| TiO2 and BiOCl photocatalysts have been widely used in the photocatalytic field due to their low cost,facile synthesis and non-toxicity.TiO2 is characteristic of the physiochemical stability and excellent photocatalytic activity;however,the rapid recombination of the photo-generated carriers and narrow photo-response range are detrimental to photocatalytic reactions.BiOCl is an important member of Ⅴ-Ⅵ-Ⅶ metal halides.BiOCl has the layered structure with the tetragonal symmetry,consisting of the alternately stacked positive [Bi2O2]2+layer and negative Cl-double layers which produces the built-in electric field and favors the separation of photo-generated carries.As to the magnetic material loaded BiOCl,i.e.magnetic catalyst,it can be recycled after photodegradation;a challenging work is to develop the novel synthesis method to realize the intimate contact between magnetic material and BiOCl and the improvement of photocatalytic performance,which deserves the further investigation.This thesis aims to improve the photocatalytic performance of TiO2 and BiOCl and reveal the related photocatalytic mechanism.The main research work and results are as follows.1.Fe4N/Fe3O4@BiOCl photocatalysts were synthesized respectively using the vapor thermal and solvothermal methods at 90,120,150 and 180 °C.The photocatalytic performance was tested by the target pollutant Rh B.Compared with the solvothermal method,in the case of the vapor thermal synthesis,the Fe4N/Fe3O4 magnetic particles exert the influence on the BiOCl growth direction because the vapor thermal synthesis enables BiOCl to come into contact intimately with Fe4N/Fe3O4 magnetic particles due to the slow hydrolysis reaction;the synthesized Fe4N/Fe3O4@BiOCl exhibits the better photocatalytic performance.The reason for the better photocatalytic performance is that the Fe4N/Fe3O4 magnetic particles are completely coated by BiOCl without the bare Fe4N/Fe3O4 magnetic particles,because the bare Fe4N/Fe3O4 magnetic particles cannot degrade Rh B.Furthermore,the higher mass ratio of BiOCl is loaded on the Fe4N/Fe3O4 magnetic particles,which is the other reason for the better photocatalytic performance.2.Using urea as the N source,(001)face exposed anatase TiO2,denoted as(001)-TiO2,was doped with N element via the vapor-thermal method at 180 ℃.The N/Ti molar ratio(RN/Ti)is 0,0.5,1,1.5,2,2.5 and 3.The photocatalytic degradation ability of all samples was evaluated using methylene blue(MB)as a target contaminant.The lattice of(001)-TiO2,ratio of exposed(001)face and particle morphology are affected by the N doping.The N element exists both in the interstitial sites of lattice and at the surface of particles.The ratio of oxygen vacancies(Ov)and Ti3+,BET specific surface area(SBET)and pore volume are increased due to the N doping.The photocatalytic degradation experiments show that the adsorption efficiency of(001)-TiO2 to MB increases from 0.1% to 51.3% and the degradation rate Kapp increases by about four times from 2.8×10-2 min-1 to 11.5×10-2 min-1 before and after the N doping.The enhancement of photocatalytic performance due to the N doping is attributed to the competing effects of SBET,the ratio of Ti3+ and Ov,the recombination probability of photo-generated carriers and the ratio of exposed(001)face.3.First,(001)-TiO2 was immersed in the HF aqueous solution for 24 h to corrode the surface of TiO2,then,using urea as the N source,(001)-TiO2 was doped with N via the vapor thermal method in different N/Ti molar ratios.Majority of N atoms exist in the interstitial sites.The N doping makes TiO2 recrystallize,reducing the ratio of the exposed(001)faces,increases the ratio of oxygen vacancies and Ti3+ which is always coupled with oxygen vacancy,enhances the absorption to the visible light and increases the pore diameter and volume of TiO2 particles.The sample with the molar ratio N/Ti = 1 exhibits the optimum photocatalytic performance: the apparent rate constant increases by three times from 2.8×10-2min-1 for the sample without N doping to 8.0×10-2 min-1;the adsorption efficiency increases from 0.1% to 53.0%.4.The N-doping of(001)-TiO2 was performed at 200,300,400,500,600 and 700 °C via the calcination method in the NH3/N2 mixture gases.The N atoms exist in the interstitial sites for the samples treated in the temperature range of 200 ~ 500 °C,while they replace O atoms for samples treated at temperatures 600 and 700 °C with the formation of the Ti O impurity phase.The increase in temperature reduces the ratio of the exposed(001)faces of TiO2,enhances the absorption to the visible light and promotes the separation of photo-generated carriers.The results of photocatalytic trials show that,under the radiation of the xenon lamp,the degradation rate to methylene blue is 2.8×10-2min-1 for the undoped(001)-TiO2,while it increases to 3.1×10-2 min-1 for the N-doped samples at 200,600 and 700 °C.Furthermore,the N-doped samples exhibit the enhanced visible light photocatalytic performance. |
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