Organohalide Precursors for the Continuous Production of Photocatalytic Bismuth Oxyhalide Nanoplates

Abstract

Metal heteroanionic materials, such as oxyhalides, are promising photocatalysts in which band positions can be engineered for visible-light absorption by changing the halide identity. Advancing the synthesis of these materials, bismuth oxyhalides of the form BiOX (X = Cl, Br) have been prepared using rapid and scalable ultrasonic spray synthesis (USS). Central to this advance was the identification of small organohalide molecules as halide sources. When these precursors are spatially and temporally confined in the aerosol phase with molten salt fluxes, powders composed of single-crystalline BiOX nanoplates can be produced continuously. A mechanism highlighting the in situ generation of halide ions is proposed. These materials can be used as photocatalysts and provide proof-of-concept toward USS as a route to more complex bismuth oxyhalide materials.

Sustainable Production of Layered Bismuth Oxyhalides for Photocatalytic H2 Production

“…The photocatalytic activity of the resultant BiOCl was found to be proportional to the percentage of {001} exposure on the particle surface. Recently, our group demonstrated rapid and scalable ultrasonic spray synthesis of BiOX (X = Cl, Br) using molecular precursors (Figure a) . We identified a bismuth lactate complex and organohalide molecules as water-soluble bismuth and halide sources, respectively.…”

“…A representative transmission electron micrograph of a resulting single-crystalline BiOCl particle is shown. Reproduced with permission from ref . Copyright 2020, American Chemical Society.…”

“…Suitable Gibbs adsorption energies of H atoms (Δ G H ) can also lead to efficient PHE . In particular, 1 wt % Pt was observed to be a good cocatalyst as it minimized the charge carrier recombination rate and provided an ideal surface for HER reactions. ,− In addition, cocatalysts can prevent photocorrosion of materials by timely consumption of photogenerated charges . Noble metals, however, are not earth abundant and are costly, leading to sustainability concerns.…”

Durable Metal Heteroanionic Photocatalysts

“…Metal oxyhalides of the type BiOX (X = Cl, Br, I) have gained significant interest owing to their ability to change the bandgap based on the halide identity. , With the increase in size of the halogen ion, the polarizability increases from Cl to I, which is associated with greater visible light absorption. , These materials consist of [Bi 2 O 2 ] +2 layers between double slabs of X – atoms. The stacking of oppositely charged layers leads to an internal electric field (IEF) within the crystal structure. − The built-up IEF facilitates separation of e – and h + when illuminated by photons of appropriate energy. , Density functional theory (DFT) calculations on BiOX photocatalysts illustrate that the VB consists primarily of hybrid O 2p and X n p orbitals, whereas the CB consists of Bi 6p orbitals .…”

“…49,51−53 Metal oxyhalides of the type BiOX (X = Cl, Br, I) have gained significant interest owing to their ability to change the bandgap based on the halide identity. 54,55 With the increase in size of the halogen ion, the polarizability increases from Cl to I, which is associated with greater visible light absorption. 50,56 These materials consist of [Bi 2 O 2 ] +2 layers between double slabs of X − atoms.…”