| Photocatalytic oxidation technology has been extensively studied in recent years in the field of wastewater treatment for its simpler operation,higher efficiency,better stability and higher mineralization rate.However,the photocatalytic oxidation technology is not most favored in wastewater treatment because of the hight cost of preparation,low rate of using natural light and bad stability of materials,making it is crucial to study photocatalytic materials with high catalytic activity and stability under visible light in the field.Since bismuth oxide?Bi2O3?was discovered as a photocatalyst in 1980s,remarkable progress has been made on the treatment of organic wastewater by Bi2O3 due to gradually in-depth reaerch on it.Bi2O3 and its composite materials have been successfully prepared by such methos as hydrolysis,template,electrochemical oxidation,liquid phase precipitation,solvent-thermal etc.,producing Bi2O3with various morphologies as fibrous,particles,spheres?hollow spheres?,flowers,flakes and rods.However,the basic research on the preparation of various morphologies through the same method and their difference performances are not sufficient,and the mechanism of photocatalysis and the degradation pathway of tetracycline hydrochloride?TCH?pollutants are still known to few.Therefore,in this paper,Bi2O3 photocatalysts with various morphologies were prepared by liquid-phase precipitation method and its construction mechanism was studied.Then,Bi2O3 photocatalysts with various morphologies were applied to the photocatalytic degradation of antibiotic wastewater-TCH,with its photocatalytic degradation mechanism and TCH degradation studied in depth.Finally,the hollow needle-like Bi2O3 photocatalyst was doped by the rare earth element of cerium?Ce?and studied its photocatalytic performances to reveal the mechanism of its photocatalytic performance with the effect of Ce doped.The main findings includes:?1?Preparation and construction mechanism of Bi2O3 photocatalytic materials with various morphologiesThe Bi2O3 photocatalytic materials with granular,porous,granular and hollow needle shapes were prepared by liquid-phase precipitation,in which Bi?NO3?3·5H2O was used as the source of bismuth,HTMA,Na2CO3,NH3·H2O and NaOH as precipitants respectively,Bi?NO3?3·5H2O as bismuth source and HNO3 solution as solvent,respectively.By adjusting the three reaction parameters of precipitant addition mass,water bath reaction temperature and heat treatment temperature,the optimal preparative conditions of Bi2O3 photocatalytic materials with various morphologies were obtained.The results indicate that for precipitant HTMA,the addition amount is 6.5 g,the water bath temperature is 65°C and the heat treatment temperature is 600°C,in the case of precipitant Na2CO3,the addition amount is 3.0 g,the water bath temperature 60°C and the heat treatment temperature is550°C.In the case of precipitant NH3·H2O,the addition amount is 7.0 g,the water bath temperature60°C and the heat treatment temperature 550°C,and for precipitant NaOH,the addition amount is 2.4g,the water bath temperature 50°C and the heat treatment temperature 400°C.Under the optimal preparation conditions of Bi2O3 photocatalytic materials with various morphologies,the intermediates in the reaction process were tested by SEM.The results show that the precipitants with different alkalinity have imapact on the rates of reaction,self-assembly and the direction of grain growth and maturation,determining the composition of the target products'precursors?the precursors were hexagonal flakes,irregular granules,irregular granules and hollow needles shapes respectively?,thus producing the Bi2O3 materials with the morphologies of irregular granules,porous,irregular granules and hollow needles shapes after heat treatment and decomposition.?2?Characterization of Bi2O3 photocatalytic materials with various morphologies and their degradation performance and degradation mechanism to TCH wastewaterThe morphologies,structure and photocatalytic performance of as prepared Bi2O3 photocatalytic materials were characterized.The results indicate that the target products prepared by the method contain Bi element and O element,with Bi being trivalent and O being bivalent,and the products are all Bi2O3 belonging to thermodynamically stable?-Bi2O3 phase.No other impurities are found in the analysis of FT-IR,XRD and XPS,indicating that the?-Bi2O3 prepared by the method has higher purity.The Bi2O3 material prepared by NaOH as the precipitant has the highest specific surface area(166.58m2 g-1),higher than that of Bi2O3 material prepared by other precipitants(HTMA:64.10 m2 g-1;Na2CO3:77.80 m2 g-1;NH3·H2O:77.58 m2 g-1),implying better adsorption capacity.The Bi2O3material with the morphologies of granular synthesized by NH3·H2O as the precipitant has the strongest absorption intensity in the visibility region and the weakest strength of PL,which suggest that the catalytic activity of the sample is higher than that of the Bi2O3 materials prepared with the other three precipitants.Taking TCH as the target degradation product and xenon lamp as the simulated visible light source,the photocatalytic properties and influencing factors?photocatalyst dosage,dissolved oxygen,solution pH and light intensity?and mechanism?photocatalytic mechanism of Bi2O3 material and degradation mechanism of TCH?of Bi2O3 material prepared by HTMA,Na2CO3,NH3·H2O and NaOH as precipitants were studied.The results find that the photocatalytic activity of the prepared Bi2O3material can be improved under suitable amount of catalyst,no aeration,suitable pH?pH=3?and stronger light intensity?450 W?.Under the light of 300 W,initial pH and optimum amount of Bi2O3materials?60 mg,60 mg,60 mg,and 55 mg?prepared by HTMA,Na2CO3,NH3·H2O and NaOH as precipitants respectively,the degradation rate of 20 mg L-1 TCH solution?100 mL?could reach 73.52%,64.41%,82.32%and 70.00%,respectively.And the degradation kinetics of TCH changes with the pseudo-first-order kinetics model.The specific surface area of granular materials prepared with NH3·H2O as precipitant is much lower than that of hollow needle-like Bi2O3.However,its photocatalytic performance is the best,which is consistent with the results of UV-Vis DRS and PL tests,indicating that the photocatalytic performance mainly depends on the absorption and utilization of visible light and the function of photogenerated electron-hole.After four reuses,the prepared Bi2O3materials still keep high degradation rate?the degradation rate was 82.32%first used and 78.80%four reuses?and low loss rate?4.77%,5.36%,3.52%and 4.44%respectively,less than 6%?for TCH solution,which exhibiting that the material has high stability and economic value.The photocatalytic screening experiments verify that the prepared Bi2O3 materials mainly uses e-,h+,and·OH to degrade TCH,and·O2-has no obvious effect on the degradation process.The photocatalytic degradation intermediates of TCH solution were tested by LC-MS/MS and the possible degradation route of TCH is deduced,which provides an important reference for the study of degradation toxicology.?3?Studied of the preparation and photocatalytic activity of Ce doped hollow needle Bi2O3materialUnder the optimal preparation conditions of hollow needle Bi2O3,Ce-doped hollow needle-like Bi2O3 photocatalytic materials were prepared by co-precipitation method and characterized.The results show that the size of Ce-doped Bi2O3 with hollow needle-like increases(the specific surface area decreases to 149.51 m2 g-1),probably due to the change of growth rate of Bi2O3 grains caused by the incorporation of Ce.The XRD tests show that the crystalline form of?-Bi2O3 in HNB-Ce is still retained,considered to be the small amount of Ce doping.The characterization by UV-Vis DRS and PL indicate that comparing with hollow needle-like Bi2O3,the absorption intensity to visible light and the inhibition efficiency of photogenerated electron-hole recombination of HNB-Ce are improved.Compared with CNB and HNB,HNB-Ce was used for photocatalytic degradation and photocatalytic masking of TCH solution under simulated visible light with 300W power.The results show that proper amount of Ce doping could improve the degradation efficiency of HNB-Ce to TCH,and the degradation efficiency of HNB-Ce with 5%doping amount is the highest?89.10%?,better than that of HNB?70.00%?and CNB?36.98%?;Ce doping could enhance the adsorption of liht,inhibit the combination of e-and h+,and enhance the utilization of·O2-and then improve the photocatalytic performance of HNB-Ce materials;In addition,the degradation model of TCH on the material conforms to the first-order kinetic equation and has good reusability.After four reuses,the degradation rate of TCH could keep at 86.68%,the morphology and the crystal type are barely changed,that show the doped materials also have good stability. |
PDF Full Text Request