2-D Carbon Doped Composite Catalysts And Its Visible-light Photocatalytic Performance

The visible-light-driven photocatalysis plays an important role in the field of environmental remediation and energy development due to its mild reaction conditions, low energy consumption, easy operation and utilizing visible-light. The photocatalyst is the key point of visible-light photocatalysis in the present research. However, traditional photocatalysts exhibit low photocatalytic activity under visible-light irradiation and the recycling of catalyst is relatively difficult. Therefore, it is highly desirable to develop reusable visible-light photocatalysts with high photocatalytic activity.In the present work, the2-D carbon materials, graphene and graphite-like carbon nitride (g-C3N4), were used to modify the bismuth ferrite and CdS photocatalyst. The Bi25FeO40-graphene, Bi25FeO40-g-C3N4and g-C3N4-CdS composite photocatalysts were synthesized and characterized. The photocatalytic behaviors of these composite photocatalysts were also investigated.A magnetic Bi25FeO40-graphene visible-light photocatalyst was prepared by a one-step hydrothermal method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, Raman spectroscopy, X-ray photoelectron spectra (XPS) and magnetic hysteresis loop measurements. Under identical hydrothermal conditions, perovskite type bismuth ferrite (BiFeO3) was obtained without graphene addition, while the presence of graphene led to the formation of sillenite type bismuth ferrite (Bi25FeO40), and graphene oxide (GO) was reduced to graphene during the hydrothermal process. The crystalline of bismuth ferrite has a certain relationship with the alkali concentration. The phase of Bi2.5FeO40was formed when the alkali concentration was low. In comparison with pure BiFeO3catalyst, the Bi2.5FeO40-graphene composite showed better magnetism property. Moreover, the addition of graphene had an effect on the particle size of photocatalyst. The photocatalytic degradation of Methylene Blue (MB) demonstrated that Bi25Fe04o-graphene photocatalyst exhibited higher catalytic activity under visible-light irradiation than BiFeO3and Bi25FeO40, due to enhanced MB adsorption and synergistic effect between Bi25Fe04o and graphene. Additionally, the photocatalytic MB degradation over Bi25FeO40-graphene followed the Langmuir-Hinshelwood model, indicating an adsorption controlled reaction mechanism.Magnetic Bi25FeO40-g-C3N4visible-light photocatalysts were prepared and characterized by XRD, SEM, BET surface area analysis, UV-vis spectra and magnetic hysteresis loop measurements. The addition of g-C3N4made the band gap of Bi25Fe04o-g-C3N4composite photocatalyst decrease. Furthermore, the g-C3N4content of Bi25FeO40-g-C3N4had an impact on the photocatalytic MB degradation. The photocatalytic efficiency increased with the increase of the g-C3N4content and then decreased with the further increase of the g-C3N4content. Bi25FeO40-(50)g-C3N4showed prominently enhanced photocatalytic activity for the degradation of MB under visible-light irradiation than that of Bi25FeO40. Additionally, the Bi25FeO40-(50)g-C3N4composite was superparamagnetic, and could be readily recovered in an external magnetic field.The g-C3N4-CdS visible-light photocatalysts were prepared and characterized by XRD, TEM, BET surface area analysis, FT-IR and UV-vis spectra measurements. The CdS-g-C3N4composite photocatalyst showed prominently enhanced photocatalytic activity for the degradation of MB under visible-light irradiation than that of CdS and g-C3N4. Such enhanced photocatalytic activity could be attributed to the high adsorption capacity of MB on CdS-g-C3N4composite photocatalyst and the synergistic effect between CdS and g-C3N4. The photogenerated electrons may transfer from g-C3N4to CdS, inhibiting the combination of photogenerated electrons and holes. Meanwhile, the gathering of photogenerated electrons in the surface of CdS suppressed the photo-oxidation corrosion of CdS. Additionally, the g-C3N4-CdS catalyst had larger surface area which provided more active adsorption sites and photocatalytic reaction centers, giving rise to enhanced photocatalytic activity. Moveover, the CdS-g-C3N4composite catalyst still maintained a high photocatalytic activity after recycle for five times, which further demonstrated that the g-C3N4-CdS is a high stability catalyst.