Recent advances in designing and developing efficient sillenite-based materials for photocatalytic applications

Sillenite materials have been the subject of intense investigation for recent years due to their unique characteristics. They possess a distinct structure with space group I23, allowing them to exhibit distinctive features, such as an electronic structure ideal for certain applications such as photocatalysis. The present research delves into the structure, synthesis, and properties of sillenites, highlighting their suitability for photocatalysis. It explores also advanced engineering strategies for designing sillenite-based photocatalysts, including heterojunction formation, morphology modification, doping, and hybrid processes. Each strategy offers advantages and limitations that are critically discussed. The review then lists and discusses the photocatalytic performance of various sillenite-based systems recently developed for common applications, such as removing hazardous organic and inorganic contaminants, and even infrequent applications, such as microbial inactivation, H2 generation, CO2 reduction and N2 fixation. Finally, valuable insights and suggestions are put forward for future research directions in the field of sillenite-based photocatalysis. This comprehensive overview would provide a valuable resource for the development of efficient photocatalytic systems to address environmental and energy challenges.

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.

Brief Theoretical Overview of Bi-Fe-O Based Thin Films

This paper will provide a brief overview of the unique multiferroic material Bismuth ferrite (BFO). Considering that Bismuth ferrite is a unique material which possesses both ferroelectric and magnetic properties at room temperature, the uniqueness of Bismuth ferrite material will be discussed. Fundamental properties of the material including electrical and ferromagnetic properties also will be mentioned in this paper. Electrical properties include characterization of basic parameters considering the electrical resistivity and leakage current. Ferromagnetic properties involve the description of magnetic hysteresis characterization. Bismuth ferrite can be fabricated in a different form. The common forms will be mentioned and include powder, thin films and nanostructures. The most popular method of producing thin films based on BFO materials will be described and compared. Finally, the perspectives and potential applications of the material will be highlighted.

Electrocatalytic performance of Sb-modified Bi25FeO40 for nitrogen fixation

The Haber-Bosch N₂ fixation method suffers from the power-consuming and harsh conditions. In contrast, the electrochemical conversion of N₂ (NRR) at room temperature and atmospheric pressure is considered a promising alternative route. In this study, we synthesized Sb-modified with Bi₂₅FeO₄₀ (BFSO/BFO) by using one-step hydrothermal treatment. The BFSO/BFO catalyst has higher selectivity to NRR than Bi₂₅FeO₄₀ (BFO) under the same applied voltage. Such large interfacial interaction area plays a critical role in transfer electron and enhances the density of current. The resulting BFSO/BFO heterojunction showed significant electrocatalytic activity under controllable voltage, which exhibited favorable average ammonia (NH₃) yield as high as 2.62 μg·h^-1·cm^-2 at -0.2 V versus RHE. Moreover, the stability of the BFSO/BFO composite was evaluated for six cycles and the results were desirable. This study provides a new insight into the design of composite catalysts using BFO, which has high activity and selectivity toward NRR.

Growth of sillenite Bi12FeO20 single crystals: structural, thermal, optical, photocatalytic features and first principle calculations

Ideal sillenite type Bi₁₂FeO₂₀ (BFO) micron sized single crystals have been successfully grown via inexpensive hydrothermal method. The refined single crystal X-ray diffraction data reveals cubic Bi₁₂FeO₂₀ structure with single crystal parameters. Occurrence of rare Fe⁴⁺ state is identified via X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The lattice parameter (a) and corresponding molar volume (V_m) of Bi₁₂FeO₂₀ have been measured in the temperature range of 30–700 °C by the X-ray diffraction method. The thermal expansion coefficient (α) 3.93 × 10^–5 K⁻¹ was calculated from the measured values of the parameters. Electronic structure and density of states are investigated by first principle calculations. Photoelectrochemical measurements on single crystals with bandgap of 2 eV reveal significant photo response. The photoactivity of as grown crystals were further investigated by degrading organic effluents such as Methylene blue (MB) and Congo red (CR) under natural sunlight. BFO showed photodegradation efficiency about 74.23% and 32.10% for degrading MB and CR respectively. Interesting morphology and microstructure of pointed spearhead like BFO crystals provide a new insight in designing and synthesizing multifunctional single crystals.

Bismuth-iron-based precursor: preparation, phase composition, and two methods of thermal treatment

Bismuth ferrite (BiFeO₃) is a promising Bi-based perovskite-type material, which is multiferroic due to the coexistence of anti-ferromagnetism and ferroelectricity. During the preparation of pure BiFeO₃ nanoparticles, however, the phase structures and species of bismuth–iron-based precursor (BFOH) were still unclear, and so related precursors were prepared. X-ray diffraction, Raman, Fourier transform infrared, and X-ray absorption near-edge structure techniques were used to probe the phase structure and species of the precursors. It was found that the precursor BFOH is composed of Bi₆O₆(NO₃)₄(OH)₂·2H₂O, Bi₆O₅(NO₃)₅(OH)₃·3H₂O, Fe(OH)₃, and α-Bi₂O₃. Calcination treatment and hydrothermal synthesis were used to prepare the pure BiFeO₃ phase from the precursor BFOH. The calcination temperature was optimized as 400 °C for preparation of the pure BiFeO₃ phase. Meanwhile, hydrothermal conditions for the synthesis of the pure BiFeO₃ phase were also optimized as follows: the reaction solution was the mixture solution of Bi(NO₃)₃·5H₂O and Fe(NO₃)₃·9H₂O with cetyltrimethyl ammonium bromide (CTAB) as the surfactant and KOH as the mineralizer; the hydrothermal synthesis was performed at 180 °C for 48 h; the concentration of KOH should be at least 3 M; and the surfactant CTAB can be used to regulate the morphology of the as-prepared BiFeO₃ nanoparticles. From the point of view of the microstructure, BiFeO₃ nanoparticles prepared by calcination or hydrothermal methods have no notable differences. A formation mechanism from the precursor BFOH to the BiFeO₃ product is proposed. By providing an understanding of the precursors, this work is very helpful in the synthesis of bismuth–iron-based nanoparticles.

Preparation and phase composition study of bismuth–iron-based precursor, and its thermal treatment by calcination and hydrothermal processes, which can be used to control the synthesis of pure BiFeO₃.

Removal of Nonylphenol by using Fe-doped NaBiO3 compound as an efficient visible-light-heterogeneous Fenton-like catalyst

Fe-doped NaBiO₃ nanoscaled compounds were prepared by hydrothermal method and evaluated as a highly efficient photo-Fenton-like catalyst under visible light irradiation. The Fe-doped NaBiO₃ compound had a specific surface area of 41.42 m² g^-1, which is considerably larger than that of NaBiO₃ nanoparticles (28.81 m² g^-1). The compound exhibited an excellent visible light-Fenton-like catalysis activity, which is influenced by the iron content of the compound and the pH value of the solution. Under the optimal conditions, the Fe-doped NaBiO₃ compound led to fast degradation of Nonylphenol with an apparent rate constant of 5.71 × 10^-2 min^-1, which was 8.23-fold of that achieved by using NaBiO₃. The significantly enhanced visible light-Fenton-like catalytic property of the Fe-doped NaBiO₃ was attributed to the large surface area and the high adsorption capacity of the compound, and the Fenton catalytic ability of iron in the compound.

Construction of Spatial Charge Separation Facets on BaTaO2N Crystals by Flux Growth Approach for Visible-Light-Driven H2 Production

Low charge separation efficiencies are regarded as obstacles that limit the improvement in the photocatalytic performance of BaTaO₂N. In this study, we demonstrated that the anisotropic facets ({100} and {110} facets) of BaTaO₂N for efficient spatial charge separation were successfully constructed using the one-pot flux-assisted nitridation approach. As a result, the photocatalytic activity for H₂ production on BaTaO₂N with coexposed {100} and {110} facets was nearly 10-fold over that of BaTaO₂N with only {100} facets and that of the conventional irregularly shaped sample. This finding provides an innovative approach to the development of efficient (oxy)nitride photocatalysts for solar energy conversion.

A facile coordination precipitation route to prepare porous CuO microspheres with excellent photo-Fenton catalytic activity and electrochemical performance

Porous CuO microspheres were prepared via a coordination precipitation route and exhibited superior photocatalytic activity and electrochemical performance.

Shape-Controlled Synthesis of Metal-Organic Frameworks with Adjustable Fenton-Like Catalytic Activity

Controllable synthesis of metal-organic frameworks with well-defined morphology, composition, and size is of great importance toward understanding their structure-property relationship in various applications. Herein, we demonstrate a general strategy to modulate the relative growth rate of the secondary building units (SBUs) along different crystal facets for the synthesis of Fe-Co, Mn_0.5Fe_0.5-Co, and Mn-Co Prussian blue analogues (PBAs) with tunable morphologies. The same growth rate of SBUs along the {100}, {110}, and {111} surfaces at 0 °C results in the formation of spherical PBA particles, while the lowest growth rate of SBUs along the {100} surface resulting from the highest surface energy with increasing reaction temperature induces the formation of PBA cubes. Fenton reaction was used as the model reaction to probe the structure-catalytic activity relation for the as-synthesized catalysts. The cubic Fe-Co PBA was found to exhibit the best catalytic performance with reaction rate constant 6 times higher than that of the spherical counterpart. Via density functional theory calculations, the abundant enclosed {100} facets in cubic Fe-Co PBA were identified to have the highest surface energy and favor high Fenton reaction activity.

Enhanced photocatalytic dye degradation and hydrogen production ability of Bi25FeO40-rGO nanocomposite and mechanism insight

A comprehensive comparison between BiFeO3-reduced graphene oxide (rGO) nanocomposite and Bi25FeO40-rGO nanocomposite has been performed to investigate their photocatalytic abilities in degradation of Rhodamine B dye and generation of hydrogen by water-splitting. The hydrothermal technique adapted for synthesis of the nanocomposites provides a versatile temperature-controlled phase selection between perovskite BiFeO3 and sillenite Bi25FeO40. Both perovskite and sillenite structured nanocomposites are stable and exhibit considerably higher photocatalytic ability over pure BiFeO3 nanoparticles and commercially available Degussa P25 titania. Notably, Bi25FeO40-rGO nanocomposite has demonstrated superior photocatalytic ability and stability under visible light irradiation than that of BiFeO3-rGO nanocomposite. The possible mechanism behind the superior photocatalytic performance of Bi25FeO40-rGO nanocomposite has been critically discussed.