Degradation Of Typical Organic Pollutants In Aqueous Solution With Advanced Oxidation Processes And Their Mechanisms Investigation

With the development of industrial society and the continuous improvement of human living standard,more and more typical organic pollutants are produced and discharged into the environment.These typical organic pollutants in water are resistant to be biodegraded and can exist in the environment for a long time,which not only endangers the growth of aquatic organisms,but also seriously threatens human health.Therefore,it is imperative to develop some efficient and environment-friendly technologies for the removal of organic pollutants.Advanced oxidation processes(AOPs)are effective methods to degrade organic contaminants in water.AOPs mainly generate free radicals(SO4·-,·OH and O2·-)and other reactive oxygen species(1O2)to degrade and mineralize pollutants.In this study,some typical organic pollutants(p-nitrophenol,aniline,chloramphenicol and sulfamethazine)were chosen as the model pollutants to evaluate the existing oxidation system and the developed catalysts via persulfate activation,catalytic ozonation,and peroxymono sulfate activation.Simultaneously,the catalytic mechanisms and degradation pathways were investigated.This study aims to provide theoretical guidance for AOPs in wastewater treatment.The main research contents are as follows:1.Silica gel(SG)was utilized as an assistant to improve the degradation efficiency of p-nitrophenol(PNP)via persulfate(PS)activated with zero-valent zinc(Zn(0)),which could significantly degrease the dosage of Zn(0).It was noted that Zn(0)could not only activate PS,but also lead to the reductive degradation of PNP.There was a significant synergistic effect between SG and Zn(0)in PS activation.The effects of SG,Zn(0)and PS dosages as well as initial solution pH on the PNP degradation in the Zn(0)/SG/PS system were investigated through batch tests,and the results indicated that the synergy between SG and Zn(0)was ascribed to the dispersion and buffering character of SG,which reduced the formation of Zn(?)oxides on the surface of Zn(0).In addition,SG could serve as an adsorbent to remove the generated Zn(?)ions,which would reduce the secondary pollution.The degradation efficiency of PNP was strongly related to the dosage of SG,PS,or Zn(0).A low pH favored of the degradation of PNP.Nevertheless,PNP could be efficiently removed in a pH range of 3 to 9.Free radical quenching experiments indicated that both SO4·-and ·OH were responsible for the oxidative degradation of PNP,especially SO4·-.Based on the analysis of HPLC-TOF-MS2 data,it could be determined that C6H7NO,C6H6O2,and C12H7N3O8 were the main intermediates generated in the Zn(0)/SG/PS system.Furthermore,the possible mechanism and the degradation pathways of PNP via Zn(0)/SG/PS were proposed.2.Sulfur-doped copper-yttrium bimetallic oxides(S-CuYO)were synthesized by a co-precipitation method and utilized for the catalytic ozonation of aniline.For comparison purposes,sulfur-doped monometallic oxides(S-CuO and S-YO)and non-doped copper-yttrium bimetallic oxide(CuYO)were also prepared through the same processes and all the catalysts were characterized by SEM,XRD,FTIR,and XPS.The results showed that the S-CuYO exhibited the highest catalytic performance among these catalysts.?Cu(?)was the main active site of S-CuYO,and sulfur doping and the synergy between?Cu(?)and?Y(?)species could provide the catalyst with more abundant surface hydroxyl groups,a larger surface area and pore size,which exposed more sites for ozone decomposition.The surface hydroxyl groups acted as a bridge could provide reactive sites for ozone adsorption and the?Cu(?)on the surface catalyzed the ozone decomposition to produce free radicals via electron transfer.Furthermore,sulfur dopant not only enhanced the stability of the S-CuYO,but also led to the reduction of?Cu(?)to?Cu(?),which maintained the high catalytic activity and recyclability of the S-CuYO.Electron paramagnetic resonance(EPR)experiment indicated that ·OH was the main active oxygen species responsible for the aniline degradation.The generation of O2·-could form H2O2,and the latter would be catalyzed by?Cu(?)to generate more ·OH.Six main intermediates of the aniline degradation were identified by HPLC-TOF-MS2.And the possible degradation pathways of the aniline by catalytic ozonation with the S-CuYO were further proposed.3.Sulfur-doped copper-cobalt bimetallic oxides(S-CuCoO)with pure Cu(I)were successfully synthesized via the above-mentioned co-precipitation method and were characterized by SEM,TEM,XRD,FTIR,and XPS.The S-CuCoO was utilized to activate peroxymonosulfate(PMS)for the degradation of chloramphenicol(CAP).For comparison,sulfur-doped monometallic oxides(S-CuO and S-CoO)and non-doped copper-cobalt bimetallic oxide(CuCoO)were also prepared via the same processes.The results demonstrated that S-CuCoO had the highest catalytic activity among the catalysts.As the main active sites,?Co had a synergy with?Cu(?)in PMS activation.Sulfur doping could improve the surface area and pore size of the S-CuCoO,and provide more sites.In addition,it also enhanced the performance and stability of copper-cobalt bimetallic oxides.The presence of?Cu(?)improved the conversion of?Co(?)to?Co(?),which maintained the high catalytic performance of S-CuCoO.Besides,the low-valent S species(SO32-and S2-)might facilitate the reduction of high-valent?Cu(?)and?Co(?),which further maintained the recyclability of S-CuCoO.Both SO4·-and ·OH radicals were responsible for the degradation of CAP in the S-CuCoO/PMS system,especially ·OH radicals.Based on the main intermediates identification and the theoretical calculations of the frontier electron densities(FEDs)of CAP,the possible degradation pathways of CAP were determined.4.The spinel CuCo2O4 was synthesized via the calcination of a copper-cobalt bimetallic oxalate precursor and was characterized by SEM,HRTEM,XRD,FTIR,and XPS to determine its composition.CuCo2O4 exhibited excellent catalytic performance in PMS activation for the sulfamethazine(SMZ)degradation.The results showed that the CuCo2O4 had higher catalytic activity than CuO and Co3O4,which was ascribed to the significant synergy between Cu and Co species.As the main active sites for PMS activation,the catalytic performance of Co species was enhanced with the addition of Cu species,which increased the torunover frequency(TOF)of SMZ degradation.Cyclic voltammograms(CV),electrochemical impedance spectroscopy(EIS)and hydrogen temperature-programmed reduction(H2-TPR)investigations revealed that the synergy of Cu and Co species in PMS activation resulted from higher electroconductibility,more electron transfer,and better redox potential of the CuCo2O4,which activated more PMS to produce SO4·-and enhanced PMS self-decomposition to generate 1O2.1O2 dominated non-radical oxidation was mainly responsible for the SMZ degradation.O2·-indirectly degraded SMZ via activating PMS to generate SO4·-and recombining to produce 102.The aniline moiety of SMZ molecule was more prone to be attacked by reactive oxygen species via the comparison of the degradation of SMZ and its sub-structural analogs.Based on the intermediates identification and the theoretical calculations of FEDs of SMZ,the possible degradation pathways of CAP were proposed.