Preparation Of Bismuth Oxyhalide-based Materials For Photocatalytic Pollutants Removal

With the rapid development of the economy and the rapid growth of the world's population,the energy crisis and environmental pollution problems have reached the point that can not be ignored and become a key issue for the people of the world to be solved urgently.As an advanced green oxidation technology,photocatalysis possess a wide range of research and application in the field of environmental pollutant treatment and energy development.Exploring appropriate strategy to promote the effective separation of photogenerated electron-hole pairs in photocatalytic materials is the key point to achieve efficient photocatalysts.In this paper,a series of strategies have been employed to optimize the bismuth oxyhalides and thus enhancing its photocatalytic performance.The microstructures and electronic structures were analyzed by XRD,XPS,FT-IR,Raman,XAFS,SEM,TEM,STEM-HAADF,BET,DRS and other characterization methods.The charge separation and migration processes were studied via photocurrent,EIS,PL and fluorescence lifetime.Combined with the behavior of photocatalytic activity,the intrinsic relationship between the structure of the catalyst and the photocatalytic activity was discussed.The defects in Bi OCl ultrathin nanosheets can be built via pits digging,which can act as an effective platform to study the defect-photocatalytic activity relationship.By virtue of scanning transmission electron microscopy,the surface defects on the BiOCl ultrathin nanosheets can be found.According to experimental and theoretical results,it can be found that the engineered defect can increase the density of states and decrease the band gap.The engineered defect can shorten the migratory paths of hole and build abundant coordination-unsaturated active atoms.The defect-rich BiOCl exhibited enhanced photocatalytic activity relative to Bi OCl ultrathin nanosheets and bulk BiOCl towards the enrofloxacin and rhodamine B?RhB?removal.At the same time,the defect-rich BiOCl nanosheets also exhibited increased photocatalytic oxygen evolution activity.Through solvothermal method combined with pH adjusting,the Bi₄O₅Br₂ photocatalyst with the thickness of about 8 nm was achieved.Through the visible light photo-degradation of tetracycline?TC?and ciprofloxacin?CIP?,the behavior of Bi₄O₅Br₂ ultrathin nanosheets was studied.It can be found that the Bi-rich Bi₄O₅Br₂ can possess an increased photo-degradation activity towards CIP and TC removal than the corresponding BiOBr ultrathin nanosheets.The ESR technique was employed to study the main active specie during the catalytic process and confirmed to be the O₂^·-.The improved photocatalytic activity of Bi₄O₅Br₂ was derived from the variational energy band structure through Bi-rich strategy.The Bi₄O₅Br₂ has a higher CB position than BiOBr,which can reduce the O₂ to produce more active specie O₂^·-.Moreover,the wider valence band and higher CB position can result in better separation of charge carriers.Single-unit-cell Bi₃O₄Br nanosheets with confined surface bismuth and oxygen defects have been prepared through template assisted solvothermal method with facile pH control for the first time.After the preparation of single-unit-cell structure,the bismuth defects are controlled to tune the oxygen defects,in which the bismuth defects favors the generation of more oxygen defects.By STEM-HAADF analysis,the surface defects of the sample can be clearly observed.The existed defects can effective tune the local atomic arrangement and electronic structure.As expected,the defect-rich single-unit-cell Bi₃O₄Br displayed enhanced photocatalytic activity than bulk Bi₃O₄Br towards hydrogen evolution and pollutant degradation.Benefiting from the unique single-unit-cell ultrathin architecture,the bulk charge separation efficiency increased.The surface defects further improve the surface charge separation efficiency.As a result,the overall charge separation efficiency of defect-rich single-unit-cell Bi₃O₄Br greatly increased and boosting the photocatalytic activity.BiOI hollow microspheres was controlled prepared via a microemulsion process with the help of ionic liquid.The whole formation process only require one hour at room temperature with a self-assembly coupled Ostwald ripening formation mechanism.Through the controlled experiment,it can be found that ionic liquid dominate the formation of hollow structure.The RhB,TC and BPA was employed as model pollutant to explore photocatalytic activity of the BiOI hollow microspheres.The improved photocatalytic performance of BiOI hollow microspheres was derived from a synergistic effect,namely multiple scattering of light,increased surface area and better separation of charge carriers.The main active species for the photo-degradation process were O₂^·-and h⁺.The carbon quantum dots?CQDs?/Bi OCl materials was prepared through a solvothermal process.The bisphenol A?BPA?and RhB was employed to study the photocatalytic activity of the achieved CQDs/BiOCl ultrathin nanosheets under near infrared,visible,and ultraviolet light irradiation.The CQDs/Bi OCl displayed greatly increased photocatalytic behavior relative to pristine BiOCl.By virtue of free radicals trapping experiments,XPS valence spectra and ESR analysis,the main active species were comfired to be O₂^·-and hole.The critical role of CQDs for the increased photodegradation behavior was come from the outstanding electron transfer behavior,improved light absorption ability and increased active sites.N-CQDs/BiOI atomically-thin nanosheet was synthesized with control.Up to now,the prepared BiOI nanosheet with 1-2[Bi-O-I]units,was regared as the reported thinnest Bi OX samples.The atomically-thin structure can enable the rapid charge transfer from the interior of BiOI nanosheet to the surface,while the surface modified N-CQDs favor the surface electron-hole separation.By virtue of this structure,both effective charge separation of the materials interior and surface can be obtained.Under the UV or visible light irradiation,the modified N-CQDs can both effective promote the photocatalytic activity improvement towards RhB removal.The main active species can be tuned in this system.Under visible light,the molecular oxygen can be effective activated via the modified N-CQDs to produce O₂^·-.Under UV irradiation,both O₂^·-and·OH can be achieved over N-CQDs/BiOI.Moreover,the concentration of active species can be further increased by N-CQDs.Ag quantum dots?Ag QDs?with size less than 5 nm was employed to couple with BiOBr nanosheets through the assistance of ionic liquid.After the introduction of Ag QDs,the photocatalytic performance of achieved Ag QDs/BiOBr sample can be significantly increased towards the removal of antibiotic agent TC and CIP under visible light.The structure-activity relationship of Ag QDs/BiOBr was exployed via different characterizations and novel role of Ag QDs for the activity improvement was proposed.It can be found that the molecular oxygen can be active to produce O₂^·-over Ag QDs by the generated hot electron in Ag QDs.At the same time,Ag QDs was found to be able to serve as separation centers of charge carriers and active sites for the photodegradation process,result in the excellent photocatalytic performance.CQDs/BiOI microsphere materials have been controlled prepared via a reactive ionic liquid?IL?assisted process.The introduction of IL could serve as a bridge to build tight coupling between BiOI and CQDs.Firstly,the oxygen-containing functional groups in CQDs can construct a powerful combination with IL through hydrogen bond.Then bismuth nitrate can react with the iodide ions in the IL to produce BiOI,and thus the CQDs can be tight coupled with BiOI.The photocatalytic activity of the as-prepared CQDs/BiOI materials was evaluated using RhB as target pollutant.The prepared CQDs/BiOI microsphere can exhibit superior photocatalytic performance for the degradation of RhB.The CQDs in the strong-coupling CQDs/BiOI can enable the effective charge separation,which accout for the higher photocatalytic activity.