Calcium Poly(heptazine imide): Reproducible Synthesis for Structural Analysis, Mechanism of CO ₂ Uptake, and Evaluation of Photocatalytic CO ₂ - to-CO Conversion
4 affiliations
- 1Department of Chemistry, National Cheng Kung University, No. 1 University Road, Tainan City, Taiwan (ROC, 701
- 2Department of Materials Science and Engineering, National Cheng Kung University, No. 1 University Road, Tainan City, Taiwan, 701
- 3Max Planck Institute for Solid State Research, Heisenbergstrasse 1, Stuttgart, Germany, 70569
- 4Department of Chemistry, Ludwig-Maximilian-University Munich, Butenandtstraße 5-13, Munich, Germany, 81377
Abstract
The framework material, calcium poly(heptazine imide) or CaPHI, is reportedly capable for CO 2 absorption, although harsh conditions from literature synthesis method result in low and unpredictable yield that hinders evaluation of its applicability for CO 2 capture and conversion (CCC). This work presents a synthesis procedure for CaPHI with cross-laboratory reproducibility and scalable to 100s mg by employing a CaCl 2 -based eutectic as synthesis medium. Comprehensive characterization confirmed the PHI structure, with Ca 2+ residing in the structural porosity having ionic conductivity of 10 -10 –10 -11 S cm -1 as estimated by electrochemical measurements. In addition to the literature’s physisorption mechanism for dry CO 2 , we demonstrated these Ca 2+ to participate in direct air capture of humid CO 2 , which chemisorbs as CaCO 3 from structural analyses. For photocatalytic CO 2 -to-CO conversion, CaPHI outperforms its K + -bearing counterpart, which we speculatively attributed to strong Ca 2+ –CO 2 interactions that concentrate this reactant near the active sites. In establishing a reliable synthesis and demonstrating its ability for CO 2 capture and photoreduction, further optimization of CaPHI’s structure, morphology and compositing with co-catalyst could reveal its potential for CCC, while incorporation of mobile Ca 2+ may represent a broad design principle warranting future research for material development for improving the efficiency of carbon capture & utilization.
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BibTeX
@misc{chang2026calcium,
title = {{Calcium Poly(heptazine imide): Reproducible Synthesis for Structural Analysis, Mechanism of CO ₂ Uptake, and Evaluation of Photocatalytic CO ₂ - to-CO Conversion}},
author = {Chi-Chen Chang and Hsin-Hui Lin and Pin-Yu Shi and Stefan Repp and Bettina V. Lotsch and Wen-Hui Sophia Cheng and Vincent Wing-hei Lau},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010817/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010817/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Calcium Poly(heptazine imide): Reproducible Synthesis for Structural Analysis, Mechanism of CO ₂ Uptake, and Evaluation of Photocatalytic CO ₂ - to-CO Conversion
AU - Chi-Chen Chang
AU - Hsin-Hui Lin
AU - Pin-Yu Shi
AU - Stefan Repp
AU - Bettina V. Lotsch
AU - Wen-Hui Sophia Cheng
AU - Vincent Wing-hei Lau
PY - 2026
DA - 2026/10/22
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010817/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010817/v1
AB - The framework material, calcium poly(heptazine imide) or CaPHI, is reportedly capable for CO 2 absorption, although harsh conditions from literature synthesis method result in low and unpredictable yield that hinders evaluation of its applicability for CO 2 capture and conversion (CCC). This work presents a synthesis procedure for CaPHI with cross-laboratory reproducibility and scalable to 100s mg by employing a CaCl 2 -based eutectic as synthesis medium. Comprehensive characterization confirmed the PHI structure, with Ca 2+ residing in the structural porosity having ionic conductivity of 10 -10 –10 -11 S cm -1 as estimated by electrochemical measurements. In addition to the literature’s physisorption mechanism for dry CO 2 , we demonstrated these Ca 2+ to participate in direct air capture of humid CO 2 , which chemisorbs as CaCO 3 from structural analyses. For photocatalytic CO 2 -to-CO conversion, CaPHI outperforms its K + -bearing counterpart, which we speculatively attributed to strong Ca 2+ –CO 2 interactions that concentrate this reactant near the active sites. In establishing a reliable synthesis and demonstrating its ability for CO 2 capture and photoreduction, further optimization of CaPHI’s structure, morphology and compositing with co-catalyst could reveal its potential for CCC, while incorporation of mobile Ca 2+ may represent a broad design principle warranting future research for material development for improving the efficiency of carbon capture & utilization.
ER -