To enhance the photocatalytic activity of TiO₂ in visible light, nickel and manganese codoped TiO₂ (NMTs) and undoped TiO₂ nanomaterials were synthesized by varying dopant concentrations using a solgel method. As prepared nano materials were characterized by using X-ray diffraction (XRD) and its results shows anatase and rutile mixed phase was observed for codoped catalyst samples. Rough morphology, irregular particle shape and elemental composition of catalyst were identified with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) respectively. The Fourier transform infrared spectroscopy (FT-IR) result revealed that the substitutional doping of Mn²⁺ and Ni²⁺ into TiO₂ lattice by replacing Ti⁴⁺ in TiO₂ lattice. This was confirmed by shifting of stretching frequencies of Ti-O-Ti from 569 cm^-1 – 608 cm^-1. The catalyst (NMT2) exhibits least band gap ( 2.7 eV), less particle size (6.5 nm) with high surface area (135.70 m²/g) when compared to undoped TiO₂ (3.2 ev, 18.3 nm, 64.09 m²/g), which were determined by UV-visible diffused reflectance spectroscopy (UV Vis-DRS), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) respectively. Based on the characterization results the efficiency of codoped catalyst were exhibits better photocatalytic degradation of indigo caramine (IC). The results show that IC has degraded within 90 minutes at doping concentrations 1.0 wt% of Ni²⁺ ion and 0.25 wt% of Mn²⁺ ion in TiO₂ (NMT2) at an optimum reaction parameter pH-3, catalyst dosage 0.080 g/L and at IC dye concentration of 0.020 g/L.

Keywords: Ni-Mn Codoped TiO₂; Indigo Caramine; Photocatalysis; Sol-Gel Synthesis;