Two-dimensional (2D) nanostructures are highly attractive for fabricating nanodevices due to their high surface-to-volume ratio and good compatibility with device design. In recent years 2D nanostructures of various materials including metal oxides, graphene, metal dichalcogenides, phosphorene, BN and MXenes, have demonstrated significant potential for gas sensors. This review aims to provide the most recent advancements in utilization of various 2D nanomaterials for gas sensing. The common methods for the preparation of 2D nanostructures are briefly summarized first. The focus is then placed on the sensing performances provided by devices integrating 2D nanostructures. Strategies for optimizing the sensing features are also discussed. By combining both the experimental results and the theoretical studies available, structure-properties correlations are discussed. The conclusion gives some perspectives on the open challenges and future prospects for engineering advanced 2D nanostructures for high-performance gas sensors devices.

Two-Dimensional Nanostructured Materials for Gas Sensing

It is highly demanded to steer the charge flow in photocatalysts for efficient photocatalytic hydrogen reactions (PHRs). In this study, we developed a smart strategy to position MoS2 quantum dots (QDs) at the S vacancies on a Zn facet in monolayered ZnIn2S4 (Vs-M-ZnIn2S4) to craft a two-dimensional (2D) atomic-level heterostructure (MoS2QDs@Vs-M-ZnIn2S4). The electronic structure calculations indicated that the positive charge density of the Zn atom around the sulfur vacancy (Vs) was more intensive than other Zn atoms. The Vs confined in monolayered ZnIn2S4 established an important link between the electronic manipulation and activities of ZnIn2S4. The Vs acted as electron traps, prevented vertical transmission of electrons, and enriched electrons onto the Zn facet. The Vs-induced atomic-level heterostructure sewed up vacancy structures of Vs-M-ZnIn2S4, resulting in a highly efficient interface with low edge contact resistance. Photogenerated electrons could quickly migrate to MoS2QDs through the intimate...

MoS2 Quantum Dot Growth Induced by S Vacancies in a ZnIn2S4 Monolayer: Atomic-Level Heterostructure for Photocatalytic Hydrogen Production

Zinc oxide (ZnO) is an adaptable material that has distinctive properties, such as high-sensitivity, large specific area, non-toxicity, good compatibility and a high isoelectric point, which favours it to be considered with a few exceptions. It is the most desirable group of nanostructure as far as both structure and properties. The unique and tuneable properties of nanostructured ZnO shows excellent stability in chemically as well as thermally stable n-type semiconducting material with wide applications such as in luminescent material, supercapacitors, battery, solar cells, photocatalysis, biosensors, biomedical and biological applications in the form of bulk crystal, thin film and pellets. The nanosized materials exhibit higher dissolution rates as well as higher solubility when compared to the bulk materials. This review significantly focused on the current improvement in ZnO-based nanomaterials/composites/doped materials for the application in the field of energy storage and conversion devices and biological applications. Special deliberation has been paid on supercapacitors, Li-ion batteries, dye-sensitized solar cells, photocatalysis, biosensors, biomedical and biological applications. Finally, the benefits of ZnO-based materials for the utilizations in the field of energy and biological sciences are moreover consistently analysed.

https://iopscience.iop.org/article/10.1088/1361-6528/ab268a/pdf

A review on ZnO nanostructured materials: energy, environmental and biological applications.

Electrochemical heavy metal detection, photocatalytic, photoluminescence, biodiesel production and antibacterial activities of Ag–ZnO nanomaterial

Utilising pseudocapacitive lithium storage is one of the most effective methods to improve the rate performance. In this work, hydrogenated anatase TiO2 nanospindles with a carbon coating (H-TiO2@C) are synthesized using a facile hydrothermal process, followed by an annealing treatment of 506 epoxy resin coated TiO2 nanospindles in a H2/Ar atmosphere. The hydrogenation process can generate rich oxygen vacancies on the outermost surface of TiO2 nanospindles. When used as an anode material for LIBs, the H-TiO2@C electrode exhibits excellent cycling ability and rate performance. It delivers a high reversible capacity of 310 mA h g−1 at 0.1 A g−1 and 126 mA h g−1 at 1 A g−1. The pseudocapacitive contribution is as high as 63.9% as revealed by cyclic voltammetry. Such an excellent electrochemical performance can be ascribed to the synergistic effect of oxygen vacancies and the carbon coating for enhancing the pseudocapacitive effect. This work may provide a new strategy to effectively improve the pseudocapacitive properties of metal oxides.

Oxygen-deficient anatase TiO2@C nanospindles with pseudocapacitive contribution for enhancing lithium storage

ZnO enhanced NiO-based gas sensors towards ethanol

Despite the great potential of heteroatom-containing polycyclic aromatic hydrocarbons in organic optoelectronics, there are very limited reports on heteroaromatics containing a B–N–B bond in the π-scaffold. Herein, stable 1,9-dibora-9a-azaphenalenyl (DBAP) derivatives, named BNB-embedded phenalenyls, are presented. The DBAP skeleton contains a three-center two-π-electron B–N–B moiety with 12 π-electrons and can be regarded as the isoelectronic structure of the phenalenyl cation. Chemical reduction of the phenyl derivative of DBAP by potassium generated the dianion containing 14 delocalized π-electrons, which can be regarded as the isoelectronic structure of the phenalenyl anion. The dianion is sandwiched and stabilized by two bulky [K([18]crown-6)]+ counterions according to its X-ray structure. However, its monoanion (an isoelectronic structure of the henalenyl radical) generated by mixing equal moles of neutral compound and dianion gave an unusual B–N–B-embedded benzo[cd]fluoranthene dianion, which again...

B–N–B Bond Embedded Phenalenyl and Its Anions

Atomic layer deposition of ZnO onto Fe2O3 nanoplates for enhanced H2S sensing

MoO2@N-doped C nanofibers (MoO2@NC NFs) were synthesized by electrospinning with polyacrylonitrile as carbon source. The in situ formed MoO2 nanocrystals are completely embedded in the carbon nanofibers, which can not only accelerate ion transition, but also act as a buffer to avoid the mechanical degradation of active material due to the volume changes during charge/discharge cycling. When used as the anode material for both Li/Na-ion batteries, the as-synthesized MoO2@NC NFs displayed excellent Li+/Na+ storage properties. As the anode for Li-ion battery, the MoO2@NC NFs display a high discharge capacity of 930 mA h g−1 at a current density of 200 mA g−1 for 100 cycles, and 720 mA h g−1 at a current density of 1 A g−1 for 600 cycles. Moreover, the discharge capacity of 350 mA h g−1 could be realized at a current density of 100 mA g−1 for 200 cycles for Na-ion battery.

/pdf/electrospun-moo-2-nc-nanofibers-with-excellentli-na-storage-h83a8wffcq.pdf

Electrospun MoO 2 @NC nanofibers with excellentLi + /Na + storage for dual applications

An olympicenyl radical, a spin 1/2 hydrocarbon radical with C2v symmetry and uneven spin distribution, remains elusive despite the considerable theoretical research interest. Herein, we report syntheses of two air-stable olympicenyl radical derivatives, OR1 and OR2, with half-life times (τ1/2) in air-saturated solution of 7 days and 34 days. The high stability was ascribed to kinetic blocking of reactive sites with high spin densities. X-ray crystallographic analysis revealed unique 20-center-2-electron head-to-tail π-dimer structures with intermolecular distances shorter than the sum of van der Waals radius of carbon. The ground state of the π-dimers was found to be singlet, with singlet-triplet energy gaps estimated to be -2.34 kcal/mol and -3.28 kcal/mol for OR1 and OR2, respectively, by variable-temperature electron spin resonance (ESR) spectroscopy. The monomeric radical species were in equilibrium with the π-dimer in solution, and the optical and electrochemical properties of the monomers and π-dimers in solution were investigated by UV-vis-NIR spectroscopy and cyclic voltammetry, revealing a concentration-dependent nature. Theoretical calculations illustrated that upon formation of a π-dimer the local aromaticity of each monomer was enhanced, and spatial ring current between the monomers was present, which resulted in an increment of aromaticity of the interior of the π-dimer.

Jing Guo

Papers

ZnO enhanced NiO-based gas sensors towards ethanol

B–N–B Bond Embedded Phenalenyl and Its Anions

Atomic layer deposition of ZnO onto Fe2O3 nanoplates for enhanced H2S sensing

Electrospun MoO 2 @NC nanofibers with excellentLi + /Na + storage for dual applications

Stable Olympicenyl Radicals and Their π-Dimers