Preparation And Photocatalytic Properties Of TiO₂/g-C₃N₄ Based Composites

TiO₂/g-C₃N₄/Ag-Ag₂O series powders with different Ag doping amount as well as TiO₂/g-C₃N₄/GO series powders with different GO mixing amount were prepared by hydrothermal method,which were based on the as-prepared and optimized titanium dioxide/20wt%graphite phase carbon nitride?TiO₂/20wt%g-C₃N₄?.The crystal structure,micro-morphology,element composition and valence state,optoelectronic properties and visible light photocatalytic activity of the samples were characterized and analyzed by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,X-ray photoelectron spectroscopy?XPS?,photoluminescence spectroscopy?PL?,Ultraviolet-visible diffuse reflectance spectra?UV-Vis DRS?,and transient photocurrent response?i-t curve?.The characterization and analysis results of the composite catalysts are as follows:I TiO₂/g-C₃N₄ binary composites with g-C₃N₄ doping amount changing from 5 to20wt%with excellent photocatalytic performance were prepared by hydrothermal method.XRD and SEM results show that the layered g-C₃N₄ graphite phase is partly and irregularly covered with anatase phase TiO₂ particles,and XPS analysis further confirms that the binary composites is composed of TiO₂ and g-C₃N_4.The results of PL spectra show that a strong fluorescence emission of TiO₂/g-C₃N₄ composites attributed to g-C₃N₄ band gap appears at the peak near 459 nm,and TiO₂/20wt%g-C₃N₄ composites with the lowest luminescence intensity.Under the same experimental conditions,the degradation rates of TiO₂,TiO₂/5wt%g-C₃N₄,TiO₂/10wt%g-C₃N₄,TiO₂/15wt%g-C₃N₄,and TiO₂/20wt%g-C₃N₄ composites were24.4%,36.4%,36.9%,37.2%,and 41.3%,respectively.TiO₂/20wt%g-C₃N₄ has the highest visible light photocatalytic efficiency,which can be attributed to the formation of heterojunction structure between TiO₂ and g-C₃N_4,suggesting the inhibition of the recombination of electron-hole pairs.II Ag-modified TiO₂/g-C₃N₄/Ag-Ag₂O heterojunction composites,which was based on the optimized TiO₂/20wt%g-C₃N₄ composites,were successfully synthesized by partially oxidizing nano-Ag particles during the hydrothermal process with Ag doping amount from0.5 to 5 wt%.The combined results of XRD,XPS,UV-Vis DRS and PL spectra show that TiO₂/g-C₃N₄/Ag-Ag₂O composites are composed of anatase TiO₂,and graphite-like g-C₃N₄,nano-Ag particles as well as some Ag-oxidized Ag₂O particles.Compared with TiO₂,TiO₂/g-C₃N₄ and TiO₂/g-C₃N₄/Ag-Ag₂O,the TiO₂/g-C₃N₄/0.5wt%Ag-Ag₂O quaternary composites exhibits stronger visible-light absorption,lower PL spectral peaks and better photocatalytic activity under visible light irradiation,in which the kinetic constant(0.003min^-1)for its degradation of MB solution is about 2.5 times of TiO₂(0.0012min^-1)and about1.3 times of TiO₂/g-C₃N₄(0.023min^-1).?TiO₂/g-C₃N₄/GO ternary composites with good photocatalytic performance were prepared by adding GO aqueous solution to the optimized TiO₂/20wt%g-C₃N₄ composites with GO doping amount changing from 5 to 20wt%.XRD and SEM results show that some anatase TiO₂ particles are successfully loaded on the g-C₃N₄ and GO carbon layers,and the grain size of TiO₂ decreases first and then increases with the addition of GO.The TiO₂/g-C₃N₄/GO ternary composites with the GO incorporation of 15wt%,TiO₂ show the smallest grain size beneficial to the improvement of the photocatalytic performance.With the degradation of MB solution under visible light irradiation,the kinetic constant(0.02224min^-1)of TiO₂/g-C₃N₄/15wt%GO composites is 18 times and 11 times of pure TiO₂ powder(0.0012min^-1)and TiO₂/20wt%g-C₃N₄ composite(0.0020min^-1),respectively,Comboned results from PL spectra,and UV-Vis DRS,i-t Curve as well as visible-light photocatalysis suggest that the formation of heterojunctions between TiO₂/g-C₃N₄/15wt%GO ternary composites with a narrow band gap effectively reduce the recombination rate of electron–hole pairs and increase the absorption of visible light.Thus providing guidance for the potential application of GO in the development of high-performance photocatalysts.