An efficient and energy saving approach to photocatalytic degradation of opaque high-chroma methylene blue wastewater by electrocatalytic pre-oxidation

The opaque methylene blue (MB) dye wastewater hard to be degraded directly by photocatalytic (PC) oxidation was successfully decomposed by a new two-step process, in which electrocatalytic (EC) pre-oxidation was followed with photoelectric synergistic catalytic (PEC) oxidation. The SnO2/TiO2 NTs electrode was used as the anode, which simultaneously has superior EC and PC performance. In the pre-oxidation step, the opaque dye wastewater is decolorized by EC oxidation, and the wastewater becomes a light transmission system, which provides the necessary condition for PC oxidation. However, the individual EC oxidation will be of low current efficiency and high energy consumption for the decreasing of the pollutants concentration in wastewater. Thus, in second stage, the PC process was introduced, and the synergistic catalytic oxidation leads to high PEC oxidation efficiency, so that the complete mineralization of the MB dye wastewater was realized. The whole process is highly efficient and energy-saving, which opens a new avenue to degrade the high-chroma or opaque dye wastewater.

► Electrocatalytic pre-oxidation method degradated methylene blue.
► Electrocatalytic pre-oxidation provides a light transmission system.
► The synergistic photoelectric catalysis is an efficient and energy-saving method.