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. This has led to release huge amounts of CO2 in the atmosphere at an unprecedented rate, causing climate change. The recently established Paris Agreement sets the goal of limiting the rise in the average global temperature to 2 degrees by 2100. If global carbon emissions continue to grow as they have in the last decade, it is projected that the 2 degrees carbon budget will be spent by 2035.
Carbon capture, storage and utilisation is regarded as one of the key technologies to reduce CO2 emissions. 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. Large point sources, such as coal- or gas-fired power plants and industrial facilities, are responsible for about half of the global CO2 emissions and generate concentrated CO2 streams, Carbon capture from these sources is easier than from thin air and can greatly contribute to reach the target set by the Paris Agreement.
Source: IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change
Metal-organic frameworks (MOFs) are crystalline and highly porous coordination polymers built from the connection of metal ions or clusters and organic linkers. They offer virtually unlimited possibilities of customisation of their crystal structure and physical-chemical properties. This is an extremely attractive feature for application in several fields, including gas sorption/separation. MOFs display high CO2 adsorption capacity and selectivity and have attracted interest as potential sorbents for carbon capture. However, most of them suffer from stability issues that have so far hindered their application in industrial contexts.
Most MOFs are based on carboxylates as organic linkers, whereas use of phosphonate linkers for construction of MOFs is not yet well established. This is due to synthetic and crystallographic challenges: 1. metal phosphonates have a pronounced tendency to form dense layered phases and obtaining porous open-framework compounds is generally considered a hard challenge; 2. they are highly insoluble and are often obtained as microcrystalline powders, thus making structural characterization a difficult task; 3. phosphonates are more versatile ligands than carboxylates, which makes their coordination chemistry less predictable. However, the excellent robustness of metal phosphonates represents a significant advantage, if compared to conventional carboxylate-based MOFs, for practical applications. This project aims at developing a new generation of ultrastable phosphonate-based MOFs by employing rigid linkers with non-linear geometry, which can prevent the formation of dense layered structures and generate ordered porosity. Formation of ultramicropores (diameter < 0.8 nm) is specifically targeted, because of the potential for selectively trapping of CO2 over other common gases (e.g. N2, CH4, CO).
This project is supported by funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 663830.
Zirconium-based MOFs (Zr-MOFs) are a subclass of MOFs known for their remarkable stability, especially in the presence of water. Nonetheless, the CO2 adsorption capacity of bare Zr-MOFs is moderate, if compared to that of the best performing MOFs. Functionalisation of Zr-MOFs using organic linkers with pending amino groups, linkers based on heterocyclic aromatic rings (such as pyridine and pyrazine) or by grafting ethanolamine to the clusters have been demonstrated to increase the affinity for CO2. It was recently discovered that Zr-MOFs can contain large amounts of structural defects without suffering from significant loss of stability and that defects are reactive sites towards exchange of terminal groups. This project takes advantage of the dynamic nature of defects in Zr-MOFs to introduce amino groups of various natures, allowing to explore a chemical variety that is non accessible through classical functionalisation routes. The resulting defect-engineered MOFs will be a novel class of stable and versatile solid sorbents with tuneable physical-chemical properties for application in carbon dioxide capture.
This project is supported by funding from the Engineering and Physical Sciences Research Council (EPSRC) through the First Grant scheme (EP/R01910X/1).