Structural, optical, and photocatalytic activity of Nd-Er co-doped CuO nanoparticles via hydrothermal route

Abstract

Copper oxide (CuO) is a widely studied p-type semiconductor due to its narrow bandgap (1.2-1.8 eV), earth abundance, non-toxicity, and stability, making it a strong candidate for various technological applications, including photocatalysis, photovoltaics, sensors, and energy storage devices. However, despite its promising properties, the photocatalytic efficiency of CuO remains limited due to rapid charge carrier recombination. To overcome this challenge, researchers have extensively explored doping strategies, particularly with rare earth (RE) elements, to enhance the optical, electronic, and structural properties of CuO. This study examined the structural, optical, and photocatalytic properties of undoped and neodymium (Nd) and erbium (Er) co-doped CuO nanoparticles produced via a hydrothermal method. The influence of Nd and Er doping on CuO was systematically analyzed using various characterization techniques. X-ray diffraction (XRD) confirmed the successful incorporation of Nd³⁺ and Er³⁺ ions into the CuO lattice for higher co-doping percentages (2-3% Er and 2% Nd)) whereas secondary phases occur for lower co-doping percentage (1% Er and 2% Nd), leading to lattice distortions that modify its structural properties. X-ray Photoelectron Spectroscopy (XPS) verified the oxidation states of Cu2+, Nd3+, and Er3+, ensuring their proper integration into the CuO matrix. Optical studies using UV-vis spectroscopy showed that co-doping resulted in overall bandgap reduction, improving light absorption and charge separation efficiency. For the photocatalytic performance of the synthesized nanoparticles, Rhodamine B (RhB) dye degradation under UV irradiation was conducted. The results demonstrated that co-doped CuO nanoparticles exhibited significantly higher photocatalytic activity compared to both undoped and Nd-doped CuO. Among the tested samples, the one with 3 mol% Er and 2 mol% Nd achieved the highest degradation efficiency of 87% within 180 minutes. This significant improvement is due to the combined effect of Nd and Er ions, which improve charge separation, and inhibit recombination. The insights from this study will pave the way for further exploration of RE-doped CuO nanostructures in advanced applications, including solar energy conversion, wastewater treatment, and next-generation optoelectronic devices.