Catalytic Degradation Of Organic Pollutants By Iron Phosphides And Its Carbon Spheres Complexes

In the process of industrial wastewater discharge,a wide variety of organic pollutants with high environmental risk will be produced,such as antibiotics,phenolic protoplasmic poisons and conjugated dyes,which seriously threaten biological health and water circulation system.Advanced oxidation technology based on peroxymonosulfate（PMS）has attracted much attention in wastewater treatment field due to its strong oxidation.Activating PMS to produce reactive oxygen species is the key to treat organic wastewater.It is worth noting that iron-activated PMS technology has been regarded as an ideal choice for the degradation of organic pollutants due to its mild reaction conditions,low cost and environmental protection,but there were still defects such as low catalytic efficiency and difficulty in recycling.Therefore,it was of great significance to develop efficient and reusable Fe-based catalytic materials.Fe-based transition metal phosphates（Fe-TMPs）had excellent catalytic activity and high electrical conductivity because the vacant 3d orbital and 3p lone pair electrons in the P atoms could regulate the surface charge states of Fe atoms.Therefore,Fe-TMPs was expected to be a promising catalytic material.In this paper,two kinds of Fe-TMPs catalysts were prepared by modification and loading of Fe-TMPs respectively,and their catalytic effects on the removal of sulfadiazine（SDZ）by activating PMS were evaluated.The main research contents were as follows:Magnetic spherical coral iron phosphate（Fe_xP）catalysts were prepared by low temperature phosphating synthesis strategy,characterized by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and scanning electron microscopy（SEM）.PMS as oxidant,sulfadiazine（SDZ）as target pollutant were selected to estimate the catalytic performance and reusability of Fe_xP.The experimental results demonstrated that the Fe_xP/PMS system could exhibit excellent catalytic oxidation performance for removing 98.2%SDZ within 24 min.Fe_xP could still remove 89.0%SDZ after being magnetically separated and reused 4 times,indicating that Fe_xP had good repeatability.In addition,Fe_xP/PMS system also had good catalytic performance on other sulfonamides antibiotics including sulfamethoxazole（MSDX）,sulfamethylthiazole（STZ）,sulfamethoxazole（SMD）and sulfamethoxazole（SMX）.When the concentration of Cl^-and SO₄^2-were less than 1 mmol/L,there was little effect on the SDZ removal,and the reaction was inhibited when the concentration increased.NO₃^-,H₂PO₄^-,CO₃^2-and HCO₃^-had obvious inhibitory effect on catalytic system.The reaction mechanism was investigated by using free radical trapping agents such as methanol（MA）,terzhuanyuedet-butanol（TBA）and L-histidine combined with Electron paramagnetic resonance（EPR）technology.The results indicated that the various reactive oxygen species including hydroxyl（·OH）,sulfate(SO₄^·-),singlet oxygen（¹O₂）,superoxide(O₂^·-)radicals involved in the Fe_xP/PMS system.In order to further improve the catalytic activity and reusability of Fe-TMPs.In situ phosphating was realized while the catalyst was loaded,nitrogen,phosphorus and iron doped resin carbon spheres（N,P,Fe-RC）catalysts with macromorphology were prepared by high temperature calcination using phosphorus-rich macroporous amino phosphoric acid chelating resin as support.N,P,Fe-RC could activate PMS to remove98.4%phenol within 12 min,and the removal rate of the phenol could reach over 91.5%after 11 cycles,indicating that N,P,Fe-RC possessed excellent reusability.Furthermore,multiple pollutants including nitrophenol（P-NP）,bisphenol A（BPA）and tetrachlorophenol（4-CP）also could be effectively removed in N,P,Fe-RC/PMS system.SO₄^2-and NO₃^-had little effect on the N,P,Fe-RC/PMS system,while Cl^-,H₂PO₄^-,CO₃^2-and HCO₃^-had inhibitory effect on the N,P,Fe-RC/PMS system.The reaction mechanism of N,P,Fe-RC activation of PMS was investigated by using free radical trapping agents such as MA,TBA and L-histidine combined with EPR.The results indicated that·OH,SO₄^·-and ¹O₂ active oxygen species were generated in the N,P,Fe-RC/PMS system.