Ultrastrong Freestanding Graphene Oxide Nanomembranes with Surface-Enhanced Raman Scattering Functionality by Solvent-Assisted Single-Component Layer-by-Layer Assembly

Holey Sheets Enhance the Packing and Osmotic Energy Harvesting of Graphene Oxide Membranes

Layered membranes assembled from two-dimensional (2D) building blocks such as graphene oxide (GO) are of significant interest in desalination and osmotic power generation because of their ability to selectively transport ions through interconnected 2D nanochannels between stacked layers. However, architectural defects in the final assembled membranes (e.g., wrinkles, voids, and folded layers), which are hard to avoid due to mechanical compliant issues of the sheets during the membrane assembly, disrupt the ionic channel pathways and degrade the stacking geometry of the sheets. This leads to degraded ionic transport performance and the overall structural integrity. In this study, we demonstrate that introducing in-plane nanopores on GO sheets is an effective way to suppress the formation of such architectural imperfections, leading to a more homogeneous membrane. Stacking of porous GO sheets becomes significantly more compact, as the presence of nanopores makes the sheets mechanically softer and more compliant. The resulting membranes exhibit ideal lamellar microstructures with well-aligned and uniform nanochannel pathways. The well-defined nanochannels afford excellent ionic conductivity with an effective transport pathway, resulting in fast, selective ion transport. When applied as a nanofluidic membrane in an osmotic power generation system, the holey GO membrane exhibits higher osmotic power density (13.15 W m-2) and conversion efficiency (46.6%) than the pristine GO membrane under a KCl concentration gradient of 1000-fold.

Enhancing Low-Frequency Microwave Absorption Through Structural Polarization Modulation of MXenes

Two-dimensional carbon-based materials have shown promising electromagnetic wave absorption capabilities in mid- and high-frequency ranges, but face challenges in low-frequency absorption due to limited control over polarization response mechanisms and ambiguous resonance behavior. In this study, we propose a novel approach to enhance absorption efficiency in aligned three-dimensional (3D) MXene/CNF (cellulose nanofibers) cavities by modifying polarization properties and manipulating resonance response in the 3D MXene architecture. This controlled polarization mechanism results in a significant shift of the main absorption region from the X-band to the S-band, leading to a remarkable reflection loss value of - 47.9 dB in the low-frequency range. Furthermore, our findings revealed the importance of the oriented electromagnetic coupling in influencing electromagnetic response and microwave absorption properties. The present study inspired us to develop a generic strategy for low-frequency tuned absorption in the absence of magnetic element participation, while orientation-induced polarization and the derived magnetic resonance coupling are the key controlling factors of the method.

Robust, Ultrathin, and Highly Sensitive Reduced Graphene Oxide/Silk Fibroin Wearable Sensors Responded to Temperature and Humidity for Physiological Detection

Skin temperature and skin humidity are used for monitoring physiological processes, such as respiration. Despite advances in wearable temperature and humidity sensors, the fabrication of a durable and sensitive sensor for practical uses continues to pose a challenge. Here, we developed a durable, sensitive, and wearable temperature and humidity sensor. A reduced graphene oxide (rGO)/silk fibroin (SF) sensor was fabricated by employing a layer-by-layer technique and thermal reduction treatment. Compared with rGO, the elastic bending modulus of rGO/SF could be increased by up to 232%. Furthermore, an evaluation of the performance of an rGO/SF sensor showed that it had outstanding robustness: it could withstand repeatedly applied temperature and humidity loads and repeated bending. The developed rGO/SF sensor is promising for practical applications in healthcare and biomedical monitoring.

Synthesis of a Ag/rGO nanocomposite using Bos taurus indicus urine for nitroarene reduction and biological activity

The present study develops a unique in situ synthesis of a catalytically and biologically active Ag/reduced graphene oxide (rGO) nanocomposite. Herein, we employed Bos taurus indicus urine to synthesize a Ag/rGO nanocomposite in an environmentally benign, facile, economical, and sustainable manner. The elemental composition analysis reveals the presence of Ag, O and C elements. The scanning electron micrograph shows the formation of spherical silver in nanoform whereas rGO is found to be flake shaped with a wrinkled nature. The synthesized nanomaterial and its composite shows a positive catalytic effect in simple organic transformation for the reduction of nitroarene compounds. Investigations were conducted into the catalytic effectiveness of the prepared nanomaterials for diverse nitroarene reduction. Then, using NaBH₄ at 25 °C, the catalytic roles of Ag and the Ag/rGO nano-catalyst were assessed towards the catalytic reduction of several environmental pollutants such as 2-, 3- and 4-nitroaniline and 4-nitrophenol into their respective amino compounds. To test their catalytic performance, bio-mimetically synthesized Ag NPs were thermally treated at 200 °C and compared with the Ag/rGO nanocomposite. Furthermore, biomedical applications such as the antibacterial and antioxidant properties of the as-prepared nanomaterials were investigated in this study.

Enabling Selectively Tunable Mechanical Properties of Graphene Oxide/Silk Fibroin/Cellulose Nanocrystal Bionanofilms

Enhancing and manipulating the mechanical properties of graphene oxide (GO)-based structures are challenging because the GO assembly is easily delaminated. We develop nacre-like bionanofilms whose in-plane mechanical properties can be manipulated through water vapor annealing without influencing their mechanical properties in the thickness direction. These bionanofilms are prepared from GO, silk fibroin (SF), and cellulose nanocrystals (CNCs) via a spin-assisted layer-by-layer assembly. The postannealing mechanical properties of the films are determined with atomic force microscopy (AFM) bending and nanoindentation, and it is confirmed that the mechanical properties of the bionanofilms are altered only in the in-plane direction. While AFM bending shows Young's moduli of 26.9, 36.3, 24.3, and 41.4 GPa for 15, 15 annealed, 30, and 30 annealed GO/SF/CNC trilayers, nanoindentation shows reduced moduli of 19.5 ± 2.6 and 19.5 ± 2.5 GPa before and after annealing, respectively. The unaltered mechanical properties of the bionanofilms along the thickness direction after annealing can be attributed to the CNC frame in the SF matrix acting as a support against stress in the thickness direction, while annealing reorganizes the bionanofilm structure. The tunability of the bionanofilms' mechanical properties in only one direction through structure manipulation can lead to various applications, such as e-skin, wearable sensors, and human-machine interaction devices.

Transfer Printing of Freestanding Nanoassemblies: A Route to Membrane Resonators with Adjustable Prestress

Freestanding nanoassemblies represent a new class of functional materials with highly responsive optical, electrical, and mechanical properties. Hence, they are well-suited for applications in advanced sensor devices. Here, it is shown that transfer printing enables the well-controlled fabrication of freestanding membranes from layered nanoassemblies: Using a polydimethylsiloxane (PDMS) stamp, thin films (thickness: ∼45 to ∼51 nm) of 1,6-hexanedithiol cross-linked gold nanoparticles (diameter: ∼3.9 ± 0.8 nm) were transferred onto surface-oxidized silicon substrates featuring square microcavities with edge lengths of ∼78 μm. After adjusting the contact pressure to 1.8 bar, intact membranes were printed in yields of ∼70%. The prestress of printed membranes was determined by measuring their resonance frequencies under electrostatic actuation. In general, the prestress values were in the ∼10 MPa range with standard deviations below 10% for parallel printed resonators. The deviations in average prestress between resonators printed onto different substrates were 21% or less. By increasing the temperature during the final transfer step from 5 to 48 °C, it was possible to tune the average prestress from ∼14 to ∼28 MPa. This effect was attributed to the pronounced thermal expansion of the PDMS stamp. Finally, by transfer printing layered films of graphene oxide/silk fibroin (GO/SF), it is shown that the approach can be adapted for the fabrication of freestanding membranes from very different nanomaterials.

Electronic effects of nano-confinement in functional organic and inorganic materials for optoelectronics

This review provides a comprehensive overview of the electronic effects of nano-confinement (from 1D to 3D geometries) on optoelectronic materials and their applications.

Fabrication of Two-Dimensional and Three-Dimensional High-Resolution Binder-Free Graphene Circuits Using a Microfluidic Approach for Sensor Applications

In this study, a simple microfluidic method, which can be universally applied to different rigid or flexible substrates, was developed to fabricate high-resolution, conductive, two-dimensional and three-dimensional microstructured graphene-based electronic circuits. The method involves controlled and selective filling of microchannels on substrate surfaces with a conductive binder-free graphene nanoplatelet (GNP) solution. The ethanol-thermal reaction of GNP solution at low temperatures (∼75 °C) prior to microchannel filling (preheating) can further reduce the GNP andprovide a homogeneous GNP solution, which in turn enhances conductivity, reduces sheet resistance (∼0.05 kΩ sq^-1), enables room-temperature fabrication, and eliminates harsh postprocessing, which makes this fabrication technique compatible with degradable substrates. This method can also be used in combination with 3D printing to fabricate 3D circuits. The feature sizes of the graphene patterns can range from a few micrometers (down to ∼15 μm in width and ∼5 μm in depth) to a few millimeters and use very small amounts of GNP solution (∼2.5 mg of graphene to obtain ∼0.1 kΩ sq^-1 of sheet resistance for 1 cm²). This microfluidic approach can also be implemented using other conductive liquids, such as conductive graphene-silver solutions. This technology has the potential to pave the way for low-cost, disposable, and biodegradable circuits for a range of electronic applications including near-field communication antennas and pressure or strain sensors.

The construction of CuCo2O4/N-doped reduced graphene oxide hybrid hollow spheres as anodes for sodium-ion batteries

Hierarchical CuCo₂O₄/N-doped reduced graphene oxide (CuCo₂O₄/N-rGO) hollow hybrid nanospheres was constructed and further applied as highly capacity anode materials for SIBs.

Selectively Enhanced Ion Transport in Graphene Oxide Membrane/PET Conical Nanopore System

Graphene oxide (GO) has become a promising 2D material in many areas, such as gas separation, seawater desalination, antibacterial materials, and so on because of its abundant oxygen-containing functional groups and excellent dispersibility in various solvents. The graphene oxide membrane (GOM), a laminar and channel-rich structure assembled by stacked GO nanosheets, served as a kind of precise and ultrafast separation material has attracted widespread attention in membrane separation field. To break the trade-off between ion permeability and ion selectivity of separation membrane based on GOM, GOM/conical nanopore system is obtained by spin-coating ultrathin GOM on PET conical nanopore, which possesses ion rectification property. Comparing to pure PET conical nanopore, the existence of GOM not only enhances the cation conductance but also makes the ion rectification ratio increase from 4.6 to 238.0 in KCl solution. Assisted by COMSOL simulation, it is proved that the GOM can absorb large amount of cations and act as cation source to improve the ion selectivity and rectification effect of GOM/conical nanopore system. Finally, the chemical stability of GOM/conical nanopore is also investigated and the corresponding results reveal that the GOM/conical nanopore system can perform the ion rectification behavior in a wider pH range than pure PET conical nanopore. The presented findings demonstrate the great potential applications of GOM/conical nanopore system in ionic logic circuits and sensor systems.

Wetting-Induced Climbing for Transferring Interfacially Assembled Large-Area Ultrathin Pristine Graphene Film

Owing to inherent 2D structure, marvelous mechanical, electrical, and thermal properties, graphene has great potential as a macroscopic thin film for surface coating, composite, flexible electrode, and sensor. Nevertheless, the production of large-area graphene-based thin film from pristine graphene dispersion is severely impeded by its poor solution processability. In this study, a robust wetting-induced climbing strategy is reported for transferring the interfacially assembled large-area ultrathin pristine graphene film. This strategy can quickly convert solvent-exfoliated pristine graphene dispersion into ultrathin graphene film on various substrates with different materials (glass, metal, plastics, and cloth), shapes (film, fiber, and bulk), and hydrophobic/hydrophilic patterns. It is also applicable to nanoparticles, nanofibers, and other exfoliated 2D nanomaterials for fabricating large-area ultrathin films. Alternate climbing of different ultrathin nanomaterial films allows a layer-by-layer transfer, forming a well-ordered layered composite film with the integration of multiple pristine nanomaterials at nanometer scale. This powerful strategy would greatly promote the development of solvent-exfoliated pristine nanomaterials from dispersions to macroscopic thin film materials.

Guanidyl-functionalized graphene/polysulfone mixed matrix ultrafiltration membrane with superior permselective, antifouling and antibacterial properties for water treatment

Mixed matrix membranes blended with graphene-based nanomaterials have great potential in water and wastewater treatment on account of their multiple functionalities. To solve the complicated biofouling problem and diversify the applications of membranes, novel synergistic antibacterial guanidyl-functionalized graphene/polysulfone (GFG/PSF) mixed matrix ultrafiltration membranes were prepared by a non-solvent induced phase separation method. The guanidyl-functionalized graphene nanosheets were achieved by a two-step grafting process consisting of amination and guanidination and exhibited high dispersibility in the casting solution, which showed good compatibility with the polymer matrix. Besides the advantages of partially reduced graphene oxide (GO) nanosheets in creating a stronger interaction with the bacterial cell membrane to destroy the bacteria, the induced bidendate binding between guanidyl groups and phosphate groups on the cell wall can make high sterilization rate even at low concentrations. Different techniques including XRD, FTIR, XPS, SEM, TEM, EDX, contact angle meter, filtration and antibacterial experiments were employed to characterize and investigate the performance of nanosheets and membranes. Compared with pure PSF membrane, the GFG/PSF mixed matrix membranes not only exhibited superior permeability and prominent antifouling property performance toward bovine serum albumin (BSA), but also displayed excellent antimicrobial activity and long-term duration toward Escherichia coli and Staphylococcus aureus.

Scalable Approach to Construct Self-Assembled Graphene-Based Films with An Ordered Structure for Thermal Management

Large-area bulk oxidized cellulose nanocrystal (OCNC)/graphene nanocomposites with highly oriented structures were produced through a straightforward, cost-effective large-scale evaporation-induced self-assembly process followed by thermal curing. Well-aligned nano-sized graphene layers were evident and separated by the OCNC planar layers, which facilitate highly interconnected and continuous thermal transport parallel to the alignment. Hence, the laminated graphene-based nanocomposites possess an excellent in-plane thermal conductivity of 25.66 W/m K and a thermal conductivity enhancement (η) of 7235% with only a 4.1 vol % graphene loading. This value is the highest recorded among all laminated composite films with <70 wt % filler content reported to date. Using this design strategy, other large-area aligned composites with other functional nanomaterials, already in large-scale production, can be made for use in a wide range of applications.

Oxidative Layer-By-Layer Multilayers Based on Metal Coordination: Influence of Intervening Graphene Oxide Layers

Layer-by-layer (LbL) fabricated oxidative multilayers consisting of successive layers of inorganic polyphosphate (PP) and Ce(IV) can electrolessly form thin conducting polymer films on their surface. We describe the effect of substituting every second PP layer in the (PP/Ce) multilayers for graphene oxide (GO) as a means of modifying the structure and mechanical properties of these (GO/Ce/PP/Ce) films and enhancing their growth. Both types of LbL films are based on reversible coordinative bonding between the metal ions and the oxygen-bearing groups in PP and GO, instead of purely electrostatic interactions. The GO incorporation leads to the doubling of the areal mass density and to a dry film thickness close to 300 nm after 4 (GO/Ce/PP/Ce) tetralayers. The film roughness increases significantly with thickness. The (PP/Ce) films are soft materials with approximately equal shear storage and loss moduli, but the incorporation of GO doubles the storage modulus. PP displays a marked terminating layer effect and practically eliminates mechanical losses, making the (GO/Ce/PP/Ce) films almost pure soft elastomers. The smoothness of the (PP/Ce) films and the PP-termination effects are attributed to the reversible coordinative bonding. The (GO/Ce/PP/Ce) films oxidize pyrrole and 3,4-ethylenedioxythiophene (EDOT) and form polypyrrole and PEDOT films on their surfaces. These polymer films are considerably thicker than those formed using the (PP/Ce) multilayers with the same nominal amount of cerium layers. The GO sheets interfere with the polymerization reaction and make its kinetics biphasic. The (GO/Ce) multilayers without PP are brittle and thin.

Assembly and Self-Assembly of Nanomembrane Materials-From 2D to 3D

Nanoscience and nanotechnology offer great opportunities and challenges in both fundamental research and practical applications, which require precise control of building blocks with micro/nanoscale resolution in both individual and mass-production ways. The recent and intensive nanotechnology development gives birth to a new focus on nanomembrane materials, which are defined as structures with thickness limited to about one to several hundred nanometers and with much larger (typically at least two orders of magnitude larger, or even macroscopic scale) lateral dimensions. Nanomembranes can be readily processed in an accurate manner and integrated into functional devices and systems. In this Review, a nanotechnology perspective of nanomembranes is provided, with examples of science and applications in semiconductor, metal, insulator, polymer, and composite materials. Assisted assembly of nanomembranes leads to wrinkled/buckled geometries for flexible electronics and stacked structures for applications in photonics and thermoelectrics. Inspired by kirigami/origami, self-assembled 3D structures are constructed via strain engineering. Many advanced materials have begun to be explored in the format of nanomembranes and extend to biomimetic and 2D materials for various applications. Nanomembranes, as a new type of nanomaterials, allow nanotechnology in a controllable and precise way for practical applications and promise great potential for future nanorelated products.

Template-Guided Assembly of Silk Fibroin on Cellulose Nanofibers for Robust Nanostructures with Ultrafast Water Transport

The construction of multilength scaled hierarchical nanostructures from diverse natural components is critical in the progress toward all-natural nanocomposites with structural robustness and versatile added functionalities. Here, we report a spontaneous formation of peculiar "shish kebab" nanostructures with the periodic arrangement of silk fibroin domains along straight segments of cellulose nanofibers. We suggest that the formation of these shish kebab nanostructures is facilitated by the preferential organization of heterogeneous (β-sheets and amorphous silk) domains along the cellulose nanofiber driven by modulated axial distribution of crystalline planes, hydrogen bonding, and hydrophobic interactions as suggested by all-atom molecular dynamic simulations. Such shish kebab nanostructures enable the ultrathin membrane to possess open, transparent, mechanically robust interlocked networks with high mechanical performance with up to 30 GPa in stiffness and 260 MPa in strength. These nanoporous robust membranes allow for the extremely high water flux, up to 3.5 × 10⁴ L h^-1 m^-2 bar^-1 combined with high rejection rate for various organic molecules, capability of capturing heavy metal ions and their further reduction into metal nanoparticles for added SERS detection capability and catalytic functionalities.

Topological Design of Ultrastrong and Highly Conductive Graphene Films

Nacre-like graphene films are prepared by evaporation-induced assembly of graphene oxide dispersions containing small amounts of cellulose nanocrystal (CNC), followed by chemical reduction with hydroiodic acid. CNC induces the formation of wrinkles on graphene sheets, greatly enhancing the mechanical properties of the resultant graphene films. The graphene films deliver an ultrahigh tensile strength of 765 ± 43 MPa (up to 800 MPa in some cases), a large failure strain of 6.22 ± 0.19%, and a superior toughness of 15.64 ± 2.20 MJ m^-3 , as well as a high electrical conductivity of 1105 ± 17 S cm^-1 . They have a great potential for applications in flexible electronics because of their combined excellent mechanical and electrical properties.

Controlling Water Intercalation Is Key to a Direct Graphene Transfer

The key steps of a transfer of two-dimensional (2D) materials are the delamination of the as-grown material from a growth substrate and the lamination of the 2D material on a target substrate. In state-of-the-art transfer experiments, these steps remain very challenging, and transfer variations often result in unreliable 2D material properties. Here, it is demonstrated that interfacial water can insert between graphene and its growth substrate despite the hydrophobic behavior of graphene. It is understood that interfacial water is essential for an electrochemistry-based graphene delamination from a Pt surface. Additionally, the lamination of graphene to a target wafer is hindered by intercalation effects, which can even result in graphene delamination from the target wafer. For circumvention of these issues, a direct, support-free graphene transfer process is demonstrated, which relies on the formation of interfacial water between graphene and its growth surface, while avoiding water intercalation between graphene and the target wafer by using hydrophobic silane layers on the target wafer. The proposed direct graphene transfer also avoids polymer contamination (no temporary support layer) and eliminates the need for etching of the catalyst metal. Therefore, recycling of the growth template becomes feasible. The proposed transfer process might even open the door for the suggested atomic-scale interlocking-toy-brick-based stacking of different 2D materials, which will enable a more reliable fabrication of van der Waals heterostructure-based devices and applications.

Improvement in Functional Properties of Soy Protein Isolate-Based Film by Cellulose Nanocrystal⁻Graphene Artificial Nacre Nanocomposite

A facile, inexpensive, and green approach for the production of stable graphene dispersion was proposed in this study. We fabricated soy protein isolate (SPI)-based nanocomposite films with the combination of 2D negative charged graphene and 1D positive charged polyethyleneimine (PEI)-modified cellulose nanocrystals (CNC) via a layer-by-layer assembly method. The morphologies and surface charges of graphene sheets and CNC segments were characterized by atomic force microscopy and Zeta potential measurements. The hydrogen bonds and multiple interface interactions between the filler and SPI matrix were analyzed by Attenuated Total Reflectance⁻Fourier Transform Infrared spectra and X-ray diffraction patterns. Scanning electron microscopy demonstrated the cross-linked and laminated structures in the fracture surface of the films. In comparison with the unmodified SPI film, the tensile strength and surface contact angles of the SPI/graphene/PEI-CNC film were significantly improved, by 99.73% and 37.13% respectively. The UV⁻visible light barrier ability, water resistance, and thermal stability were also obviously enhanced. With these improved functional properties, this novel bio-nanocomposite film showed considerable potential for application for food packaging materials.

Functional Graphene Nanomaterials Based Architectures: Biointeractions, Fabrications, and Emerging Biological Applications

Functional graphene nanomaterials (FGNs) are fast emerging materials with extremely unique physical and chemical properties and physiological ability to interfere and/or interact with bioorganisms; as a result, FGNs present manifold possibilities for diverse biological applications. Beyond their use in drug/gene delivery, phototherapy, and bioimaging, recent studies have revealed that FGNs can significantly promote interfacial biointeractions, in particular, with proteins, mammalian cells/stem cells, and microbials. FGNs can adsorb and concentrate nutrition factors including proteins from physiological media. This accelerates the formation of extracellular matrix, which eventually promotes cell colonization by providing a more beneficial microenvironment for cell adhesion and growth. Furthermore, FGNs can also interact with cocultured cells by physical or chemical stimulation, which significantly mediate their cellular signaling and biological performance. In this review, we elucidate FGNs-bioorganism interactions and summarize recent advancements on designing FGN-based two-dimensional and three-dimensional architectures as multifunctional biological platforms. We have also discussed the representative biological applications regarding these FGN-based bioactive architectures. Furthermore, the future perspectives and emerging challenges will also be highlighted. Due to the lack of comprehensive reviews in this emerging field, this review may catch great interest and inspire many new opportunities across a broad range of disciplines.

Bioinspired Graphene Oxide/Polymer Nanocomposite Paper with High Strength, Toughness, and Dielectric Constant

Graphene/graphene oxide (GO)-based paper is attracting great interest owing to its multiple functionalities. In this study, we successfully synthesized a triblock copolymer by atom transfer radical polymerization method in terms of molecular design. The copolymer was comprised of polydimethylsiloxane (PDMS) and poly(glycidyl methacrylate) (PGMA) segments. To the copolymer, the PDMS segments provided flexible characteristic, and the PGMA segments provided reactive groups and adhesiveness. Because of the above characteristics, the copolymer was used as an adhesive between the adjacent GO nanosheets for fabrication of GO/PDMS-PGMA papers. The papers showed a good combination of high tensile strength and toughness. The tensile strength and toughness of GO/PDMS-PGMA (85/15) paper reached as high as 309 MPa and 6.55 MJ·m^-3, which were 3.4 and 8.2 times higher than that of pure GO paper. Furthermore, the papers also had high dielectric constant, which may enable this kind of material to be used in electronic and engineering fields.