Hierarchically Porous Carbon With Mixture Iron And Iron Oxide Nanoparticles Used For Efficient Electro-fenton

Wastewater containing phenols,herbicides,antibiotics,and landfill leachate has become a global problem,and the development of environmentally benign technologies is imperative to treat wastewater before they are discharged into natural water bodies.Electro-Fenton(E-Fenton)is an attractive method because of its plenty generation of hydroxyl radicals(·OH,E0(OH/H2O)=1.9-2.8 V/SHE),which is the second strongest oxidizer known after fluorine and can non-selectively oxidize almost all organic compounds.Although homogeneous E-Fenton has been extensively studied,its requirements for acidic conditions(optimum pH?3)and generation of abundant sludge limit its large-scale application.Heterogeneous E-Fenton can overcome these problems by immobilizing active Fe-containing solids on inert support matrix.However,these active Fe-containing solids were mainly loaded on the surface of the matrix,which results in the problems of iron species fall off,dissolution and agglomeration shorting their working time.Herein,a novel hierarchically porous carbon with mixture iron and iron oxide nanoparticles embedded was fabricated.The embedded structure efficiently enhances the interfacial contact area of iron species with carbon matrix and suppress the dissolution and agglomeration of iron species.The catalytic activity of the composite material and the reasonable mechanism in the E-Fenton process has been investigated.The results are as follows:(1)Hierarchically porous carbon with iron and iron oxide nanoparticles(AMIL)was fabricated from MIL-100(Fe)precursor and then carbonized with Ar.When AMIL was applied as the cathode of E-Fenton,81% PFOA(50 mg/L)elimination was achieved at a low potential of-0.4 V in neutral pH within 3 h.With the increasing of the carbonized temperature(600°C-800°C),the PFOA removal rate is decreasing from 82% to 45%.Basis on the characterization analyses,the ferrous nanopaticles in AMIL enlarged with the increasing of the carbonization temperature,which results in the decrease of the active sites and then the decay of the catalytic ability.(2)Novel hierarchically porous carbon with ultradispersed iron and iron oxide nanoparticles(CAMIL)was fabricated from MIL-100(Fe)precursor and then carbonized with CO2 and Ar in environmentally benign way.When CAMIL was applied in a heterogeneous E-Fenton system,99 % phenol(50 mg/L)elimination was achieved at a low potential of-0.6 V within 60 min,which is 1.3 times higher than that of AMIL.Only 12% phenol degradation rate decays after a wide pH value changing from 5 to 9,which is more stable than homogeneous E-Fenton system(40%-60% decay).The enhanced degradation performance of the CAMIL was mostly attributed to the accessible pore channel enhanced by CO2-Ar carbonization and the embedded nano-sized iron species re-dispersed by the secondary Ar carbonization.Moreover,the coexistence of Fe0 and Fe3O4 makes Fe0 as the medium to promote the electron transfer then accelerate the circle of FeII and FeIII.On the basis of experimental results,we proposed a possible pathway of phenol degradation in this heterogeneous CAMIL E-Fenton process.The high efficiency and the well-adaptation in various pH conditions confirm the potential of the composite material as a high-performance E-Fenton cathode in practical application.