Calcium Poly(heptazine imide): Reproducible Synthesis for Structural Analysis, Mechanism of CO 2 Uptake, and Evaluation of Photocatalytic CO 2 - to-CO Conversion
Year: 2026
Type: preprint
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.
Source: ChemRxiv
Language: English
Subfield: Filtration and Separation
Field: Chemical Engineering
Domain: Physical Sciences
SDG: Climate action
Open Access status: green
OpenAlex ID: W7223184070