| In recent years,the contradiction between water environmental pollution and social industrialization has become increasingly prominent,especially the existence of some toxic and non-biodegradable organic substances,such as dyes and antibiotics.These contaminants can exist in water environment for quite a long period of time,seriously threating the human health and ecosystem.Considering of the low operation efficiency of traditional microbial water treatment methods,photocatalytic technology owning more remarkable properties is preferred.And catalysts always occupy the most critical position in it.Among sorts of photocatalysts,bismuth-base semiconductor materials represented by Bi2O3 have attracted widespread attention due to low forbidden band width and the property visible light response.But the low visible light utilization and easiness of photo-generated carriers recombination seriously limit its further promotion and application.Hence developing high-efficiency new bismuth oxide-based catalysts by modification is of great significance.In this paper,based on the electrospinning technology,Combining different preparation methods,rare earth elements Ce,Ce oxides?CeO2?,and Bi2WO6 was used to modify Bi2O3,respectively.A series of linear bismuth oxide-based composite catalytic materials with good visible light response were successfully prepared.The effect of polymers species and electrospinning parameters on the morphology of fibers were investigated.A series of characterizations were also used to study the effect of different methods on the preparation of catalysts.The as-prepaired materials were applied to remove dyes and antibiotic organic contaminents in water and get quite ideal degradation effect.Apart from this,the possible mechanism and the degradation pathway of pollutants were also researched.These will provide providing fundamental basis and technical support for the treatment and control of non-biodegradable organic contaminants in water.The research contents and main conclusions are as follows:?1?The influence of electrospinning process parameters on the morphology of the spun fibers.Using Polyvinyl Pyrrolidone?PVP?and Polyacrylonitrile?PAN?as polymer matrix materials respectively,the different polymer wt%,precursor viscosity,electrical conductivity,aging time,spinning voltage and receiving distance were set to prepare metal salt/polymer composite fibers,and the effect of process parameters on the morphology of the spun fiber was investigated.The results showed that in PVP system,the optimal materials were get when the aging time was 2h,flow rate was1mL.h-1,the PVPwt%was 7%,spinning voltage was 12KV,receiving distance was15cm.And the resulted Bi/Ce/PVP composite fiber exhibited round and smooth morphology with diameter distribution of 375±60nm.As for PAN system,the optimal spinning condition was precursor aging time of 2h,flow rate of 1mL.h-1,PANwt%9%,spinning voltage of 15KV and a receiving distance of 15cm.and the resulted Bi/PAN composite fiber also possessed quite ideal morphology but with a smaller diameter distribution of 279±36nm.?2?Preparation and the study of photocatalytic properties of Ce-doped Bi2O3catalyst.The linear tubular Ce-doped Bi2O3 composite catalysts were prepared using blend electrospinning method under the optimal spinning conditions of PVP system.Characterizations showed that grain size of composite catalysts decreased,Ce was successfully doped into Bi2O3 and replaced the lattice position of part of Bi and the band gap decreased.The study of mechanism indicated that the dope of Ce into Bi2O3formed lattice defects of impurity substitution,effectively regulating the valence band and conduction band position of catalyst,which promoted the migration of photogenerated carriers and prolonged the lifetime of them.Among of Ce-doped catalysts,the BCE4 samples with doping ratio 0.25:1?CE:Bi molar ratio?exhibited the highest photoactivity.Under visible light irradiation,the degradation rate of Methyl Orange(MO,10-2g/L),Rhodamine B(RhB,10-2g/L)and Tetracycline Hydrochloride(TCH,5×10-2g/L)reached 98.81%,83.04%and 88.89%respectively within 90min.The optimal dosage of the catalyst is 5.00g/L and the photodegradation process can be well fitted the Quasi first order kinetic process.The results of free radical trapping experiments showed that the main active substances involved in the photocatalytic reaction process were·OH radicals and holes?h+?.?3?Preparation and study of photocatalytic properties of CeO2@Bi2O3heterojunction composites.Combing the electrospinning technology and dipping load method,the visible-light-response linear CeO2@Bi2O3 heterojunction composite catalysts was successfully synthesized under PAN system and the effect of the amount load of CeO2 on the performance of composite photocatalytic materials was discussed.Researches indicated that the edge of the absorption band of the composite catalyst is red-shifted and the forbidden band width is reduced.The CeO2 and Bi2O3 combined tightly in the composite catalysts and constructed into a p-n heterostructure successfully.There was an formed internal electric field at the interface.It was beneficial to the separation of electron-hole pairs and effectively inhibit the recombination,hence the separation and transfer ability of electron-hole pairs was improved.Among all of as-prepared sampls,the NBC3 sample prepared by one impregnation?loading molar ratio Ce:Bi is 0.43?exhibited the highest photodegradation efficiency.Using this kind of materials,the rate of visible light catalytic degradation of MO(10-2g/L),RhB(10-2g/L)and TCH(5×10-2g/L)reached96.05%,84.19%and 86.14%within 90min,respectively.The optimum dosage of catalyst was 5.00g/L and the highest degradation rate constant was up to 0.02819min-1.Furtherly,the chemical properties of the composite catalyst was Stable.The results of free radical capture experiments revealed that the active substances involved in the photocatalytic process were mainly·O2-free radicals,followed by holes?h+?.?4?Preparation and the study of photocatalytic properties of Bi2WO6@Bi2O3.In PAN system,a linear microtube Bi2WO6@Bi2O3 heterogeneous composite catalyst was successful synthesized based on electrospinning technology combined with solvothermal and de-template method.Characterizations showed that the resulted heterojunction catalyst owned a legible one-dimensional tubular structure and exhibited stronger light adsorption performance than pure monomeric Bi2O3 and Bi2WO6 respectively.Among of the samples,the NBW5 sample with a molar ratio?nW:nBi?of 0.3 appeared the highest photdegradation efficiency.Within 90min reaction,the photocatalytic degradation rates of RhB(10-2g/L),MO(10-2g/L)and TCH(5×10-2g/L)reached 96.31%,96.45%and 84.19%respectively.The optimum dosage of the catalyst was 1.0g/L.and the degradation rate constant of the quasi first-order dynamic process is 0.04645 min-1.A relatively small amount of catalyst can achieve better effect of photocatalytic degradation.The photocatalyst is chemically stable and recyclable.Arrangement in order of importance of the main active substances in the photocatalytic process was:·OH>·O2->h+.?5?Using HPLC-MS/MS technology to analyze respectively the intermediate in water samples of Bi2WO6@Bi2O3 heterojunction degrading MO,RhB and TCH in different time,the possible degradation pathways were proposed.Because of the existence of the surface strong active substances?·OH,·O2-,h+?,the organic macromolecule with complex structure was gradually oxidized through continuously bond breaking and bond forming and ultimately mineralized into CO2?H2O and partial residual small organic molecule. |
PDF Full Text Request