| Environmental pollution has become an increasingly serious problem faced by countries today,the traditional means of pollution control can no longer meet the requirements,the search for new pollution control technology is imminent.In recent years,photocatalysis technology has gradually become a key technology to solve pollution problems due to its low cost,simple process and no secondary pollution.Among them,graphitic phase carbon nitride（g-C3N4）is a very promising material for photocatalytic degradation of pollutants because of its suitable forbidden band width（2.7 e V）,stable physicochemical properties,non-toxicity,cost-effective performance and simple preparation process compared with other materials.However,the currently prepared g-C3N4 material has low photocatalytic activity in the visible region,small specific surface area and easy agglomeration,resulting in its low photocatalytic performance,so it needs to be modified to enhance the photocatalytic performance of g-C3N4.The specific research and findings of this paper are as follows:（1）The S-doped g-C3N4 was prepared using thermal polymerization with thiourea as the precursor.The S-doped g-C3N4 was characterized using X-ray diffraction（XRD）,scanning electron microscopy（SEM）,ultraviolet-visible absorption（UV-Vis）and fluorescence spectroscopy（PL）,and it was found that the S-doped g-C3N4 prepared at 550℃had the best photocatalytic performance.As demonstrated by NO degradation experiments in visible light,g-C3N4 prepared at 550℃achieved 39%degradation of NO after 2 h.（2）Wet ball milling modification of S-doped g-C3N4 prepared by thermal polymerization;preparation of B-doped modified g-C3N4 by thermal polymerization reaction of boron trioxide with g-C3N4;the S-doped g-C3N4 and g-C3N4 prepared by the thermal polymerization method were calcined with 1μm titanium dioxide（Ti O2）by thermal polymerization at 500℃to prepare the binary composite heterojunction materials SCN-Ti and CN-Ti,respectively.The above-mentioned g-C3N4 before and after modification were characterized by XRD,SEM and specific surface area test（BET）.The results showed that the structures of the first two photocatalytic materials before and after modification did not change significantly,while in the prepared photocatalytic materials with heterojunction structure,the microsphere particles of titanium dioxide were attached to the surface and pores of g-C3N4,indicating that the heterojunction structure was successfully constructed,and the modified g-C3N4 had more uniform morphology,larger layer spacing and expanded specific surface area,resulting in more photocatalytic sites and enhanced photocatalytic performance.UV-Vis and PL showed that the response range of modified g-C3N4 in the visible region was expanded,the light absorption ability became stronger,the fluorescence intensity weakened compared with that before modification,and the complexation rate of photogenerated carriers became lower.（3）The photocatalytic performance of the modified g-C3N4 materials was investigated,and after 5 h of photocatalytic degradation,two groups of heterojunction photocatalytic materials with different mass ratios were preferentially selected and the best ratio of 5:5 was determined.The degradation rates of NO by SCN-Ti-5:5 and CN-Ti-5:5 were 84.9%,79.4%and 57.1%,54.9%under UV and visible light,respectively,which were higher than those of SCN,CN and Ti O2.The degradation of NO by the ball-milled S-doped g-C3N4 was 25.1%and 8.0%higher than that before the modification in UV and visible light,respectively.The degradation of NO by BCN was 25.8%and 7%higher than that by CN under UV and visible light,respectively.The stability of g-C3N4 before and after the modification was further investigated.After five cycles of NO degradation,the photocatalytic material did not reduce the NO degradation rate too much and had good stability.（4）Modified g-C3N4 was applied to degrade the organic dye methylene blue（MB）in water,added to self-cleaning coatings and porous cement concrete to degrade NO gas,respectively.The results showed that the degradation effect of the modified g-C3N4 on MB under visible light was significantly improved compared with that before modification.Meanwhile,the degradation rate of g-C3N4 on NO in self-cleaning coatings was higher in both UV and visible regions,and the higher the doping amount,the higher the degradation rate of NO pollutants,and the doping amount had little effect on the bond strength of the coatings.In porous cement concrete,the amount of admixture should not be too large.Combined with the compressive strength of concrete specimens,the optimum admixture of photocatalytic materials is about 5%～6%. |
