Preparation Of Cobalt-based Bimetallic Oxides And Their Application In The Degradation Of Chloramphenicol And Phenylphosphonic Acid In Water By Activated Peroxymonosulfate

Advanced Oxidation Processes（AOPs）have been recognized as promising technologies for organic pollutant degradation.In recent years,activated persulfate technology based on sulfate radical(SO₄^·-)has attracted much attention due to its wide p H range,long half-life and high reduction potential.The degradation of organic pollutants by peroxymonosulfate（PMS）itself is not satisfactory.PMS can be activated by ultrasound,thermal activation,photoactivation,alkali activation,transition metal activation and carbon-based materials to produce SO₄^·-.In transitional metal-activated PMS,cobalt ions show the best activation performance,but the use of homogeneous Co²⁺activated PMS is limited due to the difficulty of catalyst separation and recovery and the environmental problems caused by excessive cobalt ions.In this case,cobalt-based mixed metal oxide catalysts with the addition of exogenous metals have been developed in the advanced oxidation process based on sulfate radical.In this study,cobalt-tin bimetallic oxide（Co₃O₄-Sn O₂）and cobalt-yttrium bimetallic oxide（Co₃O₄-Y₂O₃）were synthesized and used as catalysts for the degradation of organic pollutants by PMS.Chloramphenicol is a broad-spectrum antibiotic.Water contaminated with chloramphenicol can cause human health problems such as bone marrow hemopoiesis inhibition and environmental problems.Phenylphosphonic acid is a synthetic pyrethroid insecticide,but the exposure to phenylphosphonic acid poses a health risk,such as irritation to respiratory system and skin.Therefore,effective technologies are urgently needed to remove residual chloramphenicol and phenylphosphonic acid pollutants from water and soil environment.In this study,firstly,Co₃O₄-Sn O₂catalyst was synthesized to remove chloramphenicol.Secondly,Co₃O₄-Y₂O₃catalyst was prepared to catalyze the degradation of phenylphosphonic acid and the in-situ adsorption of secondary inorganic phosphorus.And in the process of experiment,the removal effect of different systems,coexisting ions,p H and other influencing factors and possible reaction mechanism were discussed.This study mainly consisted of two parts:In Part I:The Co₃O₄-Sn O₂composite derived from bimetallic oxalates was rationally fabricated and utilized as a catalyst for peroxymonosulfate（PMS）activation towards the destruction of chloramphenicol（CAP）.The physicochemical properties of the Co₃O₄-Sn O₂were systematically characterized to discover the relationship between its structure and catalytic performance.Sn O₂as a cocatalyst with high conductivity and stability immensely improved the activity of Co₃O₄in the Co₃O₄-Sn O₂composite.Approximately 98%of CAP（10 mg/L）was eliminated by the Co₃O₄-Sn O₂（0.1 g/L）activated PMS（1.0 mmol/L）at initial p H 7 within 20 min.The rationally designed Co₃O₄-Sn O₂composite exhibited higher catalytic activity than Co₃O₄,Sn O₂,and other cobalt-based bimetallic oxides（such as Co-Fe,Co-Mn,and Co-Cu）in the PMS activation for the CAP degradation.The synergistic effect of Co₃O₄and Sn O₂endowed the Co₃O₄-Sn O₂composite with higher conductivity and more electron transfer,which was proved by the electrochemical tests.The presence of SO₄^·-,^·OH,O₂^·-,and ¹O₂during the CAP degradation was testified by both quenching experiments and electron paramagnetic resonance（EPR）spectroscopy.In addition,the catalytic mechanism and degradation pathways were further proposed via the characterization of X-ray photoelectron spectroscopy（XPS）and the identification of transformation products,respectively.This work provides a new insight into the preparation of novel catalysts and their application in wastewater treatment.In Part II:Cobalto-yttrium bimetallic oxide（Co₃O₄-Y₂O₃）was synthesized by oxalate precipitation method.The physicochemical properties of the Co₃O₄-Y₂O₃were systematically characterized to reveal the relationship between its structure and catalytic performance.The activation of peroxymonosulfate（PMS）by Co₃O₄-Y₂O₃catalyst was used to remove the phenylphosphonic acid（PPOA）and adsorb the secondary inorganic phosphorus produced from the reation.The degradation of phenylphosphonic acid in the Co₃O₄-Y₂O₃/PMS system was investigated by different factors such as initial p H,PMS concentration,catalyst dosage,coexisting ions and humic acid.The results showed that Co₃O₄-Y₂O₃could effectively activate peroxymonosulfate,and PPOA of 50μm（1.55mg-P/L）was completely degraded within 30 min.Meanwhile,100%secondary inorganic phosphorus was removed within 60 min.The TOC removal rate of phenylphosphonic acid reached 64.3%within 60 min.The degradation efficiency of PPOA in the Co₃O₄-Y₂O₃/PMS system was strongly p H-dependent,which decreased from nearly 100%in an initial p H range of 3-7 to nearly 0%at initial p H 11.The reactive oxygen species（ROS）,including sulfate radical(SO₄^·-),hydroxyl radical（^·OH）and singlet oxygen（¹O₂）,were determined by free radical inhibitor experiments and EPR.The intermediate products from the degradation of phenylphosphonic acid were identified by HPLC-QTOF-MS²and the possible degradation pathways of phenylphosphonic acid were further proposed.Co₃O₄acted as the main catalyst and Y₂O₃acted as the main adsorbent.The cobalt-yttrium component had an excellent synergistic effect in the degradation of phenylphosphonic acid.This study may provide an insight into the degradation of PPOA and the simultaneous removal of secondary inorganic phosphorus.