Study On The Preparation And Catalytic Performance Of Magnetic Core-shell Catalyst Fe₃O₄@SiO₂/SB/Cu???

The problem of global environmental pollution has become increasingly serious.The types of pollutants are numerous and complex,and pose constant threats to human survival.The textile printing and dyeing industry is an important part of the industry.It has a large amount of discharged waste water and a high concentration of pollutants.The dye waste water is one of the most difficult wastewater to be treated in industry.As a terminal treatment,biological method is widely used in the treatment of wastewater in various industries,mainly through metabolic enzymes,in which laccase oxidase and other enzymes have attracted wide attention.The copper complex with Schiff base acts as a mimetic enzyme of laccase and a Fenton-like catalyst used to degrade organic pollutants.However,such small molecule complex catalysts are difficult to separate and recover,and the active centers are easily lost.Therefore,the research of supported heterogeneous catalysts has become a hot topic.The magnetic core shell composite catalyst constructed by magnetic nanosized iron oxide is easy to recover and improve the stability and activity of the catalyst,so it has been paid more attention to.Herein,the core-shell material Fe₃O₄@SiO₂ is prepared,and the copper complex with Schiff base is covalently loaded on Fe₃O₄@SiO₂.The magnetic core-shell catalyst Fe₃O₄@SiO₂/SB/Cu?II?is obtained,and the catalytic activity and stability could be enhanced by the connecting group with a longer carbon chain.All catalysts are used to remove dyes with different structures from water.The results were summarized as follows:1)Four catalysts were prepared,catalyst 1:Fe₃O₄@SiO₂/SB?1?/Cu?II?,catalyst 2:Fe₃O₄@SiO₂/SB?2?/Cu?II?,catalyst3:Fe₃O₄@SiO₂/SB?3?/Cu?II?,catalyst4:Fe₃O₄@SiO₂/SB?4?/Cu?II?.The composition,morphology and structure of the catalysts were characterized by FT-IR spectra,DRS,UV-Vis spectra,TGA method,XRD,N₂adsorption-desorption,XPS.The effect of catalytic degradation of methyl orange was studied by spectrophotometer.The effects of temperature,pH value,hydrogen peroxide dosage and catalyst dosage on the degradation of methyl orange were investigated.The mechanical stability,chemical stability and recyclability of the catalysts were investigated.The results show that the catalyst is a magnetic core-shell supported catalyst,and its active center is SB-Cu?II?,which could effectively activate hydrogen peroxide to degrade methyl orange.The increase of temperature,the increase of hydrogen peroxide and the increase of catalyst amount are favorable for the removal methyl orange;pH value from 8 to 10 is beneficial to the degradation of methyl orange.When the concentration of the methyl orange is 30 mg/L,the most suitable degradation condition is determined:the dosage of catalyst is 15 mg/L,the temperature is 40?,pH value is9.0,the dosage of H₂O₂ is 36 mmol/L.Under the optimum conditions,the decolorization rate of methyl orange,rhodamine B and alizarin red could reach 100%after 12 h,and the decolorization rate of E,B,O,R dyes is 60⁷0%.Under the alkaline condition,the active center of the catalyst is destroyed,and the active center is stable under the condition of pH value from 2 to 10 and in the presence of electrolyte.Under the optimum conditions,the catalyst could be recycled more than 5 times in the presence of electrolyte with the active center slowly losing.2)In order to increase the anti-alkaline and activity of the catalysts,CPTES fragments were inserted between Fe₃O₄@SiO₂ and SB/Cu?II?,then the other four catalysts were prepared,catalyst 5:Fe₃O₄@SiO₂-CPTES/SB?1?/Cu?II?,catalyst 6:Fe₃O₄@SiO₂-CPTES/SB?2?/Cu?II?,catalyst 7:Fe₃O₄@SiO₂-CPTES/SB?3?/Cu?II?,catalyst 8:Fe₃O₄@SiO₂-CPTES/SB?4?/Cu?II?.The composition,morphology and structure of the catalysts were characterized by FT-IR spectra,DRS,UV-Vis spectra,TGA method,XRD,N₂ adsorption-desorption,XPS.The effect of catalytic degradation of methyl orange was studied by spectrophotometer.The effects of temperature,pH value,hydrogen peroxide dosage and catalyst dosage on the degradation of methyl orange were investigated.The mechanical stability,chemical stability and recyclability of the catalyst were investigated.The results show that the catalyst is a magnetic core-shell supported catalyst,and its active center is SB-Cu?II?,which could effectively activate hydrogen peroxide to oxidize methyl orange.The increase of temperature,the increase of hydrogen peroxide and the increase of catalyst amount are favorable for the catalytic degradation of methyl orange;pH value from 8 to 10 is beneficial to the degradation of methyl orange.When the substrate concentration is 30 mg/L,the most suitable degradation condition is determined:the dosage of catalyst is 15 mg/L,the temperature is 40?,pH value is 9.0,the dosage of H₂O₂ is 36mmol/L.Under the optimum conditions,the removal of methyl orange,rhodamine B,alizarin red and acid red dye could be achieved with the decolorization rate 100%after 12 h;the decolorization rate of E,B,O and R with bromine substituted aryl and nitro substituted aryl dyes is 73%⁸2%after 12 h.Under the alkaline condition,the active center of the catalyst is destroyed,and the active center is stable under the the condition of pH value from 2 to 10 and in the presence of electrolyte.Under the optimum conditions,the catalyst could be recycled more than 6 times in the presence of electrolyte with the active center slowly losing.It can be seen that the catalyst prepared by chain lengthening could improve the catalytic activity with the active center more slowly losing and wider substrate,but the resistance to alkaline needs to be further improved.3)The structure-activity relationship of the active center in the catalysts was examined.It is found that the catalytic activity of Fe₃O₄@SiO₂/SB/Cu?II?and Fe₃O₄@SiO₂-CPTES/SB/Cu?II?is SB?4?>SB?2?>SB?1?>SB?3?.The SB is more stable,the catalytic activity is better.The electron-donating group,the rich electron effect and the conjugated effect on the aromatic group in SB is beneficial to the stability of the active center,which could induce the better activity of the catalysts.4)The degradation products were determined by high performance liquid chromatography.The COD of the degradation solution before and after degradation was determined by Mn-method,and CO₂ gas was verified by saturated calcium hydroxide solution.It was found that the products are phenols,oxalic acid,maleic acid,pyruvic acid and CO₂,and COD_Mn decreased significantly during degradation.It shows that theremoval of dyes is not simply decolorization,but degradation and mineralization.5)The mechanism of degrading dyes by catalyst activation of hydrogen peroxide was verified by radical inhibition experiment and free radical capture experiment.The dye degradation progress was investigated by GrapHPad Prism 7 software.It was found that the decolorization and degradation of methyl orange is inhibited for the competing reaction between tert-butanol with hydroxyl radical and methyl orange with hydroxyl radical,and the2,5-dihydroxybenzoic acid is formed from the reaction of salicylic acid with hydroxyl radicals.It indicates that hydroxyl radicals are produced from hydrogen peroxide and the catalyst.Then the molecular of methyl orange is attacted and degraded by the hydroxyl radical.And the possible degradation mechanism is deduced.The result show that the degradation process of methyl orange was accorded with the Michaelis-Menten equation,which also shows that the catalysts could be used as enzyme model and the degradation process of methyl orange is an enzymatic mechanism.