Effective PMS Activation By Co₉S₈ For The Degradation Of Organic Pollutants:Insights Into The Degradation Performance And PMS Activation Mechanism

Nowadays,persulfates（e.g.peroxymonosulfate（PMS）or peroxydisulfate（PDS））-based advanced oxidation processes（AOPs）have a remarkable reputation for the oxidation of refractory organic pollutants in water.Howerer,the limited oxidation capacity of PMS urges researchers to catalyze PMS using the appropriate activation means to effectively decompose PMS into highly reactive oxygen species（ROS）such as SO₄^·-and·OH with strong oxidation capacity and low selectivity.In this regard,the heterogeneous transition metal catalysts effectively activate the PMS without any additional energy inputs.The use of heterogeneous transition metal catalysts overcomes the shortcomings of transition metal ions-based homogeneous systems,such as difficult recovery and utilization of spent catalysts,secondary pollution due to metal leaching,and strong p H dependency,which is a research hotspot.The mutual conversion of Mⁿ⁺and M^（n+1）+is a key step for the heterogeneous transition metal catalyst to activate PMS.However,in order to realize the redox cycle,M^（n+1）+needs to be further reduced to Mⁿ⁺by consuming PMS,which reduces the efficiency of the conversion of PMS to SO₄^·-in the reaction system(PMS_4?-).Non-metal heteroatomic doping is an effective way to improve the catalytic performance of the heterogeneous transition metal-based catalysts for PMS.Therefore,researchers used transition metal sulfide materials instead of transition metal oxide materials to activate PMS and assist the redox cycle between M^（n+1）+/Mⁿ⁺.However,the influence of foreign elements on the catalytic process has not been studied in depth.Therefore,in this dissertation,the acetaminophen model was used to study the efficacy and reaction mechanism of activation of PMS by Co₃O₄ and Co₉S₈ catalyst with different sulfur doping amounts.The main research contents and results were as follows:（1）Using Co₃O₄ as the precursor,Co₃O₄ catalyst and Co₉S₈ catalyst with a diameter of 150～300 nm were prepared.The analytical studies such as XRD,SEM,FT-IR,EDS,BET and other characterization results showed that with the introduction of sulfur,the lattice oxygen in Co₃O₄ was gradually replaced by sulfur atoms.As a result,the ionic valence state of cobalt was changed,and the presence of zero-valent cobalt（Co⁰）was detected in all Co₉S₈ catalysts.The actual sulfur content of 1C-Co₉S₈,2C-Co₉S₈ and 3C-Co₉S₈ catalysts were 14.3%,20.1%,and 24.8%,respectively.（2）The PMS activation properties of Co₃O₄ and a series of sulfur-doped Co₉S₈catalysts were compared.The results showed that the Co₉S₈ catalyst doped with S had better catalytic performance than the Co₃O₄ catalyst,and the activation capacity of each catalyst to PMS was as follows:1C-Co₉S₈<Co₃O₄<2C-Co₉S₈<3C-Co₉S₈.The removal efficiency of ACE in 3C-Co₉S₈/PMS system reached 92.0%within the 40 min.（3）Reactive oxygen species activated by Co₃O₄ and Co₉S₈ catalysts in the PMS system were studied by quenching experiments,EPR detection,SO₄^·-quantitative experiments,etc.The results showed that the active oxygen species in Co₃O₄/PMS and Co₉S₈/PMS system mainly included ¹O₂,SO₄^·-and·OH.With the increase of sulfur doping,the contribution rate of ¹O₂ gradually decreased and the contribution rate of SO₄^·-gradually increased.（4）The activation mechanism of Co₃O₄ and series sulfur-doped Co₉S₈ catalyst on PMS was studied by means of XPS characterization and PMS digestion experiment.The results show that the lattice oxygen reacts with PMS to form ¹O₂.For the Co₃O₄/PMS reaction system,SO₄^·-is derived from the redox cycle between Co³⁺/Co²⁺.For a series of Co₉S₈/PMS systems,under the action of S^2-,the redox cycle between Co³⁺/Co²⁺/Co⁰ increases the efficiency of conversion of PMS to SO₄^·-(_4?-).（5）The influence of various influencing factors and typical impurities in the actual water body on the performance of the 3C-Co₉S₈/PMS system was investigated.The results showed that,compared with other advanced oxidation systems,the 3C-Co₉S₈/PMS system could degrade many kinds of refractory organic pollutants,and the removal efficiency of ATZ,SMX,2,4-D,4-CP,and PN in 10 min was 91.8%,98.1%,63.8%,55.9%,and 95.0%respectively.The reaction activation energy was calculated to be 10.98 k J/mol.The system still has good performance in a wide p H range.At the same time,the system has a strong anti-interference ability to the anions and natural organic substances in the actual water.