The Construction Of Integrating Photocatalyst Under Mo-dopamine System And Investigation Of Photocatalytic Hydrogen Production From Water

The continuous consumption of fossil energy and increasingly serious environmental problems such as global warming and pollution make the application of energy transformation and sustainable development attract great attention.Obtaining hydrogen energy from solar energy directly is regarded as one of the most promising energy conversion methods.However,most of the researches in this field are still in the stage of laboratory development due to low catalytic efficiency and could not be applied in factory.In this thesis,we introduced molybdenum-dopamine（Mo-DA）system to synthesizing process in order to solve problems such as semiconductor photogenerated charge recombination.The non-noble metal molybdenum-based multi-catalyst system was established on the basis of titanium dioxide（Ti O₂）,graphitic carbon nitride（g-C₃N₄）and other optimized photocatalysts.At the same time,the mechanism of photocatalytic reaction was further explored through theoretical simulation and experimental results.The details are as follows:1.We prepared three-dimensional hierarchical flower-like anatase Ti O₂ by solvothermal process.Further coordination and polymerization process and heat treatment achieved the conversion from Mo-PDA to molybdenum carbide（Mo₂C）nanoclusters inserted in graphite carbon layer.Mo₂C owns similar electronic structure of platinum（Pt）so it acts as an active center of the reaction and a cocatalyst at the same time.It is proved that the recombination of photogenerated charges is significantly reduced while graphite carbon layer contributes to rapid transfer of photogenerated charges.Theoretical calculation shows heterojunction structure is favorable for charge transfer and decrease of charge recombination.Under UV light,the photocatalytic activity of heterostructure is 21 times higher than normal Ti O₂ and achieves high stability.2.Two-dimensional g-C₃N₄ nanosheets with high BET surface area were prepared and introduced to the Mo-dopamine system.Mo-PDA structure of the precursor was converted to molybdenum sulfide/carbon structure by sulphuration process.Surface photovoltage（SPV）analysis illustrates that the carbon layer reversed the charge distribution on the surface of the catalyst.Basing on charge density difference and work function calculation results,the photogenerated electrons will move to the surface of Mo S₂ part after adding Mo S₂ and Mo S₂ acts as a cocatalyst.The coordination structure can effectively reduce the size of Mo S₂.The integrating g-C₃N₄@Mo S₂/C catalyst owns photocatalytic activity of 712.90μmol g^-1 h^-1 under visible light.The apparent quantum efficiency（AQE）at 420 nm is 4.36%.It proves that Mo-Dopamine system is suitable for different main photocatalysts and it is a universal strategy for in-situ synthesis.3.We synthesized boron-doped and nitrogen-defect carbon nitride（BCN）via mixture heat treatment.The reduction process achieved the regulation of band structure.Spectral analysis and photocurrent test further prove the advantages of BCN in charge transfer.The BCN photocatalyst shows better photocatalytic activity for oxygen generation after loading the cobalt hydroxide（Co（OH）₂）cocatalyst via impregnation method.Furthermore,BCN/Co（OH）₂ is applied as the oxygen evolution catalyst and combined with g-C₃N₄@Mo S₂/C.The integrating Z-scheme heterojunction catalyst BCN/Co（OH）₂-CN@Mo S₂/C was obtained by electrostatic assembly approach.Under UV light,the catalyst still exhibits photocatalytic hydrogen production activity in pure water,which indicates that the introduction of molybdenum-polydopamine system and the strategy of constructing heterojunction could ultimately achieve the water splitting without sacrificial agent.It also provides an effective solution for energy conversion.