LED-Based Ultraviolet Oxidation of Pharmaceuticals: Effects of Wavelength and Intensity, pH, and TiO₂ Loading

The presence of pharmaceuticals in water resources has alarmed water and health authorities. This study evaluated ultraviolet-based oxidation as a means to decompose sulfamethoxazole, ibuprofen, and triclosan. In particular, the study evaluated using light emitting diodes (LEDs), the so-called ultraviolet LEDs (UV-LEDs), as an alternative ultraviolet source to the problematic mercury lamps that are conventionally used in the decomposition of pharmaceuticals in water. The study explored various conditions of varying ultraviolet wavelength, irradiation intensity, reaction pH, and TiO2 loading. It compared the photolytic decomposition of the pharmaceuticals with their photocatalytic decomposition. The photolytic decomposition of the pharmaceuticals was solely determined by the relation between their ultraviolet absorption characteristics and the ultraviolet emission spectra of the LEDs. Reaction pH greatly affected both photolytic decomposition and photocatalytic decomposition. The presence of TiO2 in cases where significant photolysis was present inhibited the overall decomposition process. However, in all cases, photocatalysis showed better mineralization than photolysis.