Synthesis And Photocatalytic Activities Of G-C₃N₄ Based Composites With Visible-light-driven Activity

To convert solar energy resources to chemical energy directly or degradation of environmental organic pollutants, using semiconductor photocatalysts is an effective means to solve environmental and energy issues. Metal-free polymeric photocatalyst graphite-like carbon nitride phase structure (g-C3N4) material (g-C3N4) has attracted extensive attention due to its unique properties. In this paper, in order to further expand the applications in environmental pollution control of g-C3N4-based materials, five efficient photocatalysts have been developed: AgBr/g-C3N4, g-C3N4/Ag3PO4, g-C3N4/Ag3VO4, g-C3N4/Bi2WO6 and g-C3N4/BiOI composites. And the experiment used a variety of characterization methods, like XRD, HRTEM, TEM, SEM, XPS, DRS, IR, PL to analysis chemical andphysicalabilities of the photocatalysts. Meanwhile, activity-structure relationships of the g-C3N4-based materials have been researched. The different mechanism of photocatalytic composites was also discussed.(1) Novel visible-light-driven AgBr/g-C3N4 hybrid materials were synthesized by the facile water bath method. The AgBr/g-C3N4 hybrid materials were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM), X-ray photoelectron spec-troscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL), Fourier transform infrared spectra (FTIR), Raman and the special surface area. The XRD, EDS, TEM, FTIR, Raman and XPS analyses indicated that AgBr nanoparticles were evenly distributed on the surface of g-C3N4 and the heterostructures were formed. The photocatalytic activity of the AgBr/g-C3N4 hybrid materials was evaluated using methyl orange as a target organic pollutant. The as-prepared AgBr/g-C3N4 hybrid materials displayed much higher photocatalytic activity than the pure g-C3N4 and AgBr nanoparticles. After the introduction of AgBr nanoparticles, the photocurrent of the AgBr/g-C3N4 hybrid materials was found to increase by 21 times than that of the pure g-C3N4, respectively. The increased photocatalytic activity of the AgBr/g-C3N4 hybrid materials was attributed to the synergic effect between g-C3N4 and AgBr, which included the optical property, the better dispersion and the small size. A photocatalytic mechanism and the kinetics of AgBr/g-C3N4 hybrid materials were also proposed.(2) The g-C3N4was synthesized by a hydrothermal method and g-C3N4/Ag3PO4 composites were prepared by ordinary precipitation method. The micro structure, morphology and optical properties of as-samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS),Fourier transform infrared (IR) spectra, transmission electronmicroscope (TEM) and energydispersive spectrometer (EDS). The results showed that microspheric Ag3PO4 particles were dispersed on the surface of flake-like g-C3N4, and the heterojunction was formed on the interface. The g-C3N4/Ag3PO4(2 wt%) presented the highest photocatalytic activity for MB dye degradation, and its photocurrent intensity was approximately twice that of the pure Ag3PO4. The g-C3N4/Ag3PO4 composite photocatalysts showed catalytic performance in the decomposition of colorless CIP, which eliminated sensibilization of g-C3N4/Ag3PO4 composites. Holes acted as the main active species and oxidized dye MB.(3) The synthesis of g-C3N4/Ag3VO4 hybird photocatalysts was developed to study the photocatalytic activity under visible light irradiation. The samples were characterized by X-ray diffraction (XRD), fourier transformed infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (DRS). The photocatalytic activity of g-C3N4/Ag3VO4 composites for the photodegradation of methylene blue (MB) and rhodamine B (RhB) under visible light irradiation were much higher than that of the pure g-C3N4 and Ag3VO4. The kinetics of the g-C3N4/Ag3VO4 composites were proposed to investigate the intervened effects of g-C3N4 to Ag3VO4 on the promotion of photocatalytic property. The photocurrents were measured to study the photoinduced charge-transfer properties of the g-C3N4/Ag3VO4 composites. The possible photocatalytic mechanism of the composites was proposed by implementing a series of radical trapping experiments to guide the further improvement of their photocatalytic activity. It is suggested that the outstanding photocatalytic activity of g-C3N4/Ag3VO4 composites was ascribed to the separation of the photoinduced electron-hole pairs with the integration of g-C3N4 and Ag3VO4from analyses above.(4) The g-C3N4/Bi2WO6 composite photocatalysts were prepared by impregnation method. The composites were characterized by XPS,XRD, SEM, DRS,TEM, IR and Photocurrent. The photocatalytic activity of the composites was evaluated by photocatalytic degradation of RhB pollutant under visiblelight irradiation. This result showed that 3% g-C3N4/Bi2WO6 photocatalystshowed the best photocatalytic activity for degrading RhB solution under visible light irradiation. The synergic effect between g-C3N4and Bi2WO6 was beneficialto improve photogenerated carrier separation. The mechanism of the g-C3N4/Bi2WO6composite with enhancing photocatalytic activity was studied.(5)g-C3N4/BiOI composites were prepared by solvothermal process in the presence of [Bmim]I. The heterojunction was formed in g-C3N4/Bi0I composites. Multiple characterization were used to investigate the morphology, the structureand the photocatalytic activity of thecomposites. In this paper, the ionic liquidwas not onlyused as solvent, templateandreactant, but also was acted as dispersing agent, leading to g-C3N4 being uniformly dispersed on the surface of BiOI. Three different types of dyes,like MB,RhB, MO were chosen as model pollutants to analyze the photocatalytic activity of g-C3N4/Bi0I composites. The g-C3N4/Bi0I composites exhibited higher photocatalytic performancethan that of the pure BiOI. The colourless 4-chlorophenol (4-CP) and bisphenol A (BPA) were also chosen to further evaluate the photocatalytic activity of the composites. The g-C3N4/BiOI composites also showed much higher photoactivity than that of the pure BiOI. The results showed that the formed heterojunction in the compositesled to the increasingof electron and hole separation and photocatalytic activity. A photocatalytic degradation mechanism of g-C3N4/BiOI composites was also discussed.