Thermally-induced phase transformations of CALF-20: insights into its phase stability and carbon capture properties

Dong A. Kang; Navaporn Suphavilai; Amro M.O. Mohamed; Ioannis G. Economou; Manish Shetty; Jinsoo Kim; Hae Kwon Jeong

doi:10.1039/d5ta01729g

Thermally-induced phase transformations of CALF-20: insights into its phase stability and carbon capture properties

Dong A. Kang
, Navaporn Suphavilai
, Amro M.O. Mohamed
, Ioannis G. Economou
, Manish Shetty
, Jinsoo Kim
, Hae Kwon Jeong

Research output: Contribution to journal › Article › peer-review

3 Scopus citations

Abstract

Calgary Framework 20 (CALF-20) has garnered a great deal of attention as a promising adsorbent for CO₂ capture applications due to its high CO₂ uptake capacity and excellent stability in humid environments. Multiple studies have explored its adsorption properties and separation performance, while a few studies reveal the existence of several phases of CALF-20, including α-, β-, and τ-phases. α-Phase (i.e., referred as CALF-20) is known to transform into β- or τ-phase under humid or thermal conditions, respectively. Computational studies have shown that β-CALF-20 exhibits a higher heat of CO₂ adsorption, making it more suitable for CO₂ capture compared to α-CALF-20. However, β-CALF-20, transformed from α-CALF-20 under humid conditions, is known to be less stable, thus observed only upon moisture exposure. Here, we demonstrate that β-CALF-20 can be formed solely by thermal treatment of α-CALF-20 and this thermally-derived β-CALF-20 is significantly more stable and can be readily obtained by drying as-synthesized CALF-20 at temperatures above 100 °C. Computational analyses corroborate the experimental results, affirming that the α-to-β phase transformation can be achieved solely through thermal treatment, without the involvement of water, via a modification in the Zn coordination number from 5 to 4. More importantly, this study finds that it is challenging to determine gas adsorption properties of α-CALF-20, as degassing of α-CALF-20 at elevated temperatures under vacuum almost always leads to its transformation into β-CALF-20. The resultant β-phase demonstrates a CO₂ uptake of 2.38 mmol g⁻¹ at 0.1 bar and 30 °C, along with a CO₂/N₂ IAST selectivity of 222 for a 10 : 90 CO₂/N₂ mixture, which aligns with previous reports. Consequently, these findings imply that previously reported gas adsorption properties, including carbon (CO₂) capture capacities, may have been measured on the β-phase of CALF-20, rather than the α-phase.

Original language	English
Pages (from-to)	18892-18899
Number of pages	8
Journal	Journal of Materials Chemistry A
Volume	13
Issue number	24
DOIs	https://doi.org/10.1039/d5ta01729g
State	Published - May 20 2025
Externally published	Yes

Funding

H.-K. J. acknowledges financial support from the Korea Evaluation Institute of Industrial Technology (KEIT) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea) (Project: 20018346). This work was supported in part by Brain Pool Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (RS-2024-00400935). The authors would like to thank Dr Abdoulaye Djire, Mr Ray Yoo and Ms. Jenna Vito at Texas A&M University for their assistance in obtaining N2 porosimetries of MOFs samples. The authors are thankful of Mr Andres Ramos at Texas A&M University for his experimental assistance. We are grateful to the High-Performance Computing Center of Texas A&M University at Qatar for its generous resource allocation. H.-K. J. acknowledges financial support from the Korea Evaluation Institute of Industrial Technology (KEIT) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea) (Project: 20018346). This work was supported in part by Brain Pool Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (RS-2024-00400935). The authors would like to thank Dr Abdoulaye Djire, Mr Ray Yoo and Ms. Jenna Vito at Texas A&M University for their assistance in obtaining N porosimetries of MOFs samples. The authors are thankful of Mr Andres Ramos at Texas A&M University for his experimental assistance. We are grateful to the High-Performance Computing Center of Texas A&M University at Qatar for its generous resource allocation. 2

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title = "Thermally-induced phase transformations of CALF-20: insights into its phase stability and carbon capture properties",

abstract = "Calgary Framework 20 (CALF-20) has garnered a great deal of attention as a promising adsorbent for CO2 capture applications due to its high CO2 uptake capacity and excellent stability in humid environments. Multiple studies have explored its adsorption properties and separation performance, while a few studies reveal the existence of several phases of CALF-20, including α-, β-, and τ-phases. α-Phase (i.e., referred as CALF-20) is known to transform into β- or τ-phase under humid or thermal conditions, respectively. Computational studies have shown that β-CALF-20 exhibits a higher heat of CO2 adsorption, making it more suitable for CO2 capture compared to α-CALF-20. However, β-CALF-20, transformed from α-CALF-20 under humid conditions, is known to be less stable, thus observed only upon moisture exposure. Here, we demonstrate that β-CALF-20 can be formed solely by thermal treatment of α-CALF-20 and this thermally-derived β-CALF-20 is significantly more stable and can be readily obtained by drying as-synthesized CALF-20 at temperatures above 100 °C. Computational analyses corroborate the experimental results, affirming that the α-to-β phase transformation can be achieved solely through thermal treatment, without the involvement of water, via a modification in the Zn coordination number from 5 to 4. More importantly, this study finds that it is challenging to determine gas adsorption properties of α-CALF-20, as degassing of α-CALF-20 at elevated temperatures under vacuum almost always leads to its transformation into β-CALF-20. The resultant β-phase demonstrates a CO2 uptake of 2.38 mmol g−1 at 0.1 bar and 30 °C, along with a CO2/N2 IAST selectivity of 222 for a 10 : 90 CO2/N2 mixture, which aligns with previous reports. Consequently, these findings imply that previously reported gas adsorption properties, including carbon (CO2) capture capacities, may have been measured on the β-phase of CALF-20, rather than the α-phase.",

author = "Kang, \{Dong A.\} and Navaporn Suphavilai and Mohamed, \{Amro M.O.\} and Economou, \{Ioannis G.\} and Manish Shetty and Jinsoo Kim and Jeong, \{Hae Kwon\}",

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year = "2025",

month = may,

day = "20",

doi = "10.1039/d5ta01729g",

language = "English",

volume = "13",

pages = "18892--18899",

journal = "Journal of Materials Chemistry A",

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TY - JOUR

T1 - Thermally-induced phase transformations of CALF-20

T2 - insights into its phase stability and carbon capture properties

AU - Kang, Dong A.

AU - Suphavilai, Navaporn

AU - Mohamed, Amro M.O.

AU - Economou, Ioannis G.

AU - Shetty, Manish

AU - Kim, Jinsoo

AU - Jeong, Hae Kwon

PY - 2025/5/20

Y1 - 2025/5/20

N2 - Calgary Framework 20 (CALF-20) has garnered a great deal of attention as a promising adsorbent for CO2 capture applications due to its high CO2 uptake capacity and excellent stability in humid environments. Multiple studies have explored its adsorption properties and separation performance, while a few studies reveal the existence of several phases of CALF-20, including α-, β-, and τ-phases. α-Phase (i.e., referred as CALF-20) is known to transform into β- or τ-phase under humid or thermal conditions, respectively. Computational studies have shown that β-CALF-20 exhibits a higher heat of CO2 adsorption, making it more suitable for CO2 capture compared to α-CALF-20. However, β-CALF-20, transformed from α-CALF-20 under humid conditions, is known to be less stable, thus observed only upon moisture exposure. Here, we demonstrate that β-CALF-20 can be formed solely by thermal treatment of α-CALF-20 and this thermally-derived β-CALF-20 is significantly more stable and can be readily obtained by drying as-synthesized CALF-20 at temperatures above 100 °C. Computational analyses corroborate the experimental results, affirming that the α-to-β phase transformation can be achieved solely through thermal treatment, without the involvement of water, via a modification in the Zn coordination number from 5 to 4. More importantly, this study finds that it is challenging to determine gas adsorption properties of α-CALF-20, as degassing of α-CALF-20 at elevated temperatures under vacuum almost always leads to its transformation into β-CALF-20. The resultant β-phase demonstrates a CO2 uptake of 2.38 mmol g−1 at 0.1 bar and 30 °C, along with a CO2/N2 IAST selectivity of 222 for a 10 : 90 CO2/N2 mixture, which aligns with previous reports. Consequently, these findings imply that previously reported gas adsorption properties, including carbon (CO2) capture capacities, may have been measured on the β-phase of CALF-20, rather than the α-phase.

AB - Calgary Framework 20 (CALF-20) has garnered a great deal of attention as a promising adsorbent for CO2 capture applications due to its high CO2 uptake capacity and excellent stability in humid environments. Multiple studies have explored its adsorption properties and separation performance, while a few studies reveal the existence of several phases of CALF-20, including α-, β-, and τ-phases. α-Phase (i.e., referred as CALF-20) is known to transform into β- or τ-phase under humid or thermal conditions, respectively. Computational studies have shown that β-CALF-20 exhibits a higher heat of CO2 adsorption, making it more suitable for CO2 capture compared to α-CALF-20. However, β-CALF-20, transformed from α-CALF-20 under humid conditions, is known to be less stable, thus observed only upon moisture exposure. Here, we demonstrate that β-CALF-20 can be formed solely by thermal treatment of α-CALF-20 and this thermally-derived β-CALF-20 is significantly more stable and can be readily obtained by drying as-synthesized CALF-20 at temperatures above 100 °C. Computational analyses corroborate the experimental results, affirming that the α-to-β phase transformation can be achieved solely through thermal treatment, without the involvement of water, via a modification in the Zn coordination number from 5 to 4. More importantly, this study finds that it is challenging to determine gas adsorption properties of α-CALF-20, as degassing of α-CALF-20 at elevated temperatures under vacuum almost always leads to its transformation into β-CALF-20. The resultant β-phase demonstrates a CO2 uptake of 2.38 mmol g−1 at 0.1 bar and 30 °C, along with a CO2/N2 IAST selectivity of 222 for a 10 : 90 CO2/N2 mixture, which aligns with previous reports. Consequently, these findings imply that previously reported gas adsorption properties, including carbon (CO2) capture capacities, may have been measured on the β-phase of CALF-20, rather than the α-phase.

UR - https://www.scopus.com/pages/publications/105006752105

U2 - 10.1039/d5ta01729g

DO - 10.1039/d5ta01729g

M3 - Article

AN - SCOPUS:105006752105

SN - 2050-7488

VL - 13

SP - 18892

EP - 18899

JO - Journal of Materials Chemistry A

JF - Journal of Materials Chemistry A

IS - 24

ER -

Thermally-induced phase transformations of CALF-20: insights into its phase stability and carbon capture properties

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