A Generalized Strategy for the Synthesis of Large‐Size Ultrathin Two‐Dimensional Metal Oxide Nanosheets

Two‐dimensional (2D) nanomaterials show unique electrical, mechanical, and catalytic performance owing to their ultrahigh surface‐to‐volume ratio and quantum confinement effects. However, ways to simply synthesize 2D metal oxide nanosheets through a general and facile method is still a big challenge. Herein, we report a generalized and facile strategy to synthesize large‐size ultrathin 2D metal oxide nanosheets by using graphene oxide (GO) as a template in a wet‐chemical system. Notably, the novel strategy mainly relies on accurately controlling the balance between heterogeneous growth and nucleation of metal oxides on the surface of GO, which is independent on the individual character of the metal elements. Therefore, ultrathin nanosheets of various metal oxides, including those from both main‐group and transition elements, can be synthesized with large size. The ultrathin 2D metal oxide nanosheets also show controllable thickness and unique surface chemical state.     

Kinetically Controlled Layer-by-Layer Stacking of Metal Oxide 2D Nanosheets

An efficient chemical way to finely control the layer-by-layer stacking of inorganic nanosheets (NS) is developed by tuning the type and composition of intercalant ion, and the reaction temperature for restacking process. The finely controlled stacking of NS relies on a kinetic control of the self-assembly of NS in the presence of coordinating organic cations. A critical role of organic cations in this assembly highlights the importance of the appropriate activation energy. Of prime importance is that a fine-control of the interstratification of 2D NS is highly effective not only in tailoring its pore structure but also in enhancing its electrode activity. The present study clearly demonstrates that the kinetically controlled restacking of NS provides a facile and powerful method to tailor their stacking number and functionality.     

Synthesis of Polyaniline‐Vanadium Oxide Nanocomposite Nanosheets

Summary: Polyaniline‐vanadium oxide nanocomposite nanosheets with thickness between 10 and 20 nm, and lateral dimensions in the range of hundreds of nanometers to several microns have been synthesized by in situ intercalation polymerization of aniline with layered V₂O₅ under hydrothermal conditions. The product was characterized by field‐emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT‐IR) spectroscopy, and X‐ray diffractometer (XRD). The effects of the concentration of aniline and reaction temperature on the morphologies of polyaniline‐vanadium oxide nanocomposites have also been investigated.

SEM image of tremella‐like polyaniline‐vanadium oxide nanocomposite nanosheets.     

Two-Dimensional MOF and COF Nanosheets: Synthesis and Applications in Electrochemistry

Metal–organic framework (MOF) and covalent organic framework (COF) nanosheets are a new type of two-dimensional (2D) materials with unique design principles and various synthesis methods. They are considered ideal electrochemical devices due to the ultrathin thickness, easily tunable molecular structure, large porosity and other unique properties. There are two common methods to synthesize 2D MOF/COF nanosheets: bottom-up and top-down. The top-down strategy mainly includes ultrasonic assisted exfoliation, electrochemical exfoliation and mechanical exfoliation. Another strategy mainly includes interface synthesis, modulation synthesis, surfactant-assisted synthesis. In this Review, the development of ultrathin 2D nanosheets in the field of electrochemistry (supercapacitors, batteries, oxygen reduction, and hydrogen evolution) is introduced, and their unique dimensional advantages are highlighted.     

Polyol Solvation Effect on Tuning the Universal Growth of Binary Metal Oxide Nanodots@Graphene Oxide Heterostructures for Electrochemical Applications

Tuning the uniformity and size of binary metal oxide nanodots on graphene oxide (BMO NDs@GO) is significant but full of challenges in wet-chemistry, owing to the difficulties of controlling the complicated cation/anion co-adsorption, heterogeneous nucleation, and overgrowth processes. Herein, the aim is to tune these processes by understanding the functions of various alcohol solvents for NDs growth on GO. It is found that the polyol solvation effect is beneficial for obtaining highly uniform BMO NDs@GO. Polyol shell capped metal ions exhibit stronger hydrogen-bond interactions with the GO surface, leading to a uniform cation/anion co-adsorption and followed heterogeneous nucleation. The polyol-solvated ions with large diffusion energy barrier drastically limit the ion diffusion kinetics in liquids and at the solid/liquid interface, resulting in a slow and controllable growth. Moreover, the synthesis in polyol systems is highly controllable and universal, thus eleven BMO and polynary metal oxide NDs@GO are obtained by this method. The synthetic strategy provides improved prospects for the manufacture of inorganic NDs and their expanding electrochemical applications.     

超薄Sm-MOF纳米片的合成及可见光催化降解芥子气模拟剂性能

超薄金属-有机框架材料(MOFs)纳米片具有高密度、 易暴露的表面活性位点、 较短的底物/产物扩散路径等特点, 是性能优异的异相催化剂. 本文以光活性有机配体(H₄TBAPy)和镧系金属离子Sm³⁺构筑光活性超薄MOFs纳米片, 以苯甲酸作为调节剂, 利用微波法快速合成了Sm-TBAPy二维纳米片. 利用扫描电子显微镜(SEM)、 透射电子显微镜(TEM)、 X射线衍射(XRD)、 紫外-可见漫反射光谱(UV-Vis DRS）、 傅里叶变换红外光谱(FTIR)和氮气吸附-脱附等手段表征了Sm-TBAPy二维纳米片的形貌、 结构和组成. 所合成的Sm-TBAPy为单分散二维纳米片, 宽度约为200 nm, 厚度约为12 nm, BET比表面为163 m²/g, 禁带宽度为2.62 eV. Sm-TBAPy二维纳米片在室温、 氧气氛围和可见光照射条件下, 可将芥子气模拟剂[2-氯乙基乙基硫醚(CEES)]高效、 高选择性氧化成亚砜产物CEESO, 且催化剂经过4次循环使用仍保持较高的催化性能. 结合电子顺磁共振波谱, 提出了Sm-TBAPy二维纳米片可见光催化氧化CEES的催化机理.     

Multishelled Metal Oxide Hollow Spheres: Easy Synthesis and Formation Mechanism

Uniform multishelled NiO, Co₃O₄, ZnO, and Au@NiO hollow spheres were synthesized (NiO and Co₃O₄ hollow spheres for the first time) by a simple shell‐by‐shell self‐assembly allowing for tuning of the the size, thickness and shell numbers by controlling the heat treatment, glucose/metal salt molar ratio, and hydrothermal reaction time. These findings further the development of synthetic methodologies for multishelled hollow structures and could open up new opportunities for deeper understanding of the mechanisms of shell‐by‐shell self‐assembly. Moreover, the double‐shelled NiO hollow sphere exhibits a higher photocatalytic activity for degradation of methyl orange than its morphological counterparts.     

An Overview on Graphene-Metal Oxide Semiconductor Nanocomposite: A Promising Platform for Visible Light Photocatalytic Activity for the Treatment of Various Pollutants in Aqueous Medium

Graphene is one of the most favorite materials for materials science research owing to its distinctive chemical and physical properties, such as superior conductivity, extremely larger specific surface area, and good mechanical/chemical stability with the flexible monolayer structure. Graphene is considered as a supreme matrix and electron arbitrator of semiconductor nanoparticles for environmental pollution remediation. The present review looks at the recent progress on the graphene-based metal oxide and ternary composites for photocatalysis application, especially for the application of the environmental remediation. The challenges and perspectives of emerging graphene-based metal oxide nanocomposites for photocatalysis are also discussed.     

还原态氧化石墨烯的制备及其对重金属离子的吸附性能

通过乙二胺（EDA）对氧化石墨烯（GO）进行还原制备了还原态氧化石墨烯（RGO）,利用红外光谱、拉曼光谱、热重分析和扫描电子显微镜等技术对制得的RGO进行了表征。 考察了RGO复合材料在静态吸附条件下对Pb(Ⅱ)、Cd(Ⅱ)、Cu(Ⅱ)和Mn(Ⅱ)金属离子的吸附性能。 结果表明,该吸附材料对上述4种重金属离子在25 ℃时的静态饱和吸附量分别为396.6、115.3、54.2和38.6 mg/g。 吸附于RGO上的Pb(Ⅱ)可用0.05 mol/L HCl溶液进行洗脱,再生后的RGO重复使用3次时吸附量能达到首次吸附量的85%。     

基于过渡金属硫化物/还原氧化石墨烯复合物的高性能超级电容器

组装高能量密度的非对称超级电容器需要使用比电容大、 体积变化小且循环稳定性好的电极材料. 过渡金属硫化物(TMSs)与纳米碳材料的复合物是此类电极材料之一. 采用水热法合成了由Cu-Mo硫化物在微波剥离的还原氧化石墨烯表面生长的复合材料(CuS-MoS₂/MErGO). 此复合材料在电流密度为2 A/g时具有高达861.5 F/g的比电容和良好的循环稳定性. 将1.6 V的电池电压施加在由NiS/MErGO为正极, CuS-MoS₂/MErGO为负极组装成的不对称超级电容器上时, 该电容器的功率密度为1.28 kW/kg, 且能量密度保持为54.2 W·h·kg^-1. 结果表明, TMS复合材料是一种很有前途的高性能电化学储能材料, 尤其是用于非对称超级电容器的组装.     

液相合成超薄TiO2纳米片微结构影响因素研究

二维纳米结构二氧化钛由于表面活性位点剧增可带来光催化活性的显著提高.本文通过液相法在低温条件下合成大尺寸TiO₂纳米片,重点研究溶液中硝酸浓度、熟化温度和反应物浓度对其二维结构形成过程的影响.采用透射电子显微镜（TEM）表征样品的微观形态,并结合紫外-可见吸收光谱、X射线衍射谱（XRD）、X射线光电子能谱（XPS）和傅立叶变换红外光谱分析样品的微结构性质.采用光催化还原Cr （VI）作为指示反应,评估各制备参数对二氧化钛光催化性能的影响.结果表明,硝酸浓度为0.0217~0.0721 mol·L^-1的样品在0~4℃条件下胶溶及熟化时可得到具有显著量子尺寸效应的超薄锐钛矿型TiO₂纳米片;硝酸浓度过高引起样品晶型和形态的转变,过低导致胶溶时间延长;熟化温度超过4℃会破坏二维结构的形成;提高反应物中乙醇的用量有助于分散水解产物,促进胶溶和二维结构的形成进程.     

Synthesis of Ultrathin and Grid-Structural Carbon Nanosheets Coupled with Mo2C for Electrocatalytic Hydrogen Production

Molybdenum carbide possessing a Pt-like d-band electronic structure is considered as one of potential candidates of electrocatalysts and it shows intrinsic catalytic property. However, a high carbonizing temperature easily leads to the coalescence of nanoparticles (NPs). Here, we propose a simple sol-gel route to achieve high dispersity of carbide NPs by designing a Mo-involved xerogel. The results show that molybdenum carbide NPs are dispersed and anchored on the nitrogen-doped carbon nanosheets (Mo₂C@NC). Ultrathin carbon layers resemble graphene and the network structures act as a support of carbide NPs, which can hinder NPs’ coalescence effectively. Nanpoparticles cross-coupled on network-structure nanosheets display the grid shapes. Electrochemical studies indicate that Mo₂C@NC material exhibits outstanding hydrogen evolution performance in alkaline electrolyte.     

Molecular Engineering of Metal Alkoxides for Solution Phase Synthesis of High-Tech Metal Oxide Nanomaterials

The ‘bottom-up’ synthesis of inorganic nanomaterials with precision at the atomic/molecular level offers many opportunities for the design and improvement of the nanomaterials for various applications. Molecular engineering during soft chemical processing for the synthesis of functional nanomaterials enables the desired chemical and physical properties of the precursors, such as solubility or volatility, clean decomposition, control of stoichiometry for multimetallic species to name a few, and leads to easy control of uniform particle size distribution, stoichiometry…. This Minireview illustrates some important aspects of the molecular engineering in light of some recent developments from the molecular synthesis of nanomaterials involving non-silicon metal alkoxide systems for high-tech applications.     

Controlled Assembly of Cu/Co-Oxide Beaded Nanoclusters on Thiolated Graphene Oxide Nanosheets for High-Performance Oxygen Evolution Catalysts

The use of water splitting modules is highly desired for the sustainable production of H₂ as a future energy carrier. However, the sluggish kinetics and demand of high anodic potential are the bottlenecks for half-the cell oxygen evolution reaction (OER), which severely hamper the overall conversion efficiency. Although transition metal oxides based electrocatalysts have been envisioned as cost-effective and potential contenders for this quest, nevertheless, their low conductivity, instability, and limited number of active sites are among the common impediments that need to be addressed to eventually enhance their inherent catalytic potential for enhanced OER activity. Herein, the controlled assembly of transition metal oxides, that is, Cu@CuO_x nanoclusters (NCs, ≈2 nm) and Co@CoO_x beaded nanoclusters (BNCs, ≈2 nm), on thiol-functionalized graphene oxide (G-SH) nanosheets is reported to form novel and highly efficient electrocatalysts for OER. The thiol (-SH) functionality was incorporated by selective epoxidation on the surface of graphene oxide (GO) to achieve chemically exfoliated nanosheets to enhance its conductivity and trapping ability for metal oxides in nanoscale dimensions (≈2 nm). During the electrocatalytic reaction, overpotentials of 290 mV and 310 mV are required to achieve a current density of 10 mA cm⁻² for BNCs and NCs, respectively, and the catalysts exhibit tremendous long-term stability (≈50 h) in purified alkaline medium (1 m KOH) with no dissolution in the electrolyte. Moreover, the smaller Tafel slopes (54 mV/dec for BNCs and 66 mV/dec for NCs), and a Faradic efficiency of approximately 96 % indicate not only the selectivity but also the tailored heterogeneous electrons transfer (HET) rate, which is required for fast electrode kinetics. It is anticipated that such ultrasmall metal oxide nanoclusters and their controlled assembly on a conducting surface (G-SH) may offer high electrochemical accessibility and a plethora of active sites owing to the drastic decrease in dimensions and thus can synergistically ameliorate the challenging OER process.     

Preparation of Janus Graphene Oxide (GO) Nanosheets Based on Electrostatic Assembly of GO Nanosheets and Polystyrene Microspheres

A facile and versatile method for the synthesis of Janus graphene oxide (GO) nanosheets with different structures is reported. Based on electrostatic assembly, Janus GO nanosheets can be easily functionalized with a template polymer or be defunctionalized by altering the ionic strength. By using this approach, Janus GO nanosheets are prepared successfully with hydrophobic polystyrene chains on one side and hydrophilic poly(2‐(dimethylamino)ethyl methacrylate) chains on the other side.

     

Separation and Determination of Beryllium Oxide in Glasses and Metal Oxides

Abstract

A method for the determination of beryllium oxide in glasses and in the presence of other metal oxides is described. Beryllium oxide has been separated from commonly associated metal oxides and gravimetrically determined using CDTA (1,2-cyclohexylenedinitrilo-tetraacetic acid). Using this method, separations and recovery of beryllium oxide were excellent.     

Controlled Synthesis of Ultrathin Lanthanide Oxide Nanosheets and Their Promising pH‐Controlled Anticancer Drug Delivery

Various lanthanide oxides (Sm₂O₃ and Gd₂O₃) nanostructures were synthesized by a facile hydrothermal method. The loss of surfactants on the nanocrystals surface, followed by the resultant assembly is responsible for the formation of ultrathin nanosheets. Owing to strong surface effects, the different morphologies of the Sm₂O₃:5 % Eu and Gd₂O₃:5 % Eu nanocrystals present unique photoluminescence properties. As a proof‐of‐concept application, the as‐obtained Sm₂O₃ and Gd₂O₃ ultrathin nanosheets exhibit promising pH‐controlled anticancer drug‐delivery behavior.     

Zeolitic Imidazolate Framework/Graphene Oxide Hybrid Nanosheets as Seeds for the Growth of Ultrathin Molecular Sieving Membranes

A defect‐free zeolitic imidazolate framework‐8 (ZIF‐8)/graphene oxide (GO) membrane with a thickness of 100 nm was prepared using two‐dimensional (2D) ZIF‐8/GO hybrid nanosheets as seeds. Hybrid nanosheets with a suitable amount of ZIF‐8 nanocrystals were essential for producing a uniform seeding layer that facilitates fast crystal intergrowth during membrane formation. Moreover, the seeding layer acts as a barrier between two different synthesis solutions, and self‐limits crystal growth and effectively eliminates defects during the contra‐diffusion process. The resulting ultrathin membranes show excellent molecular sieving gas separation properties, such as with a high CO₂/N₂ selectivity of 7.0. This 2D nano‐hybrid seeding strategy can be readily extended to the fabrication of other defect‐free and ultrathin MOF or zeolite molecular sieving membranes for a wide range of separation applications.     

Fabrication of Ultrathin Membranes Using 2D-MOF Nanosheets for Tunable Gas Separation

Two-dimensional (2D) metal-organic frameworks (MOF) nanosheets have emerged as novel membrane materials for gas separation. However, the development of ultrathin MOF membranes with tunable separation performances is still a challenge. Herein, we developed a facile GO-assisted restacking method to fabricate defect-free membranes with monolayer Zr-BTB nanosheets. Obtained ultrathin membranes ranging from 130 nm to 320 nm show tunable separation performances and exceed the 2008 Robeson upper bound by changing the amount of nanolayers in vertical stacking direction. Furthermore, a heating filtration method was used to change the restacking process of nanosheets in the horizontal direction. As a result, H₂/CO₂ selectivity can be enhanced by two times with the same membrane thickness (130 nm) and H₂ permeance is almost maintained to be 7.0×10⁻⁷ mol m⁻² s⁻¹ pa⁻¹. This method may provide a possible way to efficiently tune the gas separation performances of MOF membranes.