Systematic Optimization of Selected Hybrid Graphene Oxide (GO)/Metal-Organic Frameworks (MOFs) for CO2 Capture by a Combined Molecular Simulations-Experimental Approach

Abstract

Developing high-performance CO2 adsorbents and the efficient regeneration process is key to enhancing the industrial application potential of the adsorption process for CO2 capture. Some experimental studies have confirmed that hybridization of graphene oxide (GO) with Metal-Organic Frameworks (MOFs) can improve the CO2 capture performance of MOFs, but the CO2 adsorption mechanism is still unclear, and the performance needs to be improved. The main objective of this PhD thesis was to understand and improve the performance of hybrid GO/MOFs for CO2 capture by combining a molecular simulations/experimental approach. Based on GO/CuBTC and GO/UTSA-16, the CO2 adsorption mechanism of GO/MOFs was investigated by Grand Canonical Monte Carlo (GCMC). The region created by the connection between GO and MOFs was found to be the strongest CO2 adsorption region, but the stacking of GO sheets decreased the capture performance of GO/MOFs. Structures with higher CO2 capture performance were designed and their performance based on a temperature swing adsorption (TSA) process and binary mixture (15 % CO2+85 % N2) were predicted. GO/CuBTC with 65 wt.% GO showed best CO2 uptake performance and comparable specific energy consumption with amine scrubbing. The transport properties of CO2 and N2 in the selected GO/CuBTC and GO/UTSA-16 models were predicted by Molecular dynamics (MD). The impenetrable GO sheets and the stronger adsorption regions lead to the anisotropic diffusion of CO2 and N2. The breakthrough curves obtained by combining GCMC and MD confirm that the GO/CuBTC with 65 wt.% GO model has the longest CO2 breakthrough time for the selected models.
Complementary to the modeling work, hybrid GO/CuBTC were synthesized using a two-step in-situ solvothermal method. Although the GO/CuBTC with 65 wt.% GO and desired performance predicted by simulations was not achieved, the molecular simulation guided to obtain a shaped GO/CuBTC with 15 wt.% GO and good CO2 capture performance. The CO2 breakthrough curves of shaped GO/CuBTC with 15 wt.% GO and CuBTC were obtained by microwave heating fixed bed at 313 K, 1 bar, binary mixture (15 % CO2+85 % N2). Compared to CuBTC, shaped GO/CuBTC with 15 wt.% GO had a 42 % increase in CO2 adsorption capacity, and a 94 % reduction in regeneration energy consumption. Although the CO2 uptakes of the GO/CuBTC samples is lower than in the benchmark NaX, the developed strategy for GO/MOFs combining molecular simulation can guide the search for other more efficient materials. Furthermore, the two-step in-situ solvothermal for preparation of GO/MOFs－freeze drying for obtain binder-free shaped adsorbents－microwave heating for efficient regeneration can also be used in future works, as the overall strategy is effective and transferable to other GO/MOFs hybrid materials for CO2 capture and other applications.

Date of Award	Aug 2023
Original language	American English
Supervisor	Maria Lourdes Vega Fernandez (Supervisor)