Enhanced Phenol Degradation In Iron-based Heterogeneous Fenton Systems

Traditional Fenton process,one of the advanced oxidation process?AOPs?,is widely used in wastewater treatment due to its ability to produce·OH with strong oxidation capacity and non-selective toward organic pollutants.However,its practical application is limited because of the strict reaction pH,slow Fe²⁺/Fe³⁺cycle and the formation of a large amount of iron sludge.These shortcomings could be overcomed by the development of heterogeneous Fenton process,but most heterogeneous Fenton process exhibited much lower activity than homogeneous counterparts,so it is of great significance to develop lowcost and high efficient heterogeneous Fenton process.In this paper,the degradation of phenol by two iron-based heterogeneous Fenton systems and their underlying mechanisms were investigated.?1?Using mechanochemically sulfidated zero valent iron and hydrogen peroxide to construct the heterogeneous Fenton system.The results showed that S-mZVI^bm could rapidly activate H₂O₂ to degrade various organic pollutants?including phenol,chlorophenol,nitrobenzene,bisphenol A,tetracycline,etc.?.The specific surface area normalized phenol degradation rate constant of the S-mZVI^bm/H₂O₂ system was more than 5 times larger than that of the mZVI^bm/H₂O₂ system,and S-mZVI^bm/H₂O₂ system has no initial inhibition stage in phenol degradation process,confirming that the efficiency of S-mZVI^bm was higher.The results of quenching experiment and electron paramagnetic resonance test?EPR?suggested that the active species of S-mZVI^bm/H₂O₂ system was·OH.The scanning electron microscope?SEM?and X-ray diffraction?XRD?characterization combined with electrochemical test results of S-mZVI^bm before and after reaction showed that S-mZVI^bm had a faster electron transfer rate than mZVI^bm.In the reaction process,FeS basically had no consumption,but acted as an electronic conductor to accelerate the electron emission of Fe⁰ and promoted the release of Fe²⁺and the reduction of Fe³⁺,thus promoting the degradation of pollutants.?2?Using goethite??-FeOOH?,thioglycollic acid?TGA?and hydrogen peroxide to construct the heterogeneous Fenton system.The results showed that TGA had a stronger promoting effect on the degradation of phenol in?-FeOOH/H₂O₂ system than hydroxylamine?HA?and ascorbic acid?AA?.The phenol degradation rate constant of?-FeOOH/TGA/H₂O₂,?-FeOOH/HA/H₂O₂ and?-FeOOH/AA/H₂O₂ system was more than 890,67 and 44times larger than that of the?-FeOOH/H₂O₂ system.The results of quenching experiment and electron paramagnetic resonance test?EPR?suggested that the active species of?-FeOOH/TGA/H₂O₂ system was·OH.In situ attenuation total reflection Fourier transform infrared spectroscopy?ATR-FTIR?and ion influence experiments showed the formation of inner-sphere complexes between?-FeOOH and TGA.The X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?characterization combined with homogeneous experimental results showed that TGA promotes the reduction and dissolution of iron on the surface of?-FeOOH,thereby facilitating the degradation of phenol.Gas chromatography-mass spectrometry?GC-MS?results that the main aromatic intermediate degraded by phenol in?-FeOOH/TGA/H₂O₂ system was hydroquinone,indicating that hydroxylation mainly occurred in the para-position rather than the ortho-position and the meta-position.This study provides a new strategy for the degradation of organic pollutants by iron-based heterogeneous Fenton method,and further explores the mechanism of activation of H₂O₂,so as to provide guidance for water treatment technology.