Degradation of organic compounds in the dark using pre-illuminated Ag/TiO2 as a reusable Fenton-like material

Abstract

Organic compounds were successfully degraded using silver-deposited titanium dioxide (Ag/TiO2) and hydrogen peroxide (H2O2). Electrons accumulate in Ag deposits on the surface of TiO2 under UV light (λ > 320 nm) illumination; therefore, pre-illuminated Ag/TiO2 activates H2O2 to hydroxyl radicals (•OH) and induces the degradation of 4-chlorophenol (4-CP) under dark conditions. In the presence of pre-illuminated Ag/TiO2 and H2O2 at [4-CP] = 50 μM, [H2O2] = 1 mM, and [pre-illuminated Ag(3.0 wt%)/TiO2] = 0.5 g/L, 64% of 4-CP was degraded after 90 min. The UV light-induced electron storage in Ag deposits and the electron transfer from the Ag deposits to H2O2 in the dark were confirmed by measuring the UV-visible absorption spectra of Ag/TiO2 before and after UV light illumination and the addition of H2O2. The verification of •OH production via a pre-illuminated Ag/TiO2-mediated Fenton reaction was performed using fluorescence spectroscopy, and coumarin was used as a chemical probe. Experiments conducted under various conditions suggest that the optimal conditions for maximum degradation are [H2O2] = 1.0 mM, [Ag/TiO2] = 0.5 g/L, and [Ag content] = 5.0 wt%. The H2O2 activation ability of the used Ag/TiO2 was completely restored through UV light illumination. Additionally, all the tested organic compounds, including 4-CP, 2-chlorophenol, 2,4-dimethylphenol, bisphenol A, sulfisoxazole, sulfamethoxazole, and furfuryl alcohol, were efficiently degraded in a suspension of pre-illuminated Ag/TiO2 and H2O2. Pre-illuminated Ag/TiO2 can be proposed as a practical Fenton-like material for water treatment owing to its high stability and reusability.