Mechanism Of Enhanced Organic Removal Of Activated Persulfate By Visible Light Induced Ferric Reduction

The efficient removal of refractory organic pollutants is the key to the resource utilization of sewage.In recent years,Fenton-like system composed of transition metal ions Fe²⁺and PMS/PS has become a research hotspot because of its easy implementation,low cost,green and non-toxic characteristics.However,due to the rapid accumulation of Fe³⁺,Fe²⁺-PS Fenton technology faces problems such as low treatment efficiency and poor continuous oxidation performance.Based on this,this paper introduces unmodified original commercial Ti O₂ and visible light into Fe³⁺-PS system,constructs a visible light promoted heterogeneous Fenton-like system with stronger oxidation ability and sustainable degradation of organic compounds,and combines ligand metal charge transfer（LMCT）process with Fenton-like system,in order to provide new ideas for the development of advanced oxidation technology.The main research results of this paper are as follows:（1）The visible light promoted heterogeneous Fenton-like system was constructed,and the treatment performance of the system for bisphenol A（BPA）was studied combined with reaction kinetics.The results showed that BPA-Ti O₂-Fe³⁺-PS-Vis system had the best degradation effect.After 60 minutes of reaction,the degradation efficiency,reaction rate constant and mineralization of BPA were 93.1%,0.0035mmol·（L·min）^-1 and 70%respectively.At the same concentration and dosage of iron salt,its degradation effect was far better than that of traditional Fenton system.At the same time,this system could expand the application range of p H to neutral and weak alkaline.（2）The effects of key parameters including Ti O₂ dosage,Fe³⁺dosage,PS dosage,initial p H,common inorganic anions and light conditions on the treatment effect of the system were investigated.The practical application prospect of the system was analyzed in combination with the types of organic matter,the influence of background water quality and the stability of catalyst circulation.The results showed that the degradation effect of BPA could be improved by increasing the dosage of Ti O₂,Fe³⁺and PS and the light intensity in a certain range;Acidic and neutral conditions were more conducive to BPA removal,and strong alkalinity would inhibit the reaction;The system was more suitable for industrial wastewater with higher organic concentration.（3）By means of UV-Vis diffuse reflectance spectroscopy,steady-state fluorescence spectroscopy,EPR and chemical quenching,the mechanism of visible light promoting the removal of organic matter by heterogeneous Fenton-like system was explored.The results show that BPA is the electron donor of the system,and high concentration of BPA is more conducive to the reaction;Fe²⁺is generated by Fe³⁺capturing the photoelectron reduction generated by the LMCT process between BPA and Ti O₂,and the steady-state concentration of Fe²⁺ion can reach 2.7μmol·L^-1 after 60min of reaction;The generated Fe²⁺continuously activates S₂O₈^2-to produce SO₄^-·and·OH,and realizes the continuous cycle of Fe³⁺/Fe²⁺,in which·OH is the main active substance,accounting for 58.4%-66.7%.（4）The visible light promoted heterogeneous Fenton-like system was applied to the raffinate of typical production wastewater in cobalt hydrometallurgy industry.The result shows that the system can reduce the COD of raffinate about 1100-1300 mg·L^-1.The COD can still be reduced about 600 mg·L^-1 in four-round cycle experiment.At the same time,the three-dimensional fluorescence and UV₂₅₄ were greatly reduced.The molecular weight distribution before and after the reaction shows that the system preferentially reacts with macromolecules,and the overall molecular weight is transformed to small molecules.