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Metal poly(heptazine imide) (MPHI), a two-dimensional carbon nitride polymer containing monovalent metal ions (M+), has recently attracted attention as a novel visible-light-driven photocatalyst. It exhibits photochromism, changing from yellow to blue-green upon light irradiation, regardless of the metal species, and is known to enhance ionic conductivity. Consequently, it has the potential to serve as a novel photoresponsive ionic conductor. However, the excited (color-changed) state that exhibits ionic conductivity is easily deactivated by atmospheric or dissolved oxygen in solution, making its application in actual devices challenging. Therefore, in this study, we developed a composite, protonated poly(heptazine imide) (HPHI):polyvinyl alcohol (PVA), by dispersing HPHI prepared by the acid treatment of potassium poly(heptazine imide) into a matrix of the insulating polymer PVA, which possesses high oxygen-blocking properties. HPHI:PVA can maintain a color-changed state for extended periods, even in air, while sustaining a low electrical resistance state. The duration of this color-changed state can be controlled by varying the degree of PVA saponification or temperature. Furthermore, a detailed investigation of the dependence of the electrical properties of HPHI:PVA on the percentage of HPHI revealed that proton conduction in HPHI:PVA arises from the percolation of poly(heptazine imide) particles within the composite. This finding also provides fundamental information regarding the ion-conduction mechanism in other MPHI composites. This study serves as an important guideline for the future development of new MPHI composites and applied research.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: Composites, Ions, Irradiation, Proton conductivity

Date published: 2026-03-17

Publisher: American Chemical Society (ACS)

Journal:

• ACS Omega (ISSN: 24701343) vol. 11 issue. 10 p. 16835-16843

Funding:

• Ministry of Education, Culture, Sports, Science and Technology 22K05259

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1021/acsomega.6c00037

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Updated at: 2026-03-24 09:34:32 +0900

Published on MDR: 2026-03-24 12:23:56 +0900