Preparation Of Prussian Blue Analogues By Green Liquid Phase Method And Their Photocatalytic Performances

With the continuous development of modern science and technology,environmental and energy problems have become urgent challenges.Photocatalytic technology has fully demonstrated its advantages of green and environmental protection.It can decompose organic pollutants into H₂O and CO₂ by solar energy,which will not cause any burden on the environment.Among them,the preparation of high efficiency and stable photocatalyst is the core technology of photocatalysis.The proportion of visible light（43%）in solar light is much larger than that of ultraviolet light（5%）.Therefore,excellent photocatalysts are needed to have the characteristics of narrow band gap,good conductivity,thermal stability,simple preparation,non-toxic and any other characteristics.However,the reported photocatalysts generally have the following disadvantages:（1）the band gap of photocatalyst is wide,which can only take place in the ultraviolet region,so that the utilization rate of sunlight is not high;（2）the recombination rate of photogenerated electrons and holes is large,and the photocatalytic efficiency is not high;（3）the stability of photocatalyst is not high,therefore the service life of the material is short;（4）the dissolution rate of photocatalyst is high,which is easy to cause secondary pollution to the water body;（5）the modification of materials by means of doping and compounding will cause complex operation and high cost,which is not conducive to large-scale industrialization.Therefore,the development of low-cost,green,high photocatalytic activity and stability of photocatalyst is of great significance.Prussian Blue analogues（PBA）have many advantages,such as high specific surface area,narrow band gap width,high stability and so on.In this paper,three Prussian Blue analogues,PB,Co-Fe PBA and Mn-Fe PBA were prepared by green liquid phase method.Their morphology,crystal structure,photocatalytic activity and stability were studied.The main research work is as follows:1.Prussian Blue nanoparticles（PBNPs）were synthesized withβ-cyclodextrin（β-CD）as surfactant and ethanol as green solvent.The products were characterized by X-ray powder diffraction（XRD）,Field Emission Scanning Electron Microscopy（FE-SEM）,Transmission Electron Microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）and Bruno-Emmett-Teller（BET）to analyze the structure,morphology,surface elements,specific surface area and porosity,respectively.It was found that the specific surface area of PB-120 was 90.527 m² g^-1.When the as-prepared PBNPs were applied as heterogeneous photo-Fenton catalysts,they exhibit high catalytic efficiency and stability of degrading Rhodamine B（Rh B）under visible light in neutral system.The catalytic degradation of 25 mg L^-1Rh B by PB-120 only needed 15minutes,while the high degradation rate（83%）of Rh B after 4 cycles of degradation could be achieved.The as-prepared PBNPs may be employed as excellent catalysts to degrade organic pollution.2.Co₂Fe（CN）₆（Co-Fe PBA）was prepared by solvothermal method.The effects of reaction temperature and reaction time on the morphology and photocatalytic activity of Co-Fe PBA were studied by controlling single parameters.It is found that with the increase of reaction temperature and the extension of reaction time,the Co-Fe PBA will appear different degree of plate phenomenon,which is not conducive to the improvement of photocatalytic activity of the material.The optimum reaction temperature for the preparation of Co-Fe PBA is 120℃and the optimum reaction time is 12 h.The Co-Fe PBA was used for photocatalytic degradation of Rh B and MB.It was found that under the synergistic action of 100 u L H₂O₂,the photocatalytic degradation of 25 mg/L Rh B solution for 8 min and 20 mg/L MB solution for 15 min could reach 95.8%and 96.8%photocatalytic efficiency,respectively.In addition,the optimum conditions of photocatalytic degradation of Rh B were explored.The results showed that the content of photocatalyst and H₂O₂content were 5 mg and 100 u L,respectively,the concentration of Rh B was 25 mg/L.3.Mn₂Fe（CN）₆（Mn-Fe PBA）with good crystallinity and about 20 nm size was prepared in ethanol solution at 120℃,in whichβ-cyclodextrin（β-CD）was used as surfactant.This is the first time thatβ-CD was used as surfactant to prepare Mn-Fe PBA.The effects of reaction temperature on the size,morphology,specific surface area and photocatalytic activity of the products were studied.It was found that when the reaction temperature was higher than 120℃,the photocatalytic activity of Mn-Fe PBA was not improved.The photocatalytic activity of Mn-Fe PBA was demonstrated by visible light photocatalytic Rh B solution and MB solution.The experimental results showed that the degradation efficiency of 25 mg/L Rh B by Mn-Fe PBA（5 mg）at 120℃for 8 min was 90.9%,and the degradation efficiency of 20 mg/L MB（50 m L）for 8 min was 94.0%.The as-prepared Mn-Fe PBA was recycled for four times to degrade Rh B,whose UV-Vis absorption spectrum was tested,showing that the excellent photocatalytic stability of the as-prepared Mn-Fe PBA.