Enhanced Fenton-like degradation of phenol by sulfur modified -Fe2O3/Fe3O4/R-TiO2 composite coating on Ti alloy prepared by plasma electrolytic oxidation

Highly efficient sulfur modified -Fe2O3/Fe3O4/R-TiO2 coating on Ti alloy was first prepared by plasma electrolytic oxidation (PEO). XRD and SEM analysis revealed that this coating with rough and porous structure consisted of rutile (R-TiO2), -Fe2O3 and Fe3O4. XPS measurement indicated that as-prepared coating was functionalized with sulfate ( SO 4 2 − ) derived from sulfur modification, leading to acidic sites generation. Phenol degradation experiment suggested that sulfur modification could significantly enhance degradation efficiency. Under the condition of pH 4.0, H2O2 6.0 mmol l−1, 6 cm2 PEO coating and temperature of 30 °C, 97% phenol could be rapidly degraded within 15 min by sulfur modified PEO coating which was much larger than that (5.8%) by sulfur unmodified PEO coating. Fenton-like degradation of phenol by PEO coatings prepared with different amount of sulfur source revealed that degradation efficiency increased obviously with the increase of sulfur source. Although the increase in initial pH from 4.0 to 6.0 inhibited the catalytic activity of sulfur modified PEO coating, this coating still could remove 95.2% phenol under circumneutral pH (pH 6.0) within 120 min. The stability experiment revealed that Fenton-like catalytic activity decreased gradually with the increase of the cyclic number. Possible degradation mechanism indicated that strong acidic microenvironment derived from sulfur modification played an important role in enhancing catalytic activity and widening working pH range of PEO coating. Sulfur-assisted enhancement of catalytic activity of immobilized coating in this work provided a novel design thought for preparation of highly active Fenton-like catalyst with broad pH working range.