Two‐dimensional materials are responsible for changing research in materials science. After graphene and its counterparts, graphane, fluorographene, and others were introduced, waves of renewed ...interest in 2D binary compounds occurred, such as in metal oxides, transition‐metal dichalcogenides (most often represented by MoS2), metal oxy/hydroxide borides, and MXenes, to name the most prominent. Recently, interest has turned to two‐dimensional monoelemental structures, such as monolayer black phosphorus and, very recently, to monolayer arsenic, antimony, and bismuth. Here, a short overview is provided of the area of exponentially increasing research in arsenene, antimonene, and bismuthene, which belong to the fifth main group of elements, the so‐called pnictogens. A short review of historical work is provided, the properties of bulk allotropes of As, Sb, and Bi discussed, and then theoretical and experimental research on mono‐ and few‐layered arsenene, antimonene, and bismuthene addressed, discussing their structures and properties.
2D As, Bs, and Bi – arsenene, antimonene, and bismuthene – are monoelemental nanomaterials. Their properties depend significantly on crystal structure, on the number of layers or on the doping. They are easily obtained from their bulk counterparts or as deposited on surfaces. An overview of their properties is provided and their applications predicted.
Among 2D materials that recently have attracted enormous interest, black phosphorus (BP) is gaining a rising popularity due to its tunable band‐gap structure, which is strongly correlated to the ...thickness and can enable its use in optoelectronic and electronic applications. It is therefore important to provide a facile and scalable methodology to prepare single or few‐layer BP nanosheets. We propose herein a simple and fast top‐down method to exfoliate a BP crystal into nanosheets of reduced thickness by using electrochemistry. The application of an anodic potential to the crystal in an acidic aqueous solution allows control over the exfoliation efficiency and quality of the nanosheets produced. X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, and scanning transmission electron microscopy (STEM) have been applied to fully characterize the exfoliated material, which presented significantly reduced layer thickness compared to the starting bulk material.
A layered approach: A simple and fast top‐down electrochemical method for exfoliating a BP crystal into nanosheets of reduced thickness is proposed. The application of an anodic potential to the crystal in an acidic solution allows control over the exfoliation efficiency and quality of the nanosheets produced.
Deterioration of the surface of black phosphorus (BP) caused by ambient atmosphere is an undesired process, limiting broader use of BP in many areas. The mechanism of BP degradation was explained ...theoretically, and the oxidized materials were thoroughly characterized experimentally. However, the surface analysis techniques introduce only a limited insight into the real state of the material. Here, we report a thorough analysis of the composition of mixtures obtained after a prolonged exposure of suspensions of BP to atmospheric oxygen with the aim to further disclosure the processes involved in the decomposition process. The results are compared with the predicted structures of the oxidized material and confirm the results of the theoretical calculations. The comparison of reactivity of BP with reactivity of white phosphorus under similar conditions concludes a similar distribution of the products in both cases.
MoS2 and other transition metal dichalcogenides (TMDs) have recently gained a renewed interest due to the interesting electronic, catalytic, and mechanical properties which they possess when ...down‐sized to single or few layer sheets. Exfoliation of the bulk multilayer structure can be achieved by a preliminary chemical Li intercalation followed by the exfoliation due to the reaction of Li with water. Organolithium compounds are generally adopted for the Li intercalation with n‐butyllithium (n‐Bu‐Li) being the most common. Here, the use of three different organolithium compounds are investigated and compared, i.e., methyllithium (Me‐Li), n‐butyllithium (n‐Bu‐Li) and tert‐butyllithium (t‐Bu‐Li), used for the exfoliation of bulk MoS2. Scanning transmission electron microscopy (STEM), Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) are adopted for a comprehensive characterization of all materials under investigation. In addition, catalytic properties towards the hydrogen evolution reaction (HER) and capacitive properties are also tested. Different organolithium compounds exhibit different extent of Li intercalation resulting in different degrees of exfoliation. The inherent electrochemical behavior of MoS2 consisting of significant anodic and cathodic peaks as well as its capacitive behavior and catalytic properties towards hydrogen evolution reaction are strongly connected to the exfoliation compound used. This research significantly contributes to the development of large‐scale synthesis of electrocatalytic MoS2‐based materials.
Different Li intercalation compounds used to exfoliate MoS2
generate materials with significantly different electrochemical and catalytic properties. The inherent electrochemistry of MoS2 with significant anodic and cathodic peaks, its capacitive behavior, and its catalytic properties towards the hydrogen evolution reaction (HER) are strongly connected to the exfoliation compound used.
Phosphorus is a nonmetal with several allotropes, from the highly reactive white phosphorus to the thermodynamically stable black phosphorus (BP) with a puckered orthorhombic layered structure. The ...bulk form of BP was first synthesized in 1914, but received little attention until it was rediscovered in 2014 as a member of the new wave of 2D layered nanomaterials. BP can be exfoliated to a single sheet that acts as a semiconductor with a tunable direct band gap, a high carrier mobility at room temperature, and an in‐plane anisotropy. The development of BP applications is hampered by surface degradation, thus efforts to achieve effective BP passivation are ongoing, such as its integration in van der Waals heterostructures. BP has been tested as a novel nanomaterial in batteries, transistors, sensors, and photonics. This Review begins with the origin of the BP story, following the path from a bulk material to modern few/single layers. The physical and chemical properties are summarized, and the state‐of‐the‐art of BP applications highlighted.
Back to black: Black phosphorus (BP) is thermodynamically stable and has a puckered orthorhombic layered structure. It can be exfoliated to a single sheet with a tunable direct band gap, semiconducting properties, high carrier mobility at room temperature, and in‐plane anisotropy. BP is promising as a new nanomaterial for batteries, transistors, sensors, and photonics.
Two-dimensional (2D) layered materials have proven to be crucial platforms for anchored individual and isolated metal atoms acting as active single atom catalysts (SACs). Therefore, an accurate ...location of single atoms is essential for understanding the reaction mechanism and design of SACs anchored at 2D layered materials. However, the preparation of SACs with a precise location remains a great challenge. This review highlights recent advances in the preparation, characterization, and catalytic performance of SACs, focusing on single atoms anchored at 2D layered materials beyond graphene. These 2D materials include transitional metal dichalcogenides, layered double hydroxides, and MXenes. Importantly, the topic of impurities is discussed because these can be present at an even higher percentage than the single atoms at 2D layered materials. A variety of electrochemical energy applications are discussed in which SACs have a crucial role, including water splitting and carbon dioxide reduction. Finally, this review provides the latest applications and developments perspective of single metal atoms on 2D surfaces, which offers a unique opportunity to tune active sites and optimize the activity, selectivity, and stability of electrocatalysts.
Two-dimensional materials have been extensively studied over the last two decades as they represent a class of materials with properties applicable in catalysis, sensing, optical devices, ...nanoelectronics, supercapacitors, and semiconductors. The properties of 2D materials can be tuned by exfoliation into mono- or few-layered systems and mainly by surface modification, which can result, for example, in altering the band gap or enhancing material stability toward degradation. This review focuses on the derivatization of group 14 layered materials beyond graphene silicene, germanene, and stanene and summarizes their preparation as well as chemical and physical properties. This review provides the current state-of-the-art in the field and provides a perspective for future development in the field of chemical derivatization of 2D materials beyond graphene.
Three-dimensional (3D) printing technologies are emerging as an important tool for the manufacturing of electrodes for various electrochemistry applications. It has been previously shown that metal ...3D electrodes, modified with metal oxides, are excellent catalysts for various electrochemical energy and sensing applications. However, the metal 3D printing process, also known as selective laser melting, is extremely costly. One alternative to metal-based electrodes for the aforementioned electrochemical applications is graphene-based electrodes. Nowadays, the printing of polymer-/graphene-based electrodes can be carried out in a matter of minutes using cheap and readily available 3D printers. Unfortunately, these polymer/graphene electrodes exhibit poor electrochemical activity in their native state. Herein, we report on a simple activation method for graphene/polymer 3D printed electrodes by a combined solvent and electrochemical route. The activated electrodes exhibit a dramatic increase in electrochemical activity with respect to the Fe(CN)64–/3– redox couple and the hydrogen evolution reaction. Such in situ activation can be applied on-demand, thus providing a platform for the further widespread utilization of 3D printed graphene/polymer electrodes for electrochemistry.
Doping of graphene with heteroatoms is an effective way to tailor its properties. Here we describe a simple and scalable method of doping graphene lattice with sulfur atoms during the thermal ...exfoliation process of graphite oxides. The graphite oxides were first prepared by Staudenmaier, Hofmann, and Hummers methods followed by treatments in hydrogen sulfide, sulfur dioxide, or carbon disulfide. The doped materials were characterized by scanning electron microscopy, high-resolution X-ray photoelectron spectroscopy, combustible elemental analysis, and Raman spectroscopy. The ζ-potential and conductivity of sulfur-doped graphenes were also investigated in this paper. It was found that the level of doping is more dramatically influenced by the type of graphite oxide used rather than the type of sulfur-containing gas used during exfoliation. Resulting sulfur-doped graphenes act as metal-free electrocatalysts for an oxygen reduction reaction.
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