Electro-codeposition of CeO2 nanoparticles into cobalt matrix to improve the tribocorrosion performances of Co/nano CeO2 composite layers in biological solution for medical applications

Visible-Light-Induced Photocatalytic and Photoantibacterial Activities of Co-Doped CeO2

As one of the most significant rare earth oxides, the redox ability of cerium oxide (CeO₂) has become the primary factor that has attracted considerable interest over the past decades. In the present study, irregular pentagonal CeO₂ (S-CeO₂) and different amounts of (1, 4, 8, and 12% Co) cobalt-doped CeO₂ nanoparticles (Co-CeO₂ NPs) with particle sizes between 4 and 13 nm were synthesized via the microwave-assisted synthesis method. The structural, optical, and morphological studies of S-CeO₂ and Co-CeO₂ were carried out using various techniques. The shifts in the conduction band and valence band were found to cause the reduction of the band gap energies of S-CeO₂ and Co-CeO₂ NPs. Moreover, the quenching of photoluminescence intensity with more Co doping showed the enhanced separation of charge carriers. The photocatalytic activities of S-CeO₂ and Co-CeO₂ NPs for methylene blue dye degradation, 4-nitrophenol reduction, and their photoantibacterial properties under visible-light irradiation were investigated. Findings showed that, due to the lower band gap energy (2.28 eV), more than 40% of both photocatalytic activities were observed for 12% Co-CeO₂ NPs. On the other hand, higher antibacterial impact in the presence of light shows that the Co doping has a considerable influence on the photoantibacterial response of Co-CeO₂. Therefore, microwave-assisted synthesized CeO₂ and Co-CeO₂ NPs have shown potential in photocatalytic dye degradation, chemical reduction, and photoantibacterial activities.

Nanostructuring Effect of Nano-CeO2 Particles Reinforcing Cobalt Matrix during Electrocodeposition Process

The electrodeposition method was used to obtain nanostructured layers of Co/nano-CeO₂ on 304L stainless steel, from a cobalt electrolyte in which different concentrations of CeO₂ nanoparticles (0, 10, 20, and 30 g/L) were dispersed. The electrodeposition was performed at room temperature using three current densities (23, 48, and 72 mA cm^-2), and the time was kept constant at 90 min. The influence of current densities and nanoparticle concentrations on the characteristics of the obtained nanostructured layers is also discussed. An X-ray diffractometer (XRD) was used to investigate the phase structure and cobalt crystallite size of the nanostructured layers, and a contact angle (sessile drop method) was used to assess the wettability of the electrodeposited layers. The roughness of the surfaces was also studied. The results show that the nanostructured layers became more hydrophilic with increasing nanoparticle concentration and increasing current density. In the case of pure cobalt deposits, an increase in the current density led to an increase in the size of the cobalt crystallites in the electrodeposited layer, while for the Co/nano-CeO₂ nanostructured layers, the size of the crystallites decreased with increasing current density. This confirms the nanostructuring effect of nano-CeO₂ electrocodeposited with cobalt.