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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/222582
Selective CO2 capture using MOF/Graphene Oxide Materials
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[eng] In recent years, climate change has become a central concern in the scientific community, primarily caused by greenhouse gas emissions; carbon dioxide (CO2) being one of the most significant contributors. Among the proposed strategies to mitigate its impact, porous materials have emerged as a potential solution to capture these harmful gases that present a risk to both society and the environment. Among these, Metal Organic Frameworks (MOFs) stand out due to their exceptional properties, such as thermal stability, large specific surface area, high porosity and tunable functionality, all of which are crucial for efficient gas sorption.
There is notable variability in measuring CO₂ capture using MOFs in the literature, which are mostly performed at low temperatures and/or high pressures, where most porous materials perform better. These conditions are not usual in emission sources like industrial chimneys or vehicle exhausts and, to overcome this, this study explores enhancing CO2 adsorption performance and properties of MOF materials, specifically at 25ᵒC and up to 1.3 atmospheres.
The present thesis explores the development, characterization, and performance of HKUST-1 and their hybrid combination with graphene-based materials, specifically graphene oxide (GO) and reduced graphene oxide (rGO), for CO2 capture. The research aims to address urgent environmental concerns through the design of efficient adsorbents capable of capturing CO₂.
Firstly, this work focuses on the synthesis of HKUST-1/GO hybrid materials by adding GO at several concentrations, ranging from 0.15% up to 9% w/w of GO. Using Mixed- Solvent Methods (MSM), commonly used in the synthesis of MOFs, the study identifies the optimal content of GO that enhances CO2 adsorption performance at 25ᵒC and up to 1.3 atmospheres. Additionally, a novel methodology, named here as Reverse Quantification (RQ); has been developed to quantify the experimental GO content in the hybrids, addressing inconsistencies often found in literature. As a
result, it is determined that the theoretical amount of GO used during synthesis is not entirely incorporated into the HKUST-1 samples. A deviation from the ideality is observed across 0 to 9% GO range, generally resulting in lower experimental GO content than theoretically added. Since RQ is employed in all syntheses of this study, it proves, through different trends, the deviation from the ideal behavior in all cases. In this instance, the sample containing 0.25% w/w of experimental GO obtained via MSM exhibits the highest CO2 adsorption performance, with a specific value of 5.33
± 0.16 mmol CO2/g at 1.3 atm, achieving up to 80% greater CO2 uptake compared to pristine HKUST-1.
Additionally, the major focus of the research is to optimize the method of synthesis, developing a more environmentally friendly synthesis method. HKUST-1 materials are commonly synthesized by MSM using harmful and ecotoxic solvents, such as dimethylformamide, at high temperatures (85ᵒC). Consequently, mechano-chemical synthesis through the liquid-assisted grinding (LAG) method using ball milling (BM) is explored. The results confirm that this method offers a more sustainable alternative while maintaining material performance. Two synthesis scales are investigated: small-scale (sBM) and medium-scale (bBM), with GO concentrations between 0.15–2.5% w/w, based on prior results obtained by MSM. sBM samples achieved CO₂ adsorption up to 4.93 ± 0.28 mmol/g at 0.48–0.55% of experimental GO content, comparable to MSM results. In contrast, bBM samples reached
3.77 ± 0.07 mmol/g at 0.25–0.30% w/w of experimental GO, though with less correlation between GO content and performance. Overall, mechano-chemical synthesis using ball milling proves effective, potentially scalable, and environmentally friendly.
Another important aspect is the cyclability of the synthesized material, since HKUST-1/GO hybrid material presents a notable regeneration capability over multiple adsorption-desorption cycles. Hence, the incorporation of reduced graphene oxide (rGO) into the HKUST-1 synthesis is investigated. As rGO offers
potential for CO₂ desorption via electrical heating, the main goal is to synthesize hybrid HKUST-1/rGO and HKUST-1 with mixtures of the graphenic materials (GM): rGO and GO, HKUST-1/GM; and check their CO2 adsorption properties. As a result, HK-rGO samples showed slightly lower CO₂ adsorption than GO-based ones, and a maximum of 5.10 mmol/g is achieved at 0.80% w/w of experimental rGO. In contrast, HK-GM samples (rGO/GO mixtures) expose a better performance, reaching
6.00 mmol CO2/g with the best result at 0.60% GM (1:3 ratio of rGO/GO mixtures, respectively). These findings suggest that combining rGO and GO can enhance the adsorption of pure GO-based materials, making them a promising candidate for cyclable adsorption processes, with CO2 desorption via electrical heating.
Finally, this thesis also explores the interaction between water (humidity) and CO₂ during adsorption processes when using HKUST-1/GO samples, both for samples obtained via mechano-chemical methods and MSM. Further analysis explores the competition of H₂O with CO₂ during adsorption processes under post-combustion conditions, using streams of 15 % CO2 and 50% RH. Specifically, this part of the research focuses on the behavior of H2O and CO2 adsorption processes by using different characterization techniques, such as Infrared Spectroscopy (IR), Dynamic Vapor Sorption (DVS), Breakthrough Analysis (BTA) and Solid-State 13C Nuclear Magnetic Resonance (13C NMR). A competition is observed between H₂O and CO₂ for the material's adsorption sites, with H₂O molecules exhibiting a higher affinity. The results suggest that H2O adsorption is produced mainly in carboxylate and aromatic functional groups, while CO2 molecules only show preference for aromatic functional groups. The experiments also confirm that CO₂ has higher adsorption kinetics than H₂O, aligned with RMN and IR experiments. It is also determined that the incorporation of GO increases the number of favorable adsorption sites for CO₂, such as aromatic carbon, and partially blocks H2O adsorption near copper nuclei, reducing the sample degradation. As a result, HKUST-1/GO that exhibits higher CO₂ uptake also indicates enhanced cycling behavior than pure HKUST-1. On the contrary, CO₂
adsorption under humid conditions is significantly reduced, highlighting that HKUST-1/GO materials are most effective in dry environments.
Additionally, the interaction with water is studied using colorimetric sensors, as the color of HKUST-1/GO changes from light to dark blue upon drying, indicating structural changes confirmed by X-ray diffraction, linked to water content. CO₂ exposure also induces color changes that correlate with CO₂ adsorption behavior. These initial results highlight the similarity between CO₂ adsorption and colorimetry in HK-GO samples, with HKUST-1 showing color changes upon interaction with CO₂, enabling detection of adsorbed CO₂ under dry conditions.
Overall, this work contributes to the field of sustainable materials for gas capture by combining advanced synthesis techniques, aligned with the principles of green chemistry, with emerging hybrid systems. The findings support the potential of HKUST-1-graphenic materials as effective and versatile CO2 adsorbents.
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MARTÍNEZ MEDINA, Elizabeth. Selective CO2 capture using MOF/Graphene Oxide Materials. [consulta: 26 de novembre de 2025]. [Disponible a: https://hdl.handle.net/2445/222582]