Highly dispersed FeOOH to enhance photocatalytic activity of TiO2 for complete mineralisation of herbicides

Although there were many new photocatalysts reported recently, TiO2 has still been considered as one of the best candidates for real application of environmental decontamination. Fe-based oxides were synthesised as efficient and equally important non-toxic active species to improve the efficiency of TiO2 photocatalysts. Such nano-architectured FeOx/TiO2 was tested for herbicides mineralisation e.g. 2,4,6-trichlorophenol (2,4,6-TCP) and 2,4-dichlorophenoxyacetic acid (2,4-D) under full arc light irradiation. The consistent results were achieved by HPLC, TOC and UV-vis spectra measurements, which show among three Fe species, Fe4NO3(OH)(11), FeOOH and Fe2O3, FeOOH is the best to improve TiO2 activity. This active specie of FeOOH was readily controlled by synthesis temperature and precursor concentration, leading to 250 degrees C being the optimum temperature for the synthesis of very stable FeOOH/TiO2 nanocomposite with excellent photocatalytic activity, representing nearly two times activity of the benchmark PC50 TiO2 photocatalyst for all herbicides tested. Such high activity was attributed to the enhanced photo-generated electron-hole separation and improved generation of hydroxyl radicals by FeOOH. The multifunction of FeOOH is very crucial for organic pollutants mineralisation. The mechanistic studies also show that degradation of 2,4,6-TCP was mostly dominated by hydroxyl radicals and superoxide radicals. The possible degradation pathway of 2,4,6-TCP was also proposed.