Degradation of methyl orange in heterogeneous photo-Fenton reaction over V(IV)-containing oxide-phosphate coatings formed on titanium by plasma electrolytic oxidation

V-, P-containing coatings on titanium have been formed through one-step method of plasma electrolytic oxidation in aqueous electrolyte containing 0.049 mol/L Na-6 P6O18 and 0.095 mol/L NaVO3 (pH = 6) at different current densities and processing times. The coatings have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrum analysis (EDX), microprobe X-ray spectrum analysis (XSA), and X-ray photoelectron spectroscopy (XPS). As to XSA, all coatings are enriched with vanadium (11-16 at.%) and phosphorus (17-21 at.%), the ratio of which is constant and does not depend on the formation mode. According to XPS, vanadium is mainly found in the +4 oxidation state. The photocatalytic activity of oxide coatings has been investigated in the reaction of methyl orange (MO) degradation in the presence of H2O2 under UV or Vis irradiation. After 180 min of UV and Vis irradiation, 80% and 30% the MO dye, respectively, were degraded on almost all V-, P-containing PEO-coated samples. It has been suggested that their activity is determined by the formation of vanadium peroxide complexes fixed on the coating surface and, thereafter, of active radicals under the UV and Vis irradiation.

Automated summary

V-, P-containing coatings were formed on titanium using a one-step plasma electrolytic oxidation method, and were characterized using various techniques. The coatings were found to be enriched with vanadium and phosphorus, with the photocatalytic activity showing significant degradation of the MO dye under UV and visible light irradiation for 180 minutes.