| Polyvinyl alcohol（PVA）,as a synthetic macromolecular material,has the property of being soluble in hot water.It has been widely used since its invention,and one of its important applications is in the field of textile fabrics.Polyvinyl alcohol fabrics are often used in the nuclear industry as disposable cleaning wipes and protective clothing.Due to certain radioactivity after using,these polyvinyl alcohol fabrics will be stored after being compressed and encapsulated with lead,which will undoubtedly take up a lot of land resources.Polyvinyl alcohol fabrics can be processed by first degrading into small molecular substances,and then further degrading into carbon dioxide and water,And degrading polyvinyl alcohol fabrics into small molecular substances is one of the purposes of the current research.Through the research at home and abroad and the comparison of six advanced oxidation processes（AOPs）,the heterogeneous-Fenton oxidation process and persulfate oxidation process have the advantages of low energy consumption and easy operation when organic pollutants are degraded,which is more suitable for the degradation of PVA fabrics in this research.However the heterogeneous catalyst（Metals and metal oxides）generally have the disadvantages of high metal leaching rate,difficult recovery after use and complex synthesis routes.In this paper,in order to achieve the efficient degradation of polyvinyl alcohol fabrics and solve the shortcomings of heterogeneous catalysts,a new impregnation-spradrying-calcination method was proposed to prepare CuO@γ-Al2O3,Fe3CuO5@γ-Al2O3,and Ce-Cu/Fe@γ-Al2O3three different heterogeneous catalysts.The morphology,crystal structure,and surface chemical state of the prepared catalysts were characterized in detail by a series of testing methods.The degradation experiments of polyvinyl alcohol fabrics were carried out in four different reaction systems of CuO@γ-Al2O3/H2O2,Fe3CuO5@γ-Al2O3/H2O2,Ce-Cu/Fe@γ-Al2O3/H2O2,and Ce-Cu/Fe@γ-Al2O3/K2S2O8,and the reaction conditions and degradation mechanisms of four different reaction systems were studied in detail.The main research results are as follows:（1）A impregnation-spray drying-calcination method was proposed,and the CuO@γ-Al2O3catalyst was prepared,using Cu（NO3）2·3H2O andγ-Al2O3.The morphology and the physicochemical performance characterization showed that,after calcination,the CuO was loaded on the carrierγ-Al2O3,and it had a distinct fold structure.This particular structure can allow the catalyst to have a larger specific surface area,and can increase the contact area of the catalyst and the PVA,thus giving the catalyst a high catalytic efficiency.Experiments with CuO@γ-Al2O3catalyzing H2O2degradation of PVA showed that 92.56%of PVA was degraded at a reaction time of 210 s,calcination temperature of 450℃,γ-Al2O3:Cu（NO3）2·3H2O mass ratio of 1:15,p H of 7,catalyst dosage of 2.5 g/L,reaction temperature of 70℃,and H2O2dosage of 10.5 g/L.By using the EPR test,the root cause of PVA degradation by·OH,O2·-,and 1O2reactive oxygen species in the CuO@γ-Al2O3/H2O2system was demonstrated.Furthermore,the reaction mechanism of the CuO@γ-Al2O3/H2O2system that degraded PVA was clarified.Ten continuous degradation experiments showed that the prepared CuO@γ-Al2O3catalyst has certain reaction stability,but there is still room for improvement in the catalytic activity.（2）Usingγ-Al2O3,Cu（NO3）2·3H2O,and Fe3O4as raw materials,a new Fe3CuO5@γ-Al2O3catalyst withγ-Al2O3as core and CuO and Fe3O4as shell was prepared by impregnation-spray drying-calcination method.The SEM test showed that with the increase of Fe3O4dosage,the spherical structure of 2-10μm was formed gradually.XRD and XPS analysis showed that CuO and Fe3O4are supported onγ-Al2O3.The experiment of Fe3CuO5@γ-Al2O3catalyzing H2O2degradation of PVA shows that when the mass ratio ofγ-Al2O3:Cu（NO3）2·3H2O:Fe3O4is 1:15:20,calcination temperature is 450℃,p H value is 7,catalyst dosage is 2.2 g/L,reaction temperature is 70℃,and H2O2dosage is 10.5 g/L,the degradation efficiency of PVA is the best,and the degradation ratio can reach 99.61%.EPR test showed that·OH,O2·-,and 1O2species were produced in Fe3CuO5@γ-Al2O3/H2O2system,which played a leading role in the degradation of PVA.The mechanism of PVA degradation in Fe3CuO5@γ-Al2O3/H2O2system was elucidated.In addition,the PVA degradation efficiency of Fe3CuO5@γ-Al2O3catalyst decreased by 4.486%after 10 consecutive degradation experiments.The leaching experiments of Cu and Fe ions showed that the excessive leaching of Cu and Fe ions was one of the reasons for the decrease of the catalytic activity of Fe3CuO5@γ-Al2O3catalyst.（3）A series of CeFe3CuO7@γ-Al2O3catalysts were prepared usingγ-Al2O3,Cu（NO3）2·3H2O,Fe3O4,and Ce（NO3）3·6H2O as raw materials by impregnation-spray drying-calcination method.The results of SEM,XRD,and XPS showed that CeFe3CuO7@γ-Al2O3catalyst is 2-10μm spherical structure,and CuO,Fe3O4,and Ce O2are supported onγ-Al2O3.Moreover,Ce O2is dispersed on the surface of the catalyst,which can prevent the leaching of Cu and Fe elements in the catalyst during the degradation experiment.The degradation of PVA by H2O2catalyzed by CeFe3CuO7@γ-Al2O3showed that when the calcination temperature is 450℃,Ce dosage is 15%,p H is 7,catalyst dosage is 1.5 g/L,reaction temperature is 70℃,and H2O2dosage is 8.5 g/L,the degradation ratio of PVA by CeFe3CuO7@γ-Al2O3/H2O2system is 99.74%.EPR test showed that·OH,O2·-,and 1O2produced by H2O2catalyzed by CeFe3CuO7@γ-Al2O3were the causes of PVA degradation.After 10 consecutive catalytic reactions,the PVA degradation ratio of CeFe3CuO7@γ-Al2O3catalyst only decreased by 2.99%and remained above 96%.In addition,the experimental results of different reaction systems show that the appropriate amount of Ce（15%）can improve the reaction stability of Fe3CuO5@γ-Al2O3catalyst.Finally,the degradation mechanism of PVA by CeFe3CuO7@γ-Al2O3/H2O2system was clarified.（4）Degradation of PVA by K2S2O8catalyzed by CeFe3CuO7@γ-Al2O3was studied.The degradation experiments showed that CeFe3CuO7@γ-Al2O3still showed excellent catalytic activity and stability in the degradation of PVA by K2S2O8.Degradation experiments show that the degradation ratio of PVA in CeFe3CuO7@γ-Al2O3/K2S2O8system can reach 100%when the p H is 7,Ce（NO3）4·6H2O dosage is 15%,catalyst dosage is 1.25 g/L,reaction temperature is 60℃,and K2S2O8dosage is 2 g/L.EPR analysis and free radical quenching test showed that the four reactive oxygen species,SO4·-,·OH,O2·-,and 1O2,were generated in CeFe3CuO7@γ-Al2O3/K2S2O8system,which promoted the degradation of PVA.Compared with CeFe3CuO7@γ-Al2O3/H2O2system,CeFe3CuO7@γ-Al2O3/K2S2O8system has the advantages of low catalyst consumption and lower reaction temperature,but also has a longer reaction time. |
