Photocatalysis of estrone in water and wastewater: Comparison between Au-TiO₂ nanocomposite and TiO₂, and degradation by-products

Gold-modified TiO₂ (Au-TiO₂) photocatalysts were utilised for the degradation of estrone (E1), a major endocrine disrupting chemical in water and wastewater. Au-TiO₂ catalysts were synthesised by a deposition-precipitation method with gold loadings of 0-8% (wt%). The Au-TiO₂ nanocomposite exhibited superior activity compared to P25 TiO₂ under UVA (λ=365nm), cool white (λ>420nm) and green (λ=523nm) light emitting diodes (LEDs), for treating 1mgl^-1 of E1. The 4wt% Au loading was found to produce the best photocatalytic activity with a rate constant of 2.44±0.36h^-1, compared to 0.06±0.01h^-1 for P25 TiO₂, under visible light. In total 4 by-products were identified, one from negative ionization mode (m/z=269) and three from positive ionization mode (m/z=287) during photocatalysis, which were also degraded with time by Au-TiO₂. For different water matrices, the photodegradation rate of E1 decreased in the order: ultrapure water>synthetic wastewater≈wastewater effluent from membrane bio-reactor. Overall, 4wt% Au-TiO₂ demonstrated superior performance compared to P25 TiO₂ in water and wastewater.