Photocatalytic Decolorization Of Reactive Black 5 Rb5 Using Silver Based Photocatalysts

Abstract

newline Photocatalysis is one of the AOPs affecting complete mineralization of newlinepollutants under mild reaction conditions. The present study is focused on newlinemechanistic aspects of photocatalytic oxidation (PCO) of Reactive Black 5 newline(RB5, an azo dye) using silver- based photocatalaysts Ag/AgBr and Ag3PO4. newlineAgBr particles were synthesized by a simple ion-exchange method followed by newlineexposure to visible light to produce Ag/AgBr. The influence of varying Ag:AgBr newlinemolar ratio from 0 to 0.5 and the time of exposure to visible light from 0-30 min newlinewas studied to derive the synthesis conditions. It was found that the RB5 newlinedecolorization increased with the increase in Ag:AgBr molar ratio up to 0.4 and newlinedecreased at 0.5. Similarly, RB5 degradation increased with the increase in VL newlineexposure during synthesis of up to 20 min and decreased at 30 min. The effect newlineof the catalyst dose, the initial pH of dye solution, the initial concentration of newlineRB5 and the presence of common anions on RB5 decolourization was studied. newlineFurther, the contribution of reactive oxidation species (ROS) was examined newlineusing appropriate scavengers. newlineThe highest RB5 decolurization was achieved at neutral pH and at 0.5 g/L newlinecatalyst dose. The presence of chloride and sulphate ions decreased RB5 newlinedecolourization rate constant by approximately 30% while carbonate ions did newlinenot interfere. The presence of benzoquinone (BQ), dimethyl sulphoxide newline(DMSO) and oxalic acid, respectively as scavengers of O2¯, OH and newlinephotogenerated holes (h+), significantly reduced the rate and extent of RB5 newlinedecolourization. Superoxide radicals and photo-generated holes were major newlinecontributors to RB5 decolourization as compared to the hydroxyl radicals. The newlinetheoretical calculations of energy potentials of valence band (VB) and newlineconduction band (CB) also confirmed the superoxide radicals and photogenerated newlineholes as major contributors. newlineThe efficiency and the rate of RB5 degradation by Ag/AgBr under direct newlinesunlight, indirect natural radiation and indoor illumination was also tested. When newlinevii newlineexpos