Structure Manipulation And Photocatalytic Performance Of G-C₃N₄-based Photocatalysts

Photocatalytic technology is considered as one of the effective ways to solve the energy and environmental crisis by using solar energy.The semiconductor material graphite phase carbon nitride（g-C3N4）has attracted extensive attention as a photocatalyst because of its low cost,simple synthesis,high chemical stability and relatively narrow band gap（2.7 e V）.However,the photocatalytic activity of g-C3N4 is not ideal due to the low visible light utilization rate,low photocarrier separation efficiency and small specific surface area.In this thesis,g-C3N4 was modified by means of semiconductor recombination,non-metal doping and noble metal deposition,aiming at key scientific problems such as low light absorption capacity of g-C3N4 and easy recombination of photogenic electron-hole pairs,so as to obtain photocatalyst with excellent performance.The main contents are as follows:A series of Z-type La Fe O₃/lamellar g-C₃N₄ composite photocatalysts（2LFO/CNNS,LFO/CNNS and LFO/2CNNS）with different proportions were prepared by two-step calcination method,and the optimal reaction ratio（LFO/CNNS）was determined.Then,graphene（G）was introduced into the preparation process of La Fe O₃/lamellar g-C₃N₄,and Z-type heterojunction ternary composites（LFO/CNNS-0.125G,LFO/CNNS-0.25G and LFO/CNNS-0.5G）with different graphene contents were prepared.The LFO/CNNS-0.25G composite showed the highest photocatalytic hydrogen production rate(1326.5μmol h^-1 g^-1).It is 2.78,162.36 and 1.96 times of the lamellar g-C₃N₄（CNNS）,La Fe O₃（LFO）and LFO/CNNS composites,respectively,and the hydrogen production after four cycles is basically the same as the initial hydrogen production.Ag decorated P-doped g-C3N4 sheets Schottky junction Ag-（P/CNNS）was successfully constructed by two-step calcination process and silver mirror reaction.Through the observation of structure and morphology,it is proved that P is successfully doped into the skeleton of CNNS,and Ag nanoparticles are deposited on the surface of P-doped g-C3N4sheets（P/CNNS）.The doping sites of P can be determined by comparing the formation of P/CNNS after P replaces C at different positions of CNNS skeleton.The photocatalytic properties of the samples were tested by photocatalytic hydrogen production and photocatalytic degradation of rhodamine B（Rh B）,and the reaction mechanism was analyzed.The results show that the photocatalytic hydrogen production rate of Ag-（P/CNNS）is the highest(1350.95μmol h^-1 g^-1),which is 1.43 times and 1.38 times higher than that of P/CNNS and Ag decorated g-C3N4 sheets（Ag/CNNS）,respectively.After 3.5 hours of light,the decolorization rate of Rh B by Ag-（P/CNNS）was 98.9%,which was 1.52 times that of P/CNNS.