Ultrasensitive and Selective Nitrogen Dioxide Sensor Based on Self-Assembled Graphene/Polymer Composite Nanofibers

Reduced graphene oxide (rGO) sheets were self-assembled onto the surfaces of electrospun polymer nanofibers to form an ultrathin coating. These rGO/polymer composite nanofibers were used to fabricate nitrogen dioxide (NO₂) sensor. This sensor can be performed at room temperature, and it exhibited a high sensitivity of 1.03 ppm^–1 with excellent selectivity and good reversibility. Furthermore, the limit of detection was experimentally measured to be as low as 150 ppb, and this value is much lower than the threshold exposure limit proposed by American Conference of Governmental Industrial Hygienists (200 ppb)

Graphene-Based Membranes for Molecular Separation

In comparison with traditional chemical separation processes, membrane separation is much simpler and more efficient. An ideal membrane for molecular separation should be as thin as possible to maximize its solvent flux, be mechanically robust to prevent it from fracture, and have well-defined pore sizes to guarantee its selectivity. Graphene is an excellent platform for developing size-selective membranes because of its atomic thickness, high mechanical strength, and chemical inertness. In this Perspective, we review the recent advancements on the fabrication of nanoporous graphene membranes and graphene oxide membranes (GOMs) for molecular separation. The methods of fabricating these membranes are summarized, and the mechanisms of molecular separation based on these two types of graphene membranes are compared. The challenges of synthesizing and transferring large-area nanoporous graphene membranes and engineering the performances of GOMs are discussed

Highly Efficient Moisture-Triggered Nanogenerator Based on Graphene Quantum Dots

A high-performance moisture triggered nanogenerator is fabricated by using graphene quantum dots (GQDs) as the active material. GQDs are prepared by direct oxidation and etching of natural graphite powder, which have small sizes of 2–5 nm and abundant oxygen-containing functional groups. After the treatment by electrochemical polarization, the GQDs-based moisture triggered nanogenerator can deliver a high voltage up to 0.27 V under 70% relative humidity variation, and a power density of 1.86 mW cm^–2 with an optimized load resistor. The latter value is much higher than the moisture-electric power generators reported previously. The GQD moisture triggered nanogenerator is promising for self-power electronics and miniature sensors

Solution-Processed PEDOT:PSS/Graphene Composites as the Electrocatalyst for Oxygen Reduction Reaction

Composites of poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) and reduced graphene oxide (rGO) have been prepared by solution mixing and applied as electrocatalysts for oxygen reduction reaction (ORR) after treatment with concentrated H₂SO₄. The blending of rGO induces the conformational change of PEDOT chains from benzoid to quionoid structure and charge transfer from rGO to PEDOT. H₂SO₄ post-treatment can remove part of insulating PSS from the surface of the PEDOT:PSS/rGO composite film, resulting in a significant conductivity enhancement of the composite. This synergistic effect makes the H₂SO₄-treated PEDOT:PSS/rGO composite a promising catalyst for ORR. It exhibits enhanced electrocatalytic activity, better tolerance to a methanol crossover effect and CO poisoning, and longer durability than those of the platinum/carbon catalyst

A Turn-on Fluorescent Sensor for Pyrophosphate Based on the Disassembly of Cu²⁺-Mediated Perylene Diimide Aggregates

A complex between an anionic perylene diimide derivative (PDI-GlyAsp) and cupric ion has been prepared and applied to be turn-on fluorescent probe for the detection of pyrophosphate (PPi) in 100% aqueous solution. The complex formation process and PPi detection have been studied by absorption and emission spectroscopy. It was confirmed that the introduction of cupric ion into PDI-GlyAsp solution resulted in the assembly of PDI-GlyAsp into PDI-GlyAsp/Cu²⁺ aggregates, leading to the fluorescence quenching of PDI-GlyAsp. Upon addition of PPi into the above solution led to the disassembly of the aggregates due to the competitive binding of PPi with Cu²⁺ in the PDI-GlyAsp/Cu²⁺ complex, and a recovery of PDI-GlyAsp emission was observed. Therefore, the PDI-GlyAsp/Cu²⁺ complex can be applied as a turn-on fluorescent probe for detecting PPi with high selectivity and sensitivity

Transparent Polymeric Strain Sensors for Monitoring Vital Signs and Beyond

Wearable sensors that can precisely detect vital signs are highly desirable for monitoring personal health conditions and medical diagnosis. In this paper, we report an ultrasensitive strain sensor consisting of a 150 nm thick highly conductive dimethylsulfoxide-doped poly­(3,4-ethylenedioxythiophene):poly­(4-styrenesulfonate) sensing layer and an elastic fluorosilicone rubber substrate. This sensor exhibits a high sensitivity at small strains (e.g., gauge factor at 0.6% strain = 280), low limit of detection (<0.2% strain), and excellent repeatability and cycling stability. Therefore, it is promising for practically detecting vital signs, tiny human motions, and sounds. Furthermore, the semitransparent shallow blue color and the soft rubbery substrate make the strain sensor beautiful and comfortable to the human body

A General Route to Robust Nacre-Like Graphene Oxide Films

Artificial nacre-like composite films of graphene oxide (GO) with a variety of commercially available water-soluble polymers were fabricated by a gel–film transformation (GFT) technique. The blending of a polymer into the aqueous dispersion of GO can modulate the interaction between GO sheets. Typically, the attraction force between polymer and GO sheets overcomes the dominant hydration and electrostatic repulsive forces between GO sheets, promoting the gelation of GO. Cast drying the resultant GO hydrogel containing small amounts of polymer (1–20 wt % relative to GO depending on the intrinsic structures of polymers) generates layered GO composite films with tensile strengths over 200 MPa and failure strains larger than 3.0%, which are higher than those of natural nacre and most nacre-like GO films. These results indicate that GO/polymer composite hydrogels are excellent precursors for nacre-like GO films and that the GFT approach is a general route toward the large-scale fabrication of nacre-like GO films with unique combinations of high strength and high toughness

A General Route to Robust Nacre-Like Graphene Oxide Films

Artificial nacre-like composite films of graphene oxide (GO) with a variety of commercially available water-soluble polymers were fabricated by a gel–film transformation (GFT) technique. The blending of a polymer into the aqueous dispersion of GO can modulate the interaction between GO sheets. Typically, the attraction force between polymer and GO sheets overcomes the dominant hydration and electrostatic repulsive forces between GO sheets, promoting the gelation of GO. Cast drying the resultant GO hydrogel containing small amounts of polymer (1–20 wt % relative to GO depending on the intrinsic structures of polymers) generates layered GO composite films with tensile strengths over 200 MPa and failure strains larger than 3.0%, which are higher than those of natural nacre and most nacre-like GO films. These results indicate that GO/polymer composite hydrogels are excellent precursors for nacre-like GO films and that the GFT approach is a general route toward the large-scale fabrication of nacre-like GO films with unique combinations of high strength and high toughness

Trace Level Co–N Doped Graphite Foams as High-Performance Self-Standing Electrocatalytic Electrodes for Hydrogen and Oxygen Evolution

The development of eco-friendly electrocatalysts with high performance and low cost for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is significant for renewable energy storage. Here, trace level (0.11–0.18 wt %) Co–N doped graphite foam (Co–N/GF) was reported to work as a bifunctional high-performance and self-standing electrode for both HER and OER in alkaline electrolyte. The catalytic activities of Co–N/GFs with different annealing temperatures (600, 700, 800, 900, and 1000 °C) were carefully studied. Among them, Co–N/GF-900 exhibited the best HER activity and Co–N/GF-700 showed the best OER activity, achieving the current density of 10 mA cm^–2 at low overpotentials of 165 and 313 mV, respectively. In addition, both of these electrodes exhibited long-term durability. Co–N/GF electrodes were further constructed as a catalytic cathode and anode couple (Co–N/GF-900∥Co–N/GF-700) for overall water splitting, exhibiting a low cell voltage of 1.68 V and good long-term stability. Our work reveals that introducing a trace level of Co–N into graphite foam can significantly enhance its electrocatalytic activity and stability for both HER and OER

Graphene-Quantum-Dot Assembled Nanotubes: A New Platform for Efficient Raman Enhancement

Graphene quantum dots (GQDs), single or few-layer graphenes with a size of only several nanometers, are a new type of quantum dots (QDs) with unique properties. The assembly of QDs in a geometrically well-defined fashion opens up opportunities to obtain access to the full potential of assembled QDs by virtue of the collective properties of the ensembles. In the current study, we present the well-organized assembly of zero-dimensional (0D) functional GQDs into 1D nanotube (NT) arrays and demonstrate their remarkable potential as a new metal-free platform for efficient surface-enhanced Raman scattering (SERS) applications. The hierarchically porous 1D nanotube structure of 0D GQDs has been prepared by electrophoresis deposition within a nanoporous AAO template. On the basis of the unique porous nanotube architecture of GQDs, the GQD-NTs could ensure a more efficient charge transfer between the target molecules and the GQDs and thus produce much stronger SERS effect, exceeding that on flat graphene sheets. The unique architecture of 1D nanotubes of 0D GQDs provides a new point of view for designing and fabricating SERS substrates