Heterogeneous Materials Based On Transition Metals For Persulfate Activation And Organic Pollutants Removal

Advanced oxdidation processes(AOPs)based on sulfate radical(SO4·-)become a new kind of technology for water protection.Activation of persulfate(PS)were primary ways to produce SO4·-.PS includes peroxydisulfate(PDS)and peroxymonosulfate(PMS).Fe2+ was the most efficient transition metal ions for PDS activation and Co2+ for PMS.However,homogeneous activation based on transition metal ions have some disadvantage such as inducing second pollutant and so on.The key to solve the problems was to develop heterogeneous materials based on transition metals.Based on this,this article develop Li FePO4(LFP)and FeMoO4 for PDS activation firstly,and then LiCoPO4(LCP)and Co0.39Fe0.51P(CFP)for PMS activation.Specific research contents are as follows.(1)LiFePO4(LFP)based on Fe2+ was prepared and applied to activate PDS for pollutant removal.It was found that LFP/PDS system performed well in removing Orange G(OG)and other kinds of dye pollutants such as acid orange 7(AO7),methylene blue(MB),methyl orange(MO)in just 10 min.Further investigation presented that increasing doses of LFP and PDS induced increasing removal efficiency when the amount of LFP was less than 0.5 g L-1.Meanwhile,the efficiency decreased obviously when pH increased.Radical quenching experiment showed that the primary radicals were sulfate radicals.Finally,the fresh and used samples were analyzed by the means of XRD,Raman,SEM and XPS.Based on the comprehensive analysis above,the mechanism of LFP/PDS system was concluded.The mechanism was related with the conversion between LiFePO4 and FePO4.(2)FeMoO4 was prepared successfully in acidic liquid and was applied to activate PDS for pollutant removal.It was found that FeMoO4/PDS system was efficient.When the amount of FeMoO4 and PDS was less than 0.5 g L-1 and 4 mM respectively,the efficiency increased as the doses increased.Meanwhile,the removal efficiency decreased when pH increased.EPR experiment and radical quenching experiment together proved that both SO4·-and ·OH existed and the former was the primary.XRD,Raman and SEM techniques together indicated that the structure change little even after 12 cycles.Observation by the means of TEM indicated that the surface of samples changed compared with the inner part.Further investigation by XPS presented that the binding energy of Mo 3d and O 1s changed little.However,the binding energy of Fe 2p3/2 and Fe 2p1/2 all shifted toward high energy.Based on the analyis,the mechanism of FeMoO4/PDS system was concluded.Finally,the pathway of OG degradation in FeMoO4/PDS system was proposed by the means of GC-MS.(3)LiCoPO4(LCP)was prepared with traditional solid-state method,and then was applied to activate PMS for pollutant(DEP)removal.In this work,pH of solution was not needed to be adjusted,which could regard as the advantage compared with the traditional AOPs.LCP/PMS system performed well.When the amount of LCP and PMS were less than 0.1 g L-1 and 0.3 g L-1 respectively,the removal efficiency of DEP increased when the amount of LCP or PMS increased.To avoid the second pollutants,the amount of LCP and PMS was set as 0.01 g L-1 and 0.3 g L-1.Meanwhile,98% of DEP could be removed in 1 h in this condition.Radical quenching tests presented that both SO4·-and ·OH existed and the former was the primary.Finally,the fresh and used samples were analyzed by the means of XRD,Raman,SEM and XPS.Based on the comprehensive analysis above,the mechanism of LCP/PMS system was concluded.Finally,the pathway of DEP degradation in LCP/PMS system was proposed by the means of GC-MS.(4)Co0.59Fe0.41P(CFP)derived from the Prussian blue analogues(PBAs),one kind of MOFs,was prepared.And then,CFP was applied to activate PMS for DEP and DBP removal.To reduce the second pollutant and the shortcoming,the amount of CFP was 0.02 g L-1 and pH was not adjusted.It was found that HA and Cl-had adverse effect on pollutant removal.However,HCO3-had little effect.Radical quenching tests also presented that both SO4·-and.·OH existed and the former was the primary,which was similar to LCP/PMS systems.The fresh and used samples were analyzed by the means of XRD,Raman,and SEM,and little change could be found.Binding energy of Co 2p3/2 shifted to high energy,which indicated that cobalt on the surface of CFP made contributions for PMS activation.Based on this,the mechanism of CFP/PMS system was proposed.