Ag3PO4/WO3 composites with Ag3PO4:WO3 molar ratios of 85:15, 75:25, 60:40, 40:60 and 25:75 were synthesized, characterized and tested for the degradation of the antibiotic agent sulfamethoxazole (SMX) under simulated solar radiation. The composites were characterized employing the BET, XRD, UV-vis DRS, SEM-EDS and TEM techniques. Changes in SMX concentration with irradiation time were followed by HPLC. Of the various materials tested, the Ag3PO4/WO3(75:25) sample (1 m(2)/g specific surface area, 2.41 eV band gap energy) exhibited the highest activity with 90% SMX conversion (525 mu g/L initial concentration and 200 mg/L photocatalyst) achieved in just 2 min. Process efficiency was found to increase with increasing photocatalyst concentration (25-200 mg/L) and decreasing SMX concentration (2100-260 mu g/L). SMX degradation in ultrapure water (UPW) was faster than in bottled water and treated domestic wastewater containing various inorganic and organic constituents; however, certain matrix constituents such as chloride, bicarbonate and humic acid had no or even a positive effect on degradation. The addition of hydroxyl radical scavengers (t-butanol, DMPO) in excess did not affect SMX degradation, while the opposite phenomenon occurred using a hole scavenger (EDTA), which suppressed degradation. In parallel, no hydroxylated or oxygenated transformation products (TPs) were detected by UPLC-ESI-MS analysis. The Ag3PO4/WO3(75:25) sample suffered photo-corrosion resulting in the formation of metallic silver, as well as partial metal leaching in the aqueous phase, both of which contributed to a gradual loss of activity upon repeated use.