Micro-arc oxidized S-TiO2 nanoporous layers: Cationic or anionic doping?

S-doped TiO2 layers were grown on titanium substrates by MAO process. SEM results revealed a porous morphology with a pore size of 40–100 nm. Our XRD analysis showed that the anatase relative content reached its maximum value at the voltage of 500 V. The existence of sulfur in the states of S4+ and S6+ which substituted Ti4+ in the titania crystalline lattice was confirmed by XPS results; meanwhile, no S2− was detected. That is, a cationic doping was observed. EDS results showed that sulfur concentration in the layers increased with the voltage. The band gap energy was also calculated as 2.29 eV employing a UV–Vis spectrophotometer.