The Performance And Mechanism Of Efficient Iron-based Catalysts To Activate Persulfate To Degrade Emerging Pollotants

Emerging pollutants are frequently detected around the world,posing a serious threat to human health and environmental safety.Persulfate-based advanced oxidation technology has proven to be one of the most powerful technologies for the treatment of organic wastewater due to its strong oxidizing power,wide p H operating range,and mild operating conditions.Peroxodisulfate（PDS）is often used as an oxidant due to its low price and high oxidizing properties.Nontoxic,environmentally friendly,and low-cost iron-based catalysts display outstanding PDS activation performance.Among them,the iron-based heterogeneous catalyst can be recycled and reused,and has a wide range of applications.However,the catalytic performance is limited because of the limitation of the properties of iron-based heterogeneous catalysts and the low utilization rate of active materials.Therefore,designing new iron-based heterogeneous catalysts to improve catalytic performance is one of the key research contents of persulfate-based advanced oxidation technology.Precisely designing the optimal structural morphology and favorable active sites for the target reaction is the key to the preparation of efficient catalysts.The optimal material morphology can fully expose active sites,enhance mass transfer,and increase reactive contacts.Based on iron-based materials,a series of novel iron-based materials heterogeneous catalysts were developed through morphology optimization and structural control.The microscopic morphology and structural information of the materials were observed in detail using modern material characterization techniques,and the interaction mechanism between various catalysts and PDS was studied in depth with theoretical calculations.The specific research contents are as follows:1.Preparation of uniform three-dimensional flower ball-like Fe/NC materials with mesoporous structure for efficient activation of PDS.Dopamine hydrochloride was used as carbon and nitrogen sources to self-aggregate to form spherical structures in an alkaline environment with different concentrations of Fe sources,and three-dimensional flower ball-like Fe/NC was synthesized by pyrolysis in nitrogen atmosphere.The characterization results showed a three-dimensional flower ball-like microscopic morphology.When the dosage of iron salt was 100 mg,the catalyst showed the best ability to activate PDS to degrade chloramphenicol（CAP）.Under the reaction conditions of[CAP]=20 mg/L,[catalyst]=0.2 g/L,p H=6.2,and T=25℃,CAP could be completely removed within 30 min,and the removal rate of total organic carbon（TOC）was 83.9%.The removal rate constant（k）of Fe-1/NC activated PDS for CAP degradation reached 0.300 min^-1,which was 37.5 times that of NC(0.008 min^-1).After being recycled for 5 times,Fe/NC still maintains excellent stability,and Fe/NC shows excellent catalytic effect in actual pharmaceutical wastewater.Combined with quenching experiment,EPR test and M（?）ssbauer spectroscopic analysis,it was confirmed that Fe（Ⅳ）=O was the main reactive oxygen species（ROS）.According to the analysis and test results of the degradation intermediates,the possible degradation paths of CAP were proposed.2.The synergistic effect of the dual active sites enhances the catalytic activity of Fe-N-C.In the hydrothermal synthesis of zeolite imidazolate framework（ZIF-8）,Fe salts and Cu salts were confined within the cage structure of ZIF-8 molecules,and a Fe/Cu-NC dual active site catalyst was developed by pyrolysis.The characterization results showed that Fe and Cu exist in the form of Fe/Cu diatomic pairs in the Fe/Cu-N-C material.In the simulated wastewater degradation experiments with CAP as the target pollutant,the Fe/Cu-N-C@PDS system exhibited excellent catalytic performance in the p H range from 3.1 to 10.3.The Fe content of 99%was still preserved after 5cycles,indicating the excellent cycling stability of Fe/Cu-N-C.DFT calculations show that the adjacent Cu atoms effectively optimize the 3d orbital of the Fe center,which promotes the adsorption and cracking of PDS on the catalyst and thus effectively improves the oxidative decomposition of pollutants.In addition,the adjacent Cu atoms transfer electrons to Fe atoms along the Fe-Cu bond to keep them in a low valence state,thus ensuring the long-term catalytic activity of the catalyst.The results of quenching experiments and EPR analysis showed that hydroxyl radical（·OH）,sulfate(SO₄^·-)and singlet oxygen（¹O₂）species were the main ROS.3.The modulation of the electronic structure enhances the ability of Fe-NC to activate PDS for pollutant degradation.The Fe-BNC catalyst was prepared by anchoring single-atom Fe in B and N atoms co-doped C support（BNC）to achieve efficient activation of PDS to degrade bisphenol A（BPA）.The Fe-BNC@PDS system exhibits excellent degradation performance and high selectivity for BPA in a wide p H range（2.63-10.36）.Experiments and theoretical simulations show that the high activity of Fe-BNCs originates from a novel dual-pathway activation of PDS.PDS oxidation on electron-poor B atoms to form ¹O₂ and PDS reduction on electron-rich Fe atoms to generate OH and SO₄^·-,Among them,¹O₂ is the main active substance.Furthermore,the structural defects introduced by B atoms optimize the distribution of Fe 3d orbitals,while promoting the chemisorption and activation of PDS.We further loaded Fe-BNC on polyvinylidene fluoride（PVDF）microfiltration membrane for ultrafiltration system,and the simulated BPA wastewater containing PDS was stably removed when passing through the filter,which promoted the application of iron-based catalysts in practical wastewater purification.