Preparation Of Bismuth Phosphate Based Composites For Removal Organic Pollutions

Dyes and antibiotics are widely used in modern industry and social life.It may be released to the water body during the using process,which has caused great harm to the ecological environment and human health.Semiconductor photocatalytic oxidation technology,an advanced oxidation technology,can be used to remove organic pollutants from water by using solar energy as the driving force.Compared with traditional oxidation technology,the technology has some advantages such as energy saving and no secondary pollution.The development of photocatalyst is the key step of photocatalytic oxidation technology.Bismuth phosphate（BiPO₄）,with excellent performance,is a wide band gap semiconductor photocatalyst.However,BiPO₄ still has two obvious defects.First,the absorption of visible light is weak;Second,the yield of photogenerated carriers is low.To improve the visible light absorption performance and quantum utilization of BiPO₄,this paper intends to use semiconductor composite to modify BiPO₄.First,the photocatalytic performance of BiPO₄ was studied systematically.Second,three semiconductors such as BiVO₄,FeVO₄,and CuV₂O₆ with narrow band gap and GO/rGO choose to modify BiPO₄,and their photocatalytic performance were studied.Third,the corresponding artificial neural network model for photocatalytic degradation was established.The main researches are as follows:（1）Preparation and photocatalytic degradation properties of BiPO₄.The n-type BiPO₄ semiconductor photocatalyst was successfully prepared by hydrothermal method.The stucture and properties were characterized and analyzed.The results showed that the morphology of prepared BiPO₄ was prismatic,and the crystal structure was monazite low temperature monoclinic phase.The effects of catalyst dosage,initial Moxifloxacin（MOX）concentration and initial pH of solution on the photocatalytic degradation of MOX were investigated.The effects of some anions(CO₃^2-,HPO₄^2-,SO₄^2-,Cl-and F-)and cations(Na+,Zn²⁺ and Al³⁺)on the degradation of MOX were also studied.The results show that pH is the key factor in the process of MOX photocatalytic degradation over BiPO₄.The main active species in the process of the photocatalysis is·OH.（2）Preparation and photocatalytic performance of BiVO₄/BiPO₄/rGO.Using BiVO₄ and GO or rGO as modifiers,BiVO₄/BiPO₄/rGO p-n heterojunction ternary composite catalyst was prepared.The composition and structure of the composites were studied.The results show that the morphology and crystal structure of BiPO₄ and the crystal structure of BiVO₄ did not be changed after the hydrothermal.However,the morphology of BiVO₄ changed from nanorod to nanoparticle,while the size decreased significantly and the scattered BiVO₄ grew on the surface of BiPO₄.rGO and BiVO₄ are closely bound to BiPO₄.The photoelectric performance test shows that the optical absorption boundary of the composite extends from 278 nm to 494 nm,indicating that the absorption of visible light by composites is higher than that of BiPO₄.Due to the formation of built-in electric field and the high conductivity of rGO,the photo-generated carries separation efficiency and charge transfer efficiency of BiVO₄/BiPO₄/rGO is efficiently enhanced.The promotion of photocatalytic degradation performance of BiVO₄/BiPO₄/rGO is originated from the increasing of light absorption,separation of photogenerated carries,and efficiency of charge transformation.At pH=9,the degradation rate of Methylene blue（MB）is 94.4%after 100 min under visible light irradiation.At pH=11,the degradation rate of MOX is 82.0%after 70 min under visible light irradiation,which is 1.9 and 4.1 times that of BiPO₄,respectively.In addition,the MB degradation process and the initial MOX degradation process followed the first-order kinetic model.The main active species is·O2-.（3）Preparation and photocatalytic performance of FeVO₄/BiPO₄/GO.Using FeVO₄ and GO as modifiers,FeVO₄/BiPO₄/GO n-n heterojunction ternary composite catalyst was prepared.The characterization results showed that the morphology of FeVO₄ changed from irregular particles to small and uniform nanoparticles.FeVO₄ particles grew on the surface of BiPO₄ discretely.FeVO₄,BiPO₄ and GO are closely combined with each other.The photoelectric performance test shows that the optical absorption boundary of the composite extends from 278 nm to 590 nm,means the visible light absorption of composites is improved.Because of the formation of built-in electric field and the high conductivity of GO,the photo-generated carries separation efficiency and charge transfer efficiency of FeVO₄/BiPO₄/GO is increased.The promotion of photocatalytic degradation performance of FeVO₄/BiPO₄/GO is originated from the increasing of light absorption,separation of photogenerated carries,and efficiency of charge transformation.At pH=9,the degradation rate of MB is 84.0%after 100 min irradiation under visible light,the degradation rate of MOX is 49.6%after 70 min irradiation under visible light,which is 1.7 and 2.5 times that of BiPO₄,respectively.Furtherly,the MB and MOX degradation process followed the first-order kinetic model.In addition,the main active species in the degradation process is·OH.（4）Preparation and photocatalytic performance of CuV₂O₆/BiPO₄/GO.Using CuV₂O₆ and GO as modifiers,CuV₂O₆/BiPO₄/GO n-n heterojunction ternary composite catalyst was prepared.The characterization results showed that the morphology of FeVO₄ changed from nano ribbon to small and uniform nanoparticles.The small particles CuV₂O₆ grew on the surface of BiPO₄ discretely.CuV₂O₆,BiPO₄ and GO are closely combined with each other.The photoelectric performance test shows that the optical absorption boundary of the composite extends from 278 nm to 630 nm,indicating that the absorption of visible light by composites is higher than that of BiPO₄.Because of the formation of built-in electric field and the high conductivity of GO,the photo-generated carries separation efficiency and charge transfer efficiency of CuV₂O₆/BiPO₄/GO is increased.The promotion of photocatalytic degradation performance of CuV₂O₆/BiPO₄/GO is originated from the increasing of light absorption,separation of photogenerated carries,and efficiency of charge transformation.At pH=7,the degradation rate of MB is 95.7%after 30 min irradiation under visible light,and the degradation rate of MOX is 92.2%after 42 min irradiation under visible light,which is 7.1 and 18.1 times that of BiPO₄,respectively.In addition,the MB degradation process and the initial MOX degradation process followed the first-order kinetic model.The mian active species in the degradation process is·O2-.（5）The ANN model was established for the photocatalytic degradation system.The ANN model structure is that the hidden layer is a single layer and the number of nerves in the hidden layer is 11.The model has excellent fitting performance for the selected data.Factor sensitivity analysis shows that the introduction of selected narrow band gap semiconductors such as BiVO₄,FeVO₄ and CuV₂O₆ is the key factor for the improvement of the photocatalytic degradation performance of BiPO₄.Other factors such as the introduction of GO or rGO,the initial pH of the degradation solution and the degradation time have different effects on the degradation performance in different catalyst systems.The preparation conditions of the catalysts were optimized by Sparrow Search Algorithm.The stability and general degradation performance show that the photocatalytic degradation performance of the optimized sample is stable.After three cycles,the degradation rate is more than 90%.In addition to the excellent degradation performance of MB and MOX,it also has good degradation effects on other organic pollutants.