Study On The Preparation Of Graphitic Carbon Nitride And Its Photocatalytic And Field Emission Properties

With the process of industrialization and urbanization,environment pollution and energy crisis have put a great threat to our future development.The semiconductor photocatalytic technology can efficiently utilize the solar energy to generate useful chemical resources as well as ameliorate the environmental degradation.As a novel metal-free photocatalyst,the graphitic carbon nitride（g-C₃N₄）possesses many merits such as excellent physical and chemical properties,good biocompatibility and proper bandgap（～2.7e V）.Besides,it can be large-scale synthesized by a simple thermal polycondensation method.Due to these advantages,the g-C₃N₄shows great potential in photocatalytic and field emission fields.In this paper,we use a simple hydrothermal/calcination heat-treatment approach to prepare the graphitic carbon nitride/graphene composite（g-C₃N₄/r GO）and non-metal element doping g-C₃N₄tubes.We also use various analytic methods to characterize its structural information and relevant properties.The photocatalytic property of the samples was evaluated by photodegradation of Rh B solution under visible light.Besides,the field emission property was also tested by a field emission station.The main experimental content and research conclusion are listed as follows:（1）Firstly,graphene oxide（GO）was fabricated by Hummers approach;Then the GO was mixed with melamine in a certain proportion,and the final product g-C₃N₄/r GO was achieved by a simple hydrothermal/calcination method.Further research demonstrated that the introduction of r GO did not change the crystal structure of g-C₃N₄.However,the bandgap gradually decreased with the increase of r GO concentration,which was caused by the fast transfer of photogenerated electrons in g-C₃N₄.The EIS test also indicated that the transfer resistant of charge carriers in g-C₃N₄/r GO was significantly decreased.Results of photocatalytic tests showed that the photocatalytic efficiency of g-C₃N₄/r GO was dramatically enhanced,especially for g-C₃N₄/r GO-10 sample,the kinetic constant was 3.2 times larger than that of g-C₃N₄.（2）Sulfur-doped g-C₃N₄ tubes（CN-S）were synthesized by hydrothermal/calcination approach,using melamine and sulfuric acid as starting materials.Results demonstrated that the pre-treatment of melamine did not change the crystal structure of CN-S samples.The bandgap of the samples enlarged with the increased concentration of sulfuric acid,from 2.72e V of g-C₃N₄ to 2.81e V of CN-1.0S sample.Besides,the separation efficiency of photogenerated electron-hole pairs in CN-S samples was significantly promoted.In the photocatalytic test,CN-S samples showed excellent photocatalytic activity,especially for CN-0.5S sample,the decolorization rate of Rh B reached up to 88.4%in only 4min reaction.Besides,the CN-0.5S sample also showed remarkable field emission property,the E_to and E_thrwere 0.31 and 0.59V/μm,respectively.And it reached up to the highest current density of 4.97m A/cm² when the field strength at 0.82V/μm.（3）Phosphorus-doped g-C₃N₄ tubes（CN-P）were synthesized by hydrothermal/calcination method,using melamine and phosphoric acid as starting materials.The relevant experimental results indicated that the pre-treatment of melamine did not change the crystal structure of final products.The bandgap of CN-P samples enlarged with the increased concentration of phosphoric acid.What’s more,the separation efficiency of photoinduced charge carriers is significantly promoted.Results of photocatalytic tests indicated that CN-0.5P sample possessed highest photocatalytic efficiency.The decolorization rate of Rh B reached up to 91.2%in only4min and the first-order kinetic constant rate of CN-0.5P for Rh B degradation was0.6442min^-1,which was more than 10 times larger than that of g-C₃N₄.Besides,CN-05P sample also possessed excellent field emission property,the E_to and E_thr were0.87 and 1.2V/μm,respectively.And it reached up to the highest current intensity of3.34m A/cm² with low field strength.