Preparation Of Single-atom Iron-based Catalysts And Its Performance Of Persulfate Activation And Carbamazepine Degradation

Confronted with global water pollution caused by emerging contaminants in the aquatic environment,developing and applying advanced water treatment technologies are vital to clear this issue up.Among the existing technologies,the heterogeneous Fenton-like process based on persulfate（PMS）has earned growing attention due to the situ generation of reactive oxygen species with high oxidation potential,which is regarded as a promising candidate for the degradation of emerging pollutants.However,the unsatisfactory kinetics of PMS activation leads to excessive dosage of chemical oxidant and/or energy input,which hinders its practical application in actual wastewater treatment.Therefore,the development of heterogeneous catalysts with atomically dispersed active sites is essential to promote Fenton-like reaction activity,but how to precisely control the coordination configuration of active sites to further accelerate the PMS activation kinetics remains a challenge.The project of this study is to construct a visible-light assisted PMS activation system by single-atom/diatomic Fe-doped g-C₃N₄（Fe₁CN and Fe₂CN）and heterogeneous Fenton-like systems based on Fe-based single-atom catalyst（Fe-NC）with nitrogen-doped carbon support and sulfur-modified Fe-based single-atom catalyst（Fe-N/SC）activation of PMS.The main conclusions are as follows:（1）The single-atom/diatomic Fe sites were anchored on g-C₃N₄support by supramolecular assembly strategy for visible-light-assisted heterogeneous PMS activation and CBZ degradation.Firstly,the geometric and electronic structure of different metal coordination configurations were investigated and analyzed by first-principles calculations.Results demonstrated that the novel Fe₂N₆coordination configuration can enhance the electron delocalization on the catalyst surface and raise the d-band center level of the Fe center（-4.45→-2.54 e V）.Thus,the diatomic Fe sites exhibited significantly accelerated PMS activation kinetics under visible light irradiation with a CBZ degradation rate constant was 0.11 min^-1,which was 3.6 and 37.0 times that of the Fe₁CN catalyst and g-C₃N₄,respectively.Then,the quenching experiment,electron paramagnetic resonance spectra and competitive kinetics results revealed that the different PMS activation pathways dominated for the Fe₁CN catalyst（non-radical pathway,¹O₂）and Fe₂CN catalyst(radical pathway,SO₄^·-),respectively.Notably,the presence of visible light facilitated the Fe（II/III）redox cycle and active site regeneration through photogenerated electrons rather than inducing the formation of new reactive oxygen species.Finally,density functional theory simulation demonstrated that the coupling of Fe-3d orbitals significantly reduced the contribution of the antibonding state in the Fe-O bond and accelerates the O-O bond cleavage of PMS*intermediate with a decreased thermodynamic energy barrier of only-0.29 e V.（2）By applying a simple precursor modulation strategy,we successfully obtain single iron atom catalysts embedded in nitrogen-doped carbon support（Fe-NC）with indirectly coordinated S（Fe-N/SC）.CBZ was selected as the target pollutant,Fe-N/SC system showed excellent degradation efficiency and oxidizer utilization rate（～100%）,which exhibited 29.7 times higher activity than Fe-NC and was superior to most of the state-of-the-art Fe-based catalysts.According to the chemical probe method and PMSO conversion experiment,the Fe-N/SC catalyst can be selectively converted to Fe（IV）=O species by PMS,which had excellent resistance to inorganic anions and natural organic matter in the actual aqueous matrix.Furthermore,we found that the high PMS utilization rate and the Fenton-like reaction kinetics of Fe-N/SC were derived from the Fe（IV）=O induced oxidation mechanism:the Fe^IIsites transferred electrons to PMS molecules and produced Fe（IV）=O via the oxygen transfer process and then Fe（IV）=O was reduced back to Fe ^IIby CBZ.Both experimental and computational results demonstrated that the long-range interaction of heterogeneous S atom as electron donor to the Fe center,resulting in the upshift of the d-band center level（-0.32 e V）and the intermediate spin state(t_2g4e_g1)of Fe sites,thereby exhibiting moderate adsorption energy（-1.91 e V）and binding strength for PMS,which was beneficial to the subsequent O-O bond cleavage process.Moreover,the single e_gelectron in the Fe-N/SC can penetrate theπ*orbital of the O atom and form Fe（IV）=O species.