Graphene-Based Hybrid Functional Materials

Graphene is a 2D material combining numerous outstanding physical properties, including high flexibility and strength, extremely high thermal conductivity and electron mobility, transparency, etc., which make it a unique testbed to explore fundamental physical phenomena. Such physical properties can be further tuned by combining graphene with other nanomaterials or (macro)molecules to form hybrid functional materials, which by design can display not only the properties of the individual components but also exhibit new properties and enhanced characteristics arising from the synergic interaction of the components. The implementation of the hybrid approach to graphene also allows boosting the performances in a multitude of technological applications. This review reports the hybrids formed by graphene combined with other low-dimensional nanomaterials of diverse dimensionality (0D, 1D, and 2D) and (macro)molecules, with emphasis on the synthetic methods. The most important applications of these hybrids in the fields of sensing, water purification, energy storage, biomedical, (photo)catalysis, and opto(electronics) are also reviewed, with a special focus on the superior performances of these hybrids compared to the individual, nonhybridized components.

Simultaneous quantification of three tropane alkaloids in goji berries by cleanup of the graphene/hexagonal boron nitride hybrids and ultra-high-performance liquid chromatography tandem mass spectrometry

A modified quick, easy, cheap, effective, rugged and safe method was established for simultaneous determination of atropine, anisodamine, and scopolamine in goji berries by using ultra-high-performance liquid chromatography with tandem mass spectrometry. The graphene/hexagonal boron nitride hybrids were prepared and first applied as a cleanup adsorbent. Compared to classical cleanup adsorbent (C₁₈ ), the graphene/hexagonal boron nitride hybrids as adsorbent had better extraction efficiency for the detection of analytes. Under the optimal conditions, the proposed analytical method achieved satisfactory linearity (R²  > 0.995), and obtained desirable recoveries ranged from 77.4 to 94.0% with the relative standard deviation of 1.2-6.1% at the concentration levels of 3.2-13.4 µg/kg. The limits of quantitation of atropine, anisodamine, and scopolamine were, respectively, 3.2, 4.6, and 4.5 µg/kg with linearity ranged from 3.2 to 25.4 µg/kg. The modified quick, easy, cheap, effective, rugged, and safe sample preparation with ultra-high-performance liquid chromatography and tandem mass spectrometry method was successfully applied to evaluate the safety of goji berries collected from 30 plant areas in China, suggesting its applicability and suitability for the routine analysis of three tropane alkaloids in goji berries.

Direct Inkjet Printing of Aqueous Inks to Flexible All-Solid-State Graphene Hybrid Micro-Supercapacitors

In this article, the inkjet printing technique is demonstrated for the stacking of reduced graphene oxide (RGO) and molybdenum trioxide (MoO₃) nanosheets for flexible all-solid-state micro-supercapacitors. The ammonium molybdate tetrahydrate/graphene oxide ((NH₄)₆Mo₇O₂₄·4H₂O/GO) aqueous inks are facilely printed on polymide (PI) film and transformed to RGO/MoO₃ hybrids via thermal treatments at air atmosphere. The compound inks are water-based, inkjet-printable, and nontoxic for inkjet printing to form two-dimensional crystal materials. The physical properties of aqueous inks are optimized within a printable range characterized by the Ohnesorge number of 1 < Z < 14. The inkjet-printed symmetric micro-supercapacitors (MSCs) with poly(vinyl alcohol) (PVA)-H₂SO₄ gel electrolyte possess a wide voltage window of 0-0.8 V, excellent flexibility, a high volumetric specific capacitance of 22.5 F cm^-3 at 0.044 A cm^-3, as well as good cyclic stability due to the synergistic effect of RGO and MoO₃. Furthermore, the inkjet-printed composite MSCs delivered a maximum energy density of 2 mWh cm^-3 and a power density of 0.018 W cm^-3, and the capacity retention rate of inkjet-printed MSCs is still retained 82% even after 10 000 charge-discharge cycles, indicating good electrochemical properties. Above all, the as-designed inkjet printing technique shows potential for flexible and wearable energy storage electronics.

Single-Step Selective Laser Writing of Flexible Photodetectors for Wearable Optoelectronics

The increasing demand for wearable optoelectronics in biomedicine, prosthetics, and soft robotics calls for innovative and transformative technologies that permit facile fabrication of compact and flexible photodetectors with high performance. Herein, by developing a single-step selective laser writing strategy that can finely tailor material properties through incident photon density control and lead to the formation of hierarchical hybrid nanocomposites, e.g., reduced graphene oxide (rGO)-zinc oxide (ZnO), a highly flexible and all rGO-ZnO hybrid-based photodetector is successfully constructed. The device features 3D ultraporous hybrid films with high photoresponsivity as the active detection layer, and hybrid nanoflakes with superior electrical conductivity as interdigitated electrodes. Benefitting from enhanced photocarrier generation because of the ultraporous film morphology, efficient separation of electron-hole pairs at rGO-ZnO heterojunctions, and fast electron transport by highly conductive rGO nanosheets, the photodetector exhibits high, linear, and reproducible responsivities to a wide range of ultraviolet (UV) intensities. Furthermore, the excellent mechanical flexibility and robustness enable the photodetector to be conformally attached to skin, thus intimately monitoring the exposure dosage of human body to UV light for skin disease prevention. This study advances the fabrication of flexible optoelectronic devices with reduced complexity, facilitating the integration of wearable optoelectronics and epidermal systems.

Highly Efficient High-Pressure Homogenization Approach for Scalable Production of High-Quality Graphene Sheets and Sandwich-Structured α-Fe2O3/Graphene Hybrids for High-Performance Lithium-Ion Batteries

A highly efficient and continuous high-pressure homogenization (HPH) approach is developed for scalable production of graphene sheets and sandwich-structured α-Fe₂O₃/graphene hybrids by liquid-phase exfoliation of stage-1 FeCl₃-based graphite intercalation compounds (GICs). The enlarged interlayer spacing of FeCl₃-GICs facilitates their efficient exfoliation to produce high-quality graphene sheets. Moreover, sandwich-structured α-Fe₂O₃/few-layer graphene (FLG) hybrids are readily fabricated by thermally annealing the FeCl₃ intercalated FLG sheets. As an anode material of Li-ion battery, α-Fe₂O₃/FLG hybrid shows a satisfactory long-term cycling performance with an excellent specific capacity of 1100.5 mA h g^-1 after 350 cycles at 200 mA g^-1. A high reversible capacity of 658.5 mA h g^-1 is achieved after 200 cycles at 1 A g^-1 and maintained without notable decay. The satisfactory cycling stability and the outstanding capability of α-Fe₂O₃/FLG hybrid are attributed to its unique sandwiched structure consisting of highly conducting FLG sheets and covalently anchored α-Fe₂O₃ particles. Therefore, the highly efficient and scalable preparation of high-quality graphene sheets along with the excellent electrochemical properties of α-Fe₂O₃/FLG hybrids makes the HPH approach promising for producing high-performance graphene-based energy storage materials.

Graphene hybrids: synthesis strategies and applications in sensors and sensitized solar cells

Graphene exhibits unique 2-D structural, chemical, and electronic properties that lead to its many potential applications. In order to expand the scope of its usage, graphene hybrids which combine the synergetic properties of graphene along with metals/metal oxides and other nanostructured materials have been synthesized and are a widely emerging field of research. This review presents an overview of the recent progress made in the field of graphene hybrid architectures with a focus on the synthesis of graphene-carbon nanotube (G-CNT), graphene-semiconductor nanomaterial (G-SNM), and graphene-metal nanomaterial (G-MNM) hybrids. It attempts to identify the bottlenecks involved and outlines future directions for development and comprehensively summarizes their applications in the field of sensing and sensitized solar cells.