Modification And Mechanism Study Of Nano-gC 3 N 4 Photocatalyst

With the development of industry and the depletion of non-renewable resources such as fossil fuels,the environmental and energy crisis has become the primary issue urgently needed to be solved.As an inexhaustible and clean source of environmental energy,solar energy has drawn people’s attention in solving energy shortage and pollution elimination.Among them,the semiconductor photocatalytic technology is considered as renewable,economical,safe and clean technology has become the focus of research.At the same time,visible light accounts for about 44%in the solar spectrum,so it is necessary to develop efficient visible-light driven the semiconductor photocatalyst.g-C₃N₄ as a cheap,stable,non-pollution,with a unique surface structure of the new narrow-band gap polymer polymers have been widely studied.However,its photocatalytic performance under the sunlight is still unsatisfactory,which can not meet the practical application.This is usually due to poor photogenerated charge separation and low visible light utilization of g-C₃N₄.Since the holes are positively charge,it is very important to use negatively charged ion polarization to regulate the induced holes.Meanwhile,selecting phthalocyanine dye with sensitization is expected to expand its visible light response.Based on this,we carried out the modification of g-C3N4 by halogen ion with strong electronegativity and the modification of g-C₃N₄ by metal phthalocyanine to improve the photocatalytic activity of g-C₃N₄.This article mainly consists of two parts:Firstly,we explored the influence of halogen ion polarization on the charge separation of g-C₃N₄.The modification of g-C₃N₄ was modified by the introduction of Cl^-by the wet chemical method,which improved the activity of the material for the degradation of organic pollutants and CO₂ reduction.Based on the test results of steady-state photovoltage,transient photovoltage and hydroxyl radical under nitrogen conditions,the increase of photocatalytic activity is attributed to the result of Cl^-trapped holes to improve charge separation.In addition,the formation of·OH as a direct product of hole reaction is dominant in the degradation of 2,4-DCP.The degradation pathway and mechanism of 2,4-DCP,which are closely related to the·OH attack,were proposed by detecting the major intermediates during degradation.Meanwhile,the modification of g-C₃N₄ by different halogen ions（F^-,Br^-）proved that the modification of other ions in the halogen could also improve the photocatalytic activity of g-C₃N₄,however,Cl-modification was the best.Combined with the results of the atmospheric photovoltaic,it is demonstrated that both the mechanism of trapped holes by Cl-and Br-modifications and the negative surface formed by F^-modification can explain that the mechanism of surface polarization induced by halogen modification and enhances charge separation is feasible.Secondly,we investigated the effect of metal phthalocyanine modification on the visible light activity of g-C₃N₄.The modification of g-C₃N₄ with transition metal phthalocyanines was performed by impregnation.Based on the results of steady-state photovoltage,solid-state fluorescence and hydroxyl radical test,the introduction of metal phthalocyanine enhanced the photo-generated charge separation efficiency of g-C₃N₄ and enhanced the photocatalytic degradation ability of 2,4-DCP and CO₂.The photocatalytic activity of CuPc modified g-C3N4 was found to be the best.Further in-depth exploration of CuPc modified g-C3N4,found the best amount of modification.The steady-state photovoltage under nitrogen and single-wavelength hydroxyl radical test proved that the photocatalytic activity is attributed to the introduction of CuPc,forming a heterojunction with g-C₃N₄ and transferring the electron of the g-C₃N₄conduction band to the LUMO of CuPc at the energy level,the charge recombination probability of g-C₃N₄ is reduced,at the same time expanding the visible light response.