Transition Metal-Assisted Synthesis Of Red Phosphorus Photocatalysts And Their Performance And Mechanism Investigation In Hydrogen Evolution

Hydrogen is regarded as the ideal energy to replace traditional fossil fuels due to its advantages of recycling,safe,environmentally friendly,and high energy density.Photocatalytic water splitting technology is deemed an effective way of producing hydrogen energy,and the development of efficient photocatalysts is the key.As a novel elemental semiconductor photocatalyst,red phosphorus（red P）possesses an adjustable bandgap with strong visible light absorption ability,which makes it a promising candidate for photocatalytic hydrogen evolution（PHE）from water.The morphology,crystallinity,visible light absorption capacity,and photogenerated charge utilization efficiency are important factors in affecting the photocatalytic performance of red P.Among various modification strategies,reasonable modification of the physical and chemical properties of red P can be an important aspect.In this thesis,the crystal engineering and structural engineering of red P photocatalysts were investigated by performing a transition metal-assisted chemical vapor deposition（CVD）strategy,which effectively improved the PHE performance of red P.In addition,the photocatalytic mechanism of the as-prepared red P was elucidated by using ultrafast spectroscopy.The main findings and results of the studies are as follows:（1）Hetero-phase dendritic elemental red P for visible light photocatalytic hydrogen generation.The bismuth-assisted CVD method was employed to synthesize highly active dendritic red P（DRP）photocatalysts with tailored morphological features and desired balance of crystal phases with intimate heterojunction.The resultant dendritic structure,which is composed of main stems spiked with lateral branches,has distinctive crystal phases.Hittorf’s phase is formed in the main stems while the branches are made of the fibrous phase.Band position analyses confirm the more energetic conduction band in the fibrous phase while Hittorf’s phase possesses deeper valance band energy.As both crystal phases are junctioned effectively at the stem-branch intersection,the alignment of band energy between the two crystal phases facilitates the effective built-in forces for charge separation,which affords an enhanced PHE activity.In particular,we recorded a visible light PHE rate of 1280μmol g^-1 h^-1for the DRP,which is the highest activity compared to the previous reports on elemental photocatalysts.（2）Rod-like elemental red P photocatalyst for hydrogen evolution.The rod-like red P photocatalyst with high yield and regular morphological structure was prepared by a nickel-assisted CVD strategy.The results show that nickel effectively induced the uniform growth of rod-like red P with smaller particle size,which endowed it with a higher specific surface area with more active sites for photocatalytic reaction.On the other hand,the surface-modified small amount of nickel species could effectively extract the photogenerated charge carriers of red P and promote the charge separation efficiency,thereby improving the photocatalytic activity of hydrogen production from water.