The Study About Visible-light Degradation Of Dye By Carbon-doped Pyrochlore Prepared

This study focuses on the theoretical and practical significance of using solar photocatalysis to degrade refractory contaminants in wastewater.Zirconium nitrate and strontium nitrate are used as raw materials,with phenolic resin,polyaniline and graphene oxide as carbon sources,respectively.One-step carbon-doped pyrochlore composite oxide（La₂Zr₂O₇）was prepared by sol-gel method microwave digestion.The pure pyrochlore La₂Zr₂O₇ was recorded as LZO,and the composites prepared with phenolic resin as the carbon source were 50%carbon doped-La₂Zr₂O₇（C50%-LZO）,60%carbon doped-La₂Zr₂O₇（C60%-LZO）and 70%carbon doped-La₂Zr₂O₇（C70%-LZO）respectively.That polyaniline and graphene oxide were used as the carbon source to prepared composites were PANI/LZO,GO/LZO and GO/PANI/LZO.The scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,specific surface area analysis（BET）,X-ray diffraction（XRD）,and X-rays were separately performed on these carbon-doped pyrochlore catalysts.Photoelectron spectroscopy（XPS）and UV-Vis diffuse reflectance（UV-Vis）were used to characterize the effects of carbon doping on the physical and chemical properties of the pyrochlore catalyst.The effect of carbonaceous pyrochlore composite oxides on the adsorption and photocatalytic degradation of methylene blue dye has also been explored through experiments.The reaction mechanism and major oxide species during photocatalytic process have been studied by adding free radical trapping agents.Finally,the stability and corrosion resistance of the catalyst were explored.The result is as follows:（1）Carbon-doped pyrochlore composite oxides used phenolic resin as the carbon source,the samples are grayish black and the adsorption of sunlight greatly broadens the response range to visible light.From scanning electron microscopy（SEM）analysis,it can be seen that compared to purely pyrochlore（LZO）,flat and non-porous surface,the pores of the catalyst doped with phenolic resin are developed,and the specific surface area is obviously increased,showing the characteristics of activated carbon which has arbonaceous surface.The specific surface area and pore diameter analysis（BET）confirmed that the specific surface area of the phenolic resin-doped catalyst increased from 10.7666 m²/g to 151.308 m²/g,increased by about 15 times,and was found at three different doping levels 50%carbon doping amount shows the best surface morphology,because different carbon doping amounts and pyrochlore complex process lead to different surface atom coordination saturation and hole filling degree.X-ray diffraction（XRD）analysis showed that the catalyst still exhibited the crystal structure of pure pyrochlore LZO after doping with activated carbon,and the increase in the width of the crystal face indicated the insertion of carbon atoms.UV-Vis analysis showed that effectively doping carbon facilitates the extension of the π-electron conjugated structure,which makes the absorption edge of the catalyst significantly red-shifted,and the visible light response is easier,the photocarrier transfer rate is accelerated,so photocatalytic efficiency is increased.The chemical structure analysis of the catalysts by X-ray photoelectron spectroscopy（XPS）and Fourier transform infrared spectroscopy（FTIR）can prove that the phenolic resin carbon atoms can be successfully introduced into the pyrochlore,because the free-atom valence of the carbon atoms on the activated carbon end face has a very high reactivity,easy to react with other elements to form a chemical bond that dominates the surface chemical structure,is conducive to improve the adsorption and photocatalytic properties of the catalyst.Using methylene blue as the target pollutant,the adsorption performance and photocatalytic efficiency of the catalyst were explored.The results showed that the pure LZO had almost no adsorption performance,while the material doped with 50%phenolic resin showed the best adsorption effect and the specific surface area analysis.Consistent with the parameters,the photocatalytic efficiency reached about 82%,which is about 50%higher than LZO.The free radical scavenger was added to explore the main role of the catalyst in the photocatalytic reaction under visible light.The hydroxyl radical（·OH）played a leading role in the photocatalytic reaction.The superoxide radical（·O2-）And holes h+ also have a certain influence.Finally,it was proved that the prepared carbon-doped pyrochlore has good corrosion resistance and stability,and can be applied to the industrial practical market.（2）Graphene oxide and polyaniline were added during the pyrochlore sol-gel process,and a ternary structured composite catalyst was prepared by one step in situ.The ternary compound pyrochlore still has the crystal form of the perovskite LZO pyrochlore phase,and the characteristic peak of the weak PANI appears,and the broadening of the peak shape is the peak of the first peak indicating the introduction of amorphous carbon.The pyrochlore surfaces incorporating PANI,GO and GO/PANI,respectively,show different morphologies.It can be seen from the EDS-mapping images that the carbon and nitrogen atoms introduced by polyaniline and graphene oxide are evenly distributed on the surface of the catalyst.The surface area is also significantly increased,and the GO/PANI/LZO reaches 78.325 m²/g.From the TEM images,it can be clearly seen that the fiber network formed by PANI and the folded sheet structure of GO are combined with the pyrochlore LZO.The methylene blue was also used as the target pollutant to analyze the adsorption performance and photocatalytic efficiency of the catalyst.The results show that the GO/PANI/LZO ternary composite pyrochlore catalyst has relatively high adsorption capacity and significantly improved photocatalytic performance.The reason is attributed to PANI’s conjugated π electron structure as an excellent electron contributor and hole receiver,coupled with the matching and chemical bonding of the LZO band of the pyrochlore,and the photocatalytic system was realized by the graphene oxide electron transfer system.The effective separation of the electron-hole pairs in the accelerated photocarrier transfer rate,while the introduction of carbon broadens the range of visible light response,making it easier for electrons to be excited and generating more oxidizing radical species to degrade contaminant molecules.Therefore,catalytic oxidation increases the photocatalytic performance of the system.Finally,the cycle experiment proved that the prepared catalyst has good stability,and it can be recycled and reused.It is a green economical and efficient photocatalyst.