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

Over the past few decades, researchers have established artificial enzymes as highly stable and low-cost alternatives to natural enzymes in a wide range of applications. A variety of materials including cyclodextrins, metal complexes, porphyrins, polymers, dendrimers and biomolecules have been extensively explored to mimic the structures and functions of naturally occurring enzymes. Recently, some nanomaterials have been found to exhibit unexpected enzyme-like activities, and great advances have been made in this area due to the tremendous progress in nano-research and the unique characteristics of nanomaterials. To highlight the progress in the field of nanomaterial-based artificial enzymes (nanozymes), this review discusses various nanomaterials that have been explored to mimic different kinds of enzymes. We cover their kinetics, mechanisms and applications in numerous fields, from biosensing and immunoassays, to stem cell growth and pollutant removal. We also summarize several approaches to tune the activities of nanozymes. Finally, we make comparisons between nanozymes and other catalytic materials (other artificial enzymes, natural enzymes, organic catalysts and nanomaterial-based catalysts) and address the current challenges and future directions (302 references).

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes

Ionic liquids (ILs) are liquids consisting entirely of ions and can be further defined as molten salts having melting points lower than 100 °C. One of the most important research areas for IL utilization is undoubtedly their energy application, especially for energy storage and conversion materials and devices, because there is a continuously increasing demand for clean and sustainable energy. In this article, various application of ILs are reviewed by focusing on their use as electrolyte materials for Li/Na ion batteries, Li-sulfur batteries, Li-oxygen batteries, and nonhumidified fuel cells and as carbon precursors for electrode catalysts of fuel cells and electrode materials for batteries and supercapacitors. Due to their characteristic properties such as nonvolatility, high thermal stability, and high ionic conductivity, ILs appear to meet the rigorous demands/criteria of these various applications. However, for further development, specific applications for which these characteristic properties becom...

Application of Ionic Liquids to Energy Storage and Conversion Materials and Devices

Two-dimensional materials and single-atom catalysts are two frontier research fields in catalysis. A new category of catalysts with the integration of both aspects has been rapidly developed in recent years, and significant advantages were established to make it an independent research field. In this Review, we will focus on the concept of two-dimensional materials confining single atoms for catalysis. The new electronic states via the integration lead to their mutual benefits in activity, that is, two-dimensional materials with unique geometric and electronic structures can modulate the catalytic performance of the confined single atoms, and in other cases the confined single atoms can in turn affect the intrinsic activity of two-dimensional materials. Three typical two-dimensional materials are mainly involved here, i.e., graphene, g-C3N4, and MoS2, and the confined single atoms include both metal and nonmetal atoms. First, we systematically introduce and discuss the classic synthesis methods, advanced ...

Catalysis with Two-Dimensional Materials Confining Single Atoms: Concept, Design, and Applications.

Sulfur-doped disordered carbon is facilely synthesized and investigated as an anode for sodium ion batteries. Benefiting from the high sulfur doping (∼26.9 wt%), it demonstrates a high reversible capacity of 516 mA h g−1, excellent rate capability as well as superior cycling stability (271 mA h g−1 at 1 A g−1 after 1000 cycles).

A high performance sulfur-doped disordered carbon anode for sodium ion batteries

High-quality phosphorus-doped MoS2 ultrathin nanosheets with amenable ORR catalytic activity

Uniform water-soluble monolayer MoS2 quantum dots (MQDs) with lateral sizes of ≈21 nm, a clearly zigzag-terminated edge, and a hexagonal lattice structure are achieved using ammonium molybdate, thiourea, and N-acetyl-l-cysteine (NAC) as precursors and the capping reagent in a facile one-pot hydrothermal approach MQDs have good dispersity and high stability in aqueous suspension and exhibit a significantly larger direct bandgap (396 eV) compared to monolayer MoS2 nanosheets (189 eV) Pronounced blue-shifts in the wavelengths of both the excitonic absorption and intrinsic state emission with activated strong luminescence at room temperature beyond monolayer MoS2 nanosheets is demonstrated Unusual upconversion photoluminescence is also observed and is caused by two successive transfers of energy from the near-infrared (NIR) absorption generated by the NAC capping reagent to the hexagonal structure of MQDs Additional optical properties of MQDs may provide numerous exciting technological applications Here, MQDs are demonstrated as a highly selective fluorescent reagent for detecting tetracycline hydrochloride under UV and NIR irradiation

Water-Soluble Monolayer Molybdenum Disulfide Quantum Dots with Upconversion Fluorescence

Discrimination and simultaneous determination of hydroquinone and catechol by tunable polymerization of imidazolium-based ionic liquid on multi-walled carbon nanotube surfaces.

High visible light sensitive MoS2 ultrathin nanosheets for photoelectrochemical biosensing

Controllable engineering of high-electronegativity oxygen (O)-heteroatoms into MoS2 ultrathin nanosheets is realized via a facile post-modification process. The incorporated oxygen atoms impart a dramatically enhanced ORR activity to the pristine nanosheets, with a 7.8-fold current increase as well as 180 mV and 160 mV positive shifts in both onset and half-wave potentials that are almost comparable with the commercial Pt/C catalyst. Furthermore, oxygen incorporation also triggers a transformation of the process from two-electron to a four-electron process. The improved topical conductivity, as well as the preferential adsorption of oxygen molecules originating from the heteroatoms engineering is supposed to be responsible for the efficient ORR. The prospect of controllably engineering heteroatoms into MoS2 ultrathin nanosheets with versatile applications is also highlighted in this work.

Hao Huang

Papers

High-quality phosphorus-doped MoS2 ultrathin nanosheets with amenable ORR catalytic activity

Water-Soluble Monolayer Molybdenum Disulfide Quantum Dots with Upconversion Fluorescence

Discrimination and simultaneous determination of hydroquinone and catechol by tunable polymerization of imidazolium-based ionic liquid on multi-walled carbon nanotube surfaces.

High visible light sensitive MoS2 ultrathin nanosheets for photoelectrochemical biosensing

Incorporated oxygen in MoS2 ultrathin nanosheets for efficient ORR catalysis