Organic conjugated polymers have received extensive attention due to their unique electronic properties. However, there have been relatively few reports on the dark photocatalytic reactions utilizing organic conjugated polymers. Herein, we report the successful synthesis of an organic conjugated polymer based on poly (heptazine imide) nanocrystals (CNNCs) for H₂O₂ evolution and biomedical applications using a simple salt molten method and sonication–centrifugation process. The results show that these colloid CNNCs have the characteristics of photogenerated electrons accumulation and realize dark photocatalysis with high reducibility under visible light irradiation. Notably, these accumulating photogenerated electrons can reduce O₂ in darkness to produce H₂O₂. In addition, cytotoxicity tests were conducted and it was found that H₂O₂ produced under dark conditions could oxidize L-arginine (L-Arg) to NO, which effectively killed tumors in the dark. This work provides an important strategy to construct organic conjugated semiconductor nanocrystals and applying them to future energy and biomedical fields.

The diffusion, adsorption/desorption behaviors of water molecules and hydrogen molecules are of great importance in heterogeneous photocatalytic hydrogen production. In the study of structure–property–performance relationships, nanoconfined space provides an ideal platform to promote mass diffusion and transfer due to their extraordinary properties that are different from the bulk systems. Herein, we designed and prepared a nanoconfined CdS@SiO₂-NH₂ nanoreactor, whose shell is composed of amino-functionalized silica nanochannels, and encapsulates spherical CdS as a photocatalyst inside. Experimental and simulated results reveal that the amino-functionalized nanochannels promote water molecules’ and hydrogen molecules’ directional diffusion and transport. Water molecules are enriched in the nanocavity between the core and the shell, and promote the interfacial photocatalytic reaction. As a result, the maximized water enrichment and minimized hydrogen-occupied active sites enable photocatalyst with optimized mass transfer kinetics and localization electron distribution on the CdS surface, leading to superior hydrogen production performance with activity as high as 37.1 mmol·g⁻¹·h⁻¹.