Study on the Construction of Novel MoS2-based Heterojunction and Its Visible-light Catalytic Performance

Author:Zeng Ying

Supervisor:yu hong wen


Degree Year:2019





With the rapid development of the industry and agriculture,the fast growth of the population and the constant improvement of the living standard,the pollution problem of the water has become more deterioration.The traditional method of water treatment is mainly through physical separation,chemical oxidation and biodegradation.But these methods have the defects of incomplete treatment,secondary pollution,high equipment cost and so on.The semiconductor photocatalytic oxidation technology developed rapidly in recent years,and has a very important application prospect in the fields of energy and environment,which has the advantages of environmental protection,energy conservation and no secondary pollution.But the narrow light response range of the single semiconductor photocatalyst,the low quantum efficiency and the insufficient activity site caused the low photocatalytic conversion efficiency,and the poor sunlight utilization efficiency.Therefore,modification of the catalyst is an effective way to improve the photocatalytic activity.Construct heterostructure between the semiconductor and semiconductor,or the noble metal is an effective way to accelerate the separation efficiency of the photogenerated carrier and improve the photocatalytic efficiency.MoS2 was widely applied in the fields of solar energy,catalysis and electrochemistry because of its unique structure and excellent performance.However,the photogenerated electron-hole pairs of MoS2 were easy to compound,resulting in a low photocatalytic efficiency.Therefore,in this study,MoS2 semiconductor based heterostructure composites will be constructed to improve the photocatalytic activity.The main research work is divided into the following parts:(1)Flower-like MoS2 was prepared by a simple hydrothermal method,and then the MoS2/Ag2S/Ag composites were prepared by a photoreduction method.The composites were characterized by XRD,TEM,XPS,BET,etc,and applied to the photocatalytic degradation of congo red(CR),tetracycline(TC)and the pathogenic bacteria(P.aeruginosa).The results showed that the removal efficiency of CR under the visible light was 97.0%,and 92.6%for TC.The degradation pathway of tetracycline was discussed by GC-MS analysis.Moreover,the transferred path of the photogenerated electrons is proved to be a Z-scheme type by using the active group capture test and the electron paramagnetic resonance(EPR).The heterostructure shortened the transmission path of the photogenerated electrons and accelerated the separation efficiency of the photogenerated electron-hole pairs.(2)WO3@MoS2 tubular p-n heterojunction composites were first prepared by a two-step hydrothermal reaction.The BET surface area(92.4 m2?g-1)of WO3@MoS2was characterized by the BET method.The degradation efficiency of CR,RhB,MB,MO was 98.8%,89.3%,85.2%and 57.6%,respectively.The significant improvement of the photocatalytic efficiency is because(1)the one-dimensional tubular structure accelerated the transfer efficiency of photogenerated electrons;(2)the p-n heterostructure formed at the interface of WO3 and MoS2 is beneficial to the effective separation of the photogenerated electron and hole pairs.(3)On the basis of the second part study,the WO3@MoS2 hollow tubular composites was modified by Ag which was deposited by photoreduction.The composites still has a large specific surface area(85.2 m2?g-1).The WO3@MoS2/Ag combined with potassium hydrogen persulfate(PMS)was applied to the photocatalytic degradation of the environmental hormone bisphenol A(BPA).The results show that the HSO5-can be reduced to the?SO4-by?OH or?O2-and the removal efficiency of BPA is 92.5%.Furthermore,schottky junction is formed at the interface of Ag and MoS2(p-type semiconductor),so the holes in the MoS2conduction band can be attracted.This schottky junction effectively improved the separation efficiency of the photogenerated electron-hole pair.(4)The MoS2/CoFe2O4 magnetic composites were prepared by one-step hydrothermal method.The MoS2 nanosheets a large surface area(87.71 m2?g-1)inherently.The composites were characterizated by XRD,TEM,XPS,BET and other characterizations.The photocatalytic degradation of the CR and RhB organic dyes showed that MoS2/CoFe2O4 composites significantly improved the photocatalytic activity.And the degradation efficiency of the CR and RhB is still above 80%after being repeatedly used seven times.So the stability and the recycling property of the MoS2 was increased by depositing of CoFe2O4.Moreover,the transferred pathway of the electrons is presumed to be the Z-scheme system verified by the active group capture experiments.