Study On Efficacy And Mechanism Of Heterogeneous Fenton Reaction Of Fe/TiO₂ To Photo-Catalytic Degradation Of Atrazine Under Visible Irradiation

Atrazine has been the most widely used and most consumed triazine herbicide in the world for the past few decades.Due to its high chemical stability and difficult biodegradability,it is prone to cause persistent pollution to the environment,atrazine has certain biological toxicity and is recognized as endocrine disruptors?ECDs?and potential carcinogens.At present,the detection of atrazine residues in many countries and regions and has begun to threaten the health of organisms and humans.The traditional water treatment process is basically incapable of removing atrazine,and the technologies currently used to remove atrazine pollution mainly include Fenton technology and photocatalysis technology.The traditional Fenton technology has the problems of high cost and easy to cause secondary pollution.However,most of the heterogeneous Fenton catalysts studied have problems of low catalytic activity and poor cycleability,and the photocatalysis of TiO₂ is mostly limited to ultraviolet radiation.Therefore,this paper prepares a heterogeneous Fenton catalyst with low cost,high catalytic activity,good cycle performance and visible irradiation response,which solves the shortcomings of the existing heterogeneous Fenton catalyst.Provides an emergency means for controlling water pollution of EDCs such as atrazine and other sudden environmental pollution events.In this paper,a heterogeneous Fenton catalyst Fe/TiO₂ was prepared by a simple method using TiO₂ as a support.The effects of preparation conditions on the activity of the catalyst were studied and characterized by SEM,EDX,XRD,UV-vis and other instruments.The influencing factors of Fe/TiO₂ heterogeneous Fenton catalytic degradation of atrazine under visible irradiation were studied,and established an apparent kinetic model.The degradation process of atrazine was analyzed,and the intermediate product was detected by LC-MS and the possible degradation pathways were inferred.Finally,the reaction mechanism of Fe/TiO₂–H₂O₂ visible irradiation system was discussed.The main conclusions of this paper are as follows:?1?The heterogeneous Fenton catalyst Fe/TiO₂ prepared by the impregnation-evaporation-calcination method,the catalytic activity of Fe/TiO₂ in the Fenton reaction system under visible irradiation is significantly higher than that of TiO₂ and Fe₂O₃.The optimum preparation conditions of Fe/TiO₂ are:n(Fe³⁺):n?TiO₂?=1:100,calcination temperature 200°C,calcination time 2 h.The Fe element of the catalyst Fe/TiO₂ is highly dispersed in the form of?-Fe₂O₃ on the surface of TiO₂,which broadens the photoresponse range of TiO₂.?2?The optimum conditions for the degradation of atrazine by Fe/TiO₂ heterogeneous Fenton reaction under visible irradiation are:initial pH=3.00,H₂O₂ concentration of 1.6mmol/L,and catalyst dosage of 1.0 g/L.After 30 min of reaction time,the degradation rate of10 mg/L atrazine was 95.41%.The cycle performance is good,the degradation rate of atrazine is maintained at more than 90%after 5 cycles of use.?3?The degradation process of atrazine conforms to quasi-first-order reaction kinetics,and the apparent kinetic equation of heterogeneous Fenton reaction of Fe/TiO₂ to photo-catalytic degradation of atrazine under visible irradiation are:ln?C₀/C_t?=0.93C^-0.69948P^-0.76392H^0.5124D^0.70973t?0.4?H?1.6?,ln?C₀/C_t?=1.37C^-0.69948P^-0.76392H^-0.31483D^0.70973t?1.6?H?6.4?.?4?The main active species in the Fe/TiO₂–H₂O₂ heterogeneous Fenton under visible irradiation system was determined to be·OH by experiments on the degradation of atrazine by active species capture agents,and the·OH concentration increases as the reaction time increases;Cl^-and NO₃^-have a certain promoting effect on the degradation of atrazine;HCO₃^-,H₂PO₄^-,CO₃^2-and PO₄^2-have significant inhibitory effects on the degradation of atrazine;SO₄^2-has little effect on the degradation of atrazine.When treating actual wastewater,it needs to be masked when it contains high concentrations of HCO₃^-,H₂PO₄^-,CO₃^2-and PO₄^2-.?5?A series of intermediates were produced in the process of degradation of atrazine by Fe/TiO₂–H₂O₂ heterogeneous Fenton under visible irradiation system.There were 12 kinds of intermediate products analyzed by LC-MS,and three possible degradation pathways were inferred.Finally,they all degrade to cyanuric acid,and further mineralize into inorganic substances such as CO₂,H₂O,NO₃^-.?6?The reaction mechanism of Fe/TiO₂–H₂O₂ heterogeneous Fenton under visible irradiation system is:when visible light is irradiated onto the surface of Fe/TiO₂ valence band electrons?e^-?are excited to the forbidden band,and leaving holes?h⁺?in the TiO₂ conduction band.The excited electrons in the forbidden band are transferred to Fe₂O₃,which reduces Fe³⁺to Fe²⁺,than Fe²⁺react with H₂O₂ adsorbed on the surface of Fe/TiO₂ to produce·OH by heterogeneous Fenton reaction.The holes?h⁺?generated by the Fe/TiO₂ valence band react with H₂O₂ and H₂O in the system to produce·OH.