A review on bismuth-based nanocomposites for energy and environmental applications

Bismuth, a heavy metal which is found to be inexpensive and at a reduced cost, is utilized in the synthesis of different nanomaterials with novel structure, remarkable physical and chemical properties, adjustable bandgap, notable efficiency for photothermal conversion. These characteristics have made this element desirable for various applications such as storage and conversion of energy, electronics, sensors, photocatalysis, and other biomedical applications. These review papers are the vital points for the students, this report guides them to the research papers which focus on the impressive development in the area of bismuth and similar nanostructures. The purpose of the present review is to discuss the various synthesis routes of bismuth-based nanomaterials along with green synthesis, different nanostructures of bismuth, their significant properties, diverse applications and directions for the upcoming research. Therefore, with these different tuneable synthesis methods of bismuth-based nanomaterials combined with their novel properties, would elucidate on the future devices based on various nanostructures of bismuth.

Promoting optoelectronic properties of Cs2AgBiBr6 nanocrystals by formation of heterostructures with BiOCl nanosheets

Lead halide perovskite nanocrystals and their heterostructures have achieved substantial advances in optoelectronics; however, their inherent material instability and lead toxicity have driven research on alternative material systems. Herein, solution-processable heterostructures composed of lead-free double perovskite Cs₂AgBiBr₆ nanocrystals and BiOCl nanosheets were prepared through a colloidal synthesis method. Defect states were present in BiOCl and benefited carrier generation, recombination and transport in Cs₂AgBiBr₆. As a result, the light emission of the Cs₂AgBiBr₆ nanocrystals was greatly enhanced at low temperatures, and the photodetector based on the Cs₂AgBiBr₆/BiOCl heterostructure exhibited a much improved on-off ratio compared to the device based on Cs₂AgBiBr₆ alone. Our work highlights the complex nature and impact of two-dimensional heterostructure assembly on the optoelectronic properties of lead-free double perovskites and demonstrates their great potential toward environmentally friendly optoelectronic devices.

Oxygen-vacancy-rich BiOCl materials with ultrahigh photocatalytic efficiency by etching bismuth glass

Bismuth oxychloride (BiOCl) is a promising photocatalyst material for water purification to remove organic pollutants. However, BiOCl materials can only degrade pollutants under ultraviolet-light owing to their wide band gap. Herein, we propose a simple synthesis route based on Bi₂O₃–B₂O₃–ZnO–SrO–Na₂O (BBZSN) glass to fabricate 3D hierarchical-structured BiOCl materials with rich oxygen vacancies (OVs), which were introduced from BBZSN glass and inhibited the recombination of electron–hole pairs and adjusted the band structure. The photocatalytic activity of the obtained 3D hierarchical-structured BiOCl photocatalyst was evaluated by the degradation of Rhodamine B (RhB) under ultraviolet light and visible light. The experimental results suggested that the as-fabricated flower-shape BiOCl–NaCl could effectively degrade RhB under ultraviolet light (92.7%/20 min) or visible light (71.4%/20 min, 92.8%/100 min) respectively, which indicates its potential to be applied in environmental remediation.

(a) EPR spectra of (a) the as-prepared BiOCl samples under dark, (b) BBZSN and Intermediate Bi₂O(OH)₂SO₄ under dark, (c) BiOCl–NaCl under dark and ultraviolet light and (d) the as-prepared BiOCl samples under ultraviolet light.

Bismuth-Based Photocatalysts for Solar Photocatalytic Carbon Dioxide Conversion

Photocatalytic CO₂ conversion into solar fuels is an effective means for simultaneously solving both the greenhouse effect and energy crisis. In the past ten years, bismuth-based photocatalysts for environmental remediation have experienced a golden period of development. However, solar photocatalytic CO₂ conversion has only been developed over the past five years and, until now, no reviews have been published on bismuth-based photocatalysts for the photocatalytic conversion of CO₂ . For the first time, solar photocatalytic CO₂ conversion systems are reviewed herein. Synthetic methods and photocatalytic CO₂ performances of bismuth-based photocatalysts, including Sillén-structured BiOX (X=Cl, Br, I); Aurivillius-structured Bi₂ MO₆ (M=Mo, W); and Scheelite-structured BiVO₄ , Bi₂ S₃ , BiYO₃ , and BiOIO₃ , are summarized. In addition, activity-enhancing strategies for this photocatalyst family, including oxygen vacancies, bismuth-rich strategy, facet control, conventional type II heterojunction, Z-scheme heterojunction, and cocatalyst deposition, are reviewed. Finally, the main mechanistic research methods, such as in situ FTIR spectroscopy and theoretical calculations, are presented. Challenges and research trends reported in studies of bismuth-based photocatalysts for photocatalytic CO₂ conversion are discussed and summarized.

F–Bi4TaO8Cl flower-like hierarchical structures: controlled preparation, formation mechanism and visible photocatalytic hydrogen production

Hydrothermal method was employed to prepare the flower-like hierarchical structures of F–Bi₄TaO₈Cl for photocatalytic hydrogen production under visible light irradiation.

NIR-driven water splitting by layered bismuth oxyhalide sheets for effective photodynamic therapy

Two major issues of finding the appropriate photosensitizer and raising the penetration depth of irradiation light exist in further developing of photodynamic therapy (PDT).

Hydrothermal synthesis of novel BiFeO3/BiVO4 heterojunctions with enhanced photocatalytic activities under visible light irradiation

BiFeO₃/BiVO₄ heterojunction photocatalysts were synthesized by a hydrothermal method.

Graphitic carbon nitride based nanocomposites: a review

Graphitic carbon nitride (g-C(3)N(4)), as an intriguing earth-abundant visible light photocatalyst, possesses a unique two-dimensional structure, excellent chemical stability and tunable electronic structure. Pure g-C(3)N(4) suffers from rapid recombination of photo-generated electron-hole pairs resulting in low photocatalytic activity. Because of the unique electronic structure, the g-C(3)N(4) could act as an eminent candidate for coupling with various functional materials to enhance the performance. According to the discrepancies in the photocatalytic mechanism and process, six primary systems of g-C(3)N(4)-based nanocomposites can be classified and summarized: namely, the g-C(3)N(4) based metal-free heterojunction, the g-C(3)N(4)/single metal oxide (metal sulfide) heterojunction, g-C(3)N(4)/composite oxide, the g-C(3)N(4)/halide heterojunction, g-C(3)N(4)/noble metal heterostructures, and the g-C(3)N(4) based complex system. Apart from the depiction of the fabrication methods, heterojunction structure and multifunctional application of the g-C(3)N(4)-based nanocomposites, we emphasize and elaborate on the underlying mechanisms in the photocatalytic activity enhancement of g-C(3)N(4)-based nanocomposites. The unique functions of the p-n junction (semiconductor/semiconductor heterostructures), the Schottky junction (metal/semiconductor heterostructures), the surface plasmon resonance (SPR) effect, photosensitization, superconductivity, etc. are utilized in the photocatalytic processes. Furthermore, the enhanced performance of g-C(3)N(4)-based nanocomposites has been widely employed in environmental and energetic applications such as photocatalytic degradation of pollutants, photocatalytic hydrogen generation, carbon dioxide reduction, disinfection, and supercapacitors. This critical review ends with a summary and some perspectives on the challenges and new directions in exploring g-C(3)N(4)-based advanced nanomaterials.

Preparation of thickness-tunable BiOCl nanosheets with high photocatalytic activity for photoreduction of CO2

BiOCl nanosheets with different percentages of exposed {001} facets were prepared via mild hydrolysis by a controlled facile hot injection technique, which exhibited relatively high activity for photocatalytic reduction of CO₂ to CH₄.

Surface imprinting of a g-C3N4 photocatalyst for enhanced photocatalytic activity and selectivity towards photodegradation of 2-mercaptobenzothiazole

Based on Fe₃O₄/g-C₃N₄ as the support, 2-mercaptobenzothiazole (MBT) as the template molecule, and pyrrole as the functional monomer, we synthesized magnetic conductive imprinted photocatalysts (MCIPs) that were significantly efficient and stable.

Enhanced photosensitized activity of a BiOCl-Bi2WO6 heterojunction by effective interfacial charge transfer

A BiOCl-Bi2WO6 heterojunction with a chemically bonded interface was synthesized via a facile one-step solvothermal method. A series of characterization techniques (XRD, XPS, TEM, SEM, EDS etc.) confirmed the existence of a BiOCl-Bi2WO6 interface. The heterojunction yielded a higher photodegradation rate of Rhodamine B under visible light irradiation compared to its individual components. Theoretical studies based on density functional theory calculations indicated that the enhanced photosensitized degradation activity could be attributed to the favorable band offsets across the BiI-O-BiII bonded interface, leading to efficient interfacial charge carrier transfer. Our results reveal the photosensitized mechanism of BiOCl-Bi2WO6 heterojunctions and demonstrate their practical use as visible-light-driven photocatalytic materials.

Engineering BiOX (X = Cl, Br, I) nanostructures for highly efficient photocatalytic applications

Heterogeneous photocatalysis that employs photo-excited semiconductor materials to reduce water and oxidize toxic pollutants upon solar light irradiation holds great prospects for renewable energy substitutes and environmental protection. To utilize solar light effectively, the quest for highly active photocatalysts working under visible light has always been the research focus. Layered BiOX (X = Cl, Br, I) are a kind of newly exploited efficient photocatalysts, and their light response can be tuned from UV to visible light range. The properties of semiconductors are dependent on their morphologies and compositions as well as structures, and this also offers the guidelines for design of highly-efficient photocatalysts. In this review, recent advances and emerging strategies in tailoring BiOX (X = Cl, Br, I) nanostructures to boost their photocatalytic properties are surveyed.

The pure shape effect with a removing facet effect of single-crystalline anatase TiO₂ (101) for photocatalytic application

3D TiO₂ nanobipyramids (TiO₂-NPs) and 1D TiO₂ nanobelts (TiO₂-NBs) were synthesized from potassium titanate K₂Ti₆O₁₃ and characterized by X-ray diffraction (XRD) patterns, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) patterns and fast Fourier transform (FFT). The as-synthesized 3D TiO₂ nanobipyramids and 1D TiO₂ nanobelts all show high {101} facet exposed percentages and were used to investigate the shape effect of TiO₂ with the same facet exposure. 3D TiO₂ nanobipyramids (101) showed higher photocatalytic activity than 1D TiO₂ nanobelts (101). The reasons were discussed using ROS (reactive oxygen species) production, time-resolved photoluminescence spectra, XPS (X-ray photoelectron spectroscopy) spectra and ATR-IR (attenuated total reflectance infrared spectroscopy) spectra. The postulated mechanism suggests that 3D TiO₂ nanobipyramids have more step edges which results in more -OH/H₂O molecule adsorption and longer life times of photoinduced carriers than 1D TiO₂ nanobelts.