Glycine Assisted Synthesis Of BiVO₄/BiOI And Enhanced Simulated Sunlight Activity

Photocatalytic technology is a kind of advanced oxidation process,which can remove the pollutants in water effectively,and mineralize the pollutants completely without secondary pollution.Now,it has been considered as one of the treatment technology with potential application prospect.However,the traditional heterogeneous photocatalytic materials,represented by titanium dioxide,which can only be excited by fewer of ultraviolet in sunlight,because of its larger band gap.Moreover,the rapid recombination of photoinduced electrons and holes greatly lowers the quantum efficiency and lead to the lower degradation efficiency.Therefore,it is inevitable trend to developa novel and high efficiency photocatalytic materials system and enlarge its application in environmental remediation.Bismuth photocatalyst has higher efficient degradation of organic pollution,because its special shell structure and excellet visible light absorption ability.As for the bismuth,the outer electrons is 6s26p3,if lost three electrons,the orbit 6s2 and O₂ p of Bi might cause partly overlapping and formed a new band at the top of the valence band in semiconductor.Itis helpful to reduce the bandgap and increase more absorption of visible light.As well known,morphology control and heterojunction materials design are effective methods to improve the photocatalytic activity.In this work,we use the hydrothermal method,Bio-template glycine as structure-directing agent,prepared a series of BiOI photocatalyst with special morphology,and novel heterojunction photocatalyst BiVO₄/BiOI with high degradation efficiency.The photicatalysts were characterized by X-ray powder diffraction?XRD?,scanning electron microscope?SEM?,transmission electron microscopy?TEM?,N₂ adsorption-desorption isothermal,ultraviolet-visible diffuse reflection spectrum?UV-Vis/DRS?,X-ray photoelectron spectroscopy?XPS?forthe morphology,composition,structure,light absorption properties,and other surface physical and chemical properties.Rhodamine B?RhB?,salicylic acid?SA?,and gatifloxacin?GAT?were chosen as arget pollutants to evaluate the photocatalytic degradation efficiency in the simulated sunlight.The main research contents and results are following:?1?Fabricte the morphology controlled Bi OI photocatalyst: Tetragonal BiOI with uniform size petal composed microspheres morphology was synthesized for the first time usingglycine molecules as templates and Bismuth nitrate as the source of Bi³⁺ and KIas the source of I-.The molar proportions of Bi?NO₃?3·5H₂O and glycine,and hydrothermal time played important roles in the preparation process.As molar ratio is Bi:G=1:2,the hydrothermal time was 12 h,the BiOI exhibited the best reaction activity.Comapared with the BiOI prepared without glycine,the morphology of BiOI prepared with glycinewas more regular,the BET surface area was bigger.Rhodamine-B?20 ppm?and salicylic acid?10 ppm?were chosenas the goal pollutant to evaluate the simulated sunlight catalytic properties.After 60 min simulated sunlight irradiation,the degradation rate was 62.3% and 62.3% for Rhodamine-B and salicylic acid,respectively.However,the photocataytic degradation efficiency of BiOI prepared without glycine only reaches to 42.2% and 49.5%.The enhanced photocatalytic activity was mainly contributed to the bigger BET surface area after addition of glycine and formed regular layer structure,which increased the contact area with pollutant and the surface activity site.?2?Fabricte the novel p-n heterojunction BiVO₄/BiOI composite photocatalyst: Bi?NO₃?₃·5H₂O,NH₄VO₃ and KI was the source materials,and the doping ratio of BiVO₄ and BiOI,hydrothermal temperature,hydrothermal time,and pH were discussed.We optimized more regular morphology and best activity of BiVO₄/BiOI preparation condition: the BiVO₄ doping amount is 30%,pH 7.0,hydrothermal synthesis time is 12 h,hydrothermal synthesis temperature is 140 ?,glycine adding the mole ratio is Bi:G=1:2,the results showed: in the initial concentration of salicylic acid and gatifloxacinwas 10 ppm,respectively,the amount of photocatalyst was 0.1 g,after the simulated sunlight irradiation for 60 min,degradation efficiency reached to 82.2% and 98.5%;Compared with single BiVO₄ or BiOI,degradation activity increased significantly.After four cycles the30%BiVO₄/BiOI also exhibithed higher photocatalytic activity on degradation of SA and indicated the composite material has good stability.A series of characterization,for example,the optical properties,phase structure,surface photovoltage reveals the relationship between the structure and the degradation activity.Moreover,the mechanismofp-n heterojunction to increasephotocatalytic activity and the degradationpath ofsalicylic acid tested by HPLC-MS were discussed.