Hydrothermal Approach to Spinel-Type 2D Metal Oxide Nanosheets

Regioselective Friedel-Crafts Acylation Reaction Using Single Crystalline and Ultrathin Nanosheet Assembly of Scrutinyite-SnO2

Peculiar physicochemical properties of two-dimensional (2D) nanomaterials have attracted research interest in developing new synthetic technology and exploring their potential applications in the field of catalysis. Moreover, ultrathin metal oxide nanosheets with atomic thickness exhibit abnormal surficial properties because of the unique 2D confinement effect. In this work, we present a facile and general approach for the synthesis of single crystalline and ultrathin 2D nanosheets assembly of scrutinyite-SnO₂ through a simple solvothermal method. The structural and compositional characterization using X-ray diffraction (Rietveld refinement analysis), high-resolution transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and so on reveal that the as-synthesized 2D nanosheets are ultrathin and single crystallized in the scrutinyite-SnO₂ phase with high purity. The ultrathin SnO₂ nanosheets show predominant growth in the [011] direction on the main surface having a thickness of ca. 1.3 nm. The SnO₂ nanosheets are further employed for the regioselective Friedel-Crafts acylation to synthesize aromatic ketones that have potential significance in chemical industry as synthetic intermediates of pharmaceuticals and fine chemicals. A series of aromatic substrates acylated over the SnO₂ nanosheets have afforded the corresponding aromatic ketones with up to 92% yield under solvent-free conditions. Comprehensive catalytic investigations display the SnO₂ nanosheet assembly as a better catalytic material compared to the heterogeneous metal oxide catalysts used so far in the view of its activity and reusability in solvent-free reaction conditions.

Progress on two-dimensional binary oxide materials

Two-dimensional van der Waals (2D vdW) materials have attracted much attention because of their unique electronic and optical properties. Since the successful isolation of graphene in 2004, many interesting 2D materials have emerged, including elemental olefins (silicene, germanene, etc.), transition metal chalcogenides, transition metal carbides (nitrides), hexagonal boron, etc. On the other hand, 2D binary oxide materials are an important group in the 2D family owing to their high structural diversity, low cost, high stability, and strong adjustability. This review systematically summarizes the research progress on 2D binary oxide materials. We discuss their composition and structure in terms of vdW and non-vdW categories in detail, followed by a discussion of their synthesis methods. In particular, we focus on strategies to tailor the properties of 2D oxides and their emerging applications in different fields. Finally, the challenges and future developments of 2D binary oxides are provided.

Synthesis and characterization of ZnGa2O4 composites and its photocatalytic properties for energy applications

ZnGa₂O₄ nanocomposites have been widely used for photocatalytic degradation of industrial dyes. In this work, ZnGa₂O₄ was synthesized from zinc sulphate heptahydrate ZnSO₄^.10H₂O and Gallium (III) oxide (Ga₂O₃) by hydrothermal method. As prepared, ZnGa₂O₄ nanocomposites was used as a photocatalyst degradation of three organic dyes rhodamine-B, methylene blue, and methyl orange, under ultraviolet (UV) light irradiation. The ZnGa₂O₄ nanocomposites structure, morphology, size and optical properties were studied by X-ray diffraction (XRD), Fourier transform Raman spectroscopy (FT-Raman), scanning electron microscopy (SEM), Transmission electron microscopes (TEM) and photoluminescence spectra (PL). Moreover, the results explained the rate-controlling mechanisms of the dye degradation process followed by second-order kinetics. After 100 min of adsorption kinetic models, the decomposition of rhodamine-B (7.2 Ct mg/L, 5.2 Ct mg/L, and 4.1 Ct mg/L), methylene blue (42.8 qt mg/g, 44.8 qt mg/g, and 45.9 qt mg/g), and methyl orange (42.8 qe mg/g, 44.8 qe mg/g, and 45.9 qe mg/g) respectively. This investigation study offers a promising method to design more efficient ZnGa₂O₄ nanocomposites based photocatalytic degradation of industrial organic dyes.

Recent advances in the fabrication of 2D metal oxides

Atomically thin two-dimensional (2D) metal oxides exhibit unique optical, electrical, magnetic, and chemical properties, rendering them a bright application prospect in high-performance smart devices. Given the large variety of both layered and non-layered 2D metal oxides, the controllable synthesis is the critical prerequisite for enabling the exploration of their great potentials. In this review, recent progress in the synthesis of 2D metal oxides is summarized and categorized. Particularly, a brief overview of categories and crystal structures of 2D metal oxides is firstly introduced, followed by a critical discussion of various synthesis methods regarding the growth mechanisms, advantages, and limitations. Finally, the existing challenges are presented to provide possible future research directions regarding the synthesis of 2D metal oxides. This work can provide useful guidance on developing innovative approaches for producing both 2D layered and non-layered nanostructures and assist with the acceleration of the research of 2D metal oxides.

Doping Process of 2D Materials Based on the Selective Migration of Dopants to the Interface of Liquid Metals

The introduction of trace impurities within the doping processes of semiconductors is still a technological challenge for the electronics industries. By taking advantage of the selective enrichment of liquid metal interfaces, and harvesting the doped metal oxide semiconductor layers, the complexity of the process can be mitigated and a high degree of control over the outcomes can be achieved. Here, a mechanism of natural filtering for the preparation of doped 2D semiconducting sheets based on the different migration tendencies of metallic elements in the bulk competing for enriching the interfaces is proposed. As a model, liquid metal alloys with different weight ratios of Sn and Bi in the bulk are employed for harvesting Bi₂ O₃ -doped SnO nanosheets. In this model, Sn shows a much stronger tendency than Bi to occupy surface sites of the Bi-Sn alloys, even at the very high concentrations of Bi in the bulk. This provides the opportunity for creating SnO 2D sheets with tightly controlled Bi₂ O₃ dopants. By way of example, it is demonstrated how such nanosheets could be made selective to both reducing and oxidizing environmental gases. The process demonstrated here offers significant opportunities for future synthesis and fabrication processes in the electronics industries.

Role of Ga3+ promoter in the direct synthesis of iso-butanol via syngas over a K–ZnO/ZnCr2O4 catalyst

ZG, gallium cluster and ZnGa₂O₄ were formed by introducing Ga³⁺ to K–ZnO/ZnCr₂O₄ iso-butanol catalyst. Only a moderate amount of ZG promotes the space time yield (STY) and selectivity of alcohols for iso-butanol synthesis.

The synthesis and formation mechanism of nonpolar InN nanoplates

High-crystal-quality nonpolar indium nitride (InN) nanoplates were synthesized via deploying controllable chemical vapor deposition (CVD) technology using the M-plane of GaN nanowires (NWs) as a template.

Graphene oxide induced assembly and crumpling of Co3O4 nanoplates

Cobalt (II, III) oxide (Co₃O₄) has been widely studied and applied in various fields, however, it suffers from slow mass and electron transfer during applications. Herein, crumpled Co₃O₄ and Co₃O₄/reduced graphene oxide (rGO) with tunable 2D-in-3D structures were prepared by combining spray pyrolysis with a graphene oxide (GO) template. The 2D Co₃O₄ nanoplates were interconnected with each other to form a 3D ball with many wrinkles, resulting in defect enrichment on the abundant boundaries of the nanosheets, which provided more active sites for catalytic reactions. In addition, the unique 2D-in-3D structure allowed fast mass transfer and structural stability. Furthermore, the assembled structure could be understood as being composed of uniformly distributed oxygen-containing functional groups pinning metal cations on the GO surface through electrostatic interaction, and the 2D structure of the GO enabled the in situ converted Co₃O₄ to grow along the GO surface with excellent dispersion. Taking advantage of the above, the Co₃O₄/rGO balls demonstrated an excellent oxygen evolution reaction performance, an overpotential of 298 mV at a current density of 10.0 mA cm^-2 and a current density of 115.9 mA cm^-2 at the overpotential of η = 500 mV.

Band-Gap Tunable 2D Hexagonal (GaN)1-x(ZnO)x Solid-Solution Nanosheets for Photocatalytic Water Splitting

A (GaN)_1-x(ZnO)_x solid solution as a promising visible-light-driven photocatalyst for overall water splitting has attracted extensive attention. In this work, we proposed a template reactive strategy toward the synthesis of band-gap tunable 2D (GaN)_1-x(ZnO)_x nanosheets as thin as 14 nm to reduce the carrier transportation path and thus efficiently decrease the recombination of electrons and holes. It is demonstrated that the template strategy enables an ideal morphology and structure transformation from hexagonal 2D ZnGa₂O₄ nanosheets to 2D (GaN)_1-x(ZnO)_x nanosheets in the nitridation process. After the modification of 1 wt % of Rh cocatalyst, the flowerlike (GaN)_0.89(ZnO)_0.11 nanosheets show an enhanced hydrogen evolution in pure water (pH 4.5).