Heterogeneous photocatalytic degradation and mineralization of 2,4-dichlorophenoxy acetic acid (2,4-D): its performance, kinetics, and economic analysis

The photocatalytic degradation and mineralization of commercial solution of 2,4-dichlorophenoxyacetic acid (2,4-D) was carried out by UVA/P25 TiO2 and UVA/P25 Ti02/H202 oxidation processes under batch-mode conditions. In UVA + TiO2 photocatalysis (TiO2 1.5 gL-1, pH 5, initial 2,4-D 25 mg L-1), 97.47% 0.27% degradation, 39.89% 3.42% mineralization, and 65.52% 4.88% oxidation were achieved in 180 min, and in UVA +TiO2 + H202 photocatalysis (TiO2 1.5 g L-1, pH 5, initial 2,4-D 25 mg L-1, H202 150 mg L-1), 99.74% 0.08% degradation, 55.99% 2.67% mineralization, and 82.49% 1.90% oxidation were obtained in 180 min. The pseudo-first-order kinetic model fitted the experimental data well, and the photocatalytic degradation process was explained by the modified L H model; k, and KLH were 1.293 mg L-1 min(-1) and 0.232 L mg(-1), respectively. Fourier transform infrared (FTIR) spectroscopy spectra and scanning electron microscopy (SEM) analysis indicated degradation of organic bonds of the herbicide and adsorption of 2,4-D particles onto the TiO2 catalyst during 24-h experiments. Moreover, the dependence of ka on the half-life time was determined by calculating the electrical energy per order (EEO). UVA/TiO2/pp H2O2 photocatalysis may be applied as a pretreatment to 2,4-D herbicide wastewater at a pH of 5 for biological treatment.