Photocatalytic performance of Nd–TiO₂ coatings: effect of voltage and frequency

Neodymium (Nd)–titanium dioxide (TiO₂) micro-arc oxidation (MAO) coatings were formed in a phosphate-based electrolyte with the addition of neodymium (III) oxide (Nd₂O₃) using suitable voltages and frequencies. Scanning electron microscopy results revealed that the coatings varied with different voltages and frequencies. Furthermore, composition analysis showed the neodymium–titanium dioxide coatings were mainly composed of anatase and rutile phases. Meanwhile, the anatase content increased and then decreased. In addition, X-ray photoelectron spectroscopy results indicated that the titanium (Ti) 2p spin–orbit components of the neodymium–titanium dioxide coatings shifted toward a higher binding energy, suggesting that some of the neodymium (Nd³⁺) ions combined with the titanium dioxide lattice, leading to dislocation. Furthermore, photocatalytic experiment results showed that the photocatalytic activity of neodymium–titanium dioxide coatings can be greatly enhanced with a moderate amount of neodymium ions. However, an excessive amount of neodymium ions does not improve the photocatalytic activity further.