Synthesis And Photocatalytic Activities Of Graphite-like Carbon Nitride Composites With Visible Light Response

With the development of our society, the problems of energy shortage and environment pollution affect our living standard. Photocatalytic technology is one of green technologies, which has been widely used in environmental pollutant treatment and energy development. Visible-light-driven photocatalysts with high activity and stability had attracted a great deal of attention. In order to take better advantage of the new visible-light photocatalytic graphene carbon nitride (g-C3N4) in photocatalytic application, a series of composites (g-C3N4/MoO3, WO3/g-CaN4CeO2/g-C3N4and bentonite/g-C3N4) with high photocatalytic activity have been synthesized. These resulting materials were characterized by XRD, XPS, SEM, TEM, BET, DRS, PL and photocatalytic activity test, the relationship between the structure of the photocatalyst and the photocatalytic activities were also discussed in details. The main content and conclusions are summarized as follows:1. g-C3N4/MoO3composite photocatalysts were prepared with an ultrasonic dispersion-heat treatment method. The photocatalysts were characterized by XRD, SEM, HRTEM, IR, XPS and DRS etc. XRD showed the crystal phase structure of g-C3N4and MoO3were not changed after hybridization. SEM and HRTEM showed the hybrid interfaces were formed between the g-C3N4and MoO3. DRS showed the absorption edges of g-C3N4/MoO3composites shifted significantly to longer wavelengths compared with MoO3. The photocatalytic degradation of methylene blue (MB) over g-C3N4/MoO3composites followed the pseudo-first-order reaction model. The g-C3N4/MoO3(7%) composite exhibited the highest photocatalytic activity:the degradation efficiency of MB was93%under visible light irradiation for3h; the photoreaction kinetics constant value was almost4.2and1.9times as high as that of the pure MoO3and g-C3N4, respectively. The enhancement of visible light photocatalytic activity in g-C3N4/MoO3should be assigned to the effective separation and transfer of photogenerated charges originating from the heterojunction interface between MoO3and g-C3N4.2. WO3/g-C3N4composite photocatalysts were prepared by a calcination process with varying the content of WO3. The photocatalysts were characterized by TG, XRD, SEM-EDS, TEM, HRTEM, XPS, IR and DRS etc. XRD, IR, SEM-EDS and XPS showed that the composite photocatalysts were constituted by WO3and g-C3N4. SEM, TEM and HRTEM confirmed the tight hybrid interface was formed between WO3and g-C3N4. DRS showed the absorption edges of WO3/g-C3N4composites shift to longer wavelengths compared with the pure g-C3N4. BET showed the enlarged surface area of WO3/g-C3N4composites compared with g-C3N4and the increased surface area offers more surface active sites for adsorption and photocatalytic reaction. The photocatalytic degradation of MB over WO3/g-C3N4composites followed the pseudo-first-order reaction model. The WO3/g-C3N4(9.7%) composite exhibited the highest photocatalytic activity: the photocatalytic degradation efficiency of MB was97%under visible light irradiation for2h; the photoreaction kinetics constant value was4.2times and 2.9times as high as that of the pure WO3and pure g-C3N4, respectively. The degradation of4-chlorophenol (4-CP) results showed the mechanism was not the dye sensitization effect. PL and EIS analysis confirmed the more efficient separation of electron-hole pairs compared with pure g-C3N4. The remarkably increased performance of WO3/g-C3N4was ascribed mainly to the suitably band positions for WO3/g-C3N4composites to improve the separation efficiency of photogenerated electron-hole pairs.3. CeO2/g-C3N4composite photocatalysts were successfully prepared by a simple mixing-calcination technique. The CeO2/g-C3N4nanocomposites were characterized by TG, XRD, IR, TEM, HRTEM, XPS and DRS etc. TEM and HRTEM showed the CeO2were combined tightly on the surface of g-C3N4. BET showed the enlarged surface area of CeO2/g-C3N4composites compared with g-C3N4and the increased surface area offered more surface active sites for adsorption and photocatalytic reaction. The photocatalytic degradation of MB over CeO2/g-C3N4composites followed the pseudo-first-order reaction model in the degradation of MB. The CeO2/g-C3N4(13.0%) composite exhibited the highest photocatalytic activity:the photocatalytic degradation efficiency of MB was95%under visible light irradiation for2h; the photoreaction kinetics constant value was about12.2times and3.1times as high as that of CeO2and g-C3N4, respectively. The results of the degradation of4-CP and the TOC confirmed CeO2/g-C3N4composites were photocatalyts with high activity. The PL and PT analyses confirmed the efficient separation of electron and pairs under visible light. The remarkably increased performance of CeO2/g-C3N4was ascribed mainly to the well-matched overlapping band-structures for CeO2/g-C3N4composites to improve the separation efficiency of photogenerated electron-hole pairs.4. Layered bentonite/g-C3N4composite photocatalysts were synthesized through a conventional calcination method and systematically characterized by XRD, TG, TEM, IR, XPS and DRS etc. XRD, IR and XPS showed that the composite photocatalyst were constituted by bentonite and g-C3N4. TEM showed the bentonite/g-C3N4composites were constituted by abundant fluffy sheets. DRS showed the absorption edges of bentonite/g-C3N4composites shifted significantly to longer wavelengths compared with the pure g-C3N4. BET showed the enlarged surface area of bentonite/g-C3N4composites compared with g-C3N4and the increased surface area offered more surface active sites for adsorption and photocatalytic reaction. The photocatalytic degradation of MB over bentonite/g-C3N4composites followed the pseudo-first-order reaction model. The bentonite/g-C3N4(0.1) composite showed the highest efficiency for the degradation of MB. The photoreaction kinetics constant value of bentonite/g-C3N4(0.1) was about2.5times as high as that of g-C3N4. Results showed the enhanced photoactivity was mainly attributed to the efficient migration of the photogenerated electrons and holes of g-C3N4, which were induced by the electrostatic interaction between g-C3N4and negatively charged bentonite.