Degradation Of Rhodamine B By Electrochemical In-Situ Production Of Hydrogen Peroxide Coupled With Ultraviolet

Rhodamine B（RhB）is a nitrogen-containing heterocyclic dye widely used in leather,paper and textile industries.It is difficult to degrade in the natural environment and poses a threat to the aquatic environment,animal and human health.In order to determine a treatment method that can efficiently remove RhB,an electrochemically coupled ultraviolet reaction system was established in this paper.H₂O₂ was generated in situ through an electrochemical reactor,and coupled with ultraviolet to improve the ability of system to degrade RhB.Firstly,activated carbon（AC）was used to preliminarily determine the preparation conditions of the gas diffusion electrode in intermittent flow:the electrode thickness is0.6 mm,the tablet pressure is 18 MPa,and the calcination temperature is 360°C.The best materials for the electrode are determined to be CB and g-C₃N₄;The preparation method of the electrode was further optimized under flow conditions,and the best ratio of carbon material to polytetrafluoroethylene（PTFE）was determined to be 2:1,the best ratio of CB to g-C₃N₄ was 1:1.The electrode has a better stability.The electrodes prepared under the optimal conditions were characterized and analysised by SEM,XRD,XPS,and electrochemical testing.The prepared electrode surface has abundant pore structure and carbon oxide groups,which provide abundant active sites for oxygen reduction to generate hydrogen peroxide.Then studied the influence of electrolyte concentration,pH,current density,hydraulic residence time,and air chamber pressure on the amount of H₂O₂ produced,and found that the electrolyte concentration of Na₂SO₄ in the solution is 10-200 m M,pH 3-13,and air chamber pressure 0.5-3 KPa Within the range,the H₂O₂ concentration at the water outlet of the electrochemical reactor is relatively stable,and the current efficiency remains above 90%.The concentration of H₂O₂ generated linearly increases with the increase of current density and the extension of hydraulic residence time.In the end,an electrochemically coupled ultraviolet reaction system was set up to study the degradation of RhB.When the hydraulic retention time was 58 min,the electrochemically coupled ultraviolet system had a 2.6 times higher TOC degradation rate than ultraviolet alone.The electrochemical reaction system alone has the worst degradation effect on TOC and RhB.Hydroxyl radical capture experiments were carried out in three systems.In the ultraviolet and electrochemically coupled ultraviolet reaction system,the hydroxyl radical is the main oxidant for the degradation of pollutants,and in the electrochemically coupled ultraviolet reaction system,when the concentration of H₂O₂ exceeds 100 mg/L,ultraviolet light activates the decomposition of H₂O₂ to generate hydroxyl radicals,which is the limiting factor for RhB degradation and TOC removal.Taking the degradation effect of RhB and TOC as indicators and comprehensively considering economic benefits,the pollutant concentration,pH,current density and H₂O₂ concentration in the system operation are optimized under continuous flow conditions,and the optimal operating conditions of the reaction system are determined as pollution The concentration is 30 mg/L,the pH is 3,the current density is 20 m A/cm²,and the H₂O₂ concentration is 100 mg/L.Under these conditions,RhB is almost completely degraded when the hydraulic retention time is 14.5 min,and the TOC degradation rate is 90.5%when the hydraulic retention time is 58 min.It shows that the constructed electrochemically coupled ultraviolet reaction system has excellent RhB removal performance.