Photocatalytic degradation of 2,4-dichlorophenoxyacetic acid under visible light: Effect of synthesis route

The photocatalytic degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) under visible light exposure was studied using TiO2 and TiO2 doped with nitrogen (1% and 5%) that was prepared by the sol–gel (SG) and sonochemistry (SQ) methods. In fact, the sonochemical route represents a sustainable alternative for saving energy during the synthesis. The results show that the half-life time (t1/2) was 71 min for the 5% N–TiO2 photocatalyst prepared by the SQ. According to XRD results, semi-crystalline TiO2 was obtained using both synthetic routes at 400 °C. However, the presence of a dopant using the SG method causes an increase in the crystallinity of the TiO2 materials prepared, and the crystallinity of the SQ route is inhibited at higher nitrogen content. The XPS data showed the presence of nitrogen (398–401 eV) in synthesized TiO2. The results of the band gap energy (Eg) using a Kubelka–Munk transformation indicate that both methods of synthesis show higher absorbances when nitrogen was incorporated into the matrix of TiO2, leading to the decrease of Eg from 3.2 eV to 3.0 eV. The TEM analysis shows that the nanoparticles were obtained with sizing less than 40 nm, and the incorporation of nitrogen causes a decrease in the particle size. Finally, the surface properties are consistent with the observed crystallinity in the materials.

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► Two routes to incorporate urea as nitrogen precursor at TiO2 were studied.
► Nitrogen incorporation modifies the band gap energy at TiO2 structure.
► The doped materials are driven in visible light.
► Sonochemical enhances photodegradation in comparison with sol–gel method.
► 2,4-Dichlorophenoxyacetic is proposed as main degradation reaction.