Improved photocatalytic and electrochemical activities of (Nd³⁺, Yb³⁺) co-doped TiO₂ nanoparticles synthesized by hydrothermal protocol

Pure TiO₂, (Nd 5%) doped TiO₂, and (Nd 5%, Yb 3%) co-doped TiO₂ nanoparticles were prepared independently through a hydrothermal route and well characterized them with complimentary analytical techniques e.g. XRD, SEM, EDS, XPS, UV–Vis, photocatalytic and PL. The polycrystalline anatase phase and the integration of dopant ions into TiO₂ matrix was confirmed by X-ray diffraction. The crystallite size increased from 25 to 28 nm with the dual doping of Nd and Yb ions, as determined by Scherrer formula. The optical absorption edge of (Nd 5%, Yb 3%) co-doped TiO₂ shifted towards a longer wavelength, and hence band gap decreased from 3.38 to 3.03 eV, attributed to the enhanced absorption of visible light. The reduction in PL intensity indicated that electron–hole pair recombination rate decreased with the incorporation of Nd and/or Yb ions in TiO₂ matrix. The photodecomposition of methylene blue dye under visible light irradiation was remarkably improved, from 62.6 to 93.2%, when (Nd 5%, Yb 3%) co-doped TiO₂ used as photocatalyst compared to pure TiO₂ nanoparticles. The enhanced rate constant, from 0.00907 to 0.02849 min⁻¹, predicted that (Nd 5%, Yb 3%) co-doped TiO₂ photocatalyst could effectively degrade MB dye when driven by visible light. Electrochemical (CV, GCD, EIS) analysis was conducted to evaluate the electrochemical properties of (Nd 5%, Yb 3%) co-doped TiO₂, (Nd 5%) doped TiO₂, and pure TiO₂ nanoparticles. The results demonstrated that (Nd 5%, Yb 3%) co-doped TiO₂ electrode material exhibited excellent electrochemical performance for employing in supercapacitors.