Fabrication Of Iron-Based Montmorillonite Composites And Their Application In Catalytic Degradation Of Emerging Phenolic Pollutants

For decades,the presence of emerging phenolic pollutants in the environment poses serious threat to public health since most of them are toxic,endocrine disrupting and detrimental to humans’life even at very low concentrations.The treatment of emerging phenolic pollutants has attracted much attention.In recent years,advanced oxidation processes（AOPs）,in which powerful reactive oxygen species（ROS）such as sulfate radical(SO₄^·-),hydroxyl radical（^·OH）,superoxide radical（^·O₂^-）and singlet oxygen（¹O₂）will be generated,have emerged as a promising method for the degradation of emerging phenolic pollutants in water.Iron oxides can be used as good catalysts for peroxymonosulfate（PMS）activation.However,the disadvantages including serious aggregation phenomenon and the limited active sites hinder their wide application on the removal of emerging phenolic pollutants by AOPs.Clay minerals or modified clay minerals have drawn increasing attention as functional nanomaterials due to their particular advantages such as chemical and mechanical stability,large specific surface area and high cation exchange capacity.Based on the superior adsorption ability,good supporting material and template effect of montmorillonite,this study was aimed to prepare novel and efficient iron oxide/Graphene/Montmorillonite composite（?-Fe2O3-x/Graphene/Mt）,mineral-derived carbon materials and Fe⁰-Montmorillonite composite（Fe-Mt-C-H2）,which could be acted as catalyst to remove Bisphenol A（BPA）or Tetrabromobisphenol A（TBBPA）by AOPs.Moreover,this study explored the degradation mechanism of BPA or TBBPA attacked by different ROS.The main contents and results were as followed:（1）Iron-pillared montmorillonite/tetracycline complex（Fe OOH-Mt-TC）was converted into iron oxide/Graphene/Montmorillonite composite(α-Fe₂O_3-x/Graphene/Mt)through pyrolysis strategy under N₂ atmosphere,resulting in the decreased environmental risk of iron-pillared montmorillonite/tetracycline complex.During the pyrolysis process,Fe OOH and TC were converted into mixed-phaseα-Fe₂O_3-x and N-doped graphene-like carbon materials,respectively.Meanwhile,the conversion of Fe OOH significantly promoted the graphitization degree of N-doped graphene,and the carbonization of TC was also helpful to form mixed-phaseα-Fe₂O_3-x with high percent of Fe²⁺and abundant oxygen vacancies.The synergistic effect between Fe OOH and TC was beneficial to enhance the catalytic performance ofα-Fe₂O_3-x/Graphene/Mt with superior conductivity,high percent of Fe²⁺,and abundant oxygen vacancies.（2）Based on the above research foundation,this study further investigated the PMS activation ability ofα-Fe₂O_3-x/Graphene/Mt composite.The results indicatedα-Fe₂O_3-x/Graphene/Mt composite exhibited excellent catalytic performance toward PMS to rapidly eliminate TBBPA from water.The reasons were ascribed to:（a）The synergistic effect between iron oxides and graphene-like carbon materials made theα-Fe₂O_3-x@Graphene@Mt composite have superior conductivity,higher percent of structural Fe（II）and abundant oxygen vacancies,resulting in highly-efficient degradation of tetrabromobisphenol A（TBBPA）in the presence of PMS.Besides,^·OH,SO₄^·-,¹O₂ played a vital role in the TBBPA degradation process;（b）the released Br^-from TBBPA contributed to the oxidation degradation of TBBPA with the formation of halogen radicals.Alcohol radicals were generated with the addition of alcohol in PMS-based system and were beneficial to the reductive degradation of TBBPA.The formation of reactive halogen and alcohol radicals contributed to the rapid removal of TBBPA through simultaneous reduction-oxidation process.（3）With the template of mineral,organic compounds on the surface of minerals can be converted into carbon materials during pyrolysis process.The physicochemical properties of the obtained mineral-carbon composites,especially for the mineral-derived carbon materials,are highly dependent on the structure of minerals.This study investigated the effect of mineral structural on the formed carbon materials.The template of layer Mt was beneficial to overcome the aggregation of graphene-like carbon materials,enhance the graphitization degree,and improve the electrical conductivity.The phase conversion of Fe OOH could act as an inner template and activating porogen to generate hierarchical porous structure with high surface area and active sites.With the aid of double mineral-templates,the obtained carbon materials（NPC-Fe OOH/Mt）exhibited an ultra-thin carbon nanosheet structure with the doping of nitrogen,hierarchical pores,many defective sites,and excellent electrical conductivity.NPC-Fe OOH/Mt showed superior activation ability towards PMS for BPA degradation.Activation mechanism of NPC-Fe OOH/Mt towards PMS included free radical and non-radical pathways.（4）In view of the activity of Fe⁰ is inclined to reduce due to the happen of aggregation,Mt is chose as supporting material to overcome this problem.Novel Fe⁰-Montmorillonite composite（Fe-Mt-C-H₂）were successfully fabricated through a thermal reduction process in H₂ and N₂ mixed atmosphere.Benefitting from a higher degree of iron reduction,showed a better activation ability towards PMS for BPA degradation than Fe-Mt-Na BH4.For,the surface of Fe⁰ was converted into Fe₃O₄,which also exhibited good catalytic activity towards PMS.Besides,^·O₂^-and ¹O₂,instead of SO₄^·-and^·OH,were the major ROS insystem.The results of this study not only provided a novel strategy to prepare excellent iron-based catalysts for rapid removal of phenolic pollutants in AOPs,but also expanded the potential applications of mineral-based composite in environment remediation.