Preparation Of Two-dimensional Graphite Phase Carbon Nitride Composite And Its Photocatalytic Properties

In order to solve the problem of water pollution,semiconductor photocatalytic technology is an effective solution which can degradate the organic pollutants in water under the irradiation of sunlight to purify the water.Among the various semiconductor materials,the graphitic carbon nitride（g-C₃N₄）has been extensively studied due to its non-toxic,suitable band gap and excellent stability.However,bulk g-C₃N₄ exhibit a low photocatalytic degradation performance because of its small specific surface area and high photogenerated recombination rate,which restricts its practical application.In this paper,the photocatalytic performance of g-C₃N₄ was improved through the morphological control and physical composite.It is focused on the controllable preparation of photocatalysts such as g-C₃N₄ nanosheets,Ag/g-C₃N₄ composites and Ag/g-C₃N₄/reduced graphene oxide（rGO）three-dimensional（3D）aerogel.The photocatalytic performance of the samples was investigated by the degradation of methylene blue（MB）,and the relationship between the structure and properties of the materials was revealed.The main content and conclusions are as follows:（1）The g-C₃N₄ nanosheets（marked as T-g-C₃N₄,L-g-C₃N₄,H-g-C₃N₄）were prepared by thermal oxidation exfoliation,liquid exfoliation and hydrochloric acid assisted hydrothermal exfoliation.The microstructure and photocatalytic performance of g-C₃N₄ nanosheets were investigated.Resulted from SEM,TEM and AFM analysis,the thickness of T-g-C₃N₄ is thicker than L-g-C₃N₄ and H-g-C₃N₄.According to nitrogen adsorption desorption analysis,the specific surface area of the obtained g-C₃N₄ nanosheets is T-g-C₃N₄ > H-g-C₃N₄ > L-g-C₃N₄.The specific surface area directly affects the photocatalytic activity.After irradiation for 60 min,the degradation rates toward MB for T-C₃N₄,H-g-C₃N₄ and L-g-C₃N₄ are 84%,79% and 76%,respectively.H-g-C₃N₄ nanosheets were chosen for the further study because of its easy preparation,suitable thickness and relatively high photocatalytic activity.（2）Silver nanoparticles can strongly absorb visible light to improvephotocatalytic performance because of the localized surface plasmon resonance.Based on the H-g-C₃N₄ nanosheets,the Ag/g-C₃N₄ composites with different Ag contents were prepared by self-assembly.Futhermore,the effects of Ag contents on the photocatalytic properties of the composites were investigated.The introduction of Ag NPs could not only enhance the absorption of visible light but also effectively separate the photogenerated carriers,resulting in enhanced photocatalytic preformance.Among all samples,Ag/g-C₃N₄（6:5）composite exhibit the best photocatalytic activity and good stability,99% MB can be degraded within 60 min.（3）Graphene has a large specific surface area and excellent electron transfer ability,which can be used as a carrier to further improve the photocatalytic activity of materials.3D Ag/g-C₃N₄/rGO aerogel was prepared by chemical reduction-gel reaction,via introducing the GO into Ag/g-C₃N₄ composite.The results show that the obtained aerogel has a typical 3D network structure.Compared with Ag/g-C₃N₄ composite,the band-gap of aerogel can be reduced to 2.3 eV and the specific surface area of aerogel be increased to 139.509 m2/g.The obtained aerogel has enhanced visible light absorption,good adsorption and degradation performance.The degradation rate of MB was 98% after the adsorption equilibrium and the irradiation under visible-light for 30 min.The aerogel also exhibit excellent stability.Compared with the powder composites,the easilier recycle of 3D aerogel can lead to its broader practical application in water treatment.