Design,construction,and Performance Of Rare Earth Doped BiVO₄ Based Nanophotocatalyst

Photocatalysts can efficiently degrade organic pollutants using clean solar energy,and show broad application prospects in the field of wastewater treatment.Among various water pollutants,tetracycline hydrochloride（TC,broad-spectrum antibiotics）,methylene blue（MB,organic dyes）,and bisphenol A（BPA,endocrine disruptors）are difficult to degrade themselves,posing a serious threat to human health and the safety of the water environment.Traditional photocatalysts（such as Zn O and Ti O₂）can only utilize about 5%of the ultraviolet light in the solar spectrum,which limits their utilization efficiency of solar energy and practical application.The development of photocatalysts capable of utilizing near infrared（NIR）light,which accounts for more than 50%of the total solar spectrum,is crucial for the development of photocatalytic systems.Doping rare earth ions with the unique upconversion（UC）luminescence ability to convert NIR light into ultraviolet or visible light is an effective strategy for semiconductors to utilize broad spectrum sunlight.The monoclinic phase BiVO₄has become one of the hot spots in the research field of novel visible light photocatalytic materials due to its excellent properties such as corrosion resistance,non-toxicity,chemical stability,and the diversity of crystal and electronic structures.Therefore,an efficient NIR light driven photocatalyst was constructed by using monoclinic BiVO₄as a matrix and Yb³⁺/Er³⁺as the sensitizer/activator.However,the photocatalytic application of BiVO₄is still limited by its low carrier separation efficiency,slow interface dynamics and poor conductivity.In order to solve these bottlenecks,combining BiVO₄with other semiconductors to form Z-scheme or S-scheme heterostructures can overcome the shortcomings of traditional type II heterostructures in thermodynamics and dynamics,and is an effective strategy to enhance the separation efficiency of photogenerated carriers.At present,most of the BiVO₄based photocatalysts that have been synthesized are in the form of nanopowders,which are limited by easy polymerization and difficult recovery in practical applications.Controlling the size of photocatalysts at micro/nano scales can obtain highly active photocatalysts,especially heterostructured photocatalysts that combine zero-dimensional（0D）or two-dimensional（2D）with one-dimensional（1D）nanostructures,which can exhibit excellent photocatalytic activity and have attracted great attention in the field of photocatalytic materials.In this thesis,rare earth ions doped BiVO₄based 1D nanocomposites with broad spectral response were constructed by combining photocatalysts with rare earth up-converted luminescent ions.Er³⁺doped BiVO₄nanobelts with NIR light response were prepared by electrospinning.On this basis,Er/Yb co-doped BiVO₄nanobelts were prepared,and 2D/1D BiOBr/BiVO₄:Er,Yb Z-scheme heterostructure,1D/2D BiVO₄:Er,Yb/BiOCl S-scheme heterostructure,1D/0D BiVO₄:Er/Yb@Ag/Ag₃PO₄Z-scheme heterostructure were further prepared.The structure,morphology,light absorption,UC fluorescence,carrier separation characteristics,photocatalytic performance and degradation mechanism were systematically studied.The details are as follows:1.BiVO₄:Er and BiVO₄:Er,Yb nanobelts were prepared by electrospinning united with calcination.The UC emission peaks at 660,548 and 519 nm were attributed to the⁴F_9/2→⁴I_15/2,⁴S_3/2→⁴I_15/2and ²H_11/2→⁴I_15/2transitions of Er³⁺,respectively.Under simulated sunlight irradiation,the degradation efficiencies of BiVO₄:3%Er,10%Yb nanobelts for TC,BPA and MB were 78.3%/60 min,59.5%/180 min and 78.7%/120 min,respectively,which were 1.109,1.676 and 1.112 times of that of BiVO₄:3%Er,1.355,3.324 and 1.511 times of that of BiVO₄.After excitation with NIR light（980 nm laser）for 12 hours,the degradation efficiencies of BiVO₄:3%Er,10%Yb nanobelts for TC,BPA and MB were 31.3%,16.7%and 20.5%,respectively,1.267,1.876 and 1.916 times of that of BiVO₄:3%Er.Therefore,the photocatalytic activity of BiVO₄:Er was better than that of BiVO₄,and the photocatalytic activity of BiVO₄:Er/Yb was better than that of BiVO₄:Er.The significantly enhanced photocatalytic activity of BiVO₄:3%Er,10%Yb is mainly attributed to the synergistic effect of enhanced UC fluorescence,broadened spectral absorption range,increased specific surface area,and improved carrier separation efficiency.2.Novel and columnar cactus-like BiOBr/BiVO₄:Yb,Er heterostructured nanobelts with broad spectral response were synthesized by electrospinning combined with a solvothermal method.Under simulated sunlight irradiation,the degradation efficiencies of the optimal sample for TC,BPA,and MB were 89.2%/60 min,89.8%/180 min,and95.9%/120 min,respectively.The MB removal rates of the optimal sample were 1.480 and1.305 times that of BiOBr,and 14.224 and 1.841 times that of BiVO₄under NIR and simulated sunlight excitation,respectively.The excellent photocatalytic activity can be attributed to the porous structure of nanobelts that generate a large number of active sites,the upconversion effect that broaden the spectral response range,the unique 2D/1D contact interface that provides fast carrier transfer channels,and the Z-scheme heterostructure and Yb³⁺/Yb²⁺redox center that promote the spatial separation of photogenerated carriers.3.A novel S-scheme heterostructure of BiVO₄:Er,Yb/BiOCl with a 1D/2D core-shell structure was constructed by electrospinning combined with a solvothermal method.Consequently,BiVO₄:Er,Yb/BiOCl composite nanobelts degraded 97.9%and 66.1%of MB,88.8%and 68.8%of TC,and 80.8%and 22.2%of BPA driven by simulated sunlight and NIR light,respectively.Under the excitation of NIR light and simulated sunlight,the MB removal rate of the optimal sample is 1.250 and 1.280 times of that of BiOCl,and13.490 and 1.879 times of that of BiVO₄,respectively.The superior catalytic performance can be attributed to the synergism between UC fluorescence,the unique core-shell structure and the S-scheme heterostructure.In addition,the photocatalyst exhibits excellent reusability and cycle stability in photocatalytic applications.4.A novel 1D/0D BiVO₄:Er/Yb@Ag/Ag₃PO₄Z-scheme heterostructure with broad spectral response was constructed by electrospinning coupled with an ethylene glycol assisted hydrothermal method.The optimized BiVO₄:Er/Yb@Ag/Ag₃PO₄heterostructured nanofibers degrade 69.5%（9 h）and 91.3%（30 min）of TC,76.7%（9 h）and 99.4%（24 min）of MB,and 38.2%（9 h）and 94.5%（60 min）of BPA under NIR light and simulated sunlight excitation,respectively.Under NIR light and simulated sunlight excitation,the MB removal efficiencies of the optimal composite are 9.833 and 1.094 times of Ag₃PO₄,and20.184 and 11.558 times of BiVO_4,respectively.The superior photocatalytic activity can be attributed to a synergistic effect between the unique 1D/0D contact interface,the porous outer wall of BiVO₄:Er/Yb nanofibers,Ag bridged Z-scheme heterostructure,UC luminescence and the surface plasmon resonance（SPR）effect.This makes BiVO₄:Er/Yb@Ag/Ag₃PO₄heterostructured nanofibers have the advantages of broadened absorption spectrum,increased specific surface area,abundant active sites,fast electron transfer channels,and enhanced photocorrosion resistance and stability.The collaborative strategy of UC luminescence,heterostructure construction and morphology control can enhance the UC fluorescence intensity,broaden the light response range,increase the specific surface area,and improve the separation efficiency and transport efficiency of photogenerated carriers,thus significantly improving the photocatalytic performance of BiVO₄-based 1D nanocomposites.This study provides new ideas and key technical guidance for the design and development of novel and efficient photocatalysts with broad spectrum response for water pollution control.