Preparation Of CaF₂-based Magnetic Upconversion Photocatalytic/chlorine Removal Materials From Calcium-containing Ferrite Wastes

Energy shortage and environmental pollution are serious problems facing mankind in the world today.The development of effective environmental pollution control technologies to address these serious challenges and ensure sustainable development has become a top priority.Solar energy has the advantages of non-polluting and inexhaustible and is considered one of the most promising renewable energy sources in the world,while photocatalytic technology using solar energy is considered one of the effective technologies to solve the energy crisis and environmental pollution.But the general photocatalytic materials with low utilization of light energy can only use a very small amount of sunlight in the ultraviolet and part of the visible light,which has become one of the main problems restricting the development of photocatalysts.To solve the above problems,researchers have adopted methods such as metal doping,non-metal doping,and semiconductor coupling to improve the light energy utilization efficiency of photocatalytic materials.The process of effectively converting near-infrared light into visible and ultraviolet light is called upconversion luminescence,and rare earth ions have been widely concerned because of their unique d and f electron orbital structures,and the upconversion photocatalysts made with rare earth elements in semiconductor materials can achieve broad-spectrum absorption of the solar spectrum and improve the efficiency of photocatalysis.Typical upconversion materials mainly consist of activators(Er³⁺,Tm³⁺),sensitizers(Yb³⁺),and matrix materials.Fluoride has attracted the attention of many researchers due to its low phonon energy and high stability.Among them,CaF₂ is one of the most promising host substrates,because the source of Ca²⁺is abundant and very cheap.Therefore,during the preparation process,fluorine ions can be introduced to combine with the Ca²⁺in the ferrite to form CaF₂,which is used as a host material for up-conversion rare earth ion doping,to achieve the purpose of resource utilization.Bi OCl is a square structure composed of lamellae stacked together by the non-bonding of Cl atoms along the c-axis.Bi OCl has been widely used in photocatalytic wastewater treatment due to its excellent optical and mechanical properties.The high-chlorine wastewater contains a large number of chloride ions,and Bi OCl is produced by reacting with the bismuth oxide-based dechlorination agent.On this basis,rare-earth ions and magnetic matrix are introduced,so that the product after dechlorination has excellent up-conversion luminescence characteristics,while also broadening the light response range of Bi OCl is improved,and the photocatalytic efficiency is improved.In recent years,the use of upconversion luminescent materials and photocatalytic materials has become a research hotspot.In this paper,based on the resource utilization of electroplating wastewater,composite ferrite(M-Fe₃O₄)is prepared from electroplating wastewater with the help of the ferrite method,which is used as a magnetic matrix to combline with rare-earth-doped CaF₂ and semiconductor materials to prepare a broad spectrum absorption characteristic new type of magnetic upconversion photocatalytic material and dechlorination agent and remove antibiotics and chloride ions in wastewater.The main research contents are as follows:(1)The M-Fe₃O₄/Tm³⁺/Yb³⁺-CaF₂/Ti O₂ magnetic upconversion photocatalytic material was prepared by the ferrite method and co-precipitation method.The up-conversion photocatalytic material is composed of(Ca_0.8Yb_0.2)F_2.2,anatase Ti O_2,and M-Fe₃O₄.The sample can emit blue light(476 nm),red light(649 nm),and near-infrared light(700 nm)under 980 nm near-infrared light.The upconversion intensity of the M-Fe₃O₄/Tm³⁺/Yb³⁺-CaF₂ sample is very low,while the upconversion intensity of M-Fe₃O₄/Tm³⁺/Yb³⁺-CaF₂/Ti O₂ is significantly enhanced,and it's blue light(476 nm)and near-infrared light(700 nm)are strengthened about 16 times and53 times those of M-Fe₃O₄/Tm³⁺/Yb³⁺-CaF₂/Ti O₂,respectively.All samples have broad spectrum absorption performance.The results of the photocatalytic degradation experiments on the antibiotic ciprofloxacin showed that the M-Fe₃O₄/Tm³⁺/Yb³⁺-CaF₂/Ti O₂ upconversion photocatalytic materials exhibited 87.3%and 51%degradation of ciprofloxacin under full-spectrum and visible-near-infrared light irradiation,respectively,and 10%degradation of ciprofloxacin under near-infrared light(??780 nm)irradiation.In the degradation experiment of landfill leachate,the removal rate of COD and ammonia nitrogen were significantly improved compared with that under non-light conditions.The stability test of the sample shows that the degradation rate of ciprofloxacin can still reach 84%after 5 cycles.In addition,the leaching toxicity test of M-Fe₃O₄/Tm³⁺/Yb³⁺-CaF₂/Ti O₂ samples showed that the concentrations of Cr,Fe,Ni,Cu and Zn in the supernatant were far lower than those of the national regulations.All the M-Fe₃O₄/Tm³⁺/Yb³⁺-CaF₂/Ti O₂ samples are safe.(2)Using electroplating wastewater as raw material,the Ca-containing composite ferrites were prepared by the ferrite method,and the M-Fe₃O₄/Er³⁺/Yb³⁺-CaF₂/Bi₂O₃up-conversion luminescent chlorine removal material was prepared by the co-precipitation method.The upconversion chlorine removal material is composed of(Ca_0.8Yb_0.2)F_2.2,Bi₂O₃,and M-Fe₃O_4,it has a strong ultraviolet absorption intensity and bandgap of 2.91 e V.M-Fe₃O₄/Er³⁺/Yb³⁺-CaF₂/Bi₂O₃ can emit 350 ultraviolet light,407 nm violet light,520 nm and 540 nm green light,and 654 nm red light under 980nm laser excitation.Besides,the sample still has a strong upconversion luminescence intensity after the dechlorination is completed.Degradation experiments on chlorine-containing wastewater show that under the condition of p H=1,the chlorine removal efficiency of all dechlorination agents is above 95%.Under full speatrum irradiation,compared with non-light conditions,the chlorine removal efficiency is increased by 10%.In the degradation of actual chlorine-containing wastewater,within60 minutes,the dechlorination efficiency is above 99%.The results of the cyclic dechlorination experiment shows that after 6 cycles,the dechlorination efficiency of the sample is still higher than 85%.Besides,the results of the leaching toxicity test showed that the concentrations of Fe,Cr,Cu,and Bi are far lower than the national prescribed values,indicating that all samples have good safety.