| As a clean energy source,hydrogen energy provides a promising strategy to solve the problems of energy crisis and environmental pollution in the 21st century,which can be obtained by photocatalysts.Two-dimensional materials have attracted enormous attentions due to their special structure and properties,including metal-free conjugated polymer with a band gap of about 2.7 e V,good visible light response,and suitable conduction band position for hydrogen reduction.However,the weak absorption of light and poor separation performance of photo-generated electrons and holes limit its application in the field of photocatalytic hydrogen production.In this thesis,the g-C3N4 was synthesized by thermal polycondensation,which was further modified by interlayer delamination and constructing heterojunction.As a result,the modified g-C3N4 composite obtained 1～3 times higher hydrogen production rate than pure g-C3N4.The specific content includes:（1）Both of the specific surface area and the light absorption were enhanced after interlayer exfoliation.Herein,a yellow powder g-C3N4 was synthesized by thermal polycondensation,and then thin layer g-C3N4 nanosheets was obtained by liquid-phase hydromechanical ultrasonic exfoliation.According to the results of atomic force microscope,the thickness of exfoliated g-C3N4 nanosheets is about 10～15 atomic layers.The results of off-line gas chromatography showed that the hydrogen production rate was 0.426 mmol h-1 g-1.（2）In order to reduce the recombination of photo-generated electrons-holes pairs and improve the photocatalytic hydrogen production performance of g-C3N4nanosheets,few layers of phosphorene with metal-free two-dimensional layered structures were prepared by mechanical ultrasonic peeling,and then 2D/2D FBP/g-C3N4 traditional type II heterojunctions with Van Der Waals force as the binding force were fabricated by mechanical stirring.The accelerated separation and transfer of photo-generated electrons and holes improves the photocatalytic hydrogen production performance.Finally,the hydrogen production efficiency of 2D/2D FBP/g-C3N4 was doubled(1.08 mmol g-1 h-1)compared to pure g-C3N4.（3）In order to further improve the photocatalytic hydrogen production performance of g-C3N4 nanosheets,a 0D/2D/2D ternary heterojunction was proposed.Not only the 2D/2D heterojunction structure can accelerate the transfer efficiency of photo-generated electrons and holes,but also the additional of quantum dots can increase the specific surface area and active sites.All of these were conducive to accelerate the separation and transfer of photo-generated electrons and holes,thereby improving the photocatalytic hydrogen production and photoelectrochemical performances.As a result,0D/2D/2D Cd Se QDs/WS2/g-C3N4 heterojunction photocatalyst has a hydrogen production rate of 1.29 mmol g-1 h-1,which is three times higher than pure g-C3N4. |
