  Manganese oxide-coated TiO2 nanotube array (NTA) was synthesized and applied
for the (electro)catalytic oxidation of sulfide. By setting the
electrodeposition parameters and calcination temperature, the coating obtained
was MnO2 or Mn2O3, with rod or needle like morphology. Excellent catalytic
activity of the Ti/TiO2 NTA/MnxOy anodes resulted in robust and selective
oxidation of sulfide to elemental sulfur via an inner sphere complex between
the sulfide ion and Mn-oxide. The penetration of the MnxOy inside the NTA
improved adhesion and enhanced the electron transfer, thus enabling complete
and rapid electrocatalytic re-oxidation of the Mn-oxide coating. At pH 8, the
final product of sulfide oxidation was colloidal sulfur, S8, which prevented
anode passivation and enabled a stable (electro)catalytic activity in the
subsequent applications. This was observed in both synthetic electrolyte and
real sewage, thus demonstrating the efficiency of the Ti/TiO2 NTA/MnxOy anode
for sulfide oxidation in complex waste streams.
