The Surface Modification Of Graphitic Carbon Nitride And Its Photocatalytic Activity

In the context of the increasingly serious energy crisis and environmental problems,semiconductor photocatalytic technology has attracted researchers' favor for its advantages of greenness,economy and sustainable development.Graphitic carbon nitride(g-C3N4),a well-known metal-free semiconductor photocatalyst,has received much attention owing to its low cost,good stability,and visible light responsive.However,g-C3N4 was limited to use in the field of photocatalytic applications due to its poor utilization of light,photo-generated carriers easily combined and other shortcomings.In our work,two different methods were used to prepare modified g-C3N4 with improved photocatalytic activity,which were used for photocatalytic nitrogen fixation and photocatalytic degradation of pollutants,respectively.The main research conclusions are as follows:(1)Cyano-deficient g-C3N4(ACN)was synthesized by KOH etching treatment of bulk g-C3N4:bulk g-C3N4 was synthesized with melamine firstly,and followed by further KOH thermal etching under the nitrogen atmosphere.The characterization results indicated that KOH etching treatment successfully introduced the cyano groups into the framework of g-C3N4.ACN exhibited the pore and/or ladder-like thin layered structure.Meanwhile,the introduction of cyano groups reduced the conduction band position of ACN,and effectively inhibited the recombination of photo-generated electron-hole pairs.In addition,ACN introduced more chemical adsorption sites to absorb and activate nitrogen,which was beneficial to the improvement of photocatalytic nitrogen fixation efficiency.The photocatalytic experiments results showed that the total amount ammonia of catalyst,which was prepared when the mass ratio of KOH and g-C3N4 was 10%,was approximately 7.6-fold higher than that of bulk g-C3N4.(2)The composite catalyst based on g-C3N4 was prepared by one-step copolymerization of zeolitic-imadazolate framework-8(ZIF-8)and melamine.The prepared samples were confirmed as ZnO/g-C3N4 composite catalysts by XRD,XPS,SEM-DES and so on.The experimental results showed that the light absorption range of g-C3N4 showed a slight red shift with the ZnO loading in g-C3N4.In addition,the recombination rate of photogenerated carriers had been suppressed,and the photodegradation capability of sulfathiazole was improved.Trapping experiments showed that the ability of h+ and ·O2-were similar and higher than ·OH in the photocatalytic sulfathiazole degradation reaction.