Yijia He

Tactile Sensing System Based on Arrays of Graphene Woven Microfabrics: Electromechanical Behavior and Electronic Skin Application.

Nanomaterials serve as promising candidates for strain sensing due to unique electromechanical properties by appropriately assembling and tailoring their configurations. Through the crisscross interlacing of graphene microribbons in an over-and-under fashion, the obtained graphene woven fabric (GWF) indicates a good trade-off between sensitivity and stretchability compared with those in previous studies. In this work, the function of woven fabrics for highly sensitive strain sensing is investigated, although network configuration is always a strategy to retain resistance stability. The experimental and simulation results indicate that the ultrahigh mechanosensitivity with gauge factors of 500 under 2% strain is attributed to the macro-woven-fabric geometrical conformation of graphene, which induces a large interfacial resistance between the interlaced ribbons and the formation of microscale-controllable, locally oriented zigzag cracks near the crossover location, both of which have a synergistic effect on improving sensitivity. Meanwhile, the stretchability of the GWF could be tailored to as high as over 40% strain by adjusting graphene growth parameters and adopting oblique angle direction stretching simultaneously. We also demonstrate that sensors based on GWFs are applicable to human motion detection, sound signal acquisition, and spatially resolved monitoring of external stress distribution.

Highly Flexible and Adaptable, All‐Solid‐State Supercapacitors Based on Graphene Woven‐Fabric Film Electrodes

Recently, the applications of portable and fl exible devices have come to fruition, for instance, devices like fl exible touch screens [ 1 ] and fl exible solar cells [ 2 ] have become daily essentials. Such breakthroughs have dramatically stimulated the development of related technologies, such as the design and construction of energy-storage devices, one of the most important devices for human prosperity and health. Supercapacitors, which are also called electrochemical capacitors, are fast but high-power energy-storage devices. [ 3–5 ] In such devices, charges are stored in the interface of electrolyte and electrode material through the rapid and reversible adsorption/desorption of ions. [ 6,7 ] Much effort has also been made to develop thin-fi lm supercapacitors, [ 8,9 ] which are expected to possess high capacity while maintaining light weight and fl exibility. Theoretically, the two-dimensional (2D) extension of thin-fi lm supercapacitors could substantially reduce the deformation resistance from the vertical direction, which ultimately would make the entire device thin, fl exible, and easy to fold, twist, or reshape. The travel distance of electrolyte ions in thin-fi lm supercapacitors is also shorter than their counterparts. [ 10 ] Consequently, all-solid-state supercapacitors,

Effect of different gel electrolytes on graphene-based solid-state supercapacitors

A solid-state supercapacitor with a flexible, simple structure based on graphene thin film electrodes and acid/base/salt–PVA gel electrolytes is reported. The performance of six different gel electrolytes (H3PO4, H2SO4, KOH, NaOH, KCl, NaCl) in this graphene-based supercapacitor are investigated. The electrochemical properties of this highly flexible, stable supercapacitor are enhanced by optimizing the concentration of the electrolyte in polymer gel.

TiO2 enhanced ultraviolet detection based on a graphene/Si Schottky diode

Graphene/Si has been proved to form a quality Schottky junction with high photoelectric conversion efficiency at AM 1.5. However, for the ultraviolet portion of the incident light, the photoelectric performance will degrade significantly due to severe absorption and recombination at the front surface. Herein, to realize enhanced ultraviolet detection with a graphene/Si diode, TiO2 nanoparticles (NPs, 3–5 nm) are synthesized and spin-coated on the graphene surface to improve the photoresponse in the ultraviolet region. According to our results, the conversion efficiency of the graphene/Si diode at 420 nm and 350 nm increases by 72.7% and 100% respectively with TiO2 coating. Then C−2–V measurements of both TiO2 and graphene/Si diode are performed to analyze the electronic band structure of the TiO2/graphene/Si system, based on which we finally present the enhancement mechanism of photodetection using TiO2 NPs.

Galvanism of continuous ionic liquid flow over graphene grids

Flow-induced voltage generation on graphene has attracted great attention, but harvesting voltage by ionic liquid continuously flowing along graphene at macro-scale is still a challenge. In this work, we design a network structure of graphene grids (GG) woven by crisscrossed graphene micron-ribbons. The structure is effective in splitting the continuous fluid into “droplets” to generate consistent voltage using the mechanism of electrochemical energy generation. Key parameters such as flow rate, mesh number of GG, and slope angle are optimized to obtain maximum voltage in energy generation. The results suggest great potential of this graphene-based generator for future applications in energy harvesting.

Flow-induced voltage generation in graphene network

We report a voltage generator based on a graphene network (GN). In response to the movement of a droplet of ionic solution over a GN strip, a voltage of several hundred millivolts is observed under ambient conditions. In the voltage-generation process, the unique structure of GN plays an important role in improving the rate of electron transfer. Given their excellent mechanical properties, GNs may find applications for harvesting vibrational energy in various places such as raincoats, umbrellas, windows, and other surfaces that are exposed to rain.

Graphene oxide-embedded polyamide nanofiltration membranes for selective ion separation

Herein, a graphene oxide (GO)-modified piperazine (PIP) nanofiltration (NF) membrane was successfully fabricated via in situ interfacial polymerization of PIP-GO and trimesoyl chloride on a porous substrate, in which GO induced a wrinkled membrane surface with improved roughness and hydrophilicity and reduced electronegativity. Ion separation tests show that GO increases the water flux of the membranes significantly by 10–15 LMH for all the studied salt solutions. Furthermore, GO can selectively increase the retention of CaCl2 and MgCl2, but slightly decrease the rejection of MgSO4, NaCl, and KCl; this indicates an improvement in the separation performance of the PIP-GO membrane between divalent and monovalent cations with a common counter ion, Cl−. The enhanced water permeation of the PIP-GO membrane can be ascribed to its increased surface area, hydrophilicity, and ultrafast water transport between GO nanosheets. The GO-promoted selective ion separation is the result of an attenuated electrostatic attraction between Ca2+, Mg2+, and the membrane as well as the water flow-accelerated transport of Na+ and K+. Therefore, GO-modified NF membranes exhibit great potential for applications in the areas of water purification and separation.

Graphene oxide as a water transporter promoting germination of plants in soil

Graphene oxide (GO) is a graphene derivative bearing various oxygen-containing functional groups attached to the basal plane and to the edges of the graphene lattice and hence has a unique structure in which numerous hydrophobic sp2 clusters are isolated within the hydrophilic sp3 C–O matrix. In this study, the hydrophilic nature and water-transporting properties of GO were exploited to promote germination and growth of plants. It was found that a low dose of GO significantly promoted the germination of spinach and chive in soil. The oxygen-containing functional groups of GO collected water, and the hydrophobic sp2 domains transported water to the seeds to accelerate the germination of plants. The strong interaction between GO and the surfaces of soil grains stabilized GO in the soil and prevented dissipation of GO. In addition, no GO was detected either on the surface or inside the cells of plants; this finding confirmed that GO was not phytotoxic. Therefore, GO may serve as a promising nontoxic additive to increase a plant yield.

Graphene oxide as an antimicrobial agent can extend the vase life of cut flowers

Abstract“PlantNanOmics” is an emerging topic in agricultural research that explores the potential effect of application of nanomaterials on plant growth. Graphene oxide (GO) has excellent properties due to its basal carbon plane and oxygen-containing functional groups. In the present work, the antimicrobial activity of GO was exploited to extend the vase life and improve the quality of cut roses (cv. Carola). The results revealed that the cut roses cultivated in low doses of GO (0.1 mg/L) had longer vase life, larger diameter, and better water relations. Microbial contaminations at the basal stem end is the most common reason for stem blockage that causes water stress and early wilting of cut flowers. GO was found to act as a germicide, effectively inhibiting the microbial growth at the cut stem end and improving water uptake and water balance of cut roses. Therefore, GO can serve as a promising preservative to increase the ornamental value of cut flowers.

Strong Adhesion of Graphene Oxide Coating on Polymer Separation Membranes

Graphene oxide (GO) has been demonstrated as the most promising candidate for surface modification of polymer separation membranes for durable filtration applications. However, the adhesion between GO coating and polymer substrate, as the most essential issue for reliable applications, has been little explored. Herein, we developed a facile high-pressure assisted deposition method to physically anchor GO sheets on microfiltration (MF) and reverse osmosis (RO) membranes, and established a tape test procedure for assessing the adhesion of GO coating to polymer substrates based on the ASTM D3359. Through regulating the GO sources and coating process, we demonstrated that the adhesion depends sensitively on the GO flake size and deposition pressure, whereas the adhesion level dramatically improved from 0B to 5B, with decrease in the lateral size of GO and increase in the coating deposition pressure. The strong GO coatings showed evidently higher water flux than that of weak counterparts. The underlying mechanism was further analyzed and verified. Nanosize of GO and high deposition pressure favor the formation of the conformal morphologies of GO coatings on both MF and RO membranes, which allow strong interfacial van der Waals interaction because of the large contact areas and result in the strong GO coatings on membranes. These results potentially open up a versatile pathway to develop the strong graphene-based coatings on separation membranes.