Titanium dioxide nanoparticles (nTiO₂) were used in heterogeneous photocatalysis for remediation of herbicide Tordon 2,4-D. These nTiO₂ was synthesized by the sol-gel method followed by thermal treatment at 450 °C for 2 h. The structural characterization by X-ray diffraction and Rietveld refinement confirm that the mixture of phases is 21.28 % of anatase (tetragonal) and 78.12 % of brookite (orthorhombic). All vibrational modes characteristic of anatase and brookite in the interval from 85 to 1100 cm⁻¹ were confirmed using the Raman spectroscopy. The composition of nTiO₂ was studied using the X-ray spectroscopy analysis (XPS), where TiO₂ and traces of Ti₂O₃ were confirmed. The nTiO₂ exhibit strong absorption in the region of 427 nm with direct optical bandgap (E_gap) calculated equal to 2.90 eV. For all catalytic tests with nTiO₂ as a catalyst there where high photocatalytic performance. Also, the total degradation for molecules of 2,4-D herbicide in aqueous solution was obtained at 45 °C for 40 min under UVc radiation. The toxicity tests with Allium cepa bulbs show that the solutions collected after the photocatalytic treatment with nTiO₂ nanoparticles was similar when compared with the negative control (distilled water) results. Moreover, the positive control (Tordon 2,4-D solution) and residue after the photolysis test exhibited high toxicity, inhibiting the growth and development of bulbs and roots.