Study On Preparation And Photocatalytic Performance Of Graphitic Carbon Nitride Composite

Graphite carbon nitride(g-C3N4),as a semiconductor photocatalyst,it has attracted extensive interest among researchers due to its plentiful material source,nontoxicity,narrow band gap,very high thermal and chemical stability,excellent sunlight harvesting capability.The modification of g-C3N4 has been widely reported to improve the utilization of visible light and reduce the photogenerated carrier recombination.Many attempts have been carried out to improve the photocatalytic performance of g-C3N4,such as modifying structural morphology,hetero-atom doping,loading with noble metals,formin,g a heterojunction,by integrating with other semiconductors,dye sensitization and inducing carbon materials,et al.However,owing to the limitation of photocatalytic efficiency and high cost,the practical application of photocatalysis technology is limited.Carbon material and Z-scheme heterojunction were used to modify g-C3N4.Reduce graphene oxide/tungsten trioxide/graphite phase carbon nitride(RGO/WO3/g-C3N4)ternary photocatalytic composite was perepared through one-step hydrothermal method in order to improve the photocatalytic performance,the utilization efficiency of visible light and reduce the cost of preparation of the composite.The reduced graphene oxide/graphite phase carbon nitride(RGO/g-C3N4)binary composite photocatalyst was prepared by three different preparation methods:hydrothermal method,ultrasonic method and calcination method.The effect of RGO content on its photocatalytic performance under different preparation methods was investigated.Z-scheme heterostructure ternary composite photocatalyst of RGO/WO3/g-C3N4 was designed based on binary composite.The performance of the photocatalyst was evaluated.The main research contents and results are as follows:(1)Graphene oxide(GO)was synthesized by improved Hummers method,g-C3N4 was prepared by thermal polymerization.The RGO/g-C3N4 binary photocatalytic composite with different RGO content was prepared by hydrothermal method,ultrasonic method and calcination method.The structure,morphology and optical properties of the as-prepared samples were characterized.The photodcatalytic performance was evaluated through photocatalytic degradation of Rhodamine B(RhB)and Tetracycline Hydrochloride(TC-HCl)under Xenon light illumination.The photocatalytic effect and reusability of the sample were evaluated.The photocatalytic mechanism was reasonably speculated.The main results were as follows,Graphene oxide(GO)was reduced to reduced oxidation graphene(RGO)and successfully composited on carbon nitride in binary composite.RGO and g-C3N4 were combined in sheet structure in the samples prepared by hydrothermal or ultrasonic method.RGO was observed sandwiched in the matrix of g-C3N4 in the samples prepared by calcination method.Compared with g-C3N4,the absorption edge of the RGO/g-C3N4 composite showed redshift,which enhanced the utilization of visible light.The composite exhibited a lower photoluminescence intensity than pure g-C3N4,indicating that the separation rate of photogenerated carriers was higher than monomers.When the RGO content was 0.2%in sample prepared by hydrothermal,the photodegradation effciency of RhB was the best,The total removal effciency of RhB was 77.78%,which was 1.91 times higher than g-C3N4 The total removal efficiency on TC-HCl was 57.32%,which was 1.23 times higher than g-C3N4.All reaction kinetics for the photodegradation of RhB and TC-HCl over RGO/g-C3N4 follow the apparent first-order equation.RGO modified g-C3N4 with the higher separation eff-iciency of the photogenerated charges and utilization of visible light,Which was the direct reason for the enhanced photocatalytic performance.Based on trapping experiments,The main active species was h+and·O2-.There was no obvious reduction in total removal efficiency of RhB from 77.78%to 69.28%over the RGO/g-C3N4 composite during four cycles of photocatalytic process,which indicating that RGO/g-C3N4 has high reusability.(2)WO3 was selected to construct Z-scheme heterostructure due to suitable chemical stability,plentiful material source,prepared easy.Meanwhile,since the valence band position of WO3 was more positive than the valence band of g-C3N4,WO3 has higher oxidability.The high reductivity of g-C3N4,the high oxidation of WO3 and the heterostructure between them caused higher photocatalytic performance.In order to enhance the transfer of photogenerated electrons in the composite,RGO was induced to construct WO3/g-C3N4.Based on the experimental results of W03/g-C3N4 and RGO/g-C3N4,The RGO/WO3/g-C3N4 photocatalytic composite with different RGO content was synthesized by one-step hydrothermal method.The structure,morphology and optical properties of the as-prepared samples were characterized by XRD、FTIR、SEM、TEM、UV-Vis DRS、XPS and PL.The photocatalytic activity and recycling properties of as-sample were evaluated by photocatalytic degradation of RhB and TC-HCl.Based on the results of characterization and photocatalytic reactions,the photocatalytic mechanism was reasonably speculated.The main results were as follows,RGO/WO3/g-C3N4 was successfully prepared.One-dimensional nanorods like WO3 wrapped by RGO was unevenly dispersed on g-C3N4.There were closely combined to form a heterojunction.The RGO/WO3/g-C3N4 showed a broad absorption in the visible light region and lower PL emission intensity compared with g-C3N4,RGO/g-C3N4 and WO3/g-C3N4,which indicating that the recombination of the photogenerated electron-hole pairs become lower in RGO/W03/g-C3N4.when the mass ratio of WO3 and g-C3N4 was 1:1 and the content of RGO was 0.2%,the RGO/WO3/g-C3N4 exhibited the highest total removal efficiency of 97.58%under Xenon light illumination for 240min.Photocatalytic degradation of RhB was almost 3.22 times,2.39 times,1.25 times and 1.06 times higher than WO3,g-C3N4,RGO/g-C3N4 and W03/g-C3N4.Total removal efficiency of TC-HCl reached 75%,which was 3.42 times,1.61 times,1.31 times and 1.21 times higher than that of WO3,g-C3N4,RGO/g-C3N4 and WO3/g-C3N4 respectively.All reaction kinetics for the photodegradation of RhB and TC-HCl over different photocatalysts follow the apparent first-order equation.Based on trapping experiments,The order of active species was:·O2>h+>·OH>e-.It was speculated that the electron transfer between semiconductors acted up to the Z-scheme system.The total removal efficiency of the composite displayed only slight deterioration from 97.58%to 84.07%after four cycles,indicating that the RGO/WO3/g-C3N4 composite has good reusability.