Molecular recognitive photocatalysis driven by the selective adsorption on layered titanates

The composition of layered alkali titanates (M_xTi _2-x/3Li_x/3O₄; M = K⁺, Li⁺ Na⁺) was tuned to control the swelling of the titanates in water and subsequently achieve molecular-sieve-like molecular recognitive photocatalytic decomposition of aqueous organic compounds on the titanates. Layered potassium lithium titanates with different layer charge density, K_xTi _2-x/3Li_x/3O₄ (x = 0.61, 0.67, and 0.74), was first synthesized and then the interlayer K⁺ was quantitatively exchanged with Li⁺ and Na⁺ to form Li_xTi _2x-/3- Li_x/3O₄ (X= 0.61, 0.67, and 0.76) and Na_xTi_2-x/3Li_x/3O₄ 0.61, 0.67, and 0.76). The water adsorption/ desorption isotherms and X-ray diffraction patterns of the titanates revealed that the pristine K-type titanates hardly hydrated, while the Li⁺- and Na⁺-exchanged titanates expanded the interlayer space upon the hydration and the degree in the hydration was larger for the Na forms than for the Li ones and depended on the layer charge density. The present titanates were found to selectively adsorb benzene from an aqueous mixture of benzene, phenol, and 4-butylphenol and subsequently decompose benzene upon UV irradiation. The efficiency of the molecular recognitive photocatalytic benzene decomposition was related to the degree in the swelling of the titanates in water.