Paired Generation Of ·OH/SO₄^-· In Cathodic And Anodic For Removing Organophosphorus Pesticides

In the process of using many organophosphorus pesticides,it has caused great harm to the environment,and need to be treated.At present,although electrochemical treatment has good degradation effect,unipolar degradation technology has low current efficiency and can not make full use of energy.However,the cathodic reduction and anodic oxidation can be simultaneously utilized by the cathode-anode pair degradation technology,which has high current efficiency and high space-time efficiency compared with the unipolar technology.Therefore,this paper proposed a cathode-anode paired degradation of pesticides with UV-activated techniques.The method uses the air diffusion electrode as the cathode and the platinum electrode as the anode to synthesize the oxidant,and in situ activates oxidant to produce·OH/SO₄^-·by UV,and then degrades organopho-sphorus pesticide chlorpyrifos effectively.For the experiments of cathode-ultraviolet activation degradation,the best degradation conditions and active substances were found.When the initial concentration of chlorpyrifos is 25 mg/L,the aeration rate is 200 mL/min,and the current density is 40 mA/cm²,the degradation of chlorpyrifos are 100%after 60min,and the yield of orthophosphoric acid radical can reach 67.87%.Within a certain range,the initial pH of the solution has no effect on the degradation effect,while the humic acid has a great influence.With the increasing of the humic acid concentration,the rate of the degradation is becoming decreasing.The free radical quenching experiment with methanol and tert-butanol proves that there is·OH in the solution.For the experiment of anode-ultraviolet activation degradation,the best degradation conditions and mechanism were explored.When the initial concentra-tion of chlorpyrifos was 25 mg/L,with 1.0 mol/L electrolyte,0.01 mol/L inhibitor?KSCN?and 0.6 A/cm² current density,the degradation of chlorpyrifos reached more than 90%after 120 min of electrolysis.The yield of orthophosphoric acid radical is only around 10%.By adding different anion to the experiment,it was found that HCO₃^-,CO₃^2-will compete free radicals with chlorpyrifos,reducing chlorpyrifos degradation,while Cl^-would promote the degradation of chlorpyrif-os.The experiments of cyclic voltammetry proved that chlorpyrifos at low concentration does not directly degrade on the surface of platinum electrode by losing or receiving electrons,but it is oxidatively degraded by sodium persulfate.The degradation conditions were determined by the cathode-anode paired degradation of peisticides with UV-activated techniques,and it confirmed that the anode-anode paired technique can improve the current efficiency of chl orpyrifos degradation.The optimal cathode condition is 25 mg/L chlorpyrifos,200 mL/min aeration volume,air diffusion cathode;anode condition is 25 mg/L chlorpyrifos,0.01 mol/L KSCN,1.0 mol/L Na₂SO₄,45/450 mA/cm² current density,pure platinum anode.Compared with the current efficiency of the unipolar degrading chlorpyrifos,the current efficiency of the cathode-anode paired technology is up to 21.2%,which is almost two to three times of that of the unipolar degradation.