Porous Graphene Microflowers for High-Performance Microwave Absorption.

Graphene has shown great potential in microwave absorption (MA) owing to its high surface area, low density, tunable electrical conductivity and good chemical stability. To fully realize graphene's MA ability, the microstructure of graphene should be carefully addressed. Here we prepared graphene microflowers (Gmfs) with highly porous structure for high-performance MA filler material. The efficient absorption bandwidth (reflection loss ≤ -10 dB) reaches 5.59 GHz and the minimum reflection loss is up to -42.9 dB, showing significant increment compared with stacked graphene. Such performance is higher than most graphene-based materials in the literature. Besides, the low filling content (10 wt%) and low density (40-50 mg cm-3) are beneficial for the practical applications. Without compounding with magnetic materials or conductive polymers, Gmfs show outstanding MA performance with the aid of rational microstructure design. Furthermore, Gmfs exhibit advantages in facile processibility and large-scale production compared with other porous graphene materials including aerogels and foams.

Multifunctional Bicontinuous Composite Foams with Ultralow Percolation Thresholds.

Integrating ultralight weight and strong mechanical performance into cellular monolith is a challenge unresolved yet. Here, we propose a skeleton-assisted self-assembly method to design ultralight bicontinuous composite foams (BCCFs) with high mechanical robustness and ultralow percolation thresholds. Polymer foam was employed as the skeleton to support assembled graphene networks, forming BCCFs with a high tensile strength (∼80 kPa) and breakage elongation (>22.2%). The paraffin and poly(dimethylsiloxane) infiltrated BCCFs show a record low percolation threshold of 0.006 vol % and a relatively high electrical conductivity of 0.81 S m-1 at a low graphene content of 0.216 vol %. The BCCFs demonstrate high and adjustable microwave-absorbing (MA) properties. The effective absorption bandwidth (reflection loss ≤ -10 dB) for BCCFs with a low graphene loading of 3.4 mg cm-3 achieves 9.0 GHz at a thickness of 4 mm, and it further covers 13.6 GHz considering the adjustability of preferred absorption band. The BCCFs with an extremely low graphene load of 0.14 mg cm-3 were further used for durable and efficient oil adsorption, which can adsorb >60 times their own weight. The facile fabrication of bicontinuous composite foams opens the avenue for practical applications of high-strength, multifunctional, and productive graphene-based foams.

Superconducting Continuous Graphene Fibers via Calcium Intercalation.

Superconductors are important materials in the field of low-temperature magnet applications and long-distance electrical power transmission systems. Besides metal-based superconducting materials, carbon-based superconductors have attracted considerable attention in recent years. Up to now, five allotropes of carbon, including diamond, graphite, C60, CNTs, and graphene, have been reported to show superconducting behavior. However, most of the carbon-based superconductors are limited to small size and discontinuous phases, which inevitably hinders further application in macroscopic form. Therefore, it raises a question of whether continuously carbon-based superconducting wires could be accessed, which is of vital importance from viewpoints of fundamental research and practical application. Here, inspired by superconducting graphene, we successfully fabricated flexible graphene-based superconducting fibers via a well-established calcium (Ca) intercalation strategy. The resultant Ca-intercalated graphene fiber (Ca-GF) shows a superconducting transition at ∼11 K, which is almost 2 orders of magnitude higher than that of early reported alkali metal intercalated graphite and comparable to that of commercial superconducting NbTi wire. The combination of lightness and easy scalability makes Ca-GF highly promising as a lightweight superconducting wire.

Sheet Collapsing Approach for Rubber-like Graphene Papers.

Understanding and modulating the conformation of graphene are pivotal in designing graphene macroscopic materials. Here, we revealed the sheet collapsing behavior of graphene oxide (GO) sheets by poor solvents in an analogy with linear macromolecules. Triggered by poor solvents, extended GO sheets in good solvents can collapse to hierarchically wrinkled conformations. The collapsing behavior of GO enabled the fabrication of amorphous self-standing GO and graphene papers with rich hierarchical wrinkles and folds over mutliple size scales. The collapsed GO and graphene papers had a rubber-like mechanical behavior with viscoelasticity. By our collapsing method, GO and graphene self-standing papers were designed to be stiff with high modulus or to become soft with low modulus of 100 MPa at a remarkably large breakage elongation up to 23%. Our philosophy of treating graphene as a 2D polymer enables the efficient control of molecular conformations of graphene and other 2D polymers and the design of macroscopic materials of 2D nanomaterials as in the polymer industry.

Dry spinning approach to continuous graphene fibers with high toughness.

Graphene fiber (GF) has emerged as a new carbonaceous fiber species since graphene-based liquid crystals were discovered. The growing performances of GFs in terms of their mechanical performance and their functionalities have assured their extensive applications in structural materials and functional textiles. To date, many spinning strategies utilizing coagulation baths have been applied in GF, which necessitates a complicated washing process. Dry spinning is a more convenient and green method for use with fibers in the chemical fiber industry, and should be a good option for GFs; however, this technique has never been used in a system of GF. In this research, first the dry spinning technique was used to fabricate continuous GFs and the dry spun GFs showed good toughness and flexibility. The dry spinnability of graphene oxide liquid crystals was achieved by choosing dispersive solvents with low surface tension and high volatility. The dry spun neat GFs possessed high toughness up to 19.12 MJ m-3, outperforming the wet spun neat GFs. This dry spinning methodology facilitates the green fabrication of fibers of graphene and graphene-beyond two-dimensional nanomaterials, and it may also be extended to other printing technologies for complex graphene architectures.

Wrinkle-stabilized metal-graphene hybrid fibers with zero temperature coefficient of resistance.

The interfacial adhesion between graphene and metals is poor, as metals tend to generate superlubricity on smooth graphene surface. This problem renders the free assembly of graphene and metals to be a big challenge, and therefore, some desired conducting properties (e.g., stable metal-like conductivities in air, lightweight yet flexible conductors, and ultralow temperature coefficient of resistance, TCR) likely being realized by integrating the merits of graphene and metals remains at a theoretical level. This work proposes a wrinkle-stabilized approach to address the poor adhesion between graphene surface and metals. Cyclic voltammetry (CV) tests and theoretical analysis by Scharifker-Hills models demonstrate that multiscale wrinkles effectively induce nucleation of metal particles, locking in metal nuclei and guiding the continuous growth of metal islands in an instantaneous model on rough graphene surface. The universality and practicability of the wrinkle-stabilized approach is verified by our investigation through the electrodeposition of nine kinds of metals on graphene fibers (GF). The strong interface bonding permits metal-graphene hybrid fibers to show metal-level conductivities (up to 2.2 × 107 S m-1, a record high value for GF in air), reliable weatherability and favorable flexibility. Due to the negative TCR of graphene and positive TCR of metals, the TCR of Cu- and Au-coated GFs reaches zero at a wide temperature range (15 K-300 K). For this layered model, the quantitative analysis by classical theories demonstrates the suitable thickness ratio of graphene layer and metal layer to achieve zero TCR to be 0.2, agreeing well with our experimental results. This wrinkle-stabilized approach and our theoretical analysis of zero-TCR behavior of the graphene-metal system are conducive to the design of high-performance conducting materials based on graphene and metals.

Large-area potassium-doped highly conductive graphene films for electromagnetic interference shielding.

As promising carbonaceous films, graphene films (GF) have exhibited many remarkable mechanical and electrical/thermal properties of great potential for wide functional applications. However, the electrical conductivity of GF still needs to be improved and the limitation lies in the low carrier density of pure graphene. Here, we presented a post-doping method for large-area potassium doped graphene films (GF-K) and promoted the electrical conductivity of GF approaching benchmark metals. The macroscopic-assembled GF-K shows a similar color to graphite intercalation compounds. The potassium doping increased the carrier density of the GF without undermining the electronic quality of the graphene unit. The doping concentration was optimized to prepare stage-2 GF-K (C24K) with the highest electrical conductivity (1.49 × 107 S m-1), holding merits of low density (1.63 g cm-3), and high flexibility. Doped GF with better specific electrical conductivity than copper showed outstanding electromagnetic interference shielding performance. Shielding effectiveness (SE) increased from 70-85 dB for graphene film (GF) to over 130 dB for GF-K only at 31 µm thickness, which is among the best SEs in previous reports. The combination of high specific conductivity, mechanical flexibility, high EMI SE, light weight, and facile productivity enables GF-K to be promising in many high-end EMI applications such as aerospace and wearable devices.

Ultrafast all-climate aluminum-graphene battery with quarter-million cycle life.

Rechargeable aluminum-ion batteries are promising in high-power density but still face critical challenges of limited lifetime, rate capability, and cathodic capacity. We design a "trihigh tricontinuous" (3H3C) graphene film cathode with features of high quality, orientation, and channeling for local structures (3H) and continuous electron-conducting matrix, ion-diffusion highway, and electroactive mass for the whole electrode (3C). Such a cathode retains high specific capacity of around 120 mAh g-1 at ultrahigh current density of 400 A g-1 (charged in 1.1 s) with 91.7% retention after 250,000 cycles, surpassing all the previous batteries in terms of rate capability and cycle life. The assembled aluminum-graphene battery works well within a wide temperature range of -40 to 120°C with remarkable flexibility bearing 10,000 times of folding, promising for all-climate wearable energy devices. This design opens an avenue for a future super-batteries.

A density gradient of basic fibroblast growth factor guides directional migration of vascular smooth muscle cells.

The migration of vascular smooth muscle cells (VSMCs) is an important process in many physiological events. It is of paramount importance to control the migration rate and direction of VSMCs by biomaterials. In this paper, a density gradient of basic fibroblast growth factor (bFGF) was fabricated using an injection method and the bio-conjugation between heparin and bFGF. The density of bFGF gradually increased with a slope of 17 ng/cm(2)/mm. Adhesion and migration of VSMCs were studied on the bFGF gradient. The VSMCs exhibited preferential orientation and an enhanced directional migration behavior on the gradient surface. Up to 70% cells migrated towards the region with a higher density of bFGF on the gradient. However, the bFGF gradient had no effect on the cell migration rate.

Hollow fiber liquid-phase microextraction as clean-up step for the determination of organophosphorus pesticides residues in fish tissue by gas chromatography coupled with mass spectrometry.

Hollow fiber liquid-phase microextraction (HF-LPME) technique was used as a clean-up procedure for the determination of organophosphorus pesticides (OPPs) in fish tissue. In this study, eight OPPs were first extracted with acetone from fish sample, the organic extract after rotatory evaporation was then redissolved with water-methanol (95:5, v/v) solution, followed by polyvinylidene difluoride (PVDF) HF-LPME. Experimental HF-LPME and other sample preparation conditions were carefully investigated and optimized. Under the optimum conditions, good linearity were observed in the range of 20-500 ng/g, limits of detections (LODs) were in the range of 2.1-4.5 ng/g. The repeatability and recovery of the method also showed satisfactory results. Compared with traditional sample preparation method for the determination of OPPs in fish tissue, the method developed in this study eliminated the solid phase extraction (SPE) step, simplified the sample preparation procedure and lowered the cost of analysis.