Metal-free carbon dots toward bio-green hydrogen evolution via photocatalysis

Hydrogen (H₂) has emerged as a therapeutic agent with potent antioxidative and anti-inflammatory effects, offering promising applications in the treatment of neurological and cardiovascular diseases. However, the development of controllable, clean, and in situ H₂ generation strategies remains a significant challenge in biological systems. Herein, we report a metal-free carbon dot (CD) based photocatalyst synthesized via thermal polymerization of uracil, is capable of efficient and biocompatible photocatalytic H₂ evolution. The photocatalyst exhibits a well-defined structure composed of interconnected C-N five-membered rings, where nitrogen atoms serve as active sites for proton adsorption and reduction. Under simulated physiological conditions, the photocatalyst enables H₂ production without water oxidation or oxidative side reactions, thereby maintaining the ion concentration and pH stability. A H₂ evolution rate of 73.87 μmol h^-1 g^-1 is achieved, and tunable H₂ release is realized by varying the catalyst dosage, illumination time, and light intensity. Importantly, cytocompatibility tests reveal an enhanced cell viability of up to 165.6%, demonstrating the excellent biocompatibility and the potential of this system as a bio-green platform for therapeutic H₂ delivery.