Mechanism Exploration And Application Of Photocatalysts Based On Graphitic Carbon Nitride

As the polymeric semi-conductor that has received broad attention,graphitic carbon nitride(g-C3N4)shows photocatalytic activity under irradiation of light with wavelength<450 nm.Advantages such as easy-preparation,environmental friendly and chemical stable make g-C3N4 a promising photocatalyst.However,its photocatalytic performance under visible light requires further promotion due to the intrinsic narrow wavelength of absorbed light.limited specific surface area and high carriers recombination.In the past few decades.engineering strategies such as construction of Z-scheme structure,morphology alternating and Surface Plasma Resonance(SPR)to improve photocatalytic performance of based g-C3N4 photocatalysts.Therefore,our work focuses on investigating various kinds of mechanisms,mainly including the following contexts:(i)g-C3N4 nanosheets with edge-functionalized carboxyl groups(CNNS)were synthesized via Hummer’s method and were modified by Cu2+and ligand 1,2,4,5-Benzenetetracarboxylic acid(BTEC)as the product material CNNS-BTEC-Cu.The photocatalytic mechanism referred in photocatalytic process based on CNNS-BTEC-Cu was an improved metal-to-ligand charge transfer(MLCT),which significantly depended on strong pi-delocalization of BTEC.CNNS-BTEC-Cu-3 effectively absorbed light with wavelength shorter than 1100 nm and showed obvious photocatalytic hydrogen evolution capability under Near-Infrared light(λ<820 nm)irradiation.Moreover,according to result of Density Functional Theory calculation,the proposed MLCT mechanism was fully testified and the origin of both photocatalytic activity and durability were investigated(ii)Under calcination temperature of 640℃,g-C3N4 with rich thermal defects was prepared with melamine as the precursor.After modified by α-Fe2O3 nanoparticles,α-Fe2O3/d-C3N4-1 showed 1.96-fold promotion on activity of photocatalytic Tetracycline degradation compared to tranditional Z-scheme photocatalyst based on g-C3N4.The existence of two sub-gaps in d-C3N4 was testified by the result of first-order derivative of fluorescence spectroscopy(PL).After superseding α-Fe2O3 with other semi-conductors,all Z-scheme photocatalysts based on d-C3N4 showed obvious improvement on photocatalytic activity compared to those based on g-C3N4.(iii)g-C3N4 prepared with urea as the precursor was utilized to synthesize nanosheets with edge-functionalized carboxyl groups(CNNS).The obtained CNNS was employed to fabricate a series of composite materials CNNS/CN/NiOx which were used as photocatalysts in photocatalytic reduction of Cr(VI).The activity of CNNS/CN/NiOx-4 showed 4.2-and 1.7-fold improvement compared to g-C3N4 and CN/NiOx respectively.Owing to carboxyl groups on CNNS surface,CNNS/CN/NiOx effectively adsorbed Cr(VI).Moreover,due to the construction of ’perovskite-solar-cell-like’ structure where CNNS and NiOx played the role of electron transfer layer and hole transfer layer,photo-generated charge carriers were separated efficiently.