The Design Of Black Phosphorus Based Nanocomposites For Photocatalytic Water Splitting

The emergence of energy crisis and environmental pollution has become a common problem faced by mankind,the development of sustainable clean energy to replace fossil fuels is a promising strategy to solve the present dilemma.The advent of photocatalytic technology provides a potential strategy to convert sustainable solar energy into convenient and efficient chemical energy.Particularly,photolytic water splitting into hydrogen（H₂）have a potential promising to solve the current energy dilemma.Hydrogen energy is a high combustion calorific value,zero carbon emission,storable and transportable energy source,and H₂ can release more energy through direct combustion,and the final product is water,which will not cause any harm to the environment.Therefore,the primary task is the exploitation of desirable semiconductor materials with the advantages of high efficiency solar energy conversion,long time stability,low price and earth-abundant.Phosphorus is non-toxic,environmental-friendly,with little risk to human health or natural environment,and abundant in the earth’s crust.Among the several phosphorus allotropes,black phosphorus（BP）has attracted much attention and considered as a desirable material for photocatalytic hydrogen evolution owing to its high carrier mobility(≈1000 cm²v^-1s^-1)and conductivity,tunable band gap（0.3-2.0 e V）and excellent optical absorption properties.However,the rapid recombination of stimulated carriers and holes in ultrathin BP nanosheets limits its practical application in photocatalytic reactions.The composite photocatalysts composed of two or more semiconductor materials is considered as a promising strategy,which can effectively promote the separation and migration of photo-induced electrons and holes,thus enhance the photocatalytic activity.In this paper,several heterostructures were designed and constructed by 2D BP and another semiconductor,the composite photocatalysts exhibited enhance photocatalytic activity and durability.A series of characterization were carried out to explore the morphology generated carriers,band structures and structure of samples,and reveal the reaction mechanism.The main research contents and methods of this thesis are as follows:（1）A novel 2D-2D BP/Zn In₂S₄ composite photocatalyst was prepared via a facile,safe and effective method.The larger face-to-face interface contact area between 2D BP and Zn In₂S₄ provides more carrier transfer channels,thus improve the charge mobility.Additionally,the strong interlayer interaction of two components facilitates the separation and transportation of photogenerated charges on Zn In₂S₄ to the 2D BP surface through the interface.With the irradiation of simulated visible light（λ>420 nm）,the optimal hydrogen evolution rate of BP/Zn In₂S₄ heterojunction is 2378μmol h^-1.The electrochemical performances suggested that the BP/Zn In₂S₄ heterostructure can effectively promote the separation and migration of photogenerated carrier-hole pairs.（2）Based on the self-assembly and recrystallization of PDINH in aqueous solution,self-assembled PDINH supramolecular was in situ grown on the surface of 2D BP,thus constructed a metal-free 2D-2D BP/PDINH heterostructure.The compact contact interface between BP and PDINH plays an important role in promoting the excited charge transfer,and its optimal hydrogen evolution efficiency is about 5.9 times that of bare 2D BP.In addition,self-assembled PDINH forms a dense protective film on the surface of BP,which can effectively prevent the oxidation of BP.The carrier transfer efficiency and catalytic activity of the composites were investigated,and the corresponding reaction mechanism of hydrogen evolution was proposed.（3）An artificial 2D-2D Z-scheme BP/α-Fe₂O₃ heterostructures were prepared by a simple electrostatic coupling process.Benefited from the complementary synergism between BP andα-Fe₂O₃,2D BP was used as hydrogen evolution photocatalyst,whileα-Fe₂O₃ was acted as oxygen evolution photocatalyst.The reduction and oxidation of water were realized on the CB of BP and the VB ofα-Fe₂O₃,respectively.The BP/α-Fe₂O₃ heterostructure was a cheap and effective photocatalyst for simultaneous H₂ and O₂ generation.Under simulated visible light irradiation,the optimal O₂ and H₂evolution rates of this photocatalytic system are 0.29 and 0.59μmol h^-1,respectively.