Study On Modified MnO_x / Ti Electrocatalytic Film Based On Phenol Wastewater Treatment

Phenolic wastewater is a kind of highly toxic and non-biodegradable industrial organic wastewater. To solve the challenging problems in phenolic wastewater treatment, a novel electrocatalytic membrane reactor （ECMR） was proposed with MnO_x/Ti electrode membrane as anode and a stainless steel mesh as cathode. The MnO_x/Ti electrode membrane, loading MnO_x sol on tubular porous Ti electrode membrane, was prepared via vacuum method, thermal treatment and acidification. The influence of thermal treatment temperature, acidification and rare-earth doping on the MnO_x/Ti electrode membrane structure and properties was analyzed by Thermogravimetric, X-ray diffraction, H2-temperature programmed reduction, Field-emission scanning electron microscopy, X-ray photoelectron spectroscopy and Electrochemical workstation.The nano-MnO_x was synthesized by sol-gel method, MmO4 was detected at 220-300 ℃, the mixture of Mn3O4 and a-MN2O3 was identified at 300-380 ℃, in which Mn3O4 occupied the majority. The mixture grain size increased with the increase of thermal treatment temperature. The mixture crystal form changed into ε-MnO2 and y-MnO2 and the mixture grain size decreased after acidification, in which y-MnO2 occupied the majority. Besides, the MnO_x after acidification performed the best catalytic activity.The variation of MnO_x loading on porous Ti electrode membrane was similar to that of MnO_x powder in the thermal treatment, the difference was the formation of the MnTiO2 and Mn2TiO4 solid solution in the MnO_x/Ti electrode membrane. And the mixture of Mn3O4, a-Mn2O3, s-MnO2 and y-MnO2 were detected after acidification, y-MnO2 occupied the majority and the mixture grain size also decreased. With the increased of thermal treatment temperature and acidification, Mn-O binding energy increased, however, Ti-O binding energy reduced; the content of lattice oxygen increased and that of surface hydroxyl oxygen decreased, the catalytic performance was influenced by both of them. The MnO_x/Ti electrode membrane which thermal treated at 220 ℃ showed the maximum specific capacitance and the minimum charge transfer resistance. The acidified MnO_x/Ti electrode membrane performed the best catalytic performance, and the phenolic, COD and TOC removal rate was 96.45%, 84.97% and 71.26%, respectively. The results indicated that the crystal form, grain size and phase content had a greater influence on the catalytic performance compared with the electric performance.With the increase of Eu³⁺ and Ce³⁺ doping amount, the catalytic efficiency of MnO_x/Ti electrode membrane reduced after the first increase. The phenolic, COD and TOC removal rate of undoped MnO_x/Ti electrode membrane was 62.87%,55.41% and 43.27%, respectively. The optimal doping amount of Eu³⁺ was 2 mol%, the phenolic, COD and TOC removal rate was 79.60%,69.21% and 59.11%. The optimal doping amount of Ce³⁺was 25 mol%, the phenolic, COD and TOC removal rate was 86.31%,75.01% and 62.21%. And the optimal co-doping amount of Eu³⁺ Ce³⁺ was 2 mol% Eu³⁺-30 mol% Ce³⁺, the phenolic, COD and TOC removal rate reached maximum, that was 89.21%,78.92% and 66.46%. The catalytic activity was enhanced by valence conversion, electron gain and loss and oxygen adsorption and release. The co-dping MnO_x/Ti electrode membrane showed the best catalytic activity due to the coupling effect in the Eu and Ce.