Carbon nanospheres - A dark support for effective loading of Pt catalyst and protection of dye sensitizer in photocatalytic hydrogen evolution

Well-dispersed carbon nanospheres (CNS) synthesized from hydrothermal treatment of glucose solution was employed as the support for Pt catalyst in photocatalytic hydrogen evolution using Rose bengal photosensitizer under visible light. By varying pH, carbon spheres and CNS of two distinct sizes of 2-5 μm and 200 nm, respectively, could be obtained. Pt nanoparticles were evenly loaded onto CNS via a chemical reduction method. It was found that the introduction of dark colored CNS conferred remarkable enhancement in photocatalytic activity of hydrogen evolution compared to the systems using other supports such as layered double hydroxide and SiO₂ or in the absence of any support. This can be attributed to the dual roles of CNS in both dispersing Pt nanoparticles and protecting the photosensitizer from rapid photodegradation. With 1.0 wt% Pt, the Pt/CNS system showed 48 times increase in hydrogen evolution compared to the system without the support. The total turnover number for Pt/CNS with 0.5 wt% Pt was as high as 2371 in a single run. In addition, this system affords high stability with minimal changes in hydrogen evolution activity over at least four cycles.