Immobilization of Palladium Phthalocyaninesulfonate onto Anionic Clay for Sorption and Oxidation of 2,4,6-Trichlorophenol under Visible Light Irradiation

Layered double hydroxide (LDH) and dodecyl sulfonate-intercalated layered double hydroxide (SDS-LDH) with an Mg/Al ratio of 3.0 were studied as a support of anionic photosensitizer, palladium phthalocyaninesulfonate (PdPcS). The composite clays were synthesized by two different routes: (i) PdPcS intercalation into the clay galleries via direct coprecipitation and (ii) PdPcS adsorption on the clay external surface via ion exchange. Under visible light irradiation (λ > 450 nm), all the PdPcS-containing solids were effective for the sensitized oxidation of 2,4,6-trichlorophenol (TCP) in an aerated aqueous solution. But the reaction efficiency was notably different from one catalyst to another, because of different location and arrangement of the immobilized PdPcS. Among the samples studied, the highest activity was observed with the immobilized PdPcS in the SDS-LDH interlayers, where the sorbed TCP is located via partition mechanism. It was further observed that the reaction rate increased with the initial amount of TCP adsorption and with the amount of PdPcS (0.4−2.2 wt %) present in the clay. Recycling experiments demonstrated that the composite clay was relatively stable and could be repeatedly used for TCP removal only with visible light and molecular oxygen.