Preparation Of Defective Two-dimensional Layered Materials And Its Performance Of Activted Persulfate To Degrade Organic Pollutants

The advanced oxidation technology of persulfate can generate sulfate radicals（SO₄^·-）with high redox potential and has received extensive attention in the field of water treatment.How to design an environmentally friendly catalyst for efficient activation of persulfate is a research hotspot in this field.Two-dimensional layered materials,graphitic carbon nitride（g-C₃N₄）and titanium carbide（Ti₃C₂T_x）,have broad two-dimensional planes and abundant adsorption and catalytic sites,and are considered promising as efficient persulfate catalysts.However,the inert structure of the original g-C₃N₄leads to the faster recombination of photogenerated carriers in g-C₃N₄,the smaller number of unpaired electrons in the structure,and the Ti₃C₂T_xlayered structure wrapping its internal metastable low-valent titanium species,making it difficult to efficiently Catalytic persulfate.Therefore,it is urgent to seek effective modification strategies for g-C₃N₄and Ti₃C₂T_xto improve their catalytic persulfate performance.Based on this,in this thesis,oxygen-doped porous carbon nitride and defect-rich titanium carbide were prepared using a defect-regulated strategy,and their catalytic performance was evaluated by carbamazepine（CBZ）degradation experiments,and the related activation mechanism was revealed to provide new insights into the activation of perovskite by defective two-dimensional layered materials.The main research contents and conclusions of this paper are as follows:（1）Oxygen-doped porous carbon nitride（OCN）was prepared by a facile thermal polymerization method,and the degradation rate of CBZ by activated permonosulfate（PMS）under visible light irradiation was 4.1 times higher than that of bulk g-C₃N₄.The material structure characterization found that oxygen doping mainly modulates the internal electronic structure of the catalyst to provide more active sites and enhance the activation performance of PMS.At the same time,oxygen doping introduces impurity defect level,which promotes the separation of photogenerated carriers,and the lower band gap enables it to have a broader visible light response capability.Electron paramagnetic resonance and active species trapping experiments indicated that the combined action of free radical and non-radical oxidative pathways was the main mechanism of CBZ degradation.Among them,singlet oxygen is the main active material in the process of degrading CBZ,while O₂^·-and SO₄^·-play an auxiliary role in degradation.In addition,environmental factor experiments showed that chloride ions,bicarbonate ions and humic acid all significantly promoted the degradation of CBZ by OCN/Vis/PMS,while humic acid interacted with CBZ in addition to adsorption to promote the degradation reaction.Finally,high-resolution mass spectrometry identified ring condensation,hydroxylation,and carboxylation as the main degradation pathways for CBZ.（2）Defect-rich titanium carbide（VBMT）was prepared by mechanical ball milling,and the degradation rate constant of the VBMT/PMS system for CBZ(0.326 min^-1)was108.9 times higher than that of the bulk Ti₃C₂T_x(0.003 min^-1).Through a series of morphological and chemical structure characterizations,it was found that after ball milling modification,the layered structure of Ti₃C₂T_xwas destroyed,and point and plane defect sites appeared on its surface,making it more abundant in titanium vacancies and edge defect sites.The electron paramagnetic resonance spectroscopy results also showed that many metastable titanium species in the system make VBMT have a high abundance of unpaired electrons,which is beneficial to the activation of PMS by electron donation.Secondly,the density functional theory calculations and the XPS spectra of VBMT before and after the reaction show that the edge defect sites have better adsorption and activation performance for PMS,and the exposed unsaturated titanium species can directly and quickly transfer electrons to PMS,and the low price Titanium species（Ti（II）and Ti（III））are the main active sites.Through the experiment of free radical probe and high-valent metal oxide probe,it was concluded that SO₄^·-contributed 50.89%,^·OH contributed 0.95%,titanium metal oxide species and traces in VBMT/PMS degradation of CBZ system.The contribution rate of the amount of O₂^·-was 48.16%.Bader charge analysis and transition state calculations revealed that the edge defect sites without hydroxyl capping were more prone to produce titanium metal oxide species with PMS.In addition,environmental factor experiments showed that the VBMT-2/PMS system was resistant to inorganic anions and humic acids.Finally,cyclocondensation,hydroxylation,carboxylation and amine/acrylamide group cleavage were identified as the main degradation pathways of CBZ by Fukui function and high resolution mass spectrometry.