Preparation Of Carbon Composites Derived From Metal-Organic Frameworks And Their Catalytic Degradation Of 4-aminobenzoic Acid Ethyl Ester(ABEE)

Advanced oxidation technology is a kind of green technology with wide application prospects in the field of environment and energy,and the development of novel catalysts is an important research hotspot in the field of environment and energy.In this paper,prussian blue analogues（Fe_xMn_y-Fe PBAs）with different Fe/Mn molar ratios were prepared as precursors.The Fe,Mn and N co-doped porous carbon（Fe_xMn_y-Fe NCs）and N-doped porous carbon coated iron catalysts（Fe_xMn_y-Fe@NCs）were prepared by calcination.The implication of activating peroxymonosulfate（PMS）toward 4-aminobenzoic acid ethyl ester（ABEE）degradation was investigated.This paper not only has great significance for environmental pollution control,but also has theoretical reference for rational design of novel environmental catalytic materials.The conclusions are as follows:1.Catalytic degradation of ABEE by Fe,Mn and N co-doped porous carbon（Fe_xMn_y-Fe NCs）:（1）XRD/SEM/TEM tests indicated that Fe_xMn_y-Fe PBAs were successfully prepared.Fe_xMn_y-Fe NCs were prepared after calcination of Fe_xMn_y-Fe PBAs at 500℃.Fe_xMn_y-Fe NCs were mainly porous carbon containing iron and manganese oxides,which were amorphous and had a certain degree of graphitization.（2）Fe₁Mn₁-Fe NC showed the best catalytic degradation ability,with 94%ABEE removal rate and 31%mineralization rate within 30 min.（3）After 30 min of degradation by Fe₁Mn₁-Fe NC,the leaching concentrations of iron and manganese ions were 0.12mg L^-1 and 0.13mg L^-1,respectively.（4）After five cycles of repeated usage,Fe₁Mn₁-Fe NC could still achieve 77%ABEE degradation rate.（5）Fe₁Mn₁-Fe NC maintained good catalytic performance in a wide p H range（p H=3～9）.（6）The activation of PMS was mainly accomplished by consuming lattice oxygen and adsorbed oxygen/hydroxyl oxygen on the surface of Fe_xMn_y-Fe NCs to generate water and sulfate at the same time.（7）Lattice oxygen was the catalytic active site of Fe_xMn_y-Fe NCs.The catalytic mechanism was that the redox cycles between Mn²⁺/Mn³⁺/Mn⁴⁺and Fe²⁺/Fe³⁺made lattice oxygen in Fe-Mn oxides easy to accept electrons and release lattice oxygen,thus generating oxygen vacancy.（8）Superoxide radicals played a major role in catalytic degradation.（9）The proposed ABEE degradation pathways included electrophilic/radical addition on benzene ring,hydrogen absorption reaction,-NH₂ diazotization reaction,C-C bond fracture,etc.This material has a broad prospect in the field of in-situ remediation of organic pollution and degradation of organic matter in water environment.2.Catalytic degradation of ABEE by N-doped porous carbon coated iron catalysts（Fe_xMn_y-Fe@NCs）:（1）XRD/SEM/TEM results showed that Fe_xMn_y-Fe PBAs were successfully prepared.After calcination at 700℃,the obtained porous carbon was processed by acid treatment to prepare Fe_xMn_y-Fe@NCs.After acid treatment,the metal phases of most Fe Mn oxides had been removed,and the structure of Fe_xMn_y-Fe@NCs were enclosed by several graphene layers,with a certain degree of graphitization.（2）Fe₂Mn₁-Fe@NCs showed the best catalytic degradation capacity and achieved 94.5%ABEE degradation rate within 6min.（3）After 6 min of degradation by Fe₂Mn₁-Fe@NC,the leaching concentrations of iron and manganese ions were 0.06mg L^-1 and 0.02mg L^-1,respectively.（4）The binding of iron and nitrogen atoms in Fe₂Mn₁-Fe@NC was Fe N₄ coordination.（5）Pyrrollic N acted as the adsorption site of ABEE to enhance the catalytic capacity of Fe₂Mn₁-Fe@NC toward PMS activation.Singlet oxygen and superoxide radicals were the main active substances in the catalytic degradation process.（6）PMS radical generation path occurred on Fe-pyridinic N-C,while non-radical generation path occurred on pyrrollic N-C.（7）In Fe-pyridinic N-C model,the O-O bond of PMS was decomposed into·OH and·SO₄^-with an energy barrier of 19.6kcal/mol.The O-H bond fracture of PMS in the pyrrollic N-C model generated·SO₅^-and H⁺,with an energy barrier of 9.0kcal/mol.This material can be further applied to the design of other heteroatom-doped porous carbon coated metal materials and further effective organic pollution remediation.