| Catalytic ozonation due to strong oxidizing ability,fast reaction rate,high mineralization rate and simplicity of process,has been extensively used for the abatement of organic pollutants in waste water treatment.Various heterogeneous ozonation catalysts such as metal oxides,metal oxides loaded on various supports(common supports are mesoporous silica,alumina and carbon materials,etc),minerals(perovskites)and carbon materials have been used.However most of the heterogeneous ozonation catalysts have problems of low catalytic activity due to lower exposure of active sites and low mass transfer efficiency.In order to tackle these issues,in this research work,manganese oxide(MnOx)in-situ incorporated in fibrous silica nanospheres(KCC-1)and mesoporous nanocast lanthanum based perovskites(LaMO3,M =Mn,Fe)have been synthesized as ozonation catalysts.Enhancing the accessibility of active sites and the mass transfer efficiency can ultimately enhance the removal efficiency of organic pollutants in catalytic ozonation.In addition,the structure-activity relationship between different exposed crystal planes and catalytic activity is still not clear in the catalytic ozonation.By using CeO2 with different exposed crystal facets,the structure-activity relationship between CeO2 exposed facets and catalytic activity is explored.The main research and results are as follow:For the first time,manganese oxide(MnOx)incorporated mesoporous fibrous silica nanosphere(KCC-1)was synthesized by one step hydrothermal method.It was found that MnOx was evenly distributed in KCC-1 with mesoporous structure and specific surface area in the range of 391 to 413 m2 g-1 and diameter in the range of 3.35 to 3.39 nm.Oxalic acid was used as a model pollutant to investigate the catalytic activity in the presence of ozone.The experimental results showed that the optimized MnOx-0.013/KCC-1 catalyzed ozonation significantly enhanced the removal rate of oxalic acid(85%),which was significantly higher than that of ozonation alone(4%)and the conventional mesoporous MnOx-0.013/MCM-41(60%).At the same time,the structure of MnOx-0.013/KCC-1 showed good reusability and stability.After three times of repeated use,the performance did not change significantly.After 60 min of reaction,the maximum manganese leached was 0.05mg L"1 in MnOx-0.013/KCC-1/O3,which is much lower than of the MnOx-0.013/MCM-41(1.20 mg L-1).Phosphate substitution experiments showed that the hydroxyl group(-OH)on the surface of the catalyst is the active site of the catalytic process.The use of TBA(tert-Butyl alcohol)as ·OH scavenger confirmed that hydroxyl radical(·OH)was the main reactive oxygen species produced during the ozonation catalyzed by MnOx/KCC-1.Mesoporous silica nanospheres with fibrous morphology as a support is better for facilitating the mass transfer.Uniform growth of MnOx in KCC-1 facilitated the exposure of active sites and in-situ grown MnOx minimized the manganese dissolution,which in turn increased the catalytic activity.Using SBA-15 as a template,the mesoporous nano-perovskites(NC-LaMnO3 and NC-LaFeO3)as ozonation catalysts were synthesized by nanocasting method.The specific surface areas of NC-LaMnO3 and NC-LaFeO3 were 120 and 92 m2 g-1,respectively,which were 8-10 times that of the catalysts(CA-LaMnO3 and CA-LaFeO3)synthesized by citric acid assisted process without the template.Nanocast perovskites showed high concentration of acidic and basic sites than uncast perovskites and metal oxides.The mineralization of 2-chlorophenol by catalytic ozonation was investigated.The experimental results showed that NC-LaMO3 significantly enhanced the 2-chlorophenol mineralization rate;which followed the order of NC-LaMnO3>NC-LaFeO3>Ca-LaMnO3>CA-LaFeO3>Mn3O4>Fe2O3 with nearly 80.0%,68%,50%,43%,39%,and 33%respectively.This trend is consistent with the amount of acidic and basic sites on the catalysts.At the same time,the NC-LaMnO3 showed good reusability and stability.After three repeated use,the performance of the NC-LaMnO3 did not decrease significantly.After 75 min of reaction,the amount of manganese leached was only 0.1 mg L-1.Phosphate substitution experiments showed that-OH on the surface of the catalyst was the active site of the catalytic process.The use of bicarbonate as ·OH scavengers and EPR confirmed that the ·OH was the main reactive oxygen species in NC-LaMnO3/O3 process for the mineralization of 2-chlorophenol.Improved textural properties,open porous structure and easy access of reactants to the active sites of nanocast perovskites enhanced the catalytic activity.Hydrothermally synthesized CeO2 nanorods,nanocubes,nanooctahedra with different exposed facets(110)+(100),(100)and(111))respectively were used for the mineralization of p-nitrophenol in catalytic ozonation.The experimental results showed that approximately 40%TOC was removed by single ozonation,while 86%,71%,68%,64%and 60%TOC was removed by ozonation catalyzed by nanorod,nanocubes calcined at 300 ?,nanoparticles,octahedra calcined at 300 ? and nanorod calcined at 500 ? respectively.TOC removal with different exposed crystal facets followed the order of(100+110)>(100)>(111).The selected CeO2 nanorods showed good reusability and stability.After three times of repeated use,the performance of CeO2 nanorods did not significantly reduce.After 75 min of reaction,3.0 ?g L-1 Ce ions were leached.·OH,surface peroxide(O22-)and surface atomic oxygen(O-)were found to be the reactive oxygen species.Catalytic activity could be attributed to the surface basicity,defects densities/oxygen vacancy and coordinatively unsaturated sites. |
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