Photocatalytic degradation of dye naphthol blue black in the presence of zirconia-supported Ti-substituted Keggin-type polyoxometalates

Zirconia-supported Ti-substituted Keggin-type polyoxometalates, Li₅PW₁₁TiO₄₀/ZrO₂ (PW₁₁Ti/ZrO₂) and K₇PW₁₀Ti₂O₄₀/ZrO₂ (PW₁₀Ti₂/ZrO₂), were prepared by incorporating PW₁₁Ti and PW₁₀Ti₂ cluster into a zirconia matrix via a sol-gel technique. These insoluble and readily separable composites were characterized by DR-UV (DR: diffuse reflectance) and FT-IR spectra, MAS NMR, ICP-AES, and nitrogen adsorption determination, indicating that the clusters were chemically attached to the zirconia supports, and the primary Keggin structure remained intact. The photocatalytic activity of the supported PW₁₁Ti and PW₁₀Ti₂ was tested via degradation of an aqueous dye naphthol blue black (NBB). It indicated that the dye NBB can be degraded totally and mineralized into the inorganic products such as CO₂, NH₄⁺, NO₃⁻, and SO₄²⁻ ions by irradiating the composite slurry in the near-UV area. Dropped of PW₁₁Ti or PW₁₀Ti₂ cluster from the zirconia matrix into the reaction system was hardly observed during the photocatalytic tests, attributed to the strong chemical interactions between the Keggin units and the zirconia support.