A Fenton-like System Based On Green Iron Nanoparticles For The Removal Of Trimethoprim And Levofloxacin

Antibiotics are widely used in medicine,food,agriculture,animal husbandry and aquaculture.Due to the difficult degradation of antibiotics,the residual antibiotics in the environment are also increasing,endangering the natural ecological environment,but also posing a threat to human health.Advanced oxidation technology can effectively degrade organic matter,of which Fenton or Fenton-like method is the commonly used advanced oxidation technology,in this paper,using grape seed as the raw material synthesis of nano-iron（iron/cerium）as the catalyst of heterogeneous Fenton method degradation of antibiotics in water.Compared with traditional Fenton method,this method has the advantages of wide application range of pH and less amount of iron sludge.Two typical antibiotics trimethoprim（TMP）and levofloxacin（LVFX）were selected in this study.TMP is a common sulfonamide synergist,while LVFX is a third-generation fluoroquinolone antibiotic.The results are as follows:Based on the synthesis of nano-iron（Fe-NPs）from grape seeds,the nano-iron/cerium（Fe/Ce-NPs）was synthesized by the introduction of rare earth metal cerium modification.Considering the efficiency and economy,the optimal ratio of Fe/Ce-NPs was chosen as4:1.The samples before and after the Fe/Ce-NPs reaction were characterized by scanning electron microscopy（SEM）,Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）.SEM results show that the particle size of Fe/Ce-NPs before the reaction is 60～200 nm,some of the particles are bonded to form a block,but the whole is a porous structure,after the reaction occurred obvious agglomeration.FTIR,XRD and XPS show that there are zero valent iron and iron oxides in Fe/Ce-NPs,while the cerium element exists in the form of oxides Ce₂O₃ and Ce O₂.The organic matter covered on the surface of Fe/Ce-NPs particles can play a dispersing and stabilizing role.Compared with Fe/Ce-NPs and Fe/Ce-NPs combined with H₂O₂ to remove TMP from water,the results show that Fe/Ce-NPs is more efficient.The effects of reaction temperature,H₂O₂ concentration,Fe/Ce-NPs dosage,TMP initial concentration and solution initial pH on the removal were also investigated.Under the conditions of TMP concentration 30 mg/L,Fe/Ce-NPs/H₂O₂ dosage 0.27 g/L,H₂O₂ concentration 0.6 mol/L,35℃and pH 4.0 for 50 min,the removal rate of TMP can reach 100%.Both pseudo-first-order（0.9521～0.9800）and pseudo-second-order kinetic models（0.9856～0.9980）can effectively fit the degradation process of TMP by Fenton-like method,but the pseudo-second-order fitting effect is better,which indicates that the reaction process is mainly chemical reaction,and the apparent activation energy Ea is 70.54 k J/mol.This indicates that the reaction is surface-controlled.Fe/Ce-NPs/H₂O₂ catalytic removal of TMP,the main oxidation effect is·OH.Two catalytic reduction systems(Fe²⁺（?）Fe³⁺and Ce³⁺（?）Ce⁴⁺)were simultaneously catalytic decomposition of H₂O₂ to produce·OH.At the same time,Ce⁴⁺directly or indirectly promotes the conversion between Fe²⁺/Fe³⁺,promotes the release of·OH,and improves the catalytic performance of green synthesis of Fe-NPs.In order to further understand the effect of the introduction of Ce on the appearance,structure,characteristics and chemical application of the original green synthesis Fe-NPs,the green synthesis of nano-Fe and Fe-Ce bimetallic Fenton-like method to remove LVFX from water was studied.The green synthesis Fe-NPs and Fe/Ce-NPs before and after the reaction were characterized by SEM,FTIR,XRD and XPS.SEM comparison showed that the green Fe/Ce-NPs particles were larger than those of Fe-NPs particles before the reaction,but they all bonded into blocks due to magnetic force.However,Fe/Ce-NPs showed a porous structure,indicating that the addition of cerium improved the structure of the catalyst,and both of them agglomerated after the reaction.The comparison of FTIR,XRD and XPS shows that the green synthesis of Fe-NPs contains protective organic matter,zero-valent iron and its oxides,and in addition to the above substances,there are Ce₂O₃ and Ce O₂ in Fe/Ce-NPs.After the Fenton-like reaction,the valence state of Fe in Fe-NPs is transformed,while the valence state of Fe and Ce in Fe/Ce-NPs is transformed.The initial pH of solution,catalyst dosage,H₂O₂ concentration,LVFX concentration and reaction temperature were investigated.The results showed that LVFX removal rate was above 80%in the range of pH 3.0～11.0 and pH 3.0～9.0 for green Fe/Ce-NPs Fenton-like and Fe-NPs Fenton-like,respectively.Under the conditions of LVFX initial concentration of 30 mg/L,pH 5.5,30℃,1.0 mol/L H₂O₂ and dosage of 0.27 g/L catalyst,the time required for complete removal of LVFX in Fe-NPs/H₂O₂ system is 60 min.However,Fe/Ce-NPs/H₂O₂system needed 40 min,which significantly shortened the reaction time.The pseudo-first-order and pseudo-second-order kinetic models can well fit the removal processes of LVFX by the two kinds of Fenton-like systems,indicating that both reaction processes include chemical oxidation and adsorption,and both of them are mainly chemical reactions.The activation energies of green synthesis Fe-NPs and Fe/Ce-NPs for LVFX degradation were 53.65 k J/mol and 35.31 k J/mol,respectively.Fe-NPs/H₂O₂ and Fe/Ce-NPs/H₂O₂ Fenton-like systems were applied to the removal experiments of LVFX in real water samples.Under the conditions of LVFX initial concentration of 30 mg/L,pH 5.5,35℃,1.0 mol/L H₂O₂ and 0.27 g/L Fe-NPs dosage,the removal rate of LVFX reached98.39%（96.22%in deionized water）after reaction for 30 min.Under the same conditions,Fe/Ce-NPs/H₂O₂ method was used to completely remove LVFX from the actual water sample,and the time was shortened to 20 min.At the same time,the influence of three common anions,Cl^-,NO₃^-and HCO₃^-,on the removal of LVFX by Fe/Ce-NPs/H₂O₂ system was investigated.The results showed that low concentration of Cl^-and NO₃^-could accelerate the reaction,but high concentration of Cl^-and NO₃^-could inhibit the reaction,and both high and low concentration of HCO₃^-could inhibit the reaction.