The Steam Activation Route To G-C₃N₄ Nanomaterials For Photocatalytic Hydrogen Generation

Graphite phase carbon nitride?g-C₃N₄?,a new type of narrow band-gap inorganic polymeric semiconductor photocatalytic material,has outstanding characteristics such as low precursor price,simple preparation technology,good chemical stability,and outstanding photoelectron absorption performance.Recently,there have been strategic hotspots in the study field of photocatalytic hydrogen production technology.However,due to the narrow visible light response range of g-C₃N₄ materials and the high efficiency of photo-generated electron/hole pair recombination,the photocatalytic hydrogen production activity of g-C₃N₄under the induction of visible light still needs to be further improved.Therefore,in this thesis,g-C₃N₄ was synthesized in the different atmosphere of air,argon?Ar?gas and water vapor,and g-C₃N₄ nanosheets and nanoparticles were successfully prepared with improved efficiency of photocatalytic hydrogen production.Specific research work on photocatalytic hydrogen production includes the following three aspects:1.Facile one-step"polymerization-stripping"strategy toward g-C₃N₄ nanosheets.Precursor was used melamine?C₃H₆N₆?,and g-C₃N₄ nanosheets were successfully prepared by facile one-step"polymerization-exfoliation"strategy.The micro-molecular structure of the obtained g-C₃N₄ photocatalytic material and the photophysical and chemical properties of the material were analyzed by microscopic characterizations.It was found that not only the specific surface area was significantly increased,but also the photogenerated charges were separated and recombined quickly.The significant red shift in the light absorption edge of g-C₃N₄ caused by the high temperature,which naturally increased the visible light absorption range of g-C₃N₄.The performance of photocatalytic hydrogen production also reflect the improvement of the visible light absorption range.Among them,the sample prepared at 700^oC for 210 minutes has the best hydrogen production performance,which is 14 times higher than that of the pure sample prepared at 120 minutes at 550 ^oC.2.One-step steam activation strategy of guanidine hydrochloride precursor toward g-C₃N₄ nanosheets.The guanidine hydrochloride?CH₇ClN₃?was used as a precursor,and the sintering was conducted with protective atmosphere?Ar gas?and water vapor atmosphere to generate g-C₃N₄ nanosheets.g-C₃N₄ nanosheets with higher specific surface were successfully prepared by changing the atmosphere and temperature.The characteristics of the sample's crystal structure,chemical composition state,microstructural morphology,and optical absorption properties were tested by various characterization techniques analysis.The research found that g-C₃N₄ nanosheets were successfully prepared.Compared with the pure g-C₃N₄,the successfully prepared g-C₃N₄ nanosheets have a higher photocurrent response,and significantly reduced the recombination efficiency of photogenerated electron and hole pairs.By photocatalytic activity testing,the sample prepared at 600 ^oC has the best photocatalytic hydrogen production performance,and the hydrogen production reached 90.4?mol in 4 hours.It remained at 62.7?mol after 4 cycles of hydrogen production test and kept stable hydrogen production for 18 hours.3.Preparation of g-C₃N₄ nanomaterials by steam activation strategy of thiocyanuric acid.Using thiocyanuric acid?C₃H₃N₃S₃?as the precursor,a sulfur-containing g-C₃N₄photocatalytic hydrogen production material with a nanoparticles surface was prepared using different furnaces?muff furnace,tube furnace?and different atmosphere?air,Ar gas and water vapor?.By the means of XRD,IR,UV,XPS,SEM and TEM,the crystal structure,chemical composition state,optical absorption properties and apparent structure morphology of the prepared g-C₃N₄ material were analyzed.As a result,the g-C₃N₄ nanoparticle structure containing sulfur element was successfully prepared.The introduction of water vapor significantly improves the visible light response of g-C₃N₄ and reduces the charge transfer resistance.According to photocatalytic activity,g-C₃N₄ prepared under water vapor atmosphere had the largest photocatalytic activity,and the hydrogen production reached 149.8?mol in 4 hours.