Heterogeneous photocatalysis of Tordon 2,4-D herbicide using the phase mixture of TiO2

Abstract

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 (Egap) 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.