Junze Chen

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

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, electrocatalysis, batteries, supercapacitors, solar cells, photocatalysis, and sensing platforms. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.

One‐pot Synthesis of CdS Nanocrystals Hybridized with Single‐Layer Transition‐Metal Dichalcogenide Nanosheets for Efficient Photocatalytic Hydrogen Evolution

Exploration of low-cost and earth-abundant photocatalysts for highly efficient solar photocatalytic water splitting is of great importance. Although transition-metal dichalcogenides (TMDs) showed outstanding performance as co-catalysts for the hydrogen evolution reaction (HER), designing TMD-hybridized photocatalysts with abundant active sites for the HER still remains challenge. Here, a facile one-pot wet-chemical method is developed to prepare MS2-CdS (M=W or Mo) nanohybrids. Surprisedly, in the obtained nanohybrids, single-layer MS2 nanosheets with lateral size of 4-10 nm selectively grow on the Cd-rich (0001) surface of wurtzite CdS nanocrystals. These MS2-CdS nanohybrids possess a large number of edge sites in the MS2 layers, which are active sites for the HER. The photocatalytic performances of WS2-CdS and MoS2-CdS nanohybrids towards the HER under visible light irradiation (>420 nm) are about 16 and 12 times that of pure CdS, respectively. Importantly, the MS2-CdS nanohybrids showed enhanced stability after a long-time test (16 h), and 70% of catalytic activity still remained.

Single-Layer Transition Metal Dichalcogenide Nanosheet-Based Nanosensors for Rapid, Sensitive, and Multiplexed Detection of DNA

Single-layer transition metal dichalcogenide nanosheets, including MoS2, TiS2, and TaS2, are used as novel sensing platforms for sensitive and selective detection of DNA, based on their high fluorescence-quenching ability and different affinities toward single-stranded DNA and double-stranded DNA. Importantly, for the first time, a single-layer TaS2 nanosheet-based multiplexed DNA sensor is also developed.

Au Nanoparticle‐Modified MoS2 Nanosheet‐Based Photoelectrochemical Cells for Water Splitting

The surface plasmon resonance of Au nanoparticle on MoS2 nanosheet is successfully measured by the electron energy-loss spectroscopy. Furthermore, Au-MoS2 composite is developed as the photoanode material in the photo-electronchemical cell (PEC) for water splitting. Compared to the pure MoS2 -based PEC, Au-MoS2 based PEC shows the enhanced performance in the photocatalytic water splitting.

Self‐Assembly of Single‐Layer CoAl‐Layered Double Hydroxide Nanosheets on 3D Graphene Network Used as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

A non-noble metal based 3D porous electrocatalyst is prepared by self-assembly of the liquid-exfoliated single-layer CoAl-layered double hydroxide nanosheets (CoAl-NSs) onto 3D graphene network, which exhibits higher catalytic activity and better stability for electrochemical oxygen evolution reaction compared to the commercial IrO2 nanoparticle-based 3D porous electrocatalyst.

High-Yield Exfoliation of Ultrathin Two-Dimensional Ternary Chalcogenide Nanosheets for Highly Sensitive and Selective Fluorescence DNA Sensors

High-yield preparation of ultrathin two-dimensional (2D) nanosheets is of great importance for the further exploration of their unique properties and promising applications. Herein, for the first time, the high-yield and scalable production of ultrathin 2D ternary chalcogenide nanosheets, including Ta2NiS5 and Ta2NiSe5, in solution is achieved by exfoliating their layered microflakes. The size of resulting Ta2NiS5 and Ta2NiS5 nanosheets ranges from tens of nanometers to few micrometers. Importantly, the production yield of single-layer Ta2NiS5 nanosheets is very high, ca. 86%. As a proof-of-concept application, the single-layer Ta2NiS5 is used as a novel fluorescence sensing platform for the detection of DNA with excellent selectivity and high sensitivity (with detection limit of 50 pM). These solution-processable, high-yield, large-amount ternary chalcogenide nanosheets may also have potential applications in electrocatalysis, supercapacitors, and electronic devices.

Preparation of MoS2–MoO3 Hybrid Nanomaterials for Light‐Emitting Diodes

A facile strategy to prepare MoS2 -MoO3 hybrid nanomaterials is developed, based on the heat-assisted partial oxidation of lithium-exfoliated MoS2  nanosheets in air followed by thermal-annealing-driven crystallization. The obtained MoS2 -MoO3 hybrid nanomaterial exhibits p-type conductivity. As a proof-of-concept application, an n-type SiC/p-type MoS2 -MoO3 heterojunction is used as the active layer for light-emitting diodes. The origins of the electroluminescence from the device are theoretically investigated. This facile synthesis and application of hybrid nanomaterials opens up avenues to develop new advanced materials for various functional applications, such as in electrics, optoelectronics, clean energy, and information storage.

Coating Two-Dimensional Nanomaterials with Metal–Organic Frameworks

We demonstrate the coating of various 2D nanomaterials including MoS2 nanosheets, graphene oxide (GO), and reduced graphene oxide (rGO) with zeolitic imidazolate frameworks (i.e., ZIF-8) via a facile procedure. Additionally, ternary core-shell structures like Pt-MoS2@ZIF-8, Pt-GO@ZIF-8, and Pt-rGO@ZIF-8 have also been prepared. As a proof-of-concept application, a memory device based on MoS2@ZIF-8 hybrid was fabricated and it exhibited write-once-read-many-times (WORM) memory effect with high ON/OFF ratio and long operating lifetime. It is expected that MOF coated 2D nanomaterials may find wide applications in energy storage and conversion, catalysis, sensing, and information storage devices.

One-Pot Synthesis of Highly Anisotropic Five-Fold-Twinned PtCu Nanoframes Used as a Bifunctional Electrocatalyst for Oxygen Reduction and Methanol Oxidation.

Five-fold-twinned PtCu nanoframes (NFs) with nanothorns protruding from their edges are synthesized by a facile one-pot method. Compared to commercial Pt/C catalyst, the obtained highly anisotropic five-fold-twinned PtCu NFs show enhanced electrocatalytic performance toward the oxygen reduction reaction and methanol oxidation reaction under alkaline conditions.

Bioinspired Design of Ultrathin 2D Bimetallic Metal–Organic-Framework Nanosheets Used as Biomimetic Enzymes

With the bioinspired design of organic ligands and metallic nodes, novel ultrathin 2D bimetallic metal-organic-framework nanosheets are successfully synthesized, which can serve as advanced 2D biomimetic nanomaterials to mimic heme proteins.