Study On Design,Synthesis And Properties Of Bismuth Oxybromide Based Composites For Photocatalytic Degradation Of Antibiotics In Water

With the rapid growth of population and the resulting huge consumption of fossil fuels,energy demand and environmental pollution have become two important global issues facing mankind.Photocatalysis technology as an important branch of advanced oxidation process,taking solar energy as the driving force,has the advantages of energy saving,environmentally-friendly,simple operation,low cost,mild reaction conditions,etc.Therefore,photocatalysis is expected to be a new generation of environmental management technology.Bismuth oxybromide(BiOBr)is an important kind of V-VI-VII ternary inorganic semiconductor,which has been widely studied as a photocatalyst due to its good chemical stability,visible light absorption,non-toxicity,corrosion resistance and spontaneous internal electric field.However,due to the limited light absorption capacity,the lack of active sites on the surface and the rapid recombination of photogenerated carriers,the photocatalytic performance of BiOBr is far from meeting the practical requirements.In this study,BiOBr was modified by some strategies,such as heterojunction construction(type I or type II),morphological control,element doping,up-conversion effect by quantum dots and creating oxygen vacancy to remedy the above-mentioned weakness of BiOBr.Meanwhile,the photocatalytic degradation performance and mechanism towards antibiotics in water over BiOBr were studied.In this study,a theoretical innovation was made for the design and synthesis of novel bismuth oxybromide-based composite photocatalysts and their applications in pollution control.The main work and specific results of this study are described below:(1)The perylene diimide supramolecular(PDIsa)organic photocatalyst was combined with BiOBr to construct the traditional type I heterojunction by electrostatic self-assembly method.The results showed that the modification by PDIsa could improve the light absorption capacity and photogenerated charge separation efficiency of BiOBr.The results of UV-Vis diffuse reflection showed that the presence of PDIsa enhanced the absorption ability of the composites in both ultraviolet region and visible light region,as well as extended the response range for visible light.The interface electric field was formed at the interface between PDIsa and BiOBr,which drove the electrons and holes generated on BiOBr to transfer to PDIsa.And then these charges would be separated by the polarization electric field of PDIsa.The degradation efficiency of ciprofloxacin(CIP)over the optimal PDIsa/BiOBr composite was 85.2 5%under 90 min of visible light irradiation,and the quasi-first-order kinetic degradation rate was 3.2 times that of pure BiOBr.Pure PDIsa had no CIP degradation activity.In addition,the total organic carbon(TOC)removal efficiency can reach 67.3 4%within120 min.The CIP decomposition efficiency of PDIsa/BiOBr composites remained at78.71%after five times of cyclic illumination,and the FT-IR and XRD characterization results of the composites had no significant changes before and after treatment.The results of this cycle experiment fully showed that the PDIsa/BiOBr composites had a stable material structure and could be reused Trapping experiments and electron spin resonance(ESR)tests showed that superoxide radical(·O₂^-)was the most active species,and singlet oxygen(¹O₂)and hole(h⁺)played secondary role.(2)In order to promote the spatial separatio n of photoelectric charge and enlarge the specific surface area of BiOBr-based photocatalyst,traditional type II heterojunction with hierarchical structure was constructed by in-situ growth of BiOBr nanosheets with dominantly exposed(010)facets on indiu m vanadate(In VO₄)nanoparticles via microemulsion method.Compared with pure BiOBr,the In VO₄/BiOBr hierarchical composite had a larger specific surface area,which improved the affinity of the outer BiOBr with the contaminant.The formation of type II heterojunction effectively promoted the photogenerated electrons and holes to move in the opposite direction,leading to the production of the main active species,·O₂^-on the surface of BiOBr.It provided a shortened distance between·O₂^-free radicals and the absorbed CIP molecules,so that the decomposition reaction of CIP could occur as soon as possible.Resultantly,the photocatalytic removal of CIP over the optimal composite was improved compared with pure BiOBr.After 60 min of adsorption and60 min of visible light irradiation,the removal efficiency of CIP was as high as 97.04%,and the mineralization efficiency within 120 min of illumination was up to 71.88%.The Langmuir-Hinshelwood model was used to analyze the adsorption and degradation data,and the highest removal rate constant of CIP was 0.1127 mg L^-1 min^-1,which was2.12 and 70.44 times of BiOBr and In VO₄ in the identical conditions,respectively.(3)In order to enhance the intensity of interfacial electric field within heterojunction and promote the separation of photogenerated electron-hole pairs more effectively,partially etching method was conducted to in situ synthesis tin doped bismuth oxybromide(Sn-BiOBr)on the surface of bismuth oxyiodate(BiOIO ₃)template.Field emission scanning electron microscopy(SEM)images showed that this simple synthesis method could uniformly distribute Sn-BiOBr particles on the surface of BiOIO₃ nanoribbons.The UV-Vis diffuse reflectance results showed that the optical absorption range of Sn-BiOBr/BiOIO₃ composite was extended to about 500 nm,and the overall absorption capacity was higher than that of pure BiOBr.The results of photochemical experiments and Density Functional Theory(DFT)calculations showed that Sn doping could induce the redistribution of charge at the interface of BiOBr/BiOIO₃ heterojunction and increase the interfacial electric field intensity,thus further enhancing the separation ability of photogenerated electrons and holes.Therefore,the doped heterojunction showed excellent performance in degrading organic pollutants.Under visible light irradiation,the degradation efficiency of tetracycline(TC)and 2,4-dichlorophenol(2,4-DCP)reached 85.66%and 80.01%in60 min,respectively,and the degradation efficiency of rhodenine B(Rh B)was 99.90%in 20 min.The degradation rates of the above pollutants were 1.3,3.0 and 10.0 times higher than that of undoped BiOBr/BiOIO₃ composite,respectively.After five cycles,the Sn-BiOBr/BiOIO₃ composite still remained high degradation ability.In addition,the composite has excellent mineralization ability with TOC removal rates of 34.61%,56.50%and 57.73%within 60 min,respectively.(4)BiOBr was modified by nitrogen doped carbon quantum dots(N-CQDs)and oxygen vacancy(OV)to solve the problem that BiOBr could not respond to near-infrared light.SEM images showed that the morphology of the composites with oxygen vacancies changed from sheet shape to flower shape,which was conducive to multiple reflection of photons between components.UV-Vis-NIR absorption spectra showed that OV and N-CQDs had synergistic effects on the light response of BiOBr.The former could improve the intrinsic absorption capab ility of BiOBr,and thereby the fluorescence generated by the latter could be fully utilized.Photochemical tests showed that both N-CQDs and oxygen vacancies could capture photogenerated electrons,thus efficiently inhibiting the recombination of charge c arriers.In addition,N-CQDs and OV could convert O₂ to·O₂^-radicals and hydrogen peroxide(H₂O₂),respectively,through single-electron reduction and two-electron reduction.Therefore,the decomposition of TC would get improvement through direct oxidatio n reaction and indirect photo-Fenton reaction,respectively.Compared with pure BiOBr,the photocatalytic degradation of TC in all the solar wave bands by N-CQDs/OV-BiOBr composite was enhanced.The degradation efficiencies were 89.42%and 82.68%under UV and visible light irradiation,respectively,within 60 min.It was 12.11%under near-infrared light irradiation after 120 min.In addition,the composite could be effectively applied to the degradation of TC in real water environment.