Effects of Reactant Molecular Adsorption and Catalyst Structure on Photocatalvtic Activity of Graphitic Carbon Nitride

Author:Luo Yi Dan

Supervisor:dong lin zou wei xin


Degree Year:2019





With the development of industrialization in the world,energy shortage and environmental crisis have become two major problems in human society.Semiconductor photocatalysis can absorb and transform solar energy for environmental purification and renewable green energy production,which has become a very hot research topic.graphite Carbon Nitride(g-C3N4)is a two-dimensional conjugated polymer photocatalyst,which has numerous advantages:low-cost,metafree,and visible-light-active,etc.It is used for a variety of photocatalytic applications as a new generation of photocatalyst,such as:pollutants degradation,hydrogen evolution,CO2 reduction,organic synthesis,disinfection,etc.In this paper,the researches of photocatalytic mechanism and activity of g-C3N4 were carried out.The kinetics of photocatalytic degradation on g-C3N4 and the interaction between adsorption and degradation were studied.The effects of different nonmetallic elements doping in g-C3N4 in electron structure,optical properties,and photocatalytic H2 evolution activity were investigated.The interactions between g-C3N4 and SrTiO3 in the nanocompostes of g-C3N4/SrTiO3 were investigated.The important results were obtained as follows:1.Synergistic adsorption-photocatalysis processes on g-C3N4:Kinetics,models,and mechanismsThe synergy between adsorption and photocatalysis has been well recognized in contaminant photodegradation;however,the governing mechanism is still not clear.The main objective of this part is to understand the kinetic processes of synergic adsorption-photocatalysis on graphitic carbon nitrate(g-C3N4),a visible light responsive photocatalyst,in contaminant removal.An azo dye(Reactive Red 120)was selected as a model compound in the study.A range of experiments were conducted to determine the kinetics of adsorption,photodegradation,and the integrated process.Various models were used to simulate and interpret the experimental data and thus to unveil the governing mechanisms.It was found that the integrated adsorption and photodegradation of the dye by g-C3N4 were mainly controlled by:1)adsorption of dye onto g-C3N4 surface,2)photodegradation of dye in bulk solution,and 3)photodegradation of adsorbed dye on g-C3N4 surface.Both experimental and modeling results showed that the adsorption kinetic rate(3.37 min-1)was faster than those of the other two processes.In addition,the surface photodegradation kinetic rate of adsorbed dye(0.149 min-1)was much faster than that in solution(0.005 min-1).Adsorption process thus promoted the photodegradation of contaminants on g-C3N4.On the other hand,photodegradation on dye-laden g-C3N4 regenerated its adsorption capacity for multiple times,suggesting photocatalysis process can also promote the adsorption of contaminates on g-C3N4.2.Nonmetal element doped effects in g-C3N4 for photocatalytic activity enhancementGraphitic carbon nitride(2-C3N4)is considered as a promising heterogeneous catalyst for photocatalytic H2 evolution from water under visible light illumination.Herein,we present a facile one-step heating method for the synthesis of B/P/F doped g-C3N4 photocatalysts(BCN,PCN,FCN).The prepared photocatalysts were characterized and the results show that the B/P/F doping increased the interplanar stacking distance of g-C3N4,enlarged the optical absorption range,and improved photocatalytic activity of H2 evolution.FCN exhibits the highest photocatalytic activity,BCN is followed,and PCN has the lowest performance.This part studies doped effects of the nonmetal elements on the photocatalytic activities,the electronic structures as well as the band gaps of g-C3N4,in order to provide a feasible modification pathway to design and synthesize high efficient photocatalysts.3.Interfacial coupling effects in g-C3N4/SrTiO3 nanocomposites with enhanced photocatalytic activity under visible light irradiationConstructing nanocomposite is an effective method for photocatalytic activity improvement.Herein,we prepared the g-C3N4/SrTiO3 nanocomposites via a two-step mechanically milling and calcination process.The composite exhibited the highest H2 evolution activity superior to that of the pure g-C3N4 and SrTiO3 in the visible light.The results demonstrated that g-C3N4/SrTiO3 exhibited more visible light adsorption and faster photo-generated charge transfer.Furthermore,the interfacial electronic structures of g-C3N4/SrTiO3 nanocomposites were thoroughly characterized.According to the results,with the help of a strong built-in electric field presenting in the g-C3N4/SrTiO3 interface,the photo-generated electrons flow to the SrTiO3 from g-C3N4,leading to the highly-efficient electron separation and more H2O molecules photo-reduction to H2.This work explicates the significant role of built-in electric field in H2 evolution on g-C3N4/SrTiO3 photocatalyst.