Preparation And Photocatalytic Activity Of The Composites Based On Graphitic Carbon Nitride

Graphitic carbon nitride?g-C₃N₄?is a kind of two-dimensional material with layered structures.Compared with TiO₂,g-C₃N₄ has a more suitable band gap?2.7 eV?and a metal-free nature which makes it be more environmental-friendliness.More over,it has a good physicochemical stability as a result of the highly condensation of CN framework.In recent years,g-C₃N₄ has been widely used in many photocatalytic applications such as the photocatalytic hydrogen evolution,degradation of pollutants,and CO₂ reduction depended on the advantages of rich precursor source,low-cost raw materials and so on.Vanadate is a kind of photocatalytic substance which has been developed recently and has excellent photocatalytic performance.In this paper,we composite g-C₃N₄ with vanadates and then with Ag nanoparticals to prepare several composites with enhanced photocatalytic property,which will plays an important role for the applications of g-C₃N₄.The main contents are shown as following:?1?g-C₃N₄ was modified by calcinating LiCl,KCl,barbituric acid and dicyandiamide?DCDA?.The product with much larger surface area was denoted as BA-C₃N₄.We prepared BA-C₃N₄/Ag₃VO₄ composites with different ratio of BA-C₃N₄ by coprecipitation method.The SEM and TEM images show that Ag₃VO₄ particals are distributed on the layered BA-C₃N₄ compactly which facilitates the formation of heterojunction.This structure promotes the separation efficiency of the photo-induced electrons and holes.The UV spectra illustrate that the visible absorption intensity of composites is much higher than that of BA-C₃N₄,and the range is much bigger.The BET results show that the 30 wt.% BA-C₃N₄/Ag₃VO₄ sample has the biggest surface area of 31.23 m2/g.The experiments for degradating RhB solution under visible light for all samples show that the 30 wt.% BA-C₃N₄/Ag₃VO₄ sample has the best photocatalytic property.The corresponding k value is 0.138 min^-1,which is obviously higher than those of BA-C₃N₄ and Ag₃VO₄.The fourth time recycling experiments prove that the CeVO₄/g-C₃N₄ composites have a good stability and reusability.?2?We prepared CeVO₄ powders by hydrothermal method at first.Then the CeVO₄/g-C₃N₄ composites was synthesized by calcining CeVO₄ and DCDA,where the weight of DCDA is constant,CeVO₄ is variable.From the morphology image,it can be seen that CeVO₄ is composed of many spindle-shaped structures and finely distributed on the layered g-C₃N₄.This contributes to the formation of the heterojunction structure and improves the photocatalytic property of the composites.The sample S5 has the biggest absorption range and intensity of visible light,and the corresponding band gap is 2.65 eV.The BET results illustrate that the mesoporous structures are existed in the composites and the surface areas of all the composites are higher than that of the pure CeVO₄.The degradation experiments of MB solution under visible light show that the photocatalytic performance of the composites has been improved and the sample S5 is the best.The corresponding kinetic constant is 0.022 min^-1.The scavenging experiments demonstrate that ·O2-and ·OH are the two main active species in the degradation process of MB while h+ has a slight effect.The S5 sample has the lowest fluorescence intensity,proving the highest separation efficiency during the photocatalytic process.?3?We chose S5 obtained from the above experiment as a basic component.A ternary Ag/CeVO₄/g-C₃N₄ composite was prepared by ultrasonic precipitation method using S5,nitrate and sodium citrate.The composite contained different ratio of CeVO₄ is denoted as X%Ag/S5.The TEM images show that CeVO₄ and Ag particals are well distributed on the layered g-C₃N₄,where CeVO₄ has an average partical size of 50 nm as well as Ag partical size of 10 nm.The XRD results display that there are two peaks corresponding to?111?and?200?lattice plane of Ag,indicating that we successfully prepared the composites with ternary phases.The UV spectra show that the 7%Ag/S5 sample has the biggest absorption range and intensity of visible light.The corresponding band gap is 2.65 eV,much lower than that of S5.The degradation experiments of MB solution suggest that 7%Ag/S5 has the optimal photocatalytic property.The corresponding k value is 0.0462 min^-1.The enhanced photocatalytic property of the composites is not only the effect of heterojunction structure but also the surface plasma resonance effect of Ag particals.