Investigation On Bismuth Oxyhalide Based Composites Applied To Photocatalytic Degradation Of Antibiotic

As a kind of multifunctional drug,antibiotics are widely used in medical treatment,animal husbandry and other industries.The resulting abuse of antibiotics has led to the release of a large number of antibiotics and their metabolites into the environment and aroused great concern.The efficient removal of antibiotic pollutants in water has become a research hotspot.Because of the low efficiency,secondary pollution and high cost of traditional water treatment technologies,it is urgent to develop a new efficient water treatment technology.photocatalytic technology which uses green solar energy as the only energy input to eliminate pollutants in waters by initiating heterogeneous redox reactions on the surface of semiconductor photocatalysts,has been considered to be an efficient,safe,cheap and sustainable water treatment technology.Bismuth oxyhalide(BiOX),a typical class of Ⅴ-Ⅵ-Ⅶternary semiconductor materials,has been a well-deserved hotspot in the field of photocatalysis due to its unique layered structure,excellent carrier transport properties,good chemical stability,corrosion resistance,and non－toxicity.However,their further applications are limited by the poor light absorption capacity,the swift recombination of photoinduced carriers,and the slow surface reaction.In this research,BiOX was modified by dominant crystal facet exposure,quantum dot loading,bismuth-rich strategy,and heterostructure construction(type Ⅱ and type Z)to remedy the abovementioned defects of BiOX.Meanwhile,the photocatalytic performance,mechanism and application potential of BiOX-based composite materials for the removal of antibiotic pollutants were investigated.It provides new ideas and theoretical basis for the practical application of bismuth oxyhalide-based photocatalysts in the field of organic pollutants treatment.The specific contents and conclusions of this paper are summarized as follows:(1)BiOCl(BOC-001 and BOC-010)with different crystal surface exposed were prepared by pH modulation during the hydrothermal process,and then NCQDs with excellent electrical conductivity were loaded to form 10NBOC-001 and 10NBOC-010 composite,respectively.Firstly,the exposed crystal facet of BiOCl and the successful preparation of the composites were determined by XRD,XPS and TEM characterization method.Subsequently,photocatalytic degradation experiments showed that 10NBOC-010 possess the best CIP degradation performance,and its degradation rate is 21.2,10.8 and 1.9 times higher than that of BOC-001,BOC-010 and 10NBOC-001,respectively.Finally,the result of BET,photoelectrochemical experiments,and firstprinciples calculations point out that the main reason for the improved photocatalytic performance of 10NBOC-010 is the synergistic effect of {010}crystal facet and N-CQDs.The open atomic channels of the BiOCl {010}crystal facet can furnish larger accommodation space and more active sites for the adsorption of CIP moleculars and the loading of N-CQDs.Meanwhile,the loading of N-CQDs on the {010} crystal facet promotes the electrons move along the[Bi2O2]2+→ N-CQDs → Cl-covalent ring,resulting in the formation of an interfacial electric field,which is beneficial to the separation and migration of photogenerated carriers.In addition,the loading of N-CQDs improved the light absorption capability of the composites in the ultraviolet and visible light regions.Capture experiments and ESR tests manifest that ·O2plays a major role,followed by h+and ·OH during the photocatalytic degradation of CIP by 10NBOC-010.(2)Although the exposure of the dominant facet and the loading of NCQDs improved the photocatalytic activity of BiOCl,the wide band gap of BiOCl still limits its utilization of the solar spectrum.Therefore,a bismuthrich bismuth oxychloride(Bi12O17Cl2 with a suitable energy band structure was prepared by a bismuth-rich strategy,and then it was modified by forming a heterojunction with another typical two-dimensional(2D)layered material CoAl-LDH.XRD,XPS and TEM results show that a type Ⅱ heterojunction is form between the 2D Bi12O17Cl2 and 2D Coal-LDH through Co-Cl bond connecting.Subsequently,the photocatalytic performance of the CoAlLDH/Bi12O17Cl2 composite was evaluated by degrading POPs in water/wastewater under visible light and actual sunlight irradiation,and the effects of the composite photocatalyst and the treated POPs on the ecosystem were also evaluated.When the content of CoAl-LDH is 5%,the composite(5LB)has the best photocatalytic activity,91.49%(92.47%)of CIP and 79.37%(95%)of BPA can be degraded within 2 h irradiation of visible light(or actual sunlight).The enhanced photocatalytic performance can be attributed to the successful formation of a Co-Cl bond reinforced type Ⅱ heterojunction between 2D Bi12O17Cl2 and 2D CoAl-LDH,which leads to broad absorption spectra,fast photogenerated carrier migration,and abundant active site exposure.The results of free radical capture experiment,EPR,LC-MS and density functional theory showed that the photocatalytic degradation of CIP was mainly realized by h+and 1O2 attacking the active atoms of CIP molecule with high Fukui index.Finally,the cycle test of 5-LB,the real water treatment experiment and the toxicity evaluation experiment further was applied to evaluated the feasibility of the 5-LB to treat POPs in real water under irradiation of solar light.(3)Although the construction of type Ⅱ heterojunction can promote the migration of photogenerated carriers,it will reduce the redox ability of the photocatalytic system to a certain extent.The construction of Z-scheme heterojunction is an ideal method to avert the loss of redox capacity of photocatalysts.Based on the research in the previous chapter,a Z-scheme Bi12O17Cl2/Ag/AgFeO2 photocatalyst was prepared in this chapter.AgFeO2 nanoparticles were firstly deposited on the surface of Bi12O17Cl2 by in-situ precipitation method,and then Ag nanoparticles were introduced as electronic mediators by ethanol-assisted ultrasonic reduction method.XRD,XPS,SEM,TEM,BET and other methods were used to understand the basic characteristics of the as-prepared samples.The photocatalytic degradation experiment illustrates that the 20-BAF composite possesses the best photocatalytic removal performance(94.1%)for TC.The improved photocatalytic performance is mainly due to the energy band structure between Bi12O17Cl2,AgFeO2 and Ag nanoparticles promoting the formation of Zscheme system and the SPR effect of Ag nanoparticles.In addition,the capture experiments and ESR characterization manifest that the main factor in the degradation of tetracycline was ·O2-generated by electron with strong reducing ability in Bi12O17Cl2 conduction band,followed by h+in AgFeO2 valence band with strong oxidizing ability.(4)In order to further improve the utilization of long-wavelength light(Vis-NIR)for bismuth oxyhalide,firstly,a bismuth-rich bismuth oxyiodide(Bi5O7I)with good stability was prepared by a bismuth-rich strategy,and then it was combined with a narrow bandgap semiconductor Bi4O7 by a hydrothermal method.The construction of Z-scheme heterojunctions between bismuth oxyhalide and narrow-bandgap semiconductors not only extends the photoresponse range to the NIR region,but also improve the separation and transfer efficiency of photogenerated carriers.Compared with pure Bi5O7I and pure Bi4O7,the optimal composite(3-BBO)showed splendid photocatalytic effect under Vis and NIR light irradiation,and its photocatalytic degradation rate for TC under 90 min Vis and NIR light irradiation is 94.8%and 31.9%,respectively.According to the analysis of UV-Vis DRS,electrochemical experiments and DFT calculation results,the main reasons for the improvement of photocatalytic performance of 3-BBO are that the introduction of Bi4O7 extends the light response range,and the formation of the electric field at the interface of the heterojunction promotes the separation of photocarriers.The result of free radical trapping experiments,ESR experiments and frontier orbital theory showed that the attack of ·O2-,·OH and h+species on C13,C8,N28 and O19 sites of TC molecular was the main cause of TC degradation.In addition,3-BBO composites can be effectively applied to the degradation of TC in complex water environment.This study provides a theoretical basis for designing efficient broad-spectrum responsive bismuth oxyhalide photocatalysts.