more crucial for selective gas adsorption, while the surface area determined the gas uptake. The nitro-functionalized MOF nanosheets showed ideal selectivity of 91.5, 18.0, and 5.1 for CO2/N2, CO2/CH4, and CH4/N2 separations, respectively, which was among the highest comparing to previously studied MOFs. To apply MOFs in liquid adsorption involving large molecules, MOF nanosheets with open metal sites were synthesized on cellulose substrates. The obtained MOF composite adsorbents exhibited selective adsorption of dyes in organic solvent, which was attributed to the coordinate interaction between dye molecules and open metal sites in the frameworks. To achieve continuous separation processes, MOF membranes were fabricated by growing a MOF layer on porous polymeric supports. Polyethyleneamine crosslinked polydopamine coating was developed for polymer surface modification. The obtained ZIF-67@polyimide membranes exhibited methanol flux of 1.9 L∙m-2∙h-1∙bar-1 and methylene blue rejection over 99%, which was better than commercial membranes. The optimized synthetic procedures of 2D MOFs and MOF@polymer composites unveiled the key parameters in controlling the structure, morphology, and functionality of MOF materials to meet the demands in various separation processes, which is believed to guide the design and fabrication of high-performance MOF materials for broad applications.