Studies On Phocatalytic Performance And Mechanism Of The Modified Graphitic Carbon Nitride

The development of non-toxic,efficient,and low-cost methods in producing clean and renewable energy to replace the traditional fossil energy has become a hot topic.Among various strategies,converting solar energy into chemical energy through photocatalysis technology has been considered to be one of the most effective ways in solving the energy and environmental problems.The design and synthesis of efficient catalysts is important in photocatalysis.Graphitic carbon nitride（g-C3N4）,owning excellent photoactivity,outstanding stability,low cost and non-toxicity,has been widely studied and applied as a typical non-metal n-type semiconductor in the field of photocatalysis.In addition,it holds a suitable band gap of ca.2.7 e V with strong visible light responsive range.However,traditional bulk g-C3N4 usually possesses low specific surface area,high charge carrier recombination rate,narrow visible light response range,poor electrical conductivity,which strongly limit its practical applications.The modification of g-C3N4 has been demonstrated to be effective in enhancing its photocatalytic activity by improving its visible light absorption capacity,reducing the recombination rate of photo-generated electron-hole pairs and accelerating the charge transfer efficiency.In addition,the research on the photocatalytic reaction kinetics of g-C3N4 is still limited.The deep understanding on the charge dynamics in g-C3N4 can be important in the design and preparation of g-C3N4 photocatalysts with high catalytic activity.In this thesis,a series of modification strategies on g-C3N4,including the morphology improvement,element doping,and metal single-atom co-catalysts deposition,have been adopted in improving the photocatalytic activity of g-C3N4.In addition,the charge dynamics in the modified g-C3N4 systems were revealed in detail by using the ultrafast time-resolved spectroscopy.Specific findings and results are as follows:（1）Controllable preparation and characterization of P-doped ultrathin hollow gC3N4 nanosphere（P/UH-CNS）photocatalysts for efficient generation.Herein,a phosphorus（P）vapor assisted synthetic strategy was employed to fabricate the P-doped hollow g-C3N4 photocatalysts with ultrathin shell structure（< 25 nm in thickness）.The doping of P and the compression of shell thickness of the hollow g-C3N4 were induced simultaneously by the P vapor during the heating process.The as-prepared P-doped ultrathin hollow g-C3N4 sphere（P/UH-CNS）photocatalysts exhibited enlarged surface area and light responsive range,and improved charge transportation efficiency by suppressing the charge recombination and self-trapping within g-C3N4.These resulted in a high photocatalytic hydrogen evolution rate of 9653 μmol h-1g-1.The charge dynamics in this P/UH-CNS system was revealed in detail by using the ultrafast timeresolved spectroscopy.（2）Controllable preparation,characterization and photocatalytic hydrogen production performance of Pt single atom-supported mesoporous g-C3N4（Pt1/g-C3N4）.A series of Pt1/g-C3N4 photocatalysts with different contents of Pt loading were prepared by a liquid phase method using chloroplatinic acid as the precursor.The physical and chemical properties of the catalyst were characterized.The loading of Pt single atoms can effectively reduce the recombination rate of photo-generated charges in g-C3N4,thereby prolonging the lifetime of photo-generated carriers.As a result,the optimal Pt1/g-C3N4 catalyst showed excellent hydrogen production performance（2611μmol h-1g-1）and stability under visible light irradiation.