Construction Of In₂O₃-Based Heterojunction Catalysts And Their Visible-Light Catalytic Performance In Degradation Of Gaseous Ortho-Dichlorobenzene

In recent years,with the emission of industrial and vehicle exhaust,as well as the extensive use of building decorative materials,the air pollution problems caused by volatile organic compounds?VOCs?are getting worse,efficient abatement of VOCs has become a great subject which needs to be urgently solved.Wide band-gap p-block metal oxides and hydroxides consisting of a central metal ion with peculiar d10 electronic configuration exhibit superior reactivity and stability during the degradation of benzene VOCs,however these catalysts could only be excited under UV light,thus leading to low utilization of solar energy.Among p-block metal oxides,only In₂O₃ prossesses visible-light activity?Eg = 2.80 eV?,indicating that it could be a promising candicate catalyst for the degradation of benzene VOCs.Unfortunately,the efficiency of In₂O₃ is still inhibited mainly due to its limited visible-light response capacity and short lifetime of charge carriers.Against the above backdrop,herein,In₂O₃ was modified through the construction of semiconductor heterojunctions,by enhancing the visibile-light absorption ability and prolonging the lifetime of charges to improve the degradation efficiency toward benzene VOCs.Meanwhile,the structure-activity relationships between microstructures and dynamic behaviors,as well as catalytic activity were systematically investigated.Additionally,the catalytic reaction mechanisms were further elucidated by combining the in situ FTIR experiments with the analysis results of energy band structures.The primary research contents and results are as follows:?1?The ?-Fe₂O₃/In₂O₃ composite hollow microspheres were synthesized by a solvothermal-hydrothermal method.In₂O₃ possessed hollow structure,the diameter was in the range of 0.6-0.9 ?m,and the average thickness of the shell was ca.90 nm.As for the?-Fe₂O₃/In₂O₃ composites,numerous ?-Fe₂O₃ nanoparticles coated on the surface of In₂O₃ hollow spheres not only improved the visible-light utilization efficiency,but also retarded the recombination rate of photo-induced charges effectively.In comparison with the pure In₂O₃,the ?-Fe₂O₃/In₂O₃ composite hollow spheres exhibited superior catalytic activity.The conversion ratios were 88.3%and 52.4%toward gaseous toluene and ortho-dichlorobenzene?o-DCB?under visible-light irradiation??>400 nm,treaction time = 8 h?,respectively.The in.situ FTIR analysis results illustrated that benzyl alcohol,benzaldehyde and benzoic acid as intermediates were produced during the degradation of gaseous toluene,and some of these intermediates were finally decomposed into CO₂ and H₂O.?2?The ZnFe₂O₄/In₂O₃ nanoheterostructures were elaborately constructed via a hydrothermal-solvothermal procedure.In₂O₃ monodisperse nanospheres with hierarchical structure were ca.180-300 nm in diameter.As for ZnFe₂O₄/In₂O₃ nanoheterostructures,the introduction of ZnFe₂O₄ nanoparticles expanded the spectral response range and prolonged the lifetime of the photo-generated charges.The surface of In₂O₃ was partially covered by ZnFe₂O₄,this microstructure assured the formation of effective heterojunction interfaces and the optical absorption properties of In₂O₃ were not affected.The conversion ratio of gaseous o-DCB over the ZnFe₂O₄/In₂O₃ nanoheterostructures attained 68.7%under visible-light irradiation??>400 nm,treaction time = 8 h?,which was obviously higher than that over the ZnFe₂O₄-In₂O₃ physical mixture,suggesting that efficient heterojunctions formed within ZnFe₂O₄/In₂O₃ nanoheterostructures played a decisive role in achieving enhanced catalytic performance.Moreover,the degradation pathway of o-DCB was postulated according to the in situ FTIR analysis results:o-DCB molecules were firstly adsorbed at the catalyst's active sites through the ?-complexes that formed between the aromatic rings and the metal ions.Through nucleophilic substitution process,the Cl atoms of the aromatic rings were substitutedby O₂^-ions or surface hydroxyl groups and generated HCl,o-chlorophenol and catechol.o-benzoquinone species were then formed through the rearrangement of catechol.Subsquently,o-benzoquinone reacted with reactive oxygen species and the aromatic rings were cleavaged,leading to the generation of non-aromatic acetate groups?formates,acetates and maleates?.Finally,some acetate species could be further oxidized to CO₂ and H₂O.?3?A series of In₂S₃/In₂O₃ composite flower-like microspheres were prepared via a hydrothermal-in situ anion exchange approach.The In₂S₃ nanoflakes uniformly and controllably generated on the surface of the In₂O₃ microflowers constrained the combination of photo-excited charge carriers,thus prolonging the lifetime of the photo-induced charges.The ISO?II?composites exhibited an optimal degradation efficiency,the conversion ratio of gaseous o-DCB was 76.9%under visible-light irradiation??>400 nm,treaction time= 8 h?.The existence of oxygen vacancies?Vo?was revealed by the combination of Raman,XPS and low-temperature ESR,and the relative amount of Vo in In₂S₃/In₂O₃ composites was higher than that in the pure In₂O₃,Vo had a two-side effect on the photoreactivity,the moderate amount of Vo was favorable for the catalytic reaction.However,excessive surface Vo would transit into bulk Vo,thus decreasing catalytic activity.Additionally,·OH and ·O₂^-were the predominant reactive oxygen species involved in the degradation of gaseous o-DCB over In₂S₃/In₂O₃ composites.?4?The In₂O₃@PANI core-shell nanostructures,which possessed ultralong charge carriers lifetime,were synthesized via a hydrothermal-impregnation method,the short and long lifetime were 2.11 and 8.14 ?s,respectively.Strong interactions were formed between the two components,mainly in the forms of ?-? stacking,electrostatic interaction or hydrogen bonding interaction between In₂O₃ and-NH in PANI,which were beneficial to the rapid transportation of the photo-generated charges at the heterojunction interfaces.Meanwhile,the conversion ratio of In₂O₃@10%PANI heterostructures toward gaseous o-DCB attained 82.6%under visible-light irradiation??>400 nm,treaction time = 8 h?.The significantly enhanced catalytic performance could be mainly ascribed to the ultralong charge carriers lifetime and improved visible-light absorption capacity.Furthermore,the band gap analyzation and ESR detection results illustrated that ·O₂^-radicals were the dominant reactive oxygen species,while ·OH played a minor role in the degradation of gaseous o-DCB over In₂O₃@PANI composites.