Preparation Of Modified G-C₃N₄ As Photocatalyst And Study Of Photocatalytic Performance

Photocatalytic technology of semiconductor is an effective way to solve problems about the energy crisis and organic pollution.Graphite carbon nitride?g-C₃N₄?,a non-metallic semiconductor material,is similar to the layered structure of graphene.g-C₃N₄have been widely used due to superior thermal and chemical stability and the proper band gap energy?2.7 eV,acrossing the window of the redox of water?that allows it to directly utilize the visible light.However,like most other semiconductor materials,the pure g-C₃N₄ has a low efficiency of photocatalytic activity in the photocatalytic process,due to a fast recombination rate of the photogenerated electron hole pairs.That is,although the semiconductor catalyst g-C₃N₄ can absorb visible light,the utilization of visible light is not high.The study found that:?1?the element doping can modify the electronic band gap of the catalyst and enhance the light absorption;?2?the coupling with other semiconductor materials can reduce the recombination of photogenerated electrons and holes;?3?Changing the morphology of g-C₃N₄ can effectively increase the active sites of the surface and increase the photocatalytic activity of the catalyst.Among other functional materials,red phosphorus?RP?can been seen as doping elements to form impurity levels and to improve the catalytic performance.Moreover,the band gap of red phosphorus is 1.8 eV,which means that the red phosphorus has good absorption for visible light and photocatalytic performance.So it can also couple other semiconductors to form heterostructure,which can suppress the recombination of photogenerated electrons and holes.Therefore,red phosphorus can be combined with g-C₃N₄ as a non-metallic doping element and as a candidate of narrow band gap semiconductor material for the formation of heterostructures.Therefore,based on the above analysis,this master's thesis firstly studied the differences in photocatalytic performance of g-C₃N₄ with different morphologies,and then synthesize the crystalline P nanostructures compositing with P-doped g-C₃N₄,and explored the photocatalytic performance.The main contents of the paper are summarized as follows:?1?Granular g-C₃N₄ was prepared by high-temperature calcination method,using melamine as a precursor.Nanosheets g-C₃N₄ was prepared by sonication.Then,the acidified melamine was directly calcined to prepare nanofibe g-C₃N₄.The photocatalytic degradation ability of g-C₃N₄ with different morphologies was studied.?2?The amorphous red phosphorus?P?and g-C₃N₄ were vacuum sealed in quartz tube and calcined at elevated temperature.With this simple method,P has been doped into g-C₃N₄ and P nanostructures were directly grown on g-C₃N₄ to form heterostructures.By adjusting the mass ratio of red phosphorus to g-C₃N₄ in the precursor and the temperature of calcination,the optimum ratio is applied to photocatalysis.?3?The mechanism of photocatalytic performance and performance improvement of the composite P@P-g-C₃N₄ was studied.The superior performance of the composite samples result from efficient absorption of visible light and efficient separation of photogenerated electrons and holes.Firstly,although nanosheets and nanofiber-like of g-C₃N₄ have improved performance compared to the previous bulk g-C₃N₄ sample,they do not well inhibit recombination of photogenerated electrons and holes.So the improvement of photocatalytic performance is not very obvious.Then,the photocatalytic activity for composites of different mass ratios was evaluated by the photodegradation of RhB in aqueous solution and H₂ production activities under visible light irradiation.When the temperature is 500°C and the mass ratio is 15%,the composites possess the optimum photocatalytic performance.Meanwhile,the morphology of g-C₃N₄ is preserved,and nanorods of red phosphorus forms and contacts well with g-C₃N₄.That is,the addition of appropriate red phosphorus forms impurity level and heterostructure to improve the photocatalytic performance of g-C₃N₄.Family,in order to study the distinct mechanism of photocatalytic performance improvement,we tested the reproducible photocurrent responses of samples,make trapping experiments to distinguish the roles of the reactive oxygen species?ROS?in degradation of RhB and discussed the reaction mechanism with the assistant of density functional theory?DFT?calculations.The results show that the narrowing band gap promotes the absorption of visible light,and the presence of the heterostructure promotes the separation and transfer of photogenerated electrons and holes.