Efficiency And Mechanism Of Primidone Degradation In Transitional Mn-FeOOH Catalytic Ozonation

The pollution of various Emerging Contaminants?ECs?in water has become increasingly serious.Among them,pharmaceuticals and personal care products?PPCPs?,as a kind of typical trace organic pollutants,have been frequently detected in the water body,which has received widespread attention.PPCPs have great harm to the ecological environment and the health of organisms,but the conventional water treatment process only achieves limited effect on the removal of PPCPs.Therefore,developing water treatment technology for PPCPs efficiently removal in water has become research hotspots in the field of drinking water treatment.In this study,cognate metal manganese was used to attack and disturb the original crystalline structure of FeOOH,resulting in Mn-FeOOH catalysts with transitional structure.The effect of preparation parameters on catalytic activity was evaluated comprehensively,and the optimum catalyst preparation conditions were obtained,which were Mn/Fe ratio=0.13,aging pH=12,activation time=48 h,activation temperature=60?.The crystal structure and surface properties of Mn-FeOOH catalysts with different Mn/Fe ratios were further characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscope?TEM?,Fourier transform infrared spectroscopy?FT-IR?,BET specific surface analysis and X-ray photoelectron spectroscopy?XPS?.The results indicated the successful intrusion of manganese into the crystal lattices of FeOOH and the change of bonding states of Fe-O and O-H during the formation of catalysts.With the Mn/Fe ratios increased,part of the crystal lattices of FeOOH were distorted,inducing the main phase of catalyst transforming from?-FeOOH to MnFe₂O₄.The morphology of FeOOH particles also changed evidently due to the intrusion of manganese,resulting the Mn-FeOOH particles in rod-like or needle-like shape.The average length of the particles increased first and then decreased with the increase of Mn content,which was related to the change in the structure of catalyst.Incorporation of Mn also improved the surface hydroxyl density and decreased the point of zero charge of the catalysts.MnFe13 with optimum catalytic activity were applied in catalytic ozonation to degrade trace organic pollutants,and results showed that nitrobenzene,primidone and Dissolved Organic Matters?DOMs?could be degraded efficiently.Besides,MnFe13 exhibited strong reusability,less ions leaching and stable structure.Under different initial conditions,the results showed that with the increase of the initial concentration of primidone,the catalytic efficiency increased first and then decreased.When the concentration of primidone was 500?g·L^-1,a full degradation could be achieved.The degradation rate of primidone increased with the increase of ozone concentration and catalyst dosage.The degradation of primidone was obviously affected by different water quality,and inhibited by Ca²⁺,Mg²⁺,SO₄^2-and especially HCO₃^-.The initial solution pH also had a significant effect on the primidone degradation.The primidone degradation efficiency was low when the solution pH was far away from the point of zero charge of MnFe13,and the best degradation effect was achieved when the solution pH was close to the point of zero charge of MnFe13.The enhanced mechanism of primidone degradation in MnFe13 catalytic ozonation was studied.Tert-butanol was used in hydroxyl radical scavenging experiment,and the results indicated that MnFe13 catalytic ozonation followed the hydroxyl radical reaction.It was inferred that the redox electron pairs of Mn⁴⁺/Mn³⁺and Mn³⁺/Mn²⁺in MnFe13 catalytic ozonation accelerated the electron transfer between Fe,Mn and ozone molecules,promoting the rapid ozone decomposition into hydroxyl radicals.Combined with the characterization,Mn-FeOOH catalysts were transitional state crystal within a main phase transformation process,containing characteristic crystal structures of?-FeOOH,Fe?Mn?OOH and MnFe₂O₄.The experiments indicated that the ozone adsorption ability of catalysts could be improved by?-Fe?Mn?OOH phase,and MnFe₂O₄phase further enhanced the ozone decomposition compared with?-FeOOH phase.Finally,the efficiently synergy among the three structures favored the mass transfer and decomposition of ozone.MnFe13 might have the best ability to promote the adsorption and decomposition of ozone simultaneously on the catalyst surface,which enhanced the mass transfer of ozone to generate a large number of hydroxyl radicals,and improve the degradation efficiency of organic pollutants.