Uv Led As A Light Source For Photocatalytic Oxidation Of Trace Organic Contaminants

This study aims to quantify the performance of state-of-the-art UV LEDs in relation to that of mercury-vapor lamps for low-temperature photocatalytic oxidation (PCO) of organic contaminants. A LED module consisting of 12 high-output (350 mW) LEDs was designed to assume the geometry of an 8-W linear fluorescent lamp (FL). Twelve LEDs were arranged in four arrays (or rows) around a 15.6 mm diameter aluminum rod with three LEDs in a linear array over a distance of 60 mm (i.e., 20 mm space between LEDs). Light distribution and thermal profile were extensively characterized. Although the irradiance along the lateral and radial directions was not as uniform as the FL, the LED module gave rise to an average 4 mW cm-2 irradiance equivalent to the output of the FL when it was driven by a forward current (IF) and voltage (VF) of 94 mA x 20 V (i.e. 1.88 W). Radiant flux of the LED module was directly proportional to IF, offering a convenient way to study the effect of radiant flux on PCO in the same reactor. The performance of the FL- and the LEDirradiated reactors was evaluated with 50 PPMv ethanol in RH 45% air at a space time 0.94 seconds and two irradiance levels, 4 and 13 mW cm-2. Acetaldehyde was the sole oxidation intermediate detected in the effluent of all three reactors, and its concentration was lower in the LED reactor with either 4 or 13 mW cm-2 irradiance than the FL-reactor. The ethanol removal rate in reactors irradiated by FL-4 mW cm-2, LED-4 mW cm-2, and LED-13 mW cm-2 was 80, 91, and 95.5%, while their corresponding mineralization efficiency was 28.2, 44.3, and 76.2%, respectively. These results suggest that the LED-reactor is less efficient in oxidizing ethanol compared to the FL-reactor at the same irradiance level, but increasing radiant flux greatly enhances the PCO efficiency. The lower POC efficiency in the LED than the FL reactor is likely attributable to the uneven radiation of the LED module over the non-transparent photocatalyst (Silica Titania Composite); consequently, some of the catalyst received less than the average radiant flux. Strategies for addressing the challenges associated with the light distribution and heat management were also explored