Periodic Reporting for period 3 - SYNSORB (SYNergistic SORBents)
Reporting period: 2023-09-01 to 2025-02-28
Summary of the context and overall objectives of the project
This is the “Age of Gas”; disruptive new technologies must develop around the use of gases as fuels, therapies or feedstock chemicals. Specifically, new approaches to gas storage (transportation and delivery) and purification (commodities) are urgently needed to address the large energy footprint, cost and/or risk associated with existing technologies (e.g. chemisorbents). In particular, water and chemical commodity purification are global challenges, each consuming > 10% of global energy output.
SYNSORB will reduce the energy footprint of purification processes through crystal engineering (design), characterisation (structure/function) and modelling (binding interactions) studies that enable understanding of how pore size /chemistry impact the properties and performance of physisorbents. Our objective is to find the energetic sweet spots that enable new benchmarks for selectivity and working capacity for gas (e.g. CH4, C2, C3) and vapour (e.g. H2O) purification at practically relevant conditions.
Key scientific objectives include the following: (i) Understanding how pore size/chemistry impact selectivity, binding energy and kinetics of physisorption will afford fundamental knowledge concerning optimal pore size/chemistry for ultra-selective removal of both trace (< 1%) and bulk impurities. (ii) Trace gas removal from even binary gas mixtures was unattainable by physisorbents until recently, when new classes of ultramicroporous materials, HUMs (introduced by the PI in Nature, 2013, and Science, 2016) and azolate ultramicroporous materials, AUMs, were shown nto exhibit exceptional properties. The nature of HUMs/AUMs means that they offer new benchmarks for selectivity by > one order of magnitude vs. zeolites and MOFs, thereby enabling removal of trace impurities. (iii) SYNSORB will address purification of multi-component gas mixtures that mimic real world gas mixtures by using bespoke sorbents for each trace impurity, enabling 1-step removal of multiple impurities for the first time.
SYNSORB will reduce the energy footprint of purification processes through crystal engineering (design), characterisation (structure/function) and modelling (binding interactions) studies that enable understanding of how pore size /chemistry impact the properties and performance of physisorbents. Our objective is to find the energetic sweet spots that enable new benchmarks for selectivity and working capacity for gas (e.g. CH4, C2, C3) and vapour (e.g. H2O) purification at practically relevant conditions.
Key scientific objectives include the following: (i) Understanding how pore size/chemistry impact selectivity, binding energy and kinetics of physisorption will afford fundamental knowledge concerning optimal pore size/chemistry for ultra-selective removal of both trace (< 1%) and bulk impurities. (ii) Trace gas removal from even binary gas mixtures was unattainable by physisorbents until recently, when new classes of ultramicroporous materials, HUMs (introduced by the PI in Nature, 2013, and Science, 2016) and azolate ultramicroporous materials, AUMs, were shown nto exhibit exceptional properties. The nature of HUMs/AUMs means that they offer new benchmarks for selectivity by > one order of magnitude vs. zeolites and MOFs, thereby enabling removal of trace impurities. (iii) SYNSORB will address purification of multi-component gas mixtures that mimic real world gas mixtures by using bespoke sorbents for each trace impurity, enabling 1-step removal of multiple impurities for the first time.
Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far
Work performed during SYNSORB has resulted in a number of new HUM and AUM families of sorbent materials (WP1). HUMs based on new “linkers” (SIFSIX-17-Ni and TIFSIX-17-Ni) or new “linkers” and “pillars” (SIFSIX-21-Ni, NbOFFIVE-3-Ni, TIFSIX-4-Cu, and NbOFFIVE-3-Cu, SOFOUR-1-Zn, SIFSIX-22-Zn, TIFSIX-6-Zn, SNFSIX-2-Zn, GEFSIX-4-Zn, ZRFSIX-3-Zn, TAFSEVEN-1-Zn, sql-NbOFFIVE-bpe-Cu, GEFSIX-21-Cu, SIFSIX-24-Zn and SIFSIX-bidmb-Cu) have been prepared. New AUMs based on new “linkers” (Zn-atz-oba, [Co(dpt)(1,3-bib)] and X-dia-4-Co, X-dia-5-Co) have also been studied, as well as new azolate-based materials (BUT-53 to BUT-58) with larger pores suitable for larger molecules such as aromatic vapours. Several novel material families were designed, including chiral metal-organic materials (CMOMs) such as CMOM-5(NO₃), CMOM-5(BF₄), and CMOM-7, synthesized using prolinate- or mandelate-derived linkers and tailored extra-framework anions. A new set of flexible coordination networks (CNs) was also introduced, including a square lattice (sql) topology CN, sql-bib-Co-Cl, an interpenetrated diamondoid (dia) CN, X-dia-6-Ni, and double diamondoid (ddi) networks—X-ddi-1-Ni, X-ddi-2-Ni, and X-ddi-1,2-Ni—and square lattice frameworks such as X-sql-1-Cu, [Zn(5-Ria)(bphy)], and CuSO₄(1,4-bib). Additionally, light-responsive physisorbents LMA-1 and LMA-2 were developed to explore gas uptake triggered by external stimuli, and a novel CN, fcu-L-Co, is the first to exhibit a reversible guest-responsive metal oxidation state transition. In terms of material design, the development of SOFOUR-1-Zn, SOFOUR-2-Zn and CuSO4(1,4-bib) using the earth friendly anion sulfate as a pillar is particularly relevant. SOFOUR-1-Zn is the first member of a new HUM platform based upon earth-friendly chemical building blocks. The design of the first rigid HUM involving cis-bridging SIFSIX, SIFSIX-bidmb-Cu, has optimal binding sites C2H2 and was shown to exhibit high C2H2/C2H4 selectivity.
Physicochemical characterisation of sorbent platforms (WP2, WP3) was performed according to plan. Although for some of the discovered compounds no utility was found for the target SYNSORB purifications (C2H4, CH4, C3H6, C3H8), they were found to be suitable for capture of other industrially relevant gases and vapours. For example, the BUT family is extremely selective towards benzene, enabling its capture at trace concentration levels; For [Co(dpt)(1,3-bib)], stepped CO2 sorption was discovered; The third highest FMOM CH4 storage capacity was demonstrated for X-dia-6-Ni; the novel CN Ni(1,4-bib)(inca)2 exhibited potential for high CO2 selectivity over N2. In-situ characterisation and molecular modelling demonstrated that a clathrate (non-porous) coordination network undergoes rare switching between multiple non-porous phases through transient porosity, i.e. representing a new class of sorbent that is technically non-porous.
Dynamic gas column breakthrough tests (WP4) were performed on 2-component (C2H2/CO2, C2H2/C2H4), 3-component (C2H4/C2H2/CO2) or even 4-component (C2H2/C2H4/C2H6/CO2) gas mixtures. One-sorbent separation technology (OSST), was introduced, which enables mixture purification on single sorbent columns, in comparison to synergistic sorbent separation technology (SSST). OSST was demonstrated for one step purification of C2H4 by Zn-atz-oba AUM. This AUM was derived from its parent, Zn-atz-ipa, that was used in our paper (Science, 2019) to introducing the SYNSORB concept. Development of OSST technology resulted in achievement of key technological milestones of SYNSORB (#3 and #4) ahead of the schedule. Multiple materials developed during the project were evaluated under dynamic gas breakthrough conditions (WP4), confirming their potential for real-world separations. One of the most notable examples was CMOM-7, which showed outstanding dynamic separation of C₃H₈ from CH₄ and C2H₆. Breakthrough tests at 298 K and 1 bar using ternary mixtures demonstrated the production of polymer-grade propane (≥99.95%) in a single step (10.1021/acsmaterialslett.3c01157). In another study, sql-NbOFFIVE-bpe-Cu-AB, a packing polymorph of a layered HUM, achieved record-setting productivity in the dynamic separation of trace C₃H₄ from C₃H₆. Using binary gas the material completely removed 1% propyne from the stream, delivering polymer-grade propylene with a productivity exceeding 118 mmol·g⁻¹—a key industrial benchmark for polypropylene synthesis (10.1021/jacs.3c03505).
Further dynamic separation studies were performed on GEFSIX-21-Cu, SIFSIX-24-Zn, SOFOUR-2-Zn, and CuSO₄(1,4-bib) for C2H2/CO2 separation. GEFSIX-21-Cu demonstrated moderate selectivity in equimolar C2H2/CO2 mixtures and operated with a significantly lower isosteric heat of adsorption (Qst), indicating reduced energy demand for regeneration (10.1021/acsami.3c16634). CuSO₄(1,4-bib) showed strong selectivity for C2H2 over CO2 and C2H₄ across gas mixtures with ratios of 1:1, 1:9, and 1:99. This selectivity was driven by strong interactions between C2H2 and the sulfate anions in the framework (10.1021/acs.cgd.4c00094). A comparative study of SIFSIX-24-Zn and SOFOUR-2-Zn also focused on C2H2/CO2 separation. Although both materials showed similar IAST-predicted selectivities, SOFOUR-2-Zn outperformed SIFSIX-24-Zn in dynamic testing. The superior performance was attributed to the lower Qst for CO2 in SIFSIX-24-Zn, which reduced its competitive adsorption and thus decreased overall selectivity compared to SOFOUR-2-Zn (10.1039/D4SC03029J). The novel HUM SIFSIX-bidmb-Cu (10.1039/d5sc00697j) designed to have oprtimal binding sites for C2H2, displayed the second highest C2H2/C2H₄ (1/99) selectivity with a reported value of 140.2 removing C2H2 with high purity (>99% purity). It was also found to exhibit a C2H2/CO2 (50/50) selecitivty that is higher than most SIFSIX materials, with a selectivity of 20.3. Notably, SIFSIX-bidmb-Cu ranks second among sorbents that simultaneously exhibit C2H2/C2H₄ (1/99) and C2H2/CO2 (50/50) selectivities. Its demonstrated water stability positions it as a strong candidate for practical implementation in challenging C2H2/C2H₄ (1/99) separation scenarios.
In situ studies (WP5) play a critical role in understanding structure-property relationships in sorbents and optimization of separation performance in line with SYNSORB goals. This is achieved through in-house infrastructure and a network of international collaborations. In situ SCXRD and PXRD experiments conducted with L. Barbour (Stellenbosch) and S. Kitagawa (Kyoto) provided structural information about materials at specific gas pressures, giving insights to structural flexibility in [Co(dpt)(1,3-bib)] (10.1038/s41557-022-01128-3) [Cd(BTCP)(DPT)2], [Cd(BTCP)(FDPT)2] (10.1002/anie.202219039) [Cu(HQS)(TMBP)] (10.1021/acsami.2c10002) SIFSIX-21-Ni and SIFSIX-21-Cu (10.1016/j.chempr.2021.07.007) X-dia-4-Co, X-dia-5-Co (10.1021/jacs.3c01113) LMA-1 and LMA-2 (10.1002/anie.202219039) X-ddi-1-Ni family (10.1021/acs.chemmater.3c00334) sql-bib-Co-Cl (10.1002/ange.202423521) SIFSIX-bidmb-Cu (10.1039/d5sc00697j) X-dia-6-Ni (10.1021/jacs.4c03555). In addition, a new collaboration with TU Dresden, Germany, was developed, leading to discovery of CO2-loaded phase of X-dia-2-Cd (10.1039/d3ta01574b) and X-sql-1-Cu (10.1021/acsami.4c03777) and CH4 loading in X-dia-6-Ni (10.1021/jacs.4c03555). In situ PXRD experiments conducted using synchrotron radiation at beam I11 at the Diamond Light Source, UK using a custom-designed gas cell provided structural insights into crystal structure TIFSIX-17-Ni (10.1002/ange.202100240) and X-sql-1-Cu (10.1021/acsami.4c03777) and structural transformations of X-dia-2-Cd (10.1039/d3ta01574b). In addition to crystallographic studies, in situ infrared spectroscopy performed in collaboration with K. Tan (UT Dallas) provided valuable experimental insights into binding sites and the nature of interactions responsible for adsorption or co-adsorption of gases for SIFSIX-21-Ni and NbOFFIVE-3-Cu (10.1021/acsami.3c16634).
Molecular Modelling (WP5) was conducted with a PhD student jointly supervised by Mathias Vandichel at the University of Limerick. This collaboration has resulted in number of publications for SYNSORB, advancing our understanding of gas sorption in both rigid HUMs (10.1002/anie.202116145) and flexible materials (10.1021/jacs.3c01113 10.1021/acsami.4c03777 10.1021/jacs.3c03505 10.1021/acs.cgd.4c00094 10.1039/D4SC03029J 10.1002/ange.202423521 10.1021/jacs.4c03555),. In addition, SYNSORB was assisted through the long-term collaboration with the Brian Space group (North Carolina State, USA), which provided insights into the contributing factors to sorption performance of rigid HUMs (https://doi.org/10.1016/j.chempr.2021.07.007(opens in new window)) AUMs (https://www.nature.com/articles/s41467-021-26473-8(opens in new window)) and structural dynamics within flexible CNs(https://doi.org/10.1038/s41557-022-01128-3(opens in new window) https://doi.org/10.1002/anie.202219039 10.1002/anie.202219039). A collaboration with Dan Li and Shao-Jie Qin (College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, China) led to the investigation of the binding sites and mechanism for high C2H2/C2H4 (1/99) and C2H2/CO2 selectivity of SIFSIX-bidmb-Cu (10.1039/d5sc00697j) using molecular modeling.
Physicochemical characterisation of sorbent platforms (WP2, WP3) was performed according to plan. Although for some of the discovered compounds no utility was found for the target SYNSORB purifications (C2H4, CH4, C3H6, C3H8), they were found to be suitable for capture of other industrially relevant gases and vapours. For example, the BUT family is extremely selective towards benzene, enabling its capture at trace concentration levels; For [Co(dpt)(1,3-bib)], stepped CO2 sorption was discovered; The third highest FMOM CH4 storage capacity was demonstrated for X-dia-6-Ni; the novel CN Ni(1,4-bib)(inca)2 exhibited potential for high CO2 selectivity over N2. In-situ characterisation and molecular modelling demonstrated that a clathrate (non-porous) coordination network undergoes rare switching between multiple non-porous phases through transient porosity, i.e. representing a new class of sorbent that is technically non-porous.
Dynamic gas column breakthrough tests (WP4) were performed on 2-component (C2H2/CO2, C2H2/C2H4), 3-component (C2H4/C2H2/CO2) or even 4-component (C2H2/C2H4/C2H6/CO2) gas mixtures. One-sorbent separation technology (OSST), was introduced, which enables mixture purification on single sorbent columns, in comparison to synergistic sorbent separation technology (SSST). OSST was demonstrated for one step purification of C2H4 by Zn-atz-oba AUM. This AUM was derived from its parent, Zn-atz-ipa, that was used in our paper (Science, 2019) to introducing the SYNSORB concept. Development of OSST technology resulted in achievement of key technological milestones of SYNSORB (#3 and #4) ahead of the schedule. Multiple materials developed during the project were evaluated under dynamic gas breakthrough conditions (WP4), confirming their potential for real-world separations. One of the most notable examples was CMOM-7, which showed outstanding dynamic separation of C₃H₈ from CH₄ and C2H₆. Breakthrough tests at 298 K and 1 bar using ternary mixtures demonstrated the production of polymer-grade propane (≥99.95%) in a single step (10.1021/acsmaterialslett.3c01157). In another study, sql-NbOFFIVE-bpe-Cu-AB, a packing polymorph of a layered HUM, achieved record-setting productivity in the dynamic separation of trace C₃H₄ from C₃H₆. Using binary gas the material completely removed 1% propyne from the stream, delivering polymer-grade propylene with a productivity exceeding 118 mmol·g⁻¹—a key industrial benchmark for polypropylene synthesis (10.1021/jacs.3c03505).
Further dynamic separation studies were performed on GEFSIX-21-Cu, SIFSIX-24-Zn, SOFOUR-2-Zn, and CuSO₄(1,4-bib) for C2H2/CO2 separation. GEFSIX-21-Cu demonstrated moderate selectivity in equimolar C2H2/CO2 mixtures and operated with a significantly lower isosteric heat of adsorption (Qst), indicating reduced energy demand for regeneration (10.1021/acsami.3c16634). CuSO₄(1,4-bib) showed strong selectivity for C2H2 over CO2 and C2H₄ across gas mixtures with ratios of 1:1, 1:9, and 1:99. This selectivity was driven by strong interactions between C2H2 and the sulfate anions in the framework (10.1021/acs.cgd.4c00094). A comparative study of SIFSIX-24-Zn and SOFOUR-2-Zn also focused on C2H2/CO2 separation. Although both materials showed similar IAST-predicted selectivities, SOFOUR-2-Zn outperformed SIFSIX-24-Zn in dynamic testing. The superior performance was attributed to the lower Qst for CO2 in SIFSIX-24-Zn, which reduced its competitive adsorption and thus decreased overall selectivity compared to SOFOUR-2-Zn (10.1039/D4SC03029J). The novel HUM SIFSIX-bidmb-Cu (10.1039/d5sc00697j) designed to have oprtimal binding sites for C2H2, displayed the second highest C2H2/C2H₄ (1/99) selectivity with a reported value of 140.2 removing C2H2 with high purity (>99% purity). It was also found to exhibit a C2H2/CO2 (50/50) selecitivty that is higher than most SIFSIX materials, with a selectivity of 20.3. Notably, SIFSIX-bidmb-Cu ranks second among sorbents that simultaneously exhibit C2H2/C2H₄ (1/99) and C2H2/CO2 (50/50) selectivities. Its demonstrated water stability positions it as a strong candidate for practical implementation in challenging C2H2/C2H₄ (1/99) separation scenarios.
In situ studies (WP5) play a critical role in understanding structure-property relationships in sorbents and optimization of separation performance in line with SYNSORB goals. This is achieved through in-house infrastructure and a network of international collaborations. In situ SCXRD and PXRD experiments conducted with L. Barbour (Stellenbosch) and S. Kitagawa (Kyoto) provided structural information about materials at specific gas pressures, giving insights to structural flexibility in [Co(dpt)(1,3-bib)] (10.1038/s41557-022-01128-3) [Cd(BTCP)(DPT)2], [Cd(BTCP)(FDPT)2] (10.1002/anie.202219039) [Cu(HQS)(TMBP)] (10.1021/acsami.2c10002) SIFSIX-21-Ni and SIFSIX-21-Cu (10.1016/j.chempr.2021.07.007) X-dia-4-Co, X-dia-5-Co (10.1021/jacs.3c01113) LMA-1 and LMA-2 (10.1002/anie.202219039) X-ddi-1-Ni family (10.1021/acs.chemmater.3c00334) sql-bib-Co-Cl (10.1002/ange.202423521) SIFSIX-bidmb-Cu (10.1039/d5sc00697j) X-dia-6-Ni (10.1021/jacs.4c03555). In addition, a new collaboration with TU Dresden, Germany, was developed, leading to discovery of CO2-loaded phase of X-dia-2-Cd (10.1039/d3ta01574b) and X-sql-1-Cu (10.1021/acsami.4c03777) and CH4 loading in X-dia-6-Ni (10.1021/jacs.4c03555). In situ PXRD experiments conducted using synchrotron radiation at beam I11 at the Diamond Light Source, UK using a custom-designed gas cell provided structural insights into crystal structure TIFSIX-17-Ni (10.1002/ange.202100240) and X-sql-1-Cu (10.1021/acsami.4c03777) and structural transformations of X-dia-2-Cd (10.1039/d3ta01574b). In addition to crystallographic studies, in situ infrared spectroscopy performed in collaboration with K. Tan (UT Dallas) provided valuable experimental insights into binding sites and the nature of interactions responsible for adsorption or co-adsorption of gases for SIFSIX-21-Ni and NbOFFIVE-3-Cu (10.1021/acsami.3c16634).
Molecular Modelling (WP5) was conducted with a PhD student jointly supervised by Mathias Vandichel at the University of Limerick. This collaboration has resulted in number of publications for SYNSORB, advancing our understanding of gas sorption in both rigid HUMs (10.1002/anie.202116145) and flexible materials (10.1021/jacs.3c01113 10.1021/acsami.4c03777 10.1021/jacs.3c03505 10.1021/acs.cgd.4c00094 10.1039/D4SC03029J 10.1002/ange.202423521 10.1021/jacs.4c03555),. In addition, SYNSORB was assisted through the long-term collaboration with the Brian Space group (North Carolina State, USA), which provided insights into the contributing factors to sorption performance of rigid HUMs (https://doi.org/10.1016/j.chempr.2021.07.007(opens in new window)) AUMs (https://www.nature.com/articles/s41467-021-26473-8(opens in new window)) and structural dynamics within flexible CNs(https://doi.org/10.1038/s41557-022-01128-3(opens in new window) https://doi.org/10.1002/anie.202219039 10.1002/anie.202219039). A collaboration with Dan Li and Shao-Jie Qin (College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, China) led to the investigation of the binding sites and mechanism for high C2H2/C2H4 (1/99) and C2H2/CO2 selectivity of SIFSIX-bidmb-Cu (10.1039/d5sc00697j) using molecular modeling.
Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)
SYNSORB has gone beyond the state-of-the-art as follows:
-Properties: We have set new benchmarks for C3 and C6 selectivity, improved productivity for C2 and water vapour capture, and trace selecitivity for C3 (10.1021/jacs.3c03505).
-Design: we have introduced the earth friendly anion sulfate or “SOFOUR” as as a building block for high performance sorbent materials and have developed GEN2 variants (10.1021/acs.cgd.4c00094 10.1039/D4SC03029J). We developed the first rigid HUM with cis-SIFSIX pillar. We have achieved the control of sorbent flexibility by polymorphism (10.1021/acsami.4c03777 10.1021/jacs.3c03505).
-Concept: We have introduced high performance non-porous materials that rely upon transient porosity and their GEN2 variant. First ever report tuning metal oxidation state which opens up possiblities of new mechanism for sorption: fcu-L-Co (10.1021/jacs.4c09173).
-Methodology: We have introduced new methods evaluation of water sorbents that could be used for dehumidification, drying of gas mixtures and/or atmospheric water harvesting. Our green synthetic methodology led to the synthesis a new family of water stable coordination polymers: Zn, Cu, and Cd metal cations to form 2D (sql-PIBZ-Zn) and 1D (1D-PIBZ-Cu, 1D-PIBZ-Cd) (10.1021/acs.cgd.4c01606).
In terms of expected results before the end of SYNSORB, in line with its key objectives, gas mixture breakthrough tests (WP4) will be performed for methane (natural gas purification), propylene and propane purification/capture. Experiments using columns containing multiple sorbents (SSST) and single sorbent (OSST) will be performed, as well as high pressure sorption tests for gas storage applications.
In addition, WP5 has benefited from the use of a dedicated in situ PXRD instrument at the University of Limerick.
-Properties: We have set new benchmarks for C3 and C6 selectivity, improved productivity for C2 and water vapour capture, and trace selecitivity for C3 (10.1021/jacs.3c03505).
-Design: we have introduced the earth friendly anion sulfate or “SOFOUR” as as a building block for high performance sorbent materials and have developed GEN2 variants (10.1021/acs.cgd.4c00094 10.1039/D4SC03029J). We developed the first rigid HUM with cis-SIFSIX pillar. We have achieved the control of sorbent flexibility by polymorphism (10.1021/acsami.4c03777 10.1021/jacs.3c03505).
-Concept: We have introduced high performance non-porous materials that rely upon transient porosity and their GEN2 variant. First ever report tuning metal oxidation state which opens up possiblities of new mechanism for sorption: fcu-L-Co (10.1021/jacs.4c09173).
-Methodology: We have introduced new methods evaluation of water sorbents that could be used for dehumidification, drying of gas mixtures and/or atmospheric water harvesting. Our green synthetic methodology led to the synthesis a new family of water stable coordination polymers: Zn, Cu, and Cd metal cations to form 2D (sql-PIBZ-Zn) and 1D (1D-PIBZ-Cu, 1D-PIBZ-Cd) (10.1021/acs.cgd.4c01606).
In terms of expected results before the end of SYNSORB, in line with its key objectives, gas mixture breakthrough tests (WP4) will be performed for methane (natural gas purification), propylene and propane purification/capture. Experiments using columns containing multiple sorbents (SSST) and single sorbent (OSST) will be performed, as well as high pressure sorption tests for gas storage applications.
In addition, WP5 has benefited from the use of a dedicated in situ PXRD instrument at the University of Limerick.