Preparation And Photocatalytic Properties Of Non-stoichiometric Bi-O-Br Photocatalvst

As an environmental-friendly technology,heterogeneous photocatalysis through semiconductor systems has been considered to be a competitive and promising technology for environmental remediation and solar energy conversion.Various semiconductor materials have been successfully synthesized as photocatalysts for pollutants removal from air or water,CO2 capture,hydrogen generation,etc..BiOBr has been intensively investigated due to its open-layered structure,indirect transition mode and excellent photocatalytic performances.However,the performance of BiOBr is limited by its low light-harvesting ability,low reduction ability of photoelectron,and fast recombination of photo-excited electrons-holes,which are closely associated with their intrinsic bandgap levels.From the nature of substance,the valence band?VB?top of bismuth oxybromides is primarily composed of hybrid orbitals of Br 4p and O 2p orbitals,whereas the conduction band?CB?bottom mainly consists of Bi 6p orbitals.The band-gap structure of Bi-O-Br ternary compound can be regulated and controlled by adjusting the ratio value of Br,O and Bi in bismuth oxybromide materials,and then resulting in the increased photocatalytic activity.Therefore,it becomes a research focus to explore a facile and highly efficient method to synthesize non-stoichiometric Bi-O-Br photocatalysts with high photoacitivity.Based on the above consideration,the purpose of this dissertation is to investigate the Bi-O-Br ternary compound.We firstly studied the effect of preparation conditions on the microstructure of BiOBr,and found a novel green route for the synthesis of Bi₄O₅Br₂ at room temperature.Then,we conducted a systematic studies for the formation mechanism,band structure,and photocatalytic activity of Bi₄O₅Br₂.And according to the formation mechanism of Bi₄O₅Br₂,we discovered a new facile modification for achieving the band-gap of Bi₄O₅Br₂ photocatalytst continuously variable and found out the relationship between the band-gap structures and the optical properties of photocatalyst.In addition,in order to improve the reduction ability of BiOBr,we constructed a novel Z-Scheme BiOBr/Bi₁₂O₁₇Br₂ photocatalyst by controlling the ratio of ethylene glycol and water in the hyrolysis solution at room temperature.Finally,we prepared Bi₂₄O₃₁Br₁₀,Bi₂₄O₃₁Br₁₀/Bi₃O₄ Br,and Bi₃O₄ Br photocatalytsts by changing the preparation conditions and discussed their photocatalytic activities.The main research contents are as follows:?1?The BiOBr photocatalysts with different morphologies,and crystalline facets orientation were synthesized using BiBr₃ as precursor at different solvents of water,ethanol,ethylene glycol,and isopropanol.The photocatalytic activities of different BiOBr had been evaluated by the degradation of methyl orange?MO?under simulated sunlight.The results showed that the crystalline facets and morphologies of BiOBr both had an influence on the photocatalytic activities of Bi OBr.BiOBr prepared in water solvent showed superior photocatalytic activities and stability towards the degradation of MO due to its best crystallinity and unique?102?facets.The degradation efficiencies of MO could reach 91.3% after simulated sunlight irradiation for 75 min and still remain 90% degradation rate after five cycles.In addition,we found out a novel synthetic route for preparing Bi₄O₅Br₂ at room temperature.?2?A novel Bi₄O₅Br₂ photocatalyst was successfully synthesized via the structure reorganization of BiOBr at room temperature.The morphology,crystalline structure,band structure,and photocatalytic activity of Bi₄O₅Br₂ were studied and the results showed that the obtained Bi₄O₅Br₂ sample had narrower band-gap and higher light-harvesting ability than BiOBr, so the Bi₄O₅Br₂ displayed excellent visible-light-driven photocatalytic activity towards resorcinol?RC?.The degradation efficiencies of RC could reach 99.6% after visible light irradiation for 120 min over Bi₄O₅Br₂.Moreover,Bi₄O₅Br₂ displayed good stability with 97% degradation efficiency after five cycles.Finally,according to the formation mechanism of Bi₄O₅Br₂,It can be found that the water-steeping time and the quantity of NH3·H₂O both had certain influence on the photocatalytic activity of Bi₄O₅Br₂.?3?In order to clarify the relationship between band-gap and optical properties,we employed a simple iodine modification method to prepare the Bi₄O₅Br₂ phtocatalyst with continuously controllable band-gap at room temperature.The morphology,crystalline structure,band structure,and photocatalytic activity of samples were studied and the results showed that the band gap of Bi₄O₅Br₂ could be continuously modulated from 2.46 eV to 2.16 eV by governing the KI concentration.With the CB position of Bi₄O₅Br₂ was declined,the visible absorption ability was increased,then resulting in a significant enhancement of the photocatalytic performance.The maximum photocatalytic performance could arrive when the band gap of Bi₄O₅Br₂ was 2.30 eV.The bisphenol A removal efficiency could research 95% after visible light irradiation for 120 min,the NO removal efficiency could reach 31% after visible light irradiation for 30 min.?4?In order to improve the reduction ability of BiOBr,we constructed a novel BiOBr/Bi₁₂O₁₇Br₂ Z-Scheme photocatalyst by controlling the ratio of ethylene glycol and water in the hyrolysis solution at room temperature.The morphology,crystalline structure,band structure,and photocatalytic activity of samples were studied and the results showed that in BiOBr/Bi₁₂O₁₇Br₂ photocatalytic reaction system,the photogenerated electrons in CB of BiOBr could recombine speedily with the photo-induced holes of Bi₁₂O₁₇Br₂.And the holes in VB of Bi OBr and the CB electrons of Bi₁₂O₁₇Br₂,which had higher oxidation and reduction ability,then were involved in RC degradation.Therefore,the BiOBr/Bi₁₂O₁₇Br₂ composites showed superior reduction ability,and the photocatalytic activity of BiOBr were significantly improved.The RC removal efficiency could research 95% and the NO removal efficiency could research 57% after simulated solar light irradiation for 30 min.?5?In order to enrich the species of non-stoichiometric Bi-O-Br,we employed a simple hydrothermal method to prepare the BiOBr,Bi₂₄O₃₁Br₁₀,and Bi₃O₄ Br photocatalysts using Bi?NO₃?₃·5H₂O and KBr as row materials.The morphology,crystalline structure,band structure,and photocatalytic activity of samples were studied and the results showed that the band-gaps of Bi₂₄O₃₁Br₁₀ and Bi₃O₄ Br were both narrower than that of BiOBr,leading to better absorb photons in the solar energy spectrum.Therefore,Bi₂₄O₃₁Br₁₀ and Bi₃O₄ Br photocatalysts presented a remarkable visible light-driven photocatalytic activity towards photodegradation of sulfamethoxazole and NO.The degradation efficiencies of sulfamethoxazole were 76% and 65% for Bi₂₄O₃₁Br₁₀ and Bi₃O₄ Br in 180 min under visible light irradiation.The NO removal efficiencies were 26% and 20% for Bi₂₄O₃₁Br₁₀,and Bi₃O₄ Br in 30 min under visible light irradiation.