Design of MnOx/TiO2 Nanostructures for Photocatalytic Removal of 2,4-D Herbicide

Abstract

The research and modification of semiconductors through different synthesis routes allow obtaining materials with optimal properties to induce new energy levels and improve charge separation efficiency. In this context, the sol-gel method was used to synthesize TiO₂-based materials doped with different percentages of MnO_x to evaluate their photocatalytic activity in the degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in water under UV irradiation. Characterization results revealed a reduction in crystallite size to 7.2 nm. Adding MnO_x enhanced the optical absorption of TiO₂, resulting in a shift toward the red end of the spectrum of the forbidden energy band. The photocatalytic activity increased significantly with the percentage of MnO_x, reaching a maximum degradation of 70 % in 6 hours with the 3 MnTi material. This increase was attributed to the synthesis method, which facilitated the formation of nanostructured heterojunctions mainly composed of TiO₂ and MnO₂, reducing the recombination of electron-hole pairs. TEM analysis confirmed these structures. A reaction mechanism for the 3 MnTi material is proposed, considering the mobility of charge carriers and the photooxidation processes of the pollutant.