Band Gap Engineering in Quadruple-Layered Sillén–Aurivillius Perovskite Oxychlorides Bi7Fe2Ti2O17X (X = Cl, Br, I) for Enhanced Photocatalytic Performance

Abstract

Developing efficient photocatalyst for the photoreduction of CO2 and degradation of organic pollutants is an effective alternative to address increasingly serious energy problems and environmental pollution. Herein, the isostructural Sillén–Aurivillius oxyhalides, Bi7Fe2Ti2O17X (X = Cl, Br, and I; BFTOX), are fabricated for CO2 reduction and degradation of organic pollutants for the first time. Density functional theory (DFT) calculations show that the valence band maximum (VBM) of BFTOC and BFTOB is contributed by the dispersive 2p orbitals of O-atoms, providing the narrow band gap (Eg) and possibly the stability against self-decomposition deactivation. The photocatalytic activities of BFTOX are strongly affected by the halogens (Cl, Br, and I), namely, the BFTOCl sample displays outstanding activity improvement (3.74 μmol·g−1·h−1) for photocatalytic performance. This is mainly attributed to the high separation of charge carriers, small optical band gap, and extended optical absorption. This work focuses on affording a reference to develop efficient and stable photocatalysts from Sillén-Aurivillius layered oxyhalide materials.

New insights into the synthesis of Sillén–Aurivillius oxyhalides: molten salts induce interlayer halogen competing reaction

“…5a, the absorption edges of all the BaBi 4 TiNbO 11 X samples are approximately 460 nm, indicating that the BaBi 4 TiNbO 11 X oxyhalide is a type of visible light photocatalyst and halogen substitution (from Cl to Br) has little effect on its light absorption. To better compare the E g values of the samples with different halogen contents, the conventional Kubelka–Munk function was applied to the BaBi 4 TiNbO 11 X oxyhalides, as follows: 9,30,46 ( α ℏ ν ) 1/ m = A (ℏ ν − E g )where ℏ, α , and ν are the Planck constant, absorption coefficient, and light frequency, respectively. The m value of the samples was correlated with the transition properties of the semiconductor materials.…”

“…In this experiment, BiOX (X = Cl, Br) precursors were prepared via a chemical deposition process at room temperature with the precursor materials of KX (X = Cl, Br) and Bi(NO 3 )·5H 2 O, and more details about this process can be found in our previous works. 9,23,30 Then, BiOX (X = Cl, Br) and BaCO 3 were mixed in the stoichiometric ratio of 1 : 1 to prepare the BaBiO 2 X precursor at 700 °C for 10 h by the traditional SSR method.…”

“…In addition, the electrochemical workstation was also employed for the electrochemical and photoelectrochemical measurements of the BaBi 4 TiNbO 11 X oxyhalides, as described in the previous studies. 9,22,31…”

“…In this case, one promising method to extend its light absorption is narrowing the E g values of semiconductors. 9,10 In general, this often causes a mismatch between the band energy position and the redox potential of the target substances, which will weaken the reaction driving force of semiconductors. Therefore, it is of great research value to explore new visible light catalysts.…”

Bismuth-Based Z-Scheme Heterojunction Photocatalysts for Remediation of Contaminated Water

“…Recently, bismuth-based Sillen-Aurivillius structures such as Bi 4 NbO 8 Cl, Bi 4 Ti 0.5 W 0.5 O 8 Cl, Bi 7 Fe 2 Ti 2 O 17 X (X = Cl, Br, I) have been reported for photocatalysis. Due to the small band gap, ferroelectric property, ionic conductivity, layered crystal structure, and stability, they are efficient for the degradation of organic pollutants . The presence of ferroelectricity can have both direct and indirect effects on photocatalytic activity.…”