Silver halide and associated assemblages have received a great deal of interest in recent years for their ability to photochemically degrade a wide variety of substrates. In this work we examine the reactivity of an in-situ formed silver chloride colloid to degrade rhodamine B dye (RhB) - considered here as a model substrate. The AgCl(s) particles thus produced had hydrodynamic diameters between 0.2 - 1 �m and exhibited differing degradation potential as the concentrations of silver, chloride and pH were varied. Using a spectral deconvolution procedure, RhB was shown to be degraded both by de-ethylation and by destruction of the chromophore, with only minimal build-up of intermediate degradation products prior to chromophore destruction under most conditions.Complementary studies examing the production of hypochlorous acid (HOCl) in this system (in the absence of RhB) have also been performed and the reaction of RhB and HOCl examined. The reaction of RhB with HOCl led to the formation of chlorinated RhB species, which were not observed during photochemical reactions with AgCl(s). These results indicate that the hole-electron pairs formed in the primary photochemical process drive the oxidation of chloride ions to chlorine atoms, subsequently leading to HOCl production. However, in the presence of an oxidisable substrate, this reaction profile is apparently blocked, sugesting a competitive mechanism between RhB and chloride ion for oxidation, and the direct oxidation of RhB by photo-generated holes.The presence of oxygen facilitated the process greatly, with removal of oxygen considerably slowing the RhB photodegradation. This result suggests that oxygen was an effective sink for photo-formed electrons in the conduction band of AgCl(s), thereby enhancing hole-electron pair separation. Hydroxyl radical and hydrogen peroxide are also shown not to be implicated in RhB degradation.

Photocatalytic degradation of contaminants by colloidal AgCl(s): Kinetic and mechanistic insights

248th National Meeting (2014)

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