Photocatalytic Degradation of Methyl Red and Methyl Blue Dyes with Doped-Titanium Dioxide Nanoparticles in the Presence of Peroxymonosulfate Oxidant

In this study, nickel and cobalt nanoparticles were successfully synthesized through the simple reduction of nickel and cobalt salts using polyvinyl alcohol (PVA) and sodium borohydride as a reducing agent. These nanoparticles were then loaded onto the surface of supportive TiO₂ particles to prepare and assess single and double-metal-doped TiO₂ photocatalysts, such as Co-TiO₂, Ni-TiO₂, and Ni, Co-TiO₂ using a simple reduction method. These photocatalysts were utilized for the first time for the removal of methyl red (MR) and methyl blue (MB) dyes from aqueous systems. The doping of cobalt and nickel transition metals was employed to decrease the band gap of the titanium dioxide catalyst. The prepared particles underwent analysis via SEM, TEM, FT-IR, XRD, TGA, and EDX. Several important factors, such as the initial solution pH, the concentration of MR and MB dyes, temperature, and catalyst dosage were investigated. The results revealed that Ni, Co-TiO₂ NPs exhibited the highest photocatalytic degradation efficiency toward MR (approximately 98.5%) and MB (approximately 88.9%) compared to Co-TiO₂ and Ni-TiO₂ under optimal conditions (i.e. initial solution pH ~ 3, [MR] = 2, [MB] = 1, [PMS] = 1 mM, catalyst dosage ~ 0.2 g/L, and temperature ~ 298 K). The XRD peak at a 38° 2θ angle indicates the presence of cobalt, which increases with the concentration of cobalt. Moreover, all reactions occurred in an aqueous medium, and the photocatalysts remained stable during the reaction, allowing for their repeated use. Furthermore, they are environmentally friendly and have promising applications in the treatment of organic wastewater.