{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,20]],"date-time":"2026-04-20T12:57:37Z","timestamp":1776689857251,"version":"3.51.2"},"reference-count":32,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2026,4,20]],"date-time":"2026-04-20T00:00:00Z","timestamp":1776643200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100017700","name":"Henan Province science and technology research project","doi-asserted-by":"publisher","award":["242102231044"],"award-info":[{"award-number":["242102231044"]}],"id":[{"id":"10.13039\/501100017700","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Henan Provincial Science Foundation Project","award":["232300420338"],"award-info":[{"award-number":["232300420338"]}]},{"name":"Henan Provincial Science Foundation Project","award":["242300420343"],"award-info":[{"award-number":["242300420343"]}]},{"name":"special fund project of Zhengzhou basic and applied basic research","award":["ZZSZX202001"],"award-info":[{"award-number":["ZZSZX202001"]}]},{"name":"special fund project of Zhengzhou basic and applied basic research","award":["ZZSZX202002"],"award-info":[{"award-number":["ZZSZX202002"]}]},{"name":"Postgraduate Education Reform and Quality Improvement Project of Henan Province","award":["YJS2022JD50"],"award-info":[{"award-number":["YJS2022JD50"]}]},{"name":"Program for Science & Technology Innovation Talents in Universities of Henan Province","award":["24HASTIT002"],"award-info":[{"award-number":["24HASTIT002"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nanomaterials"],"abstract":"<jats:p>Photocatalytic reduction of carbon dioxide (CO2) into high-value multicarbon products, such as ethylene (C2H4), remains a significant challenge due to the difficult C-C coupling process. Potassium poly(heptazine imide) (K-PHI) is a promising photocatalyst, yet efficiently exchanging its interlayer cations to tune catalytic selectivity without causing structural degradation is difficult. Herein, an efficient and green supercritical CO2 (SC CO2) assisted ion-exchange strategy was developed to successfully prepare a series of mono-\/di-\/trivalent cation-doped M-PHI photocatalysts (M = H+, Na+, Sr+, Ca2+, Co2+, Fe3+). Systematic characterizations confirmed that the SC-CO2 treatment successfully achieved in-depth cation substitution without destroying the intrinsic heptazine framework, effectively regulating the interlayer structure and significantly optimizing the photoelectrochemical charge separation. Among the prepared samples, H-PHI exhibited the optimal photocatalytic CO2 reduction performance with an outstanding selectivity toward C2H4 generation. Under simulated sunlight irradiation for 3 h, the yields of CO, CH4, and C2H4 C2H4 C2H4 reached 3564.87, 807.32, and 40.00 \u03bcmol\u00b7g\u22121, respectively, significantly outperforming pristine K-PHI and other metal-doped samples. Crucially, isotope-tracing experiments utilizing a SC CO2-DCl treatment detected deuterated CH4 and C2H4 products, providing direct evidence that the hydrogen in the carbon products originates from the introduced protons, thereby elucidating the precise reaction pathway for C-C coupling. This study provides a green and efficient supercritical CO2 ion exchange strategy for the cation engineering of crystalline carbon nitride, and also offers new ideas and methods for designing high-activity photocatalysts for photocatalytic CO2 reduction.<\/jats:p>","DOI":"10.3390\/nano16080489","type":"journal-article","created":{"date-parts":[[2026,4,20]],"date-time":"2026-04-20T12:01:22Z","timestamp":1776686482000},"page":"489","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Green Supercritical CO2 Ion-Exchange Strategy for Cation Engineering in Polyheptazine Imides Towards Efficient Photoreduction CO2 to C2H4"],"prefix":"10.3390","volume":"16","author":[{"given":"Xin","family":"Peng","sequence":"first","affiliation":[{"name":"School of Chemistry and Chemical Engineering, Henan University of Science and Technology, Luoyang 471000, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Lina","family":"Du","sequence":"additional","affiliation":[{"name":"Henan Provincial Key Laboratory of Nanocomposites and Applications, Institute of Nanostructured Functional Materials, Huanghe Science and Technology College, Zhengzhou 450006, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Gaoliang","family":"Fu","sequence":"additional","affiliation":[{"name":"Henan Provincial Key Laboratory of Nanocomposites and Applications, Institute of Nanostructured Functional Materials, Huanghe Science and Technology College, Zhengzhou 450006, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Shouren","family":"Zhang","sequence":"additional","affiliation":[{"name":"Henan Provincial Key Laboratory of Nanocomposites and Applications, Institute of Nanostructured Functional Materials, Huanghe Science and Technology College, Zhengzhou 450006, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Junying","family":"Ma","sequence":"additional","affiliation":[{"name":"School of Chemistry and Chemical Engineering, Henan University of Science and Technology, Luoyang 471000, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,4,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"e202500329","DOI":"10.1002\/anie.202500329","article-title":"Ether-Embedded Covalent Organic Frameworks Enable Efficient Photocatalytic CO2 Reduction","volume":"64","author":"Zhou","year":"2025","journal-title":"Angew. Chem. Int. Ed."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1117","DOI":"10.1038\/s41467-023-36778-5","article-title":"Room-temperature Photosynthesis of Propane from CO2 with Cu Single Atoms on Vacancy-rich TiO2","volume":"14","author":"Shen","year":"2023","journal-title":"Nat. Commun."},{"key":"ref_3","first-page":"e23047","article-title":"Synergistic Atomic-Vacancy Engineering in Bi2S3-\u03b4\/Co-N-C. Boosting Photoelectrocatalytic Hydrogen Production via Formaldehyde Oxidation","volume":"21","author":"Li","year":"2025","journal-title":"Adv. Funct. Mater."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"9964","DOI":"10.1039\/D4CS00186A","article-title":"Recent Progress in Solar-driven CO2 Reduction to Multicarbon Products","volume":"53","author":"Li","year":"2024","journal-title":"Chem. Soc. Rev."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"21677","DOI":"10.1039\/D4TA03676J","article-title":"Recent Progress on Photocatalytic Reduction of CO2 to C2+ Products","volume":"12","author":"Zhu","year":"2024","journal-title":"J. Mater. Chem. A"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"2081","DOI":"10.1038\/s41467-026-68830-5","article-title":"Near-unity CO2-to-ethylene Photoconversion over Low Coordination Single-atom Catalysts","volume":"17","author":"Tang","year":"2026","journal-title":"Nat. Commun."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"e20354","DOI":"10.1002\/anie.202520354","article-title":"Spatially Separated C-C Coupling and Protonation on Cl-Bridged Ti-Ag Dual-Site Catalysts for Efficient Photocatalytic CO2 Reduction to C2H4","volume":"65","author":"Du","year":"2026","journal-title":"Angew. Chem. Int. Ed."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"e2505653","DOI":"10.1002\/adma.202505653","article-title":"Self-Trapped Excitons Activate Pseudo-Inert Basal Planes of 2D Organic Semiconductors for Improved Photocatalysis","volume":"37","author":"Yang","year":"2025","journal-title":"Adv. Mater."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"124910","DOI":"10.1016\/j.apcatb.2024.124910","article-title":"In-situ Construction of Bulk and Surface Defects to Activate the Near-infrared Photocatalytic Activity of Poly(heptazine imide)","volume":"365","author":"Li","year":"2025","journal-title":"Appl. Catal. B Environ."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"e202406398","DOI":"10.1002\/anie.202406398","article-title":"Engineering Polyheptazine and Polytriazine Imides for Photocatalysis","volume":"63","author":"Jing","year":"2024","journal-title":"Angew. Chem. Int. Ed."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"2165","DOI":"10.1021\/jacs.5c09930","article-title":"Theory-Guided Discovery of Ion-Exchanged Poly(heptazine imide) Photocatalysts Using First-Principles Many-Body Perturbation Theory","volume":"148","author":"Hajiahmadi","year":"2026","journal-title":"J. Am. Chem. Soc."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"e25844","DOI":"10.1002\/ange.202525844","article-title":"Solvation-Mediated Assembly for Large-Scale Synthesis of Covalent Organic Framework Membranes","volume":"138","author":"Sheng","year":"2026","journal-title":"Angew. Chem. Int. Ed."},{"key":"ref_13","first-page":"2417880","article-title":"Designing Better Electrocatalysts via Ion Exchange for Water Splitting","volume":"13","author":"Li","year":"2024","journal-title":"Adv. Funct. Mater."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"3632","DOI":"10.1021\/acsnano.5c17289","article-title":"Mechanically Strengthened Graphene Oxide: Covalent Organic Framework Membranes for Monovalent\/Divalent Cation Selectivity via Electrodialysis","volume":"20","author":"Feng","year":"2026","journal-title":"ACS Nano"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1901084","DOI":"10.1002\/advs.201901084","article-title":"Supercritical Fluid-Facilitated Exfoliation and Processing of 2D Materials","volume":"6","author":"Sun","year":"2019","journal-title":"Adv. Sci."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"2663","DOI":"10.1002\/adma.201504436","article-title":"Prospects of Supercritical Fluids in Realizing Graphene-Based Functional Materials","volume":"28","author":"Poulin","year":"2016","journal-title":"Adv. Mater."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"394","DOI":"10.1007\/s11630-019-1118-4","article-title":"Supercritical CO2, Properties and Technological Applications\u2014A Review","volume":"28","author":"Nikolai","year":"2019","journal-title":"J. Therm. Sci."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"e2301097","DOI":"10.1002\/smll.202301097","article-title":"Supercritical CO2 Directional-Assisted Synthesis of Low-Dimensional Materials for Functional Applications","volume":"19","author":"Liu","year":"2023","journal-title":"Small"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"8785","DOI":"10.1039\/D3GC04329K","article-title":"Heterogeneous Photocatalytic Synthesis of Sulfenamides with Carbon Doped Potassium Poly(heptazine imide) through Effective Electron Delocalization","volume":"26","author":"Yuan","year":"2024","journal-title":"Green Chem."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"334","DOI":"10.1038\/s41557-024-01721-8","article-title":"Isotopic labelling of Water Reveals the Hydrogen Transfer Route in Electrochemical CO2 Reduction","volume":"17","author":"Zhang","year":"2025","journal-title":"Nat. Chem."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"437","DOI":"10.1038\/s41467-024-44753-x","article-title":"Elucidating Protonation Pathways in CO2 Photoreduction Using the Kinetic Isotope Effect","volume":"15","author":"Yin","year":"2024","journal-title":"Nat. Commun."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"2534","DOI":"10.1038\/s41467-023-38052-0","article-title":"Designing Reliable and Accurate Isotope-tracer Experiments for CO2 Photoreduction","volume":"14","author":"Wang","year":"2023","journal-title":"Nat. Commun."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"41131","DOI":"10.1021\/acsami.2c12959","article-title":"Optimizing the Optical Absorption of Poly(heptazine imide) by the n \u2192 \u03c0* Electron Transition for Improved Photocatalytic H2 Evolution","volume":"14","author":"Wang","year":"2022","journal-title":"ACS Appl. Mater. Interfaces"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1700555","DOI":"10.1002\/adma.201700555","article-title":"\u201cThe Easier the Better\u201d Preparation of Efficient Photocatalysts-Metastable Poly(heptazine imide) Salts","volume":"32","author":"Chen","year":"2017","journal-title":"Adv. Mater."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"110876","DOI":"10.1016\/j.materresbull.2020.110876","article-title":"Graphene Nanoplatelets with Low Defect Density as a Synergetic Adsorbent and Electron Sink for ZnO in The Photocatalytic Degradation of Methylene Blue under UV\u2013vis irradiation","volume":"128","author":"Mahmud","year":"2020","journal-title":"Mater. Res. Bull."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"138","DOI":"10.1089\/gtmb.2018.0150","article-title":"Association of Base Excision Repair Gene hOGG1 Ser326Cys Polymorphism with Susceptibility to Cervical Squamous Cell Carcinoma and High-Risk Human Papilloma Virus Infection in a Chinese Population","volume":"23","author":"Chen","year":"2019","journal-title":"Genet. Test. Mol. Biomark."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"e2200128","DOI":"10.1002\/advs.202200128","article-title":"Proton-Driven Transformable 1O2 -Nanotrap for Dark and Hypoxia Tolerant Photodynamic Therapy","volume":"9","author":"Chen","year":"2022","journal-title":"Adv. Sci."},{"key":"ref_28","first-page":"294","article-title":"Stabilization of 3D\/2D Perovskite Heterostructures Via Inhibition of Ion Diffusion by Cross-linked Polymers for Solar Cells with Improved Performance","volume":"8","author":"Luo","year":"2023","journal-title":"Nat. Energy"},{"key":"ref_29","first-page":"100194","article-title":"Fabrication of Graphene Modified CeO2\/g-C3N4 Heterostructures for Photocatalytic Degradation of Organic Pollutants","volume":"12","author":"Zhu","year":"2023","journal-title":"Chin. J. Struct. Chem."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"169496","DOI":"10.1016\/j.cej.2025.169496","article-title":"Photocatalysis over CdS Quantum dots\/oxygen Doped g-C3N4 Z-scheme Heterojunction: Revealing the Synergistic Effects of Quantum Confinement Effect, Defect Engineering, and Z-scheme Mechanism","volume":"524","author":"Lv","year":"2025","journal-title":"Chem. Eng. J."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"349","DOI":"10.1016\/j.apcatb.2019.01.069","article-title":"Solid salt confinement effect: An Effective Strategy to Fabricate High Crystalline Polymer Carbon Nitride for Enhanced Photocatalytic Hydrogen Evolution","volume":"246","author":"Xu","year":"2019","journal-title":"Appl. Catal. B Environ."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"e2409352","DOI":"10.1002\/smll.202409352","article-title":"Revealing the Nature of Cyano Groups Modified K, O Codoped Graphitic Carbon Nitride Toward Optimized Photocatalytic H2 and H2O2 Evolution","volume":"21","author":"Ren","year":"2025","journal-title":"Small"}],"container-title":["Nanomaterials"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2079-4991\/16\/8\/489\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,4,20]],"date-time":"2026-04-20T12:30:50Z","timestamp":1776688250000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2079-4991\/16\/8\/489"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,4,20]]},"references-count":32,"journal-issue":{"issue":"8","published-online":{"date-parts":[[2026,4]]}},"alternative-id":["nano16080489"],"URL":"https:\/\/doi.org\/10.3390\/nano16080489","relation":{},"ISSN":["2079-4991"],"issn-type":[{"value":"2079-4991","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,4,20]]}}}