Effects of various treatment procedures and pulse power modes on the photoelectric efficiency of Ti-PEO photocatalysts

Highlights: • The morphology and crystal structure of titanium dioxide film can be controlled by different treatment processes. • The impregnation method can effectively increase the doping amount of manganese ions. • Bipolar pulse mode (PBP) has higher Mn doping and energy utilization efficiency. • The positive-negative cycle conversion of PBP mode is helpful to improve the reaction probability of cation to anode. In this study, various treatment methods were developed to achieve suitable structural phase control for the oxide layer of Ti plasma electrolytic oxidation (PEO) photocatalysts to improve their photoelectric conversion efficiency. To achieve the aforementioned purpose and to increase the doping efficiency, a three-stage PEO manufacturing procedure was developed and applied. In the first stage, the porous morphology and specific structural phases of a pretreated layer were controlled for doping preparation. In the second stage, doping elements were added into the surface and pores of the pretreated layer using the impregnation method. Finally, in the third stage, PEO was performed with different control parameters. The treatment factors in this study were the amount of manganese ion impregnation; the porosity, pore diameter, crystal structure, and carrier used in the treatment process; and the applied power mode. The effects of structural phase control, the Mn⁺ impregnation concentration, and the applied power modes on the carrier concentration were studied. The results indicated that the designed treatment method can effectively control the characteristics of oxide layers. By applying the impregnation method, the doping amount of Mn⁺ was increased more than five-fold compared with that in the single-step PEO treatment. Furthermore, to understand the treatment mechanism, the absorption spectrum, doping efficiency, Mn⁺ distribution, and mass transfer mechanism (of anions and cations) were investigated under direct, pulsed unipolar, and pulsed bipolar current. Finally, the functioning of the manufactured Mn: TiO₂ (PEO) photocatalyst was verified with toluene under ultraviolet A, blue, and white LED light.