Flux Synthesis, Optical and Photocatalytic Properties of n-type Sn2TiO4: Hydrogen and Oxygen Evolution under Visible Light

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• 作者：Jonathan Boltersdorf ; Ian Sullivan ; Timothy L. Shelton ; Zongkai Wu ; Matthew Gray ; Brandon Zoellner ; Frank E. OsterlohPaul A. Maggard
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：December 27, 2016
• 年：2016
• 卷：28
• 期：24
• 页码：8876-8889
• 全文大小：910K
• ISSN：1520-5002

文摘

The n-type Sn₂TiO₄ phase was synthesized using flux methods and found to have one of the smallest visible-light bandgap sizes known that also maintains suitable conduction and valence band energies for driving photocatalytic water-splitting reactions. The Sn₂TiO₄ phase was synthesized using either a SnCl₂ flux or a SnCl₂/SnF₂ peritectic flux in a 2:1 flux-to-precursor ratio heated at 600 and 400 °C for 24 h, respectively. The two types of salt fluxes resulted in large rod-shaped particles at 600 °C and smaller tetragonal prism-shaped particles at 400 °C. Surface photovoltage spectroscopy measurements produced a negative photovoltage under illumination >1.50 eV, which confirmed electrons as the majority charge carriers and ∼1.50 eV as the effective band gap. Mott–Schottky measurements at pH 9.0 showed the conduction (−0.54 V vs NHE) and valence band (+1.01 V vs NHE) positions meet the critical thermodynamic requirements for total water splitting. The Sn₂TiO₄ particles were deposited and annealed as polycrystalline films on FTO slides, and exhibited photoanodic currents in aqueous solutions under visible-light irradiation. The Sn₂TiO₄ particles were also suspended in aqueous methanol solutions and irradiated with visible and ultraviolet light. The larger rod-shaped Sn₂TiO₄ particles had the higher rates of photocatalytic hydrogen production (∼11.6 μmol H₂ h^–1) in comparison to the smaller tetragonal prism-shaped Sn₂TiO₄ particles (∼3.4 μmol H₂ h^–1). Conversely, for photocatalytic oxygen production, the rates for the smaller tetragonal prism-shaped particles in aqueous AgNO₃ solution were slightly higher (∼16.3 μmol O₂ h^–1) than for the larger rod-shaped particles (∼11.9 μmol O₂ h^–1). Apparent quantum yields of 0.995% and 0.0098% were measured for O₂ and H₂ production, respectively, under 435 nm light.