Enhanced Photocatalytic Activity in p-NiO Grafted n-TiO2 Porous Coatings

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.