Surface-Interface Control And Property Evaluation Of Functional Covalent Organic Framework Composite Materials

The advanced oxidation technologies of peroxymonosulfate（PMS）activators,shows great promise for the abatement of persistent toxic organic pollutants with environmental protection,efficient and low pH dependence,while traditional transition metal ions activation PMS reaction suffers from difficult to control reaction process and secondary pollution defects.Using different elements doping the precursor covalent organic frameworks（COFs）to form the non-metal catalyst g-C₃N₄@COF and single-atom Fe@COF catalyst for enhance PMS activation efficiency.Benefiting from the easy functionalization,interprets the relationship between the catalyst structure,doping elements species and the catalytic activity.The following studies were carried out:（1）Novel metal-free catalysts via integration of covalent organic framework（COF）and graphitic carbon nitride（g-C₃N₄@COF）with a high graphitization degree and nitrogen content were fabricated and exhibited extremely outstanding activity for peroxymonosulfate（PMS）-driven oxidation of refractory organic pollutants in water.SEM images showed many aggregated COFs crystals anchored on the irregular g-C₃N₄surface to form 3D structures.The precursors（urea,melamine,and dicyandiamide）of g-C₃N₄ determined the porous structures and properties of the g-C₃N₄@COF materials.Besides,removal efficiency of target pollutants depended on the oxidant dosage,initial concentrations of organics,temperature,pH,and inorganic anions,also analyze the stability and reuse of the catalyst.Quenching experiments and electron paramagnetic resonance（EPR）demonstrated that non-radical singlet oxygen（¹O₂）was the dominant species for the oxidation of organic pollutants via electron transfer in the g-C₃N₄@COF/PMS system.It was inferred that the good balance between graphitization degree and nitrogen content benefited to enhancing catalytic performance for the refractory pollutant degradation.（2）A covalent organic framework-confined strategy for constructing single-atom Fe dispersed on hierarchically structured porous carbon catalysts（Fe@COF-X-T,where X represents the initial mass ratio of iron salts/COF and T represents the calcination temperature）.Experimental results revealed that iron doping preferentially generate highly effective single-atom Fe-N_x active sites into the carbon framework with electronic structure modulation,endowing it with prominent catalytic properties for organics decomposition.Both quenching results and in-situ electron paramagnetic resonance spectrometry revealed that the formation of singlet oxygen（¹O₂）by the Fe@COF/PMS system was primarily responsible for the organic degradation rather than the sulfate radical and hydroxyl radical.Besides,removal efficiency of target pollutants depended on the oxidant dosage,initial concentrations of organics,temperature,and water matrix components（such as pH,dissolved organic matter）,also analyze the stability and reuse of the catalyst.Our experiments show that abundant single-atom Fe-N_x active sites with optimal binding energy can successfully activate PMS to produce ¹O₂,while the rich pyrrolic nitrogen site may act as the adsorption site for organic molecules,giving rise to remarkable Fenton-like catalytic activity.