Preparation Of Bi-based Semiconductors/MOFs Composites And Their Photocatalytic Performance

As the society grows and technology enhance continuously,serious environmental pollution becomes the main concern for realizing the sustainable development of human society.Therefore,creating the harmonious ecological environment is an important subject in the scientific community.Among various solar technologies,photocatalysis based on semiconductors has attracted wide attention as a green technology,which can convert solar energy into chemical energy and serve as a very different approach to solar energy utilization,for instance,used in the degradation of organic pollutants with excellent performance.However,the low utilization of solar energy and the high recombination of photo-generated carriers limit its practical application.Therefore,there is an urgent need to develop stable,highly efficient and wide-spectrum-responsive photocatalysts for the photocatalytic technology.The porous structure of the MOFs material makes it have a larger specific surface area,which can adsorb organic pollutants in the photocatalytic process and form more active sites on the surface of the photocatalytic material;while the Bi-based semiconductors with unique electronic structure have a narrower forbidden band width,which can more effectively improve the utilization rate of sunlight than traditional photocatalytic materials.In this work,a novel heterojunction composites material with high visible-light-driven photocatalytic activity was designed,which was constructed with Bi-based semiconductors and Metal-Organic Frameworks（MOFs）due to their good structural characteristics and matched band gap.XRD,XPS,SEM,TEM,EDS,DRS and other analytical methods were used to characterize the structure,morphology,and optoelectronic properties.The photocatalytic performance of the material was studied by the degradation of rhodamine B（RhB）under the visible light irradiation.Based on the above,this research has carried out:1.First,the BiVO₄ particles were prepared by direct precipitation method at room temperature with ultrasonic stirring.Then,BiVO₄/NH₂-UiO-66 binary composite photocatalytic material with a type II heterojunction was prepared by coupling with the NH₂-UiO-66 MOFs and BiVO₄ through microwave synthesis.The results present that the construction of heterojunctions can effectively suppress the recombination rate of photogenerated carriers and greatly improve the photocatalytic performance.When the mass ratio of BiVO₄ to the metal ligand ZrCl₄ of MOFs is 40%,the Bi VO₄/NH₂-UiO-66 shows the best photocatalytic performance.Under visible light irradiation for 150min,the degradation rate of RhB is more than 90%.Nearly no deterioration of the photocatalytic efficiency was observed after five cycles,indicating the excellent stability of as-prepared BiVO₄/NH₂-UiO-66 composites during the photocatalytic process.The radical species trapping experiments confirmed that the·O₂^-was the mainly active species involved in the degradation of RhB under the visible light irradiation.2.Peanut-shaped BiVO₄ was also prepared by the direct precipitation method at room temperature with ultrasonic stirring.Then BiVO₄/NH₂-MIL-125 binary composite material with type II heterojunction was synthesized by composing the NH₂-MIL-125（Ti）MOFs with BiVO₄ by solvothermal method.The results show that the formation of the heterojunction broadens the photo response range of BiVO₄,reduces the recombination rate of photogenerated carriers effectively,increases the mobility of photogenerated carriers,and thus improves the photocatalytic performance.It can be found that the photocatalytic material illustrates the best photocatalytic activity when the mass ratio of BiVO₄ to isopropyl titanate is 30%.The degradation rate of rhodamine B is more than 90%when exposed to visible light for 120 min.It was clearly observed that the photodegradation rate of RhB was maintained 97%after five runs under visible light irradiation,indicating the excellent stability of as-prepared BiVO₄/NH₂-MIL-125composites during the photocatalytic process.The radical species trapping experiments confirmed that the·O₂^-was the mainly active species involved in the degradation of organic pollutants under the visible light irradiation.3.Bi₄O₃Ti₁₂ was prepared firstly by the chemical precipitation method.Then,the Bi₄O₃Ti₁₂/NH₂-MIL-125 binary composite photocatalytic material with type II heterojunction was obtained by the solvothermal method followed by the high temperature treatment.The results demonstrate that MOFs materials broaden the spectral response range of Bi₄O₃Ti₁₂,improve the utilization of sunlight,reduce the recombination rate of photo-generated carriers,and improve the mobility of photo-generated carriers.Compared with single Bi₄O₃Ti₁₂ and NH₂-MIL-125（Ti）,photocatalytic performance of the binary composite has been improved.When the mass ratio of Bi₄O₃Ti₁₂ to isopropyl titanate is 5%,the composite material has the best photocatalytic activity.Under visible light Irradiation for 120 min,the degradation rate of rhodamine B solution reaches 95%.The active species trapping experiments indicates that·O^2-plays a vital role during the photocatalytic reaction,and h⁺comes second.