Effect Of Oxalate On The Catalystic Properties And Enhancement Mechanism Of Heterogeneous UV-Fenton System With ?-feOOH As Catalyst

Nowadays heterogeneous UV-Fenton process is one of the most promising technologies.However,its low catalytic efficiency limits its further application.It is of great significance to develop suitable catalyst and synergistic method to promote its application.Due to its excellent photocatalytic performance,low sensitivity to the pH value of the reaction system and its high catalytic activity for hydrogen peroxide,?-FeOOH is a widely studied photocatalytic material.In this paper,?-FeOOH was prepared by a symmetrical precipitation method and characterized by XRD,FT-IR,SEM,BET,XPS and EDS techniques.The catalytic activity of?-Fe OOH during the degradation of Orange?by the heterogeneous UV-Fenton process was evaluated.The effects of five different organic carboxylates on its catalytic ability were compared,and the enhanced mechanism of additional oxalate was discussed in detail.What is more,the limits conditions and catalytic stability of UV-Fenton system with oxalate are also discussed.The main original conclusions of the paper are drawns following parts.1.The effects of five different organic carboxylates on its catalytic ability were compared.It was found that the rate of Orange?degradation in this heterogeneous UV-Fenton system could increase significantly with oxalate as an enhancing reagent,with the peak values of enhanced efficiency reaching 116.9%when the concentration of additional oxalate was 0.4 mmol/L.Low concentration of EDTA?0.1 mmol/L?has a certain degree of enhancement on the catalytic activity.Acetate,malonate and citrate have some inhibition on the decolorization of Orange?by?-FeOOH.2.The enhanced mechanism of UV-Fenton system with oxalate:Additional oxalate could increase the concentration of iron ions leaching from the catalyst.Then the ratio of homogeneous UV-Fenton reaction in this system would be increased.On the other hand,the additional oxalate could provide a new photo-reduction pathway for Fe³⁺to Fe²⁺,enhancing the ratio of the homogeneous UV-Fenton process by increasing the Fe leaching of?-FeOOH and the concentration of hydroxyl radicals,leading to higher degradation efficiency of Orange?.However,when the concentration of oxalate is too high,the side reactions involving hydroxyl radicals will lead to a decrease on the degradation efficiency of the system.The optimal concentration of oxalate is 0.4 mmol/L3.Proposed pathways for degradation of Orange II:In the UV-Fenton system with?-FeOOH as catalyst,the degradation of Orange?began with cleavage of C-N bound,and p-Azobenzenesulfonate and 1,2-Di-Naphthoquinone were generated.With the oxidation of hydroxyl radicals,denitrogenation and desulfated group were gradually happened.After then,the naphthalene ring and benzene ring gradually opened,and finally mineralized to CO₂ and H₂O.