Effect of Enhancers and Inhibitors on Photocatalytic Sunlight Treatment of Methylene Blue

In view of the fatal illnesses caused by methylene blue (MB) which is contained in the dye waste-water, the present study focused on the use of natural sunlight in heterogeneous photocatalysis to decolorize and degradeMB. The present study also investigated the effects of enhancers (hydrogen peroxide and persulfate ion) and inhibitors (chloride and carbonate ions) on photodecolorization ofMB. Pseudo-first-order rate constants for each studied effect were determined through Langmuir-Hinshelwood model. The recommended conditions to photodecolorize 60 ppm of MB under natural sunlight were 1.0 g/L of titaniumdioxide nanopowder at initial pH 10.5 in order to achieve 85.3% decolorization (rate constant of 10.8x10(-3) min(-1)). The addition of 4,080 ppm of hydrogen peroxide and persulfate ion significantly enhanced the decolorization efficiency up to 96.6 and 99.3 %, respectively (rate constants of 66.2 and 91.0x10(-3) min(-1), respectively). However, the addition of 2,000 ppm of chloride and carbonate ions reduced the decolorization efficiency of MB to 74.7 and 70.2 %, respectively (rate constants of 7.8 and 7.3x10(-3) min(-1), respectively). The present study implied that itwas possible to use natural sunlight as a light source for photocatalytic treatment of dye in tropical countries like Malaysia.