Optimization of MnOx/Ti composite membrane anode in the electrocatalytic membrane reactor by acidification for phenolic wastewater treatment

A novel electrocatalytic membrane reactor (ECMR), assembled by MnOx/Ti (MT) composite membrane as an anode, was used to degrade phenolic wastewater. The MT composite membrane, MnOx layer with the various crystal forms coated on porous tubular Ti support, was prepared by sol–gel method and then activated further by acidification to obtain acidified MnOx/Ti (AMT) composite membrane. The XRD results showed that the crystallite size of MnOx layer distinctly decreased after acidification. This is because of the Ti support had a great effect on the crystal form and crystallite size of MnOx, especially after acidification. The results of XPS analysis showed that the interaction between Ti support and MnOx layer had great influence on the Mn–O, Ti–O binding energies and active oxygen species of MT and AMT. Treated by ECMR with AMT, the phenol, COD and TOC removal rates of the synthetic phenolic wastewater were 96.45%, 84.97% and 71.26%, which were obviously higher than that of MT, 62.87%, 50.34% and 41.25%, respectively. It was revealed that acidified MnOx as the catalysts in AMT composite membrane, with the specific crystal form, refined crystallite size and active oxygen species, exhibited a great potential in the electrocatalytic oxidative degradation of the phenolic wastewater.