Bismuth Molybdate-based Nanocomposites:Preparation And Photocatalytic Performance

In recent years,bismuth-based semiconductors have attracted much attention due to the unique visible-light-response photocatalytic performance.As a kind of typical aurivillius oxide with layered structure,bismuth molybdate was considered to be a promising photocatalyst due to its efficient charge separation and transfer.However,the photocatalytic activity of pure bismuth molybdate material was still limited by its low quantum efficiency and light conversion efficiency.Therefore,it is highly desired to build up bismuth molybdate-based composited materials to improve the catalytic activity.In this thesis,a variety of bismuth molybdate based composited material were prepared through simple synthetic methods,to improve the photocatalytic performance of bismuth molybdate materials.The mechanism of enhanced photocatalytic performance was also discussed,which lay a foundation for further development of bismuth-based photocatalyst.The main research works are summarized as follows:1.Bi/Bi_3.64Mo_0.36O_6.55.55 heterojunction nanoparticles,which was synthesized via a hydrothermal method in the ethylene glycol and NaOH reaction system.The as-prepared samples were characterized by powder X-ray diffraction（XRD）,scanning electron microscopy（SEM）,high resolution transmission electron microscopy（HRTEM）and X-ray photoelectron spectroscopy（XPS）.Moreover,the as prepared Bi/Bi_3.64Mo_0.36O_6.55heterojunction exhibited a superior photocatalytic performance in glycerol oxidation to dihydroxyacetone under simulated sunlight irradiation.The conversion and selectivity were 43%and 98%after 4 hours reaction,respectively.Compared with the reported results,the catalytic activity of Bi/Bi_3.64Mo_0.36O_6.55.55 was significantly improved.The mechanism of improved activity of Bi/Bi_3.64Mo_0.36O_6.55.55 was investigated by the fluorescence spectra（PL）,electrochemical impedance spectra（EIS）,photocurrent characterization,fourier transform infrared（FT-IR）,electron spin resonance（ESR）and trapping experiments.It indicated that the excellent performance was attributed to the Bi species load on Bi_3.64Mo_0.36O_6.55.55 in reaction solution to form a double pathway of photocatalytic oxidation of glycerol,in which the singlet oxygen and photogenerated hole were selective oxidation of glycerol simultaneously.2.Bi₂MoO₆/（BiO）₂CO₃ heterojunction was synthesized by the ion exchange method at room temperature,and the contents of（BiO）₂CO₃ can be controlled over the reaction time.The activity in the reaction system were obvious improved after the Bi₂MoO₆/（BiO）₂CO₃heterojunction constructed,because of the separation and transfer efficiency of the photogenic carrier improved.More importantly,the activity was further improved when moderate amounts of ClO^-added,because of the chlorine free radicals produced in the presence of ClO^-,which can be used in the degradation of organic pollutions.Moreover,the mineralization rate of organic pollutants also improved significantly over the analysis of total organic carbon（TOC）and ion chromatography（IC）.Compared with the traditional chlorine disinfection,the content of chlorine disinfection by-products are significantly reduced over Bi₂MoO₆/（BiO）₂CO₃-NaClO water purification system.3.Bi/Bi₂MoO₆/（BiO）₂CO₃ heterojunction composites was synthesized via a hydrothermal method in the ethylene glycol and ethanol system.The as-prepared samples were characterized by X-ray powder diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,and scanning electron microscopy（SEM）.The catalytic properties of Bi/Bi₂MoO₆/（BiO）₂CO₃ and Bi₂MoO₆/（BiO）₂CO₃ heterojunction were evaluated for catalytic oxidation of antibiotics.And the Bi/Bi₂MoO₆/（BiO）₂CO₃ showed better photocatalytic activity.Moreover,we found that Bi/Bi₂MoO₆/（BiO）₂CO₃ heterojunction formed a Z-scheme photocatalytic system,in which two kinds of reactive oxygen species（ROS）were generated,and the photodegradation performance of as prepared samples were enhanced.In this system,Bi can be used as a carrier medium to directional separation of photogenic electron and holes,and maintaining the high reducibility of photogenic electrons and the high oxidability of bare holes.However,none of ROS was produced by Bi₂MoO₆/（BiO）₂CO₃ heterojunction composites.Moreover,total organic carbon analysis（TOC）and bacteriostasis experiments showed that CIP can be completely degraded over the Bi/Bi₂MoO₆/（BiO）₂CO₃ heterojunction.The bacteriostasis of the degradation products decreased significantly,and the production of drug-resistant bacteria over the antibiotic drugs were avoided in the natural environment.