Preparation Of Bi₅O₇I Nanostructures Doped With Rare Earth Ions And Its Photocatalytic Performance

Oxygen enriched type halogen bismuth oxide?BixOyXz,X=Cl,Br,I?,whose structure is similar to the halogen bismuth oxide?BiOX,X=Cl,Br,I?,is a new type of semiconductor materials.They are made from the layers of bismuth oxide and halogen ions alternately,forming a self-build electric field and promoting the separation of electron and hole.Therefore,this kind of material has good photocatalytic performance.For these materials,the conduction band position of BisO7I is the more negative?-0.2eV?,which is easy to activate O2 molecules into ·O2 to oxidize and decompose organic pollutants,bring good photocatalytic activity under visible light.Therefore,it has attracted extensive attention for researchers.However,due to its larger band gap?Eg=22.85?2.92 eV?,the visible light response range is narrow,so it has been modified.At present,it is found that there are two kinds of crystal structures of Bi5O7I,which are orthorhombic phase??-?and monoclinic phase??-?.The reported literature is about?-Bi5O7I,and the pure phase ?-Bi₅O₇I nanostructures has not been fabricated yet.In this article,as Re?NO3?3·6H2O?Re=La,Ce,Pr,Nd,Er,Tm,Yb,Lu?are rare earth ion sources,solvothermal-thermal decomposition method is used to prepare pure phase?-Bi5O7I and rare earth ions doped micro structure Bi5O7I photocatalysts.Rare earth ions with the larger ionic radius of Re³⁺?Re=La,Ce,Pr,Nd?are doped Bi5O7I prepared Re³⁺/?-Bi5O7I microsphere structure;and rare earth ions with the smaller ionic radius of Re³⁺?Re=Er,Tm,Yb,Lu?doped BisO7I prepared Re³⁺/?/?-BisO7I microsphere structure;changing the doping concentration of Yb³⁺,0.75%Tm³⁺ and Yb³⁺ are Co-doped BisO7I,fabricating single-phase ?-BisO7I microspheres structure,and research photocatalytic performance of all composites.This article mainly includes the following three aspects work:?1?The larger radius ionic Re³⁺?Re=La,Ce,Pr,Nd?were doped to ?-Bi5O7I,which reveled that the microstructure of Re³⁺/?-BisO7I is not different from pure ?-Bi507I by XRD and TEM.The mesoporous microspheres are assembled by a lot of ultrathin nanosheets whose thickness are 10-20nm with a diameter of 2-4 ?m.The band structure of ?-Bi5O7I doped with rare earth ions(La³⁺)was characterized by means of UV-vis and XPS,and the band gap and density of states of La³⁺/?-Bi5O7I were calculated by first principles calculations,,which is consistent with the experimental results.The photocatalytic degradation of concentration of both 20mg/L bisphenol A and phenol as the liquid target pollutants,and NO simulation of atmospheric pollutant to characterize photocatalytic activity of the as-fabricated composites,the sample of 6%/La³⁺/?-Bi5O7I showed excellent photocatalytic activity,the removal rates arriving 96.6%,48.5%and 42.8%,and revealed high stability in the process of removal NO.?2?The smaller ionic radius of Re³⁺?Re=Er,Tm,Yb,Lu?were doped to ?-Bi5O7I.It can be observed Re³⁺/?/?-Bi₅O₇I hetero junction heterogeneous composite structures.The existence of the hetero junction structure was confirmed by XRD and HRTEM,but the microstructure remained unchanged.The generation of hetero junction structure has enhanced visible light response by UV-vis.The photocatalytic activity of as-prepared hetero junction structure of Re³⁺/?/?-Bi₅O₇I was evaluated under visible light by decomposing bisphenol A and phenol.The results showed that 4%Yb³⁺/?/?-Bi₅O₇I sample reveals excellent photocatalytic activity,which complete degradation of bisphenol A less than 30min and the removal rate for phenol reaching 62.9%in 60min,which is 31 and 18 times for pure ?-Bi5O7I.In addition,the photocatalytic performance of 4%Yb³⁺/?/?-Bi₅O₇I sample was test under monochromatic light.The results show that the photocatalytic performance has been greatly improved under wavelength of 450nm and 535nm monochromatic light,indicating the absorption and utilization for visible light for ?/?-Bi₅O₇I hetero junction is increased.?3?In order to investigate the effect of Re³⁺ doping concentration on the phase structure of Bi5O7I,combined with upconversion luminescence,the composites of 0.75%Tm³⁺/x%Yb³⁺/Bi5O7I?x=0-18?were preparerd by changing the doping concentration of Yb³⁺.The experimental results futher prove that the doping concentration of rare earth ions affects the phase structure of Bi5O7I.The results reveals that the phase transformation rule is ?-Bi5O7I??/?-Bi₅O₇I??-Bi₅O₇I.To our surprised,the single-phase ?-Bi₅O₇I was prepared,whose morphology still keep 2-4 ?m microspheres unchanged.All as-synthetised samples were tested by 980nm laser,confirmed the existence of up-conversion.The photocatalytic performance were evaluated by photocatalytic degradation bisphenol,showing a regular trend.Besides,the composites of 0.75%Tm³⁺/6%Yb³⁺/?/?-Bi₅O₇I and 0.75%Tm³⁺/12%Yb³⁺/?-Bi₅O₇I were tested under monochromatic light,which proved that upconversion effect has some contribution to improve the photocatalytic performance.