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石墨相氮化碳(g-C_3N_4)是一种在室温条件下最稳定的氮化碳.同时g-C_3N_4的带隙为2.7 eV,可以利用可见光催化很多反应,例如光解水、CO2还原、有机污染物降解和有机物合成.但普通体相g-C_3N_4的光催化性能不尽如人意,主要是由于普通体相材料的载流子复合效率高,可见光(<450 nm)利用率低且比表面积小.众所周知,半导体的光催化性能与材料表面状态密切相关,因此可以控制合成条件来制备有利于光催化形貌的g-C_3N_4材料.普通体相g-C_3N_4材料的比表面积较小,约为10 m2/g,导致传质作用较差,光生电子-空穴复合严重,因此制备高比表面积的g-C_3N_4材料是目前研究的热点.我们发现在550 oC下将三聚氰胺和三聚氰酸一起煅烧可以一步热合成g-C_3N_4纳米片,合成温度较低,对材料带隙影响小,同时可以提高材料比表面积,从而极大地提高了材料的光降解苯酚性能.XRD测试发现,随着前驱体中三聚氰酸比例增加,材料的主峰从27.38°显著偏移到27.72°.这表明三嗪环面内相连构成CN平面,同时CN层也会有堆叠最终形成g-C_3N_4材料.通过BET测试,g-C_3N_4纳米片的比表面积为103.24 m2/g.采用AFM分析得到g-C_3N_4纳米片的厚度为3.07 nm.研究了该g-C_3N_4纳米片的光降解性能,结果显示,在可见光照射30 min后,使用这种g-C_3N_4纳米片作为催化剂的条件下,苯酚降解率达到最优的81%.在5次循环利用后,g-C_3N_4(1:9)的降解率还能保持在80%以上,说明材料有良好的循环稳定性.这主要得益于材料的纳米片结构,在对苯酚吸附时不会有很复杂的吸附与脱附过程.同时纳米片结构可为有机污染物的吸附和原位降解提供传质通道.光反应体系中的产物由HPLC检测,分析苯酚的降解产物及产物的产量可以大致推测苯酚可能的降解历程.在三聚氰酸作用下,CN聚合层弯曲,减少了CN层之间的相互结合,同时不会对材料的带隙产生影响.同时整个合成过程无需引发剂,也不会导致CN层的基本单元和连接方式发生改变,同时由于二维片层结构,提高了材料的电荷分离效率.通过苯酚的降解实验得知三聚氰胺与三聚氰酸的比例为1:9,在550 oC下煅烧得到的g-C_3N_4纳米片的光降解性能最优,同时具有很好的催化稳定性
Graphitized carbonitride (g-C_3N_4) is the most stable carbon nitride at room temperature.At the same time, the bandgap of g-C_3N_4 is 2.7 eV, and many reactions can be catalyzed by visible light, such as photolysis, CO2 reduction, Organic pollutants degradation and organic synthesis, but the general photocatalytic performance of g-C_3N_4 is not satisfactory, mainly due to the high carrier recombination efficiency of common bulk materials, low visible light (<450 nm) utilization ratio The surface area is small.It is well known that the photocatalytic properties of semiconductors are closely related to the surface state of the material, so g-C_3N_4 material can be prepared to control the synthesis conditions conducive to the photocatalytic morphology.The general bulk g-C_3N_4 material has a small specific surface area of about Is 10 m2 / g, resulting in poor mass transfer and serious photogenerated electron-hole recombination, so preparation of high specific surface area of g-C3N4 material is currently a hot spot.We found that at 550 oC melamine and cyanuric acid Calcination can g-C_3N_4 nanosheets thermal synthesis step, the synthesis temperature is lower, the band gap of the material has little effect, and can increase the material surface area, thus greatly improving the photodegradation of phenol material performance.XRD test found that with the precursor The proportion of cyanuric acid increased and the main peak of the material shifted significantly from 27.38 ° to 27.72 °, which indicated that the triazine ring connected in the CN plane and the CN layer was stacked to form the g-C_3N_4 material. , the specific surface area of g-C_3N_4 nanosheets was 103.24 m2 / g.The thickness of g-C_3N_4 nanosheets was 3.07 nm by AFM.The photodegradation properties of g-C_3N_4 nanosheets were studied.The results showed that under visible light irradiation 30 min, the best degradation rate of phenol was 81% under the condition of using g-C_3N_4 nanosheets as catalyst.The degradation rate of g-C_3N_4 (1: 9) was maintained at 80 %, Indicating that the material has good cyclic stability.This is mainly due to the material nanosheet structure, adsorption of phenol will not have a very complex adsorption and desorption process.At the same time, the structure of nanosheets can be organic pollutants Adsorption and degradation in situ to provide mass transfer channels.The product of the photoreaction system is detected by HPLC, the degradation products of phenol and the yield of the product can be roughly inferred the possible degradation process of phenol.Under the action of cyanuric acid, CN polymer layer is bent , Reducing the mutual binding between CN layers, at the same time Will have an impact on the bandgap of the material.At the same time, the initiator does not need to be used in the whole synthesis process, and the basic unit and connection of the CN layer will not change, at the same time, the charge separation efficiency of the material is improved due to the two- Degradation experiments showed that the ratio of melamine and cyanuric acid was 1: 9. The photocatalytic activity of g-C_3N_4 nanosheets calcined at 550 oC was the best, and had good catalytic stability