Defect-engineered metal-organic frameworks for carbon dioxide capture

Lead Research Organisation: Swansea University
Department Name: School of Engineering

Abstract

Since the Industrial Revolution, mankind has started to heavily interfere with the natural carbon cycle by extracting and burning increasingly larger amounts of fossil fuels, which has led to release huge amounts of CO2 in the atmosphere at an unprecedented rate, causing climate change. In order to mitigate the effects of climate change, the recently established Paris Agreement sets the goal of limiting the rise in the average global temperature to 2 degrees by 2100. This will require keeping cumulative CO2 emissions from all anthropogenic sources since year 1860 to less than 840 gigatons of carbon. If global carbon emissions continue to grow as they have in the last decade, the 2 degrees carbon budget will be spent by year 2035. This dictates to look for alternative energy sources and sustainable processes to enable the transition to a low-carbon economy.

CO2 capture, storage and utilisation (CCSU) is regarded as one of the key technologies to reduce CO2 emissions while fossil fuels are progressively phased out. Adoption of this technology on a large scale depends on its efficiency and economic viability, demanding the constant development of new materials able to combine excellent performances with long-term stability and affordability. The ideal sorbent for CO2 capture (CC) should have high mass uptake capacity, be selective towards CO2 over other gases, be able to be regenerated with a low energy penalty and be stable over various working cycles. CC from large point sources, such as coal- or gas-fired power plants and industrial facilities, is the most attractive option. These sources are responsible for about half of the global emissions and they generate concentrated CO2 streams that are easier to treat, if compared with direct air CO2 capture.

This project aims at developing new solid sorbents for CC by exploiting defects in zirconium-based metal-organic frameworks (Zr-MOFs) to functionalise them with a wide range of amino groups. Zr-MOFs are a class of crystalline and highly porous materials constructed from the connection of hexanuclear zirconium oxide-hydroxide clusters and carboxylate linkers. They are attractive for their remarkable stability, especially in the presence of water, which makes them suitable for practical applications. The CO2 adsorption capacity of bare Zr-MOFs is moderate, if compared to that of other sorbents. Functionalisation of Zr-MOFs using organic linkers with pending amino groups or through grafting of ethanolamine to the metal clusters has been demonstrated to increase their affinity for CO2. However, these methods are rather limited in scope. Defects in Zr-MOFs are reactive sites and can be exploited to introduce functional groups that cannot be otherwise inserted in the porous structure. Functionalisation of defective Zr-MOFs with amino groups of different nature (aliphatic, aromatic, heterocyclic) will allow to investigate and evaluate the influence of a large set of parameters on their CC performances. The resulting defect-engineered MOFs will be a library of novel, stable and versatile solid sorbents with tuneable physical-chemical properties for application in CC.

Tata Steel will be part of this project as an industrial partner. This will provide an excellent case study for the proposed research, because the steelworks in Port Talbot are the largest industrial CO2 emitter in the UK and Tata Steel is committed to address this issue. The materials developed during this project will be tested in conditions relevant to CC from blast furnace gas. This gas is mainly composed of N2 (45-50%), CO (20-25%), CO2 (20-25%) and H2 (0-5%) and is normally flared, due to its low calorific value. Removal of CO2 would allow to recycle the CO-rich stream in the blast furnace for reduction of iron ore and to convert the captured CO2 into useful chemicals.

Planned Impact

The proposed work will contribute to the development of new materials necessary to the implementation of essential technologies for the establishment of a low-carbon economy. For this reason, the present project perfectly aligns with EPSRC Delivery Plan, addressing a topic of strategic importance for two of the Prosperity Outcomes identified by EPSRC: Productive Nation and Resilient Nation. In terms of Productive Nation, the project is relevant to Ambition P2 (ensure affordable solutions for National needs) and Ambition P5 (transform to a sustainable society, with a focus on the circular economy). In terms of Resilient Nation, the project is relevant to Ambition R1 (achieve energy security and efficiency) and Ambition R5 (build new tools to adapt to and mitigate climate change).

In the short term, carbon dioxide capture, storage and utilisation will be instrumental in enabling replacement of fossil fuels with renewable sources for energy production. However, while the energy sector is progressively being decarbonised, the industrial and manufacturing sector will keep on emitting considerable amounts of CO2 also in the future. Examples are steel production, where coal is crucial in the process of purification of the iron ore, and cement production, where calcination of limestone to quicklime generates CO2. Therefore, carbon dioxide capture will continue to play a crucial role in reducing the emissions from industrial sources also in the long term. Dr Taddei will work in close contact with Tata Steel during this project, tailoring the materials that he will develop for the industrially relevant case of carbon dioxide capture from blast furnace gas. In the steel industry, huge amounts of this gas are flared because of its low calorific value. Capturing CO2 before flaring and converting it to useful chemicals will generate an economic return that will allow the UK steel industry to remain internationally competitive while becoming more environmentally sustainable.

The proposed research will also impact on a societal level. Reducing CO2 emissions is a priority to avoid an increase of 2 degrees of the global average temperature by year 2100 and prevent serious consequences that would affect large part of the global population. Dr Taddei will engage in a range of educative activities to raise awareness about the issues related with climate change, the role of carbon dioxide capture and the importance of sustainable lifestyles. These will include: i. writing one article for The Conversation to promote the research performed during this project in an easily accessible style for the lay public; ii. Running an interactive outreach exhibition on carbon dioxide capture, storage and utilisation during the Swansea Science Festival, primarily addressing families; iii. visiting primary schools in the Swansea area as a STEM Ambassador to talk to the younger generation about climate change, sustainability and responsible lifestyles.

Publications

10 25 50
 
Title Recycling Carbon - An illustrated story 
Description The product is an illustrated booklet that tells the story of a carbon atom, from the moment it is extracted in the form of methane, going through conversion to carbon dioxide when burnt, captured form the atmosphere and finally catalytically converted back to methane. Illustrations were hand drawn by my wife - Carla Nicola - and I curated the text, trying to make it accessible to students in the 12-16 years age range. 
Type Of Art Artefact (including digital) 
Year Produced 2019 
Impact 500 copies of the booklet were printed out with funding from this grant. Copies were distributed during several events, for a total of about 300 handed out so far, mainly during the the Swansea Science Festival, held in Swansea in October 2019 and the 3rd International Conference on Metal Organic Frameworks and Porous Polymers, held in Paris in October 2019. The booklet was also made available online in pdf format under a CC-BY-NC-ND licence at the following website: https://www.marco-taddei.com/outreach.html It was downloaded more than 640 times from users from all over the world. Following my relocation to Italy, I plan to translate the content in Italian and distribute the booklet in outreach events organised by the Department of Chemistry and Industrial Chemistry of the University of Pisa. 
URL https://www.marco-taddei.com/outreach.html
 
Description The project is based on the hypothesis that functionalisation of highly stable zirconium-based metal-organic frameworks (Zr-MOFs) by taking advantage of defective sites, as an alternative to the classical method of functionalising the linker molecules, could generate defect-engineered MOFs with enhanced performance in CO2 capture. With this aim in mind, amine groups of various nature were introduced at defective sites through post-synthetic defect exchange.
The first step was to evaluate the effect of having the same aromatic amine groups, i.e. pyridine and aniline, as part of either the linker molecule or the defect compensating species. We chose to work with UiO-66, the prototypical Zr-MOF. We anticipated that the two methods of functionalisation would render MOFs with rather different characteristics: while post-synthetic exchange of linkers on a non-defective MOF yields a material with random distribution of functional groups and a similar porosity to the starting material, grafting of amino-functionalised monocarboxylates on a defective MOF yields a material selectively functionalised on the defective part of the framework and with considerable differences, in terms of porosity, with respect to the starting material. We successfully managed to produce defect-engineered MOFs by a simple exchange protocol in N,N-dimethylformamide (DMF) at 80 °C and found that they did indeed perform better than the pristine defective MOF, due to both the change in porosity and the presence of amine groups. However, the improvement was moderate, suggesting that more interactive functional groups should be employed, e.g. aliphatic amines.
We therefore moved to attempt the introduction of various aliphatic aminocarboxylates, bearing either primary or secondary amine groups, into two Zr-MOFs: defective UiO-66 and MOF-808 (this MOF can be considered as an "intrinsically" defective material, due to the low connectivity of the metal clusters that makes them indistinguishable, in terms of chemical reactivity, to those of a defective MOF). Due to the high solubility in water of all of the aminocarboxylates, we attempted exchange in this solvent (which is more desirable than DMF). However, we found that low exchange could be achieved, due to competition between water and the aminocarboxylates. To overcome this issue, we decided to employ the same species, but with protected amine groups, in order to prevent formation of zwitterionic species and favour their dissolution in organic solvents. This strategy proved successful and we managed to perform almost complete exchange in DMF solvent. Since the protecting group was the tert-Butyloxycarbonyl (BOC), i.e. a carbamate, we were able to post-synthetically deprotect the amine groups by simple thermal treatment of the solids. Evaluation of the CO2 performance of these products is still incomplete.
Furthermore, during the work with aromatic amines, we realised that defect-engineered UiO-66 MOFs containing aminobenzoic acids had a slightly yellowish colour (the starting material is white). This prompted us to investigate their photochemical properties, finding that the band gap of the material was indeed reduced. Further investigation proved that changing the position of the amino group with respect to the carboxylate, or increasing the amount of amine groups, could allow us to modulate the band gap in a predictable manner. The defect-engineered MOFs were tested as photocatalysts for CO2 reduction in the gas phase and degradation of the dye Rhodamine B in water, displaying improved performance when compared with the pristine MOF.
Exploitation Route The defect engineering approach here employed has proven to be very powerful to introduce within Zr-MOFs functional groups that are not accessible through classical routes employed in the literature. There are two main outcomes that could have an impact on the field of research of MOFs:
- MOFs containing aliphatic amines are seldom reported and our method provides a new avenue to introduce aliphatic amines, which could be useful for CO2 capture, as originally hypothesised during this work, but also for a range of other applications, such as catalysis, ion exchange, heavy metal removal and proton conduction.
- The demonstration that the band gap of Zr-MOFs can be tuned by judiciously choosing the nature of the defect compensation species paves the way for future work aimed at expanding the scope of the defect engineering approach to improve the photocatalytic activity of Zr-MOFs for a range of reactions of great environmental interest, including CO2 reduction to useful chemicals.
Sectors Chemicals

 
Description Collaboration with Dr Davide Tiana 
Organisation University College Cork
Department Department of Chemistry
Country Ireland 
Sector Academic/University 
PI Contribution My team and I prepared and characterised defect-engineered MOFs containing amine groups, which were studied for their CO2 capture properties and photochemical properties.
Collaborator Contribution Dr Tiana performed density funcitonal theory calculations for two different purposes: 1. Describing the electronic structure of defect-engineered MOFs containing aromatic amines in order to understand the origin of the observed band gap shrinking. A single -cluster approximation was employed because of the high computational cost of simulating a periodic structure. Yet, our approximation was found to correctly reproduce the observed trend of band gap and provide information about the effect of amine modification on the frontier orbitals. These calculations were included in a paper in Journal of Materials Chemistry A, where Dr Tiana is co-corresponding author. 2. Exploring whether the presence of aliphatic amines grafted at defective sites can lead to strong adsorption of CO2 through formation of covalent C-N bonds. A model consisting of a unit cell of UiO-66 having reo topology - representative of a defective structure - was employed and aminoalkylcarboxylic acids with different chain lengths were tested. These results are very recent and still need to be discussed in detail. The plan is to include these calculations in a forthcoming publication.
Impact The paper "BBand gap modulation in zirconium-based metal-organic frameworks by defect engineering" was published in Journal of Materials Chemistry A, with Dr Tiana as co-corresponding author.
Start Year 2018
 
Description Collaboration with the group of Dr Camille Petit 
Organisation Imperial College London
Country United Kingdom 
Sector Academic/University 
PI Contribution My team and I prepared a range of defect-engineered Zr-based MOFs having UiO-66 structure containing amine-functionalised benzoic acids and characterised them, with focus on the photochemical properties. We also tested the activity of these materials in the photocatalytic degradation of rhodamine B in water, finding that defect-engineered MOFs performed better than the pristine MOF.
Collaborator Contribution The group of Dr Camille Petit tested the MOFs prepared in our team as photocatalysts for the reduction of carbon dioxide to carbon monoxide in the gas phase in the presence of hydrogen. It was observed that defect-engineered MOFs performed better than the pristine MOF, with results comparable to those obtained with P25 titanium dioxide, a common benchmark material for the tested reaction. The collaboration is ongoing, now focusing on the computational evaluation of MOFs prepared by our team as solid adsorbents for CO2 capture using pressure swing adsorption.
Impact The results of the collaboration formed the basis for the article "Band gap modulation in zirconium-based metal-organic frameworks by defect engineering", published in the Journal of Materials Chemistry A.
Start Year 2019
 
Description School visit (Step Ahead Education Centre, Cockett, Swansea) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact The visit involved a presentation and a practical workshop on the topic of CO2 capture and utilisation in an education centre dedicated to pupils with mental health issues.
The goal of the activity is to promote the idea of recycling carbon into useful products, in a similar fashion to what is done for other materials, such as paper, plastic and glass.
Information was provided about the carbon footprint of everyday activities to raise awareness about the positive impact of adopting more sustainable lifestyles.
In the practical part, pupils used Bunchems as atomic models to simulate the chemical reactions involved in the process.
Nine pupils and two teachers attended. After initial reticence, the pupils engaged in the activity and the teachers were very happy with their involvement.

As an evidence of impact of this activity, the text of the email received from the responsible teacher shortly after the visit is reported in the following:
"Hi Marco
Thank you for giving up your time this morning. We very much appreciate any help that we can get from outside speakers.
I know our pupils are quite reticent but they have told the other pupils what they did as some asked when it was their turn!
I have passed your details on to my network of colleagues as I think you will be brilliant in a mainstream school
Once again thank you"
Year(s) Of Engagement Activity 2019
URL https://recyclingcarbon.wordpress.com/
 
Description Swansea Science Festival 2018 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact The project "Recycling Carbon" was presented as an interactive activity during a festival that attracts about 8000 people over two days. The goal of the activity is to promote the idea of recycling carbon into useful products, in a similar fashion to what is done for other materials, such as paper, plastic and glass, using Bunchems as atomic models to simulate the chemical reactions involved in the process. Information was provided about the carbon footprint of everyday activities to raise awareness about the positive impact of adopting more sustainable lifestyles.
In order to asses impact, attendants were asked to answer two questions before and after the activity: 1. Can carbon dioxide be recycled? 2. Can individuals make a difference to climate change?
After interaction with the activity, the share of people who answered "yes" to the first question grew from 61% to 93%, those who answered "no" decreased from 15% to 1% and those who answered "Don't know" decreased from 24% to 6%.
After interaction with the activity, the share of people who answered "yes" to the second question grew from 63% to 95%, those who answered "no" decreased from 28% to 3% and those who answered "Don't know" decreased from 9% to 2%.
Year(s) Of Engagement Activity 2018
URL https://www.swansea.ac.uk/research/in-the-community/swansea-science-festival/
 
Description Swansea Science Fetsival 2019 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact The project "Recycling Carbon" was presented as an interactive activity during a festival that attracts about 8000 people over two days. The goal of the activity is to promote the idea of recycling carbon into useful products, in a similar fashion to what is done for other materials, such as paper, plastic and glass, using Bunchems as atomic models to simulate the chemical reactions involved in the process. Information was provided about the carbon footprint of everyday activities to raise awareness about the positive impact of adopting more sustainable lifestyles.
About 250 copies of the booklet "Recycling Carbon - An illustrated story", printed with funding from this award, was distributed during the event.
In order to asses impact, attendants were asked to answer two questions before and after the activity: 1. Can carbon dioxide be recycled? 2. Can individuals make a difference to climate change?
After interaction with the activity, the share of people who answered "yes" to the first question grew from 70% to 93%, those who answered "no" decreased from 16% to 5% and those who answered "Don't know" decreased from 14% to 3%.
After interaction with the activity, the share of people who answered "yes" to the second question grew from 92% to 96%, those who answered "no" stayed constant at 3% and those who answered "Don't know" decreased from 5% to 2%.
Year(s) Of Engagement Activity 2019
URL https://www.swansea.ac.uk/research/in-the-community/swansea-science-festival/
 
Description Visit to St. Michael's School, Bryn, Llanelli 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact The visit was part of a series of seminars named "A level talk: Inspiring careers in STEM" in an independent boarding and day school and involved a presentation on the role of chemistry in the field of CO2 capture and utilisation, which is the goal of the outreach project "Recycling Carbon", followed by an open session during which students could ask questions about the career opportunities in this area.
As an evidence of impact of this activity, the text of the email received from the responsible teacher shortly after the visit is reported in the following: "Dear Marco, I just wanted to thank you for taking the time to come and speak to our small group of students about the role of chemistry in the battle against climate change."
Year(s) Of Engagement Activity 2019
URL https://recyclingcarbon.wordpress.com/