Impact of cobalt concentration on the structural, optical, and photoelectrochemical properties of titanium dioxide nanorods synthesized by hydrothermal method

In this investigation, the effects of cobalt doping with various concentrations of Co²⁺ ions (0, 0.1, 0.3, 0.5, 0.7 M) on the physical and photoelectrochemical properties of TiO₂ were examined using an economical hydrothermal process. Properties of the samples were analyzed using XRD, Raman, SEM, UV–Vis, PL, photocurrent, Mott-Schottky, and EIS techniques. XRD patterns indicate that Co-doped TiO₂ films were found to have a rutile phase, with crystallite sizes ranging from 16.82 to 23.52 nm. Raman spectroscopy showed peaks at 144, 443, and 609 cm⁻¹, demonstrating the formation of the rutile phase of TiO₂. SEM images revealed that TiO₂ NRs were uniformly formed in a tetragonal structure, and the grain size increased with higher doping levels. In the visible spectrum. Photoluminescence (PL) measurements showed two significant emission peaks at 520 and 700 nm, with reduced strength due to doping. UV–Vis results indicated that the optical absorption edge of the films ranging 386–417 nm, and the estimated band gap (E_g) reduced from 3.21 to 2.89 eV with increasing doping levels. The photocurrent (PC) measurements revealed that the films produced behave as n-type semiconductors. Mott-Schottky results indicated an enhancement in the flat band potential and donor density increased as the dopant concentration increased from −0.47 to −0.72 V and 1.55 × 10¹⁸ to 6.15 × 10¹⁸ cm⁻³, respectively. Additionally, EIS results indicate a reduced in the resistance of charge transfer (RCT) for doped samples compare to pure samples. This is due to the lattice distortion resulting from Cobalt doping, which enhances the efficiency of charge transfer. Our results show that Co-doped TiO₂ films are viable options for biosensors, supercapacitors, and photovoltaic applications.