Mechanochemical Synthesis of Functional Layered Materials

It has been well established that high energy ball milling of powder or powder mixtures can signi®cantly accelerate chemical reactions between two solid phases or between a solid phase and a liquid or gaseous phase [1±5], making it possible for the reactions to occur at low temperatures. It appears that the mechanical process of ball milling has little effect on the driving force for the reactions, and that the change of free energy of the system as a result of the reactions can be reasonably estimated by using available thermodynamic data [6]. It is evident that ball milling accelerates the kinetics of chemical reactions through repeated creation of fresh interfaces between reacting phases by dynamic deformation, fracturing and cold welding of the solid particles [7, 8]. If the rate of heat release by the reactions which occur during and=or immediately after each collision event is high enough to heat the powder adjacent to the collision point to a temperature higher than the ignition temperature of a combustion reaction, the combustion reaction occurs during ball milling. Many cases of combustion reactions ignited by high energy ball milling have been reported [e.g., 2, 9±11]. Reduction of one of the vanadium oxides, V2O5, to metallic vanadium by Mg, Al or Ti during high energy ball milling has been studied by Yang and McCormick [12]. It was observed that combustion reactions were ignited within 10 min of ball milling. This shows that high energy ball milling is very effective in activating chemical reactions between vanadium oxides and an active metal. In this letter, we report the ®ndings from an investigation into the chemical reactions between vanadium oxides and carbon activated by high energy ball milling. When metal oxides react with carbon, one of the reaction products is CO, or CO2, which is gaseous and readily separated from the solid reaction products. This means that use of carbon as a reducing agent can eliminate the need for an additional process to separate the reaction products which might be mixed to a very ®ne scale by ball milling. Four stainless steel balls (12.5 mm in diameter) and the powder charge, which is a mixture of 99.7% pure V2O5 powder (average particle size: 50 im) and 99% pure graphite powder (average particle size: 50 im) were placed in a hardened steel vial which was then sealed in a glove-box under an argon atmosphere. The ball milling was performed by shaking the sealed vial at a high speed using a SPEX 8000 mixer=mill. The ratio between the weight of V2O5 and graphite was determined according to the following overall reaction and with 10% of excessive graphite: 2V2O5 ‡ 5C! 4V‡ 5CO2

Powder metallurgy method was used to consolidate nickel aluminide reinforced multi-walled carbon nanotubes through planetary ball mill in order to facilitate the effective dispersion of carbon nanotubes (CNTs). In this investigation, 0.5 wt% of CNTs was added to the powder mixture of nickel and aluminum through two ball milling processes: low energy ball mill (LEBM) and high energy ball mill (HEBM). The bulk composites were synthesized by spark plasma sintering (SPS) at constant temperature, holding time, pressure of 32 MPa, 800 °C and 5 min respectively. The heating rate was varied between 50 and 150 °C/min. Microstructural evolutions of the composites were studied and densification of the composites was improved with increase in heating rate but depreciated as the heating rate was further increased. Vickers microhardness values of the fabricated composites were enhanced with increase in heating rate.

Phosphorus, one of the most abundant elements in the Earth (∼0.1%), has attracted much attention in the last five years since the rediscovery of two-dimensional (2D) black phosphorus (BP) in 2014. The successful scaling down of BP endows this 'old material' with new vitality, resulting from the intriguing semiconducting properties in the atomic scale limit, i.e. layer-dependent bandgap that covers from the visible light to mid-infrared light spectrum as well as hole-dominated ambipolar transport characteristics. Intensive research effort has been devoted to the fabrication, characterization, functionalization and application of BP and other phosphorus allotropes. In this review article, we summarize the fundamental properties and fabrication techniques of BP, with particular emphasis on the recent progress in molecular beam epitaxy growth of 2D phosphorus. Subsequently, we highlight recent progress in BP (opto)electronic device applications achieved via customized manipulation methods, such as interface, defect and bandgap engineering as well as forming Lego-like stacked heterostructures.

Two-dimensional (2D) black phosphorus (BP) has drawn tremendous attention in solar-light-driven catalytic processes for its intriguing chemical and physical properties. Benefiting from the highly anisotropic electronic structure induced by its puckered crystal geometry, 2D BP tends to have greater confinement with respect to traditional inorganic nanomaterials, thereby leading to robust many-body effects. Such Coulomb-interaction-mediated effects dominate the electronic and optical properties of 2D BP-based nanosystems, where exotic correlations between photoinduced species give rise to unique photoexcitation processes that are closely associated with the involved photocatalytic behavior. In this Perspective, we highlight the critical role of many-body effects in 2D BP-based photocatalysis and exemplify the relationships between the correlated photoinduced species-dominated photoexcitation processes and photocatalytic behavior involved therein. The relevant challenges and opportunities in pursuing efficient 2D BP-based solar energy utilization are also discussed.

This study reports the synthesis and characterization of Al-alloy/SiCpmetal matrix nanocomposite, synthesized using high energy ball milling followed by sintering employing spark plasma sintering (SPS). In the present investigation, Al 5083 alloy powder (15 μm) and 10wt.% SiC particulates (~20 nm) were milled in a high-energy planetary ball mill to produce nanocrystalline Al-alloy/SiC nanocomposite powders. X-ray diffraction analysis (XRD) was carried out for milled and un-milled powder and it was observed that, as the time of milling increased, the crystallite size of Al-alloy matrix decreased sharply. The average crystallite size of Al-matrix from XRD analysis was observed to be ~ 25 nm after 15 h of ball milling. Ball milled nanocomposite powders were consolidated and sintered employing SPS at a temperature range of 500°C with a heating rate of 300°C/min and the total sintering cycle was completed in 8 min. The mechanical properties were found to substantially increase after sintering employing SPS. Morphology of as received (un-milled) powders, milled powders and sintered nanocomposites were investigated by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM). The mechanical property evaluation of the sintered nanocomposite was done by measuring nanoindentation, micro-hardness and compressive strength.

Aluminum carbide ( Al 4 C 3) seems to be an ideal reinforcement for producing aluminum matrix composites. Al 4 C 3 has high hardness and shear strength as well as a high melting point. The dispersion of Al 4 C 3 particles in the matrix produces a pinning effect that reduces aluminum grain growth, which improves the mechanical properties. In this study, aluminum powders were mixed with 4.5 wt.% graphite and mechanically alloyed using a high-energy ball mill in order to produce Al - Al 4 C 3 nanocomposite. The structural evaluation of powder particles after different milling times was studied by X-ray diffractometry, scanning electron microscopy and microhardness measurements. The aluminum crystallite size estimated with broadening of XRD peaks by Williamson–Hall formula. XRD results suggested that the grain size of aluminum decreased to nanometer range (30 nm) during ball milling. No Al 4 C 3 formed during the mechanical alloying process. Milled powders were then annealed at 300-600 °C for 1 h under argon atmosphere. Annealing at temperatures higher than 300 °C led to formation of Al 4 C 3 phase which increased as annealing temperature increased. Aluminum grain size remained in nanometer range after annealing process. The microhardness of powder particles increased after annealing. Both effects are due to the formation of nanosized Al 4 C 3 particles.

Two-dimensional black phosphorus (BP) recently emerged as an outstanding material for optoelectronics and nanophotonics applications. In contrast to graphene, BP has a sufficiently large electronic bandgap and its high carrier mobility allows for efficient free-carrier absorption in the infrared and terahertz regimes. Here, we present a reflective structure to enhance the response of nanostructured monolayer BP at terahertz frequencies and investigate localized surface plasmon resonances in BP nanostrip arrays. Anisotropic absorption is observed in the proposed BP metamaterials due to the puckered crystal structure of the monolayer BP, and further investigations show that the plasmonic resonances are strongly depending on the geometric parameters of the nanostrips and the coupling between the adjacent nanostrips. We expect that the monolayer BP is an outstanding candidate of highly anisotropic plasmonic material for ultrascaled optoelectronic integration.

Black phosphorus, which is a relatively rare allotrope of phosphorus, was first discovered by Bridgman in 1914. Since the advent of two-dimensional (2D) black phosphorus (which is known as phosphorene due to its resembling graphene sheets) in early 2014, research interest in the arena of black phosphorus was reignited in the scientific and technological communities. Henceforth, a myriad of research studies on this new member of the 2D world have been extensively emerged. Fascinatingly, 2D black phosphorus exhibits a distinctive wrinkled structure with the high hole mobility up to 1000 cm2 V−1 s−1, excellent mechanical properties, tunable band structures, anisotropic thermal, electrical and optical properties, thus leading to its marvelous prospects in device applications. This review firstly introduces the state-of-the-art development, structural properties and preparation routes of black phosphorus. In particular, anisotropy involved in mechanical properties, thermal conductivity, carrier transport as well as optical properties is comprehensively discussed. Apart from discussing the recent progress in black phosphorus which is applied to devices (i.e. field effect transistors and optoelectronic), the review also highlights the bottlenecks encountered by the society and finally casts an invigorating perspective and insightful outlook on the future direction of the next-generation 2D black phosphorus by harnessing its remarkable characteristics for energy production.

Since its successful isolation in 2014, two-dimensional black phosphorus (BP) has triggered considerable interest ffrom physicists, chemists and material scientists. Benefitting from the unique structural and physicochemical properties, BP has been explored in various applications including photoelectric, biological and electrochemical fields. Besides, BP also shows great potential as a promising electrode material and electrocatalyst in energy storage and electrocatalytic applications, and tremendous progress has been made in these electrochemical fields in recent years. Here, this review highlights the recent experimental and theoretical progress of BP-based electrodes and electrocatalysts. The latest recent advances of BP-based functional materials in energy storage applications including lithium-, magnesium- and sodium-ion batteries, lithium–sulfur batteries and supercapacitors, are presented in detail. Further, the emerging electrocatalytic applications of BP for hydrogen evolution reaction, oxygen evolution reaction and nitrogen reduction reaction are systematically reviewed with achievements and challenges. Finally, we offer brief personal comments on the existing challenges and prospective outlook on the basis of current research progress.

Insight into ball milling for size reduction and nanoparticles production of H-Y zeolite

Fabrication of lanthanum-doped thorium dioxide by high-energy ball milling and spark plasma sintering

The structural transformation of polycrystalline Si induced by high energy ball milling has been studied. The structure and property characteristics of the milled powder have been investigated by x-ray diffraction, scanning electron microscopy, high-resolution electron microscopy, differential scanning calorimetry, Raman scattering, and infrared absorption spectroscopy. Two phase amorphous and nanocrystalline Si has been produced by ball milling of polycrystalline elemental Si. The nanocrystalline components contain some defects such as dislocations, twins, and stacking faults which are typical of defects existing in conventional coarse-grained polycrystalline materials. The volume fraction of amorphous Si is about 15% while the average size of nanocrystalline grains is about 8 nm. Amorphous elemental Si without combined oxygen can be obtained by ball milling. The distribution of amorphous Si and the size of nanocrystalline Si crystallites is not homogeneous in the milled powder. The amorphous Si formed is concentrated near the surface of milled particles while the grain size of nanocrystalline Si ranges from 3 to 20 nm. Structurally, the amorphous silicon component prepared by ball milling is similar to that obtained by ion implantation or chemical vapor deposition. The amorphous Si formed exhibits a crystallization temperature of about 660 °C at a heating rate of 40 K/min and crystallization activation energy of about 268 kJ/mol. Two possible amorphization mechanisms, i.e., pressure-induced amorphization and crystallite-refinement-induced amorphization, are proposed for the amorphization of Si induced by ball milling.

The SiBCN ceramics have garnered increasing attention as fascinating candidates for high‐temperature structural and functional applications, whose diverse properties are associated with the amorphous/crystalline state. SiBCN ceramic powders with high crystallization resistance and fine particle size is desirable for the preparation of the amorphous bulks. In this study, we synthesized a polyborosilazane (PBSZ) precursor through ammonolysis and condensation of tris(dichloromethylsilylethyl)borane and boron trichloride. Subsequently, high‐energy ball milling was employed to disintegrate PBSZ and produced SiBCN powders through pyrolysis. Compared with the powders obtained by manual grinding and low‐speed ball milling, the effect of high‐energy ball milling on the structure of PBSZ and corresponding SiBCN ceramic was investigated. Apart from the regular SiN2C2 structure, a new SiN3C structure is formed during high energy ball milling of PBSZ, and inherited in the ceramic after pyrolysis. The SiBCN powder derived from high‐energy ball milled PBSZ exhibits better crystallization resistance and finer particle size, which demonstrates potential for the preparation of amorphous SiBCN bulks.

Compared with other two-dimensional materials, two-dimensional black phosphorus (BP) has attracted extensive attention across various fields including transistors, photonics, optoelectronics, sensors, batteries and catalysis in recent years owing to its high carrier mobility, wide adjustable band gap, and in-plane anisotropy. However, the instability of black phosphorus in natural environmental conditions and the chanllenges in the fabrication of large-area, high-quality semiconducting black phosphorus nanostructures seriously have hampered its rapid development in the field of nanodevices, catalysis and biophotonics. In this work, we summarize the controlled fabrication and optical properties of highly stable BP nanostructures in recent years. The research advances in photoresponse applications, including photodetectors, nonlinear and linear photonics, photocatalysis and biophotonics, are highlighted. Additionally, the challenges and opportunities of BP nanostructures in future optoelectronic devices, photocatalysis and biophotonics are discussed.

Two-dimensional black phosphorus (BP) has drawn extensive research interest due to its promising anisotropic photonic and electronic properties. Here, we study anisotropic optical absorption and photoresponse of exfoliated BP flakes at visible frequencies. We enhance this intrinsic optical anisotropy in BP flakes by coupling plasmonic rectangular nanopatch arrays that support localized surface plasmon resonances. In particular, by combining extrinsic anisotropic plasmonic nanostructures lithographically aligned with intrinsically anisotropic BP flakes, we demonstrate for the first time a combined anisotropic plasmonic-semiconductor coupling that provides significant control over the polarization-dependent optical properties of the plasmon-BP hybrid material system, enhancing polarization-sensitive responses to a larger degree. This hybrid material system not only unveils the plasmon-enhanced mechanisms in BP, but also provides novel controllable functionalities in optoelectronic device applications involving polarization-sensitive optical and electrical responses.