Revisiting the Growth of Black Phosphorus in Sn-I Assisted Reactions

Growth of Single Crystalline 2D Materials beyond Graphene on Non-metallic Substrates

The advent of 2D materials has ushered in the exploration of their synthesis, characterization and application. While plenty of 2D materials have been synthesized on various metallic substrates, interfacial interaction significantly affects their intrinsic electronic properties. Additionally, the complex transfer process presents further challenges. In this context, experimental efforts are devoted to the direct growth on technologically important semiconductor/insulator substrates. This review aims to uncover the effects of substrate on the growth of 2D materials. The focus is on non-metallic substrate used for epitaxial growth and how this highlights the necessity for phase engineering and advanced characterization at atomic scale. Special attention is paid to monoelemental 2D structures with topological properties. The conclusion is drawn through a discussion of the requirements for integrating 2D materials with current semiconductor-based technology and the unique properties of heterostructures based on 2D materials. Overall, this review describes how 2D materials can be fabricated directly on non-metallic substrates and the exploration of growth mechanism at atomic scale.

Recent Progress on Synthesis and Properties of Black Phosphorus and Phosphorene As New-Age Nanomaterials for Water Decontamination

Concerted efforts have been made in recent years to find solutions to water and wastewater treatment challenges and eliminate the difficulties associated with treatment methods. Various techniques are used to ensure the recycling and reuse of water resources. Owing to their excellent chemical, physical, and biological properties, nanomaterials play an important role when integrated into water/wastewater treatment technologies. Black phosphorus (BP) is a potential nanomaterial candidate for water and wastewater treatment, especially its monolayer 2D derivative called phosphorene. Phosphorene offers relative adjustability in its direct bandgap, high charge carrier mobility, and improved in-plane anisotropy compared to the most extensively studied 2D nanomaterials. In this study, we examined the physical and chemical characteristics and synthetic processes of BP and phosphorene. We provide an overview of the latest advancements in the main applications of BP and phosphorene in water/wastewater treatment, which are categorized as photocatalytic, adsorption, and membrane filtration processes. Additionally, we explore the existing difficulties in the integration of BP and phosphorene into water/wastewater treatment technologies and prospects for future research in this field. In summary, this review highlights the ongoing necessity for significant research efforts on the integration of BP and phosphorene in water and wastewater applications.

Seeded growth of single-crystal black phosphorus nanoribbons

Two-dimensional materials have emerged as an important research frontier for overcoming the challenges in nanoelectronics and for exploring new physics. Among them, black phosphorus, with a combination of a tunable bandgap and high mobility, is one of the most promising systems. In particular, black phosphorus nanoribbons show excellent electrostatic gate control, which can mitigate short-channel effects in nanoscale transistors. Controlled synthesis of black phosphorus nanoribbons, however, has remained an outstanding problem. Here we report large-area growth of black phosphorus nanoribbons directly on insulating substrates. We seed the chemical vapour transport growth with black phosphorus nanoparticles and obtain uniform, single-crystal nanoribbons oriented exclusively along the [100] crystal direction. With comprehensive structural calculations, we discover that self-passivation at the zigzag edges holds the key to the preferential one-dimensional growth. Field-effect transistors based on individual nanoribbons exhibit on/off ratios up to ~104, confirming the good semiconducting behaviour of the nanoribbons. These results demonstrate the potential of black phosphorus nanoribbons for nanoelectronic devices and also provide a platform for investigating the exotic physics in black phosphorus.

Microenvironment Restruction of Emerging 2D Materials and their Roles in Therapeutic and Diagnostic Nano-Bio-Platforms

Engineering advanced therapeutic and diagnostic nano-bio-platforms (NBPFs) have emerged as rapidly-developed pathways against a wide range of challenges in antitumor, antipathogen, tissue regeneration, bioimaging, and biosensing applications. Emerged 2D materials have attracted extensive scientific interest as fundamental building blocks or nanostructures among material scientists, chemists, biologists, and doctors due to their advantageous physicochemical and biological properties. This timely review provides a comprehensive summary of creating advanced NBPFs via emerging 2D materials (2D-NBPFs) with unique insights into the corresponding molecularly restructured microenvironments and biofunctionalities. First, it is focused on an up-to-date overview of the synthetic strategies for designing 2D-NBPFs with a cross-comparison of their advantages and disadvantages. After that, the recent key achievements are summarized in tuning the biofunctionalities of 2D-NBPFs via molecularly programmed microenvironments, including physiological stability, biocompatibility, bio-adhesiveness, specific binding to pathogens, broad-spectrum pathogen inhibitors, stimuli-responsive systems, and enzyme-mimetics. Moreover, the representative therapeutic and diagnostic applications of 2D-NBPFs are also discussed with detailed disclosure of their critical design principles and parameters. Finally, current challenges and future research directions are also discussed. Overall, this review will provide cutting-edge and multidisciplinary guidance for accelerating future developments and therapeutic/diagnostic applications of 2D-NBPFs.

Facile Synthesis of Black Phosphorus Nanosheet@NaReF4 Nanocomposites for Potential Bioimaging

Black phosphorus nanomaterials (BPN) have been well developed in tumor therapy. However, lack of diagnostic function limits the development of BPN in biomedicine. Lanthanide-doped nanoparticles are considered as versatile materials for fluorescence or magnetic resonance imaging. Integration of BPN with lanthanide-doped nanoparticles was rarely reported owing to the complex synthesis processes and poor modification effect. Herein, we report a simple and general method for synthesizing BPN@NaReF₄ (Re: Gd or Y, Yb, Er) nanocomposite. TEM and XRD characterization confirm efficient combination of BPN and NaGdF₄ or NaYF₄:Yb,Er (18.2 mol %) after one-step mixing. The FTIR and XPS spectra were used to prove the generation of PO₄^3--Gd and P-Gd coordination bonds and clarify ligand exchange mechanism. The anchored nanoparticles on BPN were stable and become hydrophilic. The prepared BPN@NaGdF₄ exhibit the signals of photoacoustic and magnetic resonance imaging. The obtained BPN@NaYF₄:Yb,Er (18.2 mol %) have the potential in fluorescence bioimaging. We believe that this work will expand the applications of BPN in diagnosis and therapy together.

Urokinase loaded black phosphorus nanosheets for sequential thrombolysis and reactive oxygen species scavenging in ischemic stroke treatment

Ischemic stroke often causes devastating damage to human life and health. Excess production of reactive oxygen species (ROS) during thrombolysis will paradoxically result in neuronal injury. Neuroprotection from reperfusion injury must overcome the challenge of crossing the blood-brain barrier (BBB). A strategy including thrombolysis and ROS scavenging accompanied by BBB penetration is highly desirable for improving combination therapies in ischemic stroke. Herein, urokinase plasminogen activator (uPA) loaded on black phosphorus nanosheets (BPNs) is tested as a nanodrug for sequential thrombolysis and neuroprotection. The in vitro thrombolysis shows that the uPA-loaded BPNs can efficiently deliver uPA for thrombus dissolution. The residual BPNs after uPA release exhibit ROS scavenging effects, especially for the most common H₂O₂ and ˙OH species. Moreover, in vivo studies show that the BPNs can cross the BBB with the assistance of laser irradiation, owing to their good photothermal properties. Further experiments show the effectiveness of BPNs for attenuating reperfusion injury and achieving neuroprotection. These results highlight the promising potential of the present BPN-based nanodrugs for the treatment of ROS-related diseases.

Construction of 2D-layered quantum dots/2D-nanosheets heterostructures with compact interfaces for highly efficient photocatalytic hydrogen evolution

The emergence of two dimensional (2D) nanosheets provides flexible platforms for the construction of semiconductor heterostructures for photocatalytic hydrogen evolution. However, the compact and conformal contact between the components with different dimensions remains challenge. Herein, we anchor the 2D layered black phosphorous quantum dots (BPQDs) onto the 2D ZnIn₂S₄ nanosheets with sulfur vacancies (V-ZIS). This unique interface between 2D layered QDs and 2D nanosheets ensures a sufficient contact area between the BPQDs and the V-ZIS, which is conducive to the transport and the spatial separation of photogenerated electrons and holes. A synergistic effect of sulfur vacancies and type-Ⅱ heterojunction results in an excellent photocatalytic hydrogen evolution performance of the BPQDs/V-ZIS composites. The hydrogen evolution rate by the BPQDs/V-ZIS without any noble-metal as cocatalyst is up to 5079 μmol g^-1h^-1 under visible light irradiation with an apparent quantum yield (AQY) of 12.03% at 420 nm, which is dramatically higher than most other photocatalysts reported previously.

A hetero-phase growth method to control the crystal growth of β-antimony single crystals with high quality and large sizes

A hetero-phase crystal growth method was proposed by introducing a heteroelement to yield large antimony single crystals with high quality.

Crystallization kinetics of amorphous red phosphorus to black phosphorus by chemical vapor transport

The aRP–P4-HP–BP three-stage phase transition revealed the crystallization kinetics and nucleation mechanism of the high-quality BP crystal synthesized by the CVT reaction in the aRP–Sn–I system.

Synthesis and stabilization of black phosphorus and phosphorene: recent progress and perspectives

Two-dimensional black phosphorus (BP) has triggered tremendous research interest owing to its unique crystal structure, high carrier mobility, and tunable direct bandgap. Preparation of few-layer BP with high quality and stability is very important for its related research and applications in biomedicine, electronics, and optoelectronics. In this review, the synthesis methods of BP, including the preparation of bulk BP crystal which is an important raw material for preparing few-layer BP, the popular top-down methods, and some direct growth strategies of few-layer BP are comprehensively overviewed. Then chemical ways to enhance the stability of few-layer BP are concretely introduced. Finally, we propose a selection rule of preparation methods of few-layer BP according to the requirement of specific BP properties for different applications. We hope this review would bring some insight for future researches on BP and contributes to the acceleration of BP's commercial progress.

Expanding the Scope of 2D Black Phosphorus Catalysis to the Near-Infrared Light Initiated Free Radical Photopolymerization

In the drive toward the development of efficient and stable inorganic semiconductor materials with broadband solar absorption ability to induce various photochemical processes is a highly attractive research field. In this study, two-dimensional (2D) few-layer black phosphorus (BP) exfoliated in a solvent is utilized as photocatalyst to initiate the polymerization of various monomers under visible and near-IR (NIR) light irradiation. Upon the light exposure, few-layer BP generates excited electrons and holes, which undergo electron transfer reactions with the onium salts to form free radicals capable of initiating free radical polymerization. Among the onium salts tested, aryldiazonium salt was found to be the most efficient in the photopolymerization process owing to its favorable reduction potential with the conduction edge potential of BP. The presented strategy also provides the possibility for the in situ preparation of BP-polymer composite materials.

Growth of black arsenic phosphorus thin films and its application for field-effect transistors

Black arsenic phosphorus single crystals were grown using a short-way transport technique resulting in crystals up to 12 × 110μmand ranging from 200 nm to 2μmthick. The reaction conditions require tin, tin (IV) iodide, gray arsenic, and red phosphorus placed in an evacuated quartz ampule and ramped up to a maximum temperature of 630 °C. The crystal structure and elemental composition were characterized using Raman spectroscopy, x-ray diffraction, and x-ray photoelectron spectroscopy, cross-sectional transmission microscopy, and electron backscatter diffraction. The data provides valuable insight into the growth mechanism. A previously developed b-P thin film growth technique can be adapted to b-AsP film growth with slight modifications to the reaction duration and reactant mass ratios. Devices fabricated from exfoliated bulk-b-AsP grown in the same reaction condition as the thin film growth process are characterized, showing an on-off current ratio of 10², a threshold voltage of -60 V, and a peak field-effect hole mobility of 23 cm²V^-1s^-1atV_d= -0.9 V andV_g= -60 V.

Formation Mechanisms for Phosphorene and SnIP

Phosphorene-the monolayered material of the element allotrope black phosphorus (Pblack )-and SnIP are 2D and 1D semiconductors with intriguing physical properties. Pblack and SnIP have in common that they can be synthesized via short way transport or mineralization using tin, tin(IV) iodide and amorphous red phosphorus. This top-down approach is the most important access route to phosphorene. The two preparation routes are closely connected and differ mainly in reaction temperature and molar ratios of starting materials. Many speculative intermediates or activator side phases have been postulated especially for top-down Pblack /phosphorene synthesis, such as Hittorf's phosphorus or Sn24 P19.3 I8 clathrate. The importance of phosphorus-based 2D and 1D materials for energy conversion, storage, and catalysis inspired us to elucidate the formation mechanisms of these two compounds. Herein, we report on the reaction mechanisms of Pblack /phosphorene and SnIP from P4 and SnI2 via direct gas phase formation.

Multifunctional layered black phosphorene-based nanoplatform for disease diagnosis and treatment: a review

As an outstanding two-dimensional material, black phosphorene, has attracted significant attention in the biomedicine field due to its large surface area, strong optical absorption, distinct bioactivity, excellent biocompatibility, and high biodegradability. In this review, the preparation and properties of black phosphorene are summarized first. Thereafter, black phosphorene-based multifunctional platforms employed for the diagnosis and treatment of diseases, including cancer, bone injuries, brain diseases, progressive oxidative diseases, and kidney injury, are reviewed in detail. This review provides a better understanding of the exciting properties of black phosphorene, such as its high drug-loading efficiency, photothermal conversion capability, high 1O2 generation efficiency, and high electrical conductivity, as well as how these properties can be exploited in biomedicine. Finally, the research perspectives of black phosphorene are discussed.

Photothermal Antibacterial and Antibiofilm Activity of Black Phosphorus/Gold Nanocomposites against Pathogenic Bacteria

Black phosphorus (BP) as a layered two-dimensional (2D) semiconductor material with a tunable band gap has attracted growing attention for promising applications in diverse fields including biotechnology owing to its excellent physical and chemical properties. In this study, BP crystals were synthesized using a chemical vapor transport method and exfoliated into BP nanosheets in deoxygenated water or hexane. Next, monodisperse Au nanoparticles that were synthesized using a surfactant-assisted chemical reduction method were assembled on exfoliated BP nanosheets hexane to yield BP/Au nanocomposites. The photothermal antibacterial and antibiofilm activities of BP nanosheets and BP/Au nanocomposites were investigated against Enterococcus faecalis, a pathogenic biofilm-forming bacterium, by studying the photothermal effect and bacterial growth curve and using colony counting and live/dead fluorescence staining methods under near-infrared (NIR) light irradiation. Thanks to the higher photothermal conversion efficiency of BP/Au nanocomposites than that of bare BP nanosheets under NIR light irradiation, they destructed the bacterial cell membrane more efficiently than bare BP with the biofilm inhibition rate of 58%. It should be noted that this is the first study on the antibacterial and antibiofilm activity of BP/Au nanocomposites via a photothermal process under NIR light irradiation. This work shows the potential of BP/Au nanocomposites in fighting against pathogenic bacteria and paves the way for the exploration of antibacterial platforms based on the biocompatible 2D semiconductor BP.

Black phosphorus as a metal-free, visible-light-active heterogeneous photoredox catalyst for the direct C-H arylation of heteroarenes

Black phosphorus (BP) is for the first time employed as a metal-free, heterogeneous photoredox catalyst for the direct C-H arylation of heteroarenes with aryl diazonium salts. The arylated heteroarenes are obtained in moderate to good yields under visible-light illumination, and the protocol is shown to be applicable for the scale-up synthesis.

A self-encapsulated broadband phototransistor based on a hybrid of graphene and black phosphorus nanosheets

A phototransistor based on a hybrid of graphene and BP nanosheets with a facile fabrication method and remarkable performance is presented. Unlike previously reported single BP flake-based devices, this phototransistor employs diverse BP nanosheets with different sizes and layer numbers. The wet transfer process of graphene is exploited to integrate the liquid-exfoliated BP nanosheets into the device smoothly. Due to the diversity of BP nanosheets, the device demonstrates a broadband photo-response in the spectrum from 360 nm to 785 nm. The photo-response mechanism is revealed to be the photogating effect caused by the discrete BP nanosheets adsorbed on graphene. The phototransistor has a responsivity of 7.7 × 103 A W-1 in the near-UV region with a wide conductive channel of 200 μm. Moreover, the simplified wet transfer process of graphene leaves a self-encapsulated layer of PMMA on the as-prepared device, inducing a good atmospheric stability in the device. This report provides a valid, implantable, and facile strategy to apply BP nanosheets in a broadband, high-performing and air-stable photodetector.

Mesoporous Graphitic Carbon Nitride/Black Phosphorus/AgPd Alloy Nanoparticles Ternary Nanocomposite: A Highly Efficient Catalyst for the Methanolysis of Ammonia Borane

A novel ternary nanocomposite, mesoporous graphitic carbon nitride/black phosphorus-AgPd (denoted mpg-CN/BP-AgPd), was successfully fabricated by assembling the as-prepared AgPd alloy nanoparticles (NPs) on mesoporous graphitic carbon nitride/black phosphorus (mpg-CN/BP) binary composites. This novel nanocomposite comprises a heterojunction support material formed by two distinct nonmetallic semiconductors (mpg-CN and BP) with adaptable band gaps and edge voltages, providing enhanced catalytic activity to AgPd alloy NPs in hydrogen generation from the methanolysis of ammonia borane (AB) compared to its single components under the blue light-emitting diode (LED) light illumination. The yielded mpg-CN/BP-AgPd ternary nanocomposites were characterized by many advanced analytical techniques (transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), time-resolved spectroscopy, inductively coupled plasma-mass spectroscopy (ICP-MS), and fourier transform infrared (FTIR), and then they were tested as catalysts in hydrogen generation from the methanolysis of AB at room temperature. Several parameters such as the effect of mpg-CN/BP ratio, alloy composition, and type of the light source were studied to optimize the catalytic activity of the mpg-CN/BP-AgPd nanocomposites in the methanolysis of AB. The best catalytic activity of mpg-CN/BP-AgPd nanocomposites was obtained using an mpg-CN/BP ratio of 5/1 (wt/wt) and Ag₅₀Pd₅₀ alloy composition under the blue LED illumination at room temperature. The activity of the ternary nanocomposites was further enhanced by the acetic acid treatment, and a high initial turnover frequency of 43.7 mol(H₂) mol(catalyst)^-1 min^-1 was reported. Besides their high catalytic activity, the mpg-CN/BP-AgPd nanocomposites were reusable catalysts in the methanolysis of AB. This study also included detailed kinetics of AB methanolysis catalyzed by mpg-CN/BP-AgPd nanocomposites.

Large-Scale Production of Nanocrystalline Black Phosphorus Ceramics

Black phosphorus is currently among the most explored two-dimensional (2D) materials. Currently, the synthesis methods are dominantly based on vapor-phase growth of black phosphorus. In this manuscript, we demonstrate large-scale synthesis of black phosphorus by rapid high-pressure transition of red phosphorus. The high-pressure conversion of red phosphorus led to high-density nanocrystalline black phosphorus ceramics. The resulting material was explored in detail including structural and morphological characterization in addition to thermal and electrical transport and basic thermophysical properties. The nanocrystalline black phosphorus can be employed for large-scale production of stable few/single-layer black phosphorus colloidal solutions in various solvents.

High-Quality Black Phosphorus Quantum Dots Fabricated via Microwave-Tailored Technology

Black phosphorus quantum dots (BPQDs) have recently obtained great attention due to their high mobility and tunable bandgap features, which are beneficial for their potential application in photoelectronic devices. However, a precise synthesis of high-quality BPQDs is still a great challenge owing to the formation of an impurity phase when employing traditional methods. Herein, we demonstrate the scalable fabrication of BPQDs from mineralization-derived bulk black phosphorus (BP) single crystals by means of a microwave (MW)-assisted liquid-phase exfoliation method in ethanol. The primary results demonstrate that ethanol plays a crucial role in determining the final properties of BPQDs, such as their excellent tolerance to oxygen, good crystallinity, and uniform size. Furthermore, the mechanism behind the formation of BPQDs is proposed, revealing that a layer-by-layer disintegration process of bulk BP crystals under microwave-energy stimuli is responsible. This work may provide a novel path for the further development of BPQDs and corresponding devices.

Chemical vapor transport growth of bulk black phosphorus single crystals

Recent progress in growth of bulk black phosphorus single crystal by CVT method has been briefly reviewed with the emphasis on reaction system, nucleation and growth mechanism as well as advancement in growth of doped BP bulk single crystal.

Chemical Vapor Transport Reactions for Synthesizing Layered Materials and Their 2D Counterparts

2D materials, namely thin layers of layered materials, are attracting much attention because of their unique electronic, optical, thermal, and catalytic properties for wide applications. To advance both the fundamental studies and further practical applications, the scalable and controlled synthesis of large-sized 2D materials is desired, while there still lacks ideal approaches. Alternatively, the chemical vapor transport reaction is an old but powerful technique, and is recently adopted for synthesizing 2D materials, producing bulk crystals of layered materials or corresponding 2D films. Herein, recent advancements in synthesizing both bulk layered and 2D materials by chemical vapor transport reactions are summarized. Beginning with a brief introduction of the fundamentals of chemical vapor transport reactions, chemical vapor transport-based syntheses of bulk layered and 2D materials, mainly exampled by transition metal dichalcogenides and black phosphorus, are reviewed. Particular attention is paid to important factors that can influence the reactions and the growth mechanisms of black phosphorus. Finally, perspectives about the chemical vapor transport-based synthesis of 2D materials are discussed, intending to redraw attentions on chemical vapor transport reactions.

A Highly Effective π-π Stacking Strategy To Modify Black Phosphorus with Aromatic Molecules for Cancer Theranostics

Even though black phosphorus (BP) has exhibited outstanding capabilities in biomedical, physical, and energy fields, the issues of degradation under ambient conditions and unreactive functional interface limit its further application. There are numerous methodologies utilized to prevent BP degradation; however, these methods usually generate further problems and normally do not involve alterations to the chemically inert BP. Herein, for the first time, we propose a simple and efficient strategy to prepare and modify BP nanosheets (p-BPNSs) by employing aromatic 1-pyrenylbutyric acid through a noncovalent π-π stacking interaction. This strategy not only adopts a novel strategy for enhancing the stability of BPNSs but also paves a convenient way to anchor other active biomolecules such as a targeting effect to extend the biomedical applications of BPNSs. The modified p-BPNSs exhibit enhanced physical and chemical stabilities as well as rich carboxyl groups for further modification. In this work, RGD-modified p-BPNSs exhibit targeted photothermal therapy ability against cancer in both in vitro and in vivo studies, owing to anchoring of arginine-glycine-aspartic acid (RGD) tripeptides, which could target nanosheets into the tumor site through systematic circulation. Consequently, this work not only provides a new concept for modifying and protecting the BP but also opens a novel window for extending the biomedical application of BP by surface engineering.