The Preparation Of Loaded MnFe₂O₄ And Microwave Catalytic Degradation Of Reactive Brilliant Red X-3B

Microwave-induced catalytic degradation is considered to be an effective technology to treat refractory wastewater.In the microwave reaction,microwave interact with specific catalyst or carrier,so catalyst and carrier is very important in microwave-induced catalytic degradation.In this paper,the effective microwave absorber—loaded MnFe2O4 are successfully prepared and applied in the microwave-induced catalytic degradation of typical azo dye-Reactive Brilliant Red X-3B,the main contents are as follows:(1)Modification of reactor--The infrared thermometer and high-definition cameras were installed,which can realize a real time monitoring of the reaction process and temperature during the reaction.(2)Mnfe2O4,MnFe2O4-TiO2,MnFe2O4-SiC and MnFe2O4-diatomite were successfully prepared by coprecipitation-hydrothermal method,ultrasonic synthetic method and sol-gel method,respectively.The properties of four catalysts were characterized by XRD,BET,SEM,FTIR and Zeta potential.The XRD analysis of four catalysts showed that the characteristic diffraction peaks at 20=34.88 and characteristic diffraction peaks of SiC,TiO2 and diatomite appeared,illustrating that MnFe2O4 was well supported on the surface of supporter.The grain sizes of four catalysts are 22.87 nm(MnFe204-SiC)?27.50 nm(MnFe2O4-TiO2)?31.67 nm(MnFe2O4)and 41.20 nm(MnFe2O4-diatomite),respectively.The BET analysis indicated that the specific surface areas of four catalysts are 120.83 m2/g(MnFe2O4-SiC)?50.13 m2/g(MnFe2O4-TiO2)?17.40 m2/g(MnFe2O4)and 5.41 m2/g(MnFe2O4-diatomite),respectively.It can be seen from SEM that the particles and properties of four catalysts are uniform and excellent.The FTIR spectra analysis of four catalysts shows that the typical tetrahedral skeleton vibration appeared from 545 cm-1 to 560 cm-1,which are ascribed to IR peaks of MnFe2O4.Meanwhile,the absorption peaks of catalyst at 450-500 and 820 cm-1 are ascribed to stretching vibration of Ti-O bond and C-Si bond,while the absorption peaks at 471 and 1088 cm-1 are ascribed to bending vibration and stretching vibration of Si-O bond,respectively.Moreover,the isoelectric point(pHIEP)of MnFe2O4,MnFe2O4-SiC and MnFe2O4-TiO2 are at pH range from 6 to 7,which easily absorb the anionic dyes with negative charge,while the isoelectric point(pHIEP)of MnFe2O4-diatomite is from 3 to 4,which easily absorb the cationic dyes.(3)MW-induced catalytic degradation of Reactive Brilliant Red X-3B(20 mg/L)was investigated.The removal of RBR X-3B in four different catalysts(MnFe2O4-SiC,MnFe2O4-TiO2,MnFe2O4-diatomite and pure MnFe2O4)was 92%,77%,20%and 25%,respectively,when MnFe2O4-SiC,MnFe2O4-TiO2,MnFe2O4-diatomite and pure MnFe2O4 were used in the degradation.A similar trend appeared in TOC removal.When MnFe2O4-SiC,MnFe2O4-TiO2,MnFe2O4-diatomite and pure MnFe2O4 were added,corresponding TOC removal was 70%,45%,15%and 20%,respectively.The reactive brilliant red X-RB degradation can be divided into two stages.In the first stage,degradation followed pseudo first order kinetic model.The rate constant of degradation was 0.316 min-1(MnFe2O4),118 min-1(MnFe2O4-SiC),0.638 min-1(MnFe2O4-TiO2)and 0.104 min-1(MnFe2O4-diatomite),respectively.Moreover,the biological toxicity of the reaction soultion in the first stage is obviously enhanced and the rate of maximum inhibition reached 28.4%(MnFe2O4-SiC),31.3%(MnFe2O4-TiO2),33.8%(MnFe2O4-diatomite)and 32.5%(MnFe2O4).In the second stage,the reaction tends to be gentle;the highly toxic intermediates produced in the first stage were continuously degraded.In addition,the toxicity of wastewater reduced and the pollutant was decomposed completely.(4)The different catalytic performances of the four catalysts were caused by the introduction of supports which can affect the microwave absorbing properties of catalysts.Based on the analysis of the microwave absorbing property calculated by Matlab,the re:flection loss of MnFe2O4-SiC could reach up to-10 dB at 2.59 GHz,originating from the dielectric loss,which was the evidence that over 90%microwave power had been absorbed by the catalyst.Then the microwave power could be used in the decomposition of the azo dyes,herein,MnFe2O4-SiC was a promising microwave catalyst.Meanwhile,the rising temperatures of samples under microwave irradiation were investigated.It was established that MnFe2O4-SiC could absorb MW energy strongly,exceeding over 1400? within seconds.(5)In the case of MnFe2O4-SiC,the formation of hot spot in the reaction process was observed.In the first stage,as the reaction proceeded,the amounts of hot spots generated increased clearly;a certain peak appeared in 1.5-2min.Then the reaction speed tended to be steady,which caused the lower amount of hot spots.To verify the main active oxygen species,the scavengers(tert-Butanol and NaC2O4)were added in the degradation.It was indicated that hydroxyl radicals and superoxide anions were the significant species produced in the degradation.Moreover,in the ESR analysis,the 1:2:2:1 peak was observed,which was the evidence of hydroxyl radicals.(6)On the basis of the above analysis,the degradation mechanism had been proposed:Under the microwave radiation,the surface temperature of the catalysts could rise rapidly,followed by the generations of many "hot spots" and numerous activated sits and holes.Herein,the electron hole pairs can be generated to react with O2 and H2O to form the various active species,e.g.hydroxyl radicals or superoxide radical anion.Thus,the MW degradation process of pollutants could be enhanced significantly.