Abstract: We synthesized NiO-loaded TiO₂ porous p-n junctions by electrophoretic enhanced micro arc oxidation (EEMAO) technique which is a relatively simple and new method for producing composite coatings. Phase structure, chemical composition, and surface morphology of the NiO-TiO₂ coatings were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) techniques, respectively. Photocatalytic efficiency of the samples was studied through measuring the decomposition rate of 4-chlorophenol under UV irradiation. Results showed that the coatings mainly consisted of anatase, rutile, and nickel oxide phases. It was observed that a finer surface morphology, i.e. smaller pores, was obtained at lower voltages. Besides, the amount of nickel oxide loaded to the TiO₂ host increased with the voltage. The NiO-TiO₂ composite coatings showed a higher photoactivity than pure TiO₂ coatings revealing the effective role of NiO in decreasing the recombination rate of photogenerated electrons and holes. The maximum photocatalytic reaction rate constants for TiO₂ and NiO-TiO₂ samples were obtained as 0.0064 and 0.0131 min^-1, respectively. We also found that there was an optimum concentration of NiO where a maximum photocatalytic activity was achieved. A correlation between growth variables, structure, and photocatalytic efficiency was established.

Key words: Nickel oxide, Titanium dioxide, p-n junctions, Photocatalysis, Porous materials