Preparation Of SR-Fenton Heterogeneous Catalytic Materials And Research Of Their Catalytic Properties And Mechanism

Homogeneous sulfate radical Fenton?SR-Fenton?technology is a new advanced oxidation technology with Co²⁺ as catalyst.Compared with Fenton technology,SRFenton system is more oxidizing,with wider effective p H range,stable catalyst Co²⁺,and no chemical sludge is produced during operation.However,the catalyst Co²⁺ of homogeneous SR-Fenton system is easily lost,which only causes high operating costs,but also leads to significant potential ecological environmental risks.Heterogeneous SRFenton technology reduces the dissolution risk of Co²⁺ by adhesion and modification of the catalyst,but a large number of studies show that the free radical yield of the system is low.How to improve the catalytic efficiency of heterogeneous SR-Fenton system has become a technical bottleneck for the popularization and application of SR-Fenton.new advanced oxidation technology.Based on the analysis of the defects of heterogeneous SR-Fenton technology and the characteristics of the yolk-shell nanoreactor,the author thinks that coupling heterogeneous SR-Fenton technology to yolk-shell nanoreactor,the yield of free radicals can be promoted by "adsorption-enrichment-confined oxidation".Based on this thought,the author synthesized sole and multi yolk-shell Co₃O₄@m SiO₂ nanoreactor by selective etching method and double solution injection approach respectively.Their morphology,structure,element morphology and specific surface area were characterized.The adsorption properties of the nanoreactors and the degradation efficiency of refractory organic pollutants?ROPs?by heterogeneous SR-Fenton system with yolk-shell Co₃O₄@m SiO₂ nanoreactor were studied.The degradation pathways were analyzed by identification of degradation intermediates,and the degradation mechanism was studied.The conclusions are as below:?1?The results of scanning electron microscopy?SEM?and scanning transmission electron microscopy?STEM?showed that sole and multi yolk-shell nanoreactors were successfully prepared by selective etching method and double solution injection approach respectively.The particle size was about 300 nm of these two,and they were evenly dispersed.Each sole yolk-shell nanoreactor contained a core with a particle size of about 200 nm,and there was a small cavity area between the core and the shell.Each multi yolk-shell nanoreactor contained a number of nanospheres as cores and the rest part of nanoreactor was cavity.It was proved that the cores of the two kinds of yolk-shell nanoreactors were Co₃O₄,and the shells were SiO₂ by X ray diffraction?XRD?,X ray photoelectron spectroscopy?XPS?,X ray energy scattering spectroscopy?SEM-EDS?and scanning transmission electron microscopy X ray energy scattering spectroscopy?STEMEDX?characterization.?2?The specific surface area and porosity?BET?showed that the two kinds of yolkshell nanoreactors' shells were mesoporous SiO₂?m SiO₂?.The specific surface area of the sole and multi yolk-shell nanoreactors were 66.226m²/g and 160.198m²/g respectively,which were both significantly higher than 24.160m²/g of nano Co₃O₄.The pore volume of sole and multi yolk-shell nanoreactors were 0.274cm³/g and 0.667cm³/g respectively,which are obviously higher than 0.150m²/g of nano Co₃O₄.?3?Most of phenol,rhodamine B?RhB?and bisphenol A?BPA?were degraded in a short time by sole and multi yolk-shell Co₃O₄@m SiO₂ nanreactors.With the increase of cobalt content,the catalytic degradation performance of multi yolk-shell Co₃O₄@m SiO₂ nanoreactor was improved.The degradation rate of phenol,RhB and BPA was increased by 7.9%,11.2% and 13.1% respectively comparing multi yolk-shell Co₃O₄@m SiO₂ nanoreactor to sole yolk-shell Co₃O₄@m SiO₂ nanoreactor.The degradation rates of high and low concentration BPA by multi yolk-shell Co₃O₄@m SiO₂ nanoreactor were 81.8% and 72.4% respectively and the TOC removal rates were 41.4% and 37.4% respectively,which showed that most of ROPs was transformed into intermediates..The reaction conditions for the degradation of ROPs by multi yolk-shell Co₃O₄@m SiO₂ nanoreactor were investigated.It showed that under the condition of weak acidic or neutral p H,moderate reaction temperature,moderate n_KHSO5:n_ROPs,the degradation rates of three kinds of ROPs were the highest.When n_KHSO5:n_ROPs was 8:1,the degradation rates of phenol and RhB were the highest.The ideal ratio of for BPA degradation was 12:1.?4?Multi yolk-shell Co₃O₄@m SiO₂ nanoreactor degraded ROPs by the mechanism of "adsorption-enrichment-confined oxidation".Through the concentration difference,ROPs and KHSO5 were adsorbed through the mesoporous of the m SiO₂ shell into the nanoreactor,and were enriched.The nanoreactor catalyzed the degraded ROPs with the core Co₃O₄ as catalyst,and the adsorption volume of phenol,RhB and BPA were 23.00?19.38?12.69 mg/g respectively.Ethanol and TBA were used as inhibitors of ·OH and SO₄·-,which concluded that in the degradation systems of three ROPs,the main type of free radical was SO₄·-.The pathway of phenol degradation by nanoreactor was that benzene ring of phenol was attacked by SO₄·-and KHSO5,hydroquinone generated,and then transformed into quinone.Quinones was further degraded into organic acids by ring opening,and finally mineralization was achieved.The pathways of RhB degradation could be divided into four parts: deethyling,cracking into small molecules with benzene ring compounds,ring opening and mineralizing.The degradation pathway of BPA was that through electron transfering,BPA was conversed into hydroxyl bisphenol and corresponding quinones by SO₄·-.Furthermore,ring opening occurred to form organic acids and mineralizing achieved fianlly.The results showed that two kinds of yolk-shell Co₃O₄@m SiO₂ nanoreactors were synthesized by selective etching method and double solution injection approach respectively.As heterogeneous catalysts for SR-Fenton,they constructed a SR-Fenton system with "adsorption-enrichment-confined oxidation",and the catalytic degradation efficiency of heterogeneous SR-Fenton system was improved.The research results had strong support for further research and engineering application of SR-Fenton advanced oxidation technology.