Synthesis Parameters and Photocatalytic Activity of Titania Nanosheets

Two-dimensional TiO₂ nanosheets at large size are of importance in the electronic devices, but the synthesis is challenging. A few-layered titanate was prepared via high-temperature solid-state reaction with Cs₂CO₃ and anatase TiO₂ as precursors. The results show that the crystallinity of cesium titanate (Cs_0.7Ti_1.825O₄) as a solid reaction product is related to the several pretreatment parameters, i.e., mixing method for precursors, molar ratio of Cs/Ti, feeding amount, and calcination duration. A single phase of Cs_0.7Ti_1.825O₄ can be obtained by calcinating the precursor mixture. However, a mixed phase of rutile TiO₂ and Cs_0.7Ti_1.825O₄ is obtained when the precursors are mixed in solution. A product Cs_0.7Ti_1.825O₄ can be obtained at 800 ℃ in a molar ratio range of n(Cs)/n(Ti) of 1/(2.6–4.0). The crystallinity of cesium titanate improves with the increase of feeding amount of total precursors or calcination duration. After calcination, cesium titanate is treated using hydrochloric acid and the protonated product of H_0.7Ti_1.825O₄ is obtained. Also, few-layered titania nanosheets (Ti_0.91O₂) are obtained via exfoliation of the protonated product with amine-based macromolecules (TBAOH). The well-ordered lamellar structure of Ti_0.91O₂ is formed when the molar ratio between TBAOH ions to the exchangeable protons in the titanate is 0.5 (n(TBAOH)/n(H⁺)=0.5). Such a layered structure is annealed and used as a photocatalyst for hydrogen evolution in water under simulated solar light with ethanol as a sacrificial agent. The photocatalytic activity of the final product is related to the ratio of TBAOH/H⁺ during exfoliation, and it is indicated that the product obtained at TBAOH/H⁺ of 0.5 exhibits the optimum hydrogen evolution activity.