Study On Surface/Interface Control Based On Graphite Carbon Nitride And Photocatalytic Performance Under Visible Light

Graphite carbon nitride（g-C₃N₄）is a promising visible light photocatalyst with great development prospects in the direction of pollutant degradation and productivity.However,the bulk g-C₃N₄ prepared by traditional methods has inherent defects such as fast photo-generated electron-hole recombination rate and poor electronic conductivity,resulting in limited photocatalytic performance.In order to overcome the defects of g-C₃N₄ and improve its photocatalytic activity,morphology control,element doping,construction of heterojunction structure,carbon material loading and other strategies are more effective modification methods.This paper adopted the strategy of constructing heterojunction and element doping to improve the photocatalytic activity of g-C₃N₄,the separation efficiency of photo-generated charge,and prolong the life of photo-generated electron-hole.The construction of heterojunction promoted the separation of photo-generated carriers and improved the photocatalytic activity;the doping of ions reduced the band gap width of g-C₃N₄,allowing it to absorb and utilize more visible light.The main research contents of the paper are as follows:（1）The g-C₃N₄/（101）-（001）-Ti O₂ composite photocatalytic material was prepared in situ by solvothermal method.Through a series of characterization methods such as XRD,IR,TEM,HRTEM and XPS,it was confirmed that the g-C₃N₄/（101）-（001）-Ti O₂composite photocatalytic material was successfully synthesized.The constructed double heterojunction structure of g-C₃N₄ and（101）-（001）-Ti O₂ accelerated the transfer of photo-generated charges,improved the separation efficiency of photo-generated electrons and holes,and enhanced the redox ability of paracetamol.The TEM and HRTEM results showed that the anatase Ti O₂ nanocrystal contained 12.6%（001）planes and 87.4%（101）planes,and was grown in situ on the surface of g-C₃N₄.Under the radiation of Xenon lamp simulating sunlight,different ratios of g-C₃N₄/（101）-（001）-Ti O₂ hybrid materials all showed great degradation activity for paracetamol.The sample with a ratio of g-C₃N₄/（101）-（001）-Ti O₂=2:1 had strong photocatalytic degradation ability,and its reaction rate constants were pure g-C₃N₄ and（101）-（001）-Ti O₂ 1.69 and 4.14 times.Within 6 hours of light radiation,the photodegradation efficiency of the composite material reached66.49%.Active radical capture experiments showed that both·O₂^-and·OH were the main active species in the composite photocatalytic system.Combined with the analysis of semiconductor energy band theory,g-C₃N₄ formed a Z-type heterojunction with the（101）plane of Ti O₂,and the（101）and（001）planes of Ti O₂ itself were a type II heterojunction.In addition,g-C₃N₄/（101）-（001）-Ti O₂=2:1 also had certain selectivity,stability and recyclability.（2）The photocatalysts of g-C₃N₄,K,P,O-g-C₃N₄-x and K,P,O,S-g-C₃N₄ were prepared by thermal polymerization.The doping of the four elements of K,P,O,and S not only reduced the band gap width of g-C₃N₄ from 2.69 e V to 2.46 e V,absorbed and utilized more visible light,but also increased the density of reactive sites,inhibited the recombination of photogenerated electron-hole pairs.In an acidic（p H=3）photocatalytic system saturated with oxygen and a small amount of isopropanol,g-C₃N₄ modified by hetero-elements could increase the yield of photosynthetic hydrogen peroxide,where the production of K,P,O,S-g-C₃N₄ was the highest,and the amount of hydrogen peroxide produced reached 6231μM,which was 12.85 and 1.19 times that of pure g-C₃N₄（485μM）and K,P,Og-g-C₃N₄-3%（5246μM）,respectively.The active radical capture experiment proved that superoxide radical（·O₂^-）was the main active species in the reaction system,and the corresponding electron transfer mechanism was proposed.Through the stability test,it was proved that the material has certain stability and recyclability,and it was a green photocatalyst.（3）Under the irradiation of simulated sunlight,K,P,O,S-g-C₃N₄ showed efficient removal rates for sulfamethoxazole and tetracycline.For sulfamethoxazole,the degradation rate of K,P,O,S-g-C₃N₄ reached 97.22%within 180 minutes of light irradiation,which was 1.7 times that of pure g-C₃N₄（57.04%）.Within 30 minutes,the degradation rate of tetracycline by K,P,O,S-g-C₃N₄ could reach 64.07%,which was 1.39times that of pure g-C₃N₄（46.12%）.By investigating the influence of interference ions in the environment on the K,P,O,S-g-C₃N₄ photocatalytic system,it was shown that the presence of interference ions would more or less affect the degradation effect,or increase or inhibit.However,in the actual environment,the degradation effect of sulfamethoxazole and tetracycline were slightly reduced,which was the result of the combined effect of ions in the environment.By analyzing the degradation products of photodegradation of tetracycline,we inferred the specific possible degradation pathway of tetracycline.