Structural, morphological, and optical properties of Zn1.85M0.15TiO4 (M = Cu2+, Ni2+, Co2+, and Mg2+) spinel materials for photocatalytic applications

Spinel zinc orthotitanate (Zn 2 TiO 4 ) has attracted considerable attention as a promising semiconductor photocatalyst. Zn 2 TiO 4 and Zn 1.85 M 0.15 TiO 4 (M = Cu 2+ , Ni 2+ , Co 2+ , and Mg 2+ ) were synthesized via a two-step solid-state reaction method. Their structural, morphological, optical, and photocatalytic properties were systematically examined to evaluate the influence of metal-ion doping. XRD spectroscopy confirmed that all the prepared materials formed a cubic structure with the impurity of ZnO. The crystallite sizes of the prepared materials were in the nanometer range (40.41–45.65 nm). Morphological FESEM analysis revealed spherical-shaped particles, while EDS analysis confirmed the presence and homogeneous distribution of the constituent elements. HRTEM analysis further verified the crystalline nature of the materials through clear lattice fringes and corresponding d-spacing values. FTIR analysis confirmed the presence of functional groups associated with Zn-O and Ti-O bonding. The synthesized materials exhibited optical activity in the ultraviolet region. UV–Vis analysis demonstrated that metal-ion incorporation enhanced visible-light absorption and reduced the optical band gap energy from 3.22 eV for pristine Zn 2 TiO 4 to 2.70 eV for Co-doped Zn 2 TiO 4 . Photoluminescence analysis indicated that doping influenced the recombination behavior of photogenerated charge carriers. The photocatalytic activity of the samples was tested using MB dye under UV irradiation. The highest degradation efficiency was 92.23%, and this was achieved for the sample Zn 1.85 Ni 0.15 TiO 4 , confirming that doped Zn 2 TiO 4 is a promising photocatalyst for environmental remediation applications.