Synergetic Effects of Ultraviolet and Microwave Radiation for Enhanced Activity of TiO₂ Nanoparticles in Degrading Organic Dyes Using a Continuous-Flow Reactor

A novel continuous-flow reactor was developed to investigate the synergetic effects of ultraviolet (UV) and microwave (MW) radiation on TiO₂ nanoparticles for the enhancement of photodegradation of Direct Red-81 (DR-81) and Bromothymol Blue (BTB) dyes. The efficiency of the combined UV and MW radiation was higher than the sum of the isolated and corresponding thermal effects and directly proportional to the MW power. The % photodegradation of DR-81 after 105 min irradiation at ambient conditions was 40%, 68%, 72%, and 100% using UV/MW_100W, UV/MW_300W, UV/MW_500W, and UV/MW_700W methods, respectively. The % photodegradation of BTB under the same conditions was 58%, 78%, 82%, and 88%, respectively. High dissolved oxygen concentration increased DR-81 photodegradation, whereas ambient air conditions were optimum for BTB. The extent of photomineralization of both dyes was dependent on MW power. Degradation products showed that both dyes were successfully oxidized through different intermediate species. The properties of TiO₂ nanoparticles did not change before and after reaction; however, the positive surface charge was reduced by as much as 14 mV. Accelerated rates of dye degradation on incorporation of MW to UV were attributed to the generation of more hydroxyl and superoxide anion radicals and an increase in hydrophobicity of TiO₂.