Structure Modification And Surface Modification Of Graphite Phase Carbon Nitride And Its Photocatalytic Performance For Hydrogen Evolution

The massive environmental problems become an urgent need for clean and renewable energy in international society.With high energy density,recyclable use,environmental friendliness and no pollution,hydrogen energy is considered to be the most potential energy carrier to replace fossil energy.As an effective way to convert solar energy to hydrogen,the photocatalytic water splitting by using semiconductor materials is general reach consensus.g-C₃N₄has a suitable electronic band structure for hydrogen evolution,the absorption response for the visible light,high stability,pollution-free and simple synthesis,has become a hotspot material in research of photocatalytic hydrogen evolution.To overcome the shortcomings in g-C₃N₄such as weak photo-generated carrier transfer,narrow visible light response range and low specific surface area,this paper mainly focuses on that the physical mechanical pressure act on g-C₃N₄,ultrasonic exfoliate block g-C₃N₄and trace precious metal load on block g-C₃N₄.The specific research contents and conclusions of this paper are as follows:（1）For its long bond length and weak bond energy,the N-C₃bridge bond in g-C₃N₄tri-triazine unit is easily broken.The photoelectric performance of calcined g-C₃N₄with high temperature from urea is pressure treated under 5-20 MPa is discussed.The exposure of C and N atom from broken N-C₃bridge give rise to effective water molecules adsorption for photo-generated electrons transfer,extendπelectron delocalization and broaden the light absorption band edge.With the content at 2%of co-catalyst compared with catalyst,under the pressure of 20MPa,the optimal photocatalystic hydrogen evolution rate reach 0.71 mmol/m²/h,17times than that of the untreated sample,and the apparent quantum efficiency at 365reach 6.53%,2.49 times than that of the untreated sample.（2）In considering the common method to prepare g-C₃N₄nanosheets,such as thermal exfoliating or solvent exfoliating.In this paper,the pressure treated and untreated g-C₃N₄samples are subjected to ultrasonic exfoliating treatment at the power of 1000 W.After exfoliating,the specific surface area of the samples increase significantly,the absorption of visible to near-infrared spectrum is widened,and the expandedπelectron delocalization and quantum size effect promote the photogenerated electron migration.With the content at 2%of co-catalyst compared with catalyst,the photocatalytic hydrogen evolution rate of the pressure treated and then high-power exfoliating sample reach to 3.2 mmol/h/g,which is 1.33 times than that of the pressure treated sample,and after high-power exfoliating,the photocatalytic hydrogen production rate of g-C₃N₄under high-power exfoliating sample reach to 2.0 mmol/h/g,1.25 times than that of g-C₃N₄.（3）As a co-catalyst for g-C₃N₄photocatalytic hydrogen evolution,noble metal Pt has received wide attention due to its low hydrogen evolution overpotential,provide more active sites and larger work function.However,Pt precursor ions can not be fully reduced and are more likely to form Pt O.In this paper,the pressure treated g-C₃N₄surface is loaded by Au and Pt/Pt O nanoclusters via chronological photodeposition of auric and platinic precursors.The localized surface plasmon resonance（LSPR）effect of Au nanoparticles increases the metallic Pt content through photoreduction process,promote the transportation of photo-generated electrons and broaden the light absorption range from visible to near infrared.With the trace content at 0.6%of Au-Pt/Pt O,the photocatalytic hydrogen production rate under simulated sunlight irradiation reache to 2.5 mmol/h/g.The apparent quantum efficiency under the 420 nm excitation is estimated at 1.92%.