Study On Degradation Of Congo Red And Rhodamine B By PMS Activated With Ternary Hydrotalcite

In this study,Co Fe Ni-LDH was prepared by chemical coprecipitation method,and it was used as a novel catalyst to activate peroxymonosulfate（PMS）to degrade Congo Red（CR）and Rhodamine B（Rh B）.SEM,XRD,FTIR and VSM were used to characterize the physical and chemical properties of Co Fe Ni-LDH.Effects of initial solution p H,catalyst dosage,PMS dosage,humic acid dosage and the repeated cycles were discussed systematically through batch experiments.In addition,quenching experiment was designed to determine the effective free radical species in Co Fe Ni-LDH/PMS system.The degradation mechanism was determined based on the XPS results of Co Fe Ni-LDH before and after degradation,as well as degradation products of CR and Rh B through HPLC-MS technology.The characterization results of the catalyst indicated that the proportion of three metal elements in Co Fe Ni-LDH was coprecipitated at the designed ratio(n _Co:n _Fe:n _Ni=6:3:1).The catalyst synthesized in this study has the characterist ics of high intensity and purity,and its saturation magnetization was 1.84emu/g.Batch experiments showed that the initial p H had a significant effect on the degradation of CR and Rh B.Solution p H has little effect on the degradation of CR and Rh B in the Co Fe Ni-LDH/PMS system,and the degradation efficiencies of CR and Rh B were higher than 90%within a wide p H range of 4.0¹0.0 during 10 min reaction time.The Co Fe Ni-LDH dosage and PMS dosage exhibited a positive effect on the degradation of dyes in solution.As the Co Fe Ni-LDH dosages was set at 0.1 g/L,0.2g/L,0.4 g/L,the degradation efficiencies of CR during 3 min reaction time were found to be 45.66%,62.64%and 82.37%respectively,and the degradation efficiencies of Rh B were 27.68%,50.66%and 77.80%,respectively.While the PMS dosages were 0.5 mmol/L,1 mmol/L,2 mmol/L,5 mmol/L,the degradation efficiencies of CR were 35.18%,47.51%,61.80%and 71.84%,respectively,and the degradation efficiencies of Rh B were 45.07%,50.66%,69.67%,and 82.89%respectively.Humic acid showed an inhibitory effect on the catalytic degradation process.When the humic acid concentration was 15 mg/L,the degradation efficiencies of CR and Rh B were only 80.16%and 94.26%.Cyclic utilization experiments showed that Co Fe Ni-LDH has satisfactory stability.Cycling tests showed that after three times repeated use,the degradation efficiencies of CR and Rh B by Co Fe Ni-LDH/PMS system only dropped 7%and 9%,respectively.EDX characterization results showed that the composition proportion of Co Fe Ni-LDH after degradation changed to n _Co:n _Fe:n _Ni=6.43:3.40:1.07 from n _Co:n _Fe:n _Ni=6.48:3.47:1.19,which was comparable to elements ratio of the fresh Co Fe Ni-LDH.This fact further proved that Co Fe Ni-LDH synthesized in this study was relative stable.Quenching experiments showed that two strong oxidative species(^·OH and SO₄^–·)participated in the process of catalytic degradation of dyes by activating PMS using Co Fe Ni-LDH,and SO₄^–·played the major role in the process.The degradation process and degradation products of CR and Rh B showed that the degradation process of CR and Rh B followed by gradually fragmentation process,the organic molecules can be fully mineralized into small toxic fragments,organic compounds,or completely degraded into non-toxic CO₂ and H₂O finally.Through the analysis of mass ratio,the experiment determined the degradation intermediates and possible degradation pathways of two pollutants.These conclusions laid a theoretical foundation for the degradation principle of Co Fe Ni-LDH/PMS system.