Topotactic Transformation of Zeolite Supported Cobalt(II) Hydroxide to Oxide and Comparison of Photocatalytic Oxygen Evolution

A synthesis method that results in similar to 180 nm plate-like crystallites of beta-(Co(OH)(2) anchored on the surface of zeolite Y particles is reported. These crystals of beta-Co(OH)(2) are transformed to Co3O4 by thermal treatment without a change in morphology. Characterization of the cobalt phases and the transformation was carried out by powder X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and electron microscopy. These cobalt-based materials provide an opportunity to contrast their photocatalytic activity. Using the Ru(bpy)(3)(2+) persulfate system, the oxidation of water to oxygen was measured. The most active catalyst was beta-(Co(OH)(2), and with transformation to Co3O4, the catalytic activity declined, suggesting that beta-Co(OH)(2) is a better photocatalyst than Co3O4. The photocatalytic activity of the beta-(Co(OH)(2)/zeolite decreased during a second photocatalytic cycle, due to surface transformation to Co3O4, though the bulk of the catalyst still maintains the brucite-like beta-Co(OH)(2) structure. This is the first report on how catalytic activity is altered in the cobalt oxide system by phase transformation, keeping morphological features unchanged.