Preparation, Characterization And Photocatalytic Performance Of Bismuth Oxide-Based Microscale And Nanoscale Materials

Bismuth oxide-based microscale and nanoscale materials exhibit great application promising in the field of photocatalytic degradation owing to their good light absorption performance,large specific surface area,high photonic quantum efficiency and good chemical stability.Li-doped Bi₂O₃ nanosheets and Bi₂O₃/In₂O₃Z-type heterojunction materials have been prepared by hydrothermal method and high temperature sintering method,respectively.Co-modified Li-Bi₂O₃(CLB)composites were obtained by a photochemical deposition route using Co Cl₂ as the surface modification material.Carbon dots(CDs)regared as the"electronic carrier"were introduced into Bi₂O₃/In₂O₃ Z-heterojunction through the high-temperature vacuum calcination treatment to prepare the Bi₂O₃/CDs/In₂O₃(BCI)all-solid-state Z-heterojunction.These products were used as photocatalysts to degrade gentian violet(GV)and methylene blue(MB).These research providess necessary experimental and theoretical basis for bismuth oxide-based microscale and nanoscale materials preparation,characterization and application in photocatalytic degradation of organic pollutants,and has an important practical significance for industrial wastewater treatment.Li-Bi₂O₃ nanosheets were prepared via a hydrothermal process using sodium bismuth and lithium acetate as the raw materials.The nanosheets are composed of tetragonal Bi₂O₃ and monoclinal Li₅Bi O₅ phases.The nanosheets are overlapped alternately to form a layered structure.The thickness of each nanosheets is 50-150 nm.Solid-state UV-vis diffuse reflectance spectra showed that Li-Bi₂O₃ nanosheets were typical semiconductor materials with a band gap width of 1.62 e V.The hydrothermal temperature and duration time also have important influence on the formation of nanosheets.With the increase of the hydrothermal temperature,a large number of irregular nanoparticles were gradually transformed into regular nanocrystals,and the products change from hexagonal Li₂O₂ and tetragonal Bi₂O₃ to tetragonal Bi₂O₃ and monoclinal Li₅Bi O₅.The effects of light irradiation time and dosage of Li-Bi₂O₃nanosheets on photocatalytic degradation of GV were studied using Li-Bi₂O₃nanosheets as the photocatalyst.With the extension of the irradiation time and the increase of the amount of nanosheets,the degradation efficiency of GV was significantly improved.The photocatalytic degradation rate of GV using Li-Bi₂O₃nanosheets is 0.0087 min^-1.When the dosage of Li-Bi₂O₃ nanosheets is 30 mg,the degradation rate of 30 m L 10 mg/L GV is up to 99.7%within 360 min light irrduation.Using Co Cl₂ as raw material and methanol solution as additive,Co nanoparticles were loaded on the surface of Li-Bi₂O₃ nanosheets by a photochemical deposition route to form CLB nanostructures.Transmission electron microscopy(TEM)image showed that a large number of Co nanoparticles were randomly dispersed on the surface of the nanosheets.Solid UV-Vis diffuse reflection showed that the light absorption edge of the CLB nanostructures red-shifted to 837.2 nm,the corresponding band gap was 1.48 e V.Photocatalytic degradation of GV results showed that 30 m L10 mg/L GV solution was completely degraded when the light irradiation time extended to 120 min,and the photodegradation rate constant was 0.0257 min^-1.After four cycling degradation experiments,the CLB nanostructures still maintained high photocatalytic activity.Bi₂O₃/In₂O₃ Z-type heterojunction was prepared by water bath and high-temperature sintering process using Bi(NO₃)₃ and In(NO₃)₃ as the raw materials.The Bi₂O₃/In₂O₃ Z-type heterojunction obtained by sintering process at 500?for 2h was composed of tetragonal Bi₂O₃ and cubic In₂O₃ phases.Fourier transform infrared(FTIR)spectrum showed that the main vibration peaks of Bi₂O₃/In₂O₃heterojunction were Bi-O and In-O.The Bi₂O₃/In₂O₃ heterojunction was used as the photocatalyst to degrade GV under natural light irradiation.The results showed that the photodegradation rate could reach 97.9%after 120 min light irradiation.The photodegradation activity was obviously better than that of the Bi₂O₃ and In₂O₃.The photocatalytic degradation mechanism of Bi₂O₃/In₂O₃ Z-type heterojunction was analyzed,and the Z-type transfer route mechanism of the photogenerated carriers was proposed.CDs were introduced into Bi₂O₃/In₂O₃ Z-type heterojunction to prepare Bi₂O₃/CDs/In₂O₃ all-solid-state Z-scheme heterojunction photocatalyst,which was used to photodegrade MB.The results showed that the excellent electrical conductivity performance of CDs increased the transfer rate of the photogenerated electrons between Bi₂O₃ and In₂O₃ interfaces.The broadband light absorption ability of CDs significantly enhanced light absorption intensity of photocatalyst in visible light region.X-ray diffraction(XRD),FTIR and X-ray photoelectron spectroscopy(XPS)measurements proved that CDs were successfully introduced into Bi₂O₃/In₂O₃.TEM image showed that the crystal plane spacing of CDs was 0.551 nm.Photocatalytic degradation results showed that different amounts of CDs have effect on the photodegradation rate of MB.When CDs content was 10 mg,the prepared BCI all-solid-state Z-type heterojunction manifested the optimal photodegradation performance,the corresponding reaction rate(k)was 0.0289 min^-1,10 mg/L MB could be fully degraded within 100 min light irradiation.The value of k was 12.04,22.23,and 4.45 times than that of Bi₂O₃(k=0.0024 min^-1),In₂O₃(k=0.0013 min^-1)and Bi₂O₃/In₂O₃(k=0.0065 min^-1),respectively.