Studies On Synthesis,Characterization And Properties Of G-C₃N₄ Based Nanocomposites

Renewable energy,especially the solar energy,has attracted remarkable interest due to the dramatically serious energy crisis.As a new type of metal-free polymeric semiconductor materials,graphitic carbon nitride?g-C₃N₄?has shown superior performance in efficient hydrogen evolution from water splitting,as well as photocatalytic degradation of organic pollutants under the visible light irradiation.Owing to its unique chemical structure,g-C₃N₄ possesses excellent thermal and chemical stability,and thus it is widely applied in the photoelectricity chemistry area.However,the pristine of g-C₃N₄ exists high recombination of photoexcited electron-hole pairs and shows deficient visible light absoption,which results in poor photoelectronic performance.Various strategies have been developed to modify g-C₃N₄,such as controlling the morphology,doping elements and building nanocomposite materials with other semiconductors.In this study,to inhibit the recombination in g-C₃N₄,we select graphene oxide?GO?,TiO₂ as the composite objects,considering they are nontoxic,cheap and readily available.We design a reasonable triple-component g-C₃N₄/TiO₂/rGO?reduced graphene oxide?.In the first part,the TiO₂/rGO/g-C₃N₄?TGC?serves as the photoanode in dye-sensitized solar cell,and the stepwise band alignment reduces the photogenerated electron-hole pair recombination and thus improves the power conversion efficiency.In the second part,rGO/TiO₂/g-C₃N₄ acts as the photocatalyst in the degradation of methylene blue?MB?organic dyes,which construct a highly effective electron transfer channel and improve the photocatalytic performance.A series of detailed characterization were carried out to investigate the nanocomposite structure and the mechanism of enhanced performance.The results are listed as follows:?1?Fabrication and optimized photoelectric performance of the dye sensitized solar cells based on TiO₂/rGO/g-C₃N₄ photoanodesWe prepared TiO₂/rGO/g-C₃N₄?TGC?samples with different amounts of g-C₃N₄ and then applied these composites as photoanodes for the dye sensitized solar cells?DSSCs?by doctorblading.We established an optimized content of g-C₃N₄ as 5.5 wt.% in TGC by the measurement of photoelectric performance.Then we fabricated DSSCs with photoanodes based on TiO₂,TiO₂/g-C₃N₄,Ti O₂/rGO,TGC-2?5.5 wt.%?,respectively.The composite morphology and microstructure were characterized by XRD,SEM and TEM.TiO₂ nanoparticles anchored onto the g-C₃N₄ and rGO nanosheets and the g-C₃N₄ nanosheets were tightly overlaid on the rGO nanosheets,forming a sheet-on-sheet structure which enhanced the electron transport and suppressed charge recombination.FTIR and Raman technique were applied to determine the existence of g-C₃N₄ and rGO in the composite photoelectrode.The Raman measurement showed the evidence of GO reduction into rGO.IPCE,J-V and EIS were carried out to investigate the mechanism.As a result,the DSSC based on TGC photoanode exhibited the highest power conversion efficiency?PCE?of 5.83%,enhanced by 50.1% compared to that of pure TiO₂ photoanode.This result strongly suggested a facile strategy to improve the photovoltaic performance of DSSCs.?2?Fabrication and photocatalytic properties of the rGO/TiO₂/g-C₃N₄ compositesWe fabricated rGO/TiO₂/g-C₃N₄ composites via a facile chemical method.By varying the content of g-C₃N₄,we obtained superior samples for the degradation of MB organic dyes.The microstructure of the composite was demonstrated by XRD,TEM,XPS and Raman.The photocatalytic performance was evaluated by the degradation of MB organic dyes under the simulated solar light illumination.The result showed that the degradation rate of rGO/TiO₂/gC3N4-0.75 composite is 17.6 folds higher than that of pure g-C₃N₄.The underlying mechanism was studied based on the results of photoluminescence?PL?spectra and photocurrent measurements under light irradiation.The results indicated that under light irradiation,the excited electrons on the g-C₃N₄ would transfer easily to the conduction band?CB?of TiO₂ due to the matching energy level.Meanwhile,the excellent conductivity of rGO accelerated the photogenerated carrier separation and inhibited recombination of photoinduced electron-hole pairs.The synergistic effect of rGO and g-C₃N₄ significantly improved the photocatalytic activity in rGO/TiO₂/CN.