Intramolecular built-in electric field enhanced polymerized nitrogen-carbon homojunction π*-electron delocalization enrichment promotes photocatalytic uranium (VI) reduction

The donor-acceptor (D-A) structure in conjugated systems enhances photogenerated carrier separation efficiency due to π* electron delocalization resulting from π-π interactions. This study reports a conjugated molecular carbon-nitrogen homojunction (CNH) with inherent π* electron transitions, which intrinsically enriches electron-hole pairs in the energy band region via its built-in electric field. CNH's intermolecular π-π stacking promotes efficient U(VI) reduction by boosting carrier generation and separation. Compared to CNNH, formed by temperature-controlled thermal polymerization of melamine and urea, the introduction of -NH2 disrupts the 3-s-heptazin ring in CNH's conjugated system. Heptazine integrity directly affects π-π* electron enhancement and transition, leading to a significant decrease in U(VI) reduction efficiency. Specifically, CNH exhibits optimal efficiency, reducing U(VI) by 99.6% within 60 minutes. This work emphasizes the significance of strong built-in electric fields generated through intramolecular π-π stacking, stimulating π-π* transitions, and enriching photogenerated π* electrons in carbon-nitrogen polymers, ultimately improving U(VI) photoreduction.