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.     

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.     

Hyperbranched polyglycidol assisted green synthetic protocols for the preparation of multifunctional metal nanoparticles

Biocompatible hyperbranched polyglycidol (HBP) has been demonstrated to be an effective reducing and stabilizing agent for the synthesis of highly water-soluble monometallic (Au, Ag, Pt, Pd, and Ru) and bimetallic (Au/Pt, Au/Pd, and Au/Ru) nanoparticles (NPs), which provides a general and green protocol to fabricate metal NPs. The HBP-assisted reduction of metal ions follows an analogous polyol process. The reduction reaction rate increases sharply by increasing the temperature and the molecular weight of HBP. The size of NPs is controllable simply by changing the concentration of the metal precursor. High molecular weight HBP is favorable for the formation of NPs with uniform size and improved stability. By utilizing hydroxyl groups in the HBP-passivation layer of Au NPs, TiO(2)/Au, GeO(2)/Au, and SiO(2)/Au nanohybrids are also fabricated via sol-gel processes, which sets a typical example for the creation of versatile metal NPs/inorganic oxide hybrids based on the as-prepared multifunctional NPs.     

Surface and Interface Engineering of Graphene Oxide Films by Controllable Photoreduction

We report herein the engineering of the surface/interface properties of graphene oxide (GO) films by controllable photoreduction treatment. In our recent works, typical photoreduction processes, including femtosecond laser direct writing (FsLDW), laser holographic lithography, and controllable UV irradiation, have been employed to make conductive reduced graphene oxide (RGO) microcircuits, hierarchical RGO micro‐nanostructures with both superhydrophobicity and structural color, as well as moisture‐responsive GO/RGO bilayer structures. Compared with other reduction protocols, for instance, chemical reduction and thermal annealing, the photoreduction strategy shows distinct advantages, such as mask‐free patterning, chemical‐free modification, controllable reduction degree, and environmentally friendly processing. These works indicate that the surface and interface engineering of GO through controllable photoreduction of GO holds great promise for the development of various graphene‐based microdevices.     

Silver Nanostructures on Graphene Oxide as the Substrate for Surface-Enhanced Raman Scattering (SERS)

Nanosized surface-enhanced Raman scattering (SERS) substrates fabricated by the controlled growth of metal nanostructures on water-dispersed two-dimensional nanomaterials can open a new avenue for SERS analysis of liquid samples in biological fields. In this work, regular and uniform Ag nanostructures were grown on the surface of graphene oxide (GO) through a microwave-assisted hydrothermal method. Polyamidoamine (PAMAM) dendrimers were assembled on the surface of GO to form GO/PAMAM templates for growing Ag nanostructures, which are primarily comprised of Ag dimers and trimers. The prepared Ag/GO nanocomposites are highly dispersed and stable in aqueous solution and may be used as substrates for enhanced Raman detection of rhodamine 6?G (R6G) in aqueous solution. This special substrate provides high-performance SERS and suppresses R6G fluorescence in aqueous solution and is promising as a nanosized material for the enhanced Raman detection of liquid samples in biological diagnostics.     

Synthesis of monodisperse spherical nanocrystals

Much progress has been made over the past ten years on the synthesis of monodisperse spherical nanocrystals. Mechanistic studies have shown that monodisperse nanocrystals are produced when the burst of nucleation that enables separation of the nucleation and growth processes is combined with the subsequent diffusion-controlled growth process through which the crystal size is determined. Several chemical methods have been used to synthesize uniform nanocrystals of metals, metal oxides, and metal chalcogenides. Monodisperse nanocrystals of CdSe, Co, and other materials have been generated in surfactant solution by nucleation induced at high temperature, and subsequent aging and size selection. Monodisperse nanocrystals of many metals and metal oxides, including magnetic ferrites, have been synthesized directly by thermal decomposition of metal-surfactant complexes prepared from the metal precursors and surfactants. Nonhydrolytic sol-gel reactions have been used to synthesize various transition-metal-oxide nanocrystals. Monodisperse gold nanocrystals have been obtained from polydisperse samples by digestive-ripening processes. Uniform-sized nanocrystals of gold, silver, platinum, and palladium have been synthesized by polyol processes in which metal salts are reduced by alcohols in the presence of appropriate surfactants.     

Ultra-Permeable Dual-Mechanism-Driven Graphene Oxide Framework Membranes for Precision Ion Separations

Two-dimensional graphene oxide (GO) membranes are gaining popularity as a promising means to address global water scarcity. However, current GO membranes fail to sufficiently exclude angstrom-sized ions from solution. Herein, a de novo “posterior” interfacial polymerization (p-IP) strategy is reported to construct a tailor-made polyamide (PA) network in situ in an ultrathin GO membrane to strengthen size exclusion while imparting a positively charged membrane surface to repel metal ions. The electrostatic repulsion toward metal ions, coupled with the reinforced size exclusion, synergistically drives the high-efficiency metal ion separation through the synthesized positively charged GO framework (PC-GOF) membrane. This dual-mechanism-driven PC-GOF membrane exhibits superior metal ion rejection, anti-fouling ability, good operational stability, and ultra-high permeance (five times that of pristine GO membranes), enabling a sound step towards a sustainable water-energy-food nexus.     

氧化石墨阳离子交换容量测定过程中结构的变化

氧化石墨(GO)结构层上的碳羟基(―C―OH)和边缘羧基(―COOH)在水介质中发生质子化反应解离出的H+具有阳离子可交换性。实验采用甲醛缩合法测量了GO的阳离子交换容量(CEC),用X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱和X射线光电子能谱(XPS)分析测试手段对GO阳离子交换过程中间产物的结构变化进行了分析。结果表明,GO的CEC高达541.48 mmol/100 g。NH_4~+和Ca~(2+)交换后的GO,保持稳定的层状结构,c轴方向层间距分别增大了0.1499和0.2905 nm。NH_4+和Ca~(2+)主要以层间可交换阳离子形式存在于层间域中,并与水分子形成可交换水化阳离子层,部分以[NH_4(H_2O)_6]+和[Ca(H_2O)_6]_2+的形式存在于结构层的边缘附近,共同平衡结构层水解产生的负电荷。     

A Molecular Pillar Approach To Grow Vertical Covalent Organic Framework Nanosheets on Graphene: Hybrid Materials for Energy Storage

Hybrid 2D–2D materials composed of perpendicularly oriented covalent organic frameworks (COFs) and graphene were prepared and tested for energy storage applications. Diboronic acid molecules covalently attached to graphene oxide (GO) were used as nucleation sites for directing vertical growth of COF‐1 nanosheets (v‐COF‐GO). The hybrid material has a forest of COF‐1 nanosheets with a thickness of 3 to 15 nm in edge‐on orientation relative to GO. The reaction performed without molecular pillars resulted in uncontrollable growth of thick COF‐1 platelets parallel to the surface of GO. The v‐COF‐GO was converted into a conductive carbon material preserving the nanostructure of precursor with ultrathin porous carbon nanosheets grafted to graphene in edge‐on orientation. It was demonstrated as a high‐performance electrode material for supercapacitors. The molecular pillar approach can be used for preparation of many other 2D‐2D materials with control of their relative orientation.     

Scalable Template Synthesis of Resorcinol–Formaldehyde/Graphene Oxide Composite Aerogels with Tunable Densities and Mechanical Properties

Resorcinol–formaldehyde (RF) and graphene oxide (GO) aerogels have found a variety of applications owing to their excellent properties and remarkable flexibility. However, the macroscopic and controllable synthesis of their composite gels is still a great challenge. By using GO sheets as template skeletons and metal ions (Co²⁺, Ni²⁺, or Ca²⁺) as catalysts and linkers, the first low‐temperature scalable strategy for the synthesis of a new kind of RF–GO composite gel with tunable densities and mechanical properties was developed. The aerogels can tolerate a strain as high as 80 % and quickly recover their original morphology after the compression has been released. Owing to their high compressibility, the gels might find applications in various areas, for example, as adsorbents for the removal of dye pollutants and in oil‐spill cleanup.     

Modeling growth of organized nanoporous structures by anodic oxidation

Nanostructured porous oxides are produced by anodic dissolution of several metals. A scaling approach is introduced to explain pattern nucleation in an oxide layer, and a related microscopic model shows oxide growth with long nanopores. The scaling approach matches the time of ion transport across the thin oxide layer, which is related to metal corrosion, and the time of diffusion along the oxide/solution (OS) interface, which represents the extension of oxide dissolution. The selected pattern size is of order (dD(S)/v(O))(1/2), where d is the oxide thickness, v(O) is the migration velocity of oxygen ions across the oxide, and D(s) is the diffusion coefficient of H(+) ions along the oxide/solution interface. This result is consistent with available experimental data for those quantities, predicts the increase of pore size with the external voltage, and suggests the independence of pore size with the solution pH. Subsequently, we propose a microscopic model that expresses the main physicochemical processes as a set of characteristic lengths for diffusion and surface relaxation. It shows a randomly perturbed OS interface at short times, its evolution to pore nucleation and to stable growth of very long pores, in agreement with the mechanistic scenario suggested by two experimental groups. The decrease of the size of the walls between the pores with the interface tension is consistent with arguments for formation of titania nanotube arrays instead of nanopores. These models show that pattern nucleation and growth depend on matching a small number of physicochemical parameters, which is probably the reason for the production of nanostructured porous oxides from various materials under suitable electrochemical conditions.     

A Review on Graphene Oxide Two-dimensional Macromolecules: from Single Molecules to Macro-assembly

Graphene oxide(GO), which consists of two-dimensional(2 D) sp² carbon hexagonal networks and oxygen-contained functional groups, has laid the foundation of mass production and applications of graphene materials. Made by chemical oxidation of graphite, GO is highly dispersible or even solubilized in water and polar organic solvents, which resolves the hard problem of graphene processing and opens a door to wet-processing of graphene. Despite its defects, GO is easy to functionalize, dope, punch holes, cut into pieces, conduct chemical reduction, form lyotropic liquid crystal, and assemble into macroscopic materials with tunable structures and properties as a living building block. GO sheet has been viewed as a single molecule, a particle, as well as a soft polymer material. An overview on GO as a 2 D macromolecule is essential for studying its intrinsic properties and guiding the development of relevant subjects. This review mainly focuses on recent advances of GO sheets, from single macromolecular behavior to macro-assembled graphene material properties. The first part of this review offers a brief introduction to the synthesis of GO molecules. Then the chemical structure and physical properties of GO are presented, as well as its polarity in solvent and rheology behavior. Several key parameters governing the ultimate stability of GO colloidal behavior, including size, p H and the presence of cation in aqueous dispersions, are highlighted. Furthermore, the discovery of GO liquid crystal and functionalization of GO molecules have built solid new foundations of preparing highly ordered, architecture-tunable, macro-assembled graphene materials, including 1 D graphene fibers, 2 D graphene films, and 3 D graphene architectures. The GO-based composites are also viewed and the interactions between these target materials and GO are carefully discussed. Finally, an outlook is provided in this field, where GO is regarded as macromolecules, pointing out the challenges and opportunities that exist in the field. We hope that this review will be beneficial to the understanding of GO in terms of chemical structure,molecular properties, macro-assembly and potential applications, and encourage further development to extend its investigations from basic research to practical applications.     

Synchronous Dual Electrolyte Additive Sustains Zn Metal Anode with 5600 h Lifespan

Despite conspicuous merits of Zn metal anodes, the commercialization is still handicapped by rampant dendrite formation and notorious side reaction. Manipulating the nucleation mode and deposition orientation of Zn is a key to rendering stabilized Zn anodes. Here, a dual electrolyte additive strategy is put forward via the direct cooperation of xylitol (XY) and graphene oxide (GO) species into typical zinc sulfate electrolyte. As verified by molecular dynamics simulations, the incorporated XY molecules could regulate the solvation structure of Zn²⁺, thus inhibiting hydrogen evolution and side reactions. The self-assembled GO layer is in favor of facilitating the desolvation process to accelerate reaction kinetics. Progressive nucleation and orientational deposition can be realized under the synergistic modulation, enabling a dense and uniform Zn deposition. Consequently, symmetric cell based on dual additives harvests a highly reversible cycling of 5600 h at 1.0 mA cm⁻²/1.0 mAh cm⁻².     

Designing GO Channels with High Selectivity for CO2/N2 Separation via Incorporating Metal Ions

Graphene oxide (GO) membranes holds great potential for high-performance CO₂ capture. Aiming at enhancing the CO₂ separation performance and structural stability of GO membranes, functionalizing GO channels with metal ions confers a promising strategy. In this study, we reported the fabrication of metal ion-incorporated GO membranes with remarkably improved CO₂/N₂ separation performance. The metal ions within GO channels contribute to facilitating CO₂ transport, decreasing N₂ solubility, hindering N₂ diffusion, and form multiple interactions with GO nanosheets. After introducing Mg²⁺ ions, the CO₂/N₂ separation factor of GO membrane is remarkably increased from 4 to 48.8 with the CO₂ permeance increases 1.5 times. Moreover, the separation performance of the GO-Mg²⁺ membranes shows an excellent long-term stability owing to the structural robustness. This study could provide insights into the regulation of the microstructure of metal ion-functionalized GO membranes for highly selective transport of specific molecules.     

Highly Porous Hydroxyapatite/Graphene Oxide/Chitosan Beads as an Efficient Adsorbent for Dyes and Heavy Metal Ions Removal

Dye and heavy metal contaminants are mainly aquatic pollutants. Although many materials and methods have been developed to remove these pollutants from water, effective and cheap materials and methods are still challenging. In this study, highly porous hydroxyapatite/graphene oxide/chitosan beads (HGC) were prepared by a facile one-step method and investigated as efficient adsorbents. The prepared beads showed a high porosity and low bulk density. SEM images indicated that the hydroxyapatite (HA) nanoparticles and graphene oxide (GO) nanosheets were well dispersed on the CTS matrix. FT-IR spectra confirmed good incorporation of the three components. The adsorption behavior of the obtained beads to methylene blue (MB) and copper ions was investigated, including the effect of the contact time, pH medium, dye/metal ion initial concentration, and recycle ability. The HGC beads showed rapid adsorption, high capacity, and easy separation and reused due to the porous characteristics of GO sheets and HA nanoparticles as well as the rich negative charges of the chitosan (CTS) matrix. The maximum sorption capacities of the HGC beads were 99.00 and 256.41 mg g⁻¹ for MB and copper ions removal, respectively.     

CC Bonding of Graphene Oxide on 4‐Aminophenyl Modified Gold Electrodes towards Simultaneous Detection of Heavy Metal Ions

This paper studied the electrochemical sensors based on C? C bonding of graphene oxide (GO) on π‐conjugated aromatic group modified gold electrodes for simultaneous detection of heavy metal ions. For comparison, another sensing interface Au‐Ph‐NH‐CO‐GO, in which GO was modified to Au‐Ph‐NH₂ interfaces by amide bonding. On the basis of the principle of heavy metal ions complexation with oxygenated species on GO, the fabricated sensing interfaces were used for the simultaneous determination of Pb²⁺, Cu²⁺ and Hg²⁺. The performance of two sensing interfaces for simultaneous detection of three metal ions was compared. Au‐Ph‐GO sensing interface demonstrated higher sensitivity and better repeatability than Au‐Ph‐NH‐CO‐GO sensing interface.     

Highly Dispersible and Stable Anionic Boron Cluster–Graphene Oxide Nanohybrids

An efficient process to produce boron cluster–graphene oxide nanohybrids that are highly dispersible in water and organic solvents is established for the first time. Dispersions of these nanohybrid materials in water were extraordinarily stable after one month. Characterization of hybrids after grafting of appropriate cobaltabisdicarbollide and closo‐dodecaborate derivatives onto the surface of graphene oxide (GO) was done by FT‐IR, XPS, and UV/Vis. Thermogravimetric analysis (TGA) clearly shows a higher thermal stability for the modified‐GO nanohybrids compared to the parent GO. Of particular note, elemental mapping by energy‐filtered transmission electron microscopy (EFTEM) reveals that a uniform decoration of the graphene oxide surface with the boron clusters is achieved under the reported conditions. Therefore, the resulting nanohybrid systems show exceptional physico‐chemical and thermal properties, paving the way for an enhanced processability and further expanding the range of application for graphene‐based materials.     

Nanostructured Three‐Dimensional (3D) Assembly of 2D MoS2 and Graphene Directly Build From Acidic Graphite Oxide

A 3D highly interconnected macroporous network of reduced GO having finely dispersed few‐layered 2D MoS₂ nanosheets was constructed through direct use of acidic graphite oxide (GO) for the first time. This facile and technologically scalable process can afford efficient hydrodesulfurization electrocatalysts as potential anode materials at lower cost, and can circumvent the poor thermal stability and recyclability of the material. The strategy provided here can be the basis to design and develop practical processes to address the ultimate goal of large‐scale manufacturing of hybrids composed of 2D materials for various energy and catalysis applications.     

Graphene oxide-based two-dimensional molecular brush for efficient removal of lead and copper ions from water media

In this study, graphene oxide (GO)-based two-dimensional molecular brush was fabricated by grafting polyacrylamide onto GO nanosheets for efficient removal of Pb²⁺ and Cu²⁺ from water media. Owing to the rich oxygen and nitrogen functional groups in the composites, the synthetic GO two-dimensional molecular brush can get the maximum adsorption capacity of 268.4 mg/g for Pb²⁺ and 127.2 mg/g for Cu²⁺, respectively. Moreover, the interspaces between the stacked two-dimensional molecular brushes provide fast pathways for the diffusion of heavy metal ions. As a result, GO-based two-dimensional molecular brush can reach the adsorption equilibrium within 60 min. These results indicated that the synthetic GO-based two-dimensional molecular brush is a promising adsorbent to separate heavy metal ions from water media.     

First-Row Transition-Metal Cations (Co2+, Ni2+, Mn2+, Fe2+) and Graphene (Oxide) Composites: From Structural Properties to Electrochemical Applications

Composites of graphene (oxide) (GO) and first-row transition-metal cations (Co²⁺, Ni²⁺, Mn²⁺, Fe²⁺) are prepared by mixing GO and aqueous metal salt solutions. The amount of metal cation bound to GO nanosheets is calculated by using inductively coupled plasma mass spectrometry (ICP-MS) and the possible binding sites of the metals are investigated by means of attenuated total reflectance infrared (ATR-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements. Electrodes loaded with the metal/GO composites are prepared by a simple drop-casting technique without any binders or conductive additives. The effect of electrochemical reduction on the structure of the composite electrodes is investigated by Raman spectroscopy, XPS, X-ray diffraction (XRD) analysis, and field emission scanning electron microscopy (FESEM). A detailed electrochemical characterization is performed for the utilization of the composite electrodes for electrochemical capacitors and possible oxygen reduction reaction electrocatalysts by cyclic voltammetry (CV) and rotating disk electrode measurements. The highest areal capacitance is achieved with the as-deposited Fe/GO composite (38.7 mF cm⁻² at 20 mV s⁻¹). In the cyclic stability measurements, rCo/GO, rNi/GO, rMn/GO, and rFe/GO exhibit a capacitance retention of 44, 1.1, 73, and 87 % after 3000 cycles of CV at 100 mV s⁻¹, respectively.