Preparation Of Biochar Supported Fe₃O₄ Materials And Its Performance In Activation Of Persulfate Todegrade Ametryn

Ametryn（AMT,ametryn）is a typical triazine herbicide,which strongly inhibits the growth of broad-leaved weeds.It is widely used in the production of sugarcane,wheat,citrus and other crops,leading to its frequent detection in the environment,which poses a huge potential threat to the ecological environment health.Sulfate radical based advanced oxidation technology（SR-AOPs）is considered to be a highly efficient technology for the degradation of organic pollutants.Activated persulfate（PS,persulfate）can produce strong oxidized sulfate radical(SO₄^·-)through different oxidation processes,and iron based materials are good activators to activate PS,which have the advantages of simple synthesis,environmental friendly and efficient activation.In this paper,Fe₃O₄was used as iron source to synthesize a green and economical Fe₃O₄-biochar composite material by loading it on natural fire biochar to overcome the agglomeration problem of pure Fe₃O₄in the process of use,which was used to activate PS to degrade AMT in water and porous media.The catalytic abilities of composite,effect of environmental factors on degradation kinetics were systematically investigated.The change of physical and chemical properties for synthesized composite after activation were identified and the underdying activation mechanism were explored.Furthermore,the degradation characteristics of AMT in porous media were studied by soil column experiments.Finally,the ecotoxicity changes of AMT before and after the oxidation process were examined by Chlorella toxicity experiment.The detailed results are as follows:Firstly,natural fire biochar(BC_FP11)was collected and artificial biochar(BC₃₀₀,BC₄₅₀,BC₆₀₀)at different pyrolysis temperatures were prepared.Then biochar supported Fe₃O₄material（Fe₃O₄-BC_X）was synthesized by co-precipitation method.The morphology and structural composition of Fe₃O₄-BC_FP11were characterized by SEM,TEM,XRD,FTIR,XPS and VSM.The results showed that Fe₃O₄and BC_FP11combined successfully and the addition of BC_FP11reduced the agglomeration behavior of Fe₃O₄with no influence on the crystal phase structure of Fe₃O₄.The composite mainly contained three elements,C,O and Fe and was rich in surface functional groups of C=O、C=C、C-OH、COOH.It has a large specific surface area and a strong superparamagnetism.Then,the activation performances of the synthesized composite in water and porous media were further investigated.It was found that the adsorption abilities of the biochars towards AMT were less than 10%,and all of them have capacities to activate PS to degrade AMT.The activation efficiency of Fe₃O₄-BC_FP11towards PS to degrade AMT was between Fe₃O₄-BC₄₅₀and Fe₃O₄-BC₆₀₀and 90%AMT was degraded within 120 min.The removal rate of AMT increased in a certain range with the increase of catalyst dosage and PS concentration.The acidic conditions were favorable for the degradation of AMT,while the oxidation removal rate of AMT slowed down under neutral and alkaline conditions.The presence of chloride ion and fulvic acid greatly inhibited the degradation of AMT.Soil experiments showed that the removal of AMT by Fe₃O₄-BC_FP11/PS was related to soil types.With the low organic matter contents and high Fe and Mn contents,The removal rate of AMT can reached 85%.The results of soil column experiments showed that the fluidity of AMT in porous medium quartz sand column was strong,and the breakthrough rate is high.The addition of composite is helpful for the retention of AMT in the column,and it can activate PS to degrade AMT in the column.Finally,the reusability of the materials was compared,and the catalytic activity of the materials was still very strong after three cycles.The XPS characterization of the recycled materials showed that the content of Fe（II）decreased with the increased number of cycles,while the content of Fe（III）was the opposite,indicating that electron transfer occurred in the system,which accelerated the transformation of Fe（II）to Fe（III）and promoted the generation of free radicals.The active species were identified by quenching experiments and EPR detection.The results showed that SO₄^·-,·OH,¹O₂were all produced in the oxidation system,and SO₄^·-was the dominant free radical.The degradation products were analyzed by high performance liquid mass spectrometry.Six products were foundand and three possible degradation pathways of AMT were speculated.The main reactions are methylthio oxidation,side chain dealkylation,side chain oxidation and methylthio substitution.The toxicity test of chlorella pyrenoidosa showed that the toxicity of AMT basically disappeared after degradation,and it had no effect on the growth of Chlorella.