The Preparation And Photocatalytic Properties Of The Transition Metal Sulfide/g-C₃N₄ Composites

With the development of global industry,the environmental pollution and energy shortage caused by the massive use of traditional fossil energy are getting worse.Therefore,there is an urgent need to develop and study new energy sources?green and renewable?to alleviate the current crisis.Hydrogen is the research hotspot of clean energy.The effective conversion from solar energy to hydrogen energy can be realized by using photocatalyst.Graphite carbon nitride?g-C₃N₄?has unique energy band structure and stable physical and chemical properties,which is widely used in the field of photocatalysis.However,due to its small specific surface area and the high recombination of photo-induced carriers,the performance of photocatalytic hydrogen production is greatly limited.In order to improve the performance of photocatalytic hydrogen production,it is usually necessary to adjust the morphology to increase the active site,and to use precious metals such as Pt to modify the cocatalyst.However,the precious metals is limited and expensive,so the non-noble metal co-catalysts modifing g-C₃N₄ becomes one of the hottest researches in the field of hydrogen production.The role of cocatalyst is mainly based on the abundant hydrogen reduction sites and efficient interfacial charge transfer.In this work,g-C₃N₄ nanosheets obtained by thermal oxidation etching is used as the substrate,and appropriate cocatalyst is used to improve its photocatalytic performance.The work is as follows:?1?The g-C₃N₄ nanosheets were prepared through the melamine by thermal polymerization and thermal oxidation,and a two-step hydrothermal method was used to prepare g-C₃N₄heterojunction modified by double metal sulfide?Fe-Ni-S?.The materials were characterized and analyzed by XRD,SEM,EDS,TEM,BET,XPS,FT-IR,UV-vis and PL.The hydrogen production activity of Fe-Ni-S/g-C₃N₄ nano-heterojunction was significantly enhanced by 52 times than that of pure g-C₃N₄ nanosheets.In addition,the enhancement mechanism of photocatalytic hydrogen production was also studied,which can be attributed to the fast transfer of photo-generated electrons produced by g-C₃N₄,promoting the separation of photo-generated carriers and holes,and extending the life of photonic carriers.Moreover,the particles of co-catalyst Fe-Ni-S were about150nm,and the prepared g-C₃N₄ nanosheets had relatively large specific surface area,so more active sites could be obtained,which are considered to be an important reason for enhancement of the photocatalytic performance.?2?In order to further improve the photocatalytic performance and accelerate the transfer of solid-solid?photocatalyst-cocatalyst?and solid-liquid?cocatalyst-liquid?interface charges,2D RGO-NiS₂ co-modified g-C₃N₄ nanosheets aerogel was synthesized by thermal oxidation etching-hydrothermal method-freeze-drying process.The characterization of materials was analyzed by XRD,SEM,XRD,TEM,XPS,FT-IR,BET,UV-vis,PL and electrochemical tests.The photocatalytic activity of RGO-NiS₂ co-modified g-C₃N₄ aerogel was 67 times that of pure g-C₃N₄nanosheets.In addition,the mechanism of the photocatalytic hydrogen production was also studied by electrochemical test,which can be attributed to the the fact that the bicocatalyst accelerates the charge transfer between the two interfaces,thus the life and efficiency of photogenic carriers effectively are extended.On the other hand,the 2D RGO-NiS₂ bicocatalyst synergy modified g-C₃N₄ nanosheets unique aerogel structure with larger specific surface area by freeze drying method,which provides more active sites.These make the photocatalytic performance is improved greatly.