| Organic and heavy metal pollutants have aroused attention due to their high toxicity and degradation-resistant.Semiconductor photocatalytic technology could generate abundant active radicals,such as·O2-and·OH,under visible light irradiation,which possesses an application prospect in wastewater treatment.Graphitic carbon nitride(g-C3N4,CN),a layered metal-free polymer photocatalyst,has attracted extensive attention owing to its suitable band gap(2.7 eV),low cost,easy preparation and excellent chemical stability.However,CN has disadvantages including insufficient visible light absorption and a high recombination rate of photo-induced carriers,which hinder its practical application.Therefore,it is of great significance to properly modify CN and optimize the photocatalytic system of corresponding materials to further improve the photocatalytic performance.This study emphasized on CN-based materials,using constructing heterojunction and element doping to regulate structure for improving the separation of photogenerated carriers.The removal of organic pollutant and heavy metal was studied catalyzed by the oxalic acid(O A)-activation system.The main research contents are as follows:1.Porous CN was prepared with the thermal condensation of melamine by using different amounts of NH4Cl as the dynamic gas template.FeWO4 nanosheets was prepared with a hydrothermal method by using FeSO4·7H2O and Na2WO4·2H2O as iron and tungsten sources,respectively.The S-scheme FWO/CNS heterojunctions were prepared through the ultrasonic dispersion combined with electrostatic self-assembly approach.XRD,FT-IR,TEM,N2 adsorption-desorption and XPS techniques were used to analyze the structure and morphology of as-prepared materials.Also,the results confirmed that the electrons transfer from CNS to FWO in the obtained heterojunctions.Transient photocurrent response,EIS,PL and TRPL spectra displayed that the constructed heterojunctions greatly enhanced the separation efficiency of photoinduced carriers.1%FWO/CNS displayed the best photocatalytic performance for rhodamine(RhB)degradation among all catalysts.Moreover,compared with the single 1%FWO/CNS,the 1%FWO/CNS activated OA system(i.e.1%FWO/CNS-OA-vis system)improved the degradation rate of RhB and reduction rate of Cr(VI)by 4 times and 3 times under visible light irradiation,respectively.The synchronous degradation activity for the mixed solution of RhB and Cr(VI)could enhance the reduction of Cr(VI).In addition,1%FWO/CNS-OA-vis system had excellent cyclic stability and remained good photocatalytic activity even conducting three successive experiments.The pollutants could be effectively degraded or reduced,as well as the toxicity was significantly decreased after the reaction treated by the 1%FWO/CNS-OA-vis system according to the HPLC-MS,XPS spectra,ECPSAR predication and cytotoxicity assessment results.The trapping experiment displayed that the main active free radicals in the degradation of RhB were ·O2-and·OH.Also,ESR spectra confirmed that the FWO/CNS heterojunction could generate abundant radicals with OA activation.DFT calculation results indicated that the electrons transferred from CNS to FWO in the obtained heterojunction due to the difference of Fermi level.Correspondingly,the internal electric field was built,facilitating the separation of photo-induced carriers.2.The aforementioned part showed that the highly active complex[FeⅢ(C2O4)3]3can be formed from iron-based material and the activated OA adsorbed on the surface,following by the production of strong reductive radical·CO2-,in the presence of the 1%FWO/CNS-OA-vis system.To further improve the utilization rate of metal atoms,a series of Fe-CN materials were prepared via introducing Fe single atoms on the surface of CN with a direct calcination method by using Fe(NO3)3 as iron source.The structure,morphology,optical and photo-generated carriers separation efficiency were characterized with various techniques.The results revealed that the introduction of Fe single atoms increased the specific surface area,which was beneficial to provide more active sites.Moreover,the formation of Fe-N bond in the obtained Fe-CN materials was conducive to the charge transfer and enhanced the separation efficiency of photoinduced carriers.Under visible light irradiation,the 0.4%Fe-CN activated OA-system displayed the best photoreduction performance for Cr(VI)and the removal efficiency was 100%within 15 min.In addition,the system had excellent cycling stability and the removal efficiency was still maintained 99%within three cycles.The scavenger experiment displayed that·CO2-was the main active species in the reduction reaction.ATR-FTIR spectra manifested that the MB complex was formed on the surface of 0.4%Fe-CN,which was beneficial to enhance the photocatalytic performance. |
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