Study On The Effect Of Loaded ?-MnO₂ Particles On The Degradation Of Rhodamine B Wastewater By Three-Dimensional Electrode Reactor

The effluent after the biochemical treatment of dye wastewater still contains many complex pollutants and toxic substances,and the chromaticity exceeds the standard.There is an urgent need for an advanced treatment method that can effectively degrade dye wastewater after biological treatment.Through literature review and preliminary research,it is known that electrochemical oxidation technology is one of the effective methods for advanced treatment of benzene ring containing dye wastewater.This study firstly compared the effects of a twodimensional electrode reactor and a three-dimensional electrode reactor filled with activated carbon particles on the cyclic degradation of Rhodamine B wastewater,and then loaded ?-MnO2 on the surface of activated carbon particles by electrodeposition to enhance electrocatalysis,improve pollutant removal rate and current efficiency,and reduce energy consumption of three-dimensional electrode reactor.Under the optimal conditions of current intensity of 300 mA,O2 inputting,and electrodeposition for 3 hours,the ?-MnO2 activated carbon particle electrodes were prepared.Their Tafel slope(47.70±1.611 V-1)were lower than other controls,which showed that their had the fastest electron transport kinetics rate.Simultaneously,their electrochemically active surface area(ECSA)were 2.4 times that of pure activated carbon particle electrodes.The optimal process conditions of the three-dimensional electrode reactor filled with,?-MnO2 activated carbon particle electrodes to degrade Rhodamine B wastewater in a cycle:the voltage intensity was 5 V,the electrolyte NaCl concentration was 1 g/L,and the hydraulic retention time was 20 min.It was clear that the removal rate of Rhodamine B was as high as 98.9%,Compared with the three-dimensional electrode reactor filled with pure activated carbon particle electrodes and the two-dimensional electrode reactor,the removal rates of TOC(89.3%)were increased by 17.1%and 53.0%respectively;the average energy consumptions were saved by 137.9 KW-h/kg TOC and 251.7 KW·h/kg TOC respectively;as well as the effluent chromaticity(4.0 dilution factor)and CODcr(56.8 mg/L)both met the first level of the "Printing and Dyeing Wastewater Discharge Standard".Through the analysis of the intermediate products and degradation pathways of the electrochemical reaction of Rhodamine B,as well as various chemical and electrochemical performance tests,it was clear that the electrocatalytic mechanism of the ?-MnO2 activated carbon particle electrodes mainly included two aspects:(1)H2O was oxidated by ?-MnO2 activated carbon particles and produced physically adsorbed hydroxyl radicals(·OH).·OH combined with ?-MnO2 to form ?MnO2(·OH),which mineralized Rhodamine B into CO2 and H2O.Simultaneously?-MnO2 was released again;(2)?-MnO2(·OH)was converted to ?-MnO3,and then the intermediate products of Rhodamine B were formed through oxidatation proccesses by ?-MnO3.Simultaneously ?-MnO2 was released again.This indicated that the redox cycle of manganese(Mn6+/Mn4+)was improved electrocatalytic activity of activated carbon particle electrodes.The degradation processes of Rhodamine B was:Firstly ·OH attacked the ethyl groups on both sides of the heterocyclic ring in Rhodamine B structure,causing the molecular structure to gradually remove the ethyl groups,resulting in structural decomposition,rupture of the heterocyclic ring,and the formation of a variety of aromatic acids.Then ·OH continued to attack the benzene ring to open the ring and degrade it.Finally,after a series of reactions,Rhodamine B was gradually mineralized into CO2 and H2O.