Preparation And Photocatalytic Hydrogen Production Over G-CN Based Composite Materials

The original work on hydrogen generation using polymeric graphitic carbon nitride(g-CN) was reported by X. Wang in 2009. Since then, as a novel non-metal material, it has been catching unprecedented attention of researchers. Although new reports on photocatalytic H2 production by g-CN are emerging in an endless stream, its reaction activity is restricted by the weak visible-light absorption and low charge separation efficiency. In response to these problems, we focus on the design and synthesis of g-CN, extending its light response range and promoting its electron-hole separation. Specifically, our work involves the following aspects:(1) g-CN with large specific surface area and rich porous structure was synthesized by calcining urea at high temperature. Then,(NH4)2MoS4 was reduced to MoS2 and in situ grew on g-CN by photoinduced electrons originating from excited EB molecule. The MoS2/g-CN heterojunction was characterized by XRD, BET, TEM, UV-vis DRS, PL and XPS. The as-prepared photocatalyst demonstrated superior photocatalytic activity under visible light irradiation when EB was used as photosensitizer and triethanolamine as sacrificial reagent, and the maximal hydrogen evolution rate reached high up to 445.0 μmol h-1 in the first hour of the photocatalytic reaction. Moreover, we tested the stability of the system and found that the fast decomposition of EB would lead to a decrease of the H2 evolution rate.(2) A novel narrow bandgap graphitic carbon nitride(Lg-CN) was prepared by solvothermal method. The absorption edge of thus-obtained Lg-CN was located at 703 nm and the corresponding bandgap was 1.76 eV. Composite photocatalyst Lg-CN-TiO2/Cu(OH)2 in which Lg-CN was acted as a solid photosensitizer was prepared by hydrothermal-precipitation method and the corresponding characteractions was also conducted. The photocatalytic hydrogen production property of the as-prepared photocatalyst was tested as well and it turned out that the composite photocatalyst showed excellent photocatalytic performance in methanol solution under visible light(λ ≥ 420 nm) irradiation with an average H2 production rate up to 37.8 μmol/h when 1.5 wt% Cu(OH)2 loaded, pH 8.0 and the content of Lg-CN was 6 wt%. In addition, the good stability of Lg-CN-TiO2/Cu(OH)2 was also demonstrated by the cycling test. The photocatalyst maintained the efficient operation after three cycles.