Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Graphynes (GYs) are carbon allotropes with single-atom thickness that feature layered 2D structure assembled by carbon atoms with sp- and sp2- hybridization form. Various functional theories have predicted GYs to have natural band gap with Dirac cones structure, presumably originating from inhomogeneous π-bonding between those carbon atoms with different hybridization and overlap of the carbon 2pz orbitals. Among all the GYs, graphdiyne (GDY) was the first reported to be prepared practically and, hence, attracted the attention of many researchers toward this new planar, layered material, as well as other GYs. Several approaches have been reported to be able to modify the band gap of GDY, containing invoking strain, boron/nitrogen doping, nanoribbon architectures, hydrogenation, and so on. GDY has been well-prepared in many different morphologies, like nanowires, nanotube arrays, nanowalls, nanosheets, ordered stripe arrays, and 3D framwork. The fascinating structure and electronic properties of GDY make i...

Progress in Research into 2D Graphdiyne-Based Materials

Graphdiyne (GDY), a new two-dimensional (2D) carbon allotrope, has been receiving increased attention. Its unique sp-sp2 carbon atoms, uniform pores, and highly π-conjugated structure provide promising potential in practical applications, such as gas separation, catalysis, water remediation, humidity sensor, and energy-related fields. In the recent years, considerable efforts have been expended toward the development of well-defined GDY. However, GDY materials still face numerous challenges, including the need for a more thorough understanding of the growth mechanism, strategies for synthesizing one- or few-layer single-crystalline GDY films, characterization of basic physicochemical properties, and achievement of promising applications. This review aims at providing a comprehensive update on the synthesis of GDY and GDY-based materials, as well as their properties, including structural, electronic, mechanical, and spectral properties, and their applications in nanotechnology.

Graphdiyne: synthesis, properties, and applications

The technological evolution has been progressing for centuries and will possibly increase at a higher rate in the 21st century. Currently, in this age of nanotechnology, the discovery of more economical and sustainable novel materials has considerably increased. The abundance of two-dimensional (2D) materials has endowed them with a broad material platform in technical studies and in the expansion of nano- and atomic-level applications. The innovation of graphene has motivated considerable attention to the study of other novel 2D materials, known as modern day “alchemy”, by which scientists are trying to convert most possible periodic table elements into 2D material structures and forms. 2D material devices with high quality and good optical encoder performance have a multitude of industrial applications. However, their stability and large size restrict their applications, but these problems can be overcome by functionalization and substrate-based formation of 2D materials. Therefore, via this review, first, basic attributes of 2D materials are described, and the mechanisms to further enhance their properties are also summarized. Second, the applications of 2D materials are discussed, along with their advantages and disadvantages. Finally, some effective device-fabrication approaches, such as heterostructure approaches, are applied to further enhance the properties of 2D materials; their novel device applications and opportunities are also presented. This updated review may provide new avenues for 2D material synthesis and development of more efficient devices compared to conventional devices in different fields.

Recent developments in emerging two-dimensional materials and their applications

Inner filter effect-based fluorescent sensing systems: A review.

In this study, we systematically investigate the mechanism of single-layer MnO2 nanosheets suppressing fluorescence of 7-hydroxycoumarin and, based on this, demonstrate a new fluorescent method for in vivo sensing of ascorbic acid (AA) in rat brain. The mechanism for the fluorescence suppression is attributed to a combination of inner filter effect (IFE) and static quenching effect (SQE), which is different from those reported for the traditional two-dimensional nanosheets, and Forster resonant energy transfer (FRET) mechanism reported for MnO2 nanosheets. The combination of IFE and SQE leads to an exponential decay in fluorescence intensity of 7-hydroxycoumarin with increasing concentration of MnO2 nanosheets in solution. Such a property allows optimization of the concentration of MnO2 nanosheets in such a way that the addition of reductive analyte (e.g., AA) will to the greatest extent restore the MnO2 nanosheets-suppressed fluorescence of 7-hydroxycoumarin through the redox reaction between AA and MnO2 nanosheets. On the basis of this feature, we demonstrate a fluorescent method for in vivo sensing of AA in the cerebral systems with an improved sensitivity. Compared with the turn-on fluorescent method through first decreasing the fluorescence to the lowest level by adding concentrated MnO2 nanosheets, the method demonstrated here possesses a higher sensitivity, lower limit of detection, and wider linear range. Upon the use of ascorbate oxidase to achieve the selectivity for AA, the turn-on fluorescence method demonstrated here can be used for in vivo sensing of AA in a simple but reliable way.

Single-Layer MnO2 Nanosheets Suppressed Fluorescence of 7-Hydroxycoumarin: Mechanistic Study and Application for Sensitive Sensing of Ascorbic Acid in Vivo

Graphdiyne oxide as a platform for fluorescence sensing.

Manganese dioxide (MnO2) nanosheets have recently been demonstrated to be particularly attractive for fluorescent sensing and imaging; however, almost all MnO2 nanosheets-based fluorescent assays have been developed with emissive nanoparticles as the probes. In this study, we developed a novel strategy to use organic dyes, instead of emissive nanoparticles, as the probe to construct a platform for biosensing with excellent analytical properties. With 5-carboxyfluorescein (FAM) as a model organic dye, we firstly investigate the effect of MnO2 nanosheets on the fluorescence of FAM and find that the fluorescence intensity of FAM is considerably suppressed by MnO2 nanosheets based on the inner filter effect (IFE). To demonstrate that the MnO2 nanosheets-based fluorescence sensing platform can easily achieve a high selectivity with organic dyes as the probe, we use single-stranded DNA (ssDNA) oligonucleotide as a typical biorecognition unit, which is labeled with the FAM probe to form FAM-ssDNA. The fluorescent intensity of FAM-ssDNA is first suppressed by MnO2 nanosheets through the combination of IFE and Forster resonant energy transfer (FRET), and then recovered with subsequent hybridization with the complementary DNA oligonucleotide. To demonstrate the potential applications of the MnO2 nanosheets-based fluorescence sensing platform with organic dyes as the probes, we developed methods for simple but effective microRNA and thrombin assays. With the platform demonstrated here, the limits of detection for miR124a and thrombin are 0.8 nM and 11 nM, respectively. Moreover, the fluorescent sensing assay for thrombin exhibits high selectivity. This study essentially demonstrates a new 2D nanostructure-based fluorescent sensing platform that is robust, technically simple, and easily manipulated to achieve high selectivity and sensitivity for practical applications.

Chunxia Wang

Papers

Single-Layer MnO2 Nanosheets Suppressed Fluorescence of 7-Hydroxycoumarin: Mechanistic Study and Application for Sensitive Sensing of Ascorbic Acid in Vivo

Graphdiyne oxide as a platform for fluorescence sensing.

MnO2 nanosheets based fluorescent sensing platform with organic dyes as a probe with excellent analytical properties.