| It is well accepted-known that the semiconductor photocatalytic technology is a reliable strategy for degrading organic pollutants.This technology is low-cost and the reaction conditions are mild.Additionally,it does not cause secondary pollution to the environment.Therefore,it has been widely used in organic wastewater treatment.Among the semiconductor photocatalysts,g-C3N4 has good visible light photocatalytic activity,stable structure and high thermal stability.Specifically,the corresponding preparation procedure is convenient.On the other hand,literature has verified that BiOBr possesses excellent photocatalytic activity,presumably due to its abundant resource reserves and suitable bandgap(Eg)value.Meanwhile,graphene aerogel(GA)possesses high porosity,good conductivity and abundant oxygen-containing functional groups,endowing good conductivity and the possibilityto construct with other components(such as semiconductor photocatalysts)for forming the composites with high dispersion and stability.Also,GA is expected to promote the migration of photo-generated electrons and enhance the absorption of radiant light.In consideration of these issues,the present thesis focuses on the preparation,characterization,adsorption and photocatalytic performance of binary composites(GA-g-C3N4 and BiOBr-g-C3N4)and ternary composites(BiOBr-GA-g-C3N4).Also,the corresponding photocatalytic mechanisms are explored.The main work is as follows:1.A series of porous g-C3N4 materials are prepared from urea with the thermal polycondensation method by using different amounts of NH4Cl as the dynamic gas templates.Graphene oxide(GO)is fabricated with an improved Hummer’s method,and used to prepare the GA-g-C3N4 composites with a hydrothermal self-assembly combined with freeze-drying technology.The results show that the material prepared with a mass ratio of 3:1 for urea to NH4Cl displays the best removal performance for methylene blue(MB)dye.Moreover,GA-g-C3N4(30%)exhibits superior performance to other GA-g-C3N4 composites,GA and g-C3N4.In the presence of GA-g-C3N4(30%),the total purification efficiency for MB dye reaches 83%under the present conditions.Also,GA-g-C3N4(30%)is effective for removing rhodamine B(RhB),methyl violet(MV)and crystal violet(CV)dyes,and the corresponding removal values are 71%,64%and 55%,respectively,verifying the good universality.Other than that,the optimal GA-g-C3N4(30%)has good cycling stability,and the efficiency for MB still maintains 94%in the third run.The capture experiment results show that the active species for the photocatalytic degradation of MB are ·O2-and h+in the presence of the optimal composites.Based on the corresponding UV-vis DRS and Mott-Schottky curves,the bandgap and band positions of g-C3N4 are obtained(Eg=2.63 eV,EVB=1.57 V,ECB=-1.06 V).Photocatalyzed by GA-g-C3N4(30%),it can be inferred that hydroxyl radicals(·OH)attack the MB substrates,which are gradually degraded into small molecules,CO2,H2O,according to the corresponding LC-MS spectra.2.A series of BiOBr materials are prepared with a solvothermal method by using cetyltrimethylammonium bromide(CTAB)and KBr as Br source,Bi(NO3)2·5H2O as Bi source,and ethylene glycol as the solvent.The results show that the BiOBr flower spheres prepared with a molar ratio of 5:1 for KBr to CTAB display the best performance in the degradation of RhB under visible light irradiations.Furthermore,the optimal porous g-C3N4 with different amounts is dispersed in the precursor of the optimal BiOBr to prepare a series of BiOBr-g-C3N4 composites,in which BiOBr-g-C3N4(2%)shows higher photocatalytic activity than BiOBr,g-C3N4,and other obtained binary materials for the degradation of RhB.Correspondingly,the total purification efficiency reaches up to 86%for RhB dye within 30 min under the present conditions.Meanwhile,BiOBr-g-C3N4(2%)displays obvious photocatalytic activity for the degradation of MB,MV and CV dyes,Noticeably,the optimal binary composites has satisfactory recycling stability,and the efficiency for RhB still maintains 97%after 3 runs.The capture experiments confirm that ·OH,h+and ·O2are the main active species in the photocatalytic degradation of RhB in the presence of BiOBr-g-C3N4(2%).Based on the corresponding UV-vis DRS and Mott-Schottky curves,the bandgap and band positions of BiOBr are obtained(Eg=2.90 eV,EVB=2.86 V,ECB=-0.04 V),in addition to that of g-C3N4 as mentioned above.Photocatalyzed by BiOBr-g-C3N4(2%),according to the corresponding LC-MS spectra,it can be inferred that the ·OH radicals attack the RhB substrates to generate a series of deethylation intermediates,which are unstable and undergo mineralization,cracking into small molecular substances,CO2 and H2O.3.A series of BiOBr-GA-g-C3N4 ternary composites are prepared with a one-pot hydrothermal self-assembly combined with freeze-drying technology by dispersing the optimal BiOBr with different dosages into the precursor suspension of GA-g-C3N4(30%),respectively.The results show that BiOBr-GA-g-C3N4(15%)demonstrates the highest photocatalytic activity for the degradation of RhB and the total removal efficiency reaches 97%within 3 h under the present conditions.Additionally,the removal efficiency values are 71%and 64%for MB and MV in the presence of BiOBr-GA-g-C3N4(15%),respectively.Also,the optimal ternary composites displays stable activity even after 5 runs,suggesting satisfactory cycling stability.The capture experiments show that the active species are ·OH and h+for the photocatalytic degradation of RhB by using BiOBr-GA-g-C3N4(15%).Combined with the organic carbon(TOC)analysis and LC-MS spectra,it can be concluded that the photocatalytic degradation mechanism of RhB over the optimal ternary composites is similar to that over the above-mentioned binary ones. |
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