Study On The Construction Of Graphite-like Phase ?-conjugated Heterostructure And Its Photocatalytic Performance

The two increasing challenges in energy demands and environmental concerns due to the consumption of fossil fuels have invigorated growing awareness.Among the various techniques used to solve the problems,photocatalysis technology has gained considerable attention for the high effciency and environmental friendliness.As a lightweight mental-free semiconductor photocatalyst,graphite carbon nitride?g-C₃N₄?has elicited ripples of excitement in the research communities due to its low cost,non-toxicity,high physicochemical stability and good photocatalysis performance.However,there are several shortcomings of bulk g-C₃N₄,including short electron-hole lifetime,weak visible light absorption and high exciton binding energy,which limit its practical application.In this thesis,graphite-like?-conjugated structure photocatalysis materials were constructed to regulate energy band,expand the visible light absorption range and prolong the lifetime of photogenerated carriers for efficient photocatalytic hydrogen evolution.Several aspects content are included as following:?1?The preparation and the photocatalytic hydrogen production performance of?-conjugated carbon-doped graphite carbon nitride.?-conjugated carbon doped graphite carbon nitrides?UCN?were prepared with a simple one-step thermal polymerization method by co-polymerization of urea and 2,4,6-triaminopyrimidine?TAP?.The obtained products were characterized by XRD,TEM,XPS,etc.The photocatalytic H₂ production of the as-prepared photocatalysts were obtained by visible light irradiation.The results showed that TAP was successfully incorporated into g-C₃N₄,and the carbon-rich pyrimidine formed a large?-conjugated with the triazine ring to form carbon self-doped graphite carbon nitride.Before and after modification,the crystal structure and morphology of UCN-x were basically constant and the products showed a lamellar structure.The modified photocatalyst has a hydrogen production rate of up to 57?mol·h^-1,which is four times that of pure graphite carbon nitride.The UV-Vis diffuse reflectance spectroscopy and electrochemical experiments showed that the copolymerization of aromatic heterocyclic TAP and the doping of carbon atoms could effectively extend the?-conjugated system of g-C₃N₄,reduce the forbidden band width and regulate the energy band structure of g-C₃N₄.Therefore,the photocatalysis activity was enhanced due to the expanding visible light absorption,and the increase of the transmission efficiency of photo-generated carriers.?2?The preparation and the photocatalytic hydrogen production performance of TiO₂@UCN heterojunction.The TiO₂@UCN type II heterojunction formed by the growth of?-conjugated carbon-doped graphite carbon nitride?UCN?overlayers on the TiO₂ nanosheets.The lattice fringes of the TiO₂ nanosheets are consistence with the?101?plane of the anatase phase TiO₂.The UCN nanosheets are well wrapped around the TiO₂ nanosheets based on the results of XRD,TEM,and FT-IR.The photocatalytic hydrogen production test results show that the optimized type II heterojunction exhibits better hydrogen production performance under both visible light irradiation and full spectrum irradiation.The average H₂ production rate of TiO₂@UCN-30 was four times than that of TiO₂@UCN-0.The photocurrent intensity of TiO₂@UCN heterojunction increases and the fluorescence intensity decreases.The results indicate that the separation rate of the photo-generated carriers is improved and the lifetime of them is prolonged due to the good interfacial interaction between TiO₂ and UCN.The synergy between the two components effectively inhibits the reorganization of photo-generated charge and accelerates electron transport for efficient photocatalytic hydrogen evolution.?3?The preparation and the photocatalytic hydrogen production performance of PTI-GCN-PDI ternary heterophase junction.In order to further promote the interfacial transfer of photogenerated charges,a ternary heterophase junction photocatalyst PTI-GCN-PDI has been synthesized.Firstly,a PTI/ZnO heterojunction was prepared with the molten salt method by using cyanamide as precursor.Then the PTI was obtained by washing PTI/ZnO heterojunction to remove the ZnO quantum dots.Finally,the PTI-GCN-PDI ternary heterophase junction was synthesized with thermal polymerization method by using PTI as the basis material,urea as the precursor and pyromellitic dianhydride?PDI?as the electron intermediator.The obtained products were characterized by XRD,FESEM,BET,etc.The results showed that the shape of the obtained composite was a coiled sheet structure.Compared to the flocculent binary composite,its specific surface area was reduced.The test of photocatalytic hydrogen production under visible light showed that the modified optimized sample had a hydrogen production of 30?mol per hour,which was 3.75 and 3 times that of pure carbon nitride and non-PDI,respectively.The photocurrent test shows that the photocurrent intensity and the photocarrier separation rate of the ternary heterojuction increases.The UV-Vis diffuse reflection shows that the ternary heterophase junction broadens the visible light absorption region and enhances visible light absorption.