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

Highlights: • 93% vs. 3% E1 photodegradation by 4 wt% Au-TiO₂ vs. P25 under white light in 1 h. • E1 photocatalysis by Au-TiO₂ decreased as UVA > white > green. • Photocatalysis of E1 followed pseudo 1st order kinetics. • Photodegradation rate of E1 was adversely affected by wastewater matrix. • A photoproduct with the same m/z as E1 was formed and subsequently degraded. 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 = 365 nm), cool white (λ > 420 nm) and green (λ = 523 nm) light emitting diodes (LEDs), for treating 1 mg l⁻¹ of E1. The 4 wt% Au loading was found to produce the best photocatalytic activity with a rate constant of 2.44 ± 0.36 h⁻¹, compared to 0.06 ± 0.01 h⁻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, 4 wt% Au-TiO₂ demonstrated superior performance compared to P25 TiO₂ in water and wastewater.