Graphene Emerges as a Versatile Template for Materials Preparation

Branched polymer grafted graphene oxide (GO) as a 2D template for calcium phosphate growth

HYPOTHESIS

Graphene Oxide (GO)-templated deposition of inorganic materials through synthesis on dispersed single sheets of GO is often complicated by the loss of the desired 2D morphology owing to the coagulation of GO sheets at high salt concentrations and non-templated homogenous nucleation. Modifying GO with anionic polymer is expected to solve both problems by i) enhancing electrostatic(steric) stabilization upon exposure to high concentrations of the ionic precursors, and ii) offering additional nucleation sites at the grafted anionic moieties to avoid homogeneous secondary nucleation.

EXPERIMENTS

GO was grafted with branched copolymers of poly(ethylene glycol) methacrylate (PEGMA 500) and diethylene glycol dimethacrylate (DEGDMA) and ω-vinyl terminated methacrylic acid macromonomer (P(MAA)), the latter serving as an addition-fragmentation chain transfer agent. The colloidal stability of GO dispersions in water toward salt was evaluated before and after modification. Precipitation of calcium phosphate (CaP) was performed by incubating modified GO in the precursor solutions. The conditions were optimized to maximize the nucleation selectively onto GO without homogeneous CaP nucleation and coagulation of the GO-sheets.

FINDINGS

The copolymer grafted GO-sheets shows superior colloidal stability when dispersed in water. No aggregation occurs in the incubating ionic CaP precursor solutions. The optimum templated deposition of CaP onto the GO sheets by precipitation is to add a second shot of precursors after the nucleation stage to obtain GO sheets fully decorated with calcium phosphate nanorods without self-nucleation. Via the careful design on the GO modification and incubation process, the growth of calcium phosphate nanorods were confined in the desired 2D order exclusively, hereby achieving the goal of an efficient GO-templated synthesis.

Unraveling van der Waals epitaxy: A real-time in-situ study of MoSe2 growth on graphene/Ru(0001)

In the present work we investigate the growth of monolayer MoSe₂ on selenium-intercalated graphene on Ru(0001), a model layered heterostructure combining a transition metal dichalcogenide with graphene, using low energy electron microscopy and micro-diffraction. Real-time observation of MoSe₂ on graphene growth reveals the island nucleation dynamics at the nanoscale. Upon annealing, larger islands are formed by sliding and attachment of multiple nanometer-sized MoSe₂ flakes. Local micro-spot angle-resolved photoemission spectroscopy reveals the electronic structure of the heterostructure, indicating that no charge transfer occurs within adjacent layers. The observed behavior is attributed to intercalation of Se at the graphene/Ru(0001) interface. The unperturbed nature of the proposed heterostructure therefore renders it as a model system for investigations of graphene supported TMD nanostructures.

Pillararene-Based Supramolecular Polymers for Cancer Therapy

Supramolecular polymers have attracted considerable interest due to their intriguing features and functions. The dynamic reversibility of noncovalent interactions endows supramolecular polymers with tunable physicochemical properties, self-healing, and externally stimulated responses. Among them, pillararene-based supramolecular polymers show great potential for biomedical applications due to their fascinating host-guest interactions and easy modification. Herein, we summarize the state of the art of pillararene-based supramolecular polymers for cancer therapy and illustrate its developmental trend and future perspective.

Molecular beam epitaxy growth and scanning tunneling microscopy study of 2D layered materials on epitaxial graphene/silicon carbide

Since the advent of atomically flat graphene, two-dimensional (2D) layered materials have gained extensive interest due to their unique properties. The 2D layered materials prepared on epitaxial graphene/silicon carbide (EG/SiC) surface by molecular beam epitaxy (MBE) have high quality, which can be directly applied without further transfer to other substrates. Scanning tunneling microscopy and spectroscopy (STM/STS) with high spatial resolution and high-energy resolution are often used to study the morphologies and electronic structures of 2D layered materials. In this review, recent progress in the preparation of various 2D layered materials that are either monoelemental or transition metal dichalcogenides on EG/SiC surface by MBE and their STM/STS investigations are introduced.

Facet engineering of ultrathin two-dimensional materials

Ultrathin two-dimensional (2D) materials exhibit broad application prospects in many fields due to the enhanced specific surface area to volume ratio and quantum confinement effect. Because of the atomic thickness and various orientations, ultrathin 2D materials exposing specific facets have drawn great attention for various applications in catalysis, batteries, optoelectronics, magnetism, epitaxial template for material growth, etc. Though maintaining the atomic thickness of 2D materials while controlling crystal facets is an enormous challenge, breakthroughs are being made. This review provides a comprehensive overview of the recent advances in the facet engineering of 2D materials, ranging from a basic understanding of facets and the corresponding approaches and the significance of facet engineering. We also propose current challenges and forecast future development directions including the establishment of a facet database, the fabrication of new 2D materials, the design of specific substrates, and the introduction of theoretical calculations and in situ characterization techniques. This review can guide researchers to design ultrathin 2D materials with unique and distinct facets and provide an insight into the applications of energy, magnetism, optics, biomedicine, and other fields.

Controlled Synthesis of Mesoporous π-Conjugated Polymer Nanoarchitectures as Anode for Lithium-ions Battery

Conjugated polymers possess better electron conductivity due to large π-electron conjugated configuration endowing them significant scientific and technological interest. However, the obvious deficiency of active-site underutilization impairs their electrochemical performance. Therefore, designing and engineering π-conjugated polymers with rich redox functional groups and mesoporous architectures could offer new opportunities for them in these emerging applications and further expand their application scopes. Herein, a series of 1, 3, 5-tris(4-aminophenyl) benzene (TAPB)-based π-conjugated mesoporous polymers (π-CMPs) are constructed by one-pot emulsion-induced interface assembly strategy. Furthermore, co-induced in-situ polymerization on 2D interfaces by emulsion and micelle is explored, which delivered sandwiched 2D mesoporous π-CMPs coated graphene oxides (GO@mPTAPB). Benefiting from specific redox-active functional groups, excellent electron conductivity and 2D mesoporous conjugated framework, GO@mPTAPB exhibits high capability of accommodating Li⁺ anions (up to 382 mAh g^-1 at 0.2 A g^-1 ) and outstanding electrochemical stability (87.6% capacity retention after 1000 cycles). The ex-situ Raman and impedance spectrum are further applied to reveal the high reversibility of GO@mPTAPB. This work will greatly promote the development of advanced π-CMPs-based organic anodes towards energy storage devices. This article is protected by copyright. All rights reserved.

Graphene oxide/polyaniline-based microwave split-ring resonator: A versatile platform towards ammonia sensing

Ammonia gas sensors have always received significant attention as robust platforms for emission control, food safety, and monitoring human exhaled breath for the early diagnosis of diseases such as dysfunction of the kidney and liver. This study explores the development of a microwave-based split-ring resonator (SRR) sensor with enhanced sensitivity to detect ammonia gas at low concentrations. The sensor is based on a nanocomposite fabricated by incorporating 10 wt% of graphene oxide (GO) into polyaniline (PANI) via the in-situ polymerization of aniline monomers over the surface of the GO sheets. The addition of GO to PANI results in a high sensitivity of 0.038 dB ppm^-1 for low concentrations (1-25 ppm) and 0.0045 dB ppm^-1 for high concentrations (> 25 ppm) of ammonia gas, in a 150-400 s time interval at room temperature. The prepared sensor can selectively sense ammonia gas in the presence of other higher concentrations of hazardous gases and a wide range of relative humidity levels (15-90%). The response signal is repeatable after 30 days with less than 0.32% deviation. The developed low-cost and robust sensor has the potential to monitor ammonia gas in various applications, including medical, environmental, food, and agricultural sectors.

Ultrahigh and Durable Volumetric Lithium/Sodium Storage Enabled by a Highly Dense Graphene-Encapsulated Nitrogen-Doped Carbon@Sn Compact Monolith

Tin-based composites hold promise as anodes for high-capacity lithium/sodium-ion batteries (LIBs/SIBs); however, it is necessary to use carbon coated nanosized tin to solve the issues related to large volume changes during electrochemical cycling, thus leading to the low volumetric capacity for tin-based composites due to their low packing density. Herein, we design a highly dense graphene-encapsulated nitrogen-doped carbon@Sn (HD N-C@Sn/G) compact monolith with Sn nanoparticles double-encapsulated by N-C and graphene, which exhibits a high density of 2.6 g cm^-3 and a high conductivity of 212 S m^-1. The as-obtained HD N-C@Sn/G monolith anode exhibits ultrahigh and durable volumetric lithium/sodium storage. Specifically, it delivers a high volumetric capacity of 2692 mAh cm^-3 after 100 cycles at 0.1 A g^-1 and an ultralong cycling stability exceeding 1500 cycles at 1.0 A g^-1 with only 0.019% capacity decay per cycle in lithium-ion batteries. Besides, in situ TEM and ex situ SEM have revealed that the unique double-encapsulated structure effectively mitigates drastic volume variation of the tin nanoparticles during electrode cycling. Furthermore, the full cell using HD N-C@Sn/G as an anode and LiCoO₂ as a cathode displays a superior cycling stability. This work provides a new avenue and deep insight into the design of high-volumetric-capacity alloy-based anodes with ultralong cycle life.

Heterogeneous, 3D Architecturing of 2D Titanium Carbide (MXene) for Microdroplet Manipulation and Voice Recognition

Mismatched deformation in a bilayer composite with rigid coating on a soft substrate results in complex and uniform topographic patterns, yet it remains challenging to heterogeneously pattern the upper coatings with various localized structures. Herein, a heterogeneous, 3D microstructure composed of Ti₃C₂T_x titanium carbide (MXene) and single-walled carbon nanotubes (SWNTs) was fabricated using a one-step deformation of a thermally responsive substrate with designed open holes. The mechanically deformed SWNT-MXene (s-MXene) structure was next transferred onto an elastomeric substrate, and the resulting s-MXene/elastomer bilayer device exhibited three localized surface patterns, including isotropic crumples, periodic wrinkles, and large papillae-like microstructures. By adjusting the number and pattern, the s-MXene papillae arrays exhibited superhydrophobicity (>170°), strong and tunable adhesive force (52.3-110.6 μN), and ultra-large liquid capacity (up to 35 μL) for programmable microdroplet manipulation. The electrically conductive nature of s-MXene further enabled proper thermal management on microdroplets via Joule heating for miniaturized antibacterial tests. The s-MXene papillae were further fabricated in a piezoresistive pressure sensor with high sensitivity (11.47 kPa^-1). The output current changes of s-MXene sensors were highly sensitive to voice vibrations and responded identically with prerecorded profiles, promising their application in accurate voice acquisition and recognition.

Mechanochemical engineering of 2D materials for multiscale biointerfaces

Atomically thin nanomaterials represent a unique paradigm for interfacing with biological systems due to their mechanical flexibility, exceptional interfacial area, and ease of chemical functionalization. In particular, these two-dimensional (2D) materials are able to bend, curve, and fold in response to biologically-generated forces or other external stimuli. Such origami-like folding of 2D materials into wrinkled or crumpled topographies allows them to withstand large deformations by accordion-like unfolding, with implications for stretchable and shape-changing devices. Here, we review how mechanically manipulated 2D materials can interact with biological systems across a multitude of length scales. We focus on recent work where wrinkling, crumpling, or bending of 2D materials permits new chemical and material properties, with four case studies: (i) programming biomolecular reactivity and enhanced sensing, (ii) directed adhesion and encapsulation of bacteria or mammalian cells, (iii) stimuli-responsive actuators and soft robotics, and (iv) stretchable barrier technologies and wearable human-scale sensors. Finally, we consider future directions for manufacturing, materials and systems integration, as well as biocompatibility. Taken together, these 2D materials may enable new avenues for ultrasensitive molecular detection, biomaterial scaffolds, soft machines, and wearable technologies.

Enhanced Roles of Carbon Architectures in High-Performance Lithium-Ion Batteries

Lithium-ion batteries (LIBs), which are high-energy-density and low-safety-risk secondary batteries, are underpinned to the rise in electrochemical energy storage devices that satisfy the urgent demands of the global energy storage market. With the aim of achieving high energy density and fast-charging performance, the exploitation of simple and low-cost approaches for the production of high capacity, high density, high mass loading, and kinetically ion-accessible electrodes that maximize charge storage and transport in LIBs, is a critical need. Toward the construction of high-performance electrodes, carbons are promisingly used in the enhanced roles of active materials, electrochemical reaction frameworks for high-capacity noncarbons, and lightweight current collectors. Here, we review recent advances in the carbon engineering of electrodes for excellent electrochemical performance and structural stability, which is enabled by assembled carbon architectures that guarantee sufficient charge delivery and volume fluctuation buffering inside the electrode during cycling. Some specific feasible assembly methods, synergism between structural design components of carbon assemblies, and electrochemical performance enhancement are highlighted. The precise design of carbon cages by the assembly of graphene units is potentially useful for the controlled preparation of high-capacity carbon-caged noncarbon anodes with volumetric capacities over 2100 mAh cm^-3. Finally, insights are given on the prospects and challenges for designing carbon architectures for practical LIBs that simultaneously provide high energy densities (both gravimetric and volumetric) and high rate performance.

Template-oriented synthesis of hydroxyapatite nanoplates for 3D bone printing

The design of hydroxyapatite (HA) nanoarchitecture is critical for fabricating artificial bone tissues as it dictates the biochemical and the mechanical properties of the final product.

Nanoarchitectonic-Based Material Platforms for Environmental and Bioprocessing Applications

The challenges of pollution, environmental science, and energy consumption have become global issues of broad societal importance. In order to address these challenges, novel functional systems and advanced materials are needed to achieve high efficiency, low emission, and environmentally friendly performance. A promising approach involves nanostructure-level controls of functional material design through a novel concept, nanoarchitectonics. In this account article, we summarize nanoarchitectonic approaches to create nanoscale platform structures that are potentially useful for environmentally green and bioprocessing applications. The introduced platforms are roughly classified into (i) membrane platforms and (ii) nanostructured platforms. The examples are discussed together with the relevant chemical processes, environmental sensing, bio-related interaction analyses, materials for environmental remediation, non-precious metal catalysts, and facile separation for biomedical uses.

Ultrathin Metal Crystals: Growth on Supported Graphene Surfaces and Applications

Controlled nucleation and growth of metal clusters in metal deposition processes is a long-standing issue for thin-film-based electronic devices. When metal atoms are deposited on solid surfaces, unintended defects sites always lead to a heterogeneous nucleation, resulting in a spatially nonuniform nucleation with irregular growth rates for individual nuclei, resulting in a rough film that requires a thicker film to be deposited to reach the percolation threshold. In the present study, it is shown that substrate-supported graphene promotes the lateral 2D growth of metal atoms on the graphene. Transmission electron microscopy reveals that 2D metallic single crystals are grown epitaxially on supported graphene surfaces while a pristine graphene layer hardly yields any metal nucleation. A surface energy barrier calculation based on density functional theory predicts a suppression of diffusion of metal atoms on electronically perturbed graphene (supported graphene). 2D single Au crystals grown on supported graphene surfaces exhibit unusual near-infrared plasmonic resonance, and the unique 2D growth of metal crystals and self-healing nature of graphene lead to the formation of ultrathin, semitransparent, and biodegradable metallic thin films that could be utilized in various biomedical applications.

Beyond van der Waals Interaction: The Case of MoSe2 Epitaxially Grown on Few-Layer Graphene

Van der Waals heterojunctions composed of graphene and transition metal dichalcogenides have gain much attention because of the possibility to control and tailor band structure, promising applications in two-dimensional optoelectronics and electronics. In this report, we characterized the van der Waals heterojunction MoSe₂/few-layer graphene with a high-quality interface using cutting-edge surface techniques scaling from atomic to microscopic range. These surface analyses gave us a complete picture of the atomic structure and electronic properties of the heterojunction. In particular, we found two important results: the commensurability between the MoSe₂ and few-layer graphene lattices and a band-gap opening in the few-layer graphene. The band gap is as large as 250 meV, and we ascribed it to an interface charge transfer that results in an electronic depletion in the few-layer graphene. This conclusion is well supported by electron spectroscopy data and density functional theory calculations. The commensurability between the MoSe₂ and graphene lattices as well as the band-gap opening clearly show that the interlayer interaction goes beyond the simple van der Waals interaction. Hence, stacking two-dimensional materials in van der Waals heterojunctions enables us to tailor the atomic and electronic properties of individual layers. It also permits the introduction of a band gap in few-layer graphene by interface charge transfer.

Graphene Inks as Versatile Templates for Printing Tiled Metal Oxide Crystalline Films

There is great interest in exploiting van der Waals gaps in layered materials as confinement reaction vessels to template the synthesis of new nanosheet structures. The gallery spaces in multilayer graphene oxide, for example, can intercalate hydrated metal ions that assemble into metal oxide films during thermal oxidation of the sacrificial graphene template. This approach offers limited control of structure, however, and does not typically lead to 2D atomic-scale growth of anisotropic platelet crystals, but rather arrays of simple particles directionally sintered into porous sheets. Here, a new graphene-directed assembly route is demonstrated that yields fully dense, space-filling films of tiled metal oxide platelet crystals with tessellated structures. The method relies on colloidal engineering to produce a printable "metallized graphene ink" with accurate control of metal loading, grain size/porosity, composition, and micro/nanomorphologies, and is capable of achieving higher metal-carbon ratio than is possible by intercalation methods. These tiled structures are sufficiently robust to create free standing papers, complex microtextured films, 3D shapes, and metal oxide replicas of natural biotextures.

Urine to highly porous heteroatom-doped carbons for supercapacitor: A value added journey for human waste

Obtaining functionalized carbonaceous materials, with well-developed pores and doped heteroatoms, from waste precursors using environmentally friendly processes has always been of great interest. Herein, a simple template-free approach is devised to obtain porous and heteroatom-doped carbon, by using the most abundant human waste, “urine”. Removal of inherent mineral salts from the urine carbon (URC) makes it to possess large quantity of pores. Synergetic effect of the heteroatom doping and surface properties of the URC is exploited by carrying out energy storage application for the first time. Suitable heteroatom content and porous structure can enhance the pseudo-capacitance and electric double layer capacitance, eventually generating superior capacitance from the URC. The optimal carbon electrode obtained particularly at 900 °C (URC-900) possesses high BET surface area (1040.5 m²g⁻¹), good conductivity, and efficient heteroatom doping of N, S, and P, illustrating high specific capacitance of 166 Fg⁻¹ at 0.5 Ag⁻¹ for three-electrode system in inorganic electrolyte. Moreover, the URC-900 delivers outstanding cycling stability with only 1.7% capacitance decay over 5,000 cycles at 5 Ag⁻¹. Present work suggests an economical approach based on easily available raw waste material, which can be utilized for large-scale production of new age multi-functional carbon nanomaterials for various energy applications.

Mass production and industrial applications of graphene materials

Graphene is considered a promising material for industrial application based on the intensive laboratory-scale research in the fields of physics, chemistry, materials science and engineering, and biology over the last decade. Many companies have thus started to pursue graphene materials on a scale of tons (for the flake material) or hundreds of thousands of square meters (for the film material) for industrial applications. Though the graphene industry is still in its early stages, very significant progress in mass production and certain industrial applications has become obvious. In this report, we aim to give a brief review of the mass production of graphene materials for some industrial applications and summarize some features or challenges for graphene in the marketplace.

From Flatland to Spaceland: Higher Dimensional Patterning with Two-Dimensional Materials

The creation of three-dimensional (3D) structures from two-dimensional (2D) nanomaterial building blocks enables novel chemical, mechanical or physical functionalities that cannot be realized with planar thin films or in bulk materials. Here, we review the use of emerging 2D materials to create complex out-of-plane surface topographies and 3D material architectures. We focus on recent approaches that yield periodic textures or patterns, and present four techniques as case studies: (i) wrinkling and crumpling of planar sheets, (ii) encapsulation by crumpled nanosheet shells, (iii) origami folding and kirigami cutting to create programmed curvature, and (iv) 3D printing of 2D material suspensions. Work to date in this field has primarily used graphene and graphene oxide as the 2D building blocks, and we consider how these unconventional approaches may be extended to alternative 2D materials and their heterostructures. Taken together, these emerging patterning and texturing techniques represent an intriguing alternative to conventional materials synthesis and processing methods, and are expected to contribute to the development of new composites, stretchable electronics, energy storage devices, chemical barriers, and biomaterials.

Mini-Sized Carbon Nitride Nanosheets with Double Excitation- and pH-Dependent Fluorescence Behaviors for Two-Photon Cell Imaging

Synthesis of mini-sized carbon nitride nanosheets (CNNSs) by traditional methods remains a challenge. Herein, size-tunable and uniform mini-sized CNNSs are synthesized by hydrothermal carbonization of a single polyethyleneimine (PEI) precursor. The as-obtained mini-sized CNNSs possess uniform size, good hydrophilicity and abundant nitrogen active sites, which not only exhibit double excitation- and pH-dependent fluorescence behaviors, but also two-photon excitation fluorescence. áThe resulting CNNSs display low toxicity and can be efficiently delivered into live cells for two-photon fluorescence imaging, offering great potential as fluorescence probes in biochemical applications.

Confined Formation of Ultrathin ZnO Nanorods/Reduced Graphene Oxide Mesoporous Nanocomposites for High-Performance Room-Temperature NO2 Sensors

Here we demonstrate high-performance room-temperature NO₂ sensors based on ultrathin ZnO nanorods/reduced graphene oxide (rGO) mesoporous nanocomposites. Ultrathin ZnO nanorods were loaded on rGO nanosheets by a facile two-step additive-free solution synthesis involving anchored seeding followed by oriented growth. The ZnO nanorod diameters were simply controlled by the seed diameters associated with the spatial confinement effects of graphene oxide (GO) nanosheets. Compared to the solely ZnO nanorods and rGO-based sensors, the optimal sensor based on ultrathin ZnO nanorods/rGO nanocomposites exhibited higher sensitivity and quicker p-type response to parts per million level of NO₂ at room temperature, and the sensitivity to 1 ppm of NO₂ was 119% with the response and recovery time being 75 and 132 s. Moreover, the sensor exhibited full reversibility, excellent selectivity, and a low detection limit (50 ppb) to NO₂ at room temperature. In addition to the high transport capability of rGO as well as excellent NO₂ adsorption ability derived from ultrathin ZnO nanorods and mesoporous structures, the superior sensing performance of the nanocomposites was attributed to the synergetic effect of ZnO and rGO, which was realized by the electron transfer across the ZnO-rGO interfaces through band energy alignment.

Hierarchical Metal Oxide Topographies Replicated from Highly Textured Graphene Oxide by Intercalation Templating

Confined assembly in the intersheet gallery spaces of two-dimensional (2D) materials is an emerging templating route for creation of ultrathin material architectures. Here, we demonstrate a general synthetic route for transcribing complex wrinkled and crumpled topographies in graphene oxide (GO) films into textured metal oxides. Intercalation of hydrated metal ions into textured GO multilayer films followed by dehydration, thermal decomposition, and air oxidation produces Zn, Al, Mn, and Cu oxide films with high-fidelity replication of the original GO textures, including "multi-generational", multiscale textures that have been recently achieved through extreme graphene compression. The textured metal oxides are shown to consist of nanosheet-like aggregates of interconnected particles, whose mobility, attachment, and sintering are guided by the 2D template. This intercalation templating approach has broad applicability for the creation of complex, textured films and provides a bridging technology that can transcribe the wide variety of textures already realized in graphene into insulating and semiconducting materials. These textured metal oxide films exhibit enhanced electrochemical and photocatalytic performance over planar films and show potential as high-activity electrodes for energy storage, catalysis, and biosensing.

Controlled functionalization of graphene with carboxyl moieties toward multiple applications

A controlled functionalization strategy is exploited for producing solution-processable carboxyl-rich functionalized graphene without sacrificing the structural integrity, providing a unique and universal material platform for diverse applications.