Degradation Of Methyl Orange In Wastewater By Fe-N Modified Biochar Activated By Persulfate

In recent years,advanced oxidation technology is a new kind of oxidation method to remove refractory organic pollutants.Due to its advantages of fast reaction speed,strong oxidation capacity,simple operation,wide pH range and no selectivity,it has attracted wide attention.Biochar is a stable carbon-rich byproduct of biomass pyrolysis under low oxygen and low temperature conditions.Many studies regulate the electronic structure of carbon materials by doping of heteroatoms（N,P,S,etc.）and transition metals（Co,Fe,etc.）,thus enhancing the catalytic capacity of carbon catalysts,changing the charge distribution and destroying the inert carbon layer Fe-N codoped carbon materials（Fe-N-C）.Its unique structure and significant application prospect in heterogeneous catalysis.More and more attention has been paid to advanced oxidation reactions.In this paper,Fe-N-C biochar（Fe-N-C）was prepared by direct and simple carbonation-pyrolysis process using corn straw as carbon source.The prepared carbon materials were characterized by SEM,FTIR,XRD and BET,and the influence of doping on catalyst was obtained.This study investigated the degradation effect of Fe-N-C activated PS on methyl orange（MO）under different reaction conditions,obtained the optimal reaction parameters,and the influence of each parameter on the efficiency of the degradation system.Based on the data analysis,the following conclusions are drawn:（1）Besides the porous structure of biomass carbon materials,wormlike nanotubes and a large number of fine particles are also observed on the surface of Fe-N-C,which is mainly due to the synergistic effect of Fe and N in the process of high temperature calcination;（2）The main characteristic peaks of Fe-N-C were graphitic carbon（26.5°）,Fe（44.8°and 65.1°）,and Fe-N（43.8°）,indicating that the biochar was successfully loaded with Fe.（3）According to BET and FTIR analysis,it is concluded that C,Fe-C and Fe-N-C materials all contain a large number of microporous structures.The surface group carrying of Fe-N-C materials is similar to that of biomass C samples.Meanwhile,accumulations of double-bond or triple-bond carbon-oxygen groups are found on the surface of the materials.（4）The MO removal process of Fe-N-C co-doped biochar conforms to the second-order adsorption kinetic equation,and the adsorption process is mainly chemisorption.At the same time,the single-factor experiment shows that Fe-N-C/PS system can degrade MO to about 90%in 120 minutes.The degradation rate of MO increases with the increase of catalyst content in the range of 100-400 mg/L.When the catalyst changes from 400mg/L to 500mg/L,the degradation effect of PS system becomes worse.The pH value was highly correlated with the degradation effect of methyl orange.The higher the pH（alkaline system）,the lower the degradation efficiency of methyl orange,and the lower the pH（acidic system）,the lower the degradation efficiency of methyl orange.The addition of anions such as Cl^-,NO₃^-and HCO₃^-inhibited the activation of PS,while SO₄^2-had little effect on PS/MO system.HA had antagonistic effect on the degradation of methyl orange by PS,and the degradation rate of MO decreased with the increase of HA concentration.The mechanism of PS activation by Fe-N co-doped biochar was investigated by EPR,free radical quenching experiment and circulation experiment.According to the experimental results,·OH and SO₄·^-participate in MO removal reaction to a large extent,and·OH is the main reactive oxygen species in MO removal reaction.Therefore,it can be inferred that SO₄·^-,·OH generates OH in the reaction system.Repeated experiments show that Fe-N-C has strong reusability and stability.