Surface-bound sulfate radical-dominated degradation of 1,4-dioxane by alumina-supported palladium (Pd/Al2O3) catalyzed peroxymonosulfate.

Sulfate radicals have been demonstrated as an alternative to hydroxyl radicals in advanced oxidation processes. Unfortunately, the efficient activation of peroxymonosulfate (PMS), one of the most commonly used oxidants for the generation of sulfate radicals, still relies heavily on cobalt-bearing materials that are potential carcinogens. Although copper-iron bimetallic materials are promising activators, stoichiometric amounts of metals are required to achieve satisfactory performance. In this study, we propose a real catalytic process that is capable of degrading extremely recalcitrant 1,4-dioxane using a combination of alumina-supported metallic palladium (Pd/Al2O3) with PMS. The metal loading-normalized pseudo-first-order constant for 1,4-dioxane degradation with Pd/Al2O3 was more than 16,800 times that with copper-iron bimetallic materials. Complementary to Fenton reagents, Pd/Al2O3-PMS had a wide effective pH range from 4.0 to 8.5. In the absence of a substrate, PMS underwent more rapid decomposition under all conditions investigated, which suggests that its activation did not likely proceed via the previously proposed non-radical mechanism. On the basis of the strong inhibitory effects of common scavengers, we instead propose that surface-bound sulfate radicals were probably the dominant active species. A near-100% conversion rate of PMS to radicals was achieved with the Pd/Al2O3 catalyst.