Preparation Of Two-dimensional Layered Bismuth-based Photocatalyst And Its Degradation Performance For Organic Pollutants

Organic pollutants not only have potential toxicity and huge yields,but also are difficult to degrade,which seriously threatens ecological safety.Therefore,it is of great significance to develop effective treatment methods for organic pollutants.Photocatalytic technology is favored by researchers because of its advantages of high efficiency,green and low cost.Two-dimensional layered bismuth system semiconductor materials have attracted much attention because of their unique layered tunable electronic structure and highly exposed surface active sites,which help to accelerate the photocatalytic reaction.However,in order to explore the application value of the cheap semiconductor material,it is necessary to further broaden its spectral response range and improve the separation efficiency of photogenerated carriers.Therefore,in this thesis,the two-dimensional layered bismuth-based semiconductor material acted as the matrix,and its electronic structure and surface state were controlled through doping,structural heterojunction,defect control,etc.,to enhance the light absorption performance and charge separation ability of material.By means of a series of characterization tests,the crystal morphology and photoelectric properties of the prepared catalysts were systematically analyzed,focusing on the relationship between the structure and properties of the constructed materials.The prepared catalyst was used in the photocatalytic degradation reaction of organic pollutants,and the photocatalytic degradation mechanism of organic pollutants is revealed in detail.The main research contents and achievements are as follows.（1）Bismuth oxyhalide modified by anion/cation and its photocatalytic degradation performance.In this chapter,Bi OCl nanosheets with Sillen structure were used as the matrix material,and Bi OCl rich in oxygen vacancies（Bi OCl-OV）was obtained by hydrothermal reduction method.The surface structure of Bi OCl was controlled by the double modification of anion PO₄^3-and cation Ag⁺,and finally Bi PO₄/Bi OCl-OV/Ag Cl composites modified by anion and anion was obtained.The results showed that Bi PO₄/Bi OCl-OV/Ag Cl had high photocatalytic activity,and its photocatalytic degradation rate of tetracycline hydrochloride（TC-H）was 38 times that of the substrate Bi OCl and 22 times that of Bi OCl-OV.In addition,Bi PO₄/Bi OCl-OV/Ag Cl also showed a well effect in the photocatalytic degradation of rhodamine B（Rh B）,and the degradation rate reached 100%after 20 min of illumination.On the one hand,the superior photocatalytic performance of the composite material was due to the introduction of oxygen vacancies to form defect energy levels in the Bi OCl forbidden band,which effectively shortened the band gap,thereby enhancing the light absorption performance.On the other hand,the double modification of anion and cation promoted the formation of a double type-II heterojunction at the interface of the composite material,which enhanced the separation ability of photogenerated carriers.In addition,when tap water,Taozi Lake water,Xiangjiang River water and other actual water bodies are used as the water background substrate,the photocatalytic degradation efficiency of Rh B over Bi PO₄/Bi OCl-OV/Ag Cl could still reach 98.41%,93.16%,and 96.25%.In actual wastewater,the mineralization rate also reached 78.17%.So,Bi PO₄/Bi OCl-OV/Ag Cl own well anti-interference ability and potential for industrial applications.（2）Construction of narrow band gap bismuth oxyhalide induced by cobalt ion doping and its photocatalytic degradation performance.In this chapter,Bi OBr nanosheets with highly exposed surface atoms were used as the matrix material,and Co ions were used as the dopant.The Co-doped Bi OBr nanophotocatalyst（Co-Bi OBr）was prepared by solvothermal method.Rh B and TC-H were used as model pollutants to evaluate the photocatalytic activity of the as-prepared materials.The results showed that compared with the substrate Bi OBr,Co-Bi OBr exhibited significantly enhanced photocatalytic activity,and the degradation efficiency of Rh B and TC-H reached 98.93%and 75.46%,respectively.This was mainly because the doping of Co ions promotes a doping energy level to appear in the forbidden band of Co-Bi OBr as an intermediate state,and the band gap was shortened from 2.5 e V of the original substrate Bi OBr to 2.25 e V of Co-Bi OBr.Therefore,the light absorption capacity of as-prepared material was significantly improved,which helped to generate more photo-generated charges,thereby promoting the progress of the photocatalytic reaction.In addition,the Co-Bi OBr crystal was rich in atomic defects,the surface was relatively rough,and the specific surface area was increased,which also helped to improve the adsorption performance of the material,and the improvement of the adsorption performance further accelerated the degradation process of Rh B and TC-H dominated by photo-generated holes.（3）Preparation of Bi₅Fe Ti₃O₁₅by molten salt method and its photocatalytic degradation performance.Bi₅Fe Ti₃O₁₅has a typical Aurigillius structure,has well visible light activity,and is generally obtained by hydrothermal and solid phase methods.In this chapter,Na Cl-KCl was used as the molten salt,and the Bi₅Fe Ti₃O₁₅sample（BFTO-M）was prepared by the molten salt method.XRD results showed that compared with the Bi₅Fe Ti₃O₁₅（BFTO-H,BFTO-S）obtained by the traditional hydrothermal method and solid phase method,the BFTO-M sample prepared by the molten salt method contained a small amount of Bi OCl and Bi₂O_2.75components.Taking Rh B and TC-H as target pollutants,the photocatalytic activity of the prepared materials was evaluated.In the BFTO-H and BFTO-S reaction system,Rh B could hardly be degraded,while in the BFTO-M reaction system,the degradation effect of Rh B was significant,and the degradation rate was as high as 95.8%.This was mainly attributable to the Bi OCl/Bi₅Fe Ti₃O₁₅/Bi₂O_2.75ternary semiconductors in the BFTO-M sample forming a type-II/type-I heterojunction,which effectively improved the separation efficiency of photogenerated carriers.However,the photocatalytic degradation of TC-H over BFTO-M was not obvious,and the degradation efficiency was only 4.87%.After adding H₂O₂,the degradation rate reached 76.74%.This was because Fe in BFTO-M could form a light Fenton system with H₂O₂to further promote the degradation of TC-H.（4）Construction of Bi@Bi₃Ti Nb O₉by in-situ reduction method and its photocatalytic degradation performance.In this chapter,Bi₃Ti Nb O₉nanosheets with Aurvillius structure were used as the matrix material.The in-situ growth of Bi on Bi₃Ti Nb O₉nanosheets was realized by hydrothermal reduction method,and the Bi@Bi₃Ti Nb O₉composite material was successfully prepared.The results showed that Bi@Bi₃Ti Nb O₉exhibited significantly enhanced photocatalytic activity for TC-H degradation,and the degradation rate was 5 times higher than that of the original Bi₃Ti Nb O₉.The degradation reaction activity of Bi@Bi₃Ti Nb O₉sample was closely related to the crystallinity of the metallic Bi phase.Bi@Bi₃Ti Nb O₉also showed a well effect in the photocatalytic degradation of Rh B,and the degradation rate reached100%in 60 min.This was mainly because the photoresponse range of the prepared Bi@Bi₃Ti Nb O₉material was extended to the entire visible light region,and the light absorption capacity was significantly improved.In addition,the Schottky heterojunction formed between the metal Bi and Bi₃Ti Nb O₉effectively promoted the separation of photogenerated charges.In addition,the in-situ reduction method has also been applied to the modification of other semiconductor materials with Aurvillius structure.For example,Bi@Bi₅Fe Ti₃O₁₅was successfully constructed using Bi₅Fe Ti₃O₁₅as the base material.The as-prepared material also showed enhanced photocatalytic activity,indicating that this strategy has great potential in the tuning of Aurvillius semiconductor structure.（5）Preparation of red mud-based Bi₅Fe Ti₃O₁₅by molten salt method and its photocatalytic degradation performance.In this chapter,with the solid waste red mud produced in the process of extracting alumina from bauxite as the precursor,the red mud-based Bi₅Fe Ti₃O₁₅（RM-BFTO-M）was obtained by the molten salt method.EDS and XPS results showed that in addition to Fe elements,RM-BFTO-M also introduced Co,Ca,Al elements in red mud.UV-vis DRS,instantaneous photocurrent and EIS data showed that RM-BFTO-M exhibited enhanced light absorption performance and charge separation efficiency compared to BFTO-M sample.Taking TC-H as the target pollutant,the photocatalytic activity of as-prepared material was measured.The photocatalytic degradation rate of RM-BFTO-M was 211.8 times higher than that of BFTO-M,and the active species h⁺and·OH play a dominant role in the degradation process.LC-MS detected 6 degradation intermediates of TC-H,and the toxicity assessment showed that the acute toxicity,developmental toxicity and mutagenicity of the intermediates were significantly lower than that of TC-H.In order to reveal the mechanism of RM-BFTO-M activity enhancement,Co,Ca,and Al were artificially doped into Bi₅Fe Ti₃O₁₅.The results showed that the photocatalytic activity of the Al-doped sample was significantly enhanced,indicating that the enhancement of the photocatalytic performance of RM-BFTO-M was mainly due to the doping of Al element.