Composite Photocatalyst Preparation And Catalytic Properties Of Visible Light GC ₃ N ₄ / TiO ₂

Visible light photocatalysis has attracted much attention due to its extensive application in the fields of hydrogen generation and environmental protection. TiO2has been proved to be a competent photocatalyst for environmental applications, however, due to the wide band gap of anatase TiO2(3.2eV), it cannot be excited under visible light irradiation (λ＞400nm). Therefore, there is much interest in developing visible light-responsive TiO2with catalytic activity high enough for practical applications.(1)The g-C3N4/TiO2composite photocatalysts were prepared by a facile solid-phase method of directly heating melamine and commercial TiO2mixtures. TiO2(TO) and melamine were combined in an alumina crucible, and stirred with deionized water at room temperature. The mixture was dried at60°C for1h and then annealed to520°C in a covered muffle furnace for5h. Finally, the sample was cooled to room temperature to yield the g-C3N4-TiO2photocatalyst. Calcined temperature, calcined time and mass ratios of urea and industry TiO2were the three influence factors.(2)The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FT-IR), UV-visible diffused reflectance spectroscopy (UV-vis DRS), transmission electron microscopy (TEM) and photoluminescence spectroscopy (PL). Based on the characterization of XRD、 XPS、 FT-IR has confirmed the existence of g-C3N4.It can be observed TiO2was distributed on layered g-C3N4. The absorption sideband of g-C3N4/TiO2was red-shift and PL intensity was decreased. It implied g-C3N4/TiO2can enhance photocatalytic activity, separation of electron-hole and reduce the recombination of photo-induced carrier.(3)The photocatalytic activities under visible light were evaluated by degradation of methylene blue.The photocatalytic activity of TO-M-2.5was the best of all the samples. It was obtained under temperature520℃, calcined1h and the mass ratios of urea and titanium dioxide was2.5:1. The degradation of5mg/L MB reached91%under the visible light irradiated5h. We compared the visible light photocatalytic activity of TiO2and the samples. The photocatalytic activities in the gas experiment under visible light were evaluated by degradation of methylene blue.In the gas experiment, the degradation of NO was31%after30min irradiation.(4) The characterization of samples has confirmed the existence of g-C3N4, the absorption sideband of g-C3N4/TiO2has red-shift and widen the spectrum absorption range. When the as-prepared composite is irradiated with visible light, the electrons get promoted from the valence band (VB) to the conduction band (CB) in g-C3N4. The CB edge potential of g-C3N4is more negative than that of TiO2allowing the excited electron on the surface of g-C3N4to transfer easily to TiO2via the well-built heterojunction, significantly enhancing photocatalytic activity.