Single Unit-Cell Layered Bi2 Fe4 O9 Nanosheets: Synthesis, Formation Mechanism, and Anisotropic Thermal Expansion

As an important multiferroic material, pure and low-dimensional phase-stable bismuth ferrite has wide applications. Herein, one-pot hydrothermal method was used to synthesize bismuth ferrite. Almost pure Bi₂ Fe₄ O₉ , BiFeO₃ , and their mixture were successfully obtained by controlling the KOH concentration in the hydrothermal solutions. The as-prepared Bi₂ Fe₄ O₉ products were crystalline with Pbam space group, had nanosheet morphology, and tended to aggregate into nanofloret or random stacking. Each Bi₂ Fe₄ O₉ nanosheet was a single crystal with (001) plane as its exposed surface. Single unit-cell layered Bi₂ Fe₄ O₉ nanosheets had a uniform thickness of 1 nm. The surface energies of various (100), (010), and (001) planes were 3.6-4.0, 5.6-15.1, and 1.7-3.0 J m^-2 , respectively, in the Bi₂ Fe₄ O₉ crystal. The formation mechanism and structural model of the as-prepared single unit-cell layered Bi₂ Fe₄ O₉ nanosheets have been given. The growth of Bi₂ Fe₄ O₉ nanosheets was discussed. Thermal analysis showed that the Bi₂ Fe₄ O₉ phase was stable up to 1260 K. The thermal expansion behavior of the Bi₂ Fe₄ O₉ nanosheet was nonlinear. The thermal expansion coefficients of the ultrathin Bi₂ Fe₄ O₉ nanosheets on the a-, b-, c-axes, and on the unit-cell volume V were determined, showing an anisotropic thermal expansion behavior. This study is helpful for the controllable synthesis of ultrathin Bi₂ Fe₄ O₉ nanosheets.

Photocatalytic degradation of 1,4-dioxane using liquid phase plasma on visible light photocatalysts

The compound 1,4-dioxane (DO) irritates the eyes, skin, and mucous membrane and is classified as a carcinogen. In this study, the decomposition of DO by photocatalytic reaction using liquid phase plasma (LPP) with photocatalyst was suggested. Plasma was directly discharged as an aqueous DO solution to enhance photocatalytic decomposition activity. To increase the decomposition efficiency of DO by plasma, bismuth ferrite (BFO) prepared by a sol-gel method was introduced as a visible-light photocatalyst. In the application of LPP and BFO photocatalyst, the decomposition of DO by photocatalytic reaction was evaluated. BFO showed UV-vis diffusion reflectance spectroscopy results of absorption of UV and visible light over 600 nm, with a bandgap of approximately 2.2 eV. BFO showed visible light photochemical reaction characteristics to decompose particulate matter (PM) in the irradiation of 6 W visible light LED lamps. It seems that the narrow bandgap of BFO led to the photocatalytic activity in the visible light. In the decomposition reaction of DO with a photocatalyst and LPP, BFO showed better decomposition efficiency than TiO₂. BFO can cause photocatalytic reactions in both UV and visible light in the case of LPP irradiation, which emits strong ultraviolet and visible light.

Construction of Z-Scheme g-C₃N₄/CNT/Bi₂Fe₄O₉ Composites with Improved Simulated-Sunlight Photocatalytic Activity for the Dye Degradation

In this work, ternary all-solid-state Z-scheme g-C₃N₄/carbon nanotubes/Bi₂Fe₄O₉ (g-C₃N₄/CNT/BFO) composites with enhanced photocatalytic activity were prepared by a hydrothermal method. The morphology observation shows that ternary heterojunctions are formed in the g-C₃N₄/CNT/BFO composites. The photocatalytic activity of the samples for the degradation of acid orange 7 was investigated under simulated sunlight irradiation. It was found that the ternary composites exhibit remarkable enhanced photocatalytic activity when compared with bare BFO and g-C₃N₄/BFO composites. The effect of the CNT content on the photocatalytic performance of the ternary composites was investigated. The photocatalytic mechanism of g-C₃N₄/CNT/BFO was proposed according to the photoelectrochemical measurement, photoluminescence, active species trapping experiment and energy-band potential analysis. The results reveal that the introduction of CNT as an excellent solid electron mediator into the ternary composites can effectively accelerate the electron migration between BFO and g-C₃N₄. This charge transfer process results in highly-efficient separation of photogenerated charges, thus leading to greatly enhanced photocatalytic activity of g-C₃N₄/CNT/BFO composites. Furthermore, the g-C₃N₄/CNT/BFO composites also exhibit highly-efficient photo-Fenton-like catalysis property.

Visible-Light-Mediated Electrocatalytic Activity in Reduced Graphene Oxide-Supported Bismuth Ferrite

Reduced graphene oxide (RGO)-supported bismuth ferrite (BiFeO₃) (RGO-BFO) nanocomposite is synthesized via a two-step chemical route for photoelectrochemical (PEC) water splitting and photocatalytic dye degradation. The detailed structural analysis, chemical coupling, and morphology of BFO- and RGO-supported BFO are established through X-ray diffraction, Raman and X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy studies. The modified band structure in RGO-BFO is obtained from the UV-vis spectroscopy study and supported by density functional theory (DFT). The photocatalytic degradation of Rhodamine B dye achieved under 120 min visible-light illumination is 94% by the RGO-BFO composite with a degradation rate of 1.86 × 10^-2 min^-1, which is 3.8 times faster than the BFO nanoparticles. The chemical oxygen demand (COD) study further confirmed the mineralization of an organic dye in presence of the RGO-BFO catalyst. The RGO-BFO composite shows excellent PEC performance toward water splitting, with a photocurrent density of 10.2 mA·cm^-2, a solar-to-hydrogen conversion efficiency of 3.3%, and a hole injection efficiency of 98% at 1 V (vs Ag/AgCl). The enhanced catalytic activity of RGO-BFO is explained on the basis of the modified band structure and chemical coupling between BFO and RGO, leading to the fast charge transport through the interfacial layers, hindering the recombination of the photogenerated electron-hole pair and ensuring the availability of free charge carriers to assist the catalytic activity.

Single-crystalline Bi2Fe4O9 synthesized by low-temperature co-precipitation: performance as photo- and Fenton catalysts

A multi-functional self-assembled (001) Bi₂Fe₄O₉ nanopad was firstly synthesized by co-precipitation at 95 °C, which can drive hybrid advanced oxidation processes (HAOPs) under visible-light irradiation for the efficient degradation of bisphenol A.

Photocatalytic mechanism of Bi2Fe4O9 nanoparticles in the degradation of methylene blue

We have investigated the effects of O2, ethanol, and KI on the photocatalytic efficiency of Bi2Fe4O9 nanoparticles towards the degradation of methylene blue (MB). It is observed that O2 has a negligible effect on the photocatalytic degradation rate of the dye, whereas ethanol and KI exhibit a strong suppression of the dye degradation, with a stronger effect observed for the latter. Hydroxyl radicals are shown, by the photoluminescence technique using coumarin as a probe molecule, to be produced on the irradiated Bi2Fe4O9, and are scavenged on addition of ethanol and KI. The mechanisms involved are discussed in detail. Based on the experimental results, hydroxyl radicals and photogenerated holes are suggested to be the two main active species in the photocatalytic degradation of MB by Bi2Fe4O9 nanoparticles.