Photocatalytic water reduction using a polymer coated carbon quantum dot sensitizer and a nickel nanoparticle...

Hydrogen gas is produced photocatalytically using 470 nm light, PVP-coated carbon quantum dots (CQDs) as the photosensitizer, and nickel nanoparticles (NiNPs) as the catalyst. The effect of the amount of polyvinylpyrrolidone (PVP) on the ability of the CQD/NiNP composites to catalyze proton reduction was studied. A maximum of 330 mmols H₂/g CQD is produced using 68 μg ml^-1 of CQDs and 6 μg ml^-1 of NiNPs, with activity persisting for 4 h when 20 wt%-PVP-coated CQDs were used. The H₂ production quantum yield under these conditions is 6%. It was found that composites having higher weight percent PVP had decreased rates of H₂ production, but increased duration. Increasing the weight percent of PVP coating also increases the fluorescence quantum yield of CQDs. Fluorescence quenching titrations reveal that H₂ production could occur by either a reductive or oxidative quenching mechanism. The nanomaterials, prepared using simple methods, are used as the photosensitizer and catalyst in the proton reduction system that operates using visible light.